Shifting growth–climate limitations in Canadian forests under recent climate change

Abstract Productivity of northern forests is often expected to increase with warming, but rising atmospheric demand for water may offset these gains. Here we analyze 38,395 tree-ring chronologies from 4179 Canadian sites over 120 years to quantify how growth limitations respond to climate change. In the mid- to late 20th century, drought limitations already dominate nearly half of Canada’s forested area, while cold limitations are largely restricted to high-latitude and montane regions. Examining changes in growth limitation through time, we identify four response modes across regions: persistence, shifts from cold to drought limitation, reversals toward cold limitation after mid-century drought sensitivity, and stable cold limitation in wet hydroclimates. These patterns show that forest growth responses are not gradual, but can cross thresholds or reverse under continued warming. The results suggest that responses to warming may not translate into sustained gains across large areas of northern forests, including many commercially important regions.