摘要
研究侵蚀地区的植被在水力侵蚀和各种生态应力以及人类活动影响下的演变规律 ,建立了植被生态动力学模型。将作用于植被的各种生态应力分成长期、短期和瞬时应力 ,给出了它们的定量表达式 ,并且统一在植被生态动力学方程中 ;同时进一步得出了动力学耦合方程组的理论解。该模型应用于金沙江支流小江流域 ,结果较好地描述了流域的植被生态演变过程与侵蚀过程的关系 ,说明了治理强度和控制侵蚀对植被发育的重要性。
Vegetation dynamics is a new interdisciplinary science, studying the laws of evolution of watershed vegetation under the action of various kinds of ecological stresses, especially soil erosion. Ecological stress is defined as any kind of disturbance, natural or non-natural, on the vegetation development, which may change the vegetation cover or affect the evolution process of vegetation. Soil erosion is the most important natural ecological stress and human activities are the non-natural ecological stress. In the loess plateau of northwestern China, the vegetation is hardly developing because the extremely high rate of erosion tears down the topsoil, on which the vegetation grows. In the areas with vegetation, such as the upper reaches of the Yangtze River, erosion damages and destroys the vegetation and scars the land surface. The ecological stresses impacting the vegetation are: (1) natural stresses, such as the erosion, drought, storm, eruption of volcano, and the damages by animals, as well as pests and diseases; (2) human stresses, such as air pollution, grazing, logging, reclamation, mining, road construction, and afforestation. Afforestation is positive stress and the rests are negative stresses. In addition, indirect stress like acid rain is also caused by human activities. In many areas human activities exert much stronger impacts on the vegetation than natural stresses. The ecological stresses can be classified as long term stresses, such as erosion, air pollution, and grazing, short-term stresses, such as drought, pests and diseases, and acid rain, or instant stresses, such as volcano eruption, forest fire, logging and wind storms. Vigor reduction and mortality of vegetation may result from short-term stress acting on trees that have been predisposed to injury by long-term ecological stresses. Different from other stresses, soil erosion not only impacts the vegetation but is also affected by vegetation. In the nature, the development of vegetation cover and variation of soil erosion is affected with each other following a law of dynamics. For a watershed, vegetation and erosion may reach an equilibrium state if the circumstances maintain unchanged for a long period of time. However, the equilibrium is not stable. Ecological stresses, especially human activities, may disturb the balance and initiate a new cycle of dynamical processes. In this paper, the quantitative expressions of the long-term, short-term and instant ecological stresses are introduced based on the temporal characteristics of the stresses. Erosion is qualitatively represented by the rate of sediment eroded from unit area per year, and the vegetation is presented by ratio of vegetation cover, or simply vegetation cover, which is defined as the percentage of the area covered with trees and shrubs. Thornes proposed a model of geomorphologic process considering the rate of variation of vegetation cover with coupled differential equations. Introducing the qualitative expressions of various ecological stresses and revising the Thornes geographical model, this paper established a vegetation dynamics model and derived the theoretical solution. Data were collected from field investigations to the Xiaojiang Watershed on the Yunnan Plateau of south China. The vegetation dynamics model is well applied to the Xiaojiang Watershed, the Heishui River watershed and the Shengou Watershed. The theoretical solution agrees well with the data. The results demonstrate that the vegetation-erosion dynamics is a powerful tool for prediction of the vegetation evolution. Usually, reforestation and erosion control improves the watershed vegetation slowly in the first 10 years but much faster in the second 10 years, implying the effort of reforestation and erosion control must be a long-term strategy. Erosion control is very important for re-vegetating the hills. Mere planting trees and shrubs does not work well for greening the exposed land. The results also show that in the arid areas although people continuously reforest the hills and control erosion the
出处
《生态学报》
CAS
CSCD
北大核心
2003年第1期98-105,共8页
Acta Ecologica Sinica
基金
国家 973重点基础研究发展规划资助项目 ( G1 990 4 360 4 )
国家自然科学基金资助项目 ( 5 9890 2 0 0 )。~~
关键词
侵蚀地区
植被生态动力学模型
植被发育
生态应力
耦合方程组
vegetation dynamics model
human activities
coupled differential equations
vegetation cover
rate of soil erosion
