Common garden study reveals frost-tolerant, generalist northern seed sources are best suited to expand range of Quercus rubra

Climate change is shifting the potential suitable range of northern red oak (Quercus rubra L.) faster than it can migrate, creating an adaptation lag. Quercus rubra is prominent in eastern North American forests and important for its carbon sequestration, ecological roles, and economic significance. Our study addresses which populations of Q. rubra are best suited for climatic conditions at the northern and central range limits. Our findings can inform forestry management policies such as assisted migration, where species are transferred within their native range to mitigate the effects of climate change. We planted over 800 Q. rubra seedlings from twelve populations across the current Q. rubra geographic range in two common gardens, one at the northern range limit (Alberta, Michigan) and one in the central range (Kalamazoo, Michigan). We observed Q. rubra aboveground biomass growth, phenology (senescence, budburst), and frost damage for three years. We also measured photosynthetic capacity, stress response, photosynthetic temperature response and water use efficiency to understand the physiological limits of the populations and how they responded to the environmental conditions of the common garden. Southern seed source populations, those from warmer and wetter locations, showed greater growth increments in all years. However, southern seed sources generally had later phenological events which, coupled with their acquisitive growth strategy, resulted in them sustaining more frost damage than northern seed source populations. Northern seed sources, from colder and drier locations, had earlier budburst and were able to utilize early growing season snow melt and higher solar radiation. Northern seed sources also senesced earlier, avoiding autumn frosts. While southern seed sources accumulated more aboveground biomass, it was a trade off with greater evidence of frost damage. Northern populations also seemed to have a more conservative, generalist strategy for physiology. Northern populations had higher leaf mass per area, foliar leaf nitrogen, and photosynthetic capacity. They also had a wider photosynthetic temperature range compared to southern seed sources. More extreme weather events are predicted with climate change, which favors the more conservative generalist strategy and greater frost tolerance of northern seed sources for assisted migration at the northern range limit