Canopy cover drops hundreds of acres in Tumwater

The City of Tumwater lost about 560 acres of canopy cover from 2020 to 2025, according to its 2025 Tree Canopy Assessment Update. 

In 2020, Tumwater had 5,859.28 acres of canopy cover, which meant that 49% of its land was covered by canopy. By 2025, that number had fallen to 5,298.92 acres, which translates to 38% of coverage.

The findings were the result of an update that the city aims to conduct every five years, as part of its Urban Forest Management Plan (UFMP). Tracking the data allows the city to measure the impact of its policies and regulations on its urban forests. 

Canopy cover is assessed per each zoning district. The steepest losses came in single-family residential areas, where canopy dropped 6 percentage points to 46% from 52%, erasing 377 acres of tree cover.  

General commercial zones saw the next largest decline, losing 87 acres and falling 8 percentage points to 33%.  

Open space and green belt areas lost 66 acres, dropping canopy cover to 44% from 49%. 

Three zoning types saw minimal gains in canopy cover. Industrial lands gained 7 acres, though their overall coverage still fell by 1 percentage point since more lands have been designated for industrial use.  

Canopy cover in “other mixed use” gained 3 acres, which reflects a 1% gain, while canopy cover in the Olympia Regional Airport increased by 3 acres, but saw no change in its percentage cover. 

The UFMP sets different canopy goals for each zoning type due to their varying regulations. Five zone types have already achieved their assigned goals: general commercial, industrial, other mixed use, the Olympia Regional Airport and its non-airport lands. 

The citywide goal is 39%, which the City of Tumwater is close to with its current canopy cover of 38%. 

To produce the update, the city's Geographic Information Systems team employed machine learning to analyze aerial photos taken in April 2025. 

They used a support vector machine classifier to distinguish trees from other surfaces, and the model yielded a 97% accuracy when tested against 250 locations where the canopy cover was verified on the ground. 

For more information, check the city staff’s report for the Tumwater Tree Board’s meeting on Sept. 8. The data along with other environmental statistics is going to be part of an online dashboard the city is launching to better present its Green Team 2024 report.