Testing the consistency of local adaptation in co-occurring species for use in trait-based restoration

Background/Question/Methods

Local adaptation is common in natural populations, and trait/environment relationships can be used to select appropriate seed materials for restoration projects. Anthropogenic changes can disrupt relationships between traits and fitness, and not all species or populations have the same capacity to become locally adapted, so sourcing seeds from similar climates is not always sufficient for guaranteeing restoration success, particularly in the most disturbed areas. Finding the best seed sources for restoration may rely on describing plant traits adaptive in disturbed and invaded environments, recognizing that these traits may be different for different species and functional groups. Focusing on three taxa of grasses, two species of shrubs, and two forb taxa, we collected seeds of each from 16 locations with similar abiotic conditions, and measured seed and seedling characteristics for each species and population, including seed size, emergence timing, and root length, among others. We described trait/environment relationships, and tested the relationship between traits and performance, planting seeds in common gardens in highly invaded systems or in a competitive greenhouse environment. We asked whether similar trait/environment relationships have evolved for multiple species in the same geographic location and which potentially adaptive traits were predictive of survival.

Results/Conclusions

Seed provenance significantly impacted success in competitive restoration settings, and all species showed trait/environment relationships consistent with local adaptation. Both environment of origin and phenotypic traits predicted success in competitive environments, with generally greater predictability from environmental factors. Trait/environment relationships varied among taxa with notable commonalities: seed weight, root mass ratio, and root biomass were associated with environment of origin for 6 of 7 taxa, and early emergence and root biomass were consistently associated with seedling success across all seven taxa. Several collection locations had plants with high survival rates across taxa, suggesting that site conditions can select favorable restoration traits across the entire plant community. While species differed in trait/environment/performance relationships, we found broad support for local adaptation as well as convergence in some characteristics that confer greater survival in competitive scenarios. Further, we found that some locations might contain populations of above-average performance for multiple species, which could be used to efficiently select seed sources for restoration. Choosing native plants sources with the most adaptive traits, along with matching climates, will likely be more successful at restoring the most invaded communities.