General: Thin-leafed alder is a native, deciduous shrub or tree. The leaves are ovate, double serrated, and pointed at the tip. Male catkins are produced in the autumn in-groups of three or four. The female catkins are borne separately on the same plant in late winter or early spring. The fruit are small, brown, scale-like cones produced in early autumn. The bark is thin, smooth, and green-gray, grayish-brown, or reddish-brown (Preston 1948).
Distribution: Thin-leaf alder is distributed throughout Europe and much of North America. For current distribution, please consult the Plant profile page for this species on the PLANTS Web site.
Thin-leafed alder, grey alder, mountain alder, river alder
|Distributions of gray alder and its subspecies. Maps courtesy of USDA, NRCS. 2011. The PLANTS Database. National Plant Data Team, Greensboro, NC. (14 June 2011).|
|gray alder|| |
States and provinces (as of 2011 ):
|speckled alder||Speckled alder, the eastern subspecies, occurs at least as far west as Saskatchewan [120,192]. Little  places its distribution as far west and north as northwestern Yukon, central Northwest Territories, and central Nunavut. Its distribution is mostly continuous, with scattered populations in Michigan, Ohio, and West Virginia . |
States and provinces (as of 2011 ):
|thinleaf alder||Thinleaf alder, the western subspecies, has a mostly continuous distribution. Populations are scattered and sometimes isolated in the southern Sierra Nevada [179,192,229,229]. It has been reported in Baja California, although it may no longer occur there . |
States and provinces (as of 2011 ):
This shrub or small tree tolerates a wide range of soil types. It grows best in heavy moist soils in light shaded areas. It has a high flood tolerance and typically grows near rivers and moist stream borders on poorly developed soil. Thin-leaf alder is frequently found growing in the understory of coniferous forests on moist sites. It is also adaptable to a range of soil pH levels.
Gray alder is a tree or shrub, growing from 15 feet to 82 feet (4.6-25 m) tall. . Bark is smooth and thin [155,348], often with conspicuous lenticels  (see photo in Fire Effects and Management). The wood is soft . Leaves are oblong and serrated at the margins [208,355]. The inflorescences are small, naked  catkins. Male catkins grow in clusters of 2 to 4. They are 0.8 to 3 inches (2-8 cm) long and pendulous at maturity. Female catkins are woody and resemble cones, growing in clusters of 2 to 6 [106,120,237]. The "cones" are 0.4 to 0.8 inch (1-2 cm) long at maturity . The fruits are described as either irregular samaras  or nutlets with small, narrow wings [106,154,171,179,242,345]. They hold 1 to 4 seeds/cone scale [137,155,318]. The seeds lack endosperms, so the cotyledons are relatively small . The root system is shallow and spreading . Roots are typically infected with nitrogen-fixing, actinomycete bacteria [171,205,215,261]. A review reported that thinleaf alder fixes more nitrogen than Sitka alder (Alnus crispa subsp. sinuata) and quantities similar to those of red alder .
Gray alder is adapted to periodic flooding in spring or other run-off periods [23,204,267], although it cannot tolerate long periods of inundation. In the laboratory, speckled alder growth and root development were "severely reduced" when water levels were at or above the root crown for 30 days or more (P<0.05) [196,267]. A review ranked gray alder more flood tolerant than cottonwoods, birches, and elms but less tolerant than willows .
Morphological characteristics of the gray alder subspecies overlap (review by ). Thinleaf alder is typically more tree-like than speckled alder. The subspecies also differ in bark, leaf shape, and leaf margin characteristics [120,127,318].
Speckled alder is a spreading shrub  or small tree , growing up to 30 feet (9 m) tall  and 4.7 inches (12 cm) in diameter. Typically multistemmed with crooked branches, it is "very crooked" in form as a small tree , and only assumes tree form on high-quality sites . Its common name refers to the lenticels that give a characteristic "speckled" look to the bark . In a speckled alder community by a small stream in upstate New York, speckled alder stems averaged 14 years old, ranging from 7 to 31 years old. Stem density averaged 7,850 stems/ha . In central New York, age of mature stems ranged from 10 to 25 years. Based on stem sprouting vs. stem mortality rates, the author estimated maximum age of speckled alder clones at about 100 years .
Thinleaf alder is an open, spreading shrubby tree or shrub, growing from 15 to 39 feet (4.6-12 m) tall [120,345] and usually less than 4 inches (10 cm) in stem diameter . It often forms thickets along streams [179,231,242,345], although on upland sites it usually grows in discrete, shrubby clumps . Thinleaf alder stems on sandbars of the Tanana River, central Alaska, averaged 14 years old . Morris and others  provide a key for identifying thinleaf alder and other western shrubs in winter.
| Male and female catkins of speckled alder. |
Photo © 2005 Louis-M. Landry.
Site Characteristics and Plant Communities
Gray alder prefers moist to mesic sites throughout its distribution but occurs in a wide variety of plant communities within that moisture gradient. Its symbiotic relationship with nitrogen-fixing actinomycetes helps enrich soils; this affects plant community composition and succession. After fallen gray alder leaves and roots die and decay, their nitrogen is released back into the soil and becomes available to other plants [171,180,215]. An English poet wrote:
The alder, whose fat shadow nourisheth.
Each plant set there to him long flourisheth.
William Brown, Brittania's Pastorials. 1613.
Site characteristics: This subspecies dominates on wetlands [131,255,359], although some speckled alder-dominated sites may dry by the end of the growing season . Speckled alder grows on streambanks, lakeshores, and wet roadsides and in riparian forests, swamps and swamp edges, bogs, fens, bog or fen borders, margins of wet fields, and swales [120,127]. It often forms dense thickets [120,255]. Speckled alder communities often flood during spring run-off . In boreal ecosystems, the black spruce (Picea mariana)/speckled alder forest cover type occurs on waterlogged sites and sites with gently flowing groundwater . In Michigan, speckled alder grows along lakes and streams and in "extensive mucky" swamps . A forestry note reported that in Minnesota, speckled alder occurs on moist to mesic sites but was most common on moist sites . In Ohio, it is mostly confined to glaciated areas in the northern part of the state . Speckled alder occurs in wetlands and by streambanks in the Northern Great Plains . It may not tolerate flooding for long periods, however , and needs drainage when growing in swamps .
Speckled alder commonly occurs or codominates with willows (Salix spp.), a mixture that may be controlled by length of flooding season. Willows may tolerate longer flooding seasons than speckled alder. A laboratory study showed speckled alder was less tolerant to continuous flooding than willow species. Speckled alders suffered 33% average mortality when water levels were kept above the root crown for 2 years, while speckled alders experienced no mortality when the water level was maintained below the root crown for the same length of time .
Soils: Speckled alder tolerates a wide variety of soil textures and pH but is most common on nutrient-poor soils. It grows in sandy loam [49,160], chalky, rocky till, and mucky soils . In Ontario, speckled alder is an indicator of fine loamy-clayey soils with thick black humus; it is also an indicator of poor to rich fens with moderately decomposed organic soils . In swamps of northern Michigan, speckled alder communities tended to occur on relatively well-drained, sandy loams, while black ash/speckled alder communities occurred mostly on poorly drained, silty clay loams . In the Catskill and Adirondack mountains, speckled alder grows in limestone-, gneiss- and anorthosite-derived soils . In black ash-paper birch communities of the Great Lakes states, speckled alder was noted on minerotrophic peat substrates , and it grew in coarse woody peats in northern white-cedar (Thuja occidentalis) swamps of northern Wisconsin . It occurred on glacial till in central New York; soils were neutral to "somewhat alkaline" . It is reported on soils with pH from 3.4 to 7.7 in Ohio (review by ). In Wisconsin, speckled alder thickets occurred on peats of pH 5.5 . In jack pine (Pinus banksiana) stands in Minnesota, speckled alder was most common on medium-quality silvicultural sites (18% frequency). It also occurred on good-quality sites (7% frequency) but not on poor-quality sites (Hansen 1946 cited in ). In an assessment of Michigan shrub habitats, speckled alder occurred on the moistest, coolest, and most nutrient-poor sites when compared to other shrubs . However, speckled alder also occurs on nutrient-rich sites . On the Saskatchewan River Delta, speckled alder was positively associated with relatively nutrient-rich, shallow peat fens and levees. Soil water was alkaline and high in calcium and magnesium .
Elevation and topography: Speckled alder ranges from near sea level on the North Atlantic coast to about 2,710 feet (825 m) in the Appalachians . It grows on low-elevation alluvial soils in Nova Scotia  but at "moderately high elevations" elsewhere in Canada . It is restricted to high elevations in the southernmost portion of its range . In a tamarack bog in Itasca State Park, Minnesota, speckled alder was more abundant on hummocks (35% cover and 10% frequency) than in depressions (2% cover and <1% frequency) .
Plant communities: Speckled alder occurs in forest, shrub, and herbaceous communities. It is an important component of northern spruce-fir (Picea-Abies spp.) [22,247], red-white-jack pine (Pinus strobus-P. resinosa-P. banksiana) , Atlantic white-cedar (Chamaecyparis thyoides) , and mixed-hardwood  forests, especially at forest and bog ecotones . It also occurs in elm-ash-cottonwood (Ulmus-Fraxinus-Populus spp.) galleries and forests . In Newfoundland, it occurs in rich fens dominated by pale sedge (Carex livida) . Species diversity is generally high in wetland communities where speckled alder is an important to dominant component of the vegetation (for example, [33,114,356]).
Regional descriptions of plant communities with speckled alder and site characteristics of speckled alder habitats follow.
Great Lakes: Speckled alder is common in coniferous, mixed conifer-hardwood, shrubland, and graminoid wetland communities in the Great Lakes region. It is common, for example, in the understories of red pine forests and plantations. American hazelnut (Corylus americana) and beaked hazelnut (C. cornuta var. cornuta) usually dominate or codominate the understories . In Voyageurs National Park, Minnesota, black spruce/speckled alder communities occurred on nutrient-poor, wet sites . On the Lake Agassiz Peatlands Natural Area of Minnesota, speckled alder was abundant (covered 0.25% to 0.5% of an area) in rich swamp forests dominated by northern white-cedar, black ash (Fraxinus nigra), tamarack (Larix laricina), or white spruce (Picea glauca). It was not abundant in poor swamp forests, bogs, fens, or heaths . In northern Wisconsin, speckled alder was important to dominant in northern white-cedar swamps . It was also important to dominant in eastern redcedar (Juniperus virginiana) bogs of Ohio . On the shores of Lake Superior, a speckled alder/red raspberry /fowl mannagrass-reed canarygrass (Rubus idaeus/Phalaris arundinacea-Glyceria striata) thicket community occurred on secondary dunes, lees of high dunes, and sand flats. This community type had the highest species richness of 4 types identified .
Speckled alder is occasional to invasive on open fens and bogs of the Great Lakes states. In northeastern Ohio, it is characteristic in sedge (Carex) fens. Bottlebrush sedge (C. hystericina), hairy sedge (C. lacustris), and tussock sedge (C. stricta) are typical dominants . Speckled alder often dominates marginal fen or marginal bog zones, which separate the mires from the upland communities surrounding them .
Northeast: Speckled alder grows in coniferous forests, mixed and hardwood forests, shrublands, and open wetlands in the Northeast.
Maine: On Peak's Island, Portland, speckled alder was characteristic in the tree strata of an upland red maple (Acer rubrum) forest, parts of which had burned 3 times in 24 years, and of an unburned balsam fir (Abies balsamea) forest. At the time of the survey, speckled alder was the 2nd most common taxon on 7-year-old burned sites in the red maple forest (97% relative density and 13% frequency on 10 m² plots) and the 4th most common in the balsam fir forest (56% relative density and 16% frequency). Speckled alder clumps were also frequent in a nearby red maple swamp, where speckled alder dominated poorly drained areas of the swamp .
New England: In pitch pine (Pinus rigida)-hardwood swamp mosaics of New Jersey, speckled alder was a minor to codominant component of red maple-black tupelo-sweetbay/coastal sweetpepperbush (Nyssa sylvatica-Magnolia virginiana/Clethra alnifolia) swamps. It was most important on continuously flooded sites, declining on sporadically flooded or dry sites .
Southeast: Speckled alder occurs in mixed-hardwood, pine (Pinus spp.), and shrubland communities of the Southeast. In a 1930 study, it was a component of a climax American chestnut-yellow-poplar-eastern hemlock (Castanea dentata-Liriodendron tulipifera-Tsuga canadensis) cove forest in the Black Mountains of North Carolina . Yellow-poplar became the primary dominant in many cove forests after chestnut blight decimated American chestnut populations . In Georgia, speckled alder occurs in pond pine (Pinus serotina)-shrubland and bay (Magnolia and Persea spp.)-shrubland bogs. Shrub diversity is generally high .
The following vegetation classifications describe plant communities, and some of their distinguishing site characteristics, where speckled alder is dominant. In state and province lists, plant communities are arranged geographically from north to south and west to east.
|Great Lakes||Northeast||Southern Appalachians||Southeast|
Great Lakes, general
- black spruce-tamarack /speckled alder forest cover type; a minor type 
- black spruce/speckled alder/Sphagnum spp., northern white-cedar/speckled alder, and tamarack/speckled alder vegetation types of Isle Royal National Park; occur on peats, mucks, or wetland depressions. Speckled alder swamps occur on seasonally flooded sites .
- speckled alder-willow high bog association in Cheboygan County; forms a transitional zone between quaking aspen (Populus tremuloides) and northern white-cedar associations 
- the high bog shrub association of northern Lower Michigan. Speckled alder dominates marshy areas within this type; tamarack may invade after fire .
