Variation in overall fitness due to seed source: projections for predictive provenancing

Abstract

Seed sourcing decisions affect short- and long-term restoration outcomes. Seeds sourced closer to restoration sites are likely to be better adapted to local conditions and therefore may perform better than those sourced farther away, following assumptions of local adaptation. However, plants may not be adapted to future conditions under climate change; hence, managers are considering a predictive provenancing approach, where plant materials adapted to predicted conditions are used at a site. Currently, there is little empirical evidence available to inform this approach. To address this, we evaluate predictive provenancing using three species of forbs used in tallgrass prairie restorations (Allium cernuum, Chamaecrista fasciculata, and Rudbeckia hirta) in a common garden experiment in northeastern Illinois, U.S.A. We compared the fitness in plants sourced from three regional zones across a latitudinal gradient that represents different climate projections, relative to the planting site. Data were analyzed using Aster life-history models and generalized linear models. We found that source affected overall fitness in all three species, but no climate proxy had the highest fitness across all species. The performance at each life stage had different effects on overall fitness, which varied by source. We observed later reproductive phenology in southern-sourced plants for all three species, possibly due to adaptation to longer growing seasons. The mixed results of this study suggest that climate proxy alone would not be sufficient to determine an effective and accurate predictive provenancing strategy. Long-term tests are needed to pursue such a strategy for high-priority species.