Ecosystem carbon stocks in a forest chronosequence in Hunan Province, South China

Abstract

Forest ecosystems represent an important carbon sink. A few studies have reported carbon stocks in a forest chronosequence, the carbon stock pattern variation and proportion of each compartment remain poorly understood. The objectives of this study were to quantify carbon stocks of each compartment of forest ecosystem and access their contribution to forest carbon stocks with forest succession. Totally, 32 plots (20 m × 50 m) in different stages of forest succession were investigated, including 11 replicates for Masson pine forest at the early stage, 9 for pine-broadleaved mixed forest at the middle stage, and 12 for evergreen broadleaved forest at succession climax, to quantify carbon stocks in trees, shrubs, herbaceous plants, litter and coarse woody debris (CWD), and soil. The total ecosystem carbon stocks ranged from 193 to 257 Mg ha−1, of which vegetation carbon stocks ranged from 94 to 129 Mg ha−1. Tree biomass carbon stocks increased but shrub biomass carbon stocks decreased during forest succession. The increment of tree biomass carbon stocks was far more than that of shrub, resulting in the increases of vegetation carbon stocks during forest succession. Debris carbon stocks ranged from 4.2 to 5.6 Mg ha−1, with no significant variation across the forest chronosequence. The soil carbon stocks (top 100 cm) ranged from 96 to 132 Mg ha−1. Soil carbon stocks increased significantly during the forest chronosequence, of which soil carbon accumulation occured mainly in the topsoil (0–30 cm). There were no significant differences among the proportions of forest ecosystem carbon stocks in the chronosequence. The averages of proportions of vegetation biomass, debris and soil carbon were 46.7 %, 2.1 % and 51.2 %, respectively. Our results present robust evidence for the increasing carbon sequestration across forest succession chronosequence. Furthermore, tree growth and carbon accumulation in topsoil layer contribute equivalently to carbon sequestration during forest succession in subtropical China.