- speckled alder mire and black spruce/speckled alder forest communities of Voyageurs National Park 
- thinleaf alder/shoreline sedge (Carex hyalinolepis) and thinleaf alder/beaked sedge (C. rostrata) marginal fens of east-central Minnesota; these fens are surrounded by tamarack forests 
- speckled alder/white panicle aster-spotted sandmat (Symphyotrichum lanceolatum-Chamaesyce maculata) thickets
- dominant in the understories of tamarack, black spruce, balsam fir, and mixed-conifer forested wetlands 
Eastern North America, general
- speckled alder marginal bogs at maple-American elm (Acer spp.-Ulmus americana) transitional zones 
- speckled alder palustrine, broadleaved deciduous dominance types
- speckled alder scrub-shrub fresh wetlands 
- balsam fir/speckled alder forest cover types 
- Acadia National Park:
- red maple/speckled alder-winterberry/royal fern (Ilex verticillata/Osmunda regalis) swamp woodland association
- speckled alder-red-osier dogwood/devil's darning needles (Cornus sericea/Clematis virginiana) alluvial thicket association (typically on fens)
- speckled alder-catberry/sphagnum (Ilex mucronata/Sphagnum spp.) northern peatland shrub swamp association
- typical dominant in the short shrub layer of red spruce-white spruce forests 
- rich speckled alder fens; the fens are typically strongly minerotrophic on a woody peat substrate
- speckled alder shrub swamps of northern New York 
- speckled alder wetlands and swamp shrublands of Delaware Water Gap National Recreation Area, New Jersey and Pennsylvania [282,283]
- hazel alder/speckled alder/arrow arum-bluejoint reedgrass (Peltandra virginica-Calamagrostis canadensis) swamps in Appomattox Court House National Historical Park , Fredericksburg and Spotsylvania National Military Park , Petersburg National Battlefield , and Richmond National Battlefield , Virginia
- speckled alder-American black elderberry (Sambucus nigra subsp. canadensis ) communities on levees or floodplains where the water table is 1 to 30 inches (2.5-76 cm) below the surface and speckled alder-withe-rod (Viburnum nudum var. cassinoides) communities where the water table is 2 to 7 inches (5-18 cm) below the surface 
- high-elevation (~3,200 feet (980 m)) mixed conifer-hardwood/speckled alder forest wetland, speckled alder shrub wetland , and floodplain speckled alder tall shrub thicket  vegetation types
- wax myrtle (Myrica cerifera)-speckled alder river swamps of the St Mary's River in the Okefenokee Swamp and speckled alder-Virginia sweetspire (Itea virginica) branch swamps that form off of tributaries of the St Mary's River 
Boreal North America, general
- black spruce/speckled alder willow forest cover types; occur from Saskatchewan to Newfoundland on sites where the water table is at or above the soil surface during the growing season 
- tamarack/speckled alder forest cover types 
- pussy willow (Salix discolor)-speckled alder/meadow horsetail (Equisetum pratense) community types on the Saskatchewan River Delta 
- tamarack/speckled alder/bunchberry (Cornus canadensis) vegetation types south of James Bay 
- speckled alder/sensitive fern/Canadian mint (Onoclea sensibilis/Mentha canadensis) shoreline and bog-edge, black spruce-tamarack/speckled alder, white spruce-balsam fir/American mountain-ash (Sorbus americana)/speckled alder/bunchberry, jack pine-quaking aspen-paper birch/speckled alder-resin birch (Betula glandulosa), quaking aspen/willow-speckled alder, and eastern cottonwood (Populus deltoides)/speckled alder associations of St Lawrence Valley 
- speckled alder/Magellan's sphagnum-three-leaved Solomon's seal-naked miterwort (Sphagnum magellanicum-Smilacina trifolia-Mitella nuda) communities on deep (≥20 inches (40 cm)) organic soils 
- hardwood-speckled alder forest cover types; balsam poplar (Populus balsamifera) and quaking aspen usually dominate the overstory
- conifer-speckled alder forest cover types; black spruce and occasional northern white-cedar dominate the overstory 
- jack pine/speckled alder/Schreber's moss (Pleurozium schreberi) forest cover type 
- quaking aspen/speckled alder forest cover type on alluvial or other depositional soils 
- speckled alder community type on late-glacial fluvial deposits 
- black spruce-tamarack /speckled alder forest cover type 
- speckled alder swamp thickets with a ground layer of stiff clubmoss (Lycopodium annotinum) and/or shining clubmoss (L. lucidulum); these thickets succeed to balsam fir and/or white spruce without disturbance
- speckled alder-conifer swamps with white spruce and/or balsam fir in the subcanopy and wood horsetail (E. sylvaticum), small enchanter's nightshade (Circaea alpina) or other herbs in the ground layer; these communities are relatively unproductive as timber sites 
- black spruce/speckled alder and balsam fir/speckled alder forest types
- black spruce/speckled alder swamps 
Site characteristics: Thinleaf alder is most common on wet to moist sites (review by ). It is a frequent component of streamside vegetation throughout mountainous regions of western North America . It is considered an indicator of riparian or subirrigated sites on the Shoshone National Forest, Wyoming ; of moist, well-drained sites—especially streambanks and springs at low elevations—in central Oregon ; and of moist to wet soils in subboreal spruce (Abies spp.) and pine (Pinus spp.)-spruce ecosystems of British Columbia . Riparian sites with thinleaf alder may experience frequent flooding and/or scouring (for example, [104,114]).
Soils: Thinleaf alder grows on a variety of soil textures and nutrient levels. It grows in coarse-textured soils but is well-adapted to cold, "heavy" soils (review by ). It grows well in sand [199,339], and it is common on sandbars . In the Trout Creek Mountains, thinleaf alder grows in sand- and siltbanks about 2.6 feet (0.8 m) above stream channels . Soils supporting thinleaf alder are often rocky in mountainous areas . In Montana, thinleaf alder communities typically develop on cobble and gravel, accumulating organic debris over time . Nutrient levels of soils supporting thinleaf alder vary from poor to rich, although they are typically poor (review by ). Thinleaf alder typically establishes on poor, skeletal soils in primary succession , but it usually enriches in soils in which it grows . In the understories of coniferous forests in Blue Mountains, thinleaf alder is an indicator of productive sites .
Elevation and topography: In the conterminous United States, thinleaf alder is primarily restricted to mid- to high-elevation mountains, mountain valleys, and mesic canyons [155,208,231,241], although it grows on low-elevation sites in Alaska and Canada . In the United States, thinleaf alder ranges in elevation from near sea level in Alaska to over 10,000 feet (3,000 m) in Colorado and Arizona . Thinleaf alder populations apparently do not have exacting elevational requirements. Thinleaf alder cuttings have been successfully transplanted onto sites that vary greatly in elevational range .
|Elevational range of thinleaf alder by state|
|New Mexico||6,000-9,500 [96,228,241]; |
1,745-2,438 in Jemez Mountains 
|Texas||5,000-8,000 feet |
Thinleaf alder presence is likely more associated with moist to mesic conditions than with aspect alone. In the Wasatch Mountains of Utah, thinleaf alder was common in the bottom of Cold Canyon , but it was not noted on higher, north- or south-facing slopes, which may have drier soils . In Lassen Volcanic National Park, California, the location of willow-thinleaf alder communities was not significantly associated with aspect, but it was positively associated with relatively moist conditions (P=0.01). Willow-thinleaf alder communities were most common on steep slopes, depressions, and valley bottoms (P≤0.002). The authors attributed their presence on steep slopes to the prevalence of intermittent streams in avalanche chutes and their presence in low areas to the prevalence of concave drainage channels .Plant communities:
|Thinleaf alder in a mixed-conifer forest on the El Dorado National Forest, CA. Photo © 2009 Dr. Mark S. Brunell.|
Thinleaf alder prefers mesic to moist plant communities. These include the moist slopes of coniferous forests, riparian areas, wet meadows and grasslands, and fen and bog margins . Site moisture and elevation are critical in determining relative dominance of thinleaf alder; the surrounding vegetation usually tolerates drier conditions. On the shore of Slave Lake in Alberta, thinleaf alder codominates the understory of white spruce-paper birch communities on gravel or sand beaches that are 300 feet (90 m) or less from the lake . In the Trout Creek Mountains of Nevada, thinleaf alder communities are concentrated in low-elevation (4,920-5,300 feet (1,500-1,615 m)), narrow riparian corridors. Mountain big sagebrush (Artemisia tridentata subsp. vaseyana) typically dominates vegetation beyond the corridors, and plant species diversity is lower outside than within the riparian corridors . Willows (Salix), red-osier dogwood, common snowberry (Symphoricarpos albus), and horsetails (Equisetum) codominate with thinleaf alder in many plant communities throughout much of thinleaf alder's distribution.
Regional descriptions of plant communities with thinleaf alder and site characteristics of thinleaf alder habitats follow.
Alaska: Thinleaf alder is reported on glacial shrublands (see Successional Status), riparian and wet-upland shrublands, and spruce-birch (Picea-Betula spp.) swamps. Thinleaf alder-willow and resin birch-thinleaf alder-willow cover types are common near timberline in interior Alaska. These communities form thickets that may be "extremely dense" or open and interspersed with reindeer lichens (Cladonia) and heath (Ericaceae) . On the Tanana River of central Alaska, 5-year-old thinleaf alder communities on sandbars were codominated by feltleaf willow (Salix alaxensis), sandbar willow (S. interior), and barrenground willow (S. brachycarpa subsp. niphoclada). Balsam poplar, paper birch (B. papyrifera), and white spruce grew in the understory; meadow horsetail (E. pratense) and variegated scouringrush (E. variegatum) were dominant herbs . See Successional Status for more information on this study.
Pacific Northwest: Thinleaf alder is a component of and sometimes forms glades within coniferous forests of the Pacific Northwest; it is also important to dominant in riparian corridors. Thinleaf alder is prevalent in ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta), and fir-spruce (Abies-Picea spp.) communities . Thinleaf alder glade openings generally occur on wet to mesic sites where thinleaf alder outcompetes conifers for soil moisture .
California: Thinleaf alder grows in coniferous, western hardwood, riparian, and other wetland communities in California. The photo above shows a typical Californian thinleaf alder habitat. Thinleaf alder is frequently found on the edges of ponds, bogs, and fens . In the Klamath Mountains and Sierra Nevada, it grows on the margins of California pitcher plant (Darlingtonia californica) bogs . Prior to extensive water diversions, thinleaf alder was likely important in quaking aspen-black cottonwood (Populus balsamifera subsp. trichocarpa) riparian corridors leading to Mono Lake, which is situated in the arid Mono Basin .
Northern and Central Rockies: Thinleaf alder is reported in coniferous forests, riparian galleries and shrublands, and wetland edges. In western Montana, thinleaf alder is frequent in Douglas-fir, western hemlock-western redcedar (Tsuga heterophylla-Thuja plicata), and grand fir (Abies grandis) forests. Surveys in the Blackfoot and Flathead valleys indicate that most thinleaf alders in these forest types grow as shrubs . In southwestern Colorado, thinleaf alder grows in mixed-conifer riparian woodlands dominated by white fir (A. concolor), southwestern white pine (Pinus strobiformis), interior ponderosa pine (P. ponderosa var. scopulorum), and blue spruce (Picea pungens) .
In the Rocky Mountains, thinleaf alder-dominated riparian communities tend to occur on an elevational gradient just above narrowleaf cottonwood (Populus angustifolia) communities . In western Colorado, Baker  noted that thinleaf alder was nearly always present at varying frequencies, and sometimes dominant, along narrowleaf cottonwood and blue spruce riparian forests. Thinleaf alder, red-osier dogwood, and water birch (Betula occidentalis) formed an often impenetrable shrub layer, with thinleaf alder dominant along stream margins and becoming less frequent with distance from the streams . Thinleaf alder dominates in the upper reaches of the narrowleaf cottonwood-Scouler willow (S. scouleriana) formation in Boulder County; it may also dominate in canyon bottoms . Its distribution extends into the mountain sagebrush-mountain grassland zone, mostly above 5,000 feet (2,000 m), in the Northern Rocky Mountains (reviews by [184,256]). In the Sawtooth National Recreation Area, Idaho, thinleaf alder dominates high-gradient streams (those on steep slopes or with rapid water flows) . In northwestern Montana, thinleaf alder community types occur from 3,760 to 6,700 feet (1,150-2,040 m) elevation on moist stream edges, overflow channels, and slope seeps . Thinleaf alder is common in many riparian shrublands dominated by other species, especially willows, red-osier dogwood, and Wood's rose (Rosa woodsii) (for example, [149,284]).
Southwest: In the Southwest, thinleaf alder occurs in wetlands within desert ecosystems and at high elevations. It may be a component of or locally dominant in riparian scrublands of Arizona; these scrublands are usually dominated by Bebb willow (Salix bebbiana), Scouler willow (S. scouleriana), and/or other willow species . Thinleaf alder is an obligate riparian taxon in New Mexico, where it may dominate riparian shrublands solely or codominate with willows [96,276]. Its relative dominance generally increases with increasing elevation . Thinleaf alder is a common shrub component of narrowleaf cottonwood communities of Arizona, New Mexico , and southern Colorado. Within wet areas, it sometimes grows as low as the pinyon-juniper (Pinus-Juniperus spp.) zone in northern Arizona . In Great Sand Dunes National Monument, Colorado, it is an important component of narrowleaf cottonwood/Kentucky bluegrass (Poa pratensis) riparian communities . Its distribution extends into the Engelmann spruce-corkbark fir zone (Picea engelmannii-Abies lasiocarpa var. arizonica), from 7,000 to 9,000 feet (2,000-3,000 m)), in the Rincon Mountains of Arizona (review by ). Thinleaf alder may be locally important to dominant in alpine riparian communities of the Southwest .
The following vegetation classifications describe plant communities, and some of their distinguishing site characteristics, where thinleaf alder is dominant or is a community type indicator. In state and province lists, plant communities are arranged geographically from north to south and west to east.
|Boreal North America, general||West, general||Alaska||Pacific Northwest|
|California||Southwest||Great Basin||Northern and Central Rockies|
|Northern Great Plains||Canada|
Boreal North America, general
- black spruce/thinleaf alder willow forest cover types; occur from Alaska to Saskatchewan on sites where the water table is at or above the soil surface during the growing season 
- thinleaf alder scrub-shrub fresh wetlands 
- thinleaf alder and willow-thinleaf alder thickets; occur on floodplains, streambanks, and swamplands throughout Alaska except in the Aleutian Islands and the arctic coastal plains
- balsam poplar/thinleaf alder vegetation types; these occur mostly in interior, southwestern, and south-central Alaska, with isolated occurrences in the Brooks Range
- white spruce/thinleaf alder and black spruce/thinleaf alder vegetation types. These types occur throughout central and southern Alaska; white spruce/thinleaf alder/bluejoint reedgrass types occur up to the northern and elevational tree lines .
