基于耦合模拟的三峡库区坡面水文过程对林分结构特征的响应

By means of altering the distribution patterns of precipitation, changing the mechanics of runoff producing and the routes of runoff confluencing, and improving soil structure, the characteristics of stand structure redistributes the precipitation and further affects the hydrologic processes of rainfall, surface runoff and groundwater, hence the rationality of its distribution directly influences the eco-hydrologic function of the forests. Based on individual statistics in vegetation ecology and woods relationship (structure unit) in Modern forest ecology, quantitative study on the hydrologic effect of stand structure was conducted at five representative rainfall-runoff plots located within the Three Georges Reservoir area; based on the revealing of effect law of the properties of typical stand and its spatial distribution pattern functioning on rainfall-runoff processes at hillslope scale, the slope-scaled dynamic hydrologic model coupled with stand structure was constructed, which implemented the quantitative assessment of forestry hydrologic cycling and ecologic effect due to vegetation structure. Meanwhile, the mechanisms of runoff production and confluence in conditions of typical stand structure as well as the migration pattern of ground water through heterogeneous soils which contain root system were further studied. This research would thoroughly discuss the scientific issues in Eco-hydrologic effect in forestry, and the technology of numerical coupling would combine the research in fields of forestry hydrology, edaphology and soil and water conservation. The achievements could be directly applied into the runoff prediction with typical stand structure, which would provide technological support to the structure construction of the head-water forest within the Three Georges Reservoir area.

林分结构特征通过改变降雨分布格局、改变坡面产流机制和汇流路径、改良土壤结构，对降雨重新分配，进而影响降水、地表水、地下水等林内水文过程，其合理性直接影响森林水文生态效应的发挥。本项目采用以个体为统计单位的植被生态学和以相邻林木关系（结构单元）的现代森林生态学理论，结合三峡库区五种典型植被径流小区的观测资料，开展林分水文过程对林分结构的响应研究；在揭示典型林分覆盖属性及空间构局对坡面降雨-径流影响规律的基础上，构建基于林分结构特征的坡面水文过程模型，实现植被外貌结构对森林水文循环和生态效应的定量评价。同时，从机理上分析典型林分结构下的产汇流模式以及水分在含有根系的异质土壤结构中的运移规律。本项目将深入研究林业水文和生态效应的科学问题，应用数值耦合技术开展森林水文学、土壤学和水土保持学科的协同研究；研究成果可直接应用于对典型林分结构的产汇流预测，为三峡库区水源林的建设提供技术支撑。

以优化林分结构为基础来设计森林经营方案是目前森林经营的一个重要方向。林分结构通过改变降雨分布格局、改变坡面产流机制和汇流路径、改良土壤结构，对降雨重新分配，进而影响降水、地表水、地下水等林内水文过程，其合理性直接影响森林水文生态效应的发挥。本项目以三峡库区重庆缙云山典型林地为对象，以野外调查、原位观测、室内试验和模型模拟为手段，从垂直和水平空间角度调查林分结构参数特征，厘定影响林冠截留、树干液流、地表径流及壤中流等水文过程的典型林分结构参数体系，并将其与水文过程耦合，探讨坡面水文过程在一定降雨胁迫条件下对林分结构的响应规律。研究结果表明：1、调查缙云山9种典型林分间非空间结构、空间结构与生物多样性特征等共计11个指数，均具显著差异：呈现反J型和多峰山状的直径和树高特征显示林木总体是典型的异龄林；混角度、大小比数和聚集度等空间指数显示多数林木空间结构好，部分林分向聚集分布演变，而竹林则完全以聚集分布为主；多样性指数显示针阔混交型林多样性程度最高，竹林最低；2、收集并整理2011-2015年间的林外雨、林内雨、树干茎流、树干液流、枯落物持水、土壤入渗、地表径流、壤中流等气象水文数据；在垂直尺度，采用数学统计和通径分析等方法从17个指标中筛选出影响林内水文过程的4个典型结构特征，在水平尺度，采用室内模拟试验从水动力学角度考察不同模拟植被结构及配置对坡面流速、流态（雷诺数）、流型（弗劳德数）和阻力系数的影响，进而筛选影响坡面径流过程的林分格局参数；3、将筛选的4个关键林分结构参数郁闭度、覆盖度、角尺度和根系结构耦合至坡面水文过程的Gash冠层截留模型、坡面一维运动波模型以及饱和-非饱和水运移模型，实现林分结构在坡面水文过程模型中的耦合。本项目在坡面尺度为阐述水文过程对林分结构特征响应这一科学问题提供了一定的数据和技术支撑，为研究森林与水的关系开拓新思路，为三峡库区水源林建设和生态评价提供技术支撑。