Prairie Vegetation Monitoring

Two crew members using GPS to navigate a transect in the prairie
Field crew use GPS to navigate along a transect in the prairie at San Juan Island National Historical Park

NPS Photo

Importance & Issues

Prairies and Garry oak woodlands, once extensive in the lowlands of Washington and Oregon, are some of the most endangered ecosystems in the region. Currently, less than 3% remain, and these areas usually are in a severely degraded condition, especially because of invasive non-native species and development. Prairies and oak woodlands are key to providing habitat for many federally or state listed species including Fender‘s Valley silverspot (Speyeria zerene bremnerii Edwards, federal species of concern), Taylor‘s checkerspot (Euphydryas editha taylori Edwards, federal candidate species), Mardon skipper (Polites mardon Edwards, federal candidate species), Island marble butterfly (Euchloe ausonides insulanus), and golden paintbrush (Castilleja levisecta, federal threatened species). Restoration of these ecosystems is a priority for the National Park Service both culturally and ecologically, as well as being priority for other federal and state agencies and private conservation partners. The goal of the prairie monitoring program is to detect and describe changes in the extent and quality of prairie (herbaceous) communities in San Juan Island National Historical Park to provide baseline information for restoration planning.

Monitoring Objectives

Our primary objectives include detecting vegetation changes in the extent of physiognomic cover types, proportion of areas dominated by exotic and native species, quality of herbaceous cover types, and composition and diversity of herbaceous cover types at San Juan Island National Historical Park.


Prairie monitoring has two design stages. For the first stage, we track changes in physiognomic cover classes annually or biannually. For the second stage, we track changes in composition of herbaceous communities every 5 to 10 years. Physiognomic vegetation sampling is conducted along parallel transects across the Park using a random stratified sample. Along these transects, we record the physiognomic cover types and nativeness of the dominant vegetation species (i.e., exotic or native). During the second stage, species composition within important herbaceous cover types is monitored using 1-m square quadrats located systematically, by physiognomic vegetation type, along the transects.

Status and Trends

Status and trends of cover types are assessed through changes in origin of predominant species, species richness, the floristic quality index, and changes in species composition. Ecological integrity of cover types is classified as good, caution, or significant concern based on status of the cover types. Trends in predominant species, floristic quality, and extent of cover types are used to describe whether the status of the cover type (% native) is stable, improving, or declining.

Reports and Documents

Last updated: August 24, 2023