Subjects: Biology >> Botany >> Plant ecology, plant geography submitted time 2016-05-03
Abstract： Aims Sparse Ulmus pumila forest is an intrazonal vegetation in Onqin Daga Sandy Land, Populus simonii has been widely planted for windbreak and sand dune stabilization. Our objective was to compare the differences in carbon (C) density of these two forests and their relationships with stand age. Methods We measured the C content of tree organs (leaf, twig, stem, and root), herb layers(above ground vegetation and below ground root) and soil layers (up to 100 cm) in sparse Ulmus pumila forests and Populus simonii plantations of different stand ages, and then computed C density and their proportions in total ecosystem carbon density. In addition, we illustrated the variation of tree layer, soil layer and total ecosystem carbon density with stand age, and then estimated the C sequestration rates for these two ecosystems by the space-for-time substitution approach. Important findings The average C contents of tree layer and soil layer for sparse Ulmus pumila forests were lower than those for Populus simonii plantations. The total C density of sparse Ulmus pumila forests was half of that of Populus simonii plantations. The carbon density of soil and tree layers accounted for more than 98% of ecosystem C density in both two forests. Irrespective of forest type, the C density ratios of soil to vegetation decreased with stand age. This ratio was 1.66 for sparse Ulmus pumila forests and 1.87 for Populus simonii plantations, respectively when they were over-matured. The C density of tree layer, soil layer, and total ecosystem in both forests increased along forest development. There were significant linear positive correlations between tree layer’s C density and stand age in both forests and between the total ecosystem C density of Sparse Ulmus pumila forests and stand age. The C sequestration rate of tree layer was 5-fold higher in Populus simonii plantation than in sparse Ulmus pumila forest. The C sequestration rate of ecosystem was 0.81 Mg C hm–2 a–1 for sparse Ulmus pumila forest and 5.35 Mg C hm–2 a–1 for Populus simonii plantation. These findings have implications for C stock estimation of sandy land forest ecosystems and policy-making of ecological restoration and C sink enhancement in the studied area.
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