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. 1). The area contains not just desert shrub- Livestock grazing has been the most extensive land use in 171 119 lands, but also grasslands, cienegas and other riparian habi- the Chihuahuan Borderlands region since the arrival of Eu- 172 120 tats, and montane woodlands. The Chihuahuan Desert is a ropeans some 400 years ago. Yet the impacts of grazing have 173 121 high-elevation desert with typical elevations ranging from varied dramatically, depending on larger socio-economic and 174 122 600 to 1680 m (2000–5500 ft). political circumstances. Haciendas established in the Span- 175 123 The Chihuahuan is one of the most diverse desert ecosys- ish and Mexican periods were recurrently abandoned due to 176 124 tems in the world, rivaled only by the Great Sandy—Tanami warfare with the Apaches; some historians have argued that 177 125 Deserts in Australia and the Namib—Karoo of southern there were large herds of cattle circa 1790–1830 (Morrisey, 178 126 Africa (Olson and Dinerstein, 1998). It is world renowned 1950), but more recent scholars dispute the claim (Sheri- 179 127 as a center of diversity of cacti (family Cactaceae); many dan, personal communication, 1998). In any case, while live- 180 128 desert plants, fish, and reptile species show localized pat- stock have been documented to have had severe long-term 181 129 terns of endemism and exhibit high turnover of species with impacts in areas with consistent long-term Spanish settle- 182 130 distance (Dinerstein et al., 2000). The complexity of the ment, such as central Mexico and northern New Mexico 183 131 freshwater fish assemblages is such that the Chihuahuan (Melville, 1994), in most of the borderlands Spanish set- 184 132 is the only desert ecoregion recognized for both freshwa- tlement was more ephemeral and livestock appear to have 185 133 ter and terrestrial biodiversity; this fact contributed to its been restricted to areas near natural water sources with little 186 134 being selected as a global priority conservation site in the evidence of widespread severe or enduring impacts (Mor- 187 135 World Wildlife Fund’s Global 2000 analysis (Olson and risey, 1950; Bahre, 1991). In northern Mexico and the US 188 136 Dinerstein, 1998). While the grasslands have a high affin- where livestock production was not wholly for subsistence 189 137 ity with the North American great plains, two-thirds of the purposes, it remained a local commerce, usually associated 190 138 grass species in Chihuahuan Desert grasslands are endemic with mining settlements. 191 139 (Burquez et al., 1998). A survey of Chihuahuan Desert flora 140 and fauna is not complete, yet substantial inventories of the 3.1. The cattle boom 192 141 US portion of the desert (less than one-third of the deserts 142 area) have documented approximately 2263 species of vas- Following the Gadsden Purchase in 1854, construction of 193 143 cular plants, over 100 species of mammals and reptiles, 250 railroads into the area, and defeat of the Apaches, Anglo 194 UNCORRECTED PROOF 4 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

195 settlement increased rapidly in the 1870s and 1880s. A con- The paradigm that emerged from this work reflected two 249 196 juncture of national and international factors resulted in a prior judgments. First, the researchers believed that remov- 250 197 flood of livestock into the area, part of the “cattle boom” ing livestock would reverse the damage that excessive graz- 251 198 which spread north and west from Texas following the civil ing had occasioned. Short-term observations were general- 252 199 war (Osgood, 1929; Webb, 1931). Surpluses of investment ized to conclude that recovery would occur in as little as 3 253 200 capital in Great Britain and New England rushed to take years of complete rest (Bentley, 1902; Griffiths, 1910). Rec- 254 201 advantage of free grass on the public domain; early profits ognizing that complete destocking was economically infea- 255 202 of >25% per annum fueled a speculative bubble that over- sible for ranchers, however, researchers sought ways of man- 256 203 whelmed native rangelands (Jackson, 1956; Atherton, 1961). aging livestock that would permit ongoing recovery of for- 257 204 Integrated into national and international markets, the live- age species. The second judgment held that the cornerstone 258 205 stock industry mushroomed: numbers in New Mexico in- of reform would be exclusive grazing leases, which would 259 206 creased from 41,000 cattle and 619,000 sheep in 1870 to enable investment in improvements and reward long-term 260 207 around 800,000 cattle and 5 million sheep in 1885 (Fredrick- stewardship while maintaining public ownership (Potter and 261 208 son et al., 1998). Cattle in Arizona numbered approximately Coville, 1905). Observations and measurements were used to 262 209 38,000 in 1870; by 1891, there were roughly 1.5 million determine fixed carrying capacities for specific range types, 263 210 (Sayre, 1999). so that equitable and economical allotments could be as- 264 211 The boom resulted in the paradigmatic tragedy of the com- signed and administered. In this paradigm, “original” ca- 265 212 mons (Hardin, 1968). Homesteading laws did not allow for pacity represented a range’s potential, while actual capacity 266 213 claims large enough to support a household from livestock, served as a guide to prevent overgrazing; in theory, the two 267 214 and fencing of public domain was illegal. Consequently, set- would converge over time as recovery proceeded. 