Can current forest biomass accumulation lead to long-term carbon storage?

Background/Question/Methods

The biomass of forests across the globe is rapidly increasing in the past decades. While the rates of biomass accumulations over years/decades are much higher than those derived from chronosequences. It has been taken as the evidence of elevated carbon sink in responses to increasing atmospheric CO2 and climate warming. But there is a gap between temporal increases in forest biomass over one or two decades and the biomass carbon sequestration for a long-term period of time, because the disturbances happened at century time scales may erase the accumulated biomass over decades. For ecosystem carbon storage, with the characteristics of “slow in – fast out”, the short-term biomass accumulation rate should be always higher than it at long-term scale due to rare large disturbance events. It is unknown that how many short-term increases in biomass can be translated into long-term trends at given disturbance regimes.  We derived an analytical model linking the long-term biomass accumulation with short-term biomass increase at given disturbance regimes and analyzed the chronosequence and time series biomass data of the temperate forests of Eastern North America using this model.

Results/Conclusions

Our results showed that for most sites, the current biomass increase rates cannot maintain statistically significant higher trends of biomass accumulation than those derived from chronosequences (i.e., historic long-term rates) at current disturbance regimes. If disturbances become more frequent and severe as predicted, forest carbon storage will be reduced in the future. This analysis indicates that we should either down-regulate the expectation of the roles forests in mitigating atmospheric CO2 increases or control the disturbances of temperate forests at a low frequency.