【作者】 刘硕；

【导师】 贺康宁；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2009， 博士

【摘要】 北方地区生态环境日益恶化,植被物种多样性锐减,土壤退化、沙化现象严重,直接影响农业生产的正常进行,退耕还林还草工程应运而生,但随着时间的增长,退耕地涌现了不少问题,其中主要是人工造林模式与天然林配置模式差异性问题。若要使此工程取得良好的生态效益,在人工生态恢复过程中,须根据不同地区植被适应性特点,采取近自然方式设计退耕还林还草地配置和管理技术。根据地带性和退耕模式的不同,本文选择具有比较完整退耕序列的内蒙鄂尔多斯、青海大通、山西吕梁地区,它们依次代表了黄土高原向沙漠(地)过渡带、黄土高原向青藏高原过渡带、黄土高原丘陵沟壑带。将北方主要退耕还林还草区植被演替过程和态势进行更深层地探讨,为人工退耕还林还草的生态恢复技术模式改进提供科学参考。本文选取内蒙鄂尔多斯、青海大通、山西吕梁的退耕还林还草地作为研究对象,通过对这些地区植被的大量群落学调查,综合TWINSPAN、DCA、CCA、典型相关分析、主成分分析等多元统计分析方法,结合主要造林树种林木需水量和水环境容量,围绕环境梯度的变化与植被数量特征的响应和相互关系,进行了植被分类、群落分布与环境因子的关系、种群生态位、群落多样性、种群空间格局、群落稳定性和植物蒸腾特性等植物群落演替过程的研究,得出以下主要结论:(1)黄土高原向沙漠(地)过渡带退耕还草地植被演替态势:半流动沙地(退耕5y)缓慢正向演替阶段(沙柳群落+沙打旺群落+沙竹巴锡藜群落随机或均匀分布)→半固定沙地(退耕5～10y)快速正向演替阶段(蓝刺头狗尾草群落+牛心朴子乳浆大戟群落集群分布)→固定沙地(退耕15～25y)趋于逆向植被演替(油蒿羊柴群落和柠条滨藜群落强集群分布)。植被演替的方向和植被群落组织结构水平的变化规律主要有以下4点:①整个群落水平随着退耕年限的增长、退化程度的降低,在半流动沙地到固定沙地演化过程中,退耕还草地的群落生态特性发展不稳定,退耕还草区的群落结构和组成还未达到顶级群落水平,群落生态特性波动较大。②油蒿种群在固定沙地(退耕25y)阶段已出现优于羊柴种群的生态特征,即羊柴种群开始出现萎蔫和枯死现象,密度下降,种群衰败,种群竞争性减弱。这预示下一个演替阶段油蒿种群将取代羊柴种群。③半固定沙地(退耕15y～20y)阶段是群落变化的敏感期,但退耕地整体群落植被是从沙生植物到多年生植物的变化过程证明了退耕还草地整体朝正向演替发展的态势。④以沙柳、油蒿、小叶锦鸡儿、羊柴为代表的主要造林树种的蒸腾耗水特性研究反映出,就目前黄土高原向沙漠(地)过渡区退耕还草地水分条件而言,无法实现所选造林树种的最低保证需水量,这导致该地带的退耕还草地种群生长受到水分条件胁迫,群落植被变化易趋于逆向演替。(2)黄土高原向青藏高原过渡地带退耕还林地植被演替态势:垂穗披碱草群系呈集群型(退耕0～18y)快速正向演替→银露梅群落和匍匐栒子群落呈强集群型(退耕18y～27y)缓慢逆向演替→华北落叶松群落、中国沙棘灌木群落和青海云杉+白桦林群系呈均匀型或集群型(退耕27y～55y)平稳正向演替。以青海云杉群落及其与白桦、沙棘混交林群落为优势种群。退耕0～27y阶段,群落物种的数量和种数有较大波动,退耕45年后群落稳定。目前黄土高原向青藏高原过渡区退耕还林地的水环境容量可以满足主要造林树种的耗水需求量,即该地区植被生长不受水环境条件制约,植被演替朝正向发展。(3)黄土高原丘陵沟壑地带退耕还林地植被演替态势:退耕5y缓慢正向演替阶段→退耕10y快速正向演替(伴有逆向演替特征)。演替特征在不同坡向变化明显:阳坡地由刺槐群落→油松丁香群落,半阳坡地由沙棘群落和虎榛子连翘群落→三裂绣线菊群落和黄刺玫群落,半阴坡地由黄刺玫群落和沙棘群落→黄刺玫群落和油松丁香群落,阴坡地由黄刺玫群落和油松丁香群落→虎榛子连翘群落。以油松刺槐群落、黄刺玫群落和铁杆蒿羊胡子群落为优势种群,且各种群均以集群方式分布。其中,阳坡多样性变化最剧烈,半阳坡、半阴坡和阴坡生物多样性变化规律相近。演替发生最明显的坡位是坡度15°～30°的地段。黄土高原丘陵沟壑地带退耕还林地植被群落生态特征不稳定,不同坡向的退耕林地中的群落分布集中,优势种群间生态位重叠度大,致使种间竞争加大,灌木和草本层对资源利用率高使人工林树种油松和刺槐大面积枯死衰败,造成群落稳定性差。同时封山育林的造林成分过于单一,物种多样性较低。黄土高原丘陵沟壑地带退耕还林地林木生长条件受到水分亏缺的制约,减缓了植被生长速度,降低了植被群落正向演替的速度。(4)从黄土高原向沙漠(地)过渡带、黄土高原向青藏高原过渡地带、黄土高原丘陵沟壑地带的退耕还林还草地的植被演替过程看,北方主要退耕地植被演替态势有共性亦有异性,但总体发展趋势是正向演替与逆向演替交错进行。相同点有两点,一是退耕初期即从物种有无到有的过程里,植被生态特征均称规模态势发展、物种多样性增长幅度大,也就是发生了正向演替。二是水环境容量不满足造林树种的林木需水量时,退耕地植被演替初期植被进行正向演替的速度慢、时间长。不同点有两点:①演替中期。退耕地植被演替发展过程并不都是延续前期发展态势,如黄土高原向青藏高原过渡地带和黄土高原丘陵沟壑地带。由于种间密度过大、土壤养分和水分竞争剧烈,导致种群衰退,造成了植被群落的暂时性逆向演替。②水环境容量与林木需水量适应性影响未来植被演替整体态势。黄土高原向青藏高原过渡地带呈稳定正向发展,而另外两个地带的植被趋向逆向演替。根据3个地带主要退耕还林还草树种的耗水特性和当地水环境容量适应性分析发现,黄土高原向青藏高原过渡地带水环境容量与优势种需水量匹配,另外两个地带呈现不足状态。由此可知,当种群密度达到一定程度,种问水资源竞争加剧,导致蒸腾耗水量大、耐寒性相对弱的物种枯死,形成暂时性地表裸露,造成演替序列逆向进行,该现象是水资源量与人工选择的造林树种或密度不匹配造成的。更多还原

【Abstract】 The over human interrupting causes the degeneration of natural vegetation communities and loss of biodiversity,which happened more seriously in the northern area of China.The different extents of damages in soil quality and water resource have close relationship with producing quantity of agricultural industry,which depended on environmental elements.Hence,the project of converting lands to forest and pasture appeared accordingly.However,during several decades,a series of problems has emerged in large numbers;especially the differences between article forestation configure pattern and natural forestry pattern.We have to take the closest program to manage the converting lands according to basic environment during human ecological recovery.As the variable regions and converting lands pattern,this paper chose the comparably intact time order of converting lands to forest and pasture in 3 regions,which are Ordos in Inner Mongolia representing altiplano-to-desert transition region,Datong in Qinghai representing Qinghai-Tibetan Plateau region and Luliang in Shanxi representing hilly-gully regions of the loess plateau.As a result,it is very significant for the