PARENT SESSION
Contributed Oral Session 40: Forest Understories
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal

Examining the interactive effects of deer browsing, understory fire, and canopy gaps on eastern forest dynamics. What's driving the patterns?

Schumacher, Henry^*,1, Carson, Walter¹, Adams, Mary Beth², ¹ University of Pittsburgh, Pittsburgh, PA, USA² USDA Forest Service, Parsons, WV, USA

ABSTRACT- Radical shifts in species composition have occurred in eastern deciduous forests over the past century. These shifts have resulted in the increase in mesic species (red maple) and a decrease in oaks and hickories. These drastic shifts in species composition have largely been attributed to three primary processes: alterations of historic fire regimes, the proliferation of the deer population, and alteration of gap-phase dynamics. Previous research has shown that alone, each individual process (fire, deer, gaps) can have major impacts on species composition. However, most tests of forest dynamics investigate a single process in isolation, potentially ignoring any important interactions among processes. Because the effects of fire, gaps, and deer are most likely not mutually exclusive, we believe that tests capable of examining the interactions and relative strengths of these three processes are necessary. We have experimentally manipulated surface fires, deer herbivory, and canopy gaps to simultaneously investigate the role of these three processes on regeneration dynamics. We test the hypotheses that, 1) Periodic fires promote diversity and the regeneration of a suite of fire tolerant species, particularly oaks, 2) Over-browsing by deer prevents palatable species from establishing or entering the sapling size class and, 3) Large canopy gaps allow the regeneration of both intermediate shade-tolerant and shade-intolerant species. Our experimental design allows us to incorporate both the individual and interactive effects of these three key processes and to follow these treatment effects from the seedling through sapling stages. We found that surface fires alone did not promote the diversity of fire-tolerant species, including oaks. In addition, our results show that there is a strong interaction between fire, deer, and tree-fall gaps. In the absence of deer browsing, both tree-fall gaps and understory fire disturbances increased seedling diversity. However, the presence of deer browsing masked the effects of tree-fall gaps and led to a drastic reduction in seedling diversity after surface fires. Overall, we found that deer have important direct and interactive effects primarily driving eastern forests dynamics and should be incorporated into models of forest regeneration.

Key words: forest regeneration, deer browsing, understory fire