Growth Characteristics Of Picea Wilsonii And Its Response To Climate Change In Datong River Basin,Qinghai

Global climate change profoundly affects the growth of trees,and although many tree growth and climate related studies have been conducted in the Qilian Mountains,the effect of climate change on the growth process of Picea wilsonii has rarely been addressed.In this study,we selected three different slopes（flat slope≤15°,medium slope 15°～25°,steep slope≥25°）and two different elevations（2300 m,2600 m）of the typical pure forest samples of the Picea wilsonii in the Beishan forest area of the Datong River Basin,Qinghai.Then we analyzed the growth process of Picea wilsonii at breast height（DBH）,tree height（H）and wood volume（V）by trunk analysis and fitted the growth model of the three.We also analyzed the response process of radial growth of Picea wilsonii to climate change by dendroclimatology,and proposed the healthy management technology of Picea wilsonii natural secondary forest according to the non-spatial structure characteristics and growth law of Picea wilsnoii in order to provide a theoretical basis for the healthy management of Picea wilsonii forests in Beishan forest area.The results of the study are as follows:（1）The non-spatial structure characteristics of Picea wilsonii are significant different under different stand conditions.The diameter at breast height and tree height（DBH:18.25±0.76 cm,H:16.73±0.55 m）were significantly greater on flat slopes than on steep slopes（DBH:16.14±0.48 cm,H:13.35±0.34 m）.Tree height was significantly higher at 2300 m elevation（H:17.04±0.47 m）than at 2600 m elevation（H:13.56±0.64 m）.（2）The annual growth rate of the diameter at breast height increased faster than the average growth rate,and reached the growth peak at 20 a.The annual growth rate and average growth rate of the height reached the growth peak at 70 a.The annual growth rate and average growth rate of the wood volume increased with age,and had not reached the mature age and the growth peak at the end of the statistical period at 80 a.We chose Richards,Quadric Curve,Logistic and Gompertz as the growth models to fit the growth process of DBH,H and V of Picea wilsonii,and the Richards model has the highest accuracy with R² greater than 0.99,which can be used as a prediction model for the growth process of Picea wilsonii in this area,and the fitting equations were as follows:H=270.1862×(1-e^-0.001×T)^1.1414,R²=0.9926D=31.7334×(1-e^-0.0172×T)^1.6316,R²=0.9986V=0.5392×(1-e^-0.9991×T)¹,R²=0.9999where H is tree height;D is diameter at breast height;V is wood volume;and T is age.（3）At 2600 m altitude,the radial growth of Picea wilsonii was significantly negatively correlated with the Palmer drought severity index（PDSI）in June,July,November and December of the previous year,and showed a significant positive correlation with the precipitation in June and March of the current year and the temperature in June of the previous year,February and June of the current year,indicating that superior hydrothermal conditions can significantly promote the radial growth of Picea wilsonii at high altitudes.However,with the warming of the climate during 61 years,the precipitation in August of that year gradually changed from negative to positive correlation,and the average temperature in August and September of that year gradually changed from positive to negative correlation,indicating that the climatic factor limiting the radial growth of Picea wilsonii at high altitude during summer gradually changed from temperature to precipitation.The radial growth of Picea wilsonii at2300 m elevation gradient was significantly and negatively correlated with the temperature in June of the previous year and June of the current year,which indicated that high temperature in summer significantly inhibited the radial growth of Picea wilsonii at lower elevations.With the warming of the climate during 61 years,the radial growth of Picea wilsonii at low elevation gradually changed from negative to positive correlation with the precipitation and mean temperature in June of the previous year,which indicated that the radial growth of Picea wilsonii at low elevation was more susceptible to the limitation of moisture and temperature in the previous year,which implied that the effect of temperature and moisture on the radial growth of Picea wilsonii at low elevation had a lag.