Causes and consequences of soil resource heterogeneity in a transition oak-northern hardwood forest

Date of Completion

January 1996


Biology, Ecology|Agriculture, Forestry and Wildlife|Agriculture, Soil Science




An understanding of the distribution and abundance of soil resources is critical to a mechanistic understanding of forest community dynamics and productivity. In this dissertation, I present information on the pool sizes and turnover of several potentially growth limiting resources.^ A central question in studies of soil resource heterogeneity is whether variation in the distribution of plant species reflects the effects of intrinsic variation in the soil environment on plant competitive interactions, or whether variation in the soil environment represents an effect of plant occupancy on soil chemistry and nutrient availability? In northwest Connecticut, there appears to be an interaction between largely physical processes such as mineral weathering and biotic processes such as canopy tree regulation of the pool sizes of several elements (Chapters 2 and 3). For example, calcium availability is high beneath sugar maple trees but very low beneath eastern hemlock. The availability of calcium is intermediate between these extremes beneath the canopies of other tree species. Similar patterns were found for magnesium and aluminum availability.^ Nitrogen (N) is frequently assumed to be a potentially limiting soil resource. However, N differs from other nutrients because its distribution and abundance is largely regulated by the process of tree litter production, dispersal, and decomposition. Results of the research presented herein demonstrate that spatial variation in leaf litterfall and mid-summer net N mineralization rates are both highly correlated with the distribution of adult trees within this forest (Chapter 4). However, sapling growth did not appear to be limited by the rate of N supply (Chapter 5).^ Collectively, these results demonstrate that soil resource heterogeneity in these forests ecosystems is a predictable function of local variation in soil parent material and the distribution of adult trees. In many cases, this leads to the establishment of a feedback between soils and plants that tend to reinforce existing patterns of soil chemistry and nutrient availability. ^