Transformation Effect And Ecological Risk Assessment Of Inefficient Public Welfare Forest In Huajialing

Loess hilly area as a key area of the western reforestation and ecological environmentconstruction where soil erosion and drought coexist, and vegetation restoration is more difficult,thus forming a large area of inefficient public welfare forest. In this study, Huajialing inefficientpublic welfare forest in loess hilly region was analyzed by using typical sampling method to studythe causes of inefficient forest, summarize and evaluate the effectiveness, ecological risk andpromotion prospects of the inefficient public welfare forest transformation, aims to providetechnical support and theoretical basis for inefficient public welfare forest structure adjustment andforest quality and functionality improvement. Preliminary results showed that:1. The tree species structure in Huajialing forest was too simple, age group structure wasextremely unreasonable. The inefficient Populus hopeiensis forest had a large proportion, whichoccupied66.1%of the total forest land area, and transforming artificial Picea asperata and Pinustabulaeformis forest only occupied30.1%of the total forest land area. Among them, most of Piceaasperata and Pinus tabulaeformis forest were young forest, while most of unreconstructed Populushopeiensis forests were mature forest. The mature forest of all region occupied66.8%of the totalarea.2. The main causes of Huajialing inefficient forest were natural factors and human factors.Natural factors performanced of dry cold and gale with relatively poor soil, which did not meet theaccelerated formation of inefficient Populus hopeiensis forest which liked water, fat, light of theecological characteristics.Human factors included single species selection, large planting density,irrational stand structure, serious pest, extensive management and serious vandalism.3. The constituent structure of the Picea asperata forests was relatively simple, and the structurecharacters of arborous layer were negatively correlated with that of shrub and herb layers in thethree parts; The DBH and the height of individual plant in the Picea asperata forest mainlydistributed in small height class and diameter class, and most were young forests. There was a bigdifference in the DBH and the height of the Picea asperata forest in, middle eastern and, influencedby site conditions. Furthermore, the Picea asperata forest in middle eastern part developed betterthan western part’s and southern part’s; The artificially Picea asperata forest was repressed by thehighly planting density, and the proportion of pure forest was too high, which restricted thestructure optimization of regional forest and would lead a negative effect on sustainable development of ecological public welfare forest in loess hilly region.4. There was a big difference in per unit volume and area of different mixed Picea asperataforest in Huajialing. Among them, most of Picea asperata forest were young forest, the standvolume was limited by the density, tree growth and other factors; Populus hopeiensis, which wasthe main tree species in conifer, mostly had a poor growth and were mature forest (most Populushopeiensis in mature or over-mature age), which also affected the forest per unit volume and area;while most of coniferous forest were also young forest, but the growth condition was better,therefore, the average DBH, tree height and per unit volume and area were all than pure Piceaasperata forests’ and conifer’s.5. The soil porosity and venting quality of the pure Picea asperata forests and its mixed forestafter transforming were higher than the pure Populus hopeiensis forest’s, which showed thatinefficient public welfare forest transformation promoted the soil improvement,the soil becomeloose, more conducive to root stretching and activities. The soil total N, P, K of the pure Piceaasperata forests and its mixed forest were higher than the average content of the pure Populushopeiensis forest’s, which indicated inefficient public welfare forest transformation produced agood improvement on soil nutrient status.6. According to forest ecological risk assessment system, combined with the occurrenceprobability, intensity and extent of historical data to confirm the5major sources of Huajialingforest belt, which were drought, wind, pests, frost and trees structure. The average ecological riskindex of69forest compartments in Huajialing was0.7533which was a moderate risk. There weresignificant differences in species composition with each compartment, average ecological risk ofpure Populus hopeiensis forest> average ecological risk of pure Picea asperata forest> averageecological risk of mixed forest, which was due in silvicultural process, the stability and resilience ofmixed forest ecosystem were better than pure forest, and Picea asperata stands had stronger abilityto resist risks than pure Populus hopeiensis stands.