Assessing assisted population migration (seed transfer) for eastern white pine at northern planting sites

Assisted population migration (APM) has been proposed as an adaptive strategy to enhance forest resilience and productivity under a warming climate. Previous studies have shown tangible benefits of APM on tree growth, including eastern white pine. However, climatic conditions strongly affecting tree growth may also influence the expression of provenance variation and, consequently, benefits from conducting APM. Estimated benefits of APM at warm field trial sites thus may not be attainable at colder northerly sites. In this study, we assessed the potential benefits of APM for eastern white pine at climatically mild and cold sites using data from six field provenance trials in Ontario and Quebec, Canada. Results indicated that annual tree height increment, inter-provenance variation, and achievable benefits from provenance selection were significantly affected by climatic conditions of trial sites. At climatically warm and mild sites where frost or winter low temperature did not cause tree injury, annual height increment was more than 50 % greater and achievable benefit was about twice as large as that at cold sites near the edge of species’ natural range limit. Provenance variation in survival was, however, negligible across trials. Based on patterns of spatial provenance variation, the southern and northern limits of provenances suitable for use as seed sources for planting sites in Ontario and Quebec were delineated using latitudinal coordinates or thermal variables. The potential benefits of APM at northerly sites in anticipation of future climate change are discussed.