Fine-scale variability in growth-climate relationships of Douglas-fir, North Cascade Range, Washington

Information about the sensitivity to climate of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is valuable because it will allow forest managers to maximize growth, better understand how carbon sequestration may change over time, and better model and predict future ecosystem responses to climatic change. We examined the effects of climatic variability on the growth of Douglas-fir along an elevational gradient in the North Cascade Range, Washington (USA), at annual timescales during the 20th century. Multivariate analysis and correlation analysis were used to identify climate-growth relationships. Mid-elevation chronologies were negatively correlated with growing season maximum temperature and positively correlated with growing season precipitation. In contrast, high-elevation chronologies were positively correlated with annual temperatures and negatively correlated with previous-year winter Pacific Decadal Oscillation index. Projected increases in summer temperatures will likely cause greater soil moisture stress in many forested ecosystems. The potential of extended summer drought periods over decades may significantly alter spatial patterns of productivity, thus impacting carbon storage. It is likely that the productivity of Douglas-fir in the Cascade Range will decrease at sites with shallow, excessively drained soils, south- and west-facing aspects, and steep slopes and will increase at high-elevation sites.