The Situation Analysis Of Vegetation Succession In Converting The Land For Forestry And Pasture In Northern Main Areas

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.