Effects of climate change on biomass carbon sequestration in old-growth forest ecosystems on Changbai Mountain in Northeast China

Old-growth forest ecosystems are large carbon pools, and recent research has found that old-growth forests generally serve as global carbon sinks. However, the impact of climate change on the capacity for carbon sequestration in old-growth forest ecosystems is uncertain. Combining data from 30-year monitoring of permanent plots with that measuring variations in radial growth of dominant trees in an old-growth forest on Changbai Mountain in Northeast China, this study investigated the net biomass carbon sequestration and the effects of climate warming on carbon sequestration for dominant living trees in this forest ecosystem. The results showed that in 2010 biomass carbon density for living trees was 201.22 t ha−1 in Korean pine and broad-leaved mixed forest (KBF), 106.46 t ha−1 in spruce-fir forest (SFF), and 89.49 t ha−1 in Erman’s birch forest (EBF). During the past 30 years the net biomass carbon density has increased in KBF and EBF, with annual net increases of 1.79 t ha−1 and 1.22 t ha−1, respectively; while net carbon density has decreased in SFF, with an annual net decrease of 0.55 t ha−1. Despite the increase of carbon density in KBF, climate warming has contributed to a decrease of 0.96 t ha−1 in biomass carbon sequestration for the period of 1981–2010, an amount equivalent to 1.8% of total stand biomass carbon increase. The increase in net carbon density in KBF was primarily age- or size-related, since that forest is still maturing. The decreased density in SFF may be caused by climate-induced radial growth decline and mortality of dominant trees in these stands. For the period of 1981–2010, climate-induced decrease of carbon sequestration in SFF was 7.30 ha−1. Wind-related tree mortality in SFF may have led to the stand carbon sequestration decrease of 75.09 t ha−1, about 10.3 times that induced by climate warming. In EBF, climate warming has led to a small increase in stand carbon sequestration, and the increase in net carbon density was also primarily age- or size-related, reflecting the fact that this forest is also still maturing. Our study also suggests that the dominance of Korean pine in KBF will decrease and that of Manchurian ash will increase under continuing climate warming, which is in agreement with the results from previous forest models.

► We examine the carbon stocks and sequestration of the three old growth forest.
► Global warming has decreased the carbon sequestration in two of them.
► The increases of stand biomass carbon density were primarily age- or size-related.
► The decease of stand biomass carbon density was mainly wind-related tree mortality.