Traits, neighbors, and species performance in prairie restoration

Questions: Are traits related to the performance of plant species in restoration?  Are the relationships between traits and performance consistent across the functional groups of annual forbs, perennial forbs, and grasses?  Do the relationships between traits and performance depend on neighboring functional groups?

Location: A former agricultural field, being restored to native upland prairie, in the Willamette Valley of western Oregon USA.

Methods: Twenty-eight native species, representing three functional groups, were sown in seven different combinations.  The following summer the performance of each species was measured.  Eleven functional traits were measured from plants in the laboratory and in the field.  Correlations between individual traits and performance variables were measured and stepwise regression techniques were used to determine which sets of traits were most strongly related to performance.

Results:  Sets of traits explained up to 56% of variation in cover, and up to 48% of variation in establishment frequency.  The relationships between traits and performance were influenced by functional group identity, and the functional group identity of neighboring species also influenced species’ cover and the relationships between traits and cover.  Species’ establishment rate in monoculture was the trait most strongly correlated to both establishment and cover in mixtures.  In multi-trait models, annual forb functional group identity was strongly related to establishment in mixtures, and height, leaf weight ratio at 7 days, and seed mass were strongly related to cover.

Conclusions:  Based on the strength of the statistical models, multiple-trait models should be a useful way of predicting the performance of species prior to sowing in restoration.  The functional group identity of each species as well as the other species being sown may need to be taken into account when making predictions.

Keywords:  functional ecology; seed mixtures; seedling establishment; leaf weight ratio; seed mass; unit leaf rate