In general, accumulation of carbon in forest growth exceeds the total release from it, and thus forests globally act as a carbon sink (see, e.g. IPCC 2007). Globally the carbon stock has been on constant decline between 1990 and 2010. Forests and other terrestrial ecosystems annually absorb about 2.6 GtC (i.e. equivalent to 9.53 Gt of CO2},18,19 1.6 GtC of which re-enters the atmosphere due mainly to forest clearing and degradation, and thus the rate of carbon sequestration is 1 GtC per year (IPCC 2007].