Soil characteristics and litter dynamics in mixed deciduous forests along an urban-rural gradient

Changes in forest ecosystem structure and function resulting from urbanization can be studied using the environmental gradient paradigm. Urban-rural land use gradients are environmental gradients which are determined largely by human activity. Although gradients of land use are readily measurable, little is known about the effects of urbanization on the abiotic and biotic environment. The objectives of this dissertation are to: (1) quantify the soil environment, soil biota, and litter dynamic rates in oak stands along an urban-rural transect in the New York City Metropolitan area using a gradient analysis; (2) explain the pattern of litter dynamics by correlating litter process rates with the soil environment and biota and (3) test the relative importance of factors controlling litter dynamics using field manipulations. Elevated levels of Pb, Cu, Ni, total N and base cations were measured in forest soils at the urban end of the transect. In addition, soil temperatures were also elevated in the urban forests. The changes measured in soil chemical properties appear to be the result of local and regionally derived atmospheric pollution, which was apparently more extreme at the urban end of the gradient. Measures of land use that best explained the variation in soil chemical properties were road density and traffic volume, suggesting automobile are an important source of pollution in the study area. The forest soil environment has an effect on both the soil biota and ecosystem process rates. Heavy metals in the forest floor were negatively correlated with mycophagous soil invertebrates. Unexpectedly, litter decomposition, N mineralization, and nitrification rates were faster in urban stands and decreased with distance from the urban core. Litter collected in urban stands decomposed more slowly than litter collected in rural stands. These results are contradictory, since high N mineralization and nitrification rates are typically associated with large amounts of readily available N returning to the soil in litter. However, inputs of N from atmospheric deposition may increase N availability without necessarily influencing litter quality.