Natural Forest Structure Interpretation And Forest State Comprehensive Evaluation

Forest structure refers to the arrangement of individual trees and the connection of their attributes.The quantitative description of the spatial and size relationships among nearest neighbor trees is critical to understand the essential characteristics of forest structure,and stand state is directly related to the urgency and necessity of forest management.Therefore,the systematic interpretation of forest structural heterogeneity information and the comprehensive evaluation of stand state are crucial.Previous researches generally emphasize the accumulation of stand state or the the overall or unilateral characteristics of stand structure,did not containing other forest structural attributes or forming a complete interpretation system of forest structure.So the integrated expression of forest spatial and size structure was urgently needed,and how to scientifically measure the balance of forest state evaluation indices demanded further research.Therefore,the Quercus aliena var.acuteserrata natural forest of the Xiaolongshan Forest Region in Gansu Province was taken as an example.The uniform angle index(W),mingling(M),dominance(U)and crowding(C)were independent of each other and each index had five possible value degrees,we adopted zero-variate distribution,univariate distribution and multivariate distribution to describe three different resolution levels(i.e.,the overall,unilateral and multi-lateral characteristics)of forest spatial structure,respectively.Secondly,vertical projection dimensionality reduction and marginal distribution functions were used to reveal the quantitative relationships and intuitive expression ways among different N-variate distributions.Then coupling multivariate distribution functions(i.e.,copula method)were constructed to characterise stand spatial and size structure simultaneously.Finally,we took the stand state comprehensive evaluation of both Q.aliena var.acuteserrata natural forest and broad-leaved Pinus koraiensis forest in Jilin Province as examples,we tried to put forward indices to measure the balance among all evaluation indices of forest state based on isoperimetric theorem and equal circle theorem.The modified unit circle method was constructed to evaluate the overall stand state considering the accumulation and balance of forest state simultaneously,and thus it could give a comprehensively evaluation of the overall forest quality and effectively promote its harmonious development.The following conclusions were obtained:(1)In the Q.aliena var.acuteserrata natural forest,the whole forest and most trees were randomly distributed,well mixed and relatively dense.The most prominent characteristic of the whole forest was that most trees were randomly distributed or well mixed under different spatial structural parameter combinations.The results showed that W-U-M-C quadrivariate distribution could comprehensively characterize four aspects of forest spatial structure simultaneously,including spatial distribution pattern,tree species isolation,crowding and size differentiation degree.The proposed telescope method could systematically interpret spatial structural heterogeneous information at three different resolution levels(i.e.,the whole,unilateral and multilateral forest spatial structure).(2)The vertical projection dimensions and marginal probability distribution functions of the N-variate distribution formed by forest spatial structure parameters corresponded to several N-1-variate distributions.Therefore,the successive recursive process(i.e.,quadrivariate distribution?trivariate distribution?bivariate distribution?univariate distribution?zero-variate distribution of forest spatial structural parameters)could be realized based on vertical projection dimensionality reduction and marginal probability function,but the inverse process was not feasible.Different N-variate distributions made their respective advantages complementary to each other on quantitative characterizing forest spatial structure.3D figures with double coordinates could intuitively display the spatial structural heterogeneous information interpreted by the multivariate distributions.(3)In the Q.aliena var.acuteserrata natural forest,most individual trees under different combinations of forest size variables and/or spatial structural patameters were well mixed or randomly distributed.The majority of trees with different spatial microstructural combinations were small and medium DBH class trees or middlestory and understory trees,especially 6-7 m H class trees and/or 6 cm DBH class trees.Under same spatial distribution patterns,mingling or crowding degrees,the DBH class distributions of individual trees were inverted J-shaped distributions,while their relationships between DBH-H were asymmetric mountain-liking curves.Therefore,the copula method could effectively characterize forest spatial and size simultaneously,helping to further understanding forest structure.(4)The comparative results of several simulated stands confirmed the accumulation index?_i1 could effectively quantify the accumulation of evaluation indices of evaluation objects.The proposed?i₂??i₂and?i₂ could well express the inhomogeneity among different evaluation indices,and their evaluation results had strong consistency trend among different simulated forests.The comprehensive evaluation function F_i could comprehensively evaluate the overall quality of the evaluation object.The rank of accumulation,inhomogeneity and comprehensive evaluation results for both Q.aliena var.acuteserrata natural forest and broad-leaved P.koraiensis forest were d>a>c>b.Therefore,The proposed?i₂??i₂and?i₂could well measure the inhomogeneity among different stand state evaluation indices,and the proposed comprehensive evaluation method named improved unit circle was proved to be more comprehensive and objective when considering both the accumulation and inhomogeneity of stand state simultaneously,and thus the evaluation results had obvious implications to the diagnosis of the potential problems for forest quality and the decision-making of forest management,so as to comprehensively improve forest quality and effectively promote its balanced development.