2003 Ton Damman Award Recipient

Rachel J. Collins is the first recipient of the Ton Damman award for her presentation at the 2003 ESA meeting in Savannah. For her dissertation research at the University of Pittsburgh, Rachel examined the effects of deer herbivory on successional trajectories in forest plots with canopy gaps, fire, and fire + canopy gap disturbance. Rachel currently is a visiting assistant professor at Dickinson College. She has accepted a visiting professor position at Swarthmore for the coming year. Here is Rachel's winning abstract: Collins, Rachel J. and Walter P. Carson. University of Pittsburgh, Pittsburgh, PA. Do succession models predict the right pattern for the wrong reason: shade vs. herbivore tolerance?

Succession models typically predict the replacement pattern of species following disturbance. One of the most prominent models, the shade-tolerance model, uses species-specific tolerances of seedlings to low understory light conditions as the mechanism to predict species replacement. A second model uses shade tolerance in combination with the timing of the disturbance during succession (i.e., a stage-dependant model) as the mechanism for predicting species replacement. Both of these models are based on resource-species interactions and ignore the potential effects of herbivores in determining successional trajectories. White-tailed deer populations are at historically high levels in many areas. By neglecting the effects of browsing, these models may either fail to predict successional trajectories or make the correct prediction for the wrong reason (i.e., shade tolerance instead of herbivore tolerance). We experimentally tested the predictions of these two models with three types of disturbances: canopy gaps, understory fire, and a combination of gap and fire at two levels of herbivory. At the Westvaco Research Forest in northeastern West Virginia, we have established 64 plots (400 m2) where we have permanently tagged, identified, and measured nearly 17,000 seedlings, saplings, and adults of 26 species of trees. In the absence of deer herbivory, the shade-tolerance model correctly predicted the dominance of shade-intolerant species (i.e., pioneers) after both fire and canopy gap formation. In the presence of deer herbivory, however, shade-tolerant species (i.e., late succession) dominated after disturbances. The stage-dependant model did not consistently predict the dominant species. Herbivory is changing these successional trajectories, truncating succession, and preventing pioneer species from dominating during early succession. Thus, under current conditions of overabundant deer populations that exist throughout much of eastern North America, forest succession models that fail to explicitly incorporate herbivory or tolerance to herbivory will not consistently predict species composition and successional trajectory in forests.