中文摘要：

【目的】定量研究宁夏六盘山地区华北落叶松人工林的植被碳密度特征并揭示主要影响因子,以期为合理经营森林增强森林的碳汇等服务功能提供科学依据。【方法】在半湿润的香水河小流域和半干旱的叠叠沟小流域,设立不同坡位、密度、林龄的林分样地进行野外调查,并结合宁夏六盘山森林生态定位站多年积累的样地调查数据。根据经验方程,依据林分生长特征计算林分的生物量及其组成,利用各种生物量的碳含量计算得到植被碳密度。【结果】六盘山华北落叶松林植被碳密度为0.70-74.10 t·hm^-2,平均为30.96 t·hm^-2;对调查林分的各生长指标（密度、树高、胸径、郁闭度、林龄）而言,碳密度都是在一定范围内随结构指标增加而升高,但在密度、树高、胸径达到一定阈值（密度为1 300株·hm^-2、树高为12 m、胸径为14 cm）后就变成缓慢增加,在郁闭度达到阈值0.7后趋于稳定;碳密度随林龄的变化是小于18年生前增加缓慢,19-27年生时快速增大,达到27年生后又增加缓慢;近10年华北落叶松林植被碳密度持续增加,其中半湿润区条件下的碳密度年增量（5.57 t·hm-2·a^-1）显著（P〈0.05）大于半干旱区（2.58 t·hm^-2a^-1）。【结论】基于本研究对森林植被碳密度特征研究结果的综合分析,并考虑促进林下自然更新、形成林分复层结构、维持较高植物多样性、降低森林生态耗水、提高抵抗风雪灾害能力等方面的林分结构要求,认为六盘山华北落叶松林的多功能理想林分应是郁闭度在0.7左右、密度不高于1 300株·hm^-2,这有利于同时实现固碳增加、产水较多、自然更新和结构稳定等多重要求。

英文摘要：

【Objective 】This research was carried out to quantify the variation of biomass carbon density of Larix principis-rupprechtii plantation in Liupan Mountains of Ningxia,NW China,and to detect the influencing factors,e. g.tree age,stand density,canopy density,diameter at breast height（ DBH） and tree height. The results can guide the rational management of forests to enhance their function of carbon sequestration. 【Method 】Sample stands with various ages,slope positions,stocking densities were selected in the semi-humid small watershed of Xiangshuihe and the semiarid small watershed of Diediegou to measure the biomass carbon density. Besides the newly measured field data,the accumulated data from past investigations at the Liupanshan Forest Ecological Station were also used in this study. The biomass and its components were calculated based on empirical relations from the parameters of stand structure. Then,the biomass carbon density,or called as vegetation carbon density,was calculated using the carbon content of different biomass components.【Result】The biomass carbon density of L. principis-rupprechtii plantation was averaged at 30. 96 t·hm^-2,with a variation range of 0. 70 - 74. 10 t·hm^-2. The biomass carbon density increased with the increase of stand structure（ tree density,canopy density,DBH,tree height,and tree age）,until certain thresholds were reached;thereafter it increased slowly or stabilized. The corresponding threshold was 1 300 individual·hm^-2 for tree density,0. 7 for canopy density,14 cm for DBH,12 m for tree height. The biomass carbon density increased first slowly with increasing tree age before the age of 18 years,and increased rapidly when it aged between 19 - 27 years,and thenincreased slowly again when it was older than 27 years. The biomass carbon density maintained a continuous increase in recent 10 years,with a significantly higher increment rate of 5. 57 t · hm^-2a^-1at the semi-humid area than the rate of 2. 58 t·hm^-2a^-1at the semi-arid area（ P 0. 05）.【C