Concern over the increased use of parks and outdoor recreation areas is a perennial issue. Visitors can trample fragile vegetation, erode soil, pollute water, and frighten wildlife. Moreover, too many visitors can cause crowding, conflict, and other social impacts, thereby degrading the quality of the recreation experience. Concern over these issues was documented by the Outdoor Recreation Resources Review Commission in the early 1960s and has grown in importance as visitation to most parks and outdoor recreation areas has continued to increase. These issues are often incorporated within the conceptual framework of carrying capacity. In its most generic form, carrying capacity can be defined the amount of visitor use that can be appropriately accommodated with in a park or outdoor recreation area.
The underlying concept of carrying capacity has a rich history in the natural resource professions. In particular, it has proven a useful concept in wildlife and range management, where it generally refers to the number of animals of any one species that can be sustained in a given habitat. Carrying capacity has obvious parallels and intuitive appeal in the field of parks and outdoor recreation. However, the first rigorous applications of carrying capacity to outdoor recreation did not occur until the 1960s.
These initial scientific applications of carrying capacity suggested the concept was more complex in this new management context. At first, as might be expected, the focus was placed on the relationship between visitor use and environmental conditions. The working hypothesis was that increased visitor use causes greater environmental impact as measured by soil compaction, destruction of vegetation, and related variables. It soon became apparent, however, that there was another dimension of carrying capacity dealing with social aspects of the visitor experience. An early and important report on the application of carrying capacity to outdoor recreation, for example, reported that the study ". . . was initiated with the view that the carrying capacity of recreation lands could be determined primarily in terms of ecology and the deterioration of areas. However, it soon became obvious that the resource-oriented point of view must be augmented by consideration of human values." (Wager, 1964).
The point was that as more people visit an area, not only can the environmental resources of the area be affected, but so too can the quality of the visitor experience. Again, the working hypothesis was that increased visitor use causes greater social impacts as measured by crowding and related variables. Thus, as applied to outdoor recreation, carrying capacity has two components: environmental and social.
The early scientific work on carrying capacity has blossomed into an extended collection of literature on social aspects of outdoor recreation and their application to carrying capacity (Stankey and Lime, 1973; Manning, 1986; Shelby and Heberlein, 1986; Kuss et al., 1990). But despite the impressive literary base, efforts to determine and apply social carrying capacity have often been met with frustration. The principal difficulty lies in determining how much social impact, such as crowding, is too much. Given the substantial demand for outdoor recreation, some decline or change in the quality of the visitor experience (some perceived crowding) is inevitable. But how much decline or change is appropriate or acceptable? This issue is often referred to as the "limits of acceptable change" and is fundamental to social carrying capacity determination (Frissell and Stankey, 1972).
This issue is illustrated in Figure 1, in which two hypothetical relationships between visitor use and crowding are shown. It is clear from both that visitor-use level and perceived crowding are related: increasing numbers of visitors cause increasing percentages of visitors to report feeling crowded. However, it is not clear at what point carrying capacity has been reached. …