The influence of provenance on climate response and drought resilience of lodgepole pine in the southern Rocky Mountains, U.S.

Climate change is increasing temperatures and the frequency and severity of drought events in the western United States (U.S.), raising concerns about the persistence of widespread, ecologically important species like lodgepole pine ( Pinus contorta Dougl. var. latifolia Engelm.). We sampled a long-term provenance trial in north-central Colorado, U.S. to examine intraspecific differences in tree size, survival, growth-climate response, and drought tolerance. Using thirty years of tree-ring data and climate data relativized as the climatic distance between provenances and planting site, we evaluated the influence of provenance climate on growth-climate relationships and resistance, recovery, and resilience to a 2002 drought. We found that provenance did not impact tree size and survival, but a weak trend suggests that provenances from areas with greater growing season precipitation had larger average basal area increments. Overall, local site climate influenced annual growth more than provenance origin. Significant differences in drought resistance were found among provenances, notably, populations from warmer and wetter climates showed significantly greater resistance to drought than populations from colder, drier climates. Resilience differed between provenances with populations from cooler and wetter growing seasons showing greater resilience than populations from colder and drier growing seasons. Findings suggest that while lodgepole pine from its more southern range may exhibit flexibility under favorable conditions, climate-informed seed sourcing may become increasingly important as drought frequency and intensity increase. Long-term provenance trials provide critical insight for guiding forest adaptation efforts like forest assisted migration to enhance forest resilience under future climate change.