Hydrologic Influences on Plant Community Structure in Vernal Pools of Northeastern California

Abstract

Plant communities in vernal pools are distributed along continuous elevation gradients associated with subtle variations in microtopography, reflected in spatially heterogeneous hydrologic regimes. We quantified the role of hydrologic and environmental variables for influencing species assemblages within two vernal pool landscapes in northeastern California. A novel combination of approaches including remote photography of water depth stage gauges, vegetation sampling along elevation gradients, and topographic surveys were used to measure hydrology and plant community composition at precise locations. Multivariate analyses were used to classify vernal pool plant communities and classification tree analysis was used to model plant community distribution across hydrologic thresholds. Three plant community groups were distinguished according to localized hydrologic regimes. Inundation period and maximum depth were the only variables found to be predictive of plant distribution. Hydrologic thresholds for the three community groups were based on inundation period: Short (< 71 days), Medium (≥ 71 days but <209 days), and Long (≥ 209 days). The distribution of plant assemblages was strongly correlated with key hydrologic gradients. Quantification of such relationships will be useful in forecasting ecohydrological responses of vernal pool vegetation to climate change, helping to guide future monitoring, management and restoration efforts for these unique ecosystems.