A taxonomic, phylogenetic, and functional comparison of restoration seed mixes and historical plant communities in Midwestern oak savannas

Ecological restoration offers an effective way to promote recovery of natural communities and is particularly important for ecosystems that have experienced extensive habitat loss, such as oak savannas in the Midwestern USA. Seeds are commonly added to restoration sites to introduce desired species, but the identity and composition of which species are included in seed mixes varies greatly and may be influenced more by seed availability and cost rather than historic prevalence or ecological function. Therefore, a key question is how the composition and function of seeded species differs from what was historically present. Here, we compare the taxonomy, phylogeny, and functional traits of savanna seed mixes that are commercially available in the Midwest with historical vegetation surveys of savannas in southern Wisconsin. Species composition differs greatly between historical savannas and seed mixes; most species are unique to either seed mixes or historical savannas rather than shared between them. The functional overlap of species (measured via functional traits: seed mass, SLA, and plant height), however, is remarkably similar between seed mixes and historical savannas. The phylogenetic representation between the two groups is also similar, however seed mixes tend to not include certain plant families and species are more clustered across the phylogeny in seed mixes. Together, this suggests that restoration efforts using commercially available seed mixes may only partially recover the species composition of historical oak savannas, but that the functional capacity of restored sites is similar to the past. Determining how restoration seeding efforts compare to historical reference conditions is an important aspect of assessing whether restoration goals related to species composition and ecosystem function are being achieved and may identify gaps that can be filled when designing seed mixes.