Abstract
Natural forests in inland China are generally distributed in montane area and secondary due to a semi-arid climate and past anthropogenic disturbances. However, quantification of carbon (C) stock in these forests and the role of altitude in determining C storage and its partition among ecosystem components are unclear. We sampled 54 stands of three secondary coniferous forests (Larix principis-rupprechtii (LP) forest, Picea meyerii (PM) forest and Pinus tabulaeformis (PT) forest) on Loess Plateau in an altitudinal range of 1200-2700m a.s.l. C stocks of tree layer, shrub layer, herb layer, coarse wood debris, forest floor and soil were estimated. We found these forests had relatively high total C stocks. Driven by both higher vegetation and soil C stocks, total C stocks of LP and PM forests in the high altitudinal range were 375.0 and 368.4 t C ha-1 respectively, significantly higher than that of PT forest in the low altitudinal range (230.2 t C ha-1). In addition, understory shrubs accounted for about 20% of total biomass in PT forest. The proportions of vegetation to total C stock were similar among in the three forests (below 45%), so were the proportions of soil C stock (over 54%). Necromass C stocks were also similar among these forests, but their proportions to total C stock were significantly lower in LP and PM forests (1.4% and 1.6%) than in PT forest (3.0%). Across forest types, vegetation biomass and soil C stock simultaneously increased with increasing altitude, causing fairly unchanged C partitioning among ecosystem components along the altitudinal gradient. Soil C stock also increased with altitude in LP and PT forests. Forest floor necromass decreased with increasing altitude across the three forests. Our results suggest the important role of the altitudinal gradient in C sequestration and floor necromass of these three forests in terms of alleviated water conditions and in soil C storage of LP and PM forests in terms of temperature change.
Highlights
Montane forests are forests distributed at mid and low altitudes and a key component of mountain ecosystems [1]
The objective of this study is to examine the carbon content and its distribution among ecosystem components along an altitudinal gradient in three secondary coniferous forests on the Loess Plateau dominated by Larix principis-rupprechtii Mayr. (Prince Rupprecht’s larch), Picea meyrii Rehd. et Wils. (Meyer spruce) and Pinus tabulaeformis Carrière (Chinese pine) respectively
Among forest types, vegetation and soil C stocks were higher in LP and PM forests than in PT forest, while an inverse pattern was observed for forest floor necromass
Summary
Montane forests are forests distributed at mid and low altitudes and a key component of mountain ecosystems [1]. Less attention was paid to montane forests for their C stocks and the ecological factors controlling C storage and its partition among ecosystem components, especially to those that are distributed on Loess Plateau in China. These montane forests, dominated by pioneer conifers and broadleaves, are generally protected in the past several decades for their ecological services and becoming a potential major C sink in the region. In a forest inventory study carried out on Loess Plateau, Zhang et al [11] found a positive relationship between elevation and forest C density based on the volume-derived biomass of live trees, indicating the potential influence of the altitude in determining forest C stock in this region, while the effect of altitude on total C storage and its partition among all ecosystem components still remains unanswered
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