广西不同森林类型土壤有机碳的空间异质性

Spatial heterogeneity of soil organic carbon under different forest types across Guangxi

关键词:  土壤有机碳, 空间异质性, Kriging, 森林类型, 广西

Key words:  soil organic carbon, spatial heterogeneity, Kriging, forest type, Guangxi

摘要:

采用经典统计学和地统计学相结合的方法,研究广西10类主要森林类型不同土层(0～10、10～20、20～30、30～50、50～100 cm)土壤有机碳含量的空间异质性。结果表明:广西森林不同土层土壤有机碳平均含量变化为8.01～29.78 g·kg^-1,变异系数在50.27%～74.89%之间; 10～20 cm土层土壤有机碳的半变异函数符合球状模型,其余土层符合指数模型,且拟合效果均较好; 各土层土壤有机碳半变异函数的块金效应为16.75%～49.33%,表现为强烈或中等强度的空间自相关性; Kriging插值结果显示,不同森林各土层土壤有机碳含量的分布具有一定相似的空间分布特征,总体表现为北高南低,最高和最低值分别出现在东北和东南; 广西不同森林类型不同土壤深度土壤有机碳含量和变异系数不同,0～100 cm土壤有机碳平均含量的大小顺序为硬阔>杉木>石山林>软阔>竹林>八角>桉树>油茶>栎类>松树,总体上土壤有机碳含量随土壤深度的增加而降低,变异系数则相反。广西森林土壤的空间异质性受结构性和人为因素的共同制约,其中结构性因素起主导作用。因此,加强自然林封育和人工林保育、优化调控桉树林和经济林种植规模是提高广西森林固碳潜力的重要措施。

Abstract:

By combination of classical statistics, geostatistics and geographic information system, the spatial heterogeneity of soil organic carbon(SOC)in different layers(0-10, 10-20, 20-30, 30-50 and 50-100 cm)of ten kinds of major forest types in Guangxi were studied. Soil samples were collected from 115 sampling locations and 345 plots(50 m × 20 m), according to 10 km × 10 km grid. The results showed that the average content of SOC in different forests in Guangxi ranged from 8.01 to 29.78 g·kg^-1 and the coefficient of variation(CV)ranged from 50.27% to 74.89%. The semivariagram of SOC in 10 - 20 cm soil layer was best fitted with exponential model whereas those in other soil layers were best fitted with spherical model. The nugget effect of semivariagram of SOC in all soil layers ranged from 16.75% to 49.33%, indicating a strong or a moderate spatial autocorrelation. Kriging interpolation results showed characteristics of spatial distribution of SOC in different soil layers were similar, i.e., higher in the north while lower in the south, and the maximum and minimum occurred in the northeast and the southeast of Guangxi, respectively. The average of SOC and its CV varied with forest type and soil layer, and the average of SOC in 0 -100 cm layer followed the order: Castanopsis > Cunninghamia lanceolata > Cyclobalanopsis glauca > Liquidambar > Bambusa multiplex > Octagon > Eucalyptus > Camellia oleifera > Quercus > Pinus. On the whole, SOC decreased with increasing soil depth, while the CV exhibited an opposite trend. The spatial heterogeneity of SOC in forest of Guangxi was synthetically influenced by structural and human factors, while the structural factors played a dominant role. It is suggested that expanding the area of natural forests and plantations like Cunninghamia lanceolata while reducing the area of Eucalyptus and certain economic forests like Camellia oleifera will help increase carbon sequestration potential in forest of Guangxi.