Abstract: AimsShrublands is an indispensable part of estimating carbon density in terrestrial ecosystems, and the expansion of shrublands is considered as one of the key reasons leading to the increase of carbon density in terrestrial ecosystems in China, and yet there are great uncertainties in the carbon sink capacities of shrublands. Our objectives were to estimate the carbon density and distribution characteristics of common shrublands in North China. Methods The carbon density and distribution characteristics of two typical shrublands (Caragana jubata and Carpinus turczaninowii) in Dongling Mountain, Beijing, were measured based on the field investigation data and by employing allometric approaches. Important findings The results showed that the carbon density (427.59 t?hm-2) of C. jubatashrubland was significantly higher than that (178.19 t?hm-2) of the C. turczaninowii shrubland, in which the carbon storage of soil layer was the most (98.53%and 81.31%), and the carbon storage were 421.29 t?hm-2 and 144.89 t?hm-2, respectively. Soil organic carbon was enriched in the 0–50 cm soil layer, and showed a decreasing trend with increasing soil depth. The organic carbon density in different soil layers of the C. jubata shrubland is higher than that of the C. turczaninowii shrubland, mainly due to the lower temperature and smaller slope in the distribution area of the former, which is conducive to the accumulation of organic matter. The contribution of the shrub layer and the arbor-shrub layer to the carbon density of the entire ecosystem were relatively small (1.27% and 17.77%), with values of 5.44 and 31.69 t?hm-2, respectively. The carbon density of different organs in the arbor layer was in the order of trunk > root > branch > leaf, while the order of carbon density in the shrub layer was branch > root > leaf in both shrublands. Moreover, the carbon density of each organ in the shrub layer of C. jubata shrubland was significantly lower than that in the C. turczaninowii shrubland.The herbaceous layer and litter layer contributed the least to the total carbon density of C. jubata and C. turczaninowii shrublands (0.20% and 0.91%), with values of 0.86 and 1.62t?hm-2, respectively. The carbon density of the herbaceous layer(0.55 t?hm-2) in C. jubata shrubland was significantly higher than that (0.35 t?hm-2) in C. turczaninowii shrublands. Moreover, carbon density of the aboveground and underground parts of the herbaceous layer in C. jubata shrubland was similar, while in C. turczaninowii shrubland, the aboveground carbon density was significantly lower than that of the underground part. The carbon density of the litter layer (1.27 t?hm-2) in C. turczaninowii shrubland was significantly higher than that (0.31 t?hm-2) in C. jubata shrubland.

Key words: Shrubland, Carbon density, Ecosystem, Carbon sink, Dongling Mountain