Ability of seedlings to survive heat and drought portends future demographic challenges for five southwestern US conifers.

This article focuses on how climate change-induced warming, drying, and increased vapor pressure deficit (VPD) affect the survival of one-year-old seedlings of five southwestern US conifer species—Pinus edulis, Pinus ponderosa, Pseudotsuga menziesii, Abies concolor, and Picea engelmannii—across their elevational and moisture gradients. Using controlled incubator experiments and Bayesian proportional hazard models, the study found that seedlings of more mesic species (P. menziesii, A. concolor, P. engelmannii) are more susceptible to heat and drought stress than more xeric species (P. edulis, P. ponderosa), though the latter currently occupy warmer, drier ranges closer to lethal conditions. Climate projections under the RCP8.5 emissions scenario indicate that by late-century, extensive portions of all species’ southwestern ranges—especially lower elevations and south-facing slopes—will experience conditions that significantly reduce seedling survival, potentially leading to shifts in forest composition and increased risk of ecosystem conversion. The study highlights the importance of seedling physiological limitations in predicting forest regeneration and resilience under future climate and disturbance regimes in the southwestern USA.