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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. [ABSTRACT FROM AUTHOR]

We present a model that maps the net present value (NPV) associated with planting black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) and white pine ( Pinus strobus L.) seed sources across a study area centred on Ontario, Canada. The model accounts for climate change through the use of universal response functions, which (in principle) predict the growth of any seed source under any climatic conditions. We demonstrated the use of the model for two locations in northern Ontario; both species exhibited significant variation in NPV across the study area and significant gains associated with climate-smart seed movements. For example, the NPV associated with potential white pine seed sources varied by more than $1500·ha−1 for a planting site at North Bay, Ontario. We also compared the NPV maps with climate similarity maps to examine the degree to which simple climate matching can act as a proxy for the detailed genecology relationships contained in the universal response functions. Overall, the climate similarity maps were well-correlated with the NPV maps; however, there was poor agreement regarding white pine seed deployment from North Bay, for which the two approaches identified opposite seed transfer directions. We propose that this situation can arise when species show strong adaptation to a central climatic optimum. [ABSTRACT FROM AUTHOR]

Assisted migration (AM) is often presented as a strategy to save species that are imminently threatened by rapid climate change. This conception of AM, which has generated considerable controversy, typically proposes the movement of narrowly distributed, threatened species to suitable sites beyond their current range limits. However, existing North American forestry operations present an opportunity to practice AM on a larger scale, across millions of hectares, with a focus on moving populations of widely distributed, nonthreatened tree species within their current range limits. Despite these differences (and many others detailed herein), these two conceptions of AM have not been clearly distinguished in the literature, which has added confusion to recent dialogue and debate. Here, we aim to facilitate clearer communication on this topic by detailing this distinction and encouraging a more nuanced view of AM. [ABSTRACT FROM AUTHOR]

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