Data from: An experimental test of trait-based restoration to achieve drought tolerance and invasion resistance in two grasslands

Drought and invasive species are threats to primary productivity in
grassland ecosystems worldwide. A central challenge in ecological
restoration is establishing plant communities that can withstand these
abiotic and biotic stressors. We tested the efficacy of a trait-based
framework for enhancing drought tolerance and invasion resistance in
experimental restorations of contrasting grassland systems, a perennial
mixed-grass prairie in Wyoming, and an annual interior grassland in
California. Each experiment included four trait-based seeding treatments:
drought-tolerant, invasion-resistant, functionally diverse, and a random
control. All seeded communities were subjected to extreme precipitation
reduction (-50 % annual) and invasion by non-native annual grasses. We
asked two questions: (1) Can we establish communities from seed that meet
and maintain these desired trait-based targets? (2) Did the trait-based
seeding treatments tolerate extreme precipitation reduction or resist
invasion by non-native annual grasses? Based on analyses of compositional
dissimilarities, we found that trait-based restoration targets were more
difficult to maintain in an annual-dominant grassland rather than
perennial-dominant, and targets composed of multiple community-weighted
mean traits were more difficult to meet than targets that maximized
functional diversity. In both grasslands, plant communities with drought
tolerant traits maintained growth rates under reduced precipitation, but
these effects diminished after multiple years of drought and during
drought release. This highlights the importance of including a diversity
of strategies when restoring plant communities. Our proposed invasion
resistant traits did not consistently reduce non-native annual grass
establishment, but communities with traits that conferred drought
tolerance were the most effective at resisting invasion, suggesting that
similar traits enhance drought tolerance and resist invasion in these
grasslands. Our findings indicate that restored plant communities with
high functional diversity may be able to respond to variable conditions
better than communities with traits designed to meet specific restoration
objectives. The results from this restoration experiment suggest that our
understanding of the traits underlying drought tolerance is better than
our understanding of the traits underlying invasion resistance. However,
if drought tolerance enhances competitive ability in arid and semiarid
grassland ecosystems, then physiological theories of resource use can be
applied to enhance invasion resistance.