- balsam poplar/thinleaf alder/field horsetail vegetation types along the Alaskan Highway; occur on sands and gravels 
- successional thinleaf alder/balsam poplar stands on floodplains of the Tanana River 
- thinleaf alder rangeland types from central to southern Alaska 
- tall shrub swamp rangeland types in interior and southeastern Alaska 
- feltleaf willow-Sitka willow (Salix sitchensis)-thinleaf alder successional communities above Glacier Bay 
Pacific Northwest, general
- eastside midmontane thinleaf alder-willow (Salix spp.) riparian-shrubland habitat types of Washington and Oregon
- black cottonwood/thinleaf alder eastside riparian woodlands 
- thinleaf alder snowslide communities of the Blue Mountains; occur from 4,000 to 6,000 feet (1,000-2,000 m) elevation on slopes ≥40° 
- sometimes codominant in montane mixed-coniferous wetland forests of the Cascade and Klamath mountains 
- thinleaf alder/skunk cabbage (Lysichitum americanum) riparian plant communities of northwestern Oregon; these are on moist to continuously saturated depressions and seepage slopes 
- thinleaf alder/Kentucky bluegrass, black cottonwood/thinleaf alder, and ponderosa pine/thinleaf alder/Kentucky bluegrass community types along Catherine Creek, northwestern Oregon 
- quaking aspen/thinleaf alder communities of the Blue Mountains 
- thinleaf alder/Wood's rose, thinleaf alder/Kentucky bluegrass, and thinleaf alder/woolly sedge (Carex pellita) community types of the Trout Creek Mountains 
- quaking aspen/thinleaf alder-red-osier dogwood and quaking aspen/thinleaf alder-common snowberry plant communities of the Blue Mountains 
- thinleaf alder community type of central Oregon; found from 2,400 to 5,600 feet (270-1,700 m) elevation. This is a young, seral type that typically occurs between active stream channels and floodplains of 2nd-order and larger streams. Sometimes it occurs in quiet backwaters .
- thinleaf alder-common snowberry association on well-developed, active fluvial surfaces, thinleaf alder/queencup beadlily (Clintonia uniflora) streambank association, panicled bulrush-bigleaf sedge-thinleaf alder (Scirpus microcarpus-Carex amplifolia) association on active channel shelves; these occur in central Oregon 
- thinleaf alder spring and seep communities; occur throughout central Oregon but occupy little total acreage. This community type is usually wet year-round and rarely burns.
- thinleaf alder-common snowberry community type; most common in the Ochoco Mountains. Found on floodplains of 2nd-order and larger streams.
- thinleaf alder-Douglas spirea (Spiraea douglasii) community type of the Deschutes and Fremont-Winema National Forests. Occur from 2,200 to 5, 700 feet (730-1,700 m) on steep to moderate-gradient floodplains.
- black cottonwood/mountain alder/woolly sedge community type on the Fremont National Forest; successional to lodgepole pine/water sedge (Carex aquatilis)
- black cottonwood-Engelmann spruce/mountain alder-red-osier dogwood community type on the Winema National Forest 
- thinleaf alder/scouringrush horsetail (E. hyemale) community types on river channel banks and floodplains of the Upper Klamath Basin. Flood-return intervals were ≤3.1 years, while flood-return intervals for willow and other shrub types were generally >25 years .
- black cottonwood-thinleaf alder and black cottonwood/thinleaf alder-red-osier dogwood plant associations; major types in eastern Washington
- western redcedar/thinleaf alder plant association; a minor type in eastern Washington
- thinleaf alder series of eastern Washington. The series includes these plant associations:
- thinleaf alder-red-osier dogwood-common snowberry and thinleaf alder-common snowberry
- thinleaf alder-Douglas spirea
- thinleaf alder alluvial bar
- thinleaf alder/lady fern (Athyrium filix-femina)
- thinleaf alder/bluejoint reedgrass
- thinleaf alder/Northwest Territory sedge (C. utriculata)
- thinleaf alder/horsetail (Equisetum spp.)
- thinleaf alder/tall mannagrass (Glyceria elata)
- thinleaf alder/oak fern (Gymnocarpium dryopteris)
- thinleaf alder/skunk cabbage
- thinleaf alder/mesic forb
- thinleaf alder/firethread sedge (C. scopulorum var. prionophylla)
- thinleaf alder/reed canarygrass (Phalaris arundinacea)
- thinleaf alder/panicled bulrush (Scirpus microcarpus) 
- sometimes codominant in streamside or meadowside California red fir/Sierra laurel (Abies magnifica/Leucothoe davisiae) forest types of the Klamath Mountains 
- white fir-mixed conifer/thinleaf alder riparian, spring, and seep plant associations of the northern Sierra Nevada and the Southern Cascade Range 
- sometimes dominates riparian woodland rangeland types from 5,000 to 8,000 feet (1,500-2,400 m) in the Sierra Nevada 
- thinleaf alder-western azalea (Rhododendron occidentale)/fowl mannagrass riparian community types of the western Sierra Nevada 
- thinleaf alder riparian forest habitat types of the Southwest 
- high-elevation (6,969-8,241 feet (2,124-2,512 m)) thinleaf alder community types of Arizona and New Mexico; some willows present but cover is ≥80% thinleaf alder
- thinleaf alder-mixed-deciduous community types of Arizona and northern New Mexico; white fir, narrowleaf cottonwood and/or quaking aspen codominate 
- montane willow-thinleaf alder and mixed-deciduous thinleaf alder-willow and thinleaf alder riparian community type series of Arizona [96,276]
- montane willow-thinleaf alder and mixed-deciduous thinleaf alder-willow and thinleaf alder riparian series [96,276]
- thinleaf alder-red-osier dogwood, thinleaf alder-bluestem willow, thinleaf alder-Pacific willow (Salix lucida subsp. lasiandra), and thinleaf alder/bluejoint reedgrass temporarily flooded shrubland community types
- blue spruce/thinleaf alder-Wood's rose and boxelder (Acer negundo)/thinleaf alder forested wetland community types 
- indicator and/or codominant taxon in riparian blue spruce vegetation type series
- Bebb's willow-thinleaf alder and boxelder/thinleaf alder vegetation type series 
- narrowleaf cottonwood/thinleaf alder-red-osier dogwood community type 
- community types of the Upper and Middle Rio Grande watersheds:
- blue spruce/thinleaf alder
- narrowleaf cottonwood/thinleaf alder
- thinleaf alder-bluestem willow (Salix irrorata) 
- thinleaf alder-red-osier dogwood, thinleaf alder/mesic forb, thinleaf alder/mesic graminoid, and quaking aspen/thinleaf alder-willow (Salix spp.) temporarily flooded shrubland alliances; these have G3 rankings (vulnerable) [264,284]
- thinleaf alder/willow (S. geyeriana, S. lasiandra, S. lutea, and/or S. scouleriana) community types of western and northeastern Nevada. Ranges from 5,650 to 7,840 feet (1,720-2,390 m) elevation; surrounding communities include quaking aspen, subalpine fir, western white pine (Pinus monticola), lodgepole pine, and mountain big sagebrush 
- thinleaf alder-Wood's rose, thinleaf alder/Kentucky bluegrass, and thinleaf alder/woolly sedge community types of the Trout Creek Mountains. The thinleaf alder/woolly sedge community was found only where livestock grazing was excluded and may be successional to the thinleaf alder/Kentucky bluegrass type .
- thinleaf alder/thinleaf alder community type of the eastern Sierra Nevada and northeastern Nevada; occurs in montane valleys
- thinleaf alder/mesic forb community type of the eastern Sierra Nevada and northeastern Nevada. Thinleaf alder growth is sparser than is typical of most thinleaf alder communities. Columbian monkshood (Aconitum columbianum) and tall fringed bluebells (Mertensia ciliata) are representative forbs .
- thinleaf alder/red-osier dogwood, riparian community types of 2nd- to 4th-order streams, and thinleaf alder/field horsetail stream and meadow community types
- thinleaf alder/mesic forb riparian community types of the Uinta and Wasatch mountains and the Canyonlands area. Cow parsnip (Heracleum lanatum) and Columbian monkshood are characteristic dominant forbs.
- thinleaf alder/mesic graminoid community types of the Uinta and Abajo mountains and the Canyonlands area. Kentucky bluegrass and tickle grass (Agrostis scabra) are characteristic dominant forbs .
- thinleaf alder-willow (Salix spp.) streamside communities of upper Big Cottonwood Canyon (8,000-9,000 feet (2,400-2,700 m)) in the Wasatch Mountains. Scouler willow is typically codominant. .
Rocky Mountains, general
- thinleaf alder-water birch mountain riparian shrub plant associations by narrow, slow-moving streams of Idaho, Wyoming, and Colorado
- thinleaf alder-Drummond willow (Salix drummondiana)/field horsetail plant associations on seasonally flooded streambanks
- Rocky Mountain maple (Acer glabrum)-thinleaf alder mountain riparian shrub plant associations
- blue spruce/thinleaf alder riparian plant associations of Wyoming, Colorado, and New Mexico (review by )
- subalpine fir-Engelmann spruce/thinleaf alder riparian forest association 
- narrowleaf cottonwood/thinleaf alder-red-osier dogwood plant associations on flat streambeds and floodplains of Wyoming and Colorado (review by )
- quaking aspen/thinleaf alder temporarily flooded association 
- thinleaf alder/red-osier dogwood, thinleaf alder/mesic forb, and thinleaf alder/mesic graminoid shrubland associations 
- characteristic or dominant taxon of rich limestone fens in northern Idaho 
- thinleaf alder plant community of northern Idaho. This may be a minor type and was not well sampled as of 1991 
- thinleaf alder community types in valleys, foothills, and mountains of eastern Idaho. This is a major type from 5,200 to 6,930 feet (1,580-2,110 m) elevation on streambanks, floodplains, seeps, and canyon bottoms .
- thinleaf alder-red-osier dogwood community type of the Upper and Middle Fork Salmon River; most common on gravel- and sandbars 
- thinleaf alder-northern black currant (Ribes hudsonianum) community type of central Idaho; these occur as narrow stringer communities near perennial streams. They are successionally stable and may completely shade the streams .
- thinleaf alder-red-osier dogwood riparian communities of southwestern Idaho; sagebrush (Artemisia spp.) or conifer communities are adjacent 
- wetland and riparian indicator plant 
- thinleaf alder riparian habitat types at low to midelevations (3,760-6,700 feet (1,150-2,040 m)); occupy alluvial terraces, streambanks, and floodplains of moderate- to high-gradient streams. Typically, thinleaf alder is dense and plant species diversity is high . In thinleaf alder dominance types on midelevation alluvial terraces, the herbaceous understory is typically sparse; field horsetail and sedges (Carex spp.) are characteristic .
- dominant shrub in spruce (Picea spp.)/skunk cabbage and quaking aspen/bluejoint reedgrass riparian habitat types 
- characteristic or dominant on rich limestone fens of northwestern Montana 
- Engelmann spruce/thinleaf alder-Wood's rose/field horsetail, Engelmann spruce/thinleaf alder/bluejoint reedgrass, thinleaf alder-red-osier dogwood/meadow horsetail-field mint (Mentha arvensis), and Drummond willow-thinleaf alder riparian community types of northwestern Montana 
- thinleaf alder community types of central and eastern Montana. These are minor types at low to midelevations (4,720-6,400 feet (1,580-1,950 m)) along moderate to high-gradient streams. Bluejoint reedgrass and nonnative fowl bluegrass (Poa palustris) are typically dominant in the ground layer [151,302]. These are temporarily flooded communities, ranked G3 (vulnerable) 
- thinleaf alder wetland community type of west-central Montana; associated with year-round seeps and valley springs and characterized by high plant species diversity. Subalpine fir or Douglas-fir communities are adjacent .
- thinleaf alder community type in southwestern Montana; a minor type typically confined to moist stream edges, overflow channels, and hillside seeps. A disturbance type that may persist for "a long time" before willows or conifers replace thinleaf alder successionally .
- Engelmann spruce-subalpine fir/thinleaf alder, blue spruce/thinleaf alder, blue spruce-lodgepole pine-white fir/rose (Rosa spp.)-thinleaf alder/western wheatgrass (Pascopyrum smithii), ponderosa pine/thinleaf alder, and thinleaf alder/western snowberry riparian habitat types 
- thinleaf alder riparian type of the Medicine Bow National Forest. This type is associated with subalpine fir/grouse whortleberry (Vaccinium scoparium) habitat types of the Sierra Madre and Laramie Peaks . It may form extensive stands in moist areas.
- thinleaf alder-northern black currant community type of west-central Wyoming; these occur as narrow stringer communities near perennial streams. They are successionally stable and may completely shade the streams .
- thinleaf alder/field horsetail community type of the Shoshone National Forest; water table is at the soil surface
- thinleaf alder/mesic graminoid community type of the Shoshone National Forest; bluejoint reedgrass and beaked sedge (C. rostrata) typically dominate the understory. Stands vary from open to dense. This type may be a thinleaf alder/forb type degraded by overgrazing .
- narrowleaf cottonwood/thinleaf alder, narrowleaf cottonwood-blue spruce/thinleaf alder, and blue spruce/thinleaf alder riparian forest associations of western Colorado 
- thinleaf alder-water birch-willow (Salix spp.) riparian shrublands of the Front Range; these typically occur on the hydric limits of wet subalpine fir-Engelmann spruce forests and narrowleaf cottonwood or plains cottonwood (Populus deltoides subsp. monilifera) woodlands. On drier sites, thinleaf alder sometimes dominates the understories of subalpine fir-Engelmann spruce ravine forests .
- thinleaf alder-water birch/beaked hazelnut canyon forest association of the Front Range 
- thinleaf alder-resin birch/water sedge subalpine riparian shrub plant associations along pond margins and in spruce (Picea spp.) forest openings in Rocky Mountain National Park (review by )
- narrowleaf cottonwood/thinleaf alder riparian habitat types of the Roosevelt and Arapaho National Forests. Occurs on benches by small streams and on the floodplains of large streams .
- thinleaf alder-water birch-willow/field horsetail habitat type; common riparian type in the Middle Rocky Mountains east of the continental divide 
- thinleaf alder/field horsetail and thinleaf alder/red-osier dogwood habitat types on the Gunnison and Uncompahgre National Forests . Upland thinleaf alder-red-osier dogwood plant habitat types occur on relatively dry sites on the Gunnison National Forest (review by ).
