Diversity Relations and Succession in Californian Coastal Sage Scrub

Abstract

The facultatively drought—deciduous shrublands of coastal California and Baja California are lowest in species richness of the four Mediterranean—climate regions where this physiognomic type occurs. Alpha richness in the North American coastal sage scrub varies primarily with the abundance of herbaceous annual species. Herb levels in turn vary with differences in levels of precipitation, favorableness of temperature during the winter and spring growing season, shading by shrubs, soil nitrogen, and air pollution. Levels of herbaceous annuals are highest in the growing season following fire, and show a second pulse of abundance in stands 15—25 yr old. Mature stands of coastal sage scrub are typically low in species equitability, due at least in part to the shade—intolerance of the herbaceous understory and to reduced levels of soil nitrogen. Symbiotic nitrogen—fixing organisms are virtually absent from stands which have not burned in 20 yr or more. The pattern of postfire succession varies markedly with fire intensity; dominant shrubs sprout abundantly from root crowns only following less intense fires. While there are °50 widespread sage scrub species, more than half of the 375 species encountered in the present study of the sage scrub flora are rare in occurrence within the habitat range. In view of the reduction of the area of coastal sage scrub in California to 10—15% of its former extent and the limited extent of preserves, measures to conserve the diversity of the flora are needed.

Vegetation Composition in a Post-Fire Successional Gradient of Pinus Halepensis Forests in Attica, Greece

“…This has also been reported by other researchers (Martin 1966, Hanes 1971, Naveh 1973, Chen et al 1975, Arianoutsou 1979, Rundel 1981, Westman 1981, Van Wilgen 1981, Thanos etal1989, Papavassiliou and Arianoutsou 1993, Cocks 1994 for Mediterranean climate ecosystems. For example, Martin (1966) reported a 245% increase in the density of Leguminosae genera Amphithalea, Indigofera, Bitwninaria (ex Psoralea) and Tephrosia in a one-year old burned area of fynbos.…”

The Spanish and Mexican Baseline of California Tree and Shrubland Distributions Since the Late 18th Century

“…Another example is deduction that the Los Angeles basin was extensively covered by coastal sage scrub based on potential natural vegetation theory (Kü chler 1977). It was asserted that contemporary urbanization and agriculture extirpated 90% of this assemblage based on loss of potential habitat (Westman 1981;Keeley 2002). The Spanish baseline documents pasture and wildflower fields, not shrublands.…”

Southern California Mountains and Foothills Assessment: Habitat and Species Conservation Issues

“…There is particular concern about the degradation of coastal sage scrub because its extent has already declined by almost 80 percent due to development in the coastal basins and it is the primary habitat for the California gnatcatcher and other imperiled species (Westman 1981;Davis et al 1994; Beyers and Wirtz Historically, fires appear to have burned under a wide range of environmental conditions, exhibiting erratic smolder-and-run behavior patterns as weather and fuel conditions changed. Unsuppressed, some fires would continue for months until extinguished by rain or lack of fuel.…”

“…(Davis et al 1994;O'Leary 1990). It is now found in only about 15 percent of its former range in southern California (Westman 1981;O'Leary 1990). The remnant stands of coastal sage scrub are habitat for a growing number of endangered taxa such as the California gnatcatcher (Davis et al 1994).…”