Hailstorm damage promotes aspen invasion into grassland
Canadian Journal of Botany
Global warming is widely thought to promote the dominance of grasslands over woody vegetation, and shift the location of ecotones. In contrast, forest vegetation along the northern edge of the North American Great Plains has migrated southward over the past century into areas dominated by native grassland. Because climate change is also predicted to increase storm frequency and intensity, we quantified the impacts of an intense hailstorm on woody and herbaceous species in native grassland in the northern Great Plains of North America. The hailstorm disturbance killed or damaged mature stems of the dominant tree, aspen (Populus tremuloides Michx.), but damaged aspen stands subsequently invaded ca. 10m into neighbouring grassland. Damaged aspen stands also produced up to 20-fold more new stems having 67-fold higher total biomass compared with relatively undisturbed stands. Grasses and lichens suffered much higher rates of biomass removal (60%-76%) than did shrubs (6%-8%) immediately following the storm. The disturbance-mediated recruitment of clonal woody plants, and the unexpected sensitivity of grasses and lichens to this disturbance, may contribute to the counterintuitive expansion of trees into grasslands under a regime of increased storm frequency that is not predicted by simple ecosystem responses to warming.
Peltzer, Duane A. & Wilson, Scott D. 2006. Hailstorm damage promotes aspen invasion into grassland. Canadian Journal of Botany. 84(7): 1142-1147.