Urban Forestry

Trees in cities can contribute significantly to human health and environmental quality. Unfortunately, relatively little is known about the urban forest resource and what it contributes to the local and regional society and economy. To better understand the urban forest resource and its numerous values, the U.S. Forest Service, Northern Research Station, developed the Urban Forest Effects (UFORE) model, which is now known and distributed as i-Tree Eco at www.itreetools.org. Results from this model are used to advance the understanding of the urban forest resource, improve urban forest policies, planning and management, provide data to support the potential inclusion of trees within environmental regulations, and determine how trees affect the environment and consequently enhance human health and environmental quality in urban areas.

Forest structure is a measure of various physical attributes of the vegetation, including tree species composition, number of trees, tree density, tree health, leaf area, biomass, and species diversity. Forest functions, which are determined by forest structure, include a wide range of environmental and ecosystem services such as air pollution removal and cooler air temperatures. Forest values are an estimate of the economic worth of the various forest functions.

To help determine the vegetation structure, functions, and values of trees in Los Angeles, a vegetation assessment was conducted during the summer of 2007-2008. For this assessment, 0.1-acre field plots were sampled and analyzed using the UFORE model. Th is report summarizes results and values of:

  • Forest structure
  • Air pollution removal
  • Carbon storage
  • Annual carbon removal (sequestration)
  • Changes in building energy use
  • Potential risk to forest from insects or diseases

Though urban forests have many functions and values, currently only a few of these attributes can be assessed due to a limited ability to quantify all of these values through standard data analyses. To help assess the city's urban forest, data from 348 field plots located throughout the city were analyzed using the Forest Service's Urban Forest Eff ects (UFORE) model.

UFORE is designed to use standardized fi eld data from randomly located plots and local hourly air pollution and meteorological data to quantify urban forest structure and its numerous effects, including:

  • Urban forest structure (e.g., species composition, tree density, tree health, leaf area, leaf and tree biomass, species diversity, etc.).
  • Amount of pollution removed hourly by the urban forest, and its associated percent air quality improvement throughout a year. Pollution removal is calculated for ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide and particulate matter (<10 microns).
  • Total carbon stored and net carbon annually sequestered by the urban forest.
  • Effects of trees on building energy use and consequent effects on carbon dioxide emissions from power plants.
  • Compensatory value of the forest, as well as the value of air pollution removal and carbon storage and sequestration.
  • Potential impact of infestations by Asian long horned beetles, emerald ash borers, gypsy moth, or Dutch elm disease.

An ecosystem is a specific biological community interacting with its physical environment. A community consists of all the populations of living things in a given area, including people. The physical environment includes climate, temperature, soil and light. Both the biological community and the physical environment are continually interacting.

The physical factors significantly influence the biological community, and in turn the biological community uses and modifies the environment. To assist our efforts in developing successful landscapes, it is necessary to develop an understanding of the many relationships existing between all living things and their significance to the Los Angeles basin ecosystem.