Forest Reorganization Sustains Carbon Sequestration Under Climate Change

Abstract Forests currently mitigate anthropogenic climate change by sequestering substantial amounts of carbon, but future carbon dynamics are expected to vary across the temperate forest biome. Previously cold‐limited ecosystems with low disturbance activity could increase their carbon uptake, while water‐limited ecosystems with high disturbance activity could become a carbon source to the atmosphere. However, forests dynamically adapt to changing climate and disturbance regimes by reorganizing their composition and structure, with unclear consequences for future carbon dynamics. We asked how the carbon dynamics of reorganizing forests differ from those of resilient forests, that is, forests that conserve their composition and structure under climate change, and how shifts in composition and structure drive future forest carbon. We simulated long‐term forest and carbon dynamics under current and future climate conditions for three contrasting temperate forest national parks, spanning a gradient from low disturbance activity in Shiretoko, Japan, to intermediate disturbance activity in Berchtesgaden, Germany, and high disturbance activity in Grand Teton, Japan. Under climate change, carbon stores increased in Shiretoko, remained close to current levels in Berchtesgaden, and decreased in Grand Teton. Forests that reorganized, that is, exhibited compositional and/or structural changes, generally took up more carbon than resilient forests. Changes in forest carbon cycling were consistently associated with changes in forest structure across systems, whereas the effects of tree species composition change were less consistent. We conclude that resilience in composition and structure does not guarantee continuity in ecosystem functioning, suggesting that reorganization is necessary to maintain forest carbon stocks in a changing climate.