268 215 tlers claimed areas around water sources and relied on ad- These two judgments rested, in turn, on a set of assump- 269 216 jacent, unregulated public range for grazing. Drought dras- tions that went more or less unchallenged in the emerging 270 217 tically reduced forage production in 1885 and again in the discipline: (1) that rangelands would never find a “higher” 271 218 early 1890s, and market prices for cattle collapsed. Heav- use than livestock production; (2) that spatial and tempo- 272 219 ily indebted operators were reluctant to sell on the sagging ral variability in forage production was of secondary im- 273 220 market, and up to 75% of herds perished on the range dur- portance, as much as it could be abstracted away in carry- 274 221 ing the great drought of 1891–1893 (Wagoner, 1961; Bahre ing capacity calculations and/or mitigated by improvements; 275 222 and Shelton, 1996; Abruzzi, 1995). Photographs from the (3) that the intensity of livestock grazing was the princi- 276 223 time show large areas, previously dominated by perennial pal independent variable determining vegetation response 277 224 grasses, reduced to bare ground. The cycle repeated two on rangelands; and (4) that livestock exclusion would cause 278 225 decades later: high prices during World War I sparked expan- vegetation to revert to its earlier composition and density. 279 226 sion, followed by drought and severe post-war agricultural The exact origins of these assumptions are obscure, but it is 280 227 depression, resulting again in severe overgrazing. Regulated clear that they were imported to desert grasslands from else- 281 228 leases for grazing were implemented on forest reserves after where. The first was debated at the national level, among 282 229 1905; the desert grassland valleys remained open range until policy makers. It was advanced in the name of the Jeffer- 283 230 after 1912 (for State Trust Lands) and 1934 (for unclaimed sonian ideal of independent, democratic, family-scale pro- 284 231 federal lands, managed today by the Bureau of Land Man- ducers (Potter and Coville, 1905). Adapting this vision to 285 232 agement). non-arable rangelands, where much larger areas of land were 286 required to support a family, was problematic and grazing 287 233 3.2. Range science leases afforded a compromise with those who feared the cre- 288 ation of a quasi-aristocratic class of large property owners 289 234 The discipline of range science was born in the aftermath (Stegner, 1954). The other three derived from a venerable 290 235 of the cattle boom, as government agencies scrambled to ideal (common to both oriental and western traditions) of the 291 236 mitigate the damage and put livestock production on a more “balance of nature”, which strongly colored scholarship in 292 237 stable foundation. The southwest was judged to be the most natural history and ecology (Worster, 1977; Wu and Loucks, 293 238 severely impacted region of the country, and much of the 1995). 294 239 earliest research was conducted in the area (Chapline, 1944). Early researchers in the southwest observed numerous 295 240 Early studies estimated that carrying capacities had declined phenomena that conflicted with assumptions (2–4). David 296 241 by >40% in Texas, and even more in Arizona and New Mex- Griffiths, for example, remarked on the role of fire in sup- 297 242 ico (Smith, 1899; Griffiths, 1901; Wooton, 1908). Seminal pressing shrubs Griffiths (1910, p. 22), and on the temporal 298 243 work in these states (Bentley, 1898, 1902; Smith, 1899; Grif- irregularity of perennial grass establishment Griffiths (1910, 299 244 fiths, 1901, 1904, 1907, 1910; Jardine, 1917) established p. 12). Both Griffiths (1904) and Bentley (1902) noted the 300 245 the basic framework of range research and management for extreme variability of rainfall and biogeography in the re- 301 246 decades to come. The goal was invariably, and understand- gion, which made calculating carrying capacities extremely 302 247 ably, to restore rangelands to their “original capacity” (Bent- difficult. Bentley (1902) and Jardine (1917) stressed the im- 303 248 ley, 1902). portance of timing (rest periods) for forage recovery. But 304 UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 5

305 researchers lacked a theoretical framework to explain these model had a profound influence on southwestern range- 355 306 phenomena. lands. The construction of fences, for example—a neces- 356 307 The framework that was available, and which was sub- sary precondition for implementing the entire paradigm— 357 308 sequently applied throughout the west, relegated these gave ranchers direct financial incentive to suppress grass- 358 309 observations to the status of anomalies. It was developed land wildfires, since early fence posts were made of wood 359 310 by Clements and his colleagues at the University of Ne- (Sayre, 2002). The development of artificial water sources, 360 311 braska, based on work in the Great Plains (Tobey, 1981; distributed as evenly as the land and budgets would permit, 361 312 National Research Council, 1994). Clements (1916) postu- affected both the distribution of grazing pressure and the 362 313 lated a singular “climax community” of vegetation for any distribution of other organisms on the landscape (Landsberg 363 314 given site, determined by climatic and abiotic factors which et al., 1997; McAuliffe, 1998). As greater regulatory con- 364 315 were taken as static. As adapted for range management on trol was established on federal lands after World War I (and 365 316 National Forests by Arthur Sampson (1919), a student of later on state lands), grazing impacts became less locally se- 366 317 the Nebraska school, the climax theory understood graz- vere, but more homogeneous and extensive. Stocking rates 367 318 ing as a counter-successional or retrogressive force, which generally declined, partially counterbalanced by improve- 368 319 pushed vegetation back along a linear series of potential ments that enabled grazing in previously unutilized areas 369 320 communities. Most importantly for the present discussion, (McAuliffe, 1998). “Improved” breeds were likewise pro- 370 321 the Clements–Sampson model constructed grazing inten- moted as a means of earning equal or greater returns from 371 322 sity as the key independent variable determining vegetation smaller herds. 