Fire adaptations and plant response to fire
Fire adaptations: A review of the available literature (as of 2012) suggests redosier dogwood stems on burned sites are most likely the result of root crown, stem, or stolon sprouting. Reviews, however, report more varied postfire establishment methods, such as establishment from heat-activated, soil-stored seed (reviews [33,279]), and suggest that redosier dogwood regeneration is favored by low-severity fires that remove little of the organic layer because of long-term seed bank inputs and a natural filtering of redosier dogwood seeds through the soil surface into the upper mineral soil (review by ). Investigations into redosier dogwood's potential survival and establishment on burned sites were uncommon in the literature (as of 2012). While redosier dogwood survival on burned sites was common [10,194,244], it was not guaranteed [169,170], and while one study suggests redosier dogwood seeds are somewhat heat tolerant, heating with boiling water did not improve germination .
Plant response to fire: Several studies reported that redosier dogwood survived on burned sites by sprouting, and in one case, sprouts occurred within 7 days of burning. Researchers reported that redosier dogwood was rarely if ever killed by spring and summer prescribed fires in old fields at New York's Iroquois National Wildlife Refuge. These prescribed fires reached a maximum of 134 kW/m energy release and a maximum surface temperature of 504 °F (262 °C) . Redosier dogwood was only top-killed after cut shrubs were burned by torching in a sedge meadow in Marquette County, Wisconsin. Sprouting was vigorous and usually occurred within 7 days of treatments . Redosier dogwood emerged from soil samples collected within a week of an April fire that burned in even-aged mixed forest near Fishing Lake, Saskatchewan. Redosier dogwood stems sprouted from root or stem material in the soil samples, which were put in a lighted greenhouse. There were 2 to 5 redosier dogwood germinants/plot in soil samples from plots burned by light to moderate surface fire. There were no germinants from soil collected from severely burned plots or unburned plots .
Redosier dogwood seeds appear to be heat tolerant , and seedlings were reported within a year of burning in a riparian site in the northern Sierra Nevada . Germination of redosier dogwood seed collected from Lincoln County, Montana, was evaluated after a variety of treatments. Only 20% of seeds germinated after they were treated with boiling water, allowed to cool, and then stratified, but almost 70% of treated, ungerminated seeds remained viable . On the Plumas National Forest in the northern Sierra Nevada, redosier dogwood recovery after fire was monitored along Third Water and Fourth Water creeks. The fire burned more severely along Fourth Water Creek than Third Water Creek. Survival of redosier dogwood was similar along both creeks, with most shrubs sprouting from either root crowns or stems and rarely sprouting from both. Density of redosier dogwood seedlings was greater at the more severely burned Forth Water Creek area (26 seedlings/480 m²) than the Third Water Creek area (1 seedling/567 m²) . For more information about the pattern of burning in this and other riparian areas, see FIRE REGIMES.
One study suggests that redosier dogwood may not always survive fire. In a Douglas-fir forest, north of Ketchum, Idaho, redosier dogwood was present before but not 1 to 7 years after a prescribed fire. The fire burned on 1 August when air temperatures reached a high of about 80 °F (27 °C), relative humidity reached a low of 10% or less, and wind speeds averaged about 5 miles (8 km)/hour. All litter, herbaceous material, logs less than 3 inches (8 cm) in diameter, and all live stems less than 2 inches (5 cm) in diameter were completely consumed by the fire [169,170]. For more information on this prescribed fire and community response during the first 2 postfire years, see the research paper by Lyon (1966).
In most fire studies, redosier dogwood abundance was reduced only in very early postfire sampling or was relatively unchanged by fire. By the 2nd postfire growing season following a prescribed fire in mixed quaking aspen and Douglas-fir stands in Montana's Gallatin National Forest, density of redosier dogwood was near or exceeded prefire levels. Fire ignition was attempted on 30 April, but because of poor fire spread another fire was set on 16 May when relative humidity was 20% and air temperature was 70 to 80 °F (21-27 °C). The May fire consumed 90% to 100% of fine fuels and penetrated 2 to 4 inches (5-10 cm) deep .
|Density of redosier dogwood stems (number/acre) before and after a prescribed fire in mixed forests on the Gallatin National Forest of Montana |
|Transect||Prefire||1st postfire growing season||2nd postfire growing season|
In quaking aspen woodlands in southern Ontario, frequency of redosier dogwood was not different between burned and unburned plots, 4 months or 15 months after a low-severity surface fire. However, cover of redosier dogwood was significantly lower on burned than unburned plots (P<0.05). On 4-month-old burned plots, redosier dogwood cover averaged about 35%; on 15-month-old burned plots, cover averaged about 45%. Redosier dogwood cover on unburned plots was about 60%. Most aboveground redosier dogwood stems were killed by the fire, but underground portions of the shrubs were undamaged, and root crown sprouting was prolific . For more information about this fire and its pattern of burning, see Fuels. In old fields at New York's Iroquois National Wildlife Refuge, the density of redosier dogwood stems was not reduced from prefire levels when mowed shrubs were burned in a summer fire .
Fire studies in Wisconsin report little change in redosier dogwood abundance after fire. In a sedge meadow at Summerton Bog Nature Preserve in Wisconsin, redosier dogwood decreased only slightly from pretreatment levels after shrubs were mowed and then torched . Redosier dogwood cover was not changed by a winter prescribed fire in sedge meadow and shrub carr vegetation at Lodi Marsh in southern Wisconsin. In the sedge meadow, cover of redosier dogwood was 5% on both burned and unburned plots, and in the shrub carr, redosier dogwood cover was 8% on both burned and unburned plots. Cover on burned plots was evaluated 1 to 2 years after the 13 December fire, which burned when the air temperature was 45 °F (7 °C) and relative humidity was 55%. Flame lengths reached 3 feet (1 m), and nearly all surface litter was consumed .
