Environmental Science & Policy 218 (2002) 1–14 3 Transformations of the Chihuahuan Borderlands: grazing, fragmentation, 4 and biodiversity conservation in desert grasslands a,∗ b c 5 Charles G. Curtin , Nathan F. Sayre , Benjamin D. Lane 6 a Arid Lands Project, Box 29, Animas, NM 88020, USA 7 b USDA-ARS Jornada Experimental Range, Las Cruces, NM, USA 8 c UNESCO/Columbia University International Conference on Biodiversity and Society, New York, NY, USA 9 10 Abstract 11 Environmentalists, scientists, and land managers have long debated the role of ranching in landscape conservation with some contending 12 that ranching represents the major threat to ecological systems, while others believe it is key to long-term conservation. We contrast the 13 impacts of livestock grazing with those of the major alternative land use at this time, suburban and ex-urban development, on the semi-arid 14 Chihuahuan Desert grasslands and savannas of southern Arizona and New Mexico, USA, and northern Chihuahua and Sonora, Mexico. 15 Because landscape change has resulted from complex interactions among natural and anthropogenic disturbances, attempts to identify 16 simple causal relationships resulting from livestock are of limited ecological significance. Far more important is long-term conservation of 17 basic ecological processes at large spatial scales, which in turn requires that certain social conditions be maintained. In the face of rapid, 18 extensive suburban and ex-urban development in the region, conservation of functioning ranch units represents the most viable means 19 of sustaining ecological function. Examples of community-based adaptive management illustrate the potential of coalitions of ranchers, 20 agencies, scientists, and environmentalists to conserve biodiversity of these landscapes, protecting a matrix of publicly and privately owned 21 land through an extension of UNESCOs biosphere reserve model. © 2002 Published by Elsevier Science Ltd. 22 Keywords: Grasslands; Ranching; Community-based conservation; Landscape fragmentation; Biosphere reserve 23 24 1. Introduction niques, and (b) conversion of rangelands into smaller parcels 43 for suburban and ex-urban real estate development. Ranch- 44 25 The North American desert grasslands, like their counter- ing is the most extensive land use in the western United 45 26 parts in Africa, Asia and Australia, have long been shaped by States, with well documented historical impacts across hun- 46 27 the activities of humans (Curtis, 1956; Manning, 1997; Pyne, dreds of millions of acres of arid and semi-arid rangelands; 47 28 1997). The effects of some activities have been extreme, as these impacts have led some environmental advocates and 48 29 in the case of the extermination of mega-fauna by early in- conservation biologists to advocate curtailing or eliminating 49 30 habitants (Martin, 1984). Others, such as the fire practices livestock grazing to preserve native biodiversity (Fleischner, 50 31 of native Americans, have been more subtle but equally pro- 1994; Donahue, 1999). Although more limited spatially and 51 32 found (Dobyns, 1981; Pyne, 1982). Although these transfor- more recent than ranching, subdivision/suburbanization is 52 33 mation processes have been ongoing since the first arrival rapidly expanding, altering large areas of crop and range 53 34 of humans thousands of years ago, the pace of change has land throughout the US. As competing land uses, ranch- 54 35 increased dramatically in the period since Anglo-American ing and real estate development constitute something of a 55 36 settlement of the region in the second half of the 19th cen- dilemma for conservationists, captured in the phrase “cows 56 37 tury (Hastings and Turner, 1965; Bahre, 1991). versus condos” (Jensen, 2001; Sheridan, 2001). While ma- 57 38 In this case study, we examine two human interventions jor conservation organizations, such as The Nature Conser- 58 39 of significance to the recent history of desert grasslands in vancy have made ranch conservation a focus of their western 59 40 the southwestern United States (and indeed much of the conservation efforts, some have denied the trade-off implied 60 41 American West): (a) large-scale cattle ranching, including by the phrase (Donahue, 1999), while others have argued 61 42 its associated range improvements and management tech- that suburban development is environmentally preferable to 62 agriculture (Wuerthner, 1994). 