372 323 composition. It followed that livestock exclusion would The limits of the model were defined by other factors, 373 324 result in a return to climax conditions. Mobilized through however, which interacted with grazing in complex, unfore- 374 325 the administration of federal agencies and later quantified seen ways. Fixed carrying capacities were necessary for 375 326 by Dyksterhuis (1949) (another Nebraska student), the ranchers seeking credit from lending institutions, but they 376 327 Clements–Sampson model dominated range research and were highly misleading given the natural variability of forage 377 328 public lands administration for most of the 20th century. production on desert grasslands. The same grazing intensity 378 329 Its influence is best seen in the common practice of using could have radically different impacts depending on the 379 330 livestock exclosures as controls, and/or contrasting different timing and quantity of precipitation. And some impacts— 380 331 grazing intensities (light, moderate and heavy), in range arroyo formation and shrub encroachment, for example— 381 332 science “experiments”. were non-linear in relation to grazing: reducing or removing 382 333 Within limits, the Clements–Sampson model did work in livestock would not necessarily cause the damage to “heal”. 383 334 desert grasslands. Following overgrazing, native perennial By mid-century, the model’s shortcomings were obvious to 384 335 grass species were often replaced by annual grasses, forbs, ranchers and researchers familiar with southwestern desert 385 336 and unpalatable shrubs. Removing livestock allowed peren- grasslands. Encroachment by woody species (especially 386 337 nials to reassert themselves, a pattern that was slowed but not mesquite (Prosopis spp.), creosote (Larrea spp.), and acacia) 387 338 reversed—in the short-run, at least—where livestock num- was well advanced in much of the Chihuahuan Borderlands, 388 339 bers were reduced and carefully controlled (Griffiths, 1910). by this time, even in areas excluded from livestock for many 389 340 The failure of efforts to cultivate or otherwise reestablish na- years. The need for fire to maintain desert grasslands was 390 341 tive perennial grasses on Chihuahuan Desert grasslands may voiced (Humphrey, 1958), but it ran afoul of public senti- 391 342 have added to the appeal of the Clements–Sampson model, ments and policies crafted for managing timber. Efforts to re- 392 343 which promised “natural” recovery of palatable species un- move shrubs with bulldozers and chemicals implicitly chal- 393 344 der proper management. Subsequent applied research fo- lenged the prevailing paradigm, but a theoretical alternative 394 345 cused on calculating carrying capacities and developing im- would not emerge for several decades (Westoby et al., 1989). 395 346 provements, especially fencing, water sources, and methods 347 of cultivating and/or stockpiling non-native cultivars for use 3.3. Consequences of grazing 396 348 in drought periods (Griffiths, 1910; Jardine, 1917; Thornber, 349 1910; Wooton, 1916). Clearly livestock grazing has the potential to damage 397 350 Biodiversity was not a concern of early range scientists, desert grasslands. There is no disputing the historic con- 398 351 and even today, research linking different range manage- tribution of overgrazing to arroyo formation, soil erosion, 399 352 ment strategies and measurements of biodiversity is lacking and vegetation change (Hastings and Turner, 1965; Cooke 400 1 353 (Havstad and Coffin Peters, 1999). Nevertheless, with the and Reeves, 1976; Bahre, 1991). Yet from the perspec- 401 354 benefit of hindsight, it is clear that the Clements–Sampson tive of current conservation and management, the question 402 must be how to conserve existing biological values and—if 403 1 The intermediate disturbance hypothesis (Connell, 1978; Hobbs and possible—restore those that have been degraded. What are 404 Huenneke, 1992) would suggest that moderate grazing enhances biodiver- the consequences of current grazing? What can be expected 405 sity (Laycock, 1994). Research to test this is being conducted in short- to mid-grass prairies in Wyoming (Havstad, 2001, personal communica- to happen if it is curtailed or eliminated? 406 tion) and on the Gray Ranch in the Chihuahuan desert grasslands (Jensen, Over the last decade, a number of efforts have been made 407 2001; Curtin, 2002a), yet it remains largely untested. to answer these questions using existing research and in- 408 UNCORRECTED PROOF 6 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

409 formation. A committee of the National Research Coun- Comparisons of surveyor records and current vegetation 463 410 cil (1994) concluded that no rigorous, systematic assess- (Kelt and Valone, 1995; Rich et al., 1999), and analysis 464 411 ment of range conditions in the US was possible, due to of repeat photography and long-term data sets indicate that 465 412 inconsistent methods and inadequate data. The data that woody vegetation has expanded into grasslands over the 466 413 do exist suggest that conditions have generally improved last century (Glendening, 1952; Hastings and Turner, 1965; 467 414 over the past 60 years, but that many rangelands remain Buffington and Herbel, 1965; Grover and Musick, 1990; 468 415 degraded relative to their pre-settlement conditions (USDI Schlesinger et al., 1990; Curtin and Brown, 2001). This 469 416 BLM, 1997). Working from a global data set, Milchunas trend is not limited to the late 1800s and early 1900s, but 470 417 and Lauenroth (1993) found a pattern of increased sensi- may have increased in many locations in the borderlands 471 418 tivity to grazing with increased aridity and/or lack of an since the mid 1970s (Brown et al., 1997; Curtin and Brown, 472 419 evolutionary history of grazing, but no simple correlations 2001)(Fig. 2). While researchers from the Jornada experi- 473 420 between grazing and basic ecological indicators. Stohlgren mental range near Las Cruces, New Mexico, attribute in- 474 421 et al. (1999) analyzed data from multiscale plots in and ad- creases there to growth of existing mesquite (Havstad, per- 475 422 jacent to 26 long-term grazing exclosures in central Rocky sonal communication, 2001), vegetation transects from a 476 423 Mountain grasslands. They found no significant differences site near Portal, Arizona, indicate an increase in shrub and 477 424 in species diversity, evenness, cover of different life-forms, sub-shrub number, not just shrub size (Quo et al., 1995). 