Carbon sequestration in forest vegetation of Beijing at sublot level

Based on forest inventory data (FID) at sublot level, we estimated the carbon sequestration in forest vegetation of Beijing, China in 2009. In this study, the carbon sequestration in forest vegetation at sublot level was calculated based on net biomass production (ΔB) which was estimated with biomass of each sublot and function relationships between ΔB and biomass. The biomass of forested land was calculated with biomass expansion factors (BEFs) method, while those of shrub land and other forest land types were estimated with biomass, coverage and height of referred shrubs and shrub coverage and height of each sublot. As one of special forested land types, the biomass of economic tree land was calculated with biomass per tree and tree number. The variation of carbon sequestration in forest vegetation with altitude, species and stand age was also investigated in this study. The results indicate that the carbon sequestration in forest vegetation in Beijing is 4.12 × 106 tC/yr, with the average rate of 3.94 tC/(ha·yr). About 56.91% of the total carbon sequestration in forest vegetation is supported by the forest in the plain with an altitude of < 60 m and the low mountainous areas with an altitude from 400 m to 800 m. The carbon sequestration rate in forest vegetation is the highest in the plain area with an altitude of < 60 m and decreased significantly in the transitional area from the low plain to the low mountainous area with an altitude ranging from 200 m to 400 m due to intensive human disturbance. The carbon sequestration of Populus spp. forest and Quercus spp. forest are relatively higher than those of other plant species, accounting for 25.33% of the total. The carbon sequestration in vegetation by the forest of < 40 years amounts to 45.38% of the total. The carbon sequestration rate in forest vegetation peaks at the stand age of 30–40 years. Therefore, it would be crucial for enhancing the capability of carbon sequestration in forest vegetation to protect the forest in Beijing, to limit human disturbance in the transitional area from the plain to the low mountain area, and to foster the newly established open forest.