Forest aging limits future carbon sink in China

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S259033222400201X?dgcid=author

Authors 

Yi Leng, Wei Li, Philippe Ciais, Minxuan Sun, Lei Zhu, Chao Yue, Jinfeng Chang, Yitong Yao, Yuan Zhang, Jiaxin Zhou, Zhao Li, Xuhui Wang, Yi Xi, Shushi Peng

https://doi.org/10.1016/j.oneear.2024.04.011

17 May 2024

Highlights

•A model with forest age dynamics was used to estimate carbon sink

•China’s terrestrial carbon sink in the 2010s was estimated as 198 ± 54 Tg C yr−1

•Forest aging and the slowdown of atmospheric CO2 growth limit future carbon sink

Science for society

Forest carbon sinks are vital in efforts to mitigate climate change, as they absorb a considerable amount of human-emitted carbon dioxide. In recent decades, large-scale ecological restorations projects such as the Three-North Shelter Forest Program, the Yangtze River and Zhujiang River Shelter Forest Projects, and the Grain for Green Program have helped China recover forest area following massive loss prior to the 1960s, growing its land-based carbon sink. Young forests are more productive than older, more mature forests, which makes them more effective at absorbing carbon dioxide. However, this means that as forests age, they become less effective at mitigating climate change. Forecasting ahead to the year 2100, the work presented in this article shows that forest aging and the slowdown of atmospheric CO2 growth will reduce China’s land-based carbon sink by up to 1.1 Tg of carbon per year. Considering the commitment to achieving carbon neutrality by 2060, China needs to recognize the limitations of forests as a climate mitigation tool and promote stringent emission reductions in other sectors.

Summary

Forest age structure, shaped by past land-use and land-cover changes (LULCC), is pivotal for estimating ecosystem carbon sinks. China’s extensive LULCC in recent decades has led to a complex forest age structure, but its impact on the carbon sink remains uncertain. Here, using a process-based ecosystem model with an explicit representation of forest age cohorts, we estimate China’s terrestrial carbon sink as 198 ± 54 TgC yr−1 in the 2010s, mainly contributed by middle-aged forests. The existing forests in 2020 contribute most to the future total carbon sink, but its contribution will decrease significantly by −1.1∼−0.35 TgC yr−1 until 2100 due to forest aging and the slowdown of CO2 concentration growth. Future re/afforestation will enhance carbon sink by increasing forest area and rejuvenating forest demography. Our study emphasizes the limited future carbon sink due to forest aging, implying that realizing China’s carbon neutrality should not rely excessively on ecosystem carbon sink.

Graphical abstract

Source: ScienceDirect