Tourism based on natural environments is a huge international industry with major economic, social and environmental consequences at both local and global scales. Just how big it is depends on what we include For example, how far do we attempt to disaggre­gate or unbundle the motivations and expenditure of tourists, and the packaging of tour products, so as to distinguish built, cultural and natural attractions? How much of the indirect economic activity associated with tourism do we include, such as recreational equipment manufacturing, or recreational use of private vehicles and personal time? In very broad terms, it seems that the attractions of natural areas and their closely associated local cultures, and the various associated tourist, recreational and leisure activities, contribute around half the total economic activity attributable to the travel and tourism sector (Stueve et al., 2002) Global nature tourism, in other words, is worth at least US$250 billion a year Indeed, one past estimate (J Mallett, 1998, unpublished) suggests that the US adventure-­tourism sector alone is almost this large, if recreational equipment is included; and a more recent estimate suggests that US and Canadian national parks inject around US$250 billion a year into the North American economy, through various mechanisms including nature tourism (Eagles, 2002)