Photo of trees in front of a large mountain.
Larch forest of the Aletsch Forest Nature Reserve in Switzerland. Credit: Giles Laurent, Wikimedia Commons ( CC BY-SA 4.0 DEED)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

The world’s oceans, forests, and soils soak up about half of anthropogenic CO2 emissions, thus moderating climate change, but how long that benefit will continue is uncertain. Foresters and ecologists know that young forests with many spindly trees grow into mature forests with fewer, larger trees, in a process called “self-thinning,” which typically follows predictably constant rates. But are self-thinning rules changing with climate change and CO2 fertilization, and how will forest biomass and carbon uptake be affected?

Marqués et al. [2023] document mature forests of Switzerland shifting away from constant self-thinning during the last 60 years. Mature forest biomass increased as trees grew faster, but the rate of biomass increase was dampened by increased mortality, which must be studied to understand changing carbon dynamics. Future work should test whether this grow-fast-die-young hypothesis applies elsewhere, such as the Amazon, where rates of carbon sequestration appear to be slowing or reversing.

The authors’ conceptual model of tree growth enhancement (dG/G on the X axis) and forest stand biomass enhancement (dB/B) on the Y axis) for three hypothesized responses of tree mortality. If mortality doesn’t change (blue dot), biomass increases proportionally to tree growth. If classic self-thinning of the forest results in mortality commensurate with growth (red dot), then stand biomass doesn’t increase. If tree mortality increases somewhat but less than predicted from classic self-thinning assumptions (green dot), but forest biomass increases at a dampened rate. Credit: Marqués et al. [2023], Figure 1a

Citation: Marqués, L., Weng, E., Bugmann, H., Forrester, D. I., Rohner, B., Hobi, M. L., et al. (2023). Tree growth enhancement drives a persistent biomass gain in unmanaged temperate forests. AGU Advances, 4, e2022AV000859.

—Eric Davidson, Editor, AGU Advances

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