三北防护林体系建设工程区森林水源涵养格局变化研究

Research on the pattern and change of forest water conservation in Three-North Shelterbelt Forest Program region, China

三北防护林体系水源涵养功能是三北地区生态环境状况的重要指示器,然而,三北防护林体系水源涵养研究仍较缺乏。动态评估三北防护林体系建设工程区(三北工程区)森林水源涵养功能及其影响因素,对科学认识、保护和调控三北防护林体系森林水源涵养,制定三北工程植被建设与保护决策具有重要意义。以三北工程区森林为研究对象,通过收集和分析相关数据,在植被分区的基础上,分析三北工程区森林水源涵养时空格局与变化特征,对比研究各区不同森林类型水源涵养功能差异,揭示各区森林水源涵养功能与地形及森林状况与质量的定量关系。结果表明:(1)三北工程区森林水源涵养功能持续增强,单位面积水源涵养量从1990年的73.92mm增加到2015年的75.14mm,空间格局呈东高西低、南高北低态势。(2)森林水源涵养功能在植被分区和森林类型间差异显著,森林植被区是三北工程区森林水源涵养的主体;针阔混交林是三北工程区水源涵养功能最强的森林类型。(3)三北工程区森林水源涵养受其地形、状况与质量的影响显著,除个别植被区外,各区森林水源涵养量随坡度、覆盖度和NPP增加而增大,随生物量增加而降低,这是区域植被适应及滥砍滥伐、毁林开垦、植被建设与保护等人为干扰共同作用的结果。因此,可通过调整与优化林分结构,调控区域森林水源涵养功能。

Water conservation is an important component of forest ecosystem services, which is involved in the natural processes such as regional climate circulation, hydrologic cycle, vegetation growth and succession, and availability of soil nutrients. Thus it is an important indicator for regional eco-environment condition. Water resources in Three North Shelterbelt Forest Program region are scarce. Many researchers have attributed water scarcity in this area to large-scale artificial afforestation. Other studies have shown that climate change, the industrial development, intensive agricultural irrigation, and overdraft of groundwater were the primary causes of water resource changes. Whatever the reasons are, recent studies have shown that topography, stand condition and quality significantly influenced the regional forest water conservation. It is necessary to dynamically study the forest water conservation and its response to topography, forest condition and quality. This will be conducive to understand the achievements in ecological construction, to promote vegetation construction, and to regulate water conservation services of the Three-north Shelterbelt forest program. This study analyzed literature and applied GIS technology to analyze the hydrological characteristics of different forests, and to develop a method to dynamically assess water conservation services of different forests at a regional scale. We quantified the water conservation services of different forests in the Three North Shelterbelt Forest Program region comparing those services across different types of forests, years and vegetation zones. We also analyzed the respective effects of topography, forest condition and quality on the spatial patterns in forest water conservation services. The results were as follows:(1) the forest water conservation in Three North Shelterbelt Forest Program region has been continually enhanced. It increased from 73.92mm in 1990 to 75.14mm in 2015, and followed a decreasing trend from the east to the west, and from the south to the north.(2) There were significant differences in forest water conservation among different vegetation zones, years, and forests types. Forest vegetation zone was the main body of forest water conservation in the Three North Shelterbelt Forest Program region. The coniferous and broad-leaved mixed forest was the forest type with the highest forest water conservation.(3) The forest water conservation in the Three North Shelterbelt Forest Program region was affected by topography, forest condition, and quality respectively. Except for individual vegetation zone, the forest water conservation in vegetation zone was significantly increased with raised slope degree, vegetation coverage, and vegetation net primary productivity, while was decreased with forest biomass, which was the result of the comprehensive function of regional vegetation adaptation and human disturbance, such as excessive deforestation, destroying trees and reclamation, and vegetation construction and protection. Therefore, the regional forest water conservation can be regulated by adjusting and improving forest structure.