Species‐Level Impacts on Chaparral Root Zone Hydrology

A set of four unconfined (earthen‐walled) lysimeters in the San Dimas Experimental Forest near Los Angeles, CA, provides a unique opportunity to examine the effect of species‐level vegetation on root zone hydrology under highly controlled experimental conditions. The 28.1‐m 2 by 2.1‐m deep lysimeters were specifically designed to minimize variation of all environmental conditions except vegetation. Monocultures of buckwheat ( Eriogonum fasciculatum Benth. var. foliolosum Nutt.), chamise ( Adenstomata fasciculatum Hooke & Arn.), scrub oak ( Quercus dumosa Nutt.), and Coulter pine ( Pinus coulteri D. Don.) were planted in 1946. In 1997 two sets of soil cores were sampled from each lysimeter to evaluate species level effects resulting from 50 yr of growth. The cores were analyzed for water content, soil water potential, and pore water chloride. The chloride mass balance approach was used to estimate long‐term average fluxes and residence times of water in the lysimeters. One core from each lysimeter was also analyzed for pore water stable isotope (δ 2 H) composition. Only small differences were observed between the four species in terms of the shapes of the depth profiles and the absolute values of the hydrologic characteristics and fluxes. However, some differences were statistically significant. For example, differences in some characteristics were found between the chamise and the other species. We also observed differences between the lowest aboveground biomass group (buckwheat and chamise) versus the highest aboveground biomass group (oak and pine). These results suggest that although species‐ and biomass‐level differences in root zone hydrologic behavior appear to be minor, there are detectible differences in how these vegetation types affect the water budget in chaparral ecosystems.