Seasonal fire effects in a Saskatchewan plains rough fescue prairie
Gucker, Corey L., comp. 2005. Seasonal fire effects in a Saskatchewan plains rough fescue prairie. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/fire-studies/archibold-et-al-2005
Source
Archibold, O. W.; Ripley, E. A.; Delanoy, L. 2003. Effects of season of burning on the microenvironment of fescue prairie in central Saskatchewan. Canadian Field Naturalist. 117(2): 257-266.
Researchers studied prescribed fires on the Kernan Prairie (52°11'N, 106°42'W) near Saskatoon, Saskatchewan.
Site Description
Vegetation in this study area is likely represented by the following vegetation classifications:
- FRES38 Plains grasslands [3]
- SRM613 Fescue grassland [5]
Kernan Prairie's continental climate brings average winter low temperatures of -18 °C, summer highs of 19 °C, and annual precipitation levels of 360 mm, 30% of which is snow [2]. The soils in the study area are fine-textured Chernozems, which are described as dark, organically rich, with calcium carbonate layers below the A horizon [2]. The soils of Kernan Prairie have a surface bulk density of 1.3g/cm³. The plains rough fescue (Festuca hallii) grasslands studied occupied prairie depressions.
Researchers reported that the precipitation levels the year of the fires were 5% above normal for the months of April through September. August rainfall was much greater than normal the year fires burned. From April through September of the 1st postfire year, precipitation levels were 17% above the long-term averages.
Plains rough fescue dominates the study area's vegetation, and Kentucky bluegrass (Poa pratensis) is a common grass species. The site supports several sedge (Carex spp.) species, and important forbs include northern bedstraw (Galium boreale), white sagebrush (Artemisia ludoviciana), and white prairie aster (Symphyotrichum falcatum var. falcatum). Western snowberry (Symphoricarpos occidentalis) and rose (Rosa spp.) were the only woody vegetation identified in the study area.
The site burned in May of 1991, 3 years previous to the fires reported in this study. No information regarding this earlier fire was provided.
Prior to the fires in April 1998, researchers established 4 contiguous 10×10 m plots in an area with uniform plant cover, soil conditions, and topography [1,2].
Plant Phenology
Phenology of the prefire vegetation was not described.
The study objectives were to compare the regrowth of vegetation and the resulting microenvironments on plots burned in the spring, summer, and fall. This research project summary concentrates on the vegetation recovery; however, unburned and burned microenvironment characteristics, including surface albedos, soil temperatures, and leaf area indices, are provided in the original report.
Prior to igniting the fires, firebreaks were established around the plot to be burned. Fuel load and moisture content were determined from 0.25×0.5 m quadrats before burning. Ring fires were set in the center of the plot. Researchers monitored weather conditions and flame temperatures at 1 cm beneath the soil surface and 5, 10, 20, 50, and 100 cm above the ground [1].
Fuel load and moisture content were greatest for the fall fire and least for plots burned in spring (see table below). Fall and summer fuel loads were very similar, but fuel moistures were much greater in the fall. The fuel loads reported for this study are much greater than the average 450 g/m² fuel load reported by Redmann and others [4], who burned rough fescue-dominated sites within the Kernan Prairie in the late 1980s.The table below gives average fuel loads and fuel moistures (±s) prior to spring, summer, and fall burning [2].
| Prefire characteristics | Spring | Summer | Fall |
|---|---|---|---|
| Fuel load (g/m²) | 670±334 | 742±216 | 749±198 |
| Fuel moisture (%) | 12.7±1.8 | 14.6±3.4 | 64.5±17.3 |
Air temperature and relative humidity were highest during the summer fire. Air temperature and relative humidity were lowest during the spring fire. Wind speed was similar for all fire seasons.
