Transboundary Conservation across Scales: A World–Regional Inventory and a Local Case Study from the United States–Mexico Border Jacob C. Brenner and John G. Davis (bio) Introduction Transboundary Conservation Background A major challenge in modern natural areas conservation arises from the tendency of ecosystems to cross administrative boundaries and the simultaneous imperative to expand conservation across broad spatial (landscape or ecoregional) scales. Making conservation work amidst the many differences (social, cultural, political, and economic) that exist across borders requires special coordination. The challenge of cross-border coordination becomes acute in cases of natural areas spanning international boundaries, as they often do (López-Hoffman et al. 2009). Envisioning coordinated cross-border conservation has become a primary endeavor of large international conservation organizations (Hutton et al. 2005). As early as 1991 the Worldwide Fund for Nature (WWF) joined Flora and Fauna International and several other large organizations to promote cross-border collaboration among Uganda, the Republic of Congo, and Rwanda, forming the International Gorilla Conservation Programme (Rainer et al. 2003). In 1997, the International Union for the Conservation of Nature’s (IUCN) World Commission on Protected Areas formed its Transboundary Conservation Task Force, which was later expanded into the Transboundary Conservation Specialist Group, with the primary objective being “To promote and encourage transboundary conservation . . . while promoting peace and co-operation among nations . . . for effective planning and management of transboundary conservation [End Page 499] areas” (IUCN 2011). Indeed, transboundary conservation is one of the hallmarks of a broader boom in protected areas during the past half century (Zimmerer 2006; Brockington et al. 2008). The United Nations Environment Programme’s World Conservation Monitoring Centre (WCMC) records 227 transboundary protected areas (TBPAs) as of 2007 (Figure 1), covering more than 4.6 million square kilometers of the global land surface (Lysenko et al. 2007). Click for larger view View full resolution Figure 1. Transboundary protected areas worldwide (1988–2007) recorded by the United Nations Environment Programme’s World Conservation Monitoring Centre (Lysenko et al. 2007). A few well-known examples suffice to illustrate the global scale of the proliferation of TBPAs, as well as their variability in size and composition (Lysenko et al. 2007). On the western border of the United States and Canada, the mountains bridging the U.S. and Canadian Rockies have been protected since 1932 as Waterton Glacier International Peace Park. The total land area of all twenty-five protected areas measures 30,975 square kilometers. The Glaciares–Torres del Paine–O’Higgins Complex of South America’s southern cone consists of nine reserves protecting 67,855 square kilometers of the southern Andean high peaks. The Serengeti–Maasai complex of Kenya and Tanzania consists of fourteen reserves protecting 43,460 square kilometers of savanna wildlife habitat and ancestral homelands. The Sundarbans of India and Bangladesh consist of nine reserves and 15,000 square kilometers of tidal mangrove habitat. [End Page 500] The global expansion of the transboundary conservation movement belies its uneven geography and begs several questions. What is the regional distribution of transboundary protected areas? Is transboundary conservation more prevalent in some regions than in others? Are there hotspots where transboundary conservation initiatives are thriving or where transboundary conservation opportunities abound? The Trouble with “Transboundary” Before we address these questions about the global transboundary conservation movement we should clarify some transboundary conservation terminology. The WCMC monitors “Transboundary Protected Areas” (Lysenko et al. 2007), where the term “transboundary” suggests a single conservation reserve spanning a jurisdictional border. In reality, such is seldom the case. A more detailed definition of this type of conservation reserve is offered by Sandwith and colleagues (2001), including: • Protected areas contiguous across a national boundary • Clusters of protected areas with intervening land • Clusters of separate protected areas without intervening land • Transborder areas that include proposed protected areas • Protected areas in one country with minimal or sympathetic land use in the adjacent country Unfortunately, amplifying the definition does not lend it any greater clarity. If anything, this more ample definition increases the ambiguity concerning what constitutes a TBPA, since the only characteristic uniting these five types of protected area complexes is their spatial coincidence in a border region. By this definition we might expect most international border...