Study On Site Quality Evaluation Of Pinus Tabuliformis Plantation In Luonan,Shaanxi

Forest site classification and site quality evaluation are the basis of afforestation design,evaluation of forest potential productivity and forest management.Pinus tabuliformis has become one of the important afforestation tree species in Northwest China because of its drought and barren resistance and strong adaptability.It plays an important role in maintaining the ecological environment and water conservation.In this study,the P.tabuliformis plantation in Luonan,Shaanxi province was taken as the research object.We set up 63 sample plots,of which the size was 20 m×30 m in the study area.We investigated the growth indexes such as tree height,DBH and crown width of P.tabuliformis and recorded the site conditions such as slope,altitude,slope position and slope direction.This paper studies the relationship between the growth and site of P.tabuliformis plantation in Luonan area of Shaanxi province,so as to divide the site types and evaluate the site quality grade.The main research results are as follows:（1）The average DBH of P.tabuliformis plantation is 8.7cm in Luonan research area of Shaanxi province.The average DBH of P.tabuliformis in 10,20,30 and 40 years are 5.4cm,8.2 cm,9.6 cm and 10.4 cm respectively.The DBH distribution of P.tabuliformis conforms to the normal distribution.The diameter growth of P.tabuliformis is flat distribution and varies greatly,and the distribution curve is mostly positive deviation in the sample plot.（2）The growth of dominant trees in P.tabuliformis sample plots with different forest ages was compared and analyzed in the study area.It was found that the average DBH and tree height of dominant trees increased significantly with the growth of forest age in the sample plots.The average DBH,tree height and single tree volume of 10-year-old dominant trees of P.tabuliformis were 5.6 cm,3.4 m and 0.0055 m³respectively.The average DBH and tree height increased rapidly from 10 to 20 years,increasing by 3.3 cm and 3.9 m respectively.The average volume of a single tree increased significantly,reaching 0.0190m³,0.0160 m³and 0.0096 m³per decade.（3）The quantitative theory I is applied to the multi factor comprehensive analysis of P.tabuliformis site in Luonan:the forest age,slope,altitude,density,slope direction and slope position are selected as the influencing factors,and the prediction equation of P.tabuliformis average height is y=3.601068+3.222975?（1,2）+4.486272?（1,3）+5.413367?（1,4）+0.817348?（2,1）+0.324285?（2,2）+0.562175?（3,1）-0.000215D+0.402303?（5,2）+0.327001?（5,3）-0.074919?（6,2）.In the formula,the first number is the label of different factors,and the second number is the category number.（4）According to the four site factors of slope,altitude,slope direction and slope position,the site of P.tabuliformis plantation is divided into 36 different site types through quantitative theory I.P.tabuliformis plantation grows better on shady slope,middle slope,altitude 970-1140 m and slope<20°in Luonan county.The sample plots with medium and excellent site quality evaluation account for 65.08%of the total survey sample plots in the study area,indicating that the site conditions of most P.tabuliformis planting areas are good in Luonan County.（5）On the basis of obtaining the site quality evaluation grade,the data of 51 sample plots are discriminated and analyzed through quantitative theory II.The discrimination coordinates of sample centers of different site quality grades are obtained as follows:P_best:（0.07849,-0.0207）,P_good:（0.203492,0.244004）,P_bad:（0.458577,0.125059）.The site quality grade can be quickly judged.The back judgment accuracy of the model is 87.34%,indicating that it can be used to judge the quality grade of Luonan site.