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Global patterns and drivers of tropical aboveground carbon changes

来自 <Global patterns and drivers of tropical aboveground carbon changes | Nature Climate Change>

热带地上碳变化的全球模式和驱动因素

## Abstract:

• Tropical terrestrial ecosystems play an important role in modulating the global carbon balance. However, the complex dynamics and factors controlling tropical aboveground live biomass carbon (AGC) are not fully understood.
•  Fire emissions in non-forested African shrubland/savanna biomes, coupled with post-fire carbon recovery, substantially dominated the interannual variability of tropical AGC.
•  Fire radiative power was identified as the primary determinant of the spatial variability in AGC gains, with soil moisture also playing a crucial role in shaping trends.

## Intro:

• Tropical terrestrial ecosystems encompass more than half of the global aboveground live biomass carbon1 (AGC) and are critical components of the global carbon cycle.

-- Even relatively minor changes in tropical AGC potentially have an important influence on global atmospheric CO2 concentration, subsequently modulating climate change.

• Contemporary estimates of tropical AGC changes often hinge on broad assumptions, sparse ground data and/or inaccurate estimation methods6, leading to uncertainties in identifying tropical land carbon sources/sinks, which remain the most uncertain component of the global carbon budget.
• Satellite observations have shown that deforestation and forest degradation cause tropical forest AGC to be net carbon sources, whereas others suggested that carbon sequestration by secondary forests resulted in tropical forests being net carbon sinks.
• All in all, a key research question for the tropical carbon budget is whether losses from current disturbances in some regions are offset by recovery from past disturbances in other regions.
• Another complicating issue is that studies usually focus on forests, ignoring tropical non-forested ecosystems that have a great influence on the trends and variability in the land carbon sink, with fire often playing a critical role in their AGC changes

## Results:

Patterns of AGC loss

Regionally in tropical America, losses resulting from non-fire–forest disturbances (−0.31 PgC yr−1) marginally surpassed those of total fire emissions (−0.20 PgC yr−1). Both types of losses were predominantly located in the Brazilian ‘arc of deforestation’. Notably, the AGC loss from non-fire disturbances penetrated further into the Amazonian biome, predominantly caused by increasing forest conversion for agriculture and infrastructure development. Trends in non-fire loss estimates are also similar to previous independent estimates of AGC losses due to large-scale deforestation11, as very large-scale clearing of trees is usually associated with non-fire.

• AGC net changes and gains

In tropical America, the most prominent AGC gains were detected in the ‘arc of deforestation’ and southern Brazil, where substantial AGC losses and secondary forest regrowth have been previously recorded. The AGC gains of tropical America constituted 27% (0.54 ± 0.02 PgC yr−1) of the AGC gains across the tropics. Tropical Africa emerged as the predominant contributor to tropical AGC gains, contributing to 58% or 1.17 ± 0.03 PgC yr−1. The regions that contributed to these gains include the Central African Republic, eastern parts of South Sudan, Angola, Zambia and Tanzania. These regions, typified by shrublands and dry forests (Supplementary Fig. 2) and moist forests in southern Central African Republic, only constitute 16% of tropical lands but totalled 35% of tropical AGC gains (0.71 ± 0.01 PgC yr−1). Tropical Asia only witnessed modest AGC gains, contributing merely 15% or 0.30 ± 0.01 PgC yr−1 to the tropical AGC gains. The predominant locations for these gains include Cambodia, central Sumatra and the coastal regions of Kalimantan.

Spatial and temporal patterns of AGC changes during 2010–2020 over the tropics.

• Factors influencing AGC dynamics

使用 BRT 模型来阐明塑造 AGC 增益的空间和时间模式的因素