FIRE EFFECTS ON SOIL HETEROGENEITY BENEATH CHAMISE AND REDSHANKS CHAPARRAL

Abstract

The origin of soil heterogeneity found in Adenostoma fasciculatum and A sparsifolium chaparral was investigated in the Santa Monica Mountains, California. Possibilities were that geologic and genetic processes created inherent variability in surface soils, and/or that chaparral vegetation generated this variability. Fourteen soil properties were assessed under 17 pairs of the two shrub species before (1984) and after (1985) a wildfire. Hypotheses were that, although magnitudes of soil properties may change with fire, the inherent soil patterns would remain, while vegetation-influenced patterns might either be accentuated or obliterated. All but one of the 14 soil properties changed after fire, and 8 of these changed in the same direction for both shrub species. Different magnitudes of change, as well as opposite changes in 5 soil properties, led to an elimination of most spatial heterogeneity after fire. Eleven soil properties showed significant pre-burn differences between shrub species, while only 3 did so after fire. Vegetation influence was responsible for the spatial soil heterogeneity in the mature stand of chaparral, apparently developing over one regeneration period of about 40 years. With the obliteration of fine-scale soil differences during each fire cycle, soil heterogeneity cannot play a role in determining vegetation regeneration patterns. The creation of a more uniform substrate after fire, however, may favor sprouting over seeding strategies in postfire succession. [Key words: chaparral, fire ecology, soil properties, California.]