Previous studies have shown that old-growth forests are carbon sinks. However, the major drivers of seasonal and inter-annual variations of these carbon sinks have yet to be quantified.

　 Using eddy flux measurements from two old-growth evergreen broadleaf forests (subtropical forest and tropical forest) in southern China, researchers from South China Botanical Garden (SCBG) and Xishuangbanna Tropical Botanical Garden (XTBG) compared the seasonal and inter-annual variations in the carbon fluxes of the two forests and quantified the major drivers for these temporal variations. The researchers presented the seasonal and inter-annual variations in gross primary production (GPP), ecosystem respiration (ER), and their difference at a subtropical or tropical forest. Their responses to biotic and abiotic factors were also evaluated in the study.

The subtropical forest site (23°10′16″ N, 112°31′48″ E) is located in the Dinghushan Biosphere Reserve in central Guangdong Province, southern China. The tropical forest site (21°55′39″ N, 101°15′55″ E) is located in the Menglun Nature Reserve in Xishuangbanna, Southern China.

Their study found that the subtropical and tropical forests showed different temporal variations in carbon fluxes. The seasonal variation in net ecosystem exchange (NEE) of tropical forest was driven by ecosystem respiration (ER). The seasonal variation in net ecosystem exchange (NEE) of subtropical forest was driven by both gross primary production (GPP) and ecosystem respiration (ER). Annual rainfall was a major driver of annual carbon sequestration in the subtropical or tropical forests in southern China.

 The study entitled “Seasonal and inter-annual variations in net ecosystem exchange of two old-growth forests in southern China” has been published online in Agricultural and Forest Meteorology, http://dx.doi.org/10.1016/j.agrformet.2013.03.002