Intraspecific assisted migration (ISAM) through seed transfer during artificial forest regeneration has been suggested as an adaptation strategy to enhance forest resilience and productivity under future climate. In this study, we assessed the risks and benefits of ISAM in white spruce based on long‐term and multilocation, rangewide provenance test data. Our results indicate that the adaptive capacity and growth potential of white spruce varied considerably among 245 range‐wide provenances sampled across North America; however, the results revealed that local populations could be outperformed by nonlocal ones. Provenances originating from south‐central Ontario and southwestern Québec, Canada, close to the southern edge of the species' natural distribution, demonstrated superior growth in more northerly environments compared with local populations and performed much better than populations from western Canada and Alaska, United States. During the 19–28 years between planting and measurement, the southern provenances have not been more susceptible to freezing damage compared with local populations, indicating they have the potential to be used now for the reforestation of more northerly planting sites; based on changing temperature, these seed sources potentially could maintain or increase white spruce productivity at or above historical levels at northern sites. A universal response function (URF), which uses climatic variables to predict provenance performance across field trials, indicated a relatively weak relationship between provenance performance and the climate at provenance origin. Consequently, the URF from this study did not provide information useful to ISAM. The ecological and economic importance of conserving white spruce genetic resources in south‐central Ontario and southwestern Québec for use in ISAM is discussed.

A variety of responses to climate change have been reported for northern tree populations, primarily from tree-ring and satellite-based studies. Here we employ provenance data to examine growth and survival responses of northern populations (defined here as those occurring north of 52° N) of black spruce (Picea mariana) and jack pine (Pinus banksiana) to southward seed transfers. This space for time substitution affords insights into potential climate change responses by these important northern tree species. Based on previous work, we anticipated relatively flat response curves that peak at much warmer temperatures than those found at seed source origin. These expectations were generally met for growth-related responses, with peak growth associated with seed transfers to environments with mean annual temperatures 2.2 and 3.6 °C warmer than seed source origin for black spruce and jack pine, respectively. These findings imply that northern tree populations harbor a significant amount of resilience to climate warming. However, survival responses told a different story, with both species exhibiting reduced survival rates when moved to warmer and drier environments. Together with the growth-based results, these findings suggest that the warmer and drier conditions expected across much of northern Canada under climate change may reduce survival, but surviving trees may grow at a faster rate up until a certain magnitude of climate warming has been reached. We note that all relationships had high levels of unexplained variation, underlining the many factors that may influence provenance study outcomes and the challenges in predicting tree responses to climate change. Despite certain limitations, we feel that the provenance data employed here provide valuable insights into potential climate change outcomes for northern tree populations.

In a changing climate, delaying the time of bud flush may be advantageous to boreal forest species to reduce the risk of spring frost damage. In this study, we examined the potential effect of assisted migration of tree seed on time to bud flush for white spruce. Flushing times of seedlings from 23 white spruce provenances from Ontario were observed under varying temperature conditions simulated in controlled environment chambers. Results indicated that time to bud flush varied considerably among provenances. Although higher temperatures significantly promoted bud flushing for all provenances, provenance-by-temperature interactions were negligible, indicating stable performance of white spruce provenances for this adaptive trait. Spatial patterns of variation among provenances in bud flushing were not consistent with patterns found in range-wide provenance tests. Assisted migration of tree seed across relatively short distances is unlikely to delay bud flushing time in white spruce. Some southern populations may flush earlier at more northerly sites, which would exacerbate spring frost risk. Tree improvement may be an effective approach to utilize amongand withinprovenance variation to enhance this fitness trait for better climatic adaptation.

Our study, conducted in a controlled greenhouse environment over a single growing season, evaluated the growth of seedlings from 25 open-pollinated families of jack pine (Pinus banksiana Lamb.) under two nutrient levels (20 ppm and 200 ppm) and three water regimes (twice a week, once a week, and once every two weeks). We assessed the effects of seed weight, family, nutrient availability, and water treatments on several growth parameters, including height, root collar diameter, shoot dry biomass, root dry biomass, total dry biomass, growing period length, and shoot-to-root ratio at harvest. We found that seed weight significantly influenced all growth traits, maintaining its effect throughout the growth season, although its impact diminished over time. Jack pine families were more responsive to nutrient treatments than to variation in water availability. Genetic variation was significant for all traits except the shoot-to-root ratio, highlighting the intricate role of genetic makeup in shaping growth responses. The substantial impact of nutrient and water treatments and relatively low heritability estimates suggest that pre-conditioning seedlings through nursery management can optimize shoot-to-root ratios. The minimal family-by-treatment interaction and the consistent performance of families across treatments suggest the potential for selecting high-efficiency genotypes with enhanced nutrient use efficiency and drought tolerance.