availability of converting the land for forestry and pasture with reasonable establishment and management in northern areas.Therefore,we will achieve more reasonable pattern of converting the land for forest and pasture to arrive comfortable environment.Selecting Ordos in Inner Mongolia,Datong in Qinghai and Luliang in Shanxi as researching objects,revolving around the mutual responds and relationships between the environmental gradient and vegetation characteristics,this paper focuses on the research of the vegetation classification,the connection between community distribution and environmental factors,population niche,community diversity,community spatial pattern,community stability and transpiration effects by investigating a large number of vegetation communities in these three regions and combining multivariate statistics such as TWINSPAN,DCA,CCA,canonical correlation analysis,principal component analysis and the analysis of transpiration and water environmental capacity.The main conclusions this paper comes to are as follows:(1) The vegetation succession situation of altiplano-to-desert transition region:semi-moving dune (converting land for 5y) with slowly positive succession(Phyllotrstachys propinqua+Bassia dasyphylla, Astragalus adsurgens+Inula salsoloides,Salix psammophila with random or equal distribution)→semi-fixed dune(converting land for 5～10y) with fast positive succession(Echinops gmelini+Setaria viridis,Cynanchum komarovii+Euphorbia esula with centralized distribution)→fixed dune (converting land for 5～10y) tending to negative succession(poplar and elm plus Artemisia ordosica+ Hedysarum leave with intensively centralized distribution). There are 4 points explaining the changing pattern in the direction and organization of vegetation succession.①It is in fluctuating situation for the whole communities in different succession phrases from semi-moving dune to fixed dune.The vegetation diversity,composing ingredients and organization are all in great changing situation.Hence,present vegetation communities has not arrived the stable top-level state.②The species of Artemisia ordosica has appeared the ecological phenomenon of replacing the species of Hedysarum leave,which acts as wilting and exsiccation in the species of Hedysarum leave.It indicates that Artemisia ordosica will take over Hedysarum leave and become dominant species in next vegetation succession.③Semi-fixed dune(converting land for 5～10y) is the sensitive phrase,but whole converting land for pasture communities situation to positive succession.④The paper chose Salix psammophila,Artemisia ordosica,Caragana arborescens,Hedysarum leave as main forestation tree species to test their transpiration characteristic.Combining with the analysis water resource situation,the result shows that tree water requirement is unmatchable with water environmental capacity in altiplano-to-desert transition region.Therefore,the vegetation growing will be intimidated by less water,and the vegetation succession tend to negative situation.(2) The vegetation succession situation of Qinghai-Tibetan Plateau region:Elymus nutans community with centralized distribution in fast positive succession(converting land for 0～18y)→Potentilla glabra community and Contoneaster adpressus community with intensively centralized distribution in slowly negative succession(converting land for 18～27y)→Picea crassifolia+Betwla platyphylla community and Hippophae rhamnoides community with equal or centralized distribution in stable positive succession.The sensitive phrase is in the process of converting land for 0～27y,when vegetation community has strong fluctuation in species numbers and individual numbers.This fluctuation will decline after converting land for 45y.At present,the water capacity can satisfy the main forestation tree water requirement in Qinghai-Tibetan Plateau region,which means the vegetation natural growing is not restricted by water quantity.As a result,the vegetation succession normally tends to be positive direction.