More info for the terms: active layer
, low-severity fire
, organic soils
, prescribed fire
, relative frequency
, wildfire Fire adaptations:
Tussock cottongrass is "fire adapted" [266
]. Archibold [12
] and Rowe [280
] characterized tussock cottongrass as a "fire resister". Tussock cottongrass has many traits that allow it to survive and establish after fire. At maturity, its tussock growth form helps protect its meristematic tissue (see IMMEDIATE FIRE EFFECT ON PLANT
); however, young tussock cottongrasses are not well developed and are less resistant to fire damage [12
]. Tussock cottongrass has deep roots
. It produces tillers
that sprout from a corm
after fire. Its small, light-weight seeds may be dispersed
by wind or water after fire. It has both a transient and persistent seed bank
. Its seeds readily germinate
in high light and at relatively high soil temperatures, conditions often present after fire [12
]. Out of 30 species examined in black spruce forests in interior Alaska, tussock cottongrass and bluejoint reedgrass (Calamagrostis canadensis) ranked highest in expected occurrence after fire [32
Plant response to fire: Tussock cottongrass may establish from soil-stored and/or wind-blown seeds after fire [73,123,227]. If tussocks survive fire, they typically tiller, and cover reaches unburned control levels in as little as 2 years ). Viable tussock cottongrass seeds are often buried in organic soil horizons [123,227] (see Seed banking). Since viable tussock cottongrass seeds are located up to 11 inches (29 cm) deep in organic soils , some viable seed is usually available after fire that does not burn down to mineral soil . However, Gartner and others  stated that because viable tussock cottongrass seed was present only in the uppermost soil horizons on Kuparuk Ridge, only shallow disturbances would leave tussock cottongrass seeds in the soil seed bank. The authors noted, however, that fires in tundra often do not burn organic soils deeply and leave some organic soil remaining. For example, tussock-shrub tundra fires in western Alaska in 1977 burned most vegetation but removed ≤2 inches (5 cm) of the approximately 11-inch (28 cm) thick wet organic horizon . Tussock cottongrass seeds are unlikely to survive fire if burned  (see Immediate fire effects on seeds). However, wind may disperse seeds from nearby sources, and surviving on-site plants may produce abundant seeds soon after fire  (see Seed production after fire). Tussock cottongrass seedlings are often some of the first to appear on burned sites, but seedling establishment may be low (see Plant establishment and plant growth after fire). Seed production after fire:
Tussock cottongrass flower and seed production often increase soon after fire. In the spring and early summer following a fire, tussock cottongrass is "often stimulated to such profuse flowering that the ground appears to be covered with snow" (Ratcliffe 1964a cited in [270
]). Thirty-eight days after the Kungiakrok Creek Fire, tussock cottongrass flower buds had developed [266
]. One year after a "light" fire in Alaska tussock tundra, Wein [365
] found "dramatically" increased flowering of tussock cottongrass; there were 3 to 10 times more seedheads on a burned than an unburned area. Tussock cottongrass "showed abundant flowering" 2 years after the 1968 Inuvik Fire [363
]. Katz (1926 cited in [270
]) recorded similar observations in central Russia. After a 1977 wildfire on Nimrod Hill, the "most striking" visual change in tussock-shrub communities between postfire years 1 and 2 was the increased density of tussock cottongrass culms. One year after the fire, tussock cottongrass culm density was 2 to 6/m², but 2 years after the fire densities had increased by 10 times, to 20 to 60/m² [261
]. Increased spikelet density may persist for at least 6 years after fire. Spikelet density of tussock cottongrass was higher on burned than unburned plots 3 to 6 years following a fire at Imuruk Lake on the Seward Peninsula (Table 8
]. On 4 prescribed burns in Alaska and the Northwest Territories (Elliott Highway, Caribou Hills, Mosquito Fork, and Inuvik), tillers flowered during postfire year 2. Flowering was greater for burned than unburned tussocks (Table 7
) (P<0.05) [370
]. On the Elliott Highway site, postfire establishment of tussock cottongrass resulted in a second wave of seedling recruitment the ninth postfire year [228
]. Wein [365
] attributed increased flowering and seedhead production on burned areas in Alaska to nutrients released by fire; translocation of stored nutrients within plants; warmer soils; and a deeper active layer.Table 7.
