There are numerous environmental  benefits to trees in urban settings. These include the capture of carbon dioxide by trees, shading, and habitat for wildlife. Urban forests can also act as natural storm water management areas by filtering particulate matter (pollutants, some nutrients, and sediment), by absorption of water and by facilitating evapotranspiration to reduce runoff. Evergreen trees generally have greater stormwater benefits than deciduous trees in our climate where the majority of rainfall is in the winter. Trees also reduces noise levels, provides recreational benefits, and increases property values.
To estimate the benefits that the various cities of the Tualatin Basin are achieving from urban forestry, we used aerial photos and i-Tree software from the USDA Forest Service to estimate the average density of tree canopy cover within the city limits of each city.  Here are the results.

  City Canopy
  Durham 49.0%
  Lake Oswego* 47.6%
  Rivergrove 37.3%
  West Linn* 33.7%
  Portland* 27.7%
  Beaverton* 25.6%
  Tigard* 25.0%
  Tualatin* 22.9%
  Sherwood* 21.0%
  Hillsboro 17.1%
  Forest Grove* 16.0%
  Gaston 15.5%
  North Plains 15.3%
  King City 15.0%
  Cornelius 13.0%
  Banks* 11.2%


   *TREE CITY USA

Urban Forestry in the Tualatin River Basin

CityofDurhamCanopy
Made in the shade:  Half of the City of Durham Oregon is covered by tree canopy.

One city has decided not to be content with the current situation.  Tigard City Council adopted an Urban Forestry Master Plan to increase tree canopy from its current level of 25% to 40% citywide by 2047.  Tigard provide incentives for developers to protect tree groves and gives away free street trees to Tigard residents.

Many cities participate in the Tree City USA program which sets standards for urban forestry. They have achieved Tree City USA status by meeting four core standards of sound urban forestry management: maintaining a tree board or department, having a community tree ordinance, spending at least $2 per capita on urban forestry and celebrating Arbor Day.  Local cities that have attained Tree City USA status are indicated in the table above.

Tigard’s program takes steps to prevent pre-development clearing.  Often developers will clear a property prior to annexation in order to avoid tree mitigation fees.  Loss of tree canopy from pre-development clearing increases stormwater runoff, reduces property values, and eliminates ecosystem services in a way that does not make economic sense.  Tigard contacts property owners in newly urbanizing areas and provides incentives and flexible regulation that reduces the loss of tree canopy.

Pre-development clearing like this on South Cooper Mountain adds to urban runoff and makes no economic sense. 

Volunteers have a tremendous role in increasing tree canopy in our cities.  Groups like Friends of Trees and Tualatin Riverkeepers have many opportunities to plant trees in the fall, winter and spring.