Douglas-fir trees will likely experience more stress from drier air as the climate changes than they will from less rain, computer modeling by Oregon State University scientists shows. The research is important because Douglas-fir are widespread throughout the Pacific Northwest, an iconic species with ecological, cultural and economic significance, and learning how the trees respond to drought is crucial for understanding forest sensitivity to a shifting climate. Douglas-fir grow in a range that stretches from northern British Columbia to central California, and also includes the Rocky Mountains and northeastern Mexico. In Oregon, Douglas-fir are found in a variety of mixed conifer and hardwood forests, from sea level to 5,000 feet. …The OSU study, published in Agricultural and Forest Meteorology, simulated the response of a 50-year-old stand of Douglas-fir on the Oregon Cascade Range’s west slope to less rain and higher “vapor pressure deficit,” or VPD—basically the atmosphere’s drying power.