【作者】 方江平；

【导师】 项文化；

【作者基本信息】 中南林业科技大学 ， 生态学， 2010， 博士

【摘要】 西藏亚高山暗针叶林是我国森林资源中保存较为完好的天然林之一,对西藏原始林芝云杉林生态系统结构、生物量与生产力、水文效益及养分循环的系统研究,可为揭示西藏亚高山暗针叶林高蓄积量的规律提供科学依据,也进一步丰富我国高海拔地区森林生态系统研究。西藏原始林芝云杉林群落中有53科116属144种植物,其中蔷薇科和菊科为优势科,单种科属植物所占比例较大,温带属占总属的76.14%。群落物种丰富度和多样性指数较低,而均匀度和优势度指数较大,说明该群落处于演替顶级。林分中以中大径级的乔木个体为主,种群处于稳定至衰退型阶段。空间点格局分析表明,在小尺度范围内小径级的云杉个体趋于集群分布,随着树木的生长,乔木个体呈随机分布。林内林窗以大于100 m2的大林窗为主,其形成木以中径级的干折为主。林分更新主要在中林窗中发生,其更新数量是相邻林冠的3.45倍,并且幼树高度增长了1.5倍。西藏原始林芝云杉标准木近80%的生物量集中在树体中下部,86%的根生物量集中在0～0.60 cm的土层中。在水平分布上,枝和叶在开阔空间生物量较高,而根在各方向上无差异。林分的总生物量为367.49 t.hm-2,其中乔木层的比例最大(75.28%),其次为凋落层、下木层、死亡木、灌木层、层间植物(藤本+苔藓)、草本层。在乔木层中生物量分布是干材>树根>树皮>树枝>树叶,并且随着树木的生长,干材和树皮的比例递增,而枝、叶所占比例递减,地上与地下部分比值也在逐渐减小西藏原始林芝云杉林年净初级生产力为10.65 t·hm-2·a-1,其中乔木层生产力最高(46.96%),其次为凋落物、下木层、灌木层、苔鲜层、草本层和层间植物。在乔木层中生产力分布规律为干材>树枝>树叶>树根>树皮。林芝云杉直径与树高生长速度不同步,整个生长过程可分为幼龄期、速生期和速生稳定期,其中速生期可长达100年,加之无病虫毒的发现,导致林芝云杉蓄积量极高。西藏原始林芝云杉林的年降水量为716.4 mm,主要集中在4-9月份。在生长季节中,林冠截留量为338.6 mm,林内穿透水量为316.3 mm,而树干茎流量仅为0.9mm。林下凋落厚度5.0 cm,最大持水率323.13%,有效持水量为92.26 t.hm-2,凋落层由上到下,持水量呈下降趋势。林下土壤随深度增加,容量逐渐增大,而最大持水量、毛管持水量和最小持水量都在逐渐下降,同样土壤毛管孔隙度和总孔隙度也在下降,表明土壤的持水能力随深度的增加而逐渐减弱。大气降水中各养分元素较低,经过林冠之后,SO42-、Zn和Cl-的浓度有所下降,而其它元素增加。经过土壤之后,SO42-、Zn和Fe浓度下降,其它元素的浓度升高。西藏原始林芝云杉林年凋落量为3.40t·hm-2·a-1,其中云杉枝和叶凋落量各占24.3%、26.1%。1年内呈现两个凋落高峰期,分别在生长初期和末期。分解样品袋置于苔藓下方分解速率最快,初始分解速率与环境温度呈正线性相关。凋落叶的分解速率比小枝快,1年后前者失重率比后者高3倍,半衰期分别为1.75年和8.08年。随分解时间的推移,凋落物中K元素含量下降最快,1年后其养分元素含量下降了近1/2,而Ca元素在分解中途含量还相对升高。各养分元素在分解过程中释放量存在明显差异,1年后K元素释放76.36%,而Ca元素仅释放24.01%。西藏原始林芝云杉标准木中干材养分元素含量最低,N、P、K元素在当年叶含量较高。林内土壤层积累的养分最多,但有效利用率仅1-3%。乔木层养分积累主要在干材中,而叶中最少。5种养分元素的积累速率为104.81 kg·hm-2·a-1,排序为Ca>N>K>P>Mg,但在乔木层各器官中各元素积累速率不相同。林分年归还总量达到169.288 kg·hm-2·a-1,其中地上凋落物年归还量最高,其次是地下凋落物,各归还元素的排序为Ca>N>K>Mg>P。西藏原始林芝云杉林中各器官的碳元素含量差异不大。生态系统中碳储量高达305.6 t.hm-2,其中乔木层储量最多,占总量的48.29%,其次是土壤层,占总量的38.31%。林分年固碳速率为3.58 t·hm-2.a-1,其中以乔木层固碳速率最大,占总量的70.57%。更多还原

