Study On Community Characteristics Of Pine And Oak Mixed Forest In The Middle Part Of Qinling Mountains

The objective of study is pine and oak mixed forest in the middle part of Qinling Mountain. The thesis focuses on the community characteristics of pine and oak mixed forest in the middle part of Qinling Mountain though typical sampling and random sampling techniques. Meanwhile, the thesis applies TWINSPAN to classify associations and DCCA to analyze the effects of environmental factors on communities’distribution and analyzes the relationship between biodiversity and environmental factors. The study shows:(1) Pine and oak mixed forest community is mainly distributed in the alpine zone of1000-2000m elevation. Due to different environment, the landscape scale is different in the south and north slope.The study sets34typical samples and records296species vascular plants, which belong to77families and178genera. Among those there are72Angiospermae plants,2Gymnospermae plants, and3Pteridphyta plants. The widely-distributed species include Pinaceae, Fagaceae, Rosaceae, Compositae, Gramineae, and Liliaceae. Tree layer has49species of plants, shrub layer has106species of plants, herb layer has141species of plants. The canopy of three layers are tree>herb>shrub.(2) Pine and oak mixed forest in the middle part of Qinling Mountain is classified into13associations based on TWINSPAN. There are:I Pinus armandii+Quercus aliena var.accuteserrata+Toxicodendron vernicifluum-Rubus corchorifolius+Celastrus orbiculatus-Carex rigescens, ⅡPinus.Tabuliformis+Quercus aliena var.accuteserrata+Cornus macrophylla-Lonicera Japonica+Celastrus orbiculatus-Carex tristachya+poa pretensis, ⅢPinus. Tabuliformis+Quercus aliena var.accuteserrata-Schisandra chinensis-Carex tristachya+Clematis florida, Ⅳ Pinus armandii+Pinus.Tabuliformis+Quercus aliena var.accuteserrata-Smilax chinal-Carex tristachya+Carex siderosticta, Ⅴ Pinus. Tabuliformis+Quercus aliena var.accuteserrata+Toxicodendron vernicifluum-Symplocos paniculata-Rubia cordifolia+Carex siderosticta,ⅥPinus. Tabuliformis+Quercus aliena var.accuteserrata-Rubus corchorifolius-Calamagrostis epigeios+Carex rigescens,ⅦPinus armandii+Pinus.Tabuliformis+Quercus aliena var.accuteserrata-Smilax stans-Carex rigescens+poa pretensis,Ⅷ Pinus.Tabuliformis+Quercus aliena var.accuteserrata-Litsea cubeba-Rubia cordifolia+Carex siderosticta, Ⅸ Pinus.Tabuliformis+Quercus aliena var.accuteserrata-Schisandra chinensis+Smilax stans-Carex tristachya+Rubia cordifolia, X Pinus.Tabuliformis+Quercus acutissima-Smilax stans+Symplocos chinensis-Agropyron cristatum, XI Pinus armandii+Quercus aliena var.accuteserrat-Euonymus alatus+Carex rigescens,ⅫPinus.Tabuliformis+Quercus aliena var.accuteserrata-Lespedeza buergeri-Roegneria kamoji, ⅩⅢ Pinus.Tabuliformis+Quercus variabilis-Lespedeza bicolor-Deyeuxia Clarion-Carex lanceolata. The associations whose dominant species are Pinus tabuliformis+Quercus aliena var.accuteserrata are the most, which takes up40%of the total number. This kind of association is the major mixed type in the middle part of Qinling Mountain.(3) Through analyzeing the DBH and height of tree layer of every association, after natural succession process for a long time, association Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅵ、Ⅶ will change from Pine and Oak mixed to Quercus aliena var. accuteserrata association; association Ⅵ、Ⅶ、Ⅸ、Ⅹ、 ⅩⅢ will remain the mixed type; association Ⅰ、Ⅺ will evolve to Pinus tabuliformis association.(4) The association of samples and the DCCA ordination of samples clearly reflect the relationship between the pattern of forest communities and environmental gradients. The first of DCCA ordination axes indicates the altitude and slope position gradients, and the second of that indicates the aspect and slope gradients. The correlation coefficients of elevation, slope and DCCA one and two axis arrived the most values respectively(-0.9462,-0.7957), so the main factors restricting distribution of the communities are altitude and slope in this area.(5) The index of species diversity shows between1200-1400m and1600-1700m the values of Simpson index、Shannon-Wiener index and Pielou index fall significantly, but the value of Patrick index raise significantly. Patrick index and Shannon-Wiener index, of three layers are herb>shrub>tree; Pielou index and Simpson index of three layers are shrub>herb>tree. Through analysis it can be concluded that altitudinal gradient has little effect on species diversity of associations, and human disturbance is a main factor which influences biodiversity.(6) The analysis of environmental factors and biodiversity shows:Exponential regression between Patrick index and0-20cm available phosphorus reaches significant level(P=0.0266), Binomial regression between Patrick index and20-40cm,40-60cm available potassium reaches significant level(P=0.026, P=0.0196). Binomial regression between Pielou index and20-40cm available nitrogen reaches significant level (P=0.0459). Linear regression between Shannon-Wiener index and standardization aspect reaches significant level (P=0.0384); Simpson index has no significant relation with all environmental factors. Thus, it can be concluded that aspect and other environmental differences are the main factor which cause species diversities of different associations of pine and oak mixed forest in the middle part of Qinling Mountains.