Variations in the live biomass and carbon pools of Abies georgei along an elevation gradient on the Tibetan Plateau, China

Abstract

The spatial distribution of montane forest biomass and C pools along altitudinal gradients and the role of the climate gradient on the Tibetan Plateau are not well-understood. To determine how live biomass and C pools in montane forests vary along an elevation gradient, the biomass and C content of fir trees (Abies georgei), the most widespread forest type on the Tibetan Plateau, were measured from 3100masl to 4400masl. The total live biomass of the forest nonlinearly declined by 66.2% with the elevation gradient, with most of the biomass reduction (covering almost 94% of the total reduction) occurring at altitudes lower than 3400masl and at altitudes above 3900masl, and the C concentration of the aboveground components (stems, leaves and branches) of A. georgei were positively correlated with the biomass variation along an elevation gradient. The total C pool of A. georgei (stand and root C) decreased from 259.73±11.75tC/ha at 3100masl to 87.29±8.21tC/ha at 4300masl, whereas the biomass C pool allocation in the roots increased by 2.5% at the same altitude. A possible explanation for these marked shifts in the biomass and C allocation from above to belowground along an increasing elevation gradient is discussed, including the limitation of the N supply and the effect of lower temperatures. The annual air temperature and precipitation were positively correlated with the live biomass and C stocks along an elevation gradient. The live biomass C is allocated more to aboveground components with increasing temperature and precipitation.