Tree Species-Driven Effects On Above- and Below-Ground Feedbacks In An Urban Forest.

Urban trees are increasingly being valued for their economical contributions based on the environmental functions that they provide to urban ecosystems (e.g. carbon sequestration, shading, erosion, run-off control, etc.). Based on 2002 data, total compensatory value for urban forests in the United States was estimated at $2.4 trillion. Forest value increases when a greater proportion of forest trees are healthy with large diameters yet, maintaining tree health for longevity is met with a vast array of challenges (diverse land use, diverse ownership/management, limited root space, soil compaction, tree damage, pollution, etc.). Although maximizing tree growth is recognized as a critical urban forestry objective, few forest health preservation programs exist. From the emerging plant-soil paradigm in plant ecology, it is clear that feedbacks between plants and soil may determine larger level patterns such as ecosystem level variability and landscape level productivity. Including urban soil function and integrating urban soils into forest management will help managers understand the effects of tree management decisions. This study tested for the presence of feedbacks between soil quality and tree health (good, fair, poor), as well as between soil quality and tree species (Gleditsia triancanthos, Acer saccharinum, Acer platanoides, and Tilia americana). Soil quality parameters included measurements of available nitrogen and phosphorus, total nitrogen and carbon, pH, moisture, infiltration, and compaction. This study demonstrates that heterogeneity is a central characteristic of the urban forest and that future attempts to test relationships between species and soil should incorporate site differences through detailed and complete site histories. GIS technology can manage large amounts of heterogeneous data in easily accessible databases that can be used to generate practical tools, such as maps of urban forest above- and belowground characteristics.