Soil organic carbon density and its influencing factors of major forest types in the forest region of Northeast China.

The five main forest types, i. e. larch forest, birch forest, coniferous mixed forest, broad-leaved mixed forest, and coniferous and broadleaved mixed forest, with varied age classes (young, mid-agedv, pre-mature, and over mature) were selected to investigate the variation of soil organic carbon density in the forest region of Northeast China. Results showed that both soil organic carbon content and density were relatively larger in the top soil layer across the five forest types, decreased gradually with soil depth, and varied insignificantly with either forest type or forest age class. The forest soil carbon density was concentrated in the top 20 cm of soil which accounted for 84. 7% - 86-1%, 51. 7% -59. 8% and 51. 2% -53. 4% of total soil carbon density in the Daxing' an, Xiaoxing' an and Changbai mountains, respectively. The total soil organic carbon density decreased significantly with increasing latitude, which might be attributed mainly to the thickness of soil layers in forest region of Northeast China. [ABSTRACT FROM AUTHOR]