Monitoring Prairies in San Juan Island National Historical Park to Protect Natural and Cultural Resources
Rochefort RM , Boetsch JR , Antonova N , Howlin S, Mitchell J, Owen T. 2026. Monitoring Prairies in San Juan Island National Historical Park to Protect Natural and Cultural Resources. Science Report. NPS/SR—2026/437. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2318382
San Juan Island National Historical Park (SAJH) protects some of the last remaining prairies in Washington state. Over 60% of the American Camp unit is dominated by grasslands that have persisted since the end of the glacier era, approximately 11,700 years ago. In 2007, the National Park Service initiated prairie monitoring at SAJH to document status and trends in cover and ecological condition of these vegetation communities using repeatable, rapid assessment of physiognomic class and vegetation quality along line-intercept belt transects. Sampling was designed to address a hierarchy of monitoring questions linked to management objectives, including the maintenance of broad landscape structure (e.g., forest versus herbaceous) associated with the cultural landscape and the continued ecological integrity of plant communities. We found that while physiognomic cover was similar today to the historic reference period (36% forest:61% non-forest), the ecological condition of grasslands or prairies was threatened by introduced grasses and shrubs. Additionally, between 2007 and 2017, we found significant declining trends in the proportion of area with herbaceous types with an estimated trend of −0.58% per year. The estimated trend in high-quality native herbaceous vegetation also decreased at a rate of −0.08% per year, but the trend was not significant. Transects proved to be an economical and reliable method for monitoring long-term trends in landscape cover with transient crews, but detailed vegetation monitoring (i.e., species frequency and relative abundance) is needed to better assess prairie condition over time
- Type
- Published Report
- Authors
- Rochefort, Regina; Boetsch, John; Antonova, Natalya; Howlin, Shay; Mitchell, Jason; Owen, Theodore
- Date of Issue
- 2026-06
- Publisher
- National Park Service
- DOI
- 10.36967/2318382
- Units
- NRSS , SAJH
- Keywords
- grassland vegetation, herbaceous quality, NCCN synthesis report, physiognomic type, prairie vegetation monitoring, rapid assessment, transect