| The implementation of large-scale aerial seeding afforestation has cultivated rich reserve forest resources for the whole country.Affected by special afforestation methods,its stand characteristics were different from those of artificial forests in the general sense.In addition,due to its large scale,the problem of aerial seeding forest tending and management was becoming more and more prominent.Most of the aerial seeding forests degenerate into "low-quality and low-efficiency forests",which cannot effectively exert their functional benefits.Reasonable spatial structure of forest was the basis for exerting various functions of forest.Therefore,understanding the spatial structure characteristics of aerial seeding forest stand and mastering its change law plays an important role in the management of aerial seeding forest.Taking the Pinus tabuliformis aerial seedling forest in Liuling forest area as the research object.Based on the unitary distribution of spatial structure parameters to explore the spatial structure characteristics of P.tabuliformis aerial seeding forest in different aspect,the comprehensive evaluation method and entropy weight method were used to construct a comprehensive index of spatial structure for quantitative description and hierarchical evaluation of its spatial structure.Taking this as the objective function of stand spatial structure optimization,the optimization simulation of P.tabuliformis aerial seeding forest was carried out,which provides a theoretical basis for the optimization of stand spatial structure and the formulation of reasonable management measures.The main results were as follows:(1)The DBH growth of P.tabuliformis aerial seeding forest in different aspect was in the state of moderate to inferior,there were many small size trees in the forest,and the tree size differentiation was obvious;The average uniform angle index of stand in each aspect was within the range of [0.475,0.517].The horizontal distribution pattern of trees belongs to random distribution pattern,and the horizontal distribution of trees is ideal;the average storey index of each aspect stand: sunny slope(0.339)< shady slop(0.402)< semi sunny slope(0.435)< semi shady slope(0.472)slope,all aspect stands belong to open light environment,and the sunlight condition of sunny slope stand is the best;From the average competition index of stand,the stands in each aspect were under medium competition pressure;the difference of stand mixing degree among different aspect was significant.Most trees in the sunny slope stand belong to zero mixing,the stand as a whole belongs to weak mixing,and the single species aggregation of P.tabuliformis was serious;the semi sunny slope stands were moderately mixed,and the single species aggregation of P.tabuliformis was obvious;Semi shady slope and shady slope belong to intensity mixing,and the level of stand mixing was high.(2)Combined with entropy weight method and comprehensive evaluation method,the comprehensive index of spatial structure was constructed.The objective weight of each spatial structure parameter was determined by entropy weight method.The order of weight was as follows: neighborhood comparison(0.2896),mingling index(0.2500),open comparison(0.1721),storey index(0.1412),competition index(0.0864)and uniform angle index(0.0605).The comprehensive index of stand spatial structure: sunny slope < semi sunny slope < semi shady slope < shady slope,the evaluation grade of stand spatial structure was grade 3,about 1/3 of the trees in each aspect,the evaluation grade of stand spatial structure is grade 1 and 2,and there were many trees with unreasonable spatial structure.(3)Taking the comprehensive index of spatial structure as the objective function,the optimization model of stand spatial structure of P.tabuliformis aerial seeding forest was constructed,and the investigation sample plots were simulated and optimized.All spatial structure indexes were improved to varying degrees,which could achieve the goal of optimizing stand spatial structure. |
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