Using urban land-use types to assess global climate change effects on forests: evidence from sapling growth in Louisville, Kentucky.
Tripler, Chris*,1, 2, Carreiro, Margaret1, Canham, Charles2, 1 University of Louisville, Louisville, Kentucky2 Institute of Ecosystem Studies, Millbrook, New York
ABSTRACT- Global change models predict tree species distributions in North America will shift in response to the anticipated 2-4 °C rise in air temperature over the next 100 years. These range shift predictions are largely based on differences in water use efficiencies among tree species in response to temperature change. Validating the predictions of these biogeographic models remains a challenge. We explore the possibility that environmental conditions in urban areas can be analogs of future environmental change. Some cities have sufficiently large forest remnants to conduct comparative studies of species growth under the influence of increased temperature, nitrogen deposition, ozone, and potentially elevated CO2. We compared radial and height increment growth for eight naturally occurring sapling species in a forest fragment (> 300 ha) in the city of Louisville, Kentucky with a similar rural forest. Using maximum likelihood statistics, we found that Sugar Maple (Acer saccharum) and White Ash (Fraxinus americana) had comparatively higher radial growth in the urban forest (AICc > 7). American beech (Fagus grandifolia), Chestnut Oak (Quercus rubra), and Shagbark Hickory (Carya glabra) had increased radial growth in the rural forests (AIC c > 4). For these five species, height growth increment was found to increase in rural forests under 2, 10 and 40% full sun light conditions (AIC c > 4), except for beech under 2% full sun in which height growth was greater under urban forest conditions. No differences in radial or height increment growth were found for the three remaining species red maple (Acer rubrum), white oak (Quercus alba), and red oak (Quercus rubra). These preliminary findings suggest that some oak species are not likely to expand their distributions into areas predicted by biogeographic change models. Further, shade-tolerance competitive rank orders inside urban forests still appear to favor dominance by the shade-tolerant species, sugar maple and beech.
Key words: forest dynamics, sapling growth, global change, urban ecology
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