- narrowleaf cottonwood/thinleaf alder riparian community types along the Animas River  and in the Gunnison Basin 
Utah (see entries in Great Basin)Northern Great Plains
Great Plains, general
- thinleaf alder shrub swamps of Iowa, Minnesota, North Dakota, and Manitoba 
- balsam poplar-thinleaf alder vegetation types along the Dempster Highway and the Foothills Gas Pipeline; occur on riverine floodplains and terraces without permafrost 
- Bebb willow-pussy willow-thinleaf alder vegetation types along the Peace-Athabasca Delta; common on levees that seldom flood 
Propagation from Seed: Seed is best sown as soon as it is ripe in a cold frame. If Alnus incana seeds are not sown in the fall, they require cold stratification for three months before germination. Sow the seeds in containers or seed trays containing a slow release fertilizer. Firm the medium and place the seeds thinly and evenly on top. When large enough to handle, the seeds can be placed into individual pots. If growth is sufficient, they may be planted into their permanent positions in the summer, if not they can be planted in the spring.
larva of Agromyza alnivora mines leaf of Alnus incana
Other: sole host/prey
Plant / resting place / on
adult of Cryptocephalus bipunctatus may be found on Alnus incana
Remarks: season: 4-late 8
Foodplant / saprobe
superficial stroma of Daldinia petriniae is saprobic on wood of Alnus incana
In Great Britain and/or Ireland:
Foodplant / saprobe
stroma of Hypoxylon petriniae is saprobic on dead Alnus incana
Other: unusual host/prey
Foodplant / parasite
hypophyllous uredium of Melampsoridium betulinum parasitises live leaf of Alnus incana
Remarks: season: 8-10
Other: unusual host/prey
Foodplant / parasite
hypophyllous, subepidermal, scattered or in groups telium of Melampsoridium hiratsukanum parasitises live leaf of Alnus incana
Foodplant / pathogen
Phytophthora alni infects and damages tarry spotted trunk of Alnus incana
Other: minor host/prey
Foodplant / spot causer
amphigenous colony of Ramularia hyphomycetous anamorph of Ramularia alnicola var. alnicola causes spots on live leaf of Alnus incana
Fire Management Considerations
Early postfire environments generally favor gray alder establishment and growth. As a nitrogen fixer, gray alder can have important ecological effects on postfire plant and soil fauna succession. In riparian areas, sprouting gray alders help stabilize burned banks and shores. Gray alder may provide little protection in riparian areas burned by fire severe enough to kill the roots. Dead and decaying thinleaf alder roots seldom provide substantial protection from erosion during heavy spring run-off . To date (2011), research on using prescribed fire in wetland communities with gray alder was limited, and further research is needed before guidelines for burning in gray alder riparian and wetland zones can be made. Speckled alder: Prescribed fire may help control speckled alder on silvicultural sites and on open mires. Related prescribed fire studies and management recommendations available are summarized here.
In the Great Lakes states, frequent prescribed fires (no return interval given) can help control speckled alder, beaked hazelnut, and American hazelnut in the understories of red pine plantations. Summer fires best prepare a mineral soil seedbed necessary for natural red pine regeneration, and the generally drier fuels results in severer fires and better shrub control than spring prescribed fires .
On plantations, interference of postfire speckled alder regeneration with conifer regeneration and growth may be minimal on moist lowland sites where fire has prepared a mineral seedbed for conifers. Speckled alder and mountain alder "grew well" on such sites 10 years after clearcutting and 8 years after a late spring (2 June 1970) prescribed fire on a jack pine/black spruce plantation in southeastern Manitoba. Chrosciewicz  concluded that even though "plant competition was generally much more severe" on moist lowland sites than on dry or fresh upland sites, the alders and other postfire regeneration "had no detrimental effect on regeneration of commercial tree species, including pine" on moist lowland sites. Postfire conifer establishment was poor on the upland sites, which the author attributed to lower than normal precipitation and consequently, drier than normal soils, during the first 2 postfire growing seasons . Another study by Chrosciewicz , near Winnipeg, Manitoba, had similar results. Five years after low- and moderate-severity spring (late May) prescribed fires, shrub cover, including speckled alder, averaged 15% to 20% in regenerating black spruce stands. This "rather luxuriant vegetation" "seemed to provide valuable shelter to the spruce seedlings in their early development" . See the Research Project Summary on Chrosciewicz's  research for information on the fire prescriptions, fire behavior, and for details of black spruce's postfire response.
Early spring burning—after snowmelt but before soil thaw—may help control speckled alder and other woody invaders in wetlands. Researchers found that early spring prescribed burning was more cost-effective than early and late summer cutting or late manual torching for reducing woody encroachment in a tussock sedge-bluejoint grass wetland meadow in Wisconsin. Additionally, it caused the least disturbance to groundlayer vegetation and to the soil. The researchers warned that due to sprouting of woody species (which occurred after all fire and cutting treatments), prescribed fire must be viewed as an ongoing treatment strategy. Speckled alder was a component of the woody vegetation, although Sandberg's birch (Betula × sandbergii) and red-osier dogwood had the most cover. Fire effects on speckled alder alone were not measured .
Managers of the Lac St-Francois National Wildlife Area in Quebec found that neither a single wildfire nor mechanical treatment (double-cutting shoots) controlled speckled alder invasion on an acidic, water sedge-hairy sedge fen in the short term, while stump applications of herbicide reduced speckled alder but also reduced nontarget plants. The wildfire had burned part of the fen prior to the study, and plots were established on sections of the burn that were "highly invaded by small to medium-sized individual alder shrubs". Speckled alder root crowns were located at or below the water table. All of 40 speckled alder individuals on study plots survived the fire and were sprouting "vigorously" in postfire year 1. For the double-cut treatment, stems were cut to the root crown in mid-June, with a 2nd cutting of new sprouts in early August. The next year, 80% of cut plants were sprouting "vigorously". While conceding that another cut would increase speckled alder mortality, the authors found cutting too ineffective and costly to justify further cuttings. Foliar applications of glyphosate in July gave 100% control of speckled alder but also killed more nontarget plants than considered acceptable (no limits given). For cut-stump glyphosate treatments, either August or March application gave good control (79% and 93%, respectively). The March treatment was preferred, because it was more effective and accessibility was greater on the frozen winter ground than on the wet summer ground . The authors noted that based on other research [46,161], very frequent prescribed fires (1 or 2 fires annually over 5 years) may control speckled alder but would "carry very high operation costs" and possibly be detrimental to the fen. However, they considered prescribed fire a viable option for long-term control of speckled alder .
Thinleaf alder: Recommendations for prescribed fire use in thinleaf alder communities are few and sometimes contradictory. Prescribed fire in these communities may increase plant community productivity or conversely, be used as a tool to control thinleaf alder. Olason and Agee  note that although fires were probably historically frequent in riparian Douglas-fir forests of the Pacific Northwest, it may be necessary to "totally protect" riparian forests in areas where favorable salmonid habitat is limited. They suggest treating upslope forests with prescribed fire or fire-surrogate treatments, speculating that such treatments would make wildfires less likely to burn into moist portions of riparian zones .
Others suggest that excluding fire from riparian zones may be harmful in the long term. On the Payette National Forest, Idaho, a low-severity May prescribed fire in an upland subalpine fir-Engelmann spruce community burned only slightly into an alder (Alnus spp.)-dominated riparian zone. Comparing these results to late summer wildfires in the same communities, the authors found that with wildfires, the area burned in riparian communities was proportionate to that burned in the upland communities. While fire severity was generally lower in the riparian than the upland communities, portions of the riparian zones burned at high severity. The authors concluded that in riparian zones, spring prescribed fire is not an ecological surrogate for fall wildfire and that a "prescribed fire regime" of repeatedly burning upland communities while excluding fire from riparian forests may eliminate important natural disturbances from riparian and stream habitats . Besides wildfire itself, these disturbances may include postfire erosion, altered stream channels, altered stream temperatures, and altered species composition of the aquatic animal communities [8,107].
Effects of prescribed fires in riparian and wetland zones may be difficult to predict. Prescribed fire may help control thinleaf alder and other woody invasives in freshwater wetlands . Jacobson and others' study  provides management recommendations for reducing woody encroachment on open fens. However, in forests, thinleaf alder may increase after overstory removal by prescribed fire and/or cutting, especially on wet sites. Researchers in British Columbia report that although moderate to severe fires are needed to "set back the growth" of thinleaf alder, such fires rarely carry in the wet to moist sites where thinleaf alder usually grows .
Thinleaf alder-dominated communities may recover more quickly than adjacent upland communities. Six years after the Diamond Peak Wildfire Complex on the Payette National Forest, woody plant cover in thinleaf alder-dominated riparian communities was greatest on sites where fire severity was greatest (P=0.05). Across 6 riparian sites burned at varying severities, total woody cover ranged from a low of 8% in postfire year 2 to 30% in postfire year 6. The authors found that in postfire year 6, "little recovery had taken place in the upland (ponderosa pine) community" .A May wildfire in a quaking aspen-balsam poplar/thinleaf alder-red alder community reduced nesting and hiding cover for ruffed grouse in the short term. Alders (thinleaf and red alder combined) averaged 8.0 feet (2.4 m) tall 1 year before and 3.5 feet (1.1 m) tall 1 year after the fire. Along a 2,000-foot (600 m) transect, alders <3 feet (2 m) tall averaged 35.8 stems/transect before fire and 3.8 stems/transect 1 year after fire. On drumming sites used by male ruffed grouse, alders <3 feet tall averaged 28.7 stems/transect before fire and 2.9 stems/transect after fire. In postfire years 1 and 2, estimated ruffed grouse numbers in burned areas averaged 50% of ruffed grouse numbers 1 year before fire. By postfire year 3, density of males in unburned drumming areas was almost 3 times that of males in burned drumming areas . See the FEIS review of ruffed grouse for details.
Gray alder experiences a wide variety of FIRE REGIMES across its broad distribution in North America. For example, ponderosa pine woodlands in the Pacific Northwest and California historically experienced mostly low-severity surface fires with an average return interval of 13 years , while mixed-hardwood-spruce forests of the Northeast historically experienced mostly stand-replacement fires at intervals of 400 years or more . As an early-successional species that sprouts after fire, gray alder is likely to flourish in wetland plant communities where fire is frequent or severe enough to maintain or create open conditions. This is likely true across the species' worldwide distribution. Scots pine-Norway spruce (Pinus sylvestris-Picea excelsa) forests of Scandinavia, where European gray alder is an important component of the vegetation, historically experienced frequent, low-severity surface fires and mixed-severity fires under a fire regime similar to that of ponderosa pine and mixed-conifer forests of the western United States. Frequent understory fires helped maintain European gray alder in the understory (review by ). Speckled alder: Little information was available on fire frequency and fire behavior in riparian and wetland plant communities where speckled alder is an important to dominant member of the plant community. One study, near Thunder Bay in Ontario, found wildfire did not carry well once it reached a speckled alder community. A stand-replacement wildfire burned a mixed hardwood-coniferous forest, but the fire slowed or stopped in riparian zones dominated by speckled alder. Speckled alder showed scorching and damage to top branches but was otherwise unharmed, and "little damage was evident in the riparian zone" . Research is needed on FIRE REGIMES of riparian and wetland plant communities in the eastern United States.
Summaries of several fire studies in plant communities where speckled alder was important or dominant follow.
Red-white-jack pine ecosystems of the Great Lakes states historically experienced frequent, low-severity surface fires. Frequent fires prevented development of late-successional tree species such as white spruce and red maple, and also inhibited spread of understory shrubs including speckled alder, mountain alder (A. viridis subsp. crispa), beaked hazelnut, and American hazelnut. Heinselman  reported that in these ecosystems, both the late-successional tree and the shrub layers are maturing and expanding under fire exclusion. A fire history study on Pictured Rocks National Lakeshore, Michigan, found red-white-jack pine shoreline forests with speckled alder had a mean fire-return interval of 21.8 years before European settlement, with fire-return intervals lengthening after the early 18th century. At the time of study (1985), the area had not experienced fire for the past 84 years .
A study of fire scarring in red and jack pines near Lake of the Clouds in northern Minnesota found fire-return intervals ranging from 16 to 62 years between 1691 and 1818. Speckled alder was a dominant shrub in the area. Over the previous 1,000 years, lake sediment analyses showed a mean fire-return interval of about 70 years; speckled alder pollen was present in most sediment cores sampled across the 1,000 years . A similar lake sediment study in Boundary Waters Canoe Area also found a mean fire-return interval of about 70 years over the past 1,000 years; speckled alder pollen was present in all cores sampled across that time. The extant plant community was a quaking aspen-paper birch/speckled alder forest .
Red spruce-balsam fir-white spruce forests of the Northeast historically experienced infrequent, stand-replacement fires at 150- to 300+-year intervals. Surface fires were "extremely uncommon". Speckled alder is an early-successional species in these forests .
The black spruce/speckled alder forest cover type of boreal North America is reportedly a stable type that regenerates into forests of similar composition after fire . Information on FIRE REGIMES for this type was not found in the literature. In general, boreal black spruce forests experience stand-replacement fires at intervals of 50 to 150 years .
A study by Jacobson and others  suggests that historically, infrequent fires may have reduced encroachment of speckled alder and other woody species into open mires in the Northeast. Frequent fires, however, may favor sprouting woody taxa such as speckled alder. A study at Crystal Fen in northern Maine suggested that frequent fires combined with high drainage favored encroachment of speckled alder and other woody species. Charcoal analysis of the fen showed fire was uncommon before a railroad was constructed in the area. Fire frequency increased after 1937, when a drainage ditch was excavated next to a railbed, drying out vegetation, and sparks from diesel-powered trains ignited fires frequently. A survey of tree ages showed that "many" speckled alder, northern white-cedar, and other woody species established between 1937 and 1950. Fire frequency dropped after 1950, when diesel engines replaced steam engines, ignition sources became uncommon, and for undescribed reasons, the fen began flooding again. Increased moisture and no fire, however, did not open the fen: Woody species continued establishing on areas of the fens that, based on pollen and charcoal records, historically had few to no woody plants. The authors recommended restoring the historical drainage pattern, cutting woody species, and/or introducing prescribed fire to restore the open fen .
As of 2011, almost no literature was available on FIRE REGIMES of pine or hardwood ecosystems of the Southeast where speckled alder formed a substantial component of the vegetation. A review reported that pond pine and bay (Magnolia and Persea spp.) shrubland bogs, of which speckled alder is a component, burn at irregular, 5- to 50-year intervals. Nearby bog communities with low shrub diversity tend to have less frequent fire-return intervals than the bog communities with high shrub diversity .
See the Fire Regime Table for speckled alder for further information on FIRE REGIMES of vegetation communities in which speckled alder may occur.
Thinleaf alder: Historical FIRE REGIMES for riparian zones of the western United States are not well studied [307,311], although more is known of FIRE REGIMES in riparian and wetland areas of the West than those of the East. Historically, thinleaf alder glades and thickets in the Northern Rocky Mountains probably burned less frequently than surrounding coniferous forests, but at "higher intensity" than surrounding vegetation. Davis and others  speculated that thinleaf alder thickets may be maintained by infrequent fire. In most years, thinleaf alder thickets in riparian zones do not burn . Similarly, thinleaf alder stands growing on seeps and springs may burn rarely .
