Climate impacts on lodgepole pine ( Pinus contorta) radial growth in a provenance experiment

Abstract

A potentially confounding radial-growth interaction exists at the intersection of two well-known principles, one in the field of dendrochronology and the other in quantitative genetics. From a dendrochronology perspective, tree populations growing in climatically marginal environments are expected to be more sensitive to seasonal and annual climate than those growing in optimal climate zones. From a genetics perspective, marginal populations may be adapted to grow a small amount each year and then shut down to prevent climate-induced mortality, or they may be adapted to respond to favourable climate conditions when available. We examined the relative strength of these forces using data from 12 populations of 34-year-old lodgepole pine ( Pinus contorta) trees growing in 16 provenance-trial sites in western Canada. Growth generally correlated positively with annual temperature and negatively with summer aridity. The sensitivity of radial-growth to interannual climate fluctuations was both site and provenance-related, with the highest sensitivities occurring among populations from warm, central provenances growing at cold, marginal sites, and among populations from cold, marginal provenances growing at warm, central sites. The correlations between climate and growth varied regionally; notably, populations from warm provenances growing at warm sites responded more strongly to summer aridity, while populations from cold provenances growing at warm sites responded more to annual temperature. Our finding that sensitivity varied among populations growing under similar climate conditions indicates that sensitivity is influenced by genetics as well as by site climate, but the regional specificity of the growth responses did not support a single hypothesis for the influence of genetics on growth among populations from marginal vs. central locations. Implications of our study for forest productivity under climate change are more positive for trees growing in cool locations, where overall warmer temperatures will lead to increased growth, than in warm locations, where the negative effects of arid summers may counteract the positive effects of warmer annual temperatures.