Progress in Mapping Vegetation on Santa Cruz Island and a Preliminary Analysis of Relationships with Environmental Factors Julia Allen Jones 1 , Steven A. Junak 2 , and R.J. Paul 3 'Department of Geography, University of California, Santa Barbara, CA 93 106 2 Santa Barbara Botanic Garden, Santa Barbara, CA 93105 ³Environmental Studies Program, University of California, Santa Barbara, CA 93106 Abstract - 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. Introduction Santa Cruz Island is the most ecologically diverse of the four northern Channel Islands, because of its large size, rugged topography, ¹Current Address: Department of Geosciences, Oregon State University, Corvallis, OR 97331 complex geology, the availability of ground- water and the presence of a central valley (Junak 1987). These features and their effects on precipitation, soil moisture, and cold air drainage patterns affect the distribution of the island's vegetation and flora. This note describes and evaluates a recent contribution to vegetation mapping of the island, where recent changes in management are likely to change the distribution and composition of plant cover (Hochberg et al. 1980). The island's flora includes about 500 native taxa and more than 40 taxa endemic to the California Islands (Channel Islands National Park & Santa Barbara Botanic Garden 1987). The occurrence and distribution of these endemics are being monitored and expanded through the efforts of the California Natural Diversity Data Base, the Nature Conservancy, the Santa Barbara Botanic Garden, the University of California and other organizations. The preliminary map described here estimates the cover by vegetation classes on the island in 1985. The previous map of the island's vegetation (Minnich 1980) was photo- interpreted from 1970 1:22,000 color infrared (CIR) aerial photographs. The 1980 map distinguished eight major vegetation classes: grassland, chaparral, coastal sage scrub, woodlands, riparian, conifer forest, barren areas, and woody exotics, which were further broken down by dominant species. Minnich (1980) attributed vegetation patterns on the island to fire, grazing and other environmental factors. In the present study we quantified the relationships between vegetation and environmental factors by digitizing the 1985 vegetation map as one data layer of a geographical information system (GIS) which is being prepared as an aid for island Third California Islands Symposium 97