Composition of maritime Chaparral related to fire history and soil, Burton mesa, Santa Barbara county, California

Maritime chaparral of Burton Mesa, California was sampled to determine trends in species richness, vegetation structure, and composition after fire. Species cover is estimated in 75 100 m2 plots distributed among 28 sites that range from 1 to 50+ years since burning. Twenty-eight plots were located under coast live oaks ( Quercus agrifolio) that are scattered among the chaparral shrubs, and 47 plots located in surrounding chaparral. Vegetation data were analyzed and related to stand age, soil depth, texture, and pH, and distance from the coast using Detrended Correspondence Analysis (DCA) and Canonical Correlation Analysis (CCA). Species richness is highest during the first 3-5 years after fire, but is more strongly related to total evergreen shrub cover than stand age. Physiognomic trends in chaparral samples are similar to those reported for other chaparral types. Oak understories differ from chaparral in that annuals decline more rapidly during the first 10 years after fire, and subshrubs are not as important. The composition of the herb layer under oaks is associated with stand age and distance from the coast. In chaparral samples, composition of perennials is related to stand age, distance from the coast, depth to a subsoil pan, soil pH, and soil texture. The composition of annuals and biennials in chaparral is related to stand age, canopy coverage by evergreen shrubs, depth to a subsoil pan, and distance from coast. After fire in California chaparral, regeneration of shrubs by sprouts and seeds produces a rapid return of the vegetation present before the burn (e.g., Sampson 1944, Horton and Kraebel 1955, Sweeney 1956, Hanes 1971, Keeley et al. 1981; reviews in Hanes 1977 and Vogl 1981). A diverse flora of herbs and subshrubs also flourishes for several years after fire, declining or disappearing with closure of the shrub canopy (Christensen and Muller 1975, Hanes 1971, J. Keeley et al. 1985, S. Keeley et al. 1981, Schlesinger et al. 1982). Patterns in post-fire vegetation development vary depending on chaparral composition, fire timing and intensity, and the physical attributes and disturbance history of the site (Keeley and Zedier 1978, Malanson and O'Leary 1985). Most studies of chaparral succession have been located on the steep slopes and shallow soils of the Transverse and Peninsular ranges of California. Although general vegetational trends are known, more research is needed to Madrono, Vol. 35, No. 3, pp. 169-195, 1988 This content downloaded from 157.55. 39.112 on Wed, 07 Sep 2016 05:01:39 UTC All use subject to http://about.jstor. org/terms 170 MADRONO [Vol. 35 understand how physical and biotic factors interact to control local and regional variation in post-burn vegetation recovery. We have studied post-fire succession in maritime chaparral on Burton Mesa, near Lompoc, California. We chose this area for two reasons. Since 1938, at least 27 fires have occurred in a small area (ca. 4000 ha) of uniform climate, geology, and topography, providing a relatively large sample for analyzing patterns of chaparral development after fire. Moreover, there is a practical reason for analyzing this chaparral community. Burton Mesa supports a rich chaparral flora with many endemic taxa (Ferren et al. 1984). As in other maritime chaparral communities, much acreage has been converted to residential, agricultural, and military uses, and most remaining areas are under development pressure and are experiencing invasion by exotic weeds such as Carpobrotus edulis and Cortaderia jubata (Griffin 1978, Jacks et al. 1984). Of the approximately 9000 hectares of original upland habitat, we estimate that only 5890 ha of Burton Mesa chaparral existed in 1938 and less than 3500 ha remain today. An understanding of vegetation ecology and regeneration after fire is needed to provide a basis for adequate protection and management of the remainder of this threatened, endemic-rich chaparral. In this paper we describe the modern fire history of Burton Mesa, document the importance of subsoil morphology, distance from the coast and stand age in determining stand composition, and compare post-fire development with that occurring in other chaparral types.