黄土高原中西部刺槐人工林生态系统碳密度及其影响因子

为阐明黄土高原中西部刺槐人工林碳密度区域分布特征及其主要影响因子,基于野外样地调查和室内样品分析估算了黄土高原中西部4个栽培区域的刺槐人工林生态系统碳密度及其分布特征,并利用相关性分析和主成分分析分析了影响生态系统碳密度的主要因子(林分、地形、土壤和气候等)。结果表明:调查区5个林龄的刺槐人工林生态系统生物量为34.13—133.08t/hm~2,不同区域之间各组分生物量存在显著性差异。植被层平均碳含量为221.93—454.67 g/kg,总体上表现为乔木层平均碳含量高于灌、草层,枯落物层平均碳含量最低,不同区域乔木、灌木、草本平均碳含量均存在显著性差异。刺槐人工林生态系统碳密度均值为106.86 t/hm~2,其中土壤层碳密度占刺槐人工林生态系统总碳密度的64.09%,是刺槐人工林生态系统碳密度的主要组成部分。植被层碳密度为38.68 t/hm~2,其中乔木层碳密度(33.88 t/hm~2)占植被层碳密度的87.58%,灌木、草本、枯落物所占比例依次为1.98%(0.77 t/hm~2)、2.00%(0.77 t/hm~2)、8.43%(3.26 t/hm~2)。不同区域土壤、生态系统碳密度均存在显著性差异。相关性分析和主成分分析表明,刺槐人工林生态系统碳密度与林龄、降水量呈显著正相关关系,与林分密度、平均气温、海拔和坡度的相关关系不显著,上述林分因子、地形因子和环境因子转化的主成分方差累积贡献率为91.07%,其中林龄和降水量是影响刺槐人工林生态系统碳密度的主要因子,方差贡献率为37.22%。

Ecosystem carbon density of Robinia pseudoacacia plantations and influencing factors in the middle and western Loess Plateau

Plantations are believed to be a mitigating measure against the predicted rising CO₂levels.As important carbon sinks,Robinia pseudoacacia plantations have been planted extensively on the Loess Plateau owing to the ability of this species to adapt to different soil and climatic conditions and its tolerance to drought and erosion.However,little is known regarding the efficiency of R.pseudoacacia regarding biomass allocation,ecosystem carbon density partitioning,and factors influencing these aspects,especially in different planted regions.Thus,the objective of the present study was to investigate the ecosystem carbon density of R.pseudoacacia plantations and evaluate their relationship with different influencing factors in diverse planted regions.In the present study,a set of 14 sample plots were established in 4 major planted areas of R.pseudoacacia plantations (Baiyin,Pingliang,Yan''an,and Qingyang) in the middle and western Loess Plateau,China.Field investigations and laboratory analyses were undertaken to quantify the ecosystem carbon density and analyze its influencing factors.The main results are that the average biomass in the plantation ecosystems of five different age groups was 34.13-133.08 t/hm² and the average carbon concentration of the vegetation pool was 221.93-454.67 g/kg.The average biomass in different components was significantly different among the four distribution regions,as were the average carbon concentrations of arbor layer,shrub layer,and herb layer.The carbon concentrations in the different components were in the order of:arbor layer (435.94 g/kg)> shrub layer (365.19 g/kg)> herb layer (310.53 g/kg)> litter layer (264.08 g/kg).The average carbon density of the studied ecosystems was 106.86 t/hm².The proportion of soil layer carbon density was 64.09%,and soil layer carbon density was the major constituent of the carbon density of the ecosystem.The carbon density of the vegetation layer was 38.68 t/hm².The carbon density of the arbor layer was 33.88 t/hm²,which accounted for 87.58% of the vegetation layer carbon density.The carbon density of the shrub layer,herb layer,and litter layer were 0.77 t/hm²,0.77 t/hm²,and 3.26 t/hm²,respectively,which accounted for 1.98%,2.00%,and 8.43% of the vegetation layer,respectively.Soil organic carbon density and ecosystem carbon density were all significantly different among the four regions.Correlation analysis indicated that ecosystem carbon density was positively correlated with stand age and precipitation.In contrast,its relationships with forest stand density,slope gradient,elevation,and annually mean temperature were not statistically significant.Principal component analysis indicated that stand age and precipitation were the first principal component affecting ecosystem carbon density;elevation and annually mean temperature were the second principal component;and the slope gradient was the third principal component.These variables accounted for 91.07% of the variance of ecosystem carbon density.The effect of different factors on ecosystem carbon density was discrepant.Stand age and precipitation were the primary factors affecting ecosystem carbon density.The differences in forest ecosystem carbon density were due to the combined effects of climate,topography,forest stand factors,and management.Therefore,these influencing factors need to be considered when using forest-investigated data to estimate forest ecosystem carbon stock,especially at larger scales.