EDITOR'S CHOICE: Confronting contingency in restoration: management and site history determine outcomes of assembling prairies, but site characteristics and landscape context have little effect

Abstract

The outcomes of ecological restoration are notoriously unpredictable, but we have no general predictive understanding of this contingency. Management decisions can have strong effects on restoration outcomes, but in other cases may be overwhelmed by site characteristics (e.g. soil conditions), landscape context (e.g. abundance of similar habitat) or historical factors (e.g. priority effects). However, we generally cannot predict which of these four classes of drivers will affect restoration outcomes. Disparate aspects of restoration outcomes (e.g. species richness, beta diversity and community composition) and their unique responses further complicate our understanding. Finally, these four classes of drivers might differentially affect subsets of the restored community, where, for example, management might shape the abundance and distribution of species of the target community, while other species are more contingent on site, landscape or historical factors. 2. Here, we used variation partitioning to compare the relative importance of management, site, landscape and historical factors for determining the plant community outcomes of 27 prairie restorations in south-west Michigan. 3. We found that management, especially the composition, diversity and density of seed mixes applied, and history, especially site age, were the most important drivers of prairie restoration species richness, beta diversity and composition. Site and landscape factors were only rarely important for restoration outcomes. 4. Finally, we found that comparing the unique responses of sown and non-sown species typically increased our understanding of the dynamics contributing to community-wide restoration outcomes. 5. Synthesis and applications. This is, to our knowledge, the first quantitative comparison of how four major classes of drivers determine the outcome of restoration. Historical legacies and management decisions, but generally not landscape context or local site conditions, shaped plant communities at restored sites. These findings represent an important step towards developing a more predictive framework for understanding contingency in restoration outcomes.

Plant community response to switchgrass (Panicum virgatum) population source in establishing prairies

“…Propagule pressure is a strong driver of population establishment in the early stages of community assembly in experimental grasslands (Kempel et al 2013), shrub-steppe systems (Schantz et al 2015), and restored prairies (Grman et al 2013). Propagule pressure is a strong driver of population establishment in the early stages of community assembly in experimental grasslands (Kempel et al 2013), shrub-steppe systems (Schantz et al 2015), and restored prairies (Grman et al 2013).…”

“…Propagule pressure is a strong driver of population establishment in the early stages of community assembly in experimental grasslands (Kempel et al 2013), shrub-steppe systems (Schantz et al 2015), and restored prairies (Grman et al 2013). Grman et al (2013) examined 27 prairie sites and found that sownspecies richness decreased with increasing seeding densities of dominant grass species. Few field studies have examined plant diversity across a range of dominant-species densities and results have been mixed.…”

The economic value of grassland species for carbon storage

“…Restoring species richness on CRP grasslands to levels observed for the remnant grasslands (from S = 6 to S = 11) would confer a value for the increased carbon storage of ~$2.350 billion (calculated as the area of CRP lands, 12.34 million ha, multiplied by the sum of the marginal values per unit area for the 7th through the 11th species shown in Table 1 for the mid-range estimate of the social cost of carbon, $137.26 MT C −1 ). Practices as simple as using more diverse seed mixes can promote higher species richness in prairie restoration ( 35 , 36 ). Although this may be more expensive up front than seeding monocultures ( 37 ), the valuation shown here provides a means to evaluate the long-term economic benefits from carbon storage and other ecosystem services flowing from increased diversity compared to the higher up-front costs.…”

Forest restoration following surface mining disturbance: challenges and solutions

“…The diversity and species composition of a seed mix can be the primary factor influencing the species richness and composition of the resulting community (Grman et al 2013) and thus requires careful consideration for mined areas slated for reforestation. An herbaceous ground cover is often seeded on reclamation sites to control erosion (Fig.…”