In general, fires are less frequent in riparian and wetland areas of the West than in drier areas . At low- to midelevations in the southern Cascade Range and Klamath Mountain regions of California, fire-return intervals in riparian areas overall are about twice those of surrounding areas, but fire intensity is generally greater when the riparian areas burn . Fire-return intervals near intermittent and ephemeral streams are likely similar to those of surrounding areas . In most years, perennial stream communities may serve as firebreaks (review by ). A fire management plan for Craters of the Moon National Monument, Idaho, states "there is no evidence that fire is necessary to maintain the (riparian) vegetation type in this area". However, the authors speculated that infrequent, periodic fire would probably improve the health and productivity of shrubs and that most shrubs, including thinleaf alder, would survive fires that were "not too frequent" . Arno and Harrington  suggest that prior to 1900, riparian ponderosa pine communities in the western United States burned 2 to 5 times per century. Fire-return intervals in riparian and wetland communities may vary across time and space, however.
In riparian zones where thinleaf alder is known or likely to occur, fires tend to have longer return intervals, and burn at higher severity, than in upland sites ([115,268,310]), Arno 2001 personal communication ). This trend is not strong or consistent in all areas, however. Fire frequency and severity have been lower in some riparian areas compared to adjacent upland areas; other sites have similar fire histories on riparian and upland zones. Factors affecting fire-return intervals in riparian zones include soil and plant moisture, fire exclusion, livestock grazing, logging, damming and other water-flow regulation, and presence of invasive species that alter fuel characteristics . Coniferous riparian forests may have historically been too moist to burn in some years; consequently, low- and moderate-severity fires in upland areas would often extinguish at the riparian zone. In an Alberta study of upland and riparian lodgepole pine, subalpine fir-Engelmann spruce, white spruce, and balsam poplar communities on the Jumping Creek Watershed, landform was the primary driver of fire frequencies. Using time-since-fire distributions, the authors found that riparian zones and the larger, entire-watershed area had similar mean fire frequencies. At a fine scale, however, fires were less frequent near stream channels with gravel- or sandbars, whereas terraces above straight streams without bars tended to burn at same frequency as the overall watershed. From 1851 to 1890, fire-return intervals averaged 71 years in riparian and 48 years in entire-watershed zones, respectively. After 1891, fire-return intervals lengthened to 208 and 178 years, respectively. The authors concluded that on the Jumping Creek Watershed, except for bars, areas adjacent to streams were just as likely to burn as upland areas . Understory vegetation was not surveyed in the study, but thinleaf alder is known to occur in the area.
Two studies suggest a trend of longer fire-return interval in riparian Douglas-fir than upland Douglas-fir forests. In Douglas-fir forests on the Steamboat Creek Watershed in southwestern Oregon, mean fire-return intervals were longer in riparian than upland sites (37 vs. 31.5 years), but the difference was not significant. Fire-return intervals ranged from 4 to 167 years on riparian and 2 to 110 years on upland sites. The authors speculated that fires were historically common, of mixed severity, and patchy on their study sites, with a high likelihood of fire in both riparian and upland zones. They suggested that historically, many riparian forests burned when upslope fires backed into riparian zones . On eastside riparian Douglas-fir forests in the Cascade Range of Washington, fire-scarred trees were consistently fewer in riparian than on upland sites. The authors concede that fewer fire scars does not necessarily mean fewer fires; fires in the riparian zone could have been mostly low-severity surface fires that caused less scarring than fires in upland areas, or fires could have been more severe, stand-replacement fires that left fewer standing live, fire-scarred trees than in upland zones. Plant association groups in riparian forests had 25% to 42% fewer wildfires than similar plant associations on sideslopes. Fire-return intervals ranged from 11 to 46 years in riparian forests and from 7 to 39 years on sideslopes. On sideslopes, stands on south-, east-, and west-facing slopes in riparian zones were older than those in nonriparian zones (P≤0.1); differences in stand ages between riparian and nonriparian sites on north-facing slopes were not significant .
On the Shasta-Trinity National Forest in the Klamath Mountains of California, fire-return intervals in riparian and upland mixed-conifer forests were compared. Intervals between fires were consistently longer in riparian vs. upland sites :
|Fire-return intervals of riparian and upland mixed-conifer sites in the Klamath Mountains |
|Site||Mean fire-return interval (range)||Time period||Number of stumps sampled|
|Root Creek, |
|33 years (7-56)||1673-1880||4|
|Root Creek, |
|7 years (3-44)||1749-1924||14|
|North Fork Shotgun Creek, |
|16 years (5-56)||1710-1916||9|
|North Fork Shotgun Creek, |
|8 years (4-64)||1622-1887||16|
In a fire history study of Jeffrey pine, white fir, and mixed-conifer forests of the Sierra Nevada in which thinleaf alder was "highly abundant", fire-return intervals were usually similar on riparian and upland sites. On 36 paired riparian and upland sites on the Lassen and Tahoe National Forests, only 9 paired sites had significantly different fire-return intervals (P≤0.1). Fire-return intervals ranged from 15.3 to 86.5 years on riparian sites and from 10.0 to 56.3 years on upland sites. They averaged 30.0 and 27.8 years on riparian and upland sites, respectively. Most fire scarring (88% on riparian and 79% on upland sites) happened in late summer and early fall, after tree-ring growth had stopped .
Fires in the spruce-birch and aspen ecosystems of interior Alaska are usually stand-replacing and often extensive [234,344], burning "for days with high intensities, covering vast acreages" . Fire frequency is poorly known but probably ranges from 75 to 150 years. In quaking aspen/thinleaf alder stands on Ester Dome, fire kill was the primary cause of tree mortality .
Near Rainbow Lake in Wood Buffalo National Park, Alberta, a fire history study found charcoal evidence of at least 12 local fires in 840 years, with a mean return interval of 69 years. In some cases, thinleaf alder pollen counts (a surrogate for thinleaf alder density) peaked about 35 years after a fire; however, thinleaf alder pollen counts declined after 6 of the local fires. The extant plant community is mixed hardwood-conifer. Thinleaf alder is most common at the lake margins, along with scattered black spruce and tamarack .
See the Fire Regime Table for thinleaf alder for further information on FIRE REGIMES of vegetation communities in which thinleaf alder may occur.
Because gray alder adds nitrogen to soils and typically grows in moist soils, gray alder communities are usually highly productive ; hence, their fuel loads can be large. Gray alder may produce a "dense" litter layer . However, because gray alder prefers moist sites, in most years gray alder communities may act as firebreaks. Riparian zones with gray alder are often buffer zones where upland fires decrease in severity or stop . Speckled alder and thinleaf alder communities are placed in fuel model 0  and fire group 0 , respectively; these plant communities do not burn readily [282,312]. Communities in fuel model 0 are described as vegetation types in which fire will not carry due to saturated ground or standing water, discontinuous fuels, and/or lack of ladder fuels . However, with dry weather and the accumulation of dry fuel, riparian areas can become corridors for fire spread .Speckled alder: A prescribed burning guideline for Ontario reports that speckled alder communities do not burn well under conditions needed for prescribed fires. McRae  found that in boreal black spruce-white spruce-quaking aspen forests of Ontario, prescribed fires did not typically spread into drainageways dominated by speckled alder. Because there was no combustible slash, these drainages acted as fire barriers . An extension publication recommends speckled alder as an ornamental due to its low flammability .
Several publications provide help for estimating fuel loads in speckled alder habitats. See these publications: [314,329] for information on models to estimate speckled alder biomass in the northern United States and Canada. Buech and Rugg [47,48] provide equations to predict aboveground biomass of speckled alder. Their model was developed in northern Minnesota [47,48]. A photoseries for assessing fuels in coniferous forests of northern Ontario provides size class breakdowns and photos for live and woody surface fuels in black spruce, black spruce-tamarack, black spruce-jack pine, black spruce-poplar (Populus spp.), balsam fir-black spruce, paper birch-white spruce, and poplar-white birch stands , all of which may include speckled alder as a component of the vegetation (see Site Characteristics and Plant Communities).
In the laboratory, speckled alder's heat of combustion and total heat release were about average for shrubs of the Northeast .
Several studies provide what may be representative examples of fuel loads in speckled alder habitats. In a speckled alder/goldenrod (Solidago spp.) community in upstate New York, speckled alder production averaged 730 g/m²/year. Leaves and twigs comprised 42% of total production; 25% was in the boles; 21% in branches; and 12% in fruits. Herbaceous production averaged 241 g/m², yielding a total aboveground production of 971 g/m² for the speckled alder community . A New York study found total speckled alder production averaged 2,225 g/m², 21% of which was roots .
In commercial forests in Michigan, speckled alder biomass was least in oak-hickory and greatest in tamarack stands . In a similar study across commercial forests in the Northern Great Lakes (northern Minnesota, northern Wisconsin, and the Upper Peninsula of Michigan), speckled alder biomass was least in jack pine and greatest in balsam fir stands . No information on stand ages was available.
|Speckled alder biomass by forest type|
|Forest type||Michigan ||Northern Great Lakes |
|eastern white pine||118||3,368|
In Nova Scotia, speckled alder biomass averaged 83 kg/ha in dense mixed-conifer, 140 kg/ha in dense mixed-hardwood, and 1,150 kg/ha in open mixed-conifer forests .
Thinleaf alder: Thinleaf alder thickets are somewhat fire-resistant because the duff is usually cool and moist, and the undergrowth is sparse . The generally moist conditions in thinleaf alder stands usually inhibit fire spread (review by ). Even when fires are severe in upland areas, riparian zones may remain unburned or burn with lower severity. However, fires may burn severely in riparian areas in drought years . A fire management plan for Lassen National Park, California, reported that natural fires seldom ignite in black cottonwood-thinleaf alder woodlands; instead, those woodlands are generally firebreaks. However, old stands with diseased and downed trees may be "quite flammable", especially if white fir or red fir has formed ladder fuels in the understory .
In many forested riparian areas, live and dead fuel structure and loads have altered due to fire exclusion. Arno and Harrington  report that in riparian ponderosa pine communities of the West, where thinleaf alder is known to occur, most sites are dominated by dense, shade-tolerant trees such as grand fir, and the shrub and ground layers are sparse.
On 3 thinleaf alder wetland communities in west-central Montana, total aboveground plant productivity ranged from 3,320 to 4,820 lbs/acre. Of that total, shrubs averaged 316 lbs/acre, forbs averaged 1,200 lbs/acre, and graminoids averaged 2,713 lbs/acre .
Several studies described below provide what may be representative examples of fuel loads in thinleaf alder habitats by the Tanana River in Alaska. Yarie and Mead  present models to estimate twig and leaf biomass of thinleaf alder and other species of the Tanana River Basin.
On sandbars of the Tanana River, total production in 5-year-old thinleaf alder thickets averaged 20,000 kg biomass/ha (including root biomass). Production peaked in 15-year-old thickets at an average of 65,000 kg/ha, while 20-year-old thickets averaged 95 kg/ha . On thinleaf alder-dominated floodplains of the Tanana River, thinleaf alder biomass was almost 5 times greater in 20- vs. 5-year-old stands. Codominant willows and horsetails comprised much smaller portions of the total plant community biomass (3.2-8.7%) .
|Distribution of biomass (kg/ha) in thinleaf alder-dominated stands of different ages |
|Sample||5 years||15 years||20 years|
|Thinleaf alder biomass*||8,751||27,810||42,741|
|% of total plant community biomass||42.9||43.5||45.1|
|Total down woody fuel biomass||not available||10,464||16,389|
|Total litter biomass||4,340||4,134||4,390|
|*Above- & belowground biomass mass was measured for live plants.|
After late February logging, a prescribed broadcast burn in July reduced fuels in a white spruce/thinleaf alder/feathermoss (Hylocomium sp.) forest on the Tanana River floodplain. The fire "substantially" decreased organic material on the soil surface and exposed mineral soil. Down and dead woody fuels were reduced an average of 67%, mean depth of the forest floor was reduced 43%, and the soil organic layer was reduced 2.9%. See Zasada and Norum  for information on the fire prescription and fire weather conditions.
Fire adaptations and plant response to fire
Fire adaptations: Gray alder has many adaptations that can aid its postfire recovery. It sprouts from the root crown and/or roots after top-kill. Root crown sprouting is most common (see Vegetative regeneration), while root sprouting may occur when fire is severe enough to kill the root crown. Gray alder may also establish from seed; this may include seed dispersed from on-site, crown-stored "cones" (, review by ), wind- or water-dispersed seed originating from off-site parents, or seed in the transient soil seed bank . Some of gray alder's adaptations to riparian environments, including tolerance of high light and the ability to sprout after repeated top-kill, may also benefit gray alder in early postfire environments . Plant response to fire: Speckled alder
Speckled alder sprouts from the root crown after top-kill by fire. Its postfire sprouting response is likely strongest on sites that are moist during the growing season . In a review of fire responses of plant taxa in northern coniferous forests, Heinselman  classified speckled alder as fire-tolerant.
A prescribed April fire top-killed most speckled alders in a study site on the Allegheny River floodplain of Pennsylvania. Open areas with individual trees burned well, but dense stands of speckled alder carried fire mostly on the edges. The fire top-killed 55% of speckled alder stems. By postfire month 9, most burned speckled alders were sprouting at or within 2 inches (5 cm) of the soil surface, from near the bottoms of the stems or from the root crowns. However, sprouting in speckled alder was not related to fire; it occurred on burned and unburned stems at approximately the same rate, 90%. Sampled stems produced an average of 8 to 10 sprouts, with basal diameters ranging from 0.1 to 0.5 inch (3-12 mm) and heights ranging from 9 to 47 inches (22-120 cm). Twelve percent of speckled alder stems were browsed, probably by white-tailed deer and cottontails . See the Research Project Summary of this paper for information on the burning conditions and effects of the fire on hawthorns (Crataegus sp.) in the same area.
A few studies show speckled alder may be more common in early than late postfire succession. In a fire chronosequence study in black spruce-jack pine ecosystems of northern Ontario, speckled alder was most common on wet peatlands burned 1 to 3 years prior (P=0.05). Burn ages ranged from 0 to 57 years . Speckled alder reached greatest postfire abundance in postfire year 10 in red pine-black spruce forests of Saskatchewan . In a chronosequence of 9 burned black spruce/mountain-laurel (Kalmia latifolia) forests in Terra Nova National Park, Newfoundland, speckled alder was present only on a 20-year-old burn, with 2% mean cover. Burn ages ranged from 1 to 38 years . In quaking aspen, jack pine, and black spruce swamp communities of Itasca County, Michigan, speckled alder occurred in 7 of 9 burns surveyed. The burns were from 1 to about 58 years old . A review of fire succession in balsam fir forests of the Northeast reported that speckled alder thickets may replace balsam fir after fire and that those thickets may persist for decades before trees establish .
