Climate change in the 21st century will affect tree growth in the Pacific Northwest region of North America, although complex climate-growth relationships make it difficult to identify how radial growth will respond across different species distributions. In this study, I used a novel method to examine potential growth responses to climate change at a broad geographical scale with a focus on visual inspection of patterns and applications beyond sampled areas.

Projected changes in climate were examined within species distributions of mountain hemlock (Tsuga mertensiana), subalpine fir (Abies lasiocarpa), Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) in Washington and Oregon based on three different future climate scenarios. By drawing on knowledge from previous climate-growth studies and organizing information into climate space plots, I inferred directional changes in future radial growth. Results indicate that increased moisture stress will reduce growth throughout the distribution of Douglas-fir, but growth may increase at some energy-limited locations. Decreased snowpack will increase growing season length and increase growth of subalpine fir and mountain hemlock at most locations, although growth may decrease at some low-elevation sites.

An altered Pacific Northwest climate will elicit different growth responses from common conifer species within their current distributions. The methodology developed in this study allowed for qualitative extrapolation of climate-growth relationships from individual sites to entire species distributions and can identify growth responses where climate-growth data are limited.