Vegetation dynamics, fire, and the physical environment in coastal central California

Used aerial photographs to measure transition rates as evidence for mosaic shifts among grassland, coastal sage scrub, chaparral, and oak woodland communities at Gaviota State Park, between 1947-1989. In unburned plots without livestock, transition from grassland to coastal sage scrub was 0.69% per year, coastal sage scrub to oak woodland was 0.30% per year, and oak woodland to grassland was 0.08% per year. In burned plots without livestock, and in unburned plots where livestock were not excluded, transition rates were lower, except for conversion of oak woodland to grassland. In burned plots, a high rate of transition of coastal scrub to grassland was measured. Some transition rates varied with substrate and topographical position, indicating that fire, grazing, and the physical environment interacted to determine direction and rate of vegetation change. Only portions of the vegetation of these landscapes may be dynamic, with some patches in certain combinations of environment and disturbance that change rapidly, and other patches that remain static as edaphic or topographic climax communities. -from Authors