Urban forestry policies needed

by Mike Singleton

A continuation of urban forestry issues presented last month, this letter was presented on October 10 at the San Diego City Council Rules Committee, chaired by Mayor Dick Murphy, and referred to the City Manager for review and recommendations.

t is very clear that the urban forest must be considered as an integral part of any energy conservation plan. Both federal and state governments, along with many other public institutions, have data that undeniably shows that our urban areas are continuing to become hotter and hotter each year, and that this heat island scenario increases energy demand and worsens air quality.

    The unique thing about peak energy use during heat waves in the City of San Diego is that, even with a heat wave, the interior temperature of most homes just slightly crosses over the line of comfort. But it crosses the line enough to make it important for people to run air conditioning and fans. And it crosses the line exactly when peak demand throughout the state - and the extremely high costs of energy - are at their worst.

    If we had a true urban canopy in this city, then the shade from many of these trees would lower the air temperature between 8 and 12 degrees. This is done by direct absorption of solar energy, through the shading of dark surface pavements that build heat quickly, and through evapo-transpiration that actually serves to cool the air.

    It is during these heat wave conditions that we also have the greatest air quality problems. The urban heat island phenomenon directly encourages the formation of smog, which in turn keeps large numbers of individuals inside their homes with their air conditioners on. Trees, on the other hand, cleanse and fix some of the very components that support the formation of smog. During heat waves, either you are outside under trees, where the air is not as heavy, or you are inside a house that does not have a great heat gain, with the windows open for a breeze, or you are in a home with the windows shut and the air conditioning on.

    Cutting overall energy use is important, but cutting peak-time energy use will be critical in the near future. An urban forestry campaign and program will be essential as an important part of any energy conservation program. Preserving our existing tree canopy, including those in, under and around power lines, is equally important. It is ironic that the most extensive deforestation program in the state (CPUC forced power line clearances out to 22 feet from a power line) has just been completed over the last few years and that undergrounding of utility lines, which would make urban reforestation possible, has all but ceased in the state. On top of this, in the state's desire to take over the transmission line system from the private investor utilities, the removal of all trees under these transmission lines is being considered to reduce the annual costs of tree trimming. This is short sited.

    The lack of an urban forest policy may not be shortsighted. But it will be an oversight if this factor is not included in future policies. When coupled with the stormwater delay and absorption of runoff, the traffic calming aspects of tree lined streets, the encouragement of walking and the air quality benefits, it is difficult to understand why trees have not become a focus of any public energy policy development or urban planning in general.

A 10-Step Plan For


City of San Diego, Tree Advisory Board

  1. Assign City Staff under the new energy conservation department to work with the Urban Forester and the TAB in developing data and policies regarding the Urban Forest and energy conservation.
  2. Fund an “Urban Forest Overview” project that determines the State of the Urban Forest and the historic and current tree canopy percentages for the City and the region. Existing data to be used will include historic canopy data, aerial photographs, GIS data, tree inventory information, tree disease trends, tree removal records, tree planting record, and the previous study sponsored by SANDAG regarding the State of the Urban Forest. This project will require funding for the purchase of “City Green” or other GIS analysis software that quantifies the level of canopy and provides tools for determining the benefits of an urban canopy. This project would require the cooperation of SANGIS, SANDAG and other city departments as well as a consultant.
  3. Consider and adopt the proposed tree protection ordinance and the adjustments to the Council Policy on tree removals, giving priority to significant tree resources that are playing an important role in decreasing urban heat gain. An important factor in both of these proposed actions is the requirement for tree replanting. Seriously strengthen the requirement for tree replacement that recognizes the lost benefits from removals and replaces a similar level of biomass.
  4. Develop a program that analyses city policies (development review, long range planning, city capital projects) to integrate tree canopies as an important part of energy conservation. Also, require that a Neighborhood Action Plan that identifies tree resources and opportunities become an integrated part of community planning and community plan documents.
  5. Consider and more fully support the concept of Landscape Maintenance Assessment or other Benefit Assessment Districts that focus on tree plantings and proper maintenance. The formation of these districts may be one of the most effective funding sources for implementing an urban forestry program.
  6. Consider a program where residential improvement projects (above a certain threshold) are required to plant a tree in front of the residence if one does not currently exist. A similar program requiring street trees be added where they are missing could be tied with the sale of the home.
  7. Set up and fund a city program (either handled by staff or under long term contracts) that would be responsible for the watering and basic health care of any tree planted within city right of way. A crew of several individuals with a few water trucks and associated pruning/maintenance equipment may be all that is required. This program would remove one of the major roadblocks to tree plantings since many property owners will not sign a maintenance agreement.
  8. Have all City of San Diego Capital projects be subject to the same or equal level of landscape requirements under the landscape ordinance that private development is required to do.
  9. Direct that mitigation requirements for new projects include the contribution into a tree-planting fund for any impacts that cumulatively affect the air quality, stormwater runoff, public safety, and urban heat increases of the city. Work with SANDAG to make this a requirement of the entire region. Often project mitigations are limited to demonstrable significant impacts only, even though most all projects result in some increase in traffic, air pollutants, decreased pedestrian/bike safety, increased runoff and heat gain from paved or other hard surfaces.
  10. Properly fund an urban forestry program that can pro-actively research and react to major tree diseases and pest problems that have the potential of substantially decreasing the urban forest canopy.

    Mike Singleton is a member of the City of San Diego's Tree Advisory Board. His email is: mikektua.com.