Patterns of leaf tannin variation in chestnut oak (Quercus prinus) and black oak (Quercus velutina) with respect to topography in a southeastern Ohio oak-hickory forest1

in low light and high nutrient environments. To test this hypothesis, we evaluated the patterns of leaf tannin chemistry in two species of oak (Quercus velutina L. and Q. prinus L.) utilizing protein precipitation methods. Leaves were sampled from mature, forest-grown, canopy trees found in a southeastern Ohio oak-hickory forest. To evaluate the effects of environment, we sampled along a natural gradient using trees from contrasting northand south-facing slopes. To assess the patterns of variation in tannin abundance among populations, we sampled multiple trees from three different sites. Thus, data were analyzed for patterns of variation with respect to slope aspect and population. Quercus prinus trees growing on south-facing slopes had significantly greater amounts of leaf tannins than those on north-facing slopes but did not exhibit significant population differences in foliar tannin content. In contrast, Q. velutina trees on north- and south-facing slopes did not differ significantly in foliar tannin content but did exhibit significant population differences in foliar tannin content. Different species may have varying responses to the environmental stress associated with topography. Environment may have a considerable effect on leaf tannin content at the landscape scale. However, in some cases, populations may also contribute to variation and need to be considered when evaluating patterns of secondary plant metabolite distribution and/or plant-animal interactions.