Study On The Gully Vegetation Of Junger Loess Hill-Gully Region

Junger loess hill-gully region is situated in the transition zone of Loess Plateau and Ordos Plateau.Its climate belongs to typical semiarid continental one and its zonal vegetation is Stipa bungeana steppe.Here,the interlaced gullies and hill ridges constitute a very special "gullies-hill ridges complex system",in which the water and heat are redistributed due to fragmented and interlaced gully landforms,finally leads to the complex and unique vegetation type,i.e.gully vegetation.At present,researches on the characteristic,distribution and succession of gully vegetation are far less than sand vegetation and mountain vegetation.The systematic deep researches on gully vegetation are helpful to develop research field of vegetation ecology and can provide scientific basis for establishing natural regionalization scheme reasonably,which are also practically significant to vegetation construction and comprehensive management of soil and water conservation in the loess hilly-gully region.Last ten years,although Stipa bungeana steppe mainly distributed on the hill ridges was seriously damaged because of natural and human factors,the gully natural vegetation here was not destroyed basically by human.Therefore it is an ideal loess hilly and gully region for studing gully vegetation.The main results were as follows by four years field investigations,experimental observations and deeply study with great concentration.1.Characteristic of the plant species in Junger loess hill-gully regionThe life form spectrum,water ecotype spectrum and flora geographic composition of the plant species in Junger loess hill-gully region were all similar to the composition of mountain species in the same zone.The gully system was not only one of the enrichment centers of biodiversity in steppe region,but also a accommdated section and diffused corridor of different flora components.1.1 Species compositionThere was abundant species composition.A total of 472 vascular plant species were recorded in Junger loess hill-gully region,belonging to 245 genera and 73 families,according to the specimens collected through field investigating.The species richness was higher than that in Musu sandland and Dongsheng tableland.1.2 Life form spectrumThe composition of life form spectrum was of high diversity.Comparing with Stipa bungeana steppe,the proportion of natural shrubs increased by 7%,and that of perennial herbs decreased by 10%despite of their absolute predominance.,The proportion of trees,woody climbers, hemi-parasitic shrubs,parasitic herbs,biennial herbs and ephemeroid plants was small(6.8%,of which trees occupied 3.2%),but their existence greatly enriched the plant life form spectrum of hilly and gully region.1.3 Water ecotype spectrumBeing obviously different from the predominance of xerophytes in typical steppe,the plant water ecotype spectrum in Junger loess hill-gully region mainly consisted of mesophytes,the proportion of which were 29.4%higher than that of xerophytes.1.4 Flora geographic compositionThe flora geographic composition of Junger loess hill-gully region was mainly composed of 43.65%temperate zone components and 31.15%east Asian components,and the steppe components were only at the third place occupying 14.82%of total.The flora geographic composition was more similar with that of mountain in steppe region(such as Daqing mountain, Jiufeng mountain and saihanwula mountain),that is,the proportion of east Asian forest components was distinctly higher than that of steppe components.2.Community types of the gully vegetation in Junger loess hill-gully regionThere were 4 vegetation types in the gully,they are sparse forest,shrub,steppe and low wetland, including 34 formations and 134 associations.The sparse woods included 3 formations:Form. Juniperus rigida,Form.Platycladus orientalis and Form.Ailanthus altissima.The shrub contained 7 formations which were Form.Rosa xanthina,Form.Hippophae rhamnoides subsp,sinensis,Form. Ulmus macrocarpa,Form.Zizyphus jujuba var.spinosa,Form.Periploca sepium,Form.Caragana stenophylla and Form.Caragana davazamcii.14 formations were comprised in steppe involving Form.Artemisia giraldii,Form.Artemisia sacrorum,Form.Caryopteris mongholica,Form. Artemisia ordosica,Form.Lespedeza davurica,Form.Thymus serpyllum,Form.Bothriochloa ischoemum,Form.Stipa bungeana,Form.Stipa grandis,Form.Stipa breviflora,Form.Stipa gobica, Form.Poa sphondylodes,Form.Leymus chinensis and Form.Cleistogenes caespitosa.And there were 10 formations within low wetland vegetation composed of Form.Calamagrostis pseudophragmites,Form.Carex duriuscula,Form.Agrostis gigantean,Form.Phragmites australis, Form.Carex appendiculata,Form.Eleocharis intersita,Form.Scirpus triqueter,Form.Typha angustifolia,Form.Typha minima and Form.Potamogeton sp..3.Concept and characteristic of the gully vegetation3.1 Concept of gully vegetationGully vegetation is regarded as the combination of various plant communities developing on different soils and parent materials(matrix) in the gully with warm-dry(on sunny slop), cool-moist(on shady slop) and warm- humid(in open gully floor) environmental conditions,which is distinctly different from the zonal vegetation types.It can be viewed as neither a single vegetation type nor an unit in vegetation classification system,but the vegetation compound series combined by a group of different vegetation types according to certain rule.3.2 Characteristic of the gully vegetation①The gully vegetation in Junger loess hill-gully region generally possessed some cross-region and super-zonal vegetation types with higher stability.For example,in the gully of Junger loess hill-gully region with suitable habitats the stable communities could be formed from Form.Juniperus rigida,Form.Platycladus orientalis,Form.Ailanthus altissima,Form.Rosa xanthina,Form.Hippophae rhamnoides subsp,sinensis,Form.Zizyphus jujuba var.spinosa,Form. Ulmus macrocarpa,Form.Bothriochlo aischoemum in forest steppe region and Form.Stipa breviflora in desert steppe region.