Researches On The Relationship Between Structure And Ecologial Function Of Water And Soil Conservation Forests In Low Mountains And Hills Region Of Central Hubei Province

Water and soil conservation forest is mainly one type of ecological forest in low mountains and hills region of central China. Taking forest farms of Taizi mountain in Hubei Province as an example, totally selecting four pure forests (including Pinus massoniana stand, Cupressus funebris stand, Cunninghamia lanceolata stand and Quercus acutissima stand) and four mixed forests (such as coniferous and broad-leaved mixed forest, deciduous broad-leaved forest, Quercus acutissima mixed forest and coniferous mixed forest), in this research we focus on revealing the relationship between structure and function on the scale of stands and landscape. The purpose of the study is to provide more theoretical and practical evidences for ecology management of water and soil conservation forests in low mountains and hills of central China.The main results are as follows:(1) On the basis of analsing the characteristics of stand structure, it was clear to draw the following conclusions. The values of LAI of each stand in summer ranged from2.514-3.689, and the deciduous broad-leaved forests had the largest LAI values. The diameter distribution of pure stands were more close to normal distribution during the increse of stand age, however, the diameter distribution of mixed stands had three kinds of curves:reverse J-shaped curve, approximately normal distribution curve and multiple mountain-shaped curve. On the whole,50percent of8mixed stands had low mingling degree, and the mingling degree of coniferous and broad-leaved mixed forest were lower than those of deciduous broad-leaved forest. The nearly-mature stands and mature stands of four pure forests had the relatively high species richness of shrub layer. The species richness of shrub layer in mixed stands was8-10.The shrub coverage of all stands vary from7%to40%. In P. massoniana forests, the values of57and Cj between middle-aged stand and mature stand were biggest, which showed the shrub species in two stands had highest similarity.(2) The range of soil bulk density was from1.32g/cm3-1.41g/cm3. The values of capillary porosity varied from18.19%to54.75%, and the values of non-capillary porosity ranged from4.55%to15.28%. According to the national grade of soil nutrient, the soil in study area has the rich content of organic matter, total nitrogen, available nitrogen and available potassium,but the content of total phosphorus is scarce. The variation of soil nutrient in the layer of0-20cm reaches to middle level. By using factor analysis,the function of conserving soil was evaluated. It shows that there are some differences among each stands on conserving soil, and deciduous broad-leaved forests, Q.acutissima stands and C.funebris nearly-mature stand have optimal ecological function in order.(3)To analyse the water-holding capacity of canopy, shrub-herb layer, litter layer and soil layer, nine indexes were selected,which were biomass of branches and leaves maximum water capacity of canopy, biomass of shrub-herb, maximum water capacity of shrub-herb, litter total amount, effective retain capacity, non-capillary water-holding capacity and maximal water-holding of soil. The function of water-holding capacity was evaluated with the method of factor analysis. It can be conclused that deciduous broad-leaved forests, Q.acutissima stands and C. funebris pure stands have better ecological functionr.(4) The ecological function (including soil conservation and water-holding capacity) model of water and soil conservation forest in study area was constructed by analytic hierarchy process(AHP), then an integrated score for each stand was obtained. The results indicate that Q. acutissima stands, deciduous broad-leaved forests, and C. funebris nearly-mature stand rank at the top of the list, which means those type of stands have greater ecologial functions. Ecological functions of P. massoniana nearly-mature stand, P. massoniana mature stand, C. lanceolata nearly-mature stand, C. lanceolata nearly-mature stand, and coniferous and broad-leaved mixed forest are better than those of the coniferous mixed forest and the juvenile stand of three coniferous pure stands.(5) The significant influences of the stand structure factors on the ecological function factors were expounded by stepwise regression and path analysis.The factors, including soil thickness,LAI, litter thickness,tree mingling degree and stand age,have significant effect on the phsical and chemical property of soil. Stand age, stand desity and litter thickness have major impact on the water-holdig capacity of stands. Litter thickness is a key factor for the ecological functions of soil and water conservation forests. The model of stand structure and its ecological function is constructed as following, where Z is the quantitative indicator of ecological function of water and soil conservation forest, Xi stand age, X2stand density, X3stand average DBH, X4LAI, X5 average height, X6tree mingling degree, X7species richness of shrub-herb layer, X8coverage of shrub-herb layer, Xg litter thickness and X10soil thickness.(6) Based on the survey data of sub-compartments and stock map, the landscape structure and ecological function of water and soil conservation forests in Shilong farm and Xiannv farm were analyzed. The study area was divided into8landscape elements, which are P. massoniana forest, C. funebris forest, C. lanceolata forest, Q. acutissima forest, coniferous and broad-leaved mixed forest, deciduous broad-leaved forest, Q. acutissima mixed forest and coniferous mixed forest. The indexes of landscape structure, such as NP, CA, PA, PD, PA CV, ED, SI, FD and AI were selected in the article. After stepwise regression and precision test, the model of landscape structure and its ecological function was founded: Where Y1is total content of soil nutrient in water and soil conservation forests, Y2is the index of water-holding capacity in soil and water conservation forests, X1is PA, X2is PA CV, JX3is PD, X5is SI, X6is FD, X7is AI.(7) In summary, the deciduous broad-leaved forest, Q. acutissima mixed forest, Q.acutissima pure forest and C. funebris pure forests in study area have the optimum ecological function. Referring to the structure characteristic of these4types of stands, the ideal structures of water and soil conservation forestsin study area are established from the stand level. In a word, the ideal structures means uneven-age, mutiple layers and tree species mixed structure. In details, the ideal structures need to fit such characteristics: LAI>2.733, the diameter distribution of reverse J-shaped curve or approximately normal distribution, stand mingling≥0.5,the coverage of shrub-herb layer≈55%, species richness of shrub-herb layer>16, litter thickness>35cm. The role of litters should be cared about in the practice of forest ecology management.