与平原/低地相比，山区（主要指典型中高山区）环境具有其本身固有的诸多属性。山区环境的复杂性表现在山地诸要素的垂直地带性规律与非地带性规律及其相互叠加上，而其不确定性是由山地环境和物质本身的不稳定性所决定。山区环境的脆弱性和敏感性表现在山区生态系统抗干扰能力低，容易在外界因素的诱导下偏离生态阈值，甚至出现崩溃。由于高山与河流的阻隔，山区聚落和社区常常表现出分散性、封闭性以及文化的多样性和相对稳定性等特点。山区人地关系地域系统由环境系统和人口系统组成，山区环境对人口具有限制和制约作用，而人口对环境则表现出适应与改造的趋向。山区人口与环境的关系既可以表现为相互恶化，也可以表现为良性互动，其中间过程是通过人类对土地的不同利用方式而得以实现。

All ecosystems on earth have been under the influence of human beings. It is also true for mountain ecosystem. Comparing with ecosystem on plains/low lands, mountain ecosystem is characteristic of complexity and uncertainty, fragility and sensitivity. Mountains are three dimensional systems, of which the complexity is displayed in their verticality, non verticality and compilation of both. Due to the complexity of mountains, it has been very hard to give mountain a well understood definition. The uncertainty of mountains lies in their instability of internal structure and high potential energy. The fragility and sensitivity of mountain eco environment is displayed in that mountain ecosystems usually have a low capability to resist external disturbance and it is easy for them to exceed ecological threshold or even to go to collapse under external influences. The fragility of mountain eco environment is determined by its bio physical features: high elevation, cold climate, thin air, thin layer of soil, low concentration of organic matters in soil and slow biochemical process. It is usually hard for soil and vegetation in mountains to rehabilitate and restore once they are destroyed. In most cases degradation of mountain environment is an irreversible process. Due to physical constraints, mountain settlements or communities have showed their characteristics of scattering, closeness and stability. Considering the interaction between population and environment in mountains, environment, on one hand, may be a constraint for human activities. Although human being is a keystone species in earth ecosystem, human activities are always constrained by environment. It is more like this in mountains where physical environment is harsh. Humans,on the other hand, are able to adapt to their environment by transhumance, physiological adaptive reaction, storage of foods and cultivation of wild plants. The man earth relationship in mountains may take two forms: mutual deterioration or mutual amelioration in different types of land use such as farming, animal husbandry, forestry, settlement construction and mining.