Including multiple measures of biodiversity, like taxonomic, functional and phylogenetic diversity, when studying restoration allows us to better understand restorations in terms of community assembly. Restored habitats often fall short of meeting their diversity goals, and have lower plant diversity than remnant natural areas. Lower diversity in restored sites may be because plant assemblages used to restore degraded sites (e.g., restoration seed mixes) have insufficient diversity. Potential diversity contained within seed mixes can be further constrained through dynamics of germination, emergence and establishment at restored sites. We tested how functional and phylogenetic diversity of seed mixes influenced diversity of resulting established assemblages, using the Midwestern tallgrass prairie as a study system. We set up a field plot experiment that fully crossed two levels of functional diversity with three levels of phylogenetic diversity. Each plot was seeded with 15 species drawn from a pool of 127 species used in prairie restoration. For a phylogenetically stratified subset of 32 species, we also tested the effects of seed traits on germination in the lab, and emergence in the field. We had two main questions: First, do functional and phylogenetic diversity of the planted seed mix impact emergence of individual species within the seed mix, and second, do seed functional traits and phylogeny of the species themselves predict their germination, emergence, and establishment?
Results/Conclusions
Initial results from the field experiment show that the diversity of the seed mix was predictive of plant emergence. Surprisingly, though, fewer planted species emerged in high phylogenetic diversity plots, relative to plots with lower phylogenetic diversity (r2 = 0.153, F2,69 = 6.23, P = 0.003). We also found that seed traits, particularly seed shape traits, along with the phylogenetic position of species, were predictive of laboratory germination. Closely related species had similar germination responses. Our finding that high phylogenetic diversity seed mixes had lower established richness than low phylogenetic diversity mixes may be transitory, as this was the first year of the experiment. However, if these findings are robust to additional years of data, they may help to explain the common finding that restored habitats fall short of meeting biodiversity goals. Even if high-diversity mixes are seeded, individual species that contribute to the diversity of seed mixes, may never emerge in restored communities. A better understanding of mechanisms that drive germination, emergence and establishment from seed mixes can help managers tailor restoration strategies to better meet biodiversity objectives.