湖南省森林土壤有机碳密度及碳库储量动态

基于2000—2014年文献和著作资料中的湖南省森林土壤剖面有机碳含量数据,湖南会同杉木林生态系统国家野外科学观测研究站近15年的实测数据,分析了湖南省主要森林类型土壤有机碳密度,结合1983年至2009年湖南省4次森林资源清查数据,研究了湖南省森林土壤有机碳库储量的动态特征。结果表明:湖南省主要森林类型土壤有机碳算术平均含量在9.53—22.86g/kg之间,灌木林最高,土壤有机碳含量的分异主要发生在0—40 cm土层,0—80 cm土壤层有机碳密度在95.44—181.30 t C/hm2之间,平均为137.15 t C/hm2,主要分布在0—40 cm土层中,随土壤深度增加,各森林类型土壤有机碳密度的差异下降,受森林类型的影响减弱。从1983—1987年到2009年,湖南省乔木林土壤层(0—80 cm)有机碳库储量净增加了414.86×106t C,面积加权平均有机碳密度提高了10.98 t C/hm2,不同乔木林土壤层(0—80 cm)有机碳库储量的差异随着时间进程逐渐增大,主要分布在杉木林、松木林、阔叶林。天然林是湖南省乔木林土壤有机碳库储量的主要贡献者,人工林土壤有机碳储量正逐步提高,经济林、竹林、灌木林对湖南省森林土壤层(0—80 cm)有机碳库储量贡献不同,且动态变化趋势也不同。森林土壤层有机碳库储量的变化与各森林类型面积的变化密切相关,而各森林类型面积的增减,与各项林业政策的实施密切相关。因此,人类活动深刻影响森林土壤的碳汇功能。

Dynamic properties of soil organic carbon in Hunan's Forests

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 a comprehensive 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 from 1983 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 tC/hm² in the 0-80 cm soil layer, with an average of 137.15 tC/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 tC and the area weighted average of SOC density increased 10.98 tC/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.