外来树种的耗水特征及其对环境水资源的影响

外来树种常被作为"先锋树种"广泛引种,在荒山造林和水土保持方面发挥了积极作用;然而,不少外来树种具有高耗水和强抗旱的水分利用特性,耗水量大、水分消耗快,若不加甄别地引种会影响甚至危害本土森林生态系统的健康。目前,部分被引种的外来树种已造成入侵;同时,在当前水资源缺乏的形势下,外来树种的引种安全问题已成为全球关注的生态环境问题。本文综述了外来树种在生态系统、整树、叶片及枝条水平的耗水特性,分析了外来树种对引种地水资源的影响。前期的研究结果显示,被引种的外来树种在生态系统及整树水平的耗水量普遍高于乡土树种,但对水资源的影响却因受控于多个因素如环境、气候、植物个体等而不尽相同;同时还显示,外来树种在叶片和枝条水平的耗水特性更多地体现了其应对环境变化的水分利用策略。研究还就提高外来树种耗水特性研究的准确性和提升外来树种危害风险的预警能力方面,提出了若干研究方向,旨在为森林管理者和政府部门平衡外来树种的经济效益和生态效应提供借鉴和指导,以期降低外来树种引种风险,增进生态安全。

Water use strategies of alien trees and their impacts on water resource

Alien tree species play significant roles in forestation and conservation of soil and water. Due to their fast growth-induced high water consumption and drought resistance characteristics, many alien tree species have affected and even damaged native forest ecosystems, and some species have been reported to be the noxious invasive species. These alien tree species have caused significantly environmental problems. Regarding water consumption of alien tree species, we reviewed their water use strategies in scales of ecosystem, whole tree, leaf and branch. We also analyzed their impacts on underground water quality and nutrient cycling, and water resource of local forest ecosystem. The results demonstrate that the alien tree species usually consume more water than local native species at whole-tree and ecosystem levels, and the hydraulic adjustment of alien trees to different soil water availability are presented mostly at leaf and branch level. However, it is not necessarily to prove that they have the negative impacts on local water resources as such impacts are closely associated with many factors including environment, climate and tree individual characters. At last, in order to improve the water use research and risk assessment of alien tree species, we proposed several research concerns in the near future. Firstly, precisely evaluating the effects of alien trees on water resource largely depends on the well-recognition of their water use regulation, therefore both the evaluation and regulation studies should be strengthened. Moreover, applying key water use characteristics in risk assessment systems and in alien tree species database construction could be considered as efficient and important pathways not only for invasion plants control, but also in forestation water management. This review is applicable for forest managers and government to balance the economic and ecological outcomes of alien trees, and to improve ecological safety.