Science News

Urban Ecosystems & Social Dynamics

Winter 2012

Science that makes a difference.

Tree Growth Equation Models

It is well-known that large trees provide more ecosystem services than small trees. However, the science of predicting tree size is hindered by few long-term studies tracking tree growth and a poor understanding of the effects of multiple stressors on health. PSW scientists helped organize an international symposium on urban tree growth, with papers published in a special issue of the journal Arboriculture & Urban Forestry. Their paper describes research that has developed over 1,800 growth equations from measurements on over 17,000 trees in 16 U.S. cities (because patterns of tree growth vary by region and species there are multiple growth equations). This science is improving the accuracy of models that quantify urban forest function and value and helping managers select, locate and manage trees to more effectively cool urban heat islands, conserve energy, filter air pollutants, reduce runoff, sequester carbon and promote human well-being. Greater awareness of tree benefits, increased investment in tree management and more productive urban forests are resulting from this research. Copies of the paper are available at: McPherson, E.G; Peper, P.J. 2012. Urban tree growth modeling. Arboriculture & Urban Forestry. 38(5): 175-183. For more information contact Dr. Greg McPherson (; 530-759-1723).

Tree Carbon Calculator

In partnership with CAL FIRE Urban and Community Forestry and EcoLayers, PSW is announcing a beta release of the public version of the Tree Carbon Calculator, a computer tool to help the public estimate carbon and energy impacts of trees on a single family residential property. Using a Google Map interface, the program allows users to “capture” trees on their property and see the amount of carbon stored at present and into the future. Carbon calculations are based on the only methodology approved by the Climate Action Reserve’s Urban Forest Project Protocol for quantifying carbon dioxide sequestration from tree planting projects. Also included are effects of the trees on energy used for heating and cooling residential buildings. This beta release (end-user test) will help interested parties learn about opportunities to save energy and reduce the carbon footprint of their residential property based on existing and planned landscape designs. Future releases of ecoSmart Landscapes will include tools for the assessment of rainwater interception due to trees; runoff reduction, water conservation, and infiltration based on landscape configurations, and fire risk to the buildings. These applications are based on 20 years of research on tree growth dynamics and urban forestry by scientists at the USDA Forest Service, Pacific Southwest Research Station and University of California Davis. Users access the software through the ecoSmart Landscapes Portal at For more information contact Dr. Greg McPherson (; 530-759-1723).

California Municipal Forest Health Threat Assessment

The “California Municipal Forest Health Threat Assessment” reports the extent to which California’s municipal forests are at risk from insect pests and plant disease threats. The assessment integrated two existing software applications and data from 30 California street and park tree inventories. The two tools used in the analysis were the Pest Vulnerability Matrix and i-Tree Streets. A report card concept was developed to identify and prioritize forest traits contributing to each tree population’s vulnerability to loss. The analysis focused on four indicators: species/size structure, age structure, pest threat, and potential asset loss. Letter grades (A through F) were assigned to each of the four indicators and a final grade to each city. The grades allow cities to compare themselves with other cities, reveal areas of proficiency and deficiency and serve as a baseline for tracking progress. Prioritized recommendations are helping communities to increase the resilience of their municipal forests through improved tree selection, monitoring, integrated pest management, and removal and replacement planning. Citations: Kotow, L.; McPherson, E.G. 2012. California Municipal Forest Health Threat Assessment. Final report to USDA Forest Service, Forest Health Monitoring. USDA Forest Service, Pacific Southwest Research Station. [Contact for a copy]; Kotow, L.; McPherson, E.G. In press. California Municipal Forest Health Threat Assessment. General Technical Report PSW-GTR-xxx. Albany, CA: USDA Forest Service, Pacific Southwest Research Station. For more information contact Dr. Greg McPherson (; 530-759-1723).

Urban Ecosystem & Social Dynamics Program Manager: Dr. Deborah Chavez (

USDA Forest Service