COS 258-4 - Monitoring grassland recovery following wildfire using satellite imagery.

Background/Question/Methods

In the fall of 2017, two grass wildfires ignited in South East Alberta and carried into Saskatchewan, burning approximately 28 000 hectares of native grassland. While grassland fire is a normal component of the disturbance regime, understanding the impact of fire on productivity is critical as agricultural producers manage these grasslands for cattle production. Over the past five years, we have evaluated grassland productivity and diversity recovery from both plot-scale and landscape-scale perspectives. We compared community data from paired burned and unburned plots for our plot-scale analysis. We evaluated the landscape-level effects of wildfire severity on productivity recovery using remotely sensed images to (1) determine variation in fire severity across the entire burn area and (2) how variation in fire severity impacts how biomass recovers through time.

Results/Conclusions

Five years following the wildfires, we found that biomass production has not completely recovered in burned areas, while fire effects on plant community composition have become undetectable. Using the bare soil index as a proxy for fire severity, we found that the high-intensity fire removed nearly all vegetation and standing litter in the entirety of the burned area. Some variation in fire intensity was detectable, and primarily determined by environmental gradients such as slope and aspect. In areas where fire would have moved quickly uphill, we found lower fire severity than in areas where the fire would have moved more slowly downhill. Using the normalized difference vegetation index as a proxy for live biomass productivity, we found that previously highly productive areas recovered faster than previously low productive areas. Further, we found that site capability (soil fertility) and weather influenced the recovery of biomass productivity. Overall, these results suggest that pre-fire grassland condition may be an important determinant of the rate of grassland productivity recovery.