Variations of carbon stock with forest types in subalpine region of southwestern China

Subalpine forests in southwestern China were exploited extensively in the second half of the 20th century. Old growth forests (OGFs) dominated by firs had largely been replaced by spruce plantation forests (SPFs), spruce and birch mixed forests (SBMs), natural birch forests (NBFs), and fir and birch mixed forests (FBM). The main objectives of this study are to quantify the ecosystem carbon (C) stock in these five forest types and to estimate their C sequestration capacity. Sixty-nine stands were sampled across the Miyaluo forest region located in the subalpine zone of southwestern China. The C stocks in the tree-layer, understory, herbs, mosses, forest floor, coarse woody debris (CWD) and soil were estimated. The mean total biomass in SPF, SBM, NBF, FBM, and OGF was 125.9, 131.2, 135.7, 191.7, and 651.1 t/ha, respectively. The OGF had the highest level of C stock. Total biomass and C density were significantly higher in FBM than those in SPF, SBM and NBF. FBM had a significantly higher mean annual increment (MAI) than all other types. Soil C accounted for a large proportion (68.4–76.5%) of the ecosystem C pools in SPF, SBM, NBF and FBM, but only 40.5% C was stored in the OGF’s soils relative to 51.5% in the biomass. Of the C stock in the upper 0–80 cm soil, about 50% was stored in the upper 0–20 cm, and more than 74% in the upper 0–40 cm. Soil C stock in OGF, NBF and FBM was significantly higher than that in SPF and SBM. Soil disturbance during timber harvest, site preparation and tree planting explains less soil C stock in the SPF and SBM stands compared to other forest types. These results suggest natural mixed forest restoration can be a promising approach for increasing C sequestration capacity in the subalpine region. Also, reducing soil disturbance during forest management practices plays an important role in increasing the soil C stock.

► C stocks in subalpine forest in southwestern China were estimated. ► Total biomass and mean annual increment were compared among four restoration types. ► Natural mixed restoration can be a better approach for increasing C sequestration. ► Reducing soil disturbance plays an important role in increasing soil C stocks.