黄土高原防护林建设的恢复生态学与生态水文学基础

Restoration ecology and eco-hydrology sciences:the basis for construction of protection forests on the Loess Plateau,China

以控制土壤侵蚀和提高土地生产力为主要目标的防护林建设是黄土高原植被建设与生态恢复的主体。在对国内外防护林建设研究进行回顾的基础上,从恢复生态学与生态水文学视角探讨了我国西北黄土高原地区防护林建设目标、防护林建设研究尺度、防护林建设基础理论等,并提出今后黄土高原防护林建设研究方向,其目的在于,通过探讨进一步明确当前黄土高原防护林建设的问题,为该区防护林体系建设提供指导依据。防护林建设除了要达到侵蚀防治等功能的正常发挥外,其终极目标应强调水-沙平衡这一生态水文学目标的实现。防护林建设需要从不同尺度予以理解,除林分尺度的结构优化与功能调控技术以及小流域尺度空间对位配置技术外,区域尺度地带性植被和适宜覆盖率的确定也应为防护林建设的内容。为实现防护林建设的生态水文学目标,防护林建设应遵循恢复生态学中的水分限制因子理论、生态适宜性理论、生物多样性理论以及群落演替理论,这就要求防护林建设总体应以林-水平衡为核心,在实现区域植被地带性及微观尺度适地适树的同时,考虑次生林主要树种的引入,以促进防护林建设生物多样性及群落顺行演替。总体来看,黄土高原防护林建设应基于恢复生态学与生态水文学加强以下研究:(1)针对气候变化,加强防护林建设气候变化适应性评价研究,建立适应性防护林可持续经营管理理论与技术体系;(2)针对立地条件空间异质性,加强高分辨率植被恢复适宜性评价研究,建立定量的植被恢复适地适树适群落理论体系;(3)以恢复生态学原理为指导,加强潜在植被空间分布格局的复原与预测研究,建立近自然防护林建设植被恢复模式;(4)针对全球气候变化与资源性缺水问题,加强基于物理过程分布式生态水文模型的模型模拟研究,为防护林体系建设中植被空间分布、结构组成与规模提供决策依据。

To combat severe soil erosion and improve the land productivity,construction of protection forests has been widely implemented as one of the key ecological restoration efforts on the Loess Plateau in Northwestern China.After giving a brief introduction of the concept of protection forests defined by the various researchers,several issues with respect to the goal of protection forests,the scales and the principles for developing protection forests were examined from the viewpoints of restoration ecology and eco-hydrology.A few recommendations were proposed to provide the theoretical foundations for construction of protection forests.We argue that,in addition to soil erosion control,the ultimate of protection forests in the Loess area should serve both water regulation and erosion control.We should recognize the hierarchical system of protection forests.In addition to the structural-optimization techniques at the stand level and the spatial arrangements measures at the watershed level,determination of both zonal vegetation types and the coverage on the regional scale should be considered in designing protection forests.To succeed in constructing protection forests and fulfilling the established targets,several theories should be followed in practice,including the principle of water balance,the theory of ecological suitability,the biological diversity,and the theory of ecosystem regeneration and succession.Construction of protection forests should not alter the balance of water availability and tree growth requirement.Dominant tree species of secondary forests should be encouraged to enhance forest succession and bio-diversity when implementing the conventional principle of ＂tree and site match＂.We conclude that the following four key aspects should be reinforced：（1） evaluation of the vulnerability of protection forests,and developing adaptation strategies for managing protection forests under a changing climate and variability;（2） implementation of the principle of ＂tree-site match＂ by assessment of suitability of reforestation at high spatial and temporal resolution based on the interactive relations between soil,hydrology,vegetation,and climate;（3） predicting the spatial distribution of potential vegetation of the loess area using restoration ecology theories and constructing the protection forests with the pattern of close-to-nature to restore the vegetation of the Loess area;（4） understanding the hydrological responses of protection forests to the change in vegetation patterns,species composition,as well as coverage using physically-based distributed eco-hydrological models;developing theories for forest restoration design on forest structure and spatial distributions of protection forests.