Frequent fire likely favors speckled alder over conifers. Speckled alder thickets may form after stand-replacing fire in northern white-cedar communities . In a northern white-cedar swamp in Michigan, speckled alder was most abundant in an area that burned 3 times in 30 years. The authors reported that dense growth of speckled alder and willows now occur on sites where the northern white-cedars experienced the greatest fire kill .
Speckled alder increased over 10 postfire years on a hybrid spruce clearcut that was slashburned at low to moderate severity. The site was on the Mackenzie Forest District in subboreal British Columbia. Speckled alder was the dominant shrub before and after the fire, with abundance at postfire year 10 exceeding its prefire cover and frequency. Speckled alder's prefire cover and frequency were 4.6% and 50%, respectively. At postfire year 10, it had 8.9% cover and 67% frequency. Overall, shrub height was more in postfire year 10 than before fire, primarily due to the rapid postfire growth of speckled alder and Rocky Mountain maple. See the Research Paper of Hamilton's  study for details on the fire prescription, fire behavior, and postfire responses of other species in the plant community.
Two studies suggest that speckled alder responds similarly to fire and logging. Pooled across plant communities and stand ages, there was no significant difference in speckled alder frequency between wildfire-burned (37.0%) and logged (31.4%) stands in Minnesota. Surveys were conducted in naturally regenerated quaking aspen, jack pine, and black spruce communities that were 25 to 100 years old . In a black spruce forest in west-central Quebec, there was no significant difference in speckled alder cover on the edges of burns and clearcuts. Burns were 3 to 4 years old, and clearcuts were 2 to 5 years old .
Both wildfire and clearcutting apparently favored speckled alder; its average frequency was higher than that of any other deciduous shrub after both disturbances in surveys in northeastern Ontario . Speckled alder was more frequent after clearcutting than after wildfire, but a longer period of postdisturbance succession on burned vs. clearcut stands makes direct comparisons difficult. Time since fire averaged 89.6 years, while time since logging averaged 22.9 years: Given speckled alder's role in early succession in this area, greater abundance in the younger, logged communities seemed likely. On clearcut stands (n=131), speckled alder averaged 6.9% frequency in the canopy and 18.47% cover in the subcanopy. Both wildfire and clearcutting apparently favored speckled alder; its average frequency was higher than that of any other deciduous shrub after both disturbances .
Thinleaf alder sprouts from the root crown after top-kill by fire ([38,164,346], reviews by [35,92,312], observations reported in ). Stem density may increase after fire due to multiple sprouts arising from single root crowns (review by ). A review of fire responses of British Columbian shrubs states that thinleaf alder is "set back by moderate or severe fires" . An anecdotal account from central Oregon reports that in thinleaf alder-dominated riparian communities, thinleaf alder withstands low-severity surface fires but is killed by more severe fires . Root sprouting is possible, however, and further investigations are needed to ascertain thinleaf alder's response to moderate and severe fires.
Thinleaf alder establishes on burns from on- or off-site, wind- or water-dispersed seed (reviews by [35,312]). Wind may disperse seed onto burns from "considerable distances" . Seedlings may also establish from seed in crown-stored "cones" after late summer fires (reviews by [35,312]). Viereck and Schandelmeier  reported that fire usually kills crown-stored seed in Alaskan alders such as thinleaf alder, but alder seeds are typically blown onto burns from off-site parents. Alders in lightly burned areas may produce "large numbers" of seeds in early postfire years . Thinleaf alder may establish in early postfire years after stand-replacement fires in lodgepole pine. In the Bitterroot Mountains of northern Idaho, thinleaf alder often establishes from wind-blown seed around postfire year 3 . Establishment from soil-stored seed may also occur (see Seedling establishment).
In a greenhouse study using soil from a wildfire-burned area near Slave Lake in Alberta, thinleaf alder sprouted from the roots but did not emerge from the seed bank. Soil samples were collected a week after the fire (cut in blocks 27.4² inches (177 cm²) across and least 4 inches (10 cm) deep). Thinleaf alder sprouted from soil blocks where fire had been "intense", averaging 23% cover after 2 years in the greenhouse. Thinleaf alder did not sprout from soil blocks collected from lightly burned or unburned sites. The plant community was mixed hardwood-conifer dominated by quaking aspen .
After summer wildfires on the Plumas National Forest, California, fewer thinleaf alders sprouted on upland sites—where fire crowned—than on gravelbars, where fire was less severe. Postfire response of vegetation on 2 streams, Third Water and Fourth Water creeks, was evaluated in postfire year 1. On the 1st and 2nd terraces above the creeks' gravelbars, the plant community was an incense-cedar-white fir/Eastwood manzanita-huckleberry oak (Arctostaphylos glandulosa-Quercus vaccinifolia) forest. Thinleaf alder dominated the gravelbars .
|For each topographic position, mean relative density of thinleaf alder and percent of burned thinleaf alders that sprouted along Third and Fourth Water creeks in postfire year 1 |
|Topographic position||Gravelbar||1st terrace||2nd terrace||Riparian-zone slope|
|Site||% of total||% sprouting||% of total||% sprouting||% of total||% sprouting||% of total||% sprouting|
|Third Water Creek |
|Fourth Water Creek |
On hybrid spruce-Engelmann spruce plantations in subboreal British Columbia, thinleaf alder abundance was similar on clearcuts prepared for planting by either prescribed burning or mechanical treatment (blading). Across treatments, mean thinleaf alder cover ranged from 17% to 25% on plantations <7 years old .
In a study of disturbed forests near the Peace River in northern Alberta, thinleaf alder was strongly positively associated (P<0.001) with frequently flooded sites (~1-10 years) but not with recent burns (5- to 20-year-old) or older burns (>20 years). Most (48%) of the white spruce and hardwood forests originated after flooding; fewer regenerated after logging (32%) or stand-replacing fire (19%). Thinleaf alder was recorded only on flooded sites. It was typically present in the earliest seral stages after flooding, establishing on gravelbars, levees, and the lowest stream terraces .
Thinleaf alder may occur in late postfire succession. On 12 white fir sites in Sierra County, California, that had experienced stand-replacing wildfires, thinleaf alder occurred only on study plots that had burned 80 years or more prior to the study. Time since fire ranged from 5 to 277 years .
In sagebrush ecosystems of the West, mesic thinleaf and other alder shrublands may establish after fire, or they may be self-sustaining .
POSTFIRE REGENERATION STRATEGY :
Tree with adventitious buds, a sprouting root crown, and root sprouts
Tall shrub, adventitious buds and a sprouting root crown
Geophyte, growing points deep in soil
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)
Ground residual colonizer (on site, initial community)
Immediate Effect of Fire
More info for the terms: association, basal area, bog, climax, cover, density, fen, fire exclusion, hardwood, litter, peat, shrub, shrubs, succession, taiga, wildfire
Gray alder tolerates full sun to light shade. It is an important colonizer in primary succession. It is also successionally important after stand-replacing events such as fire and logging  and in canopy gap succession . Its ability to fix nitrogen (see SITE CHARACTERISTICS AND PLANT COMMUNITIES) can enhance site quality for later-successional species. Plant response to fire provides information on gray alder and postfire succession.
Speckled alder prefers open sites [106,171,205] but tolerates moderate shade (Shirley 1932 cited in ). Studies in Michigan found that it occurred on open to closed sites but was most common on lightly shaded, cool sites [16,36]. In southern-boreal, quaking aspen forests of Quebec, speckled alder was associated with relatively high light transmission at 7 to 13 feet (2-4 m) above ground level (P<0.001). Thirty percent of full sun was the highest light level achieved on most sites .
Speckled alder is an important shoreline and meadow colonizer, and it is successional in mires and other wet to damp areas throughout its range . In Michigan, it colonizes sand dunes by Lake Huron . In New York, it is a characteristic taxon on unstable beachgrass (Ammophila breviligulata) dunelands . On an estuary on the St Lawrence River, Quebec, speckled alder seedlings and saplings showed 28% cover, the greatest of any colonizing shrub taxa. Drifting ice, wave action, and frequent flooding inhibited establishment of less tolerant shrubs along the shoreline . By upland oak-hickory communities, floodplains with speckled alder generally succeed to sycamore, elms, and red maple (review by ). Speckled alder may be invasive in sedge (Carex spp.) wetland meadows of Wisconsin, especially with fire exclusion . Speckled alder is noted in the older zones of bogs in Michigan . In bog succession, speckled alder generally establishes after litter from mosses and low ericaceous shrubs has formed a peat layer. Without disturbance, trees such as tamarack and black spruce establish after speckled alder, willow, and other shrubs . Speckled alder may be the pioneer woody taxon in swamps that succeed to red maple .
The successional pathway of acidic mires and other wetland communities may alter after speckled alder establishment [9,38]. Since speckled alder is a nitrogen fixer, acid-loving bog and fen species may be replaced successionally by species with higher nutrient requirements. On a kettle bog in Ohio, speckled alder established on a Magellan's sphagnum mat and was displacing acid-loving herbs such as purple pitcher-plant (Sarracenia purpurea) and round-leaved sundew (Drosera rotundifolia) . Speckled alder is more characteristic of fen and bog margins than of the mires themselves, although it sometimes establishes in mires with peaty soils . On the Lac St-Francois National Wildlife Area in Quebec, speckled alder invaded a water sedge-hairy sedge (C. lacustris) fen. Over several decades, speckled alder became dominant over about 10% of the wetland that had formerly been sedge fen . Woody invasion of herbaceous bogs and fens in eastern North America has been attributed to fire exclusion [9,38], although altered hydrologic regimes may also play a role . A 1938 study of the speckled alder-willow high bog association in Cheboygan County, Michigan, found speckled alder and willows were casting dense shade and becoming "scraggly". They were being replaced successionally by red-osier dogwood, black spruce, tamarack, and northern white-cedar. Charred logs and stumps in the bog indicated that fire had cleared the area of trees in the past . In contrast to speckled alder replacing herbs successionally in wetlands, beaked sedge has established and spread in speckled alder-withe-rod (Viburnum nudum var. cassinoides) communities of east-central West Virginia .
In forests, speckled alder may be important after logging, insect attacks, and/or disease. On logged black spruce forests of northeastern Ontario, speckled alder was most common in forests <40 years old, forming dense shrub layers of up to 570 to 600 stems/0.01 ha. In older stands, speckled alder was less important, forming a "diffuse canopy" on most sites. It remained dense in seeps and by open water, however. The authors surmised that speckled alder was probably present in low numbers in the prelogged forest and increased rapidly after logging [43,44]. Speckled alder was prevalent after an eastern spruce budworm attack and subsequent clearcutting in balsam fir-paper birch communities in Ontario. Speckled alder density ranged from 109 stems/ha to 6,667 stems/ha on 8- to 12-year-old clearcuts . In early secondary succession, deforestation due to Dutch elm disease tended to favor speckled alder and other shrubs . In hardwood swamps of central New York, speckled alder was "frequently encountered" in gap succession following death of overstory American elms to Dutch elm disease. It occurred in both small gaps created by the death of single trees and in larger gaps created by deaths of multiple trees .
Speckled alder is generally unimportant in late-successional forests. It was a mostly minor component of late-successional eastern hemlock-black spruce-red maple forests of northeastern Pennsylvania, attaining high density and cover only in canopy gaps . However, a 1934 publication reported speckled alder as characteristic of climax balsam fir forests in Itasca County, Minnesota. It was also present in earlier succession .
Speckled alder may be of minor importance in old field succession. It formed thickets on old fields in New York [49,175,176]. In southeastern Ontario, speckled alder seedlings were found 19 years after abandonment of ploughed hay fields, although in low numbers (<1% frequency). Speckled alder was also present in adjacent silver maple/roundleaf serviceberry (Acer saccharinum/Amelanchier sanguinea) forest. It presumably established in the old field from wind-blown seed originating from the forest . In an old-field study, speckled alder was an early-seral shrub on the Piedmont Plateau of North Carolina. It preferred wet bottomlands that had been used as hayfields, sometimes forming dense, shoulder-high thickets. Speckled alder was also noted in old fields 34 and 45 years after abandonment on a site succeeding to loblolly pine (Pinus taeda) forest. Its density in the loblolly pine habitat ranged from 1.9 stems/16 m² on a 34-year-old field to 4.1 stems/16 m² on a 45-year-old field. In an adjacent old field on logged streambanks succeeding to paper birch, speckled alder was present 6 and 14 years after abandonment at densities of <2 stems/16 m². In old fields succeeding to mixed-hardwood bottomlands, it was found in 8- and 32-year-old fields (densities not recorded). None of the old-field plant communities surveyed was older than 55 years .
Thinleaf alder is moderately shade tolerant. Thinleaf alder is adapted to nearly all types of disturbance , including severe disturbance , and is most common in early succession. It can grow in forest understories, but it is found more often on open sites. Sprouts may tolerate shade better than seedlings (review by ). To date (2011), most successional studies on plant communities with gray alder had been conducted on Alaskan sites in primary succession.
Thinleaf alder is an early-successional shrub in riparian zones in primary succession . The willow/alder stage typically forms on bare floodplains . On the Tanana River in interior Alaska, it typically establishes on bare to nearly bare, recently deposited alluvium . Feltleaf and/or sandbar willow may establish first [1,55]. Thinleaf alder and balsam poplar dominate in midsuccession, after which balsam poplar and finally, white spruce, dominate the overstory . A 5-year-old thinleaf alder sandbar community on the Tanana River was a "nearly impenetrable" thicket of thinleaf alder, feltleaf willow, sandbar willow, and barrenground willow. The shrubs were uniformly about 10 feet (3 m) tall, 0.8 inch (2.0 cm) in stem diameter, and averaged 49,699 stems/ha. Balsam poplar, paper birch, and white spruce grew in the understory; meadow horsetail and variegated scouringrush were dominant herbs. In 15-year-old stands, feltleaf willow was overtopping thinleaf alder, and shrub density declined to 2,827 stems/ha. Groundlayer vegetation was nearly all meadow horsetail . By Glacier Bay, Alaska, thinleaf alder occurs about 15 to 20 years after glacier recession, in the "late pioneer" stage. About 25 to 30 years after recession, thinleaf alder forms closed stands, presenting an "almost impenetrable barrier". At 30 to 35 years, black cottonwoods begin to establish .
According to a 1923 study by Cooper , thinleaf alder may be abundant even in late succession after glacier recession. Herbs, especially dwarf fireweed (Chamerion latifolium), dominated the northernmost, pioneer community, but thinleaf alder and willows were also establishing. Feltleaf willow-Sitka willow-thinleaf alder communities occurred in isolated patches and on midlatitude landscapes; midlatitude sites had a longer period of recession than the northern sites. Thinleaf alder was "nearly everywhere dominant" and eventually overtopped the willows. Sitka spruce forests occurred in the southernmost portion of the landscape, which had the longest time since glaciation. Thinleaf alder persisted in these late-successional forests, typically at greater abundance than in the pioneer stage .
