PARENT SESSION
Poster Session # 14: Forest Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Vegetation-environment relationships among four canopy-layers in an old-growth mixed mesophytic forest.

McEwan, Ryan ^*,1, Muller, Robert², McCarthy, Brian¹, ¹ Department of Environmental and Plant Biology, Athens, OH, USA² Santa Barbara Botanical Garden, Santa Barbara, CA, USA

ABSTRACT- Previous work in an old-growth mixed mesophytic forest has indicated that Acer rubrum and Acer saccharum are dominant in the understory strata, while xerophytic oak species (e.g. Quercus montana) are becoming increasingly restricted to the overstory canopy. This apparent shift in dominance is similar to that seen in xeric oak forests throughout the eastern U.S. and yet the species composition and environmental conditions in those oak forests represent only one extreme of the gradient present in mixed mesophytic forest systems. We examined the oak-to-maple transition phenomenon within our mixed mesophytic study site in order to examine vegetation-environment relationships among woody species in four canopy-strata. We hypothesized that 1) the most important environmental variables determining vegetation structure would differ among canopy-layers and 2) relative abundance of Acer and Quercus would be maximized under very different environmental conditions. Overstory vegetation was arrayed in Canonical Correspondence Analysis space along a gradient of soil fertility (Ca, r = -0.72) and elevation (r= 0.76). In the midstory, soil fertility (Ca, r = -0.78), elevation (r = 0.66) and light availability (r= 0.57) were important factors. Vegetation patterns of the shrub-layer and the ground-layer were driven by soil fertility (Ca, r = -0.84, r = -0.78, respectively) and soil pH (r = 0.63, r = 0.75, respectively). Across strata, Quercus sp. were consistently located in ordination space in upper elevation areas with high light availability and low soil pH. Acer rubrum was located near the center of each diagram, suggesting plasticity, and Acer saccharumappeared to be restricted to more nutrient rich areas. Though a dominance shift seems to be underway, our data indicate that the environmental criteria necessary for maximum relative dominance of Acer and Quercusare similar between strata.

Key words: Acer saccharum, vegetation-environment relationship, Acer rubrum, Quercus spp.