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WATER-USE ALONG A HYDROLOGICAL GRADIENT IN CENTRAL FLORIDA: A TALE OF TWO PINUS SPECIES
Brooks, J R. WATER-USE ALONG A HYDROLOGICAL GRADIENT IN CENTRAL FLORIDA: A TALE OF TWO PINUS SPECIES. Presented at Application of Stable Isotope Techniques to Ecological Studies, Braunschweig, Germany, May 8-11, 2000.
Although central Florida is relatively flat, the distribution of species on the landscape is controlled by subtle changes in elevation. Along a four-meter elevation gradient, xeric sandhill vegetation dominated by Pinus palustris (Longleaf pine) gives way to mesic pine flatwoods dominated by Pinus elliotti (Slash pine). I examined the water-use and gas-exchange of these two species to understand what regulates their different distributions on the landscape. In the xeric sandhill, the water table depth was approximately 4 meters below the surface whereas in the mesic flatwoods the water table was less than one meter below the surface. Using dD analysis, both species use groundwater most of the time. Due to the mesic nature of the flatwoods, Pinus elliotti had lower water-use efficiency as indicated by d13C analysis of the foliage. However, during an extreme drought where the water table depth dropped over a meter below its average in both ecosystems, Pinus palustris was able to utilize surface rain events whereas Pinus elliottii did not. As a result, Pinus palustris was able to maintain gas-exchange activity during the drought, but Pinus elliottii shut down. In conclusion, both species utilize groundwater sources under normal conditions, but in the xeric sandhill, Pinus palustris can also utilize surface rain events to offset droughtier conditions, whereas in the more mesic environment, Pinus elliottii relies strictly on groundwater.