Detecting Vegetation Changes using Satellite Imagery and GIS

By Lisa Levien, USDA Forest Service, and Chris Fischer, Department of Forestry and Fire Protection

As human and natural forces modify the landscape, resource agencies find it increasingly important to monitor and assess these alterations. Changes in vegetation affect wildlife habitat, fire conditions, aesthetic and historical values and ambient air quality. Alterations directly influence management and policy decisions across all ownerships. Methods for monitoring vegetation change range from intensive field sampling and plot inventories to extensive analysis of remotely sensed data. Aerial photography can detect change over relatively small areas and at reasonable cost, but satellite imagery has been proven more cost effective for large areas.

The USDA Forest Service’s forest pest management program (FPM) and the California Department of Forestry and Fire Protection (CDF) fire and resource assessment program (FRAP) are cooperating in a statewide change detection program covering California over a five-year period. The state is divided into five project areas. The goal of the program is to implement long-term, low cost and high quality monitoring to identify trends in forest health, assess changes in vegetation extent and composition, and provide data for updating regional vegetation, fire perimeter and fuels maps. This program provides current monitoring information across all ownerships and vegetation cover types represented in California. In areas of increased urban development, special project activities are being considered to monitor the movement of urbanization.

Landscape changes are detected through two phases. The first phase looks at the differences in two image dates. Changes in cover are identified along a continuum from large increases to large decreases in vegetation. In the second phase, cause of change is identified and quantified using related information, including fieldwork.

The program is in its third year and has successfully shown that the change methods can be applied to hardwood and coniferous forest environments. Analysis of the change data provides information to assess landscape-level changes in vegetation extent and composition, and affords information on causal agents having the greatest impact throughout a project area. Preliminary analysis incorporating the change data into existing programs such as fire history mapping, timber harvest plan monitoring, and the integrated hardwoods resource management program also has proven successful. Accuracy assessment procedures are being implemented in the current project area to quantify vegetation change more correctly.

The statewide change detection program continues to look for new partners as it maps changes and vegetation in each of California’s bioregions. For more information: Lisa Levien (USFS) at (916) 454-0803 e-mail: llevien/r5_rsl@fs.fed.us, or Chris Fischer (CDF) at (916) 227-2670 e-mail: chris_fischer@fire.ca.gov.