Mean tussock cottongrass seedling density, tussock cottongrass culm density, and active layer depth in prescribed burned and unburned areas in 4 field sites in Alaska and the Northwest Territories [370
] Site Date Seedlings/m² Culms/m² Active layer depth (cm) Burned Unburned Burned Unburned Burned Unburned Alaska Elliott Highway 18 June 130 0* 13 <1* 17 9* 18 August 248 0* no data no data 58 46* Mosquito Fork 3 June 3 0 8 1 21 no data 15 August 2 0 no data no data 50 37* Northwest Territories Caribou Hills 24 June 30 0* 20 6* 18 11* 7 September 11 0* no data no data 42 29* Inuvik 16 June 16 0 29 7* 19 12* 5 August 22 12 no data no data 46 37* *Differences between burned and unburned significant at P<0.05. Table 8.
Density of tussock cottongrass spikelets in different-aged burns in tussock tundra in the Noatak River and Seward Peninsula areas of Alaska [265
] Location Time since fire Spiklets/m² Burned Unburned Noatak River 5 weeks 0 3 5 years 15 1 10 years 5 no data Imuruk Lake, Seward Peninsula 1 year 5 2 3 years 104 3 6 years 124 3
Seedling establishment and plant growth after fire: Fire provides a favorable seedbed for tussock cottongrass establishment , and increased availability of nutrients after fire stimulates postfire growth [51,370]. In a comparison of tussock cottongrass seedling emergence on different substrates in a laboratory in Alaska, burned peat showed highest rates of emergence for surface-sown seeds; emergence was more than twice as great on burned peat as on mineral soil. Mean seedling fresh weights per pot were 191, 154, 104, and 7 mg for burned peat, raw peat, decomposed peat, and mineral soil, respectively (P<0.05). The authors suggested that seedling fresh weight was greatest on burned peat because the fire released nutrients and enriched the peat  (see Germination).
Tussock cottongrass seedlings are often abundant after fire. Racine  noted the occurrence of "abundant" tussock cottongrass seedlings on charred peat following the 1977 Seward Peninsula fires. On Nimrod Hill, tussock cottongrass seedlings were densest in burned moist sedge tussock-shrub tundra, followed by burned dry shrub tundra, and lastly by burned wet sedge-shrub tundra . Thirty-eight days after the 21 June Kungiakrok Creek Fire (1982) in tussock cottongrass-shrub tundra on the Noatak National Preserve, Alaska, tussock cottongrass averaged almost 30 seedlings/m². It presumably germinated from the seed bank . On 4 burned field sites in Alaska and the Northwest Territories, establishment of tussock cottongrass seedlings was "dramatic" .
Postfire mortality of seedlings may be high. Two months after a late June fire near at the Elliot Highway site, tussock cottongrass seedling density was 198 seedlings/m² on burned peat between tussocks. Seedlings emerged on sides and tops of burned tussocks but at an unreported, but lower density. Although "substantial densities" of seedlings survived winter, very few of these lived until the following fall . One and 2 growing seasons after the 1977 fire on Nimrod Hill, seedlings of tussock cottongrass were "fairly abundant" in intertussock spaces; however, 2-year-old tillering seedlings were found only occasionally, suggesting low seedling survival from postfire year 1 to 2 . Twenty-four years after the fire, tussock cottongrass density had increased by 0.3 to 0.4 tussock/m² from 4 years before the fire . Although tussock cottongrass seedlings established within a few weeks after the moderate severity 1982 Kungiakrok Creek Fire, few or none survived . By midgrowing season 1 year after a low-severity fire in Alaskan tussock tundra that burned all litter and aboveground vegetation but little peat, there were >200 tussock cottongrass seedlings/m², but by the next spring, very few of the seedlings had survived . For more information, see Seedling establishment after disturbance.
New tussock cottongrass growth may appear soon after fire (e.g., [361,365]), and tussock cottongrass is often one of the first species to recover after fire . New growth may be evident within 3 weeks of fire [361,365]. For example, new tussock cottongrass growth was evident on 17 July in a wet tundra community in the Mackenzie River Delta region of the Northwest Territories that was burned under prescription on 23 June .
Fire generally reduces tussock cottongrass cover and biomass, but tussock cottongrass usually recovers quickly. After the low- to moderate-severity 1977 wildfire on Nimrod Hill, tussock cottongrass cover decreased on the shallow (2%-3% slope) footslopes from 34% 5 years before the fire to 16% to 20% in postfire year 1. Between postfire years 1 and 3, tussock cottongrass cover increased on the footslope by 9% to 20%. At one site, tussock cottongrass cover continued to increase until postfire year 24, when the study ended; at 2 other sites, tussock cottongrass cover remained the same (Table 9) . Twenty-three years after the Kungiakrok Creek Fire, the total vascular cover was 98%, an increase of 50% since 38 days after the fire. The increase resulted primarily from increases in tussock cottongrass and Bigelow sedge . Table 9.
