A VEGETATON MAP OF NAPA COUNTY USING THE MANUAL OF CALIFORNIA VEGETATION CLASSIFICATION AND ITS COMPARISON TO OTHER DIGITAL VEGETATION MAPS

In 1995, the Manual of California Vegetation introduced a quantitatively based method for classifying and mapping vegetation in California. We used this method to develop a classification of vegetation types for Napa County, which we then used to attribute the polygons of a new vegetation map. The new map was produced by on-screen digitizing over USGS Digital Orthophoto Quarter Quads (DOQQ's) with the aid of ancillary digital maps. We identified the distribution of 56 landcover types, 48 dominated by natural vegetation, at the alliance or aggregated alliance level, in 28,456 polygons across 2042 km². The effective minimum mapping unit is below one hectare. The methods used, the mapping classification system developed, and the extents of landcover types mapped are presented. In a comparison with two previous digital vegetation maps for the area, the US Forest Service's CalVeg and the Gap Analysis Program's GAP maps, the MCV map had finer spatial and floristic resolution. The MCV map has 15 more vegetation types than CalVeg and 22 more vegetation types than GAP. The MCV map contains more riparian corridors and isolated wetlands, identifying 157 km² of these types, compared to 7 km 2 for CalVeg and a non-spatial result for GAP.