Progress in Mapping Vegetation on Santa Cruz Island and a Preliminary Analysis of Relationships with Environmental Factors

This note describes and evaluates a recent contribution to vegetation mapping of Santa Cruz Island based on interpretation of 1985 color infrared aerial photographs (scale 1:24 000). The map was digitized to create a GIS data layer, in order to cross-tabulate the occurrence of vegetation classes with other geographical variables, namely digitized slope, aspect, and substrate data from maps. Cross-tabulations of the digitized data reveal marked co-occurrences of vegetation cover types with particular locations, slopes, aspects and geologic substrates. These strong patterns appear to reflect unqualified microclimatic variation due to maritime influences, elevation, and exposure. They also apparently reflect four attributes of substrates: disturbance (both natural and anthropogenic), soil nutrient status and degree of development, and to a lesser extent, relief and drainage. The distinct vegetation patterns on Santa Cruz Island, although modified by 140 yr of feral animal grazing and concomitant losses of woody vegetation cover, are apparently similar to those of vegetation in the near coast ranges of the California mainland. Further analysis of the spatial relationships among vegetation, topography, and substrate such as those demonstrated here could be utilized for mapping and management of island resources.