A geographic information system (GIS) was created to quantify vegetation changes over the last 100 years. Four maps which represented the pre 1900, 1940, 1960, and 1990 eras were produced to identify major changes that have occurred in the GCV due, in part, to hydrologic alterations associated with the Central Valley Project (1945) and the California State Water Project (1968).
The Pre-1900 Base Map was the most difficult to construct due to the limited information recorded at that time. Vegetation polygons were developed from several independent map sources. The quality of information on the source maps varies by area and by source. Map series were more readily available for the 1945, 1960 and 1990 time periods.
The maps are GIS-based and can be used to estimate vegetation change over time. In all cases attempts were made to gather the best information available and to create a bank of accessible information that can be utilized in future research efforts.
We see this project as a good base for continued additions and refinements rather than as an end product. We would like to invite other interested federal and state agencies to participate in the project.