Structure Optimization Technology Of Near-natural Stand Based On Water Water Conservation Function

Most of the existing artificial forests in Datong county,Qinghai Province,originated from the"Tree planting and grass planting activities in Northwest China"in the 1980s,followed by several state-level forest construction and protection projects.Since the classification of forest management began in 2003,the plantation and natural secondary forests in this area have been classified as ecological public welfare forests.After 20 years of ban management,the problems of these plantations gradually emerged,with single structure and function and poor stability,low forestry productivity,and most of the stands did not have the water conservation function of the plateau water tower area.Aimed at this situation,this study analyzes the site under the condition of main forest types in the vertical structure of canopy layer,litter layer and soil layer water conservation function of impact factor,build a set of evaluation for various types of forest water conservation functions of the comprehensive evaluation index system,and the research area of forest types on water conservation function evaluation.According to the evaluation results of water conservation function,the low-efficiency forest and its target stand types were determined,and the corresponding measures of forest structure adjustment were proposed for different stand types,so as to form a set of natural stand control technology in alpine hilly area of Qinghai Province.The main research results and conclusions are as follows:(1)Taking the types of stand on the shallow slope of a high mountain as an example,the factors affecting the water conservation function of the forest canopy,litter layer,and soil layer were analyzed,and the main influencing factors were determined.Canopy closure,canopy water holding capacity,litter thickness,effective litter storage capacity,0-20cm capillary porosity,0-60cm capillary porosity,0-20cm non-capillary porosity,0-60cm There are 10 main factors such as non-capillary porosity,0-20cm saturated hydraulic conductivity and 0-60cm saturated hydraulic conductivity.Based on this,an index system for evaluating the function of water conservation is established(2)AHP and comprehensive scoring methods were used to evaluate the water conservation function of the stand types of each site type.The results show that the types of stand with the best water conservation function under each site condition are:high shallow mountain shade gentle slope-Picea crassifolia kom×Betula platyphylla suk,medium shallow mountain overcast steep slope-Picea crassifolia kom×Populus cathayana rehd,medium shallow mountain and steep slope-Populus cathayana rehd,moderate shallow mountains and gentle slopes-Juniperus przewalskii kom×Caragana intermedia,low shallow mountain shade gentle slope-Picea crassifolia kom,low shallow mountain shade steep slope-Populus cathayana rehd,low shallow mountain shade gentle slope-Juniperus przewalskii kom.These stand types can be taken as the structure of the target stand type in the afforestation and stand structure reconstruction under the same site conditions.Other forest stand types were included in the scope of transformation,among which the Picea crassifolia kom,Betula platyphylla suk and Populus cathayana rehd on the shady-slope and Caragana intermedia on the sunny slope had the worst water conservation function under many site conditions,and were taken as the objects of spatial structure transformation of key stands.The same method was used to evaluate the water conservation function of the vegetation in Ta'ergou Forest Farm,Xishan Forest Farm,and Yangjiazhai Forest Farm.The results showe:The water conservation capacity of the dense Picea crassifolia kom,too dense Picea crassifolia kom×Larix principis-rupprechtii mayr,Betula platyphylla suk and Populus cathayana rehd×Betula platyphylla suk with severe snow are poor in Ta'ergou Forest Farm.The water conservation capacity of Populus cathayana rehd,Betula platyphylla suk,Larix principis-rupprechtii mayr and Picea crassifolia kom×Populus cathayana rehd are poor in Xishan Forest Farm.The water conservation capacity of Caragana intermedia is poor in Huangxi Village Forest Farm of Yangjiazhai.These types of forests are used as the object of structural transformation of vegetation in each area.(3)Taking the no.17 sample plot of Picea crassifolia kom in Targou Forest Farm as an example,the target stand type of Picea crassifolia kom was determined as Picea crassifolia kom×Betula platyphylla suk.According to the tree homogeneity index and constraint conditions,two selective cutting and one supplementary planting were finally adopted in the 17 sample plot to adjust the stand structure.After the adjustment of stand structure,the stand was in medium mixed and the distribution of trees was random.Canopy water capacity decreased by 2.35t/hm~2,the effective storage of litter decreased by 5.12t/hm~2,the maximum retention storage increased by 19.57t/hm~2,and the water conservation function was greatly improved.After the transformation,the growth vitality of Picea crassifolia kom was released,which provided conditions for the natural regeneration of the stand.The result of this adjustment is still far from the expected target stand,and it needs long-term structural management to adjust this stand structure to the optimal one.(4)According to the evaluation results of water conservation function,the forest types with strong water conservation capacity were taken as the basis for the structural transformation of low-efficiency forest,and the spatial structure of the forest was analyzed and optimized.In order to make the stand form mixed-age multilayer and have natural renewed stand structure,the structural transformation mode was developed for the low-efficiency forest:Picea crassifolia kom was arranged in pure forest of Betula platyphylla suk.Picea crassifolia kom was arranged in pure forest of Populus cathayana rehd.The mixed forest of Picea crassifolia kom×Larix principis-rupprechtii mayr was arranged with Betula platyphylla suk after density control and structure optimization.Betula platyphylla suk in pure forest of Larix principis-rupprechtii mayr.Pure forest of Caragana intermedia after the flat stubble,the forest was equipped with Juniperus przewalskii kom.