基于水源涵养的流域适宜森林覆盖率研究——以平通河流域(平武段)为例

Study on optimum forest coverage for water conservation: a case study in Pingtonghe watershed (Pingwu section)

适宜森林覆盖率的研究是流域防护林空间布局的基础研究,对流域内防护林林种和林分结构调整有着重要的指导意义。以对土壤饱和蓄水量的贡献大小为依据,人力可控和可测为原则进行流域有林地水源涵养功能评价指标筛选。采用群组AHP法剔除因子间相关性较大的指标,筛选出了地形-土壤因子、林分因子、干扰强度因子共计12个指标;用层次分析法(AHP)计算各指标对土壤饱和蓄水量的权重,以此权重计算各有林地小班水源涵养的等级值以及每个等级对应的面积。以流域历年(40a)最大日降雨量147.2 mm计算流域适宜森林覆盖率。结果表明:林分因子(0.637)>干扰强度因子(0.258)>地形-土壤因子(0.105),即影响平通河流域有林地水源涵养功能最大的因子是林分因子,其次是干扰度因子;流域基于水源涵养的适宜森林覆盖率为57.09%,变幅为43%—73%。

Appropriate forest coverage is the basis of spatial layout for watershed protection forest and is an important indicator for regulating sheltering forest and stand restructuring in watershed.In this paper soil saturated water holding capacity（SWC） was selected as the indicator for assessing water conservation function at watershed scale.analytic hierarchy process（AHP） method was applied to eliminate indicators with close relevance.12 indicators related to landform（position on slope and slope gradient）,-soil（soil types and soil depth）,forest（structure,standing volume,crown cover and stand age） and disturbance regimes（forest types,distance from villages,elevation and annual per capita income） were used to estimate soil saturated water holding capacity were selected for the assessment.The AHP method was applied to calculate each indicator′s weight to SWC,based on which water conservation class of each forested sub-compartment were calculated.The maximal daily rainfall of 147.2mm in last 40years was thenused to predict the optimum watershed forest coverage.The result indicated that the most important factor for assessing water conservation is forest factors（0.637）,followed by disturbance factors（0.258） andlandform-soil factors（0.105） The optimum forest coverage in the assessed watershed is 57.09%,with ranging from 43%—73%.