Critical seed transfer distances for selected tree species in eastern North America

Forest planting events present key opportunities to enhance forest adaptation and growth through the selection of appropriate growing materials (seeds and seedlings). Critical to such efforts is knowledge of the climatic distance that seed sources can be moved before significant growth forfeitures are incurred. These limits, referred to here as critical seed transfer distances (CSTD), can be used to identify a potential seed procurement region for any given planting site and can readily incorporate climate change projections. We assembled provenance trial data from a variety of sources and employed transfer functions to derive CSTDs for five major tree species in eastern North America. Optimal height growth at test sites was associated with modest warm‐to‐cold (i.e. northward) seed transfers of 1.6°C on average. Calculated transfer limits were large, indicating that seed sources could be moved significant climatic distances before height growth was less than 90% relative to that of the local seed source. These broad relationships, which were relatively consistent across species, would allow considerable flexibility in resulting seed transfer systems; however, given the significant uncertainty surrounding climate change—particularly in the location and timing of extreme weather events—prudent application of seed transfer limits may be appropriate. Synthesis: We assembled and analysed a significant amount of provenance data to derive novel information on seed movement limits for five tree species in eastern North America. This information will support forest managers in ongoing efforts to incorporate climate change into forest regeneration operations.