478 425 soil texture, or soil percentage of N and C between grazed The data indicates that there are no consistent problems or 479 2 426 and ungrazed sites when examined at large scales (1000 m solutions, but that numerous factors are involved that vary 480 427 plots). The effects of current grazing, they concluded, are spatially and temporally. 481 428 highly variable, inconsistent, and probably minor compared 429 to other disturbances. In a quantitative review of the lit- 3.4.1. Climate 482 430 erature, Jones (2000) found that grazing is most likely to Shrub increases and declines in grasses have occurred 483 431 impact soil related variables, followed by litter cover and in both grazed and ungrazed sites, and are correlated with 484 432 biomass and rodent diversity and richness. More impor- climatic shifts, suggesting that recent “desertification” (de- 485 433 tantly, however, she found that most grazing studies did fined as increases in shrubs and declines in grasses) is not 486 434 not follow basic experimental design requirements, or care- simply a result of grazing (by itself or in combination with 487 435 fully document a range of different use and rest intensi- drought). Rather, higher levels of winter rain, coupled with 488 436 ties, making it impossible to identify consistent responses dry summers, appear to have favored shrub growth over 489 437 to grazing even when statistically significant results oc- grasses (Brown et al., 1997). Analysis of historical ground 490 438 curred. photography back to the 1880s in the Chiricahua Moun- 491 439 Taken together, these studies indicate that there are no tains documents an additional epoch of woody species 492 440 consistent impacts associated with livestock grazing per se; increase in the 1920s and 1930s (Curtin, unpublished). 493 441 that climate, substrate, evolutionary history, and other distur- This supports work by Neilson (1986) and Swetnam and 494 442 bance factors are often more important in determining vege- Betancourt (1998), which indicates that these climatically 495 443 tation response than the number—or presence—of livestock driven vegetation patterns are cyclic and a pervasive part of 496 444 (Curtin, 2002b). In short, the ecology of rangelands cannot southwestern ecosystems. Tree ring chronologies indicate 497 445 be comprehended through the tacitly Clementsian lens of that the recent high levels of rainfall have not occurred 498 446 grazing versus no grazing. in nearly 2000 years (Swetnam and Betancourt, 1998) 499 and thus represent an important perturbation within this 500 447 3.4. Consequences of dynamic interactions in the system. 501 448 borderlands 3.4.2. Fire 502 449 In light of these findings, conservationists, land managers, Fire was historically prevalent in most grasslands and 503 450 and scientists need to focus their efforts not on the presence woodlands in the borderlands region, and changes in veg- 504 451 or absence of livestock, but on the interaction of grazing with etation are undoubtedly also associated with many decades 505 452 other dynamic processes (Curtin, 2002b). The structure and of fire suppression (McPherson and Weltzin, 2000; Webster 506 453 composition of grasslands are outcomes of complex interac- and Bahre, 2001). In the early 20th century, Griffiths (1910) 507 454 tions among a finite set of variables including background observed that mesquite trees increased in grasslands after 508 455 factors (biological diversity, ecosystem resistance and re- fire ceased to be common. Overgrazing in that period re- 509 456 silience, geology, geography, and substrate) and dynamic duced fine fuels and thereby retarded fire spread. Later, fire 510 457 driving forces including climate, fire, and herbivory (by both suppression efforts and woody species encroachment had 511 458 cattle and native species) (Frank et al., 1998; McPherson a similar effect, regardless of grazing pressure. In Mexico, 512 459 and Weltzin, 2000; Curtin and Brown, 2001). Conversion by contrast, natural fire ignitions remained common in re- 513 460 of grasslands to shrub-dominated communities through dy- mote upland areas (grazed or ungrazed) (Swetnam et al., 514 461 namic, non-linear processes exemplifies this newer under- 2001). Today, however, the opposite pattern is beginning to 515 462 standing. emerge: greater fire suppression in Mexico (through direct 516 UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 7

Fig. 2. Though the Chihuahua grasslands and associated montane ecosystems were dramatically altered in the late 1800s, this pattern of change has continued or even increased through the 20th century. For example, in the Chiricahua mountains sites, such as at Faraway ranch depicted above have undergone several epochs of vegetation change through the 19th and 20th centuries, with 28% cover by woody species in 1912, 35% in 1935, and 55% in 1999 (Curtin, unpublished). These cycles of vegetation change create the need for continual management to sustain borderlands ecosystems including restoration of fire, which requires open, unfragmented landscapes.

