Latitude of seed source impacts flowering phenology and fitness in translocated plant populations

Seed sourcing strategies have received considerable attention in the restoration literature and are a key component of effective management for restoration and conservation of natural areas. Research and discussion tend to focus on optimal distances and environmental similarities between seed sources and planting sites. However, given the increasing calls for assisted gene flow and assisted migration, greater consideration of translocating populations in specific directions across climatic gradients is warranted. To the extent that local adaptation proceeds primarily in response to climatic conditions, assisted gene flow across climatic gradients is likely to promote species persistence in the face of climate change. However, if species are adapted to other abiotic and biotic factors, translocating populations across climatic gradients may have unintended and potentially maladaptive consequences. Here, we used extensive collections of seed materials from across the state of Minnesota, a field planting that established common conditions at a location that was near the southern extreme of all the source locations, and subsequent aster modeling of fitness data to examine the overall fitness consequences of translocating populations across the landscape. We found that populations from cooler, northern sources tended to have higher fitness than those from warmer, more southern locations. In addition, populations from more northern locations tended to have earlier flowering phenology relative to populations from more southern sources, perhaps conferring a fitness advantage. Taken together, our results suggest that latitude of origin may be an important factor to take into consideration during seed source selection for restoration work, and that the direction of the effects can be at odds with expectations based on climatic considerations.