Plant associations of La Jolla Valley, Ventura County, California

Wildland habitats provide a multitude of physical and aesthetic resources which are of critical value to modern society. Recognizing and properly managing these resources requires extensive base information relating to the character, function, and abundance of the natural elements present. This study was conducted in order to evaluate the vegetation present in La Jolla Valley, a 7.3 sq km upland drainage basin in the western Santa Monica Mountains, Ventura County, California. The objectives of the study were: (1) to identify and survey the dominant vegetative elements within the La Jolla Valley area; (2) to classify the vegetation into particular plant associations based on species composition and abundance, and map their distribution; (3) to assess the occurrence of the vegetation in relation to topographic geologic, and cultural parameters. A method of measurement involving 100-foot line transects was used to survey the vegetation occurring in the study area. A total of 174 transects were conducted within the four physiognomic plant groups present: woodland, chaparral, coastal sage scrub, and grassland. Within these physiognomic plant groups eleven plant associations have been identified and described: Quercus agrifolia, Adenostoma fasciculatum-Lotus scoparius, Lotus scoparius, Eriogonum cinereum-Lotus scoparius, Lotus scoparius-Salvia leucophylla, Salvia leucophylla-Artemisia californica, Salvia mellifera-Lotus scoparius, Rhus laurina, Avena barbata-Bromus spp., Avena barbata-Lolium perenne, Phalaris aquatic-Avena barbata. The study indicates that topographic slope, exposure, moisture supply, soil type, and cultural disturbance significantly affect the present distribution and composition of the La Jolla Valley area vegetation. Southerly sun exposures, steep slopes, and gravelly well-drained soils favor the development of shrubland. High moisture supply and fine-textured loamy soils promote the development of grassland and woodland. Grassland is further promoted through cultural disturbance, such as historical agricultural practices and the recurrence of fire.