Trees are a critical part of Seattle’s infrastructure that provide essential benefits to our environment, health, and well-being. Trees manage stormwater, provide shade and reduce heat, improve our health, and provide habitat for our wildlife. Healthy tree canopy also contributes to the character and beauty of our city while helping counter climate pollution, promote climate justice, and create healthy and sustainable communities.
Seattle’s goals are to achieve 30 percent citywide canopy cover by 2037; improve tree health and resilience; and increase equitable distribution of trees. These goals will support healthy communities that are more resilient to the impacts of climate change. Preliminary findings of the 2021 Canopy Cover Assessment show the city has seen a net loss of 255 acres of tree canopy, an amount roughly equal to the size of Green Lake, since 2016. Many factors contribute to this canopy loss.
Seattle’s Urban Forestry team has been reviewing the data to better understand where and how these changes occurred and what proactive investments can help reverse the trend in the future. Key findings shared in January’s Urban Forestry Commission meeting include:
Tree canopy cover is not equitably distributed across our City
The 2021 Canopy Cover Assessment shows there are inequities in Seattle’s tree canopy, with low-income and BIPOC communities that are already experiencing disproportionate climate, health, and economic impacts having the least amount of canopy cover at the baseline (2016) assessment, and losing more canopy since. There is a high correlation between areas of low canopy cover and areas of health inequities, lower air quality, and higher heat indexes, including parts of Beacon Hill, Georgetown and South Park.
Neighborhoods in the two highest levels of disadvantage in the Office of Planning and Community Development’s Race and Social Equity (RSE) Composite Index had 16% lower canopy than the areas in the two lowest categories of disadvantage in 2016. By 2021, the gap between canopy in the highest disadvantage areas and lowest categories of disadvantage expanded to 20%.
Development and healthy tree canopy coverage can coexist
During the time of the study, 2016 – 2021, Seattle’s population grew 8.5%, adding approximately 58,000 people and more than 47,500 housing units. In neighborhood residential zones, tree canopy declined 1.2% (87 acres). Most of the 87 acres of net canopy loss in neighborhood residential zones were in parcels that did not have new development projects completed during the study period. However, canopy was lost at a greater rate on parcels where development happened.
Tree canopy expansion and development of new housing are both critical elements of the City’s efforts to address climate change, create affordability, and build livable, resilient, and thriving communities. These areas will need creative planning, a strong regulatory framework, and community partnerships to sustain and grow canopy.
Our trees are experiencing added strain due to climate change
As our climate changes, Seattle is experiencing more instances of extreme heat, insects and pest outbreaks, droughts, and flooding events. Our aging, mostly second growth forest trees are especially vulnerable to these conditions and are increasingly coming down on their own or requiring removal. As part of our forest management strategies and succession planning, these trees are also sometimes removed to allow for establishment of conifer trees, which take longer to grow and contribute to the canopy.
At the same time, climate change is making the need for trees even more important. Additional analysis of King County Heat Watch data paired with the 2021 Canopy Cover showed that at a micro-scale a 5% increase in canopy resulted in 2 degrees cooler temperature (see hexagon map below). Based on these numbers, increasing canopy in low-canopy neighborhoods is critical to our long-term heat preparedness strategy.
Trees in Parks and natural areas are under strain and regrowth is steady but slow
Our forested parks and natural areas saw higher net loss than other areas of the city – over 100 acres of net canopy lost, a 5.1% decline. While canopy loss in these areas happened at a similar rate as other areas of the city, growth happened more slowly. Since the Park District was established in 2015 and greatly increased funding for the Green Seattle Partnership program, Seattle Parks and Recreation has planted a greater number of seedlings annually, including tens of thousands of seedlings, mostly native conifers, during the 2016-2021 assessment period. These small trees grow slowly, and gains from this new canopy will take more time to show up in our canopy.
Next Steps for the Canopy Cover Assessment
The city is slowly losing ground on its goal to achieve 30 percent citywide canopy cover by 2037, but understanding this canopy change data will help develop strategies to grow and maintain our urban forest and build a Seattle that is sustainable, equitable, and climate-resilient.
Over the next few weeks, the City will continue to refine analyses and conduct additional stakeholder engagement. In February 2023, the city will release the complete report which will provide final, comprehensive analysis by land management unit and include recommendations to help identify strategies to stop the current backslide and advance equity focused planting and maintenance to grow a healthy, equitable, sustainable and resilient urban forest.