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Abstract
This study tested the following hypotheses: (1) tree transpiration varies in space in response to changes in vapor pressure deficit ( D); and, (2) edaphic conditions determine the range of that spatial variability. Two sites were used: one dominated by aspen ( Populus tremuloides) in the well-drained area and by alder ( Alnus incana) in the poorly drained area; the other was dominated by sugar maple (Acer saccharum) and contained a patch of red pine (Pinus resinosa). The spatial range of transpiration decreased with increasing D in both sites and was driven by tree size. In the Aspen site, spatial tree transpiration correlated inversely with soil moisture and total nitrogen but no similar relationship was found in the Maple site. These results showed that tree species and size drive spatial transpiration and were correlated with edaphic conditions. Thus, scaling from individual tree transpiration to the landscape in time and space should incorporate atmospheric and edaphic conditions.
