Windstorm Disturbance Without Patch Dynamics: Twelve Years of Change in a Minnesota Forest

In an old-growth Pinus–Populus–Acer forest, treefall areas did not diverge from undisturbed control areas over a 12-yr period following windstorm disturbance. Woody plant populations sampled in 1984, 1992, and 1996 changed significantly over time, but changes in treefall areas did not differ from changes in control areas in plant species richness, composition, or vegetation structure. Preexisting tall shrubs and windfirm saplings cast heavy shade even where canopy trees blew down, preventing formation of deep lightgaps and limiting resource heterogeneity on the forest floor. Thus, in this forest, disturbance by moderate windstorm did not initiate the sort of patch dynamics that enriches diversity by admitting light-demanding species into the understory. The unresponsiveness of the understory, juxtaposed with heavy mortality to shade-intolerant species, suggests that moderate windstorms will neither initiate patch dynamics nor set back succession, but will instead hasten successional takeover by shade-tolerant trees in such forests.