Outdoor recreational activities are connected with the supply of and the demand for natural resources. Examples of outdoor recreation which may stress natural environment are visits to national parks, and activities in lakes such as fishing, swimming or canoeing (Murphy, 1985). Natural resources which may be relevant for recreational purposes are, among others, forests, canyons, lakes or bays (see also McConnell, 1985 for an exposition of outdoor recreation in the frame of natural resources). The definition of outdoor recreation with its dependency on natural resources means that recreational activities such as tennis or golf are of only limited relevance, because usually they do not have direct links to natural resources.