Ecological filter theory and functional traits provide a useful framework for understanding how different species successfully establish in ecological restoration. Plant functional traits can provide insight into how species respond to local environmental filters by showing how traits co-vary with survival. More frequent drought and elevated temperatures in California will increase climatic water deficit, enhancing the abiotic filters that plants must pass through to survive. Phylogenetic relationships can help show the degree of conservatism in traits and provide information about biotic filters. To determine how functional traits are linked to survival and are affected by drought, we planted 12 native species in 2016 under 60% rain-out shelters that simulate a 1-in-100 year drought. Experiments were conducted in an invaded coastal grassland in central California. We annually censused survival and growth rates, quantified plant community composition and measured the functional traits of all planted species and the 12 most abundant species (9 nonnative, 3 native) in 2018 and 2019. Functional traits included growth rate, specific leaf area, major vein length per unit area, leaf thickness, leaf C:N, leaf lobedness, and leaf δ13C. Effects of treatments, traits and phylogenetics on survival were estimated using Cox proportional hazards.
Results/Conclusions
We found that there was greater cover of native species and lower nonnative species cover in drought treatments. Changes were driven by increases native perennial species and nonnative forbs and decreases in annual grasses. Plants in drought tended to have lower leaf C:N, lower total nitrogen, and higher leaf lobedness. Planted species with more resource conservative traits, such as higher leaf δ13C, leaf lobedness, and lower growth rate, had lower overall hazard risk than those with less conservative traits. Plants that were more phylogenetically related had higher Cox proportional hazard, indicating that shared traits among recently divergent species were important for determining plant hazard for drought in this coastal grassland. The phylogeny of our study species suggests that trait conservatism in relation to drought occurs at the Family level. Functional traits had a greater impact on modeling hazard for plant communities on droughted compared to control plots. In summary, there were significant changes in species composition over four years under the drought shelters. Certain leaf functional traits help highlight the species that have the highest hazard risk for drought in this coastal grassland. Trait conservatism can help model early survival in relation to drought may expand the choice of species suitable for coastal grassland restoration.