Quantitative evaluation of atmospheric CO2 sink into forest soils from the tropics to the boreal zone during the past three decades

Abstract

A model of soil carbon cycling in forest ecosystems was applied to predict the soil carbon balance in nine forest ecosystems from the tropics to the boreal zone during the past three decades (1965–95). The parameters of carbon flows and initial conditions of carbon pools were decided based on data obtained in each forest stand. Assumptions for model calculation were: (i) primary production (i.e. litterfall and root turnover rates) increased with increasing CO2 concentrations in the atmosphere (10% per 40 p.p.m. CO2); and (ii) temperature increased by 0.6°C per 100 years, but precipitation changed little. The simulation employed a daily time step and used daily air temperature and precipitation observed near each forest stand over an average year during the last decade. The model calculations suggest that the accumulation of total soil carbon increased 8.5–10.4 tC (ton of carbon) ha−1 in broad‐leaved forests from the tropics to the cool‐temperate zone during the past three decades, but the amount of soil carbon (3.0–8.4 tC ha−1) increased much less in needle forests from the subtropical to boreal zones during the same period. There is a linear relationship between the increasing rate of soil carbon stock during the past three decades (1965–95) in forest stands concerned (RMS, % per 30 years) and annual mean temperature of their soils (T0,°C), as: RMS = 0.34T0 + 4.1. Based on the data of carbon stock in forest soil in each climate zone reported, the global sink of atmospheric CO2 into forest soil was roughly estimated to be 42 GtC (billion tons of carbon) per 30 years, which was 1.4 GtC year−1 on average over the past three decades.