After spring prescribed fires in Minnesota and Wisconsin, both increases and decreases in redosier dogwood stem density occurred. Changes between prefire and postfire stem densities were not consistently related to the composition of stands, fire season, fire spread rates, or fire intensity. Prescribed fires occurred in the spring or fall, when most vegetation was probably dormant. Air temperatures ranged from 55 to 78 °F (13-26 °C) and relative humidities were 22% to 49% at the time of burning. Fires were conducted 4 to 9 days after the last rain, and fuel moisture contents ranged from 8.3% to 14.8%. Density of redosier dogwood stems was evaluated at the end of the 1st postfire growing season .
|Density of redosier dogwood stems before and after prescribed fires in quaking aspen and mixed hardwood stands in Minnesota and Wisconsin |
|Site characteristics||Fire characteristics||Redosier dogwood stem density (number/ha)|
|Season||Energy (kJ/m²)||Rate of spread (m/min)||Frontal fire intensity (kW/m)||Prefire||Postfire|
|Site 1: mixed hardwood||Spring||4,570||1.8||139||1,656||988|
|Site 2: pure quaking aspen||Spring||4,560||8.8||672||8,648||10,020|
|Site 3: mixed hardwood||Spring||4,560||1.8||139||1,606||988|
|Site 4: mixed hardwood||Spring||4,553||1.5||115||791||2,076|
|Site 5: mixed hardwood||Fall||4,531||2.1||161||1,680||1,384|
|Postfire tree mortality (5.1-10.2 cm diameter size class) was greatest at Site 2, next greatest at Site 3, and least at Site 6.|
Early postfire succession: Redosier dogwood has been reported on burned sites 100 days to 30 years following fire. Redosier dogwood occurred on burned plots 100 days after a severe fire in a northern white-cedar-balsam fir stand near Ottawa, Ontario. The wildfire occurred on 23 June 1999, spread at a rate of 16 feet (5 m)/minute, and produced flame heights of more than 100 feet (30 m). The stand had not burned since 1870 . In mixed-conifer forests in northern Idaho's Bitterroot Mountains, redosier dogwood often occurred within 2 to 3 years of fire on moist sites . In treeless muskegs of north-central Wisconsin, redosier dogwood was classified as an invader on sites burned by prescribed fire. Although precise time since fire associated with redosier dogwood establishment was not provided, it was likely within 10 years of burning . In southeastern Wisconsin, redosier dogwood was the most common shrub in quaking aspen woodlands about 30 years after a severe fire in a marl and peat marsh. The fire started in August and continued to burn through the winter. In some areas with dry peat, the fire burned a foot (0.3 m) deep .
Fires and logging: Although abundance may be reduced, redosier dogwood typically survives in burned clearcut stands. On a clearcut site in the Mackenzie Forest District of British Columbia, average redosier dogwood cover was greater before than after prescribed burning. In the western white spruce (Picea glauca × P. engelmannii)-devilsclub forest type, redosier dogwood cover averaged 1.8% after clearcutting. Cover was less than 1% in the 1st growing season after a low- to moderate-severity, fall prescribed fire. By the 10th postfire year, redosier dogwood cover was still less than 1%; however, frequency of redosier dogwood was greater in the 10th postfire year than it was in clearcut and unburned stands . When disturbed and undisturbed western redcedar-western hemlock stands in northern Idaho were compared, redosier dogwood did not occur in undisturbed, closed-canopy stands. Frequency of redosier dogwood ranged from 1% in logged but unburned stands to 12% in logged and pile burned stands. The age of disturbed stands ranged from 11 to 40 years . In boreal mixedwood stands in southeastern Manitoba, the cover and frequency of redosier dogwood in logged stands averaged 5.3% and 10%, respectively. In burned stands cover and frequency averaged 1.8% and 8%, and in stands impacted by severe bud worm outbreak, cover and frequency averaged 1.3% and 5%. Time since disturbance in the stands ranged from 10 to 16 years . In mixed-hardwood stands in Minnesota's Chippewa National Forest, dogwoods (redosier dogwood and alternate-leaf dogwood) made up a much greater proportion of plots that were burned 2 years after clearcutting than plots that were not burned after clearcutting. Stands were evaluated for the first 8 years following disturbance. The prescribed fire burned in May when the previous 6 days had been free of rain, relative humidity was 29%, air temperature was 69 °F (20.6 °C), and wind speed was 16 feet (5 m)/second. The fire consumed nearly all fuels less than 3 inches (7.6 cm) in diameter. The researcher reported that dogwoods were "encouraged" by fire .
Multiple fires: In the Great Lakes region, redosier dogwood occurred on repeatedly burned sites. In northwestern Minnesota's Beltram Island State Forest, prescribed fires were set in May of 1968, 1971, 1973, and 1975. Each fire burned 59% to 90% of the study area, which was, at the time of the first fire, dominated by mature quaking aspen. The researchers reported that most of the quaking aspen stands were converted to shrublands dominated by plums (Prunus spp.) and redosier dogwood after burning . In oak savannas in east-central Minnesota, 2 to 19 prescribed fires were conducted over a 20-year period, primarily in the spring. Regression analyses indicated that redosier dogwood decreased with increasing fire frequency (r = -0.233), but the relationship was not significant (P=0.476) . At Summerton Bog in central Wisconsin, 2 consecutive spring fires failed to reduce shrub cover, and after the fires, redosier dogwood "appeared to" increase .
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