The pattern of willows, and sometimes cottonwoods, establishing before thinleaf alder is typical in riparian succession. On bare gravel bars of Meadow Creek on the Starkey Experimental Forest, Oregon, thinleaf alder established at lower densities (0.96 stem/50 m²) than sandbar willow and black cottonwood . Along the Animas River in southwestern Colorado, narrowleaf cottonwood/thinleaf alder communities occur upland from narrowleaf cottonwood/tickle grass communities and are considered a latter successional community type than the narrowleaf cottonwood/tickle grass community .
Thinleaf alder shrub communities are initiated and maintained by disturbances that are often severe. Historically in northwestern Montana, disturbances have included placer mining, ice jams, log transport [32,151], and fire. On Emigrant Creek near Burns, Oregon, thinleaf alder colonized a new alluvial fan 6.5 years after deposition following an intense thunderstorm. Cattle had grazed the area for at least 30 years . Thinleaf alder snowslide communities in the Blue Mountains are maintained by avalanches and soil slippage . Along the San Miguel River in southwestern Colorado, thinleaf alder shrub communities occupied less area than that of later-successional, narrowleaf cottonwood/thinleaf alder communities. Thinleaf alder shrubland also had shorter flood-return intervals (averaging <10 years) than those of narrowleaf cottonwood/thinleaf alder communities (averaging about every 50 years) .
Thinleaf alder may facilitate establishment of later-successional riparian species, likely due in part to its ability to fix nitrogen. On floodplains of interior Alaska, for example, balsam poplar and feltleaf willow establish in nitrogen-enriched soil beneath thinleaf alder, although root crowding and shading by thinleaf alder may interfere with growth of later-establishing species on many floodplain sites (reviews by [53,54]). On floodplains near Fairbanks, there was a "marked" increase in exchangeable soil potassium, calcium, magnesium, manganese, and phosphorus within 5 years of thinleaf alder establishment, but there was no consistent increase in soil mineral content from 5 to 20 years after thinleaf alder establishment. Soil pH decreased beneath thinleaf alder stands over 20 years, while soil cation exchange and organic matter increased. At study year 20, most of the total aboveground plant biomass (~43 kg/ha of ~48 kg/ha total) and basal area (7,142 stems/ha of 7,241 stems/ha total) was thinleaf alder .
Experiments on the Tanana River floodplain showed changes in soil nutrient dynamics and soil microbe community composition as aboveground succession proceeded from thinleaf alder to balsam poplar. As balsam poplar gained dominance, soil carbon became increasingly more available and soil nitrogen became increasingly less available to soil microbes. Thus, the soil biota changed from carbon-limited microbes under thinleaf alder dominance to nitrogen-limited microbes under balsam poplar dominance .
Thinleaf alder occurs in all stages of forest succession, although it is most prevalent in early forest succession. It pioneers in forest communities of British Columbia, sometimes persisting in mature forests . Thinleaf alder is seral in Douglas-fir, spruce, and other coniferous forests in the West (for example, ). In forested habitats, the thinleaf alder shrub community is usually an early- to midsuccessional seral stage that arises after severe disturbance. Conifers or taller hardwoods typically replace thinleaf alder successionally . Near Slave Lake in Alberta, thinleaf alder sprouts were more common on sites logged 28 years prior than adjacent sites burned by wildfire 28 years prior (P<0.05). Study sites were dominated by quaking aspen, balsam poplar, and paper birch . Thinleaf alder often dominates the understory of midseral spruce/bluejoint grass forest habitat types in Montana . In northwestern Montana, thinleaf alder was abundant in Engelmann spruce/skunk cabbage riparian communities from early-seral (logged and heavily grazed) to late-seral and climax stages. It dominated early stages of succession in Engelmann spruce/field horsetail and Engelmann spruce/bluejoint reedgrass riparian communities . In central Alaska, thinleaf alder thickets are often replaced successionally by balsam poplar, which in turn is replaced by white spruce, then black spruce . Thinleaf alder occurred late in the succession of white spruce-Engelmann spruce forests on the east slope of the Rocky Mountains in Alberta . By the Peace River in northern Alberta, thinleaf alder was dominant in old-growth white spruce forests. It was most common in canopy gaps, although it persisted in the understory. It also occurred in resin birch clearcuts . In central Alberta, thinleaf alder was more common in mature quaking aspen-balsam poplar-white spruce forest than on edges of 16-year-old clearcuts (P=0.05) .Browsing pressure may alter succession in forest ecosystems with thinleaf alder. Browsing may favor thinleaf alder at the expense of more palatable browse species. In spruce-birch taiga forests of interior Alaska, browsing pressure by moose favored thinleaf alder and quaking aspen over more palatable willow species . In northern Idaho, ungulate browsing helps maintain shrubfields, which contain thinleaf alder and other seral shrubs. Heavy browsing, however, may accelerate succession to conifer species, which are less palatable .
Cloning is apparently the primary means of spread in established stands of gray alder (review by ). Gray alder sprouts from the root crown [35,38,175,208]. It can also sprout from roots, including root offsets [175,176,298], and layers. Root sprouting and layering are apparently less important than root-crown sprouting , although root sprouts distant from the parent plant have been noted for both speckled alder and European gray alder (review by ). Haeussler and others  report that sprouting "can be expected" after mechanical site preparation. In a Magellan's sphagnum bog in Ohio, speckled alder sprouted after cut-stump herbicide applications, growing up to 3 feet (1 m) in one growing season . Gray alder does not spread rapidly, but its clones can be long-lived. In a central New York study, 4 speckled alder populations were monitored for 4 years. There was no seedling establishment on study plots during that time. Clump sprout production and stem mortality were variable within and among populations, although no clumps died out. No lateral extension of clones via root sprouting occurred. Annual sprout production averaged about 3 live stems/clump .
In a study comparing root anchorage of riparian species in Italy, European gray alder was less resistant to uprooting by flood than Lombardy poplar (Populus nigra) or Elaeagnus willow (Salix elaeagnos) . This relative ease of uprooting may allow for vegetative spread of gray alder when root fragments are torn off, distributed downstream, and sprout.
Seedling establishment and plant growth
Gray alder seedling establishment may be rare except in primary succession or on disturbed, open sites. In central New York, 4 populations of speckled alder showed no seedling establishment over 3 years . In a Freeman maple-white ash swamp in New York, speckled alder establishment averaged 10 seedlings/100 m². One-year-old seedlings averaged 5.2 inches (13.1 cm) tall; 2-year-old seedlings averaged 13.5 inches (34.3 cm) tall .
Soil disturbance and/or exposed mineral soil favor gray alder establishment (, review by ). In Michigan, the margins of American beaver ponds were favorable sites for speckled alder germination and establishment . In a Swedish field experiment, European gray alder seedling survival was higher in mineral soil (34%) than in humus (9%) .
Gray alder seedling establishment on new sandbars and on banks with receding floodwaters is common, although other substrates also provide favorable establishment sites. After a flood on the Connecticut River, for example, speckled alder seedlings were noted in a sugar maple swamp in an oxbow . On Lassen National Forest, thinleaf alder established most often near wide stream channels on sand- or gravelbars. Thinleaf alder seedling establishment was negatively correlated with canopy cover (P=0.02) and litter depth (P=0.002) and positively correlated with solar radiation (P=0.002) . In a greenhouse experiment in France, flooded European gray alder seedlings grew fastest on moist, sandy loams that were flooded and drained daily . In boreal quaking aspen-paper birch ecosystems near Slave Lake, Alberta, thinleaf alder established on decaying logs and stumps . Gray alder germinants apparently tolerate slightly drier conditions than willow germinants .
Gray alder seedlings grow rapidly under favorable conditions (, review by ). Monsen and others  report that thinleaf alder seedlings are "very competitive and vigorous. Once established, few plants can grow as rapidly". In central New York, annual growth increments of 4 speckled alder populations ranged from 0 to 2.8 inches (1.1 cm). Growth rate was generally greatest in midsized stems (0.8-1.5 inches (2.0-3.9 cm) DBH, P<0.01). In one population, gypsy moths removed nearly 100% of foliage in July, but stems leafed out again in late summer. Slowed growth and/or stem mortality was anticipated as a result of the defoliation but was not recorded . Speckled alder seedlings proved "remarkably tough when placed in the field" after growing in a greenhouse. Ninety-seven percent survived their first year .
Speckled alder may grow rapidly after canopy removal (review by ). MacLean  reported that after clearcutting in boreal quaking aspen-paper birch-spruce communities in Ontario, understory speckled alder gained height growth quickly and spread vegetatively. From small clumps with few stems, speckled alder typically formed a tall, closed-shrub canopy within 10 to 12 postharvest years. Some regeneration from seed was also apparent. Best growth occurred on moist to very moist clay loams . Speckled alder also grew rapidly following clearcutting on black spruce peatlands in Ontario. Ten years after harvest, speckled alder averaged 5 to 6 feet (1.5-1.8 m) tall and 16,000 to 30,000 stems/acre. Speckled alder crown closure ranged from 40% to 80% .
Colonizing gray alders may facilitate subsequent gray alder establishment and colony expansion. Below receding glaciers above Glacier Bay, Alaska, thinleaf alder established as widely scattered individuals. These individuals were centers of aggregation from which thinleaf alder thickets spread .
Ungulate browsing can substantially reduce growth of thinleaf alder on heavily browsed sites. On big game winter rangelands near the Clearwater River in northern Idaho, thinleaf alder's annual biomass accumulation averaged 0.23 g/m² in ungulate exclosures. Study plots outside exclosures, which were subject to moose, elk, and mule deer foraging, did not contain thinleaf alder, Rocky Mountain maple (Acer glabrum), or several other important browse species .
One study found midsized speckled alder sprouts suffered the least mortality among size classes. Over 3 growing seasons in New York, short speckled alder stems (<4.6 feet (1.4 m) tall, minimal DBH) died most often, while midsized stems (6.6-13 feet (2.0-3.9 cm) DBH) showed less mortality than larger sprouts. Sampling was conducted in 4 early-successional speckled alder thickets. Variation in stem mortality and growth was greater within populations than across sites (P<0.05 for all variables) .
Gray alder has a transient seed bank; seed longevity in the field or in water is short . Even in dry storage, seeds do not remain viable for more than 2 years . In a Freeman maple-white ash (Acer × freemanii-Fraxinus americana) swamp in New York, speckled alder seed density was 0.01 seed/120 cm². Speckled alder had 0.9% cover in aboveground vegetation . In dry Douglas-fir forests of south-central British Columbia, thinleaf alder seed was present in the soil seed bank on unlogged and unburned sites. Thinleaf alder seed was not found in the soil seed bank on adjacent sites that were either clearcut 5 or 10 years prior or burned at low or high severity 5 years prior. Thinleaf alder was not present in aboveground vegetation on any of the study sites .
Pollination and breeding system
Genetic differences among populations are generally small in species with wind-dispersed pollen and seeds (for example, ), such as gray alder. Allozyme studies of speckled alder in central Quebec showed high rates of gene flow and weak genetic differentiation among 4 populations .
Spatially, the genetic make-up of individuals in speckled alder thickets may be random. Studies of 4 speckled alder thickets in New York showed clones were randomly distributed, and clumps of single genotypes were not aggregated. Thus, the author concluded that although speckled alder regenerates vegetatively, sexual regeneration was driving the genetic structure of these 4 populations .
- Pollination and breeding system
- Seed production
- Seed dispersal
- Seed banking
- Seedling establishment and plant growth
- Vegetative regeneration
Growth Form (according to Raunkiær Life-form classification)
More info for the terms: geophyte, phanerophyte
Raunkiaer  life form:
Fire Regime Table
Gray alder seeds are usually nondormant ([27,300], review by ) and, under favorable conditions, may germinate immediately after dispersal (review by ). However, some seed lots may require a stratification period, from a few days to over winter (review by ). Moist soil (, review by ) and temperatures from approximately 50 to 77 °F (10-25 °C)  are required for germination.
Gray alder seed viability is generally low (review by ), but preliminary studies suggest that light enhances germination (, review by ). Some laboratory studies found only 5% viability in thinleaf alder seeds (review by ). In greenhouse trials, speckled alder showed low seed viability (4-42%). Germination of filled seed varied from 0 to 50%, with presoaking and light increasing germination rates . For thinleaf alder seeds collected near Fairbanks, germination averaged 90% for seeds cold-stratified in light and 5% for seeds cold-stratified in dark. Unstratified seed showed 100% germination in light and ≤13% germination in dark . Gray alder seed may germinate without light, however. In a laboratory study, speckled alder showed no significant difference in time to germination and germination rate in dark vs. light, averaging 10 days to germination, and 36% germination, in both light and dark .
Wind and water disperse thinleaf alder seeds ([81,93], reviews by [35,312]). In waterways of Alaska, thinleaf alder seeds stayed afloat for "long periods of time" (Densmore 1976 personal observation ). On a floodplain of Little Otter Creek in Vermont, speckled alder seed was found in floodwaters but not in seed rain deposited on soil. The surrounding plant community was a red maple-sugar maple (Acer saccharum) forest .
Life History and Behavior
More info for the term: phenology
Gray alder's catkins are formed the previous growing season and are exposed in buds during winter. In spring, gray alder flowers before leaf-out and stem elongation [120,171,176]. Male catkins drop in late spring, shortly after pollination [176,261]. There is "considerable" leaf drop in summer and fall . Seeds disperse in fall or winter, although female catkins remain on the plant [171,176,261]. Both male and female catkins form the year prior to opening, so in fall, gray alders usually display immature male and female flower clusters, immature fruits, and old female catkins [171,176,261]. Phenology of speckled and thinleaf alder is as follows:
Molecular Biology and Genetics
Barcode data: Alnus incana
Statistics of barcoding coverage: Alnus incana
Public Records: 6
Specimens with Barcodes: 23
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Please consult the Plants Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status and wetland indicator values.
Gray alder may compete with timber species, sometimes occupying highly productive sites . When speckled alder is in the understory, clearcutting may result in dense speckled alder stands . Dense stands may prevent or impede conifer regeneration, although scattered individuals present little threat to planted conifers (review by ). In northwestern Ontario, speckled alder occurred on wet to moist, nutrient-poor to nutrient-medium sites. It was implicated in competing with conifers for light and moisture but credited with fixing atmospheric nitrogen . On the Tanana River floodplain in central Alaska, thinleaf alder inhibited growth of understory white spruce seedlings by shading and root competition. Thinleaf alder's dense litter layer may also inhibit conifer establishment .
