Previous studies show that southwest China has the largest forest carbon biomass storage and the largest carbon sink in China.  However, this area is subject to climate change and may be vulnerable.

It is imperative to understand the carbon exchanges and their responses to climate change in Yunnan Province (the main portion of Southwest China) where models suggested may experience decreased precipitation and increased temperatures. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences chose four representative forest ecosystems (savanna, tropical, subtropical, and subalpine) to study the carbon exchanges and responses to climatic control in Yunnan. 

The researchers employed 29-site-years of eddy covariance data to observe the state, spatio-temporal variations and climate sensitivity of carbon fluxes (gross primary productivity (GPP), ecosystem respiration (R_eco), and net ecosystem carbon exchange (NEE)) in the four forest ecosystems. 

They found that the old-growth forest ecosystems in Yunnan are currently playing an important role in the regional and global carbon cycle and mitigating the global increase in CO₂. The NEP decreased when the GPP was greater than some threshold and that their relationship is best expressed as a quadratic model. 

The carbon sinks might significantly weaken in the savanna and tropical rainforest under increasing temperature. Carbon sequestration might decrease in both the savanna and tropical rainforest under future warming. 

In contrast, the carbon sink may increase in the subtropical and subalpine because of the lower mean annual temperature and relative abundance of mean annual precipitation in the subtropical and subalpine ecosystems. 

Meanwhile, changes in precipitation and soil moisture caused significant variations in the NEE in the savanna and tropical rainforest but had only a slight influence on the NEE in the subtropical and subalpine ecosystems. 

The study entitled "Carbon exchanges and their responses to temperature and precipitation in forest ecosystems in Yunnan, Southwest China" has been published in Science of The Total Environment.