517 intervention or indirectly, through higher levels of grazing), ing and intensity of precipitation as much as by the fire it- 533 518 while increasing efforts are made to restore fire to some US self. Grasses showed a strong positive response to fire when 534 519 ecosystems. accompanied by relatively high soil moisture, and a neu- 535 520 While fire is considered essential to the survival of most tral response or short-term declines during drought (Curtin, 536 521 grasslands (Manning, 1997; Pyne, 1997), the role of fire in 2002c). These results are consistent with recent findings at 537 522 desert grasslands has been questioned due to data indicating the Jornada experimental range (Drewa, personal communi- 538 523 negative effects on black grama (Bouteloua eriopoda), a ma- cation, 2001). 539 524 jor desert grassland species (Reynolds and Bohning, 1956; 525 Cable, 1965; McPherson, 1995; McClaran and Van Deven- 3.4.3. Herbivory 540 526 der, 1995). Recent data from the Gray Ranch in New Mex- While the impact of cattle on vegetation composition has 541 527 ico contradict this finding, and suggest that the negative ef- long been appreciated, recent studies have documented that 542 528 fects documented in previous studies probably resulted from native species may actually be more important in structuring 543 529 coincident drought conditions. Numerous vegetation tran- desert ecosystems. Birds, insects, and small mammals have 544 530 sects in the Malpai Borderlands of southeastern Arizona and all been found to have major effects on vegetation and the 545 531 southwestern New Mexico indicate that vegetation response biological diversity of arid lands (Crawford, 1986; Chew 546 532 to burns is largely climatically driven, mediated by the tim- and Whitford, 1992; Hawkins and Nicoletto, 1992; Gibbons 547 UNCORRECTED PROOF 8 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

548 et al., 1993; Guo et al., 1995; Weltzin et al., 1997; Brown, ulation growth rates of 2.5–13%. Arizona and New Mexico 599 549 1998; Bock and Bock, 2000; Curtin and Brown, 2001). are among the fastest growing states in the US, with annual 600 550 Long-term studies by Curtin et al. (2000) indicate that population growth rates in the 1990s of 11.2% (doubling 601 551 small mammals are important in dampening the effects of time: 5.8 years) and 9.1% (doubling time: 7.9 years), respec- 602 552 recent climatically driven vegetation change. Increases in tively. This growth is disproportionately concentrated out- 603 553 woody vegetation were much higher in small mammal exclo- side of existing urban boundaries (Atlas of the New West, 604 554 sure plots than in adjoining control areas. This led Curtin and 1997). In Chihuahua and Sonora, Mexico, meanwhile, bor- 605 555 Brown (2001) to hypothesize that livestock grazing might der cities are rapidly expanding, a process accelerated by 606 556 have a similar effect. In a comparison of winter grazed range- the North American Free Trade Agreement (NAFTA). Tens 607 557 land near Rodeo, New Mexico, with an adjoining ranch un- of thousands of Mexicans are migrating to these cities for 608 558 grazed since the late 1960s, increases in woody vegetation industrial work as international competition and declining 609 559 were two-fold in the grazed habitat, and six-fold in the ab- state subsidies render their previous agricultural livelihoods 610 560 sence of grazing. This suggests that cattle grazing, like that untenable. 611 561 of native species, may have served to mitigate vegetation Demographic growth alone cannot explain the urban 612 562 change in the face of recent climatic patterns. boom, however. Even as the population of US metropoli- 613 563 Livestock numbers in the Chihuahuan Borderlands dur- tan areas has increased, their population densities have 614 564 ing the cattle boom were sufficiently high that their impacts generally declined, due to the enlarged home and lot sizes 615 565 appear to have overshadowed (or overwhelmed) some of the associated with suburban development (“sprawl”). A wide 616 566 other factors. But this is no longer the case. Today, ecol- range of government policies—from highway construction 617 567 ogists recognize that the interactions among climate, fire, and mortgage insurance to zoning and taxation—has en- 618 568 herbivory, and vegetation are neither linear nor determinis- abled and/or encouraged this spatial pattern (McKenzie, 619 569 tic, and that the precise outcome of a given interaction may 1994). As evidenced in marketing materials that promote 620 570 never be precisely predictable. What is clear is that simply a “ranching lifestyle”, suburban development places a pre- 621 571 removing livestock will not, by itself, result in restoration of mium on physical isolation, views, wildlife, and other 622 572 earlier conditions at most sites (Curtin, 2002b). As a recent “amenity values” symbolically linked to the famous mythol- 623 573 state-of-the-knowledge review specific to the US–Mexico ogy of ranching (Sayre, 2002). Ironically, the development 624 574 Borderlands concluded, “although livestock grazing (partic- of “ranchettes” has come at the expense of actual working 625 575 ularly in combination with other factors) played an important ranches, which declined by more than 100,000 (more than 626 576 role in vegetation change shortly after Anglo settlement, ex- 10%) nation-wide between 1980 and 1996 (The Nature 627 577 cluding livestock from most sites now will have little or no Conservancy, unpublished). 