Seattle’s Urban Forest Stewardship Plan calls for Seattle reaching a 30% canopy goal by 2037. Seattle’s current tree canopy is about 23%.
The UFSP states that Seattle’s land are is 54,379 acres.
A Seattle canopy cover of 30% canopy = 16,314 acres.
Seattle’s current canopy cover of 23% canopy = 12,507 acres.
16,314 acres – 12,507 acres = 3807 additional acres of canopy cover needed by 2037.
3807 acres / 23 years = 165.52 acres of new canopy needed every year to reach 30% canopy goal by 2037
Portland, Oregon in their city-wide Tree Policy and Regulatory Improvement Project report, June 2011, calculated that planting 900 medium size canopy trees (on average) would generate only 12 acres of future canopy growth annually.
165.52 acres/ 12 acres X 900 trees = 12,414 new average medium size trees need to be planted in Seattle each year to reach a 30% canopy goal by 2037. This assumes each year there is also no net loss of canopy as the baseline and that 100% of the planted trees survived which is unrealistic.. These trees are in addition to replacing any lost during development or removed from private property or removed in the public sector like street trees or park trees.
Detailed analysis of Portland’s calculations is in Volume 1 – Recommended Draft Report to City Council Dec 2010 starting on page 144 – Tree Canopy Benefits, Financial Impacts and Budget Proposal” Portland calculated that their tree ordinance would for the same amount of money spent on just planting trees on 12 acres, they could generate about 140 acres of canopy per year.
Currently Seattle has no requirement to replace most trees cut down as a result of development on private property except as part of green factor which can mostly be met by other means. Seattle public trees that are removed are replaced on a 2 for 1 basis but the process does not specifically address tree size. While the Seattle Comprehensive Plan calls for a no net loss of tree canopy every year there is no overall city department or entity that is tracking the net loss or gain of trees citywide each year.