Research On Stand Structure Regulation Technology Based On Forest Health

"Tree planting and grass planting activities in Northwest China"in Haidong loess area of Qinghai Province since 1980s,after several periods,the"Three North"shelterbelt construction project,natural forest protection project,and conversion of farmland to forestry project have formed an artificial forest with a basic green area.During this period,the afforestation design mainly adopted the unrevised"Afforestation Technical Regulations GB/T 15776",the timber structure design of the timber forest,and the pure forest design was horizontal and vertical;At the beginning of this century,after China's forestry management began to be classified,large-scale plantation forests and secondary forests in the northwest were classified as ecological public welfare forests.After nearly 20 years of closed management,due to lack of parenting management,with the growth of trees,the existing forest canopy,stand density,tree species composition and age composition are extremely unreasonable,the structure and function of artificial forest are single and its stability is poor,and the problems of pests and rats appear constantly.In this study,the ecological public welfare forest in three areas of Datong County,Xining City,Qinghai Province were studied,to build a forest health assessment system,using analytic hierarchy process and comprehensive index method to conduct forest health assessment in three research areas,according to the results of forest health evaluation,target forests suitable for improving forest health level in various regions were selected,and two typical plots were selected for structural control.The forest structure control technologies suitable for Anmentan,Targou,and Yangjiazhai were summarized and proposed.The main conclusions are as follows:(1)The weight value of 22 selected health evaluation indexes was determined by AHP,the health index of 32 woodlands was determined by comprehensive index method,and the health grade was determined,the results showed as follows:the middle age mixed forest growing on the shady slope was the healthiest;Pure broadleaf forests are healthier than pure coniferous forests,and middle-aged forests are healthier than younger and mature forests.The forest growing on the sady slope is healthier than that growing on the sunny slope.(2)Through the study on the distribution map of forest health in three study areas,it is concluded that:The main forest land in the Anmentan is the sub healthy forest land,accounting for 81.33%of the total,and the area is 98.21 hm~2;The area of forest land above the healthy state is 92.92 hm~2,accounting for 94.9%in the Targou;The proportion of forest land in sub-health state of Yangjiazhai is 46.4%,and the area is 80.94hm~2;The area of forest land above the health level in the three study areas is 195.55hm2,accounting for 49.7%of the total area of forest land in the study area,it accounts for the most,forests in the study area are generally healthy.(3)The criterion-level indicator health score is:Stand structure(0.2965)>Site condition(0.1328)>Stand resistance(0.0923)>Stand productivity(0.0731).The main reasons that affect the health of forest stand are as follows:The forest density is too high and the forest composition is single,which makes the soil water content of forest land low,the productivity of forest is low and the resistance is poor.(4)Structural optimization control measures for typical forest land:Two adjustments were made to Qinghai Spruce Forest No.1,Adjust it from uniform distribution to random distribution,the average mixing degree increased from 0.0192 to 0.4706,and changed from near zero to moderate.The average angular scale of No.13 forest land was adjusted from 0.3619 to 0.3334,it is adjusted from cluster distribution to random distribution,the average mixed degree of stand increased from 0 to 0.5868,and the mixed degree changed from zero to intensity.(5)According to the results of forest health evaluation,the target forest stand with structural adjustment is selected,combined with the control measures of typical forest land,the corresponding structural control principles are put forward,the target trees and disturbed trees should be determined reasonably,and the disturbed trees should be cut according to the reasonable density of forest land;For the felled forest land,other tree species shall be allocated in the form of random distribution,main configuration forms:Planting qinghai spruce in populus cathay forest;Planting white birch in qinghai spruce forest;Planting qinghai spruce in white birch forest;Planting caragana in sabina przewalskii forest;Planting sabina przewalskii in caragana shrub forest.