When using mechanical treatment to control gray alder, the root crown must be destroyed to prevent sprouting. Stems in contact with soil may layer; layering is common after logging . These sources: [38,51] provide information on controlling speckled alder with herbicides.
Although it is not heavily browsed when other forage is available, livestock concentrated in riparian areas sometimes overbrowse and trample thinleaf alder. In northeastern Oregon, thinleaf alder density was significantly greater on ungrazed gravelbar communities than on riparian sites with livestock (P<0.01) . In extreme cases, thinleaf alder becomes scattered and short, with mostly broken branches, and streambanks of thinleaf alder communities degrade to dish shapes. In central Oregon, it took at least 5 years for thinleaf alder to recover from such overbrowsing, and at least 2 to 5 years for streams to reform banked channels, which had become dish-shaped with trampling . Ehrhart and Hansen  provide management guidelines for grazing cattle in riparian zones.
Cultivars, improved and selected materials (and area of origin)
Somewhat available through native plant nurseries within it range.
Thin-leaf alder often occurs in dense thickets, which reportedly results from underground rhizomes or suckers (Dayton 1931). If plants are damaged, sprouting can occur from the stump, root collar, or from the root crown following fire. After top-removal of plants by beavers, they have been observed to sprout heavily from the cut.
Propagation from cuttings is not recommended and plants are not widely available in nurseries.
Relevance to Humans and Ecosystems
Value for rehabilitation of disturbed sites
Gray alder helps protect and stabilize streambanks and other riparian areas [215,256,261] and is used for erosion control . Banks stabilized with gray alders can withstand "relatively severe" spring run-off . Gray alder's shade provides mesic habitats for groundlayer herbs . Its symbiotic relationship with nitrogen-fixing bacteria makes it a good selection for planting in nitrogen-depleted soils . Seeds and plants are commercially available .
Thinleaf alder: Thinleaf alder is used in revegetation projects [62,256]. It is recommended for riparian revegetation in the Intermountain West  and the Northern and Southern Rocky Mountains . It is particularly recommended for high-gradient, high-velocity, low- to midorder streams . See these sources: [104,154,183,256,309] for propagation information.
Importance to Livestock and Wildlife
Gray alder provides winter browse, although wildlife may not prefer it (review by ). This preference may be unexpected because the foliage is high in nitrogen (for example, [180,235]). However, gray alder may be a secondary source of wildlife browse due to its wide distribution and local abundance . Gray alder utilization is generally highest from late fall to early spring . Songbirds eat gray alder seeds , and squirrels consume the catkins (review by ).
White-tailed deer and lagomorphs browse speckled alder . It provides winter forage (review by ), but browsing wildlife are likely to avoid speckled alder if more palatable species are available. In a winter deer yard in Quebec, white-tailed deer browsed red-osier dogwood and pussy willow more than expected, and speckled alder less than expected, based on availability .
In cafeteria feeding trials in Wisconsin, captive ruffed grouse avoided speckled alder catkins, preferring those of quaking aspen and willows. The authors speculated that secondary metabolites in speckled alder catkins rendered the speckled alder catkins unpalatable .
Mule deer browse thinleaf alder sparingly [261,348], although thinleaf alder may be more important in winter . Mountain goats also use thinleaf alder , and livestock may browse thinleaf alder heavily in riparian areas 
Arthropods and mollusks consume gray alder. Millipedes browse fresh speckled alder leaf litter . Landsnails (Cepaea nemoralis) also browse speckled alder leaf litter . Speckled alder is a host of alder aphids (Prociphilus), which feed only on alders (Alnus) . Alder aphids are a larval food of the harvester butterfly (Feniseca tarquinius) .
Palatability and/or nutritional value: Gray alder's palatability is rated poor to fair for big game animals. Sprouts and young plants are preferred over older browse (, review by ). Its palatability for livestock is rated from poor in the Southwest to fair in the Pacific Northwest and California. Gray alder is generally more palatable to cattle than to domestic sheep and goats .
Songbirds, grouse, and American woodcocks eat gray alder buds, seeds, and catkins (reviews by [142,160]). See Grodzinski and Sawicka-Kapusta  for information on the nutritional value of gray alder seeds.
Speckled alder is not a preferred browse taxon; it is used primarily as winter forage. It was ranked very low in palatability among woody taxa (22nd among 23) that white-tailed deer used as forage . On the Apostle Islands of Wisconsin, speckled alder was 1 of 4 taxa that white-tailed deer chose last as browse; 28 taxa were tested . A habitat suitability model, developed for coniferous and aspen-birch ecosystems of the Great Lakes region, lists speckled alder as low-preference browse for moose during the growing season . A study on Isle Royal, Michigan, found moose used speckled alder less than expected based on speckled alder's availability and nutritional content (P≤0.05) . American beavers, however, used speckled alder as much as expected (P<0.05) .
Thinleaf alder is generally unpalatable to wild ungulates [151,223], cattle, and horses. It is fairly palatable to domestic sheep . Wild ungulates browse new thinleaf alder growth but generally avoid mature thinleaf alder  except as emergency winter forage. On summer rangelands in Tehama County, California, mule deer browsed thinleaf alder less than expected based on availability .
In Alaska, feltleaf willow and balsam poplar were more palatable to browsing mammals when grown in the shade of thinleaf alder than when grown in the open (Rohleder 1985 cited in ).
Cover value: Gray alder provides shade and hiding cover for many vertebrate species.
Speckled alder: In a Quebec study, speckled alder was the dominant streamside shrub in an ecosystem supporting brook trout, American mink, and Appalachian brook crayfish (Cambarus bartoni), the American mink's primary prey species in that stream . The federally endangered bog turtle  is positively associated with speckled alder wetlands (review by ). In Alberta, white spruce/gray alder/horsetail/moss (Equisetum/Hypnum and Polytichum spp.) riparian communities provide shade and reduce water temperatures in trout streams .
Speckled alder is critical for American beavers. They use speckled alder for den and dam construction more than they use it as browse [103,222]. In Algonquin Provincial Park, Ontario, the number of speckled alder stems found in American beaver dams (403 stems) was over twice that of speckled alder stems found in their food caches (176 stems). Speckled alder was selected for dam construction about 4 times as often as spruces, which were the next most preferred . In another Algonquin Provincial Park study, American beavers used speckled alder more than expected. Although speckled alder composed 25.6% of the standing vegetation, 49.2% of stems that American beavers felled were speckled alder. Speckled alder cover and basal area increased significantly with distance from American beaver dens (P<0.009) [101,102].
Speckled alder provides important cover for American woodcocks, ruffed grouse [99,266], and other birds. Speckled alder thickets provide critical feeding, nesting, molting, and premigratory staging habitat for American woodcocks ([252,258,266,291], Sheldon 1967 cited in ). In Michigan, ruffed grouse used speckled alder for cover in drumming sites (review by ). A study in eastern hemlock-red maple/speckled alder-mountain-laurel riparian corridors of Pennsylvania found the number of obligate wetland bird species, such as kinglets and flycatchers, was significantly higher in undisturbed speckled alder riparian corridors than in speckled alder-dominated riparian corridors disturbed by residential or agricultural development . Niemi and Pfannmuller  provide a list of bird species using speckled alder-dominated wetlands as breeding and nesting habitat in Minnesota and Michigan.
Thinleaf alder: Thinleaf alder provides cover for snowshoe hares  and big game animals . Mule deer, white-tailed deer, and elk use thinleaf alder communities for thermal and hiding cover . American beavers use thinleaf alder to make their dens (review by .
Thinleaf alder provides cover for aquatic organisms. Dense thinleaf alder thickets provide thermal and shade cover for fish. Thinleaf alder and associated shrubs stabilize stream channels, and overhanging banks reduce erosion [32,151]. In Oregon, thinleaf alder on streambanks provide cover, food, and shade for salmonids . In the Trout Creek Mountains, thinleaf alder-Wood's rose overstories shaded over 70% of the stream channels of 4 streams, while the more open thinleaf alder/woolly sedge communities shaded about 50% of the stream channels. Dense woolly sedge that grew over the streambank enhanced trout habitat .
Cattle loaf in thinleaf alder stands, although dense thinleaf alder thickets may impair access. Heavy cattle trampling may degrade thinleaf alder habitats by creating dish-shaped stream channels and reducing cover of palatable herbs [32,151].
Other uses and values
Ethnobotanic: Native Americans reportedly pounded the wood of thin leaf alder into a powder to produce a red dye (Lanner 1983). The wood was occasionally used for firewood. It is also valued by cabinetmakers and is used in making clogs, bowls, and woodcuts.
Wildlife: Cottontails, muskrats, moose, elk, deer, and snowshoe hares eat the leaves and twigs. Redpolls, siskins, chickadees, and goldfinches eat alder seeds, buds, and catkins. Beavers eat the bark and build dams with the stems.
Agroforestry: Alnus incana is an excellent pioneer species for revegatating disturbed riparian areas or as a mass planting to achieve a screen or windbreak. Thin-leaf alder is used in tree strips for windbreaks, which are planted and managed to protect livestock, enhance production, and control soil erosion. Windbreaks can help communities with harsh winter conditions better handle the impact of winter storms and reduce home heating costs during the winter months.
It is a small to medium size tree 15–20 m (49–66 ft) tall with smooth grey bark even in old age, its life span being a maximum of 60 to 100 years. The leaves are matt green, ovoid, 5–11 cm (2.0–4.3 in) long and 4–8 cm (1.6–3.1 in) broad. The flowers are catkins, appearing early in spring before the leaves emerge, the male catkins pendulous and 5–10 cm (2–4 in) long, the female catkins 1.5 cm (0.6 in) long and one cm broad when mature in late autumn. The seeds are small, 1–2 mm (0.04–0.08 in) long, and light brown with a narrow encircling wing. The grey alder has a shallow root system, and is marked not only by vigorous production of stump suckers, but also by root suckers, especially in the northern parts of its range. The wood resembles that of the black alder, but is somewhat paler and of little value.
There are four to six subspecies, some treated as separate species by some authors:
- Alnus incana subsp. incana (Grey alder). — Northern Europe and northwestern Asia, and central and southern Europe in mountains, mainly in the regions of the Alps, Carpathians and the Caucasus.
- Alnus incana subsp. hirsuta (Spach) Á. & D.Löve (=A. hirsuta Spach); Manchurian alder. — In mountains of Northeast Asia and Central Asia.
- Alnus incana subsp. kolaensis (N.I.Orlova) Á. & D.Löve. — Subarctic northeast Europe.
- Alnus incana subsp. oblongifolia (=Alnus oblongifolia); Arizona alder. — Madrean Sky Islands of southwestern North America, in Arizona, New Mexico, and Northwestern Mexico.
- Alnus incana subsp. rugosa (Du Roi) R.T.Clausen (=A. rugosa Du Roi); Speckled alder. — Northeastern North America, including the Northeastern United States.
- Alnus incana subsp. tenuifolia (Nutt.) Breitung (=A. tenuifolia Nutt.); Mountain alder, or thinleaf alder. — Western North America, including New Mexico to California and Alaska.
Alnus incana is a light-demanding, fast-growing tree that grows well on poorer soils. In central Europe, it is a colonist of alluvial land alongside mountain brooks and streams, occurring at elevations up to 1,500 metres (4,900 ft). However, it does not require moist soil, and will also colonize screes and shallow stony slopes. In the northern part of its range, it is a common tree species at sea level in forests, abandoned fields and on lakeshores. It is sometimes used for afforestation on non-fertile soils which it enriches by means of nitrogen fixing bacteria in its root nodules. Several species of Lepidoptera use grey alder as a food plant for their caterpillars. See List of Lepidoptera that feed on alders. In the Boreal forest area of Canada, A. incana is often associated with black spruce in the forest type termed black spruce/speckled alder.
- Flora of North America. 2009
- "Alnus incana subsp. tenuifolia". Jepson Herbarium: Jepson eFlora. Retrieved January 28, 2013.
- "Alnus incana subsp. tenuifolia (mountain alder)]". Calflora. Retrieved January 28, 2013.
- "Alnus tenuifolia — Mountain Alder". PFAF Plant Database. Retrieved January 28, 2013.
- C. Michael Hogan. 2008
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- Stevenson, Matilda Coxe 1915 Ethnobotany of the Zuni Indians. SI-BAE Annual Report #30 (p. 80)
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- Flora of North America. 2009. Alnus incana
- C. Michael Hogan. 2008. Black Spruce: Picea mariana, GlobalTwitcher.com, ed. N. Stromberg
Names and Taxonomy
For speckled alder (Alnus incana subsp. rugosa):
Alnus incana (L.) Moench var. americana Regel 
Alnus rugosa (Du Roi) Spreng. [106,171,231,295,304,350,359]
Alnus rugosa (Du Roi) Spreng. var. americana (Regel) Fernald [37,304]
Alnus rugosa (Du Roi) Spreng. var. rugosa
Alnus rugosa (Du Roi) Spreng. forma hypomalaca Fern [37,304]
For thinleaf alder (Alnus incana subsp. tenuifolia):
Alnus incana (L.) Moench var. occidentalis (Dippel) C.L. Hitchc. [208,304]
Alnus incana (L.) Moench var. virescens S. Watson
Alnus Ã purpusii Callier
Alnus tenuifolia Nutt. [155,208,231,242]
Alnus incana (L.) Moench subsp. rugosa (Du Roi) R.T. Clausen, specked alder [120,137,192,205,237,255]
Alnus incana (L.) Moench subsp. tenuifolia (Nutt.) Breitung, thinleaf alder [120,167,179,192,355]
European gray alder, Alnus incana (L.) Moench subsp. incana, is native to western Europe [120,127]. It has been introduced in the northeastern United States . Since variation in the subspecies is continuous rather than discrete, gray alder subspecies are sometimes difficult to tell apart (, review by ). Speckled alder and thinleaf alder intergrade where their ranges overlap, mostly in Saskatchewan and Manitoba [106,120,127,231].
In this review, gray alder refers to information that is general to the species. Speckled alder refers to A. i. subsp. rugosa, and thinleaf alder refers to A. i. subsp. tenuifolia.
Gray alder hybridizes with European alder (A. glutinosa), an introduced species . Speckled alder hybridizes and intergrades with hazel alder (A. serrulata) [120,231,295]. Speckled alder × hazel alder hybrid swarms may occur in Massachusetts and elsewhere . Thinleaf alder may hybridize with red alder (A. rubra) in Idaho .
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