Mean cover and density of tussock cottongrass after the 1977 tussock-shrub tundra wildfire on Nimrod Hill in the central Seward Peninsula [267
] Variables Time since fire (years) Footslope (2%-3% slope) Footslope (5%-7% slope) Site 1 Site 2 Site 3 Site 4 Site 5 Cover (%) 1 16 17 20 8 15 3 27 29 40 13 23 24 34 29 40 31 31 Density (tussocks/m²) 1 4.5 4.5 4.2 3.2 4.0 3 4.5 5.2 4.8 3.5 4.3 24 4.3 5.7 4.6 3.6 4.3
In Alaskan tundra, tussock cottongrass cover and/or biomass on burned sites can exceed that of unburned control sites in as little as 1 to 13 years and remain higher than unburned controls for more than 20 years [107,162,265]. For example:
- Two and a half years after the 1988 Selawik National Wildlife Refuge wildfire burned 209,088 acres (84,615 ha) in northwestern Alaska, tussock cottongrass biomass and relative frequency were greater in burned plots in tussock tundra than in adjacent unburned plots .
- One year after a fire on an Elliott Highway site, the proportion of the total aboveground vascular plant biomass comprised of tussock cottongrass was greater on burned than unburned control plots; production of tussock cottongrass harvested in late August was 15.0 g/m² on a burned site and 17.8 g/m² on an unburned site . Tussock cottongrass contributed 54% of the total aboveground vascular plant biomass in the burned site 13 years later . The fire apparently "released tussock cottongrass from competition" and provided a short-term nutrient pulse . By postfire year 24, the proportion of total plant biomass comprised of tussock cottongrass on burned plots (24%) was similar to that before fire, but the proportion in control plots had decreased to only 3% of total aboveground vascular plant biomass  (Table 10). The decline in the proportion of tussock cottongrass biomass between postfire years 13 and 24 may have been the result of continued invasion by other plants and thus, increased interspecific competition within tussocks. .
- Studies of the 1977 burns on the Seward Peninsula and the Noatak and Kokolik rivers found that vascular plant cover returned to unburned control or prefire levels in 6 to 10 years. At all sites, most regrowth was tussock cottongrass .
- Following the 1981 Ulukluk Creek Fire in northwestern Alaska (a 5-acre (2 ha) wildfire in low shrub-tussock tundra), average cover of tussock cottongrass rose from <1% 1 month after the fire to >30% 3 years after the fire, while unburned control plots ranged from 13% to 20% tussock cottongrass cover. Even 14 years after the fire, tussock cottongrass cover was 11% higher on burned plots than unburned plots [162,163]. By 24 years after the fire, cover was similar: 43% in burned plots and 42% in unburned plots .
- On the Seward Peninsula, tussock cottongrass cover in burned areas exceeded cover in unburned areas by 19% 20 years after the 1977 Wagon Wheel Fire, and by 20% 25 years after the 1972 Pargon River Fire. The authors concluded that "large, vigorous tussocks of tussock cottongrass were a finding common to tundra burn sites aged 14 to 25 years" on the Seward Peninsula .
- A wildfire of "unusually" high severity, with deep charring of organic soils, burned across the forest-tundra ecotone near Inuvik, Northwest Territories, in 1968. Tussock cottongrass cover was relatively similar 5 and 22 years after the fire in both forest-tundra and tundra. Unburned controls were only measured in postfire year 5 because visual observations suggested that unburned controls "changed very little" between 5 and 22 years after the fire  (Table 11).
Table 10. Proportion of the total aboveground vascular plant biomass comprised of tussock cottongrass (%) on burned and unburned tussock tundra 1, 13, and 24 years after fire on an Elliott Highway site near Fairbanks, Alaska [347
] Years after fire Burned Unburned 1 33.3 20.2 [370
] 13 54.3 4.1 [107
] 24 24 3 [347
] Table 11.
