Common garden study reveals frost-tolerant 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 functions, and economic significance. Our study addresses which populations of Q. rubra are best suited for climatic conditions at its northern and central United States range limits. Our findings can inform management decisions involving 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 representing the current Q. rubra geographic range in two common gardens, one at the northern range limit (Alberta, Michigan, USA) and one in the central range (Kalamazoo, Michigan, USA). We observed Q. rubra aboveground growth, phenology (senescence, budburst), and frost damage for three years. At the central range site, southern seed source populations from warmer and wetter locations showed greater relative growth rate. At the northern range site, northern seed sources, from colder, drier locations, had greater relative growth rate. Southern seed sources generally had later phenological events which resulted in them sustaining more frost damage than northern seed source populations in the spring and autumn. Northern seed sources 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. More extreme weather events are predicted with climate change, which favors the phenology, frost tolerance, and greater growth rate of northern seed sources for assisted migration at the northern range limit