Distribution of plant life history types in California chaparral: the role of topographically‐determined drought severity

Abstract

Spatial patterns of shrub life history and Ceanothus distribution are examined in relation to topographically-medi- ated differences in drought severity within 3 watersheds on the coastal and inland flank of the Santa Ynez Mountains, Califor- nia. Spatially distributed fields of drought severity are simu- lated for the studied watersheds using high-resolution digital terrain data and daily climate data in combination with a process-based hydro-ecological model (RHESSys). Field sam- ples of species composition are spatially integrated with the distributed drought data for analysis of ecological relation- ships. Patterns of seedling recruitment type correspond to topographic variability in drought severity in ways that are consistent with concepts presented in the literature. Species that depend on fire for recruitment are increasingly repre- sented with increasing drought severity, the converse also applies. Sites that experience moderate drought severity per- mit co-dominance of species from both recruitment modes. Residual analysis suggests that some of the unexplained vari- ability is related to substrate. Analyses also indicate that the distribution of 5 Ceanothus shrubs reflect differences in drought severity in ways that are consistent with their resistance to water stress-induced xylem dysfunction. Species from the subgenus Cerastes sort in accordance with moisture availabil- ity and have unique spatial distributions. Results are evaluated and discussed with respect to studies on plant morphology, resource use and seedling establishment patterns.