Abstract:An ecological threshold refers to a point or zone in the relationship between two or more ecological variables at which relatively abrupt change occurs from one ecological condition to another in an ecosystem. The impetus for this change comes from a small additional change in one or more key factors. Ecological thresholds are ubiquitous in natural ecosystems. There are two main types of ecological thresholds that can theoretically occur in natural systems, ecological threshold point and ecological threshold zone. The attributes, function or process of an ecosystem will change abruptly around the point-type threshold. Zone-type ecological thresholds imply a more gradual shift or transition from one state to another, rather than an abrupt change at a specific point in time, as suggested in point-type threshold. Zone-type ecological thresholds are probably more common in nature than point-type thresholds. Research on ecological thresholds has important theoretical and practical meanings for natural resources conservation and sustainable ecosystem management, which have been the highlights in ecology and related areas. A lot of research on ecological threshold has been carried out in forest, grassland, lake and ocean ecosystems for different ecological factors and from different points of view. There is still great uncertainty about the nature of ecological thresholds and how they are related in different spatial scales. More synthetic and quantitative study is needed to improve the ability of applying knowledge of ecological thresholds in ecosystem management. Much progress and research will be made in the areas of global change and ecological responses.