祁连山林区基于水源涵养能力的人工林近自然度评价体系建立

建立近自然度评价体系对于修复森林生态功能、保障森林可持续发展有着重要的意义,然而近自然度尚未有统一的评价体系。祁连山地区的森林系统承担着我国西部重要的水源涵养功能,对其现存的人工林客观地开展基于水源涵养能力的近自然评价是亟需解决的问题。以祁连山东部金禅沟、塔尔沟小流域40个不同林分起源的云杉纯林、白桦纯林、云杉白桦混交林为对比研究样地,对涉及近自然度和水源涵养能力的指标进行敏感性分析,筛选出中高敏感度指标,通过欧氏距离法结合熵权法定量评价人工林近自然度,通过模糊物元法定量评价森林水源涵养能力,然后采用6种方法对近自然度和水源涵养得分分布进行拟合(R²>0.4),并利用K-means法建立了4个近自然度评价等级。研究表明祁连山东部地区大部分人工林近自然度评级处于半天然林阶段,通过改造纯林为针阔混交林可以同时提高其近自然度与水源涵养能力。研究旨在构建基于水源涵养能力的近自然度评价体系,为森林生态服务功能修复提供理论支持。

Establishing near-naturalness evaluation system of artificial forest based on water conservation ability in the outer edge of Qilian Mountains in Qinghai Province

The evaluation of near-naturalness is a widely discussed topic at present. It is of great significance to restore forest ecological function and protect forest sustainable development by establishing a near-naturalness evaluation system. However, there is no unified evaluation system for forest near-naturalness. This study focuses on the construction of near-natural evaluation based on water conservation capacity and provides theoretical support for the restoration of forest ecosystem services. In order to explore the management mode of near-natural forests, this paper takes the artificial forest in the outer edge of Qilian Mountains in Qinghai as a case study. The forest in Qilian Mountains plays an important role for water conservation in western China. However, in the early stage, some plantations were planted according to the timber forest structure. As a result, there are widespread problems such as poor stability of forest system, low water conservation function, and difficulty in sustainable development of forests. It is an urgent problem to objectively evaluate the water conservation capacity of existing plantations and explore the near-natural management measures of forests. In this study, 40 spots planted with the Picea crassifolia Kom. forest, Betula platyphylla Suk. Forest, and Picea crassifolia Kom. and Betula platyphylla Suk mixed forest with different stand origins in Jinchangou and Talgou small watershed in the eastern Qilian Mountains were investigated. Sensitivity analysis was carried out on the indexes related to naturalness and water conservation ability, and the medium and high sensitivity indexes were selected. The forest water conservation function was evaluated quantitatively by fuzzy matter element method, and the near-natural degree of artificial forest was evaluated quantitatively by Euclidean distance method combined with the entropy weight method. Six methods were used for regression fitting (R²>0.4) of near-naturalness and water conservation scores, and four near-naturalness evaluation levels were established by K-means method. The results showed that most of the artificial forests in the eastern Qilian Mountains were in the semi-natural forest stage, and the near-naturalness and water conservation ability of the pure forests could be improved by transforming them into mixed forests. In the meanwhile, the study demonstrated that the forests in the semi-natural stage were the key object of forest transformation. By transforming semi-natural forests, the water conservation capacity of local forests can be greatly improved. In addition, the study still needs to investigate the near-natural forests to improve the progress of the evaluation system and further explore the near-natural forest management measures for semi-natural forests.