628 578 impact on abundance of woody plants or non-native herbs Ranches in the US are typically comprised of a patchwork 629 579 during the next several decades” (McPherson and Weltzin, of deeded land and leases to graze on state and/or federal 630 580 2000, p. 4). lands. It is the deeded land that is immediately subject to 631 subdivision and development; this is usually a minority of a 632 ranch, though it may amount to tens of thousands of acres. 633 581 4. Transformation of the Chihuahuan Borderlands II: Most deeded parcels were originally claimed under the var- 634 582 urbanization ious homesteading laws in effect between 1862 and 1934. 635 As a result, they tend to be scattered across the landscape, 636 583 If assumptions (2–4) were mistaken in desert grasslands wherever water could be found at that time. This means, 637 584 from the beginning, assumption (1) held true until approxi- moreover, that deeded acres tend to correspond with the ar- 638 585 mately 1970: arid and semi-arid rangelands had no “higher” eas of greatest ecological value or potential: riparian areas, 639 586 value, economically speaking, than for livestock production. springs and seeps, and floodplains. Larger ranches usually 640 587 Since that time, however, another value has eclipsed live- contain many old homesteads, consolidated over the years 641 588 stock: real estate development. Today, the value of land for and managed as a unit within a matrix of state and federal 642 589 development can be 4–100 times its value for livestock pro- lands (Sheridan, 2001). 643 590 duction, even in remote areas. The consequences of land use Leases to graze on state or federal lands usually transfer 644 591 conversion for biodiversity are not known in detail, but they when the deeded lands are sold. Their value at sale is deter- 645 592 are potentially severe and far less reparable than those as- mined by the productive capacity that they contribute to the 646 593 sociated with present livestock grazing (Havstad and Coffin ranch, calculated in animal units. In this way, leases form 647 594 Peters, 1999, p. 635). part of the equity value of the ranch even though the land 648 remains publicly owned. When the number of animal units 649 595 4.1. Socio-economic causes of ranch conversions permitted under a lease decreases, this equity value dimin- 650 ishes proportionately. 651 596 The Chihuahuan Borderlands are undergoing unprece- Over the last four decades, ranches in the desert grass- 652 597 dented population growth. Between 1990 and 1995, border lands of southern Arizona and New Mexico have performed 653 598 counties in Arizona, New Mexico, and west Texas had pop- rather poorly when viewed as businesses. Cattle prices have 654 UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 9

655 steadily declined in real terms, meaning that returns have highly valued for their scenic beauty or recreational oppor- 711 656 stagnated. Costs for labor, equipment, insurance, taxes, fuel tunities (Rowe et al., 2001). 712 657 and other inputs have increased. Meanwhile, the market 658 value of ranches has increased, sometimes dramatically, in 4.2. Ecological consequences of ranch conversions 713 659 response to the area’s growing population and demand for 660 housing. The value of deeded acres for actual or poten- The subdivision of the grasslands into ranchettes af- 714 661 tial development has come to define the market price of fects biodiversity at two scales. At a local scale it changes 715 662 most ranches, especially near urban areas and along high- species composition within a few hundred meters of a home. 716 663 way corridors. The combined result of these trends is that Odell and Knight (2001) studied the effects of ex-urban 717 664 the rate of return-on-investment for ranching has dwindled development in short-grass steppe of eastern Colorado, a 718 665 to well below market norms (Martin and Jefferies, 1966; grassland of comparable structure to many desert grass- 719 666 Starrs, 1998). Rates of return of less than 3% are common; lands. They found that birds near ranchettes were of the 720 667 in years of low rainfall and/or low market prices, many same generalist species (e.g. robins, black-billed magpies, 721 668 ranches lose money. A recent analysis of federal grazing and brown-headed cowbirds) as found near higher density 722 669 permittees, based on a random sample survey, found that urban environments. Songbirds, such as blue-gray gnat- 723 670 50.4% of public land ranches depend on non-ranching in- catchers, orange-crowned warblers and dusky flycatchers, 724 671 come and can thus be classified as “hobby ranches” (Gentner, were usually not present until hundreds of meters away 725 672 1999). from developments. Carnivores exhibited similar patterns, 726 673 Viewed as investments, however, ranches have been good with domesticated species near homes and coyotes and 727 674 long-term investments over the past 40 years. As cities have foxes farther away. The effects of urbanization thus ramify 728 675 grown and expanded, land values have increased. Ranch- beyond the boundaries of developed areas. Moreover, the 729 676 ers have become “land rich and money poor”, and many species associated with ranchettes have been documented to 730 677 have sold out at high prices, willingly or under pressure of depress populations of native species and overall biodiver- 731 678 debts or estate tax