The Wieslander Vegetation Type Maps were produced in California in the 1920’s and 30’s. Products from this effort include plot data, photos, and vegetation maps covering over 40% of the state. Since 1998, jurisdictional and regional vegetation maps have been produced in California using a methodology which also incorporates plot data and photos and uses the National Vegetation Classification System as a basis. Here we compare the two datasets in multiple locations in the state to explore ecological questions but with a focus on issues that could limit or confuse analyses; including scale, geodetic and methodological issues, and classification issues.

Results/Conclusions

Detailed positional information should not be stressed in comparisons, since many differences occur between the geodetic accuracy of the two data sets. However, broader regional differences such as summaries of ranges of vegetation and species composition may be discernable. Thematic comparisons can be more realistically made after a thorough understanding of the differences in the classifications and using ancillary attributes to bring both products into greater parity. The broader goals and purposes of the more recent mapping effort enable for manipulation of GIS data to mach certain more restricted and limited attributes of the early maps. It is important to understand these limitations before attempting comparisons of certain features such as tree canopy species composition, seral stage, and potential differences in regeneration.