Vegetation response to fall wildfire in the mixedgrass prairie of western Canada

Abstract

Post-fire rangeland management is typically a period of rest on the Great Plains of North America, but recent research has questioned if long periods of rest are necessary. This study was designed to test different intervals of post-fire rest from defoliation during the first growing season after wildfire. Further, this study monitored the length of time needed and variables affecting vegetation recovery on ungrazed native rangeland in the mixedgrass prairie of Alberta and Saskatchewan, Canada. While post-fire plant production and subsequent June defoliations did not differ from the non-clipped control, July defoliation negatively influenced plant production on burned and non-burned subplots. However, these differences may be explained by the high intensity of defoliation (2 cm) imposing more stress on plants during July defoliation due to a greater relative amount of vegetation removed. Although post-fire June defoliation did not have negative impacts to plant production, there was very little vegetation present at this point in the growing season. Further, litter mass was reduced by wildfire and all defoliation treatments. Percent crude protein increased on burned areas in June of the first post-fire growing season, but this difference disappeared by July. When monitoring vegetation on grasslands in the absence of grazing, by the third post-fire growing season total plant production on burned subplots was reduced by 25% compared to non-burned and litter remained 65% lower on burned subplots. I found a positive relationship between total plant production and litter mass, which indicates that litter is important for plant growth. Importantly, I found a positive relationship between total plant production and pre-burned range health scores, which may indicate that pastures that are managed to maintain or improve rangeland health will improve the rate of post-fire plant recovery. Overall, this research has added to the current body of knowledge on grassland wildfires and it should help better inform post-fire grazing management practices.