Abstract:

Objective: The comprehensive evaluation of forest quality is the premise and key of forest management decision-making. In order to solve the imbalance development of forest caused by simply emphasizing the accumulation of stand quality, this paper attempted to propose different homogeneity indices based on isoperimetric theorem and equal circle theory, and to construct more universal evaluation function, so as to provide a reference for the problem diagnosis and precise improvement of stand quality. Method: The forest quality comprehensive evaluation of Quercus aliena var. acuteserrata natural forest in Xiaolong Mountains forest region in Gansu Province(a and b), broad-leaved Pinus koraiensis forest in Jiaohe forest region in Jilin Province(c and d) and simulated natural forests(d and f) were taken as examples. 10 indexes were selected from forest structure and vitality, each index was normalized and positive firstly, and the radius and central angle of each sector in unit circle represented the value and weight of each index. The extracted area of the closed graph was used to characterize the accumulation of forest quality(ω_i1). The indices α_i2 and β_i2 were constructed based on the relationships between extracted area and arc length, and the isoperimetric theorem. Similarly, another index γ_i2 was proposed based on the relationships between area and perimeter in the equal circles. The forests(c and e, d and f) with equal accumulation values were used to verify the validity of these three homogeneity indexes of forest quality(ω_i2). Then, a comprehensive evaluation function F_i was constructed based on the geometric mean value of ω_i1 and ω_i2 to compare the quality of four natural forests. Result: When the accumulative values of all evaluation indices were equal, the homogeneity values of α_i2, β_i2 and γ_i2 in the broad-leaved P. koraiensis forest stands c and d were smaller than those simulated stands e and f, showing a consistent evaluation result. The accumulation, homogeneity and comprehensive evaluation sorting results of both Q. aliena var. acuteserrata natural forest and broad-leaved P. koraiensis forest were d > a > c > b. Therefore, the stand d had the best forest quality, followed by stands a and c, and the stand b was the worst. Conclusion: The value and weight of each index could be represented by the radius and central angle of each sector in improved unit circle, respectively. ω_i1 could effectively quantify the accumulation of stand quality. The existed β_i2 and newly proposed α_i2 and γ_i2 could well express the homogeneity among different evaluation indices of forest quality, and their evaluation results have strong consistency among different natural forests. The comprehensive evaluation method of stand quality simultaneously considering accumulation and homogeneity was more comprehensive and objective, and its results would present obvious implications to the potential problems diagnosis of forest quality and the decision-making of forest management, so as to effectively improve the forest quality and promote their balanced development.

Key words: homogeneity, accumulation, comprehensive evaluation, Quercus aliena var. acuteserrata natural forest, broad-leaved Pinus koraiensis forest