obligations. The majority of ranchers’ sity. Maestas and Knight are currently undertaking a study 732 679 equity now derives from the possibility of subdivision and contrasting birds, carnivores, and plants in protected areas, 733 680 development—in other words, terminating the ranch opera- ranches, and ranchettes. The initial results indicate that 734 681 tion and converting to another land use. protected areas and ranches have comparable biodiversity 735 682 Research conducted elsewhere in the west indicates that and species composition, while in the vicinity of ranchettes 736 683 as landscapes become more suburbanized, increasing diffi- the usual suite of generalist or domesticated species were 737 684 culties with ranching combine with growing expectations of documented (Knight et al., 2002). In short-grass prairie 738 685 lucrative land sales to make the ranching community more in eastern Colorado, Bock and Bock found reduced plant 739 686 hostile to land use control. Escalating land prices increase species diversity even in protected areas adjoining subdivi- 740 687 the costs of incentive-based land conservation programs, and sions (Bock, personal communication, 2000). 741 688 attrition of the ranching community threatens the economic At a larger scale, and perhaps more importantly, ex-urban 742 689 and social viability of ranching. “There comes a point when development tends to eliminate the possibility of restor- 743 690 the landscape begins to be widely recognized as ‘urban’ in ing natural processes. While fire has been the dominant 744 691 character, rather than rural. At this threshold, ranchers shift ecological process in many grassland and savanna ecosys- 745 692 from thinking about ranching as a long-term part of the land- tems (McClaran and Van Devender, 1995; McPherson 746 693 scape to a phenomenon moribund in their locale. Committed and Weltzin, 2000; Swetnam et al., 2001), under existing 747 694 to ranching as a lifeway, they look elsewhere to continue it, institutional arrangements it takes only a small number 748 695 less concerned with the future of the functionally compro- of homes to render fire management effectively impos- 749 696 mised land they now occupy, and more concerned for the sible at the landscape level. Similarly, housing develop- 750 697 short haul with maintaining their opportunity to liquidate” ments in former floodplains—where much deeded land 751 698 (Liffmann et al., 2000). is concentrated—frequently eliminate the option of heal- 752 699 Almost all ranches of any size in southeast Arizona and ing arroyos and restoring pre-entrenchment hydrological 753 700 southwest New Mexico depend on state and/or federal graz- regimes. 754 701 ing leases for their viability. The deeded lands are too small 702 (and in many cases too fragmented) to sustain enough live- 4.3. Strategies to slow fragmentation 755 703 stock to support a household. If the leases are lost or severely 704 cut, the ranch’s deeded acres are rendered valueless for At the regional level, the conversion of ranch lands to 756 705 ranching purposes. In most cases this leaves ranch owners suburban uses is fundamentally driven by a decline in re- 757 706 little choice but to subdivide their private lands—or sell to turns to livestock production relative to rising land values. 758 707 someone who intends to subdivide—to secure their equity. Even lands remote from urban areas carry investment backed 759 708 Thus, stocking rate cuts—often imposed as a result of lit- expectations of potential residential development, whether 760 709 igation by environmental groups—may actually accelerate or not the present owner seeks to capitalize on them. On 761 710 the trend towards ex-urban development, especially in areas an individual or local level, these structural incentives are 762 UNCORRECTED PROOF 10 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

763 countered by a suite of personal, cultural, and environmen- 4.3.2. Community-based conservation, restoration, and 818 764 tal values that resist economic “rationality” (Gentner, 1999). science 819 765 Numerous studies have found that profit is not high among Community-based conservation focuses on local residents’ 820 766 ranchers’ motivations to continue ranching (Smith and Mar- roles and interest in maintaining the landscapes on which 821 767 tin, 1972; Gentner, 1999; Liffmann et al., 2000; Rowe et al., their livelihoods and values depend. It has been widely 822 768 2001). accepted and applied in developing countries (Western 823 769 Effective strategies to slow fragmentation must address, et al., 1994), but rarely employed in North America (West- 824 770 and connect, both levels. Three strategies that have been em- ern, personal communication, 2000). A notable exception 825 771 ployed in the Chihuahuan Borderlands are: (a) conservation is the Malpai Borderlands Group, an organization dedi- 826 772 easements and purchase of development rights (PDR) pro- cated to conservation of an 780,000 acre ecosystem in the 827 773 grams, (b) community-based conservation, restoration and Arizona–New Mexico Borderlands. 