| Conditions during fire | Spring | Summer | Fall |
|---|---|---|---|
| Air temperature (°C) | 10 | 26 | 20 |
| Relative humidity (%) | 35 | 50 | 40 |
| Wind speed (m/s) | 3 | 4 | 2.5 |
The researchers measured fire temperature regimes using 4 replicate chromelalumel thermocouples at each of the above ground distances shown below. Temperatures were recorded at 10-second intervals. The summer fire produced the highest soil and aboveground temperatures. Fire temperatures remained above 50 °C for 5 minutes or longer at 5, 10, and 20 cm above the soil surface during the summer fire. Litter accumulation and low soil moisture were identified by the researchers as the probable causes of increased soil temperatures during the summer fire. The fall and spring fires produced similar fire temperature regimes. However, the spring fire produced temperatures greater than 50 °C for almost 2 minutes longer than the fall fire at 5 cm above the soil surface. The table below provides the average maximum fire temperatures and durations for the seasonal fires.
| Distance above ground (cm) | Spring | Summer | Fall | |||
|---|---|---|---|---|---|---|
| Mean maximum temperature (°C) | Duration above >50 °C (min) | Mean maximum temperature (°C) | Duration above >50 °C (min) | Mean maximum temperature (°C) | Duration above >50 °C (min) | |
| 100 | 89 | 1 | 156 | 2.7 | 151 | 1.7 |
| 50 | 134 | 1.2 | 209 | 3.5 | 174 | 2 |
| 20 | 292 | 2 | 269 | 5 | 280 | 2.3 |
| 10 | 336 | 3 | 290 | 5.7 | 316 | 2.7 |
| 5 | 227 | 5.2 | 330 | 7.2 | 324 | 3.3 |
| -1 | 8 | — | 44 | — | 14 | — |
Fire Effects on Plant Community
Assessing the effects of fire seasonality on the vegetation of Kernan Prairie involved comparisons between burned and unburned plots. No prefire data were available. Without preburn data it is difficult to interpret the results for those species occurring only in a single treatment. The researchers cautioned that "the restriction of species to a treatment plot likely reflected its comparative rarity at the site rather than a consequence of the fire."
Grasses and shrubs were significantly taller (on the unburned plot than on any of the burned plots at the end of the 2nd postfire growing season. However, biomass production of grasses and shrubs was significantly greater (P<0.05) on the fall burned plot than on the unburned plot. Forb biomass production was greater on all burned plots than on the unburned plot, although not significantly. Forb biomass was greatest on the spring burned plot. The mean biomass (g/m²±s) of grasses at end of the 2nd postfire growing season is given below:
| Life form | Unburned | Spring | Summer | Fall |
|---|---|---|---|---|
| Grasses | 0.4±0.09a* | 0.26±0.03ab | 0.17±0.03b | 0.17±0.05b |
| Forbs | 0.06±0.01a | 0.14±0.03a | 0.11±0.02a | 0.08±0.04a |
| Shrubs | 0.18±0.04a | 0.03±0.01ab | 0.09±0.02ab | 0.31±0.07b |
* Values in the same row with same letter are not significantly different (P<0.05).
Individual species were also investigated. The following tables and remarks compare burned and unburned plots at the end of the 2nd postfire growing season. Rough fescue coverage was greatest on the spring burned plot. Sun sedge (Carex inops subsp. heliophila) coverage was greater on all burned plots than on the unburned plot. Coverage of most other graminoid species was lower or similar on burned plots than on the unburned plot. Kentucky bluegrass coverage was much lower on spring and summer burned plots than on unburned or fall burned plots. Porcupinegrass (Hesperostipa spartea) coverage was lowest on the fall burned plot and greatest on the unburned plot. The complete list of graminoid species and their percent coverage on burned and unburned plots at the end of the 2nd postfire growing season is given below.
