| This research work focuses on natural shrub communities of Zagunao arid valley, which is the first-grade tributary of the upper reaches of the Minjiang river. This paper intend to find the critical environment factors which influence diversity and production of shrub communities on the basis of analysis of the plant characteristic, minimum species area, elevation patterns of species diversity, elevation patterns of bio-productivity, relationship between species diversity and bio-productivity and correlation between species diversity or bio-productivity and environment factors. This makes a detailed foundation and theoretical basis for vegetation restoration of arid valley region in the upper reach of Minjiang River. The results as follows:1. In this investigation region, there are 107 species of vascular bundle plant, which belong to 41 families and 88 genera separately. There are 45 shrub species, which belong to 20 families and 34 genera separately, and 62 herb species, which belong to 29 families and 56 genera separately. Thetype of plant is poor. There are obviously important families, including Leguminosae, Compositae, Rosaceae and Graminea.With the rising of elevation, the structure characteristic of shrub communities change from arid shrub communities to semi-moist shrub communities, and change from simple to complicated on the basis of analysis of the composition of dominant species, life-form spectrum, species frequency, and so on. It indicates that there is obvious pattern of species replacing along elevation gradients.2. Based on species-area curve, the minimum sampling areas (containing 60～90% species) are determined at different elevations.The sequences among 4 elevation gradients of shrub communities' minimum species areas (MSA) are 2 165m＞1 957m＞1 558m＞1 750m on north facing slope (NFS) and 2 200m＞1 985m＞1 578m＞1 781m on south facing slope (SFS). The MSA decreases first, and then increases with the rising of elevation. At elevation below 2000 m, the MSA on NFS are larger than that on SFS. However at the elevation around 2200 m, there is no difference among different facing slopes.Hence the MSA are set as 100m~2 (10mxl0m) and 200m~2 (10mx20m) could be satisfied with different precision level, and could reduce the number of sampling plots and work load in field investigating.3. The sequences among 4 elevation gradients ofαdiversity of shrub communities are 2165m＞1957m＞1558m＞1750m on NFS and 2200m＞1985m＞1578m＞1781m on SFS. Theαdiversity decreases first, and then increases with the rising of elevation. The scopes ofαdiversity's increasing and decreasing between elevation gradients are different. And it shows that: SFS＞NFS, herb＞shrub. At the elevation around 2200m, herb'sαdiversity on SFS are larger than NFS. Except for that, shrub and herb'sαdiversity on NFS are larger than that on SFS.4. Theβdiversities of shrub and herb between sampling sites at elevation around 1 550m and sampling sites at other elevations in NFS and SFS increase with the rising of elevation. Species and eco—environment have large difference between lower elevation and higher elevation. Between different communities, the species' similarity decreases, the rate of species' replacing increases with the rising of elevation.Theβdiversities of shrub between two bordering sampling sites increase first, and then decrease with the rising of elevation on NFS. But theβdiversities of shrub between two bordering sampling sites increase with the rising of elevation on SFS. Theβdiversities of herb between two bordering sampling sites decrease with the rising of elevation on NFS. But theβdiversities of herb between two bordering sampling sites decrease first, and then increase with the rising of elevation on SFS. The shrub species difference is very obvious from elevation 1750m to 1957m on NFS, and is very obvious from elevation 1985m to 2 200m on SFS. The herb species differences are very obvious from elevation 1578m to 1 750m on NFS, and is very obvious from elevation 1985m to 2200m on SFS. In these elevations, the species' replacing rate is very quick.5. The shrub layer's biomass takes the absolute proportion in shrub communities on NFS and SFS. On NFS, the sequence of all layers' biomasses in shrub communities is: shrub layer＞herb layer＞moss layer＞litter layer. In SFS, the sequence of all layers' biomasses in shrub communities is: shrub layer＞herb layer＞litter layer＞moss layer. In two slope facings, the sequence of all organs' biomasses of the shrub layer is: root＞stem and branch＞leaf＞flower and fruit. The underground biomass of shrub communities accumulates richly.The sequences among 4 elevation gradients of all layers' biomass and all organs' biomasses of the shrub communities are 2165m＞1957m＞1558m＞1750m on NFS and 2 200m＞1985m＞1578m＞1781m on SFS. The biomass decreases first, and then increases with the rising of elevation. The total biomass's differences of shrub communities are very obvious from elevation 1750m to 1957m on NFS, and is very obvious from elevation 1 985m to 2200m on SFS.All layers' biomass and all organs' biomasses of the shrub communities on NFS are larger than that on SFS. The ratio between underground biomass and aboveground biomass of shrub and herb layer increases first, and then decreases with the rising of elevation.6. The species diversity-bioproductivity patterns of shrub and herb in shrub communities are linearly increase. It means that bioproductivity of ecosystem increases along with species diversity's increasing. The many kinds of factors, such as species diversity, species formation, biological characteristic of plant, climate and interfering intensity, have influence on relationship between species diversity and ecosystem function.7. Lacking water, full alkalescency, calcification and low effective fertile level are the major characteristic of soil in this region. The sequences among 4 elevation gradients of soil chemical fertile are 2165m＞1957m＞1558m＞1750m on NFS and 2200m＞1985m＞1 578m＞1781m on SFS. The soil chemical fertile on NFS is richer than that on SFS.8. The result of correlation analysis between species diversity or bio-productivity of shrub communities and environmental factors indicates that there are positive correlations between environmental factors (elevation, slope facing, soil moisture, available N, available K, Organic matter, total N, total K) and species diversity or bio-productivity. And there are negative correlations between environmental factors (pH value, available P, total P and total Ca) and species diversity or bio—productivity. The results of step—regress analysis and principal component analysis indicate that vegetation distribution is affected synthetically by soil moisture, soil nutrient and micro—topography.
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