②The types of vegetation were various and.restrictive factors were complex in Junger loess hill-gully region.The distribution of gully vegetation was affected by many ecological factors including:i its own characteristics of gully,such as slope degree,slope aspect,slope length,gully width,soil type and matrix of gully and slope;ii zonal climate and adjacent geology and geomorphology,all of which resulted in relative complex gully vegetation types.③The gully vegetation in Junger loess hill-gully region had an obscure characteristic of continuous and gradual change.For instance,Artemisia giraldii steppe could distribute from Loess Plateau in northern Shaanxi to the south of Junger in Inner Mongolia,and brokenly northward to upstream gully heads of various river course in this region,but didn't further expand due to the prevention of Kubuqi sandland and Donsheng tableland.In the northward diffusion process of some community types distributed in the south of this region,the gradual transition from the hill ridges to the gully and gradual change process of distribution from the sunny slopes to the shady slopes were found.4.Succession rule of gully vegetation in Junger loess hill-gully region4.1 The positive succession series of gully vegetation on the loess matrixOn the shady slope,the successive phases were as follows:bunching stage of pioneer plants dominated by rhizome grasses and annual and biennial herbs—caespitose small grasses—high caespitose grasses——shrubby high caespitose grasses.On the sandshale shady slope of the gully covered with loess,the communities could develop further into sparse forest stage.On the sunny slope,the succession series included the following phases:bunching stage of annual and biennial pioneer herbs——small half-shrub——small caespitose grasses——caespitose grasses——shrubby caespitose grasses.And on the sandshale shady slope of the gully covered with loess,the gully communities could develop further into sparse forest steppe or sparse forest stage.Half-shrubs could not only be found in each stage of the community succession on shady and sunny slope,but also become constructive species.4.2 The positive succession series of the communities developed on the bare soft rock gully cliff was the following:sparse shrubs and half-shrubs(or bare gully and slope)——shrubs -half-shrubs-perennial forbs-rhizome grasses——shrubs-half-shrubs and caespitose small grasses——shrubby half-shrubs-caespitose grass steppe.4.3 The positive successive phases of the gully vegetation on the sandshale matrix were as follows: sparsehalf-shrub communities——half-shrubs-forbs——half-shrubs-caespitose small grasses——half -shrubs-caespitose grasses——shrubby half-shrubs-caespitose grasses——sparse forest steppe,and sparse forest could be further developed in some sections with better water conditions.5.Ecological effect of the gully vegetation in Junger loess hill-gully region5.1 The most direct effect was the increase of land area in the hill-gully region.Take small watershed Wufendi gully(a third level tributary of Yellow river situated in its right bank) for example,the existence of the gully made its actual area increase by 34.5%compared with its projection area,and therefore the biomass of natural vegetation increased by 32%(not including artificial vegetation).In the hill-gully region where the proportion of gully area was 30.2%of the whole watershed,the land surface area of the watershed could increase by 10.4%resulted from the gully.5.2 The gully slope was the vital place for soil and water loss in Junger loess hill-gully region,so the gully vegetation distributed on the slopes played an important role for soil and water conservation.The measurement of runoff and sediment indicted that the soil erosion amount of the slopes with vegetation obviously decreased and could reduce by 50 times than non-vegetation slopes under the case of high intensive rainfall(38.3 mm,24h).The experimental results showed that there was significant difference between the effects of heavy rainfall on soil erosion amount of the slopes with and without vegetation(＜0.05).5.3 There was distinct improvement effect of soil fertility for gully vegetation,especially for the vegetation distributed on the shady slope.For instance,the soil organic matter contents in 0-10cm soil layer in the Form.Artemisia sacrorum+Stipa grandia and Form.Stipa grandis distributed on the shady slope were 12.44g/kg and 11.43 g/kg,respectively 10.04 g/kg and 9.03 g/kg higher than those in loess matrix,just close to the soil improvement effects of about 30-yearold Robinia pseudoacacia woods and Platycladus orientalis woods. Differentiation of moisture and temperiture in gully environment is a obvious charicterastic, i.e.dry and worm in sunny slope,wet and cool in shady slope,worm and wet in gully bottom etc..It should be fully considered the charicterastic of habitat differentiation during vegetation consruction in Junger leoss hill-gully region.For this reason,it was suggested that:①herb vegetation is suited to hill ridge and sunny slope;②shrub grassland,Steppe-woodland or sparse woods;③artificial forest and agricultural farmland.