| Common name | Scientific name | Unburned | Spring | Summer | Fall |
|---|---|---|---|---|---|
| Grasses | |||||
| thickspike wheatgrass | Elymus lanceolatus ssp. lanceolatus | 0.1 | 0 | 0.1 | 0.1 |
| slender wheatgrass | Elymus trachycaulus | 1.3 | 0.5 | 0.1 | 0.3 |
| plains rough fescue | Festuca hallii | 11.3 | 13.2 | 7 | 8.8 |
| spikeoat | Helictotrichon hookeri | 0 | 0 | 0 | 0.1 |
| porcupinegrass | Hesperostipa spartea | 5.6 | 4.9 | 3 | 2.2 |
| prairie Junegrass | Koeleria macrantha | 0 | 0.2 | 0 | 0.1 |
| green needlegrass | Nassella viridula | 0.5 | 0.2 | 0.7 | 1.5 |
| western wheatgrass | Pascopyrum smithii | 0 | 0 | 0.1 | 0.2 |
| Kentucky bluegrass | Poa pratensis | 6.8 | 0.2 | 1.3 | 5.4 |
| Sedges | |||||
| needleleaf sedge | Carex duriuscula | 0.4 | 0.1 | 0.3 | 0.7 |
| sun sedge | Carex inops subsp. heliophila | 1.4 | 2.6 | 3.2 | 3.7 |
| obtuse sedge | Carex obtusata | 1 | 1 | 0 | 0 |
The effect of fire on Kernan Prairie forb species was variable. Few species had greater density on all 3 burned plots; however, most forbs had their greatest density on 1 of the burned plots. The same was true for the 2 shrub species. Forb and shrub densities (stems/m²) on burned and unburned plots at end of 2nd growing season are provided below [1].
| Common name | Scientific name | Unburned | Spring | Summer | Fall |
|---|---|---|---|---|---|
| Forbs | |||||
| common yarrow | Achillea millefolium | 2.7 | 8.3 | 1.7 | 8.3 |
| pygmyflower rockjasmine | Androsace septentrionalis | 0.7 | 5.7 | 14 | 0 |
| white sagebrush | Artemisia ludoviciana | 23.7 | 9.7 | 3.3 | 20.3 |
| purple milkvetch | Astragalus agrestis | 0 | 2.3 | 0 | 13.7 |
| bluebell bellflower | Campanula rotundifolia | 2 | 0 | 0 | 0 |
| field chickweed | Cerastium arvense | 0.7 | 0 | 0 | 0 |
| northern bedstraw | Galium boreale | 13 | 8.3 | 5 | 17 |
| old man's whiskers | Geum triflorum | 0.7 | 9.3 | 11.7 | 0 |
| stiff goldenrod | Oligoneuron rigidum var. rigidum | 0 | 6 | 0.3 | 0 |
| field locoweed | Oxytropis campestris | 0 | 0 | 14.3 | 0 |
| spiny phlox | Phlox hoodii | 1.7 | 1.3 | 0.7 | 0.7 |
| tall cinquefoil | Potentilla arguta | 0 | 4.7 | 1.7 | 0.7 |
| cutleaf anemone | Pulsatilla patens ssp. multifida | 0 | 0 | 0 | 1.3 |
| maidens-tears | Silene vulgaris | 0.3 | 0 | 0 | 0 |
| Missouri goldenrod | Solidago missouriensis | 0.3 | 0.3 | 11 | 0 |
| white prairie aster | Symphyotrichum falcatum var. falcatum | 91.7 | 69.3 | 138.7 | 99.3 |
| smooth blue aster | Symphyotrichumlaeve var. laeve | 1.3 | 7.3 | 10.3 | 0 |
| American vetch | Vicia americana | 0.3 | 0 | 0 | 0.7 |
| hookedspur violet | Viola adunca | 0 | 2.7 | 2 | 0 |
| Shrubs | |||||
| fringed sagebrush | Artemisia frigida | 3.7 | 2.3 | 1.7 | 2.7 |
| rose | Rosa spp. | 4.3 | 17.3 | 1 | 1.7 |
| western snowberry | Symphoricarpos occidentalis | 37.3 | 28.7 | 42.3 | 35.7 |
Spring, summer, and fall fires behave differently and have different effects on the vegetation. In the case of Kernan Prairie, no single fire season produced more biomass, density, or coverage of all species. Fire seasonality may have a selective effect on the prairie vegetation. The information provided in this study may be valuable in directing change in prairie communities.
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4. Redmann, R. E.; Romo, J. T.; Pylypec, B.; Driver, E. A. 1993. Impacts of burning on primary productivity of Festuca and Stipa-Agropyron grasslands in central Saskatchewan. The American Midland Naturalist. 130(2): 262-273. [35391]
5. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]