Evaluating the potential of red spruce (Picea rubens Sarg.) to persist under climate change using historic provenance trials in eastern Canada

Abstract

Red spruce (Picea rubens Sarg.) is an important tree species in northeastern North America. The impact of climate change on this tree species is expected to vary regionally, but may be negative within Canada’s eastern Acadian Forest Region as temperatures there are expected to rise by 2–6 °C by 2100 under the business-as-usual Representative Concentration Pathway (RCP) 8.5 climate forcing scenario. In this study, we use one series of historic provenance trials from northeastern North America to evaluate the capacity of red spruce to persist under climate change by analyzing measurements of tree height and diameter at breast height (DBH) in relation to differences between provenance origin climate and test site climate (i.e., climate differentials).Within the range of climate differentials tested, warming (i.e., when the test site was warmer than provenance origin) did not appear to have a deleterious effect on red spruce growth, but cooling (i.e., moving provenances to colder, more northerly sites) did negatively affect growth by reducing height and diameter. Indeed, warmer temperatures, relative to provenance origin, increased tree size, especially for the most northern provenances, suggesting red spruce at the northern extent of its geographical range in northeastern North America is currently cold suppressed and located in non-optimal climates. However, our capacity to test warming effects on more southerly provenances was limited in this study by lack of available test sites south of red spruce’s climatic range. Among the eight climate variables tested, changes in frost free period and mean annual temperature had the most significant impact on tree size. In general, temperature-related climate variables had stronger effects than moisture-related variables. Overall, our results provide important insight for foresters when considering the future management of red spruce in the Acadian Forest Region and the selection of climate adapted seed source.