Functional groups, traits, and the performance of species in restoration

In ecological restoration, species that are sown to increase native plant diversity vary in their performance and establishment. This study set out to investigate some of the potential processes influencing native plant performance, including interactions between plant functional groups, and traits associated with the success of species in restoration. Twenty-eight species native to upland prairies of the Willamette Valley of Oregon were sown in different seed mixtures in field plots in a former agricultural field. These species were divided into three a priori functional groups: annual forbs, perennial forbs, and grasses. Native cover, biomass, and species richness were compared among treatments to determine whether interactions among functional groups influenced the performance of functional groups. Competition was greater within than between functional groups, particularly within annual forbs. Native cover and biomass increased significantly with the number of functional groups sown; however, non-native plant abundance was found to influence native performance much more than functional group richness. Sown native richness was not strongly influenced by either functional group richness or non-native abundance.

To investigate relationships between species traits and performance, eleven different traits were measured on both laboratory and field-grown plants. Species cover and establishment frequency were used as response variables in multiple regression models relating traits with species performance in the seed mixture treatments. Several traits were strongly related to native performance, indicating that traits may be useful in predicting the performance of species in restoration. Significant interaction terms between functional group identity and traits indicate that the relationship between traits and performance depended on functional group. The relationship between traits and performance also depended on the identity of neighbor species.