Influences of annual weather variability on vernal pool plant abundance and community composition

• Native vernal pool plant species tend to respond positively to winter precipitation.
• Some non-native plant species in vernal pools respond negatively to winter precipitation.
• Ponding seems to be an ecological filter impairing the establishment of some non-native species.
• Elevation seems to be a predictor of vernal pool ponding.

Vernal pools, also termed temporary wetlands, promote key ecosystem services such as floodwater retention and provide unique habitat for many organisms. Despite their ecological value, vernal pools are declining worldwide. Because vernal pools are strongly influenced by variation in annual precipitation that fills the pools, climate change and alterations in precipitation regimes could drastically alter these fragile communities. To understand how annual variation in precipitation and temperature affect vernal pool plant community composition, we examined vernal pool vegetation data collected over a 10 year period. We used native and non-native plant frequencies to explore the dynamics between species frequency and weather variability. We further analyzed fine-scale site topography to explore the effects of spatial variability on ponding. We identified key differences between native and non-native plant species’ responses to weather variability and ponding. Over all, most native species tended to respond positively to precipitation accumulations in the early growing season, but some native species frequencies were negatively associated with precipitation accumulations in the late growing season. Some non-native species were negatively associated with increases in precipitation in either the early or late growing season. Inundation appears to act as an ecological filter, impairing the establishment of some non-native species. In addition, elevation was a predictor of ponding—lower elevation pools tended to have higher clay concentrations and promote greater ponding depths, which could enhance the effects of the inundation filter. Together, these findings will assist conservation and management efforts in understanding the climatic and physical factors that influence vernal pool plant community ecology.