【Abstract】 Subalpine dark coniferous forest in Tibet is one of the relatively intact natural forests in China. Structure, biomass, productivity, hydrology and nutrient cycling were investigated in a P. likiangensis var. linzhiensis forest ecosystem in order to examine the mechanism of forming a high stock volume in the forest and provide the basic data of structure and functions of forest ecosystems in the high elevation area.There were 116 generas,53 families and 144 species of plants in the primary P. likiangensis var. linzhiensis forest in Tibet, in which Rosaceae and Asteraceae were dominant families. The community was composed mainly of temperate generas (76.14%), and generas and families with single species had a large proportion too. Species richness and diversity index were low, while the evenness and dominance index were high, indicating that the community was at the climax succession stage. The forest, with pitch and large diameter trees to be predominant, had a descending population growth. Analysis of the spatial point pattern showed that small diameter picea tended to have an aggregated distributed pattern in small area, and arbor was close to a random distribution pattern as growth. The gap makers of the forest based on large canopy gap with area of more than 100 m2 were mainly pitch diameter stem break. The main regeneration of the stands was middle gap, as regeneration amount and height growth of saplings of middle gap were 3.45 and 1.5 times that of the adjacent canopy respectively.Appropriately 80% of the biomass was accumulaited in the lower part of tree,86% of root biomass was concentrated in the 0～0.60 cm in the soil of standard wood of the primary P. likiangensis var. linzhiensis in Tibet. On the horizontal pattern, branch and leaf biomass in the open space was higher, but no difference in root in all directions. The total forest biomass was 367.49 t·hm-2, of which the tree layer consisted of the largest proportion (75.28%), followed by litter layer, the understory layer, dead wood, the shrub layer, interlayer plants (vines+moss), herb layer. The distribution of biomass in tree layer was ranked in the order of stem> root> bark> branches> leaves, and with the growth of trees, the proportion of stem and bark increased, while the branches and leaves the proportion decreased and the ratio of leaves and roots gradually reduced.The net primary productivity of the primary P. likiangensis var. linzhiensis forest in Tibet was 10.65 t·hm-2·a-1, in which tree layer had the most productive (46.96%), followed by understory layer, shrub layer, moss layer, herbaceous layer and the layer of plant. The law of productivity distribution of tree layer was ranked in the order of stem> branches> leaves> roots> bark. The diameter and height growth rate of the primary P. likiangensis var. linzhiensis forest was not synchronized. The whole growth process could be divided into the young, fast growing and fast-growing stable. The fast-growing period could be up to 100 years, coupled with the interference of non-toxic pest, and the accumulation of the P. likiangensis var. linzhiensis is very high.The annual precipitation in the primary P. likiangensis var. linzhiensis forest in Tibet was 716.4 mm, mainly occuring in the period from April to September. During the growing season, canopy interception was 338.6 mm, forest penetration of water was 316.3 mm, stem flow was only 0.9 mm. Litter average ply was 5.0 cm, maximum water holding capacity was 323.13%, the effective holding capacity is up to 92.26 t·hm-2, litter layer from top to bottom, water holding capacity decreased. Forest soil increased with depth, capacity increased, but the maximum water holding capacity, capillary water holding capacity and the minimum water holding capacity are gradually decreased, the same as soil capillary porosity and total porosity, it indicated that the water holding capacity of soil with depth increased gradually weakened. The nutrients in precipitation were lower. After passing through the canopy, SO42-, Zn, and Cl- concentrations in the throughfall decreased, while the other elements in the throughfall increased. After infiltration through the soil, SO42-, Zn and Fe concentrations decreased, while the other elements increased.Litter production in the P. likiangensis var. linzhiensis forest in Tibet was 3.40 t·hm-2·a-1, of which the amount of spruce branches and leaf litter consisted of 24.3%, 26.1%. Highest litter production occurred in the early and late growth of a year. When the sample bags was placed below moss, the decomposition rate was high. The initial decomposition rate and environmental temperature was linearly correlated. The leaf litter decomposed rate faster than twigs, and weight loss rate was 3 times higher after one year. The half-life of litter leaf decomposition was 1.75 years, while litter sticks were up to 8.08 years. With the decomposition time, K concentration in litter decreased fastest, after one year other nutrient elements decreased by nearly 1/2, but Ca concentration relatively increased in the middle process of decomposition. The nutrient release in the decomposition process differed significantly. For example, the release of K was 76.36%, while the release of Ca was only 24.01% one year later.The nutrient content was the lowest in stem of standard wood of the primary P. likiangensis var. linzhiensis forest in Tibet. While N, P, K elements in leaves were higher in the year. Accumulation of forest soil nutrient level was highest, but the effective utilization rate was only 1～3%. Nutrient was mainly accumulated in tree layer, in particular in dry wood, while the least was in leaves. Five nutrient element accumulation rate was 104.81 kg·hm-2·a-1, and the order was ranked as Ca> N> K> P> Mg, but the accumulation rate of each element vared in different organs of the tree layer. The total return amount of forest was up to 169.288 kg·hm-2·a-1, in which the return amount of litter was highest, followed by ground litter. The order of the return elements was ranked in the order of Ca> N> K> Mg> P.Carbon content were similar in different organs of the primary P. likiangensis var. linzhiensis. Carbon storage of ecosystem was up to 305.6 t·hm-2, which mainly came from the tree layer, accounting for 48.29% of the total, followed by the soil layer, accounting for 38.31%.Forest carbon sequestration rate was 3.58 t·hm-2·a-1,which the tree layer of the carbon sequestration rate was highest, accounting for 70.57% of the total carbon fixation rate.更多还原