(3) The vegetation succession situation of hilly-gully regions of the loess plateau:converting land for 5y with slow positive succession→converting 10y with fast positive succession(coming along characteristics of negative succession).All ecological characteristics of succession in four different slope gradients are obvious:sunny slope is Robinia pseudoacacis community→P.tabulaeformis+Syzygium aromaticum Merr.EtPerry community,semi-sunny slope is hippophae and Ostryopsis davidiana+Forsythia suspensa Vahl community→Spiraea trilobata Linn.+Artemisia spp and R.xanthina community,semi-negative slope is R.xanthina community and hippophae→R.xanthina community and P.tabulaeformis+Syzygium aromaticum Merr.EtPerry community,negative slope is R.xanthina community and P.tabulaeformis+Syzygium aromaticum Merr.EtPerry community→Ostryopsis davidiana+Forsythia suspensa Vahl.The dominant species includes P.tabulaeformis,Robinia pseudoacacis,R.xanthina,A.sacrorum,Carex rigescens with centralized distribution.Distinctive diversity changes happened in sunny slope instead of similar changes in other three slopes.The most obvious gradient affecting species communities diversity locates between 15°and 30°.The converting land for forest in hilly-gully regions of the loess plateau has unstable community diversity characteristics and intensive distribution between different communities,so that species competition comes into a severe state.Shrubbery and herbaceous layer take up a large number of resources,which results in overarea fading of P.tabulaeformis and Robinia pseudoacacis.Therefore,the whole community is in unstable situation because of over pure forestation tree species. Due to water deficient,the normal plant growing is restricted in hilly-gully regions of the loess plateau.As a result,the processing rate of positive succession comes down gradually.(4) Concluding above three regions vegetation succession process and situation,the total situation in northern main converting land to forest and pasture tend to intersecting pattern between positive and negative succession.There are both common and differentia in the succession process.There are two common points in different converting lands.One is the prophase of succession belonging to positive process with most of community characteristics increasing fast.The other is the slow type of succession in the prophase all because of the dissatisfaction between tree water requirements and water environmental capacity.The differences also have two parts.The prime one is the medium phrase.Some of the regions have reversal direction of vegetation succession,such as Qinghai-Tibetan Plateau region and hilly-gully regions of the loess plateau.This phenomenon is raised by over species density,competition for soil nutritious ingredient.As a result,most of them declined and the whole vegetation communities’ succession temporarily come into negative succession.The other is the different future situation of vegetation succession depending on variable regions.Qinghai-Tibetan Plateau region has been come into a kind of stable succession phrase rather than the others.The reason according to this phenomenon is based on the competition of different vegetation communities for less regional water resource.The deficient water environmental capacity induces fluctuating vegetation succession process.更多还原