Soil Organic Carbon in Old-Growth Forests

 HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/articles/V10/N9/B2.jsp" http://www.co2science.org/scripts/CO2ScienceB2C/articles/V10/N9/B2.jsp

Reference
Zhou, G., Liu, S., Li, Z., Zhang, D., Tang, X., Zhou, C., Yan, J. and Mo, J. 2006. Old-growth forests can accumulate carbon in soils. Science 314: 1417. 

Background
The authors note that "old-growth forests have traditionally been considered negligible as carbon sinks because carbon uptake has been thought to be balanced by respiration." As a result, they report that "the soil carbon balance of old-growth forests has received little attention."

What was done
In an attempt to rectify this situation, Zhou et al. say they "conducted a study to measure the long-term dynamics (1979 to 2003) of soil organic carbon stock in old-growth forests (age > 400 years) at the Dinghushan Biosphere Reserve in Guangdong Province, China."

What was learned
The eight scientists report that "soil organic carbon concentration in the top 20-cm soil layer increased between 1979 and 2003 from about 1.4% to 2.35% at an average rate of 0.035% each year," also noting that "measurements on a total of 230 composite soil samples collected between 1979 and 2003 suggested that soil organic carbon stock in the top 20-cm soil layer increased significantly during that time (P < 0.0001), with an average rate of 0.61 Mg C ha^-1 year^-1."

What it means
In discussing their results, Zhou et al. state that although "the driving forces for this observed high rate of soil organic carbon increase in the old-growth forests are not clear at present," their study "suggests that the carbon cycle processes in the belowground system of these forests are changing in response to the changing environment [our italics]." 

We agree, having reported frequently on analogous observations in the aboveground portions in such forests (see, for example, many of the items we have archived under the heading of  HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/subject/f/forestold.jsp" Forest (Old) in our Subject Index, where the researchers involved in the work reported there have often suggested that the ongoing rise in the air's CO2 content is likely a - or even the - the primary force behind the phenomenon, aided by warming and in some cases enhanced nitrogen deposition.

Reviewed 28 February 2007