Oral Abstract Details

Author(s):
Julia Bartens and Eric Wiseman

Affiliation:
Department of Forest Resources and Environmental Conservation, Virginia Tech

Presentation Type:
Oral

Topic Area:
Science delivery and exchange of information for natural resource professionals, policymakers, and private citizens

Abstract Text:
Municipalities use ordinances and zoning to ensure that tree canopy cover is replenished during land development. Many localities have refined their regulations to enforce their long-term canopy cover goals, requiring developers to plant trees to provide minimum canopy cover for the project site within a specified period of 15 to 30 years. To fulfill site plan requirements, developers specify tree planting densities based on anticipated canopy growth during the attainment period. However, these calculations are typically based on observations of trees growing in non-limiting environments such as nurseries and arboreta, which are not representative of typical urban conditions. Urban conditions are oftentimes very heterogeneous due to the great degree of disturbance providing various soil conditions ranging from adequate to unacceptable. Hence, tree size predictions cannot be generalized for all planting sites and designs and have to be based on research resulting in models that include the factors that significantly influence tree growth. Planting plans and development regulations that do not account for urban soil constraints on tree growth may over-estimate the capacity to replenish canopy cover or even under-estimate the potential of the site leading to bigger trees than suitable. We are currently researching urban tree growth rates in highly urbanized conditions to reduce the uncertainty about tree canopy development and improve canopy cover management practices. Our research objectives are to 1) determine which soil chemical or physical factors best predict tree development, and 2) estimate tree growth rates across a range of tree pit sizes and soil conditions. During summer 2008, we collected site and tree data on 80 trees in Washington DC (Quercus phellos and Zelkova serrata) and 100 trees in Jacksonville, FL (Quercus virginiana) of various sizes. We chose trees in confined spaces to avoid any unaccountable influences due to escaping roots to nearby lawns or yards. The soil conditions the trees are growing in were determined by measuring the available soil volume, taking composite samples for soil chemical and texture analyses, and measuring the penetration resistance and moisture content of the soil. Tree parameters, namely tree height, canopy dimensions, and DBH, were measured to determine the development of the tree. In addition, increment cores were taken from each tree to determine the age and its growth rate. Trees in urban setting are exposed to various conditions above and below ground. These conditions result in differences in tree development and thus growth rates. Consequently, we cannot assume a certain age at a certain DBH. By analyzing increment cores for each tree we hope to be able to determine the inflection age of the tree, the age at which the resources were limited and tree growth rate declined. Empirical modeling and tree ring analysis are being used to identify soil parameters that significantly influence tree growth and to quantify changes in tree growth through time. We will present our research findings to date and discuss the implications for managing tree canopy cover in urban areas.