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Ecological Section

Montgomery, Rebecca A. [2], Lopez, Omar R. [3], Lopez, Krista Farris [3], Givnish, TJ [1].

Determinants of shade tolerance and its importance for local species distributions of S. Appalachian trees.

The Southern Appalachian mountains support the highest tree species diversity in the U.S. with over 30 species represented in the forest canopy. Local distributions of these trees vary along topographic and elevation gradients to create a compositional mosaic across the landscape. What factors determine local distribution of trees in the Southern Appalachians? We posit that differences among species in shade tolerance play an important role in determining local species distributions. Here, we evaluate the importance of a number of physiological determinants of shade tolerance across a gradient from low topographic positions (coves) to exposed ridges. Across the topographic gradient, understory light availability varies from 3-13% full sun. Species differ in leaf phenology with early leafing (e.g. Aesculus, Halesia) more common in coves than on ridges. Early-leafers show high rates of photosynthesis in spring and low rates in summer, whereas late-leafers show higher rates in summer (see also BSA 2004 abstract by Givnish et al.). Down regulation in respiration rates between spring and summer varies from 0-83%, with early-leafers (Halesia) showing the greatest down regulation. Species from shady summer sites (e.g. Acer saccharum in coves and on mid-slopes) show more rapid rates of induction than species from more open ridges (e.g. Quercus prinus) and the earliest leafers show slower rates of induction loss than later leafing species. These data suggest that enhanced carbon gain due to early leafing, low summer respiration rates, and rapid photosynthetic induction influence shade tolerance in S. Appalachian tress and are important for understanding species distributions from coves to ridges. Reciprocal transplant studies are planned to determine the extent to which these species differences are due to genetic versus environmental factors.

Related Links:
Leaf phenology and hydraulic conductance in S. Appalachian trees

1 - University of Wisconsin-Madison, Botany, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
2 - University of Minnesota, Forest Resources, 1530 Cleveland Avenue N, Green Hall 115, St. Paul, Minnesota, 55108, USA
3 - University of Wisconsin-Madison, Botany, 180 Sutton Road, Bryson City, North Carolina, 28713, USA

shade tolerance
Appalachian Mountains
leaf phenology

Presentation Type: Paper
Session: 29-12
Location: Wasatch (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 11:00 AM
Abstract ID:805

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