西北地区红桦天然次生林立地质量评价OACSTPCD

A total of 85 temporary plots of natural secondary forest of Betula albosinensis were set up in Shaanxi,Ningxia,Gansu and Qinghai provinces.Using age-tree height and DBH data as analytical re-sources,9 tree growth models were selected to fit the guide curve,and the site index table and site form ta-ble were compiled by the method of relative advantage height.The site quality in four different regions was compared by the two methods to realize the scientific evaluation of site quality of natural secondary forest of B.albosinensis in northwestern China.The results showed that the optimal guiding curve equations of the site index and site form were H=18.073/{1+exp[-(A-22.571)/9.144]} and H=19.793/{1+exp[-(D-12.218)/6.588]},respectively,and the fitting correlation coefficients were above 0.95.The basal age was determined to be 40 a,the basal DBH to be 20 cm,the exponential distance to be 2 m,and a total of 6 site quality grades of 10-20 m were demarcated.The site index table and the site form table showed that the Chi-square values of the two tables were both less than the critical value,and the accuracies of the drop point test were 95％and 97.5％,respectively,which met the accuracy requirements of the table prepara-tion.Both of the two methods could well reflect the site quality of the natural secondary forest of B.al-bosinensis.Moreover,the two methods showed a good consistency in the site quality evaluation of the four regions,among which the site quality of Shaanxi Huoditang Forest Farm was the best,followed by Ningxia Erlonghe Forest Farm.The site qualities of Qinghai Beishan Forest Farm and Gansu Taoping Forest Farm was in general level.