Factors affecting plant diversity during post‐fire recovery and succession of mediterranean‐climate shrublands in California, USA

Abstract

ABSTRACTPlant community diversity, measured as species richness, is typically highest in the early post‐fire years in California shrublands. However, this generalization is overly simplistic and the present study demonstrates that diversity is determined by a complex of temporal and spatial effects. Ninety sites distributed across southern California were studied for 5 years after a series of fires. Characteristics of the disturbance event, in this case fire severity, can alter post‐fire diversity, both decreasing and increasing diversity, depending on life form. Spatial variability in resource availability is an important factor explaining patterns of diversity, and there is a complex interaction between landscape features and life form. Temporal variability in resource availability affects diversity, and the diversity peak in the immediate post‐fire year (or two) appears to be driven by factors different from subsequent diversity peaks. Early post‐fire diversity is influenced by life‐history specialization, illustrated by species that spend the bulk of their life cycle as a dormant seed bank, which is then triggered to germinate by fire. Resource fluctuations, precipitation in particular, may be associated with subsequent post‐fire diversity peaks. These later peaks in diversity comprise a flora that is compositionally different from the immediate post‐fire flora, and their presence may be due to mass effects from population expansion of local populations in adjacent burned areas.