Climate change is one of the greatest threats to biodiversity, but we still lack understanding of how sensitivity to climate varies across species’ geographic ranges. We examined the long-term (1930-1979) sensitivity of ponderosa pine (Pinus ponderosa), a widespread tree species, to climate variability across the western U.S. via a synthesis of published tree-ring data (International Tree-Ring Data Bank) and multiple climate products. We compared tree-rings to a set of relatively uncorrelated climate variables that reflected previous research on ponderosa pine (water-year precipitation, April-July precipitation, May-July vapor pressure deficit; VPD and winter minimum temperature). We used a hierarchical cluster analysis to assess geographic patterns of climate sensitivities. We also examined how climate sensitivities (Pearson's correlation coefficients) varied along climate corresponding gradients.
Ponderosa pine growth was sensitive to water-year precipitation, May-July VPD and April-July precipitation throughout its range, but sensitivities were greatest in the southern Rockies and northern Great Plains. Conversely, sensitivities were generally weaker and more heterogeneous in Pacific populations and the Southwest. Sensitivities to winter minimum temperatures were generally positive and negative in Pacific and interior populations, respectively. We identified one cluster of largely climate-insensitive populations, mostly in Oregon. Climate sensitivities were linearly related to position along corresponding climate gradients, except for May-July VPD, but the unevenness of these relationships suggests that local adaptation mediates climate sensitivities. Broader implications include: 1) sensitivities to climate are heterogeneous throughout species’ ranges, 2) all populations, regardless of range position, may be vulnerable to climate change and 3) future conservation strategies should consider localized, individualistic responses to climate change and that disproportionate focus on southern or northern range limits may be misguided.