Forest reorganization sustains carbon sequestration under climate change

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, i.e., 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 for three contrasting
temperate forest national parks, spanning a gradient from low disturbance
activity in Shiretoko, JP, to intermediate disturbance activity in
Berchtesgaden, DE, and high disturbance activity in Grand Teton, US. Under
climate change, carbon stores increased in Shiretoko, remained close to
current levels in Berchtesgaden, and decreased in Grand Teton. Forests
that reorganized, i.e., exhibited compositional and/or structural change,
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 could be necessary to maintain forest
carbon stocks in a changing climate.