Urban Ecosystem Analyses

Three scientific studies of San Antonio’s urban forest have been conducted. Known as Urban Ecosytem Analyses, these studies use high resolution multi-spectral aerial photography, advanced satellite imagery, computer image analysis, and sophisticated air pollution models combined with on-the-ground surveys. Stormwater management, air pollution removal, stormwater contaminant removal & energy savings of trees were evaluated, both currently and historically, to show changes over time.

The first analysis

In November, 2002, the first Urban Ecosystem Analysis for San Antonio was published. Aside from proving the enormous economic value of our urban forest, it showed an alarming loss of tree canopy cover over a 16 year period from 1985 to 2001.

Animation of Bexar County tree canopy loss, 1985-2001
Animation showing tree canopy loss in Bexar County, 1985-2001. City limits are outlined in red.

Phase 2 Study

Report cover

In September, 2003, Urban Ecosystem Analysis Phase 2: Data for Decision Making was published. This study used high-resolution (1 meter pixel) true-color imagery shot by the Ikonos satellite. Because the first study used low resolution Landsat imagery, more tree canopy cover was resolved in the Phase 2 study. This reflects only the increased sensitivity of the measuring instruments and not an actual increase in tree canopy.

Phase 2 recommended a 35% overall tree canopy cover for San Antonio. Additionally, the study measured tree canopy cover over the Edwards Aquifer recharge and transition zones in Bexar County. In 2003, that tree canopy cover was 43%. However, the huge Stone Oak master planned development had only 2% canopy cover in one typical residential enclave.

2009 High Resolution Study

Cover page from May, 2009 Urban Ecosystem Analysis

In May, 2009 yet another UEA was completed. Two-foot pixel resolution, 4-band, multi-spectral aerial photographs, which are 690 times more detailed than images from the Landsat satellite, were used to measure tree canopy with unprecedented accuracy.

This ultra high resolution study measured 38% tree canopy cover over the city limits. Unfortunately, some misrepresented the results of the study as proof that land development was causing tree canopy to increase. Measurements made using Landsat images showed a 3.4% tree canopy loss between 2001 and 2006. Over the Edwards Aquifer Recharge Zone, tree canopy loss was even more severe at 6.0%.

The City of San Antonio relied on the recommendations of this study in revising its tree ordinance in 2010. One of the key features of this ordinance is a post-development canopy cover requirement designed to achieve a 40% overall tree cover goal.

Alamo Forest Partnership | c/o Mark Bird | Cliff Morton Development and Business Services Center | 1901 S Alamo St | San Antonio TX 78204 | (210) 207-0278