63 ∗ Corresponding author. Present address: 274 Mitchell Road, Cape Eliz- Regardless of the point of view, the full ecological im- 64 abeth, ME 04107, USA. Tel.: +1-207-767-4211; fax: +1-207-767-4211. pacts of ranching and suburban development have yet to 65 E-mail address: [email protected] (C.G. Curtin). be assessed. Understanding the relations between ranching 66 1 1462-9011/02/$ – see front matter © 2002 PublishedUNCORRECTED by Elsevier Science Ltd. PROOF 2 PII: S1462-9011(02)00020-5 2 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 67 and subdivision requires historical, economic, and ecolog- on the Chihuahuan Borderlands for several reasons. First, it 79 68 ical analysis sensitive to the particular conditions of spe- is a region of extraordinarily rich biodiversity, lying at the 80 69 cific landscapes (Sayre, 2002). Here, we explore the dy- juncture of six major biomes. Second, it has experienced 81 70 namics and impacts of these activities in the Chihuahuan dramatic environmental change in the past 140 years, much 82 71 Desert grasslands and savannas located in southern Ari- of it related to livestock grazing. Third, it was the site of 83 72 zona and New Mexico, USA, and northern Chihuahua and seminal research in range science and extraordinary efforts 84 73 Sonora, Mexico—an area we term the Chihuahuan Border- at range restoration. Finally, it is home to some of the most 85 74 lands (Fig. 1). creative and successful efforts to integrate ranching with 86 75 The conservation importance or biodiversity of an organ- conservation (Western, 2000; Curtin, 2002a). 87 76 ism or landscape reflects not just its total abundance, but also Following a brief description of the area, the case study 88 77 its relative abundance (or rarity), and its biological and cul- is divided into three main sections. First, we examine the 89 78 tural importance (Wilson, 1988). We have chosen to focus effects of cattle ranching on the biodiversity of the border- 90 Fig. 1. This study focuses on the Mexico–US Borderlands between El Paso, Texas and Tucson, Arizona. The area encompasses the upper elevation Apachean subregion that includes mountains and adjoining grasslands and the lower elevation grasslands and shrublands within the northern portionsof the northern Chihuahuan subregion (after Dinerstein et al., 2000). UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 3 91 lands, with particular attention to grazing, ranch manage- bird species, 20–25 amphibian species, and 250 species of 144 92 ment, and the evolution of scientific understanding of the butterflies (Dinerstein et al., 2000). 145 93 area’s ecosystems. Next, we consider the accelerating pro- The grasslands and savannas of the Chihuahuan Desert, 146 94 cess of conversion of ranch lands to residential uses, focusing like arid and semi-arid ecosystems worldwide, have been 147 95 on underlying economic dynamics and ecological and cul- disproportionately disturbed and/or destroyed by human ac- 148 96 tural implications. The third section is devoted to initiatives tivities and desertification (Sears, 1935; Curtis, 1956; Reis- 149 97 and strategies employed by local communities to conserve ner, 1986; Manning, 1997). Between 25 and 50% of current 150 98 both the biodiversity and the traditional ranching culture of shrublands (40% of the landscape) may have been grasslands 151 99 the region. The case study concludes with a brief considera- as recently as 200 years ago. At present, approximately 20% 152 100 tion of the environmental and social implications of the Chi- of the landscape contains grasslands, but much of this area 153 101 huahuan Borderlands case for UNESCOs biosphere reserve has a strong shrub component (Dinerstein et al., 2000). 154 102 concept. We suggest that the work being done by community We focus on the grasslands and savannas (including those 155 103 conservation initiatives in the region is consistent with this that have converted to shrublands) of the northern Chi- 156 104 approach and may serve as an example for biodiversity con- huahuan Desert, in southeastern Arizona and southwestern 157 105 servation beyond the network of formally recognized areas. New Mexico. The diversity of this portion of the border- 158 lands is arguably the highest on the continent (Brown and 159 Kodric-Brown, 1995), because it lies at a biogeographic 160 106 2. The setting crossroads: the intersection of the Chihuahuan and Sono- 161 ran deserts, Sierra Madre and Rocky Mountains, and Great 162 107 As defined by the World Wildlife Fund’s Biological As- Plains and Great Basin grasslands and shrublands. In addi- 163 108 sessment (Dinerstein et al., 2000), the Chihuahuan Desert tion to being highly biodiverse, it also serves as a crucial cor- 164 2 109 covers 629,000 km (243,000 square miles) in Mexico and ridor between the North and South American continents, and 165 110 USA. Though historically described as covering a smaller between some of these continents’ major biomes (Gehlbach, 166 111 area (e.g. Brown and Lowe, 1980), according to the most 1981). As such, its conservation is essential to preserving 167 112 recent analysis by Dinerstein et al. (2000), the Chihuahuan dynamic evolutionary processes at a continental scale. 168 113 Desert ecoregion is a complex landscape matrix composed 114 of a series of basins and ranges with a central highland 115 extending from Zacatecas, Mexico, north to the southern 3. Transformation of the Chihuahuan Borderlands I: 169 116 edge of Albuquerque, New Mexico, USA, and from roughly cattle ranching 170 117 El Paso, Texas, west to the valleys just above Tucson and 118 Arizona (Fig.