Background
The authors write that Japanese cedar (Chrytomeria japonica D. Don) is one of the most important plantation tree species in Taiwan, representing 10% of the total plantation area, due to its "robust growth performance" and the country's "suitable climatic and soil properties." And because old forests have generally been thought of as being in a carbon-neutral state, as per Odum (1969), they note that the stand age for most Japanese cedar plantations in Taiwan has typically ranged from 30 to 50 years, citing Wang (1977). So what would happen if they let the cedar trees grow a little longer before harvesting them?

What was done
Determined to find the answer to this question, Cheng et al. selected "twelve even-aged Japanese cedar stands along a stand age gradient from 37 to 93 years," with the aim of investigating tree density, mean diameter at breast height (DBH), basal area (BA) and canopy height and biomass carbon stocks, after which they went on to determine various relationships among these stand characteristics and tree biomass and stand age.

What was learned
Quoting the four researchers, "present Japanese cedar plantations in the Xitou area of Taiwan are still developing," and "live tree biomass carbon stocks continue to accumulate beyond the normal rotation period or even beyond a stand age of 90 years."

What it means
As a result of these data-driven facts, Cheng et al. conclude that "if Japanese cedar stands are not harvested, they can provide a carbon sink by storing carbon in tree biomass," such that "in association with the increases in tree DBH with stand age, maintaining this ageing process can be a forest management mechanism for the reduction of greenhouse gas emissions."

References
Odum, E.P. 1969. The strategy of ecosystem development. Science 164: 262-270.

Wang, T.T. 1977. Tree biomass production in Cryptomeria stands of different age classes. Journal of the Agricultural Association of China 102: 59-76.