Population Dynamics after Wildfires in Sagebrush Grasslands

Abstract

Population dynamics of herbaceous and shrub species were investigated in big sagebrush/Thurber needlegrass communities burned in wildfires. The sites burned are representative of extensive areas of degraded rangelands in the central Great Basin. Herbaceous succession after wildfires in these communities is dominated by the dynamics of populations of the alien annual grass downy brome. Downy brome caryopses are greatly reduced by most large wildfires, but the plants originating from surviving downy brome caryopses respond dynamically to the released environmental potential. The response may include hybridization and recombination. The result is a purge of native annual species from the community and the failure of seedlings of native perennial grass species to become established. Root and crown sprouting of the native shrubs, green rabbitbrush and horsebrush, occurs after the wildfire has killed the dominant big sagebrush. Green rabbitbrush sprouts produce abundant achenes, which readily germinate and grow. The reestablishment of downy brome dominance predisposes the vegetation to recurring wildfires and cyclic environmental degradation.