Temporal changes in species composition in Fescue Prairie: relationships with burning history, time of burning, and environmental conditions

Abstract

Historically, fires occurred throughout the year in the Fescue Prairie of Canada, but little is known about plant community responses to burning at different times of the year. Composition of plant communities was determined annually for 6 years after burning one or three times in a remnant Fescue Prairie in central Saskatchewan. A multiple-response permutation procedure indicated that plant community composition was different in the two burning histories (P < 0.001) and among times of burning (P < 0.001). Variables related to plant community composition after burning were evaluated using Non-metric Multidimensional Scaling. Three gradients explained 86% of the variation in composition of plant communities. Environmental conditions leading up to burning and at the time of burning correlated poorly with species composition. Differences in composition of plant communities were attributed primarily to burning history, cumulative precipitation in the 12 months before sampling, cumulative cold-stress days in the 12 months before sampling, cold-stress days in March and April, and months since burning. Plant communities burned once responded negatively to increasing cold-stress days while those burned three times responded positively to cold-stress days. Cover of Festuca hallii and Symphoricarpos occidentalis was 88 and 350% greater after one burn as compared to three burns, whereas cover of Carex obtusata, Carex pensylvanica, and Elymus lanceolatus was 126, 53, and 220% greater after three burns than after one burn. Festuca hallii, Galium boreale, Pulsatilla patens ssp. multifida, Symphoricarpos occidentalis, and Symphyotrichum ericoides had the highest indicator value of a single burn; Carex obtusata, Elymus lanceolatus, and Koeleria macrantha had the greatest indicator values for sites burned three times. Longer-term effects of burning history exert a strong influence on plant community composition while short-term conditions after burning, namely, precipitation and cold-stress days, appear important in controlling species responses and composition of plant communities in Fescue Prairie.