湖南省森林土壤有机碳密度及碳库储量的动态

Abstract

Soil organic carbon( SOC) represents a large component of the global carbon cycle,and the SOC pool varies in forest ecosystems depending on species composition,growth stage and management practice. In order to accurately evaluate SOC distribution and dynamics in forests in Hunan Province of China, we reviewed, assembled and analyzed acomprehensive data package collected from(1) published estimates of SOC contents in various forested soil profiles( a total of 277 soil profiles in the province) in the past 15 years( from 2000 to 2014),(2) four times of forest inventory data from1983 to 2009 in Hunan' s forests,( 3) long-term field measurements in the Key National Observation Station of Central South University of Forestry and Technology in Huitong County,Hunan Province of China over the past 15 years(2000—2014) and(4) field surveys of 59 soil profiles taken from ten typical forest types in the province during the period of 2008 to 2014. All forests in the province were classified into four categories of timber-forests,economic-forests,bamboo-forests and shrub-forests. The timber-forests were further divided into eight major forest types based on the species composition of the forest stands. The results showed that the arithmetic average of SOC contents ranged from 9. 53 to 22. 86 g / kg in the four main forest categories,of which the shrub-forests had the highest SOC content. The differences of SOC mainly occurred in the 0—40 cm of soil layer among the studied forest groups. SOC density was in the range of 95. 44—181. 30 t C / hm2 in the 0—80 cm soil layer,with an average of 137. 15 t C / hm2 in the examined forests. The differences of SOC density among the forest groups declined with the increase of soil depth,and the effect of forest types on variation of SOC density was gradually weakened with the increasing soil depth. From 1983 to 2009,SOC pool( 0—80 cm soil depth) increases in Hunan's timber-forests with a net increase of 414. 86 × 106 t C and the area weighted average of SOC density increased 10.98 t C / hm2 in the studied timber-forested soils( 0—80 cm soil depth) as well. The difference of SOC pool gradually increased with aged stands of timber-forests,mainly occurring in Chinese fir( Cunninghamia lanceolata) forests,Masson Pine( Pinus massoniana) forests and broad-leaved forests. Among the forest types,natural forest accounted for a large percentage( 50%) of the total SOC storage in Hunan's forests. But the proportion of SOC in plantation forests increased as the plantation areas gradually increased in the studied province. Economic-forests,shrub-forests and bamboo-forests made different contributions to the total SOC pool( 0—80 cm soil depth) in Hunan' s forests,depending upon planting areas,cultivate systems and management practices. The changes in SOC pool in studied forests were closely associated with the alteration of forested area,convention of forest types and land use changes. These changes in terms of forested area and forest type were related to the formation and implementation of forestry policies in local,province and national levels. Our study suggested that human activities would influence SOC pool in forest ecosystems in regional scale through altering forested area and forest types.