Mean percent cover (SE) of tussock cottongrass in forest-tundra and tundra that burned near Inuvik, Northwest Territories, in August 1968 [204
] Community Mean cover (%) 5 years after fire 22 years after fire Unburned control Burned Burned Forest-tundra 4.3 (3.3) 5.0 (5.0) 3.9 (2.3) Tundra 6.3 (2.5) 6.1 (1.7) 7.8 (2.5)
Little information was available on tussock cottongrass response to fire in the Great Lakes region. Two years following prescribed burning in a muskeg in north-central Wisconsin, average frequency of tussock cottongrass was 27.5% in burned areas and 35.0% in adjacent unburned areas; the difference was not statistically significant .
For information about tussock cottongrass seedling establishment and plant growth after fire in Europe, see these sources: [154,155,269,270].
Vegetative growth after fire: Tussock cottongrass often produces tillers after fire. Tussock cottongrass plants recover quickly from unburned live stem bases. In tussock-shrub tundra, they may account for most vascular plant cover during the first 4 to 5 years after fire . Twenty days after the Kungiakrok Creek Fire, tussock cottongrass growth in tussock cottongrass-shrub tundra was already "well underway", with tillers about 6 inches (15 cm) long. Fire had removed about 2 to 4 inches (5-10 cm) of the 5- to 6-inch (12-14 cm) organic horizon between tussocks, and thaw depth was about 4 inches deeper on burned than unburned areas. Standing water was present at the bottom of the intertussock spaces on the burned area . Soon after the low- to moderate-severity 1977 fire in tussock-shrub tundra on Nimrod Hill, new leaves developed "rapidly" from tussock bases . On the Elliot Highway site, tussock cottongrass tillers sprouted during the first postfire growing season following a 25 June prescribed fire in tussock cottongrass tundra . Tussock cottongrass recovered "quickly" during the first 3 years after the 1981 Ulukluk Creek Fire that burned in lichen-tussock tundra, "demonstrating vigorous basal sprouting from tussock bases and heavy flowering" . For more information on this topic, see Vegetative growth after disturbance.
Plant nutrients and depth of thaw after fire: Tussock cottongrass nutrient content is often high after postfire nutrient flushes. Late summer regrowth of tussock cottongrass "proved to be relatively high in protein content", and therefore, in nitrogen, following a fire in Kotzebue Sound in 1977 . On 4 burned field sites in Alaska and the Northwest Territories, tussock cottongrass plants in burned areas had higher nitrogen, potassium, calcium, and magnesium content than plants in unburned areas. This was attributed to release of nutrients, increased active layer depth, and greater microbial activity after fire . Almost 2 years after the 1988 Selawik National Wildlife Refuge wildfire, late winter protein content and in vitro digestibility of tussock cottongrass were higher in samples collected from burned than unburned plots. Postfire increases in protein content, digestibility, and availability of tussock cottongrass may make burned tussock tundra an attractive feeding area for caribou in late winter . For more information, see IMPORTANCE TO LIVESTOCK AND WILDLIFE.
After fires, tussock cottongrass plants may benefit from a deepened active layer and warmer soils [365,370]. On 4 burned sites in Alaska and the Northwest Territories, tussock cottongrass seedling and culm densities were greater where fire had deepened the active soil layer. For example, in the Caribou Hills, Northwest Territories, the active layer was 160% deeper in burned than unburned areas in spring, and in the fall, it was 140% deeper (Table 8); thus, the growing season was longer on the burned areas . Vavrek and others  proposed that because tussock cottongrass roots may grow to the bottom of the active layer (e.g., [71,371]) (see Roots), the species may obtain nutrients at greater depths than shallow rooting species. Thus, a persistent increase in the active layer may prolong dominance by tussock cottongrass in burned communities . Brown and others  reported an increased thaw of 140% to 160% 4 years after a fire in a black spruce/Eriophorum spp. tussock community in eastern Alaska. They also reported a 141% and 152% increase in thaw depth in a 1-year-old burn in an Eriophorum spp. tussock community with scattered black spruce in central Alaska. Wein and Bliss  documented warmer soils, increased nutrient cycling, greater tussock cottongrass growth, and more abundant tussock cottongrass flowering for burned tussock cottongrass communities as well. Kryuchkov (1968 cited in ) reported that before wildfire in eastern Siberia, the upper permafrost layers were 20 to 28 inches (50-70 cm) thick. Fire thawed the upper permafrost layers; warmer soils and the resultant moisture release stimulated tussock cottongrass growth and increased tussock cottongrass cover soon after fire. A few years after the fire, however, the active layer was only 16 to 18 inches (40-45 cm) thick due to the insulating effect of thick postfire vegetation (Kryuchkov 1968 cited in ).