Data from: Native plant traits and invasibility of restored communities: Importance of environmental context and trait hierarchies

During community assembly, theory predicts trait convergence among species
due to environmental filtering, and trait divergence due to biotic
filtering. Learning how traits of non-native species enable them to
overcome these filters informs the process of invasion. We manipulated
mixtures of native plants in a large restoration project in Southern
California that was initially dominated by non-native annual grasses and
forbs but was restored to a mixture of native shrubs, grasses, and
forbs.  We measured subsequent establishment and performance by
three non-native species (Brassica nigra, Salsola tragus, and Sonchus
oleraceus) on N- and S-facing slopes to investigate relationships between
the abiotic environment, native community composition, and invasibility in
the context of trait-driven ecological filters. We then evaluated which
community metrics influenced invader performance and tested whether
relationships between invader performance and community-weighted traits
varied depending on slope aspect. Plots with slow-growing native shrubs
contained less of the fast-growing invasive, Brassica nigra.
Invasibility was greatest in native communities restored with native grass
and on N-facing slopes. Traits of individual species indicated relatively
greater biotic as compared to environmental filtering. For example,
abundance of Phacelia cicutaria, a native annual with traits most like
invasive Brassica nigra, was negatively correlated with abundance of that
invasive. Several community-weighted trait metrics were also significantly
related to invasibility, but the direction of the relationship varied
depending on the specific functional trait, community-weighted trait
measure (mean or dispersion), invader, and slope aspect. The native
functional group that was more likely to prevent invasion by non-native
annual species (native shrubs) was different from the single species that
most prevented invasion (a native forb). In restoration planning,
functional groups and trait values of individual species may point to
different mixtures of native species that prevent invasion by specific
non-natives, depending on priority effects. Understanding the priority
effects and trait hierarchies that underly biotic filtering appears
critical to interpreting community-weighted traits and their complexity of
responses to environmental variation in space and time.