Using phylogenetic information to guide prediction in tallgrass prairie restoration
Restored sites often fail to reach targets pertaining to community structure and key functions, and low taxonomic (species) diversity likely contributes to widely cited performance deficits in restorations. What has rarely been considered is the phylogenetic diversity of restored communities—how broadly from across the 'tree of life' assemblages are drawn. This is an important gap, as rapidly accumulating evidence indicates that phylogenetic diversity is a strong predictor of functional trait diversity and key ecosystem functions that are important in a restoration context, such as productivity and food-web support. We investigated phylogenetic and functional dimensions of vegetation diversity in 19 prairie restorations in northeastern Illinois, comparing patterns with those observed in 41 tallgrass-prairie remnants used as reference sites. We constructed a maximum likelihood community phylogeny using gene-sequence data from GenBank to estimate phylogenetic diversity and used trait data from the literature and the TRY consortium to estimate functional diversity. Measures of alpha and beta diversity and trait analyses were used to test the hypotheses that (1) key functional traits would be phylogenetically non-random, (2) phylogenetic diversity would be lower in restorations than in remnants, and (3) the functional-trait portfolios of restored sites would be depauperate relative to reference conditions.
Key traits, including woodiness, plant height, leaf nitrogen, and seed mass were phylogenetically non-random (clustered) in both restored and remnant prairies. Restored sites were less phylogenetically diverse than remnants (12% less on average, p < 0.0001). This was driven in part by disproportionate representation of closely related species from the Sunflower (Asteraceae) and grass (Poaceae) families. In addition, numerous plant families observed in remnant sites were absent from restored sites. Consistent with traits showing phylogenetic signal, trait diversity was positively correlated with phylogenetic diversity, which explained much of the plot-level variation in trait diversity: 19–51% of variance for five univariate and three multivariate measures. AIC-based model selection indicated that phylogenetic diversity was a necessary complement to species richness for explaining functional trait diversity. The lower phylogenetic diversity found in restorations could have important functional consequences. It is also a potentially widespread phenomenon, as restorations are influenced by legacies of disturbance, and disturbance has been shown to decrease phylogenetic diversity across numerous ecosystems and taxonomic groups. Incorporating phylogenetic considerations is an under-considered, potentially powerful tool for helping to better predict and achieve restoration of biodiversity.