828 774 science, and (c) grassbanking. Incorporated as a non-profit in 1994, the Malpai Bor- 829 derlands Group is an outgrowth of the traditional grazing 830 775 4.3.1. Conservation easements and PDR programs association which worked to sustain the local commu- 831 776 Conservation easements and PDR programs are legal tools nity through cooperative land management and livestock 832 777 that remove development potential from a ranch’s private marketing (Remley, 2000). Malpai ranchers had noticed a 833 778 lands in exchange for money and/or other consideration. steady decline in grasslands relative to shrublands in their 834 779 Economically, this allows ranch owners to liquidate the spec- area and they determined that the reintroduction of fire 835 780 ulative portion of their property values while retaining the was essential to preserving their landscape and a viable 836 781 agricultural value and the right to continue ranching. The ranching economy (McDonald, 1996). What was new about 837 782 value of an easement is generally understood as the differ- the Malpai Borderlands Group was that its goals revolved 838 783 ence between the present market value and the value of the around sustaining natural processes, in addition to the tra- 839 784 land encumbered by the easement. This can range from 20 ditional goals of sustaining rural livelihoods. To achieve 840 785 to 90% of the present market value of a ranch (Veslany, these goals they realized they needed the involvement of 841 786 2001). members of the scientific and conservation communities 842 787 Once the right to subdivide has been extinguished, the (Curtin, 2002a). The resulting emphasis on peer reviewed 843 788 ranch’s value rests on its productivity for livestock (and, po- science and constructive interaction between local peo- 844 789 tentially, other values not yet marketable, such as function- ple and researchers is unprecedented in community-based 845 790 ing watersheds, wildlife, etc.). This gives the ranch owner conservation efforts (Western, personal communication, 846 791 strong incentive to preserve and improve range conditions. In 2000). The Malpai Borderlands Group has demonstrated 847 792 other words, these legal tools restore the incentive structure that collaboration can achieve conservation goals unob- 848 793 on which pre-World War II range policies were premised tainable by any of these groups working alone (Curtin, 849 794 (see assumption (1) above). 2002a). 850 795 Conservation easement and PDR programs have been es- Numerous other community-based groups have emerged 851 796 tablished by a variety of private and public entities in the Chi- in recent years to address various dimensions of the 852 797 huahuan Borderlands, although they are more recent and less ranching-conservation-subdivision situation in the Chi- 853 798 well funded than their precursors in the eastern United States huahuan Borderlands region. Many are focused on particular 854 799 (Veslany, 2001). Aside from funding, the biggest obstacle landscapes (like the Malpai Borderlands Group) or water- 855 800 these efforts face is that they can only cover ranchers’ deeded sheds: the Altar Valley Conservation Alliance, the Upper 856 801 acres. The state and federal lands that constitute the majority Gila Watershed Alliance, and the Catron County Citizens 857 802 of most ranches cannot be so encumbered. Conservation of Group, for example. The Quivira Coalition, a non-profit 858 803 deeded ranchlands cannot succeed in the long-term unless based in Santa Fe, New Mexico, takes another approach. 859 804 public lands tenure issues are also resolved because ranch- This cooperative organization of environmentalists, ranch- 860 805 ers are unlikely to sell or donate conservation easements on ers, and scientists, works to advance what it terms “The 861 806 their deeded property if there is a reasonable chance of los- New Ranch” through meetings, publications, projects and 862 807 ing access to adjacent public lands. In that event, the deeded workshops across the southwest. The New Ranch (Sayre, 863 808 land would lose most or all of its value for livestock pro- 2001) synthesizes recent models in range ecology with suc- 864 809 duction, and its value for other purposes would be reduced cessful management practices developed by ranchers on the 865 810 or eliminated by the easement. Meanwhile, state trust lands ground. Like the Malpai Group’s efforts, The New Ranch 866 811 must, by law, generate maximum revenue for beneficiaries is based on replacing confrontation with cooperation, and 867 812 and are thus subject to commercial or residential develop- focuses on restoring ecological processes to sustain ru- 868 813 ment. At present, the only solution to this dilemma is to do ral communities and open space (Winder, 1999). Quivira 869 814 what the Malpai Borderlands Group has done: include an Coalition projects include reclamation of old mine tailings 870 815 escape clause in the conservation easement, under which the piles, riparian restoration, monitoring, drought management 871 816 easement terminates automatically in the event of loss of as- workshops, and efforts to resolve disputes between ranchers 872 817 sociated grazing leases. and government agencies. 873 UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 11

874 4.3.3. Grassbanking and Brown, 2001). Its economic and cultural impacts, mean- 927 875 Communal management of rangelands and sharing of while, would be dramatic because subdivision of private 928 876 grazing rights has been a part of ranching cultures for lands would increase the level of fragmentation by orders of 929 877 hundreds of years (Starrs, 1998), while landscape rest and magnitude, effectively eliminating the use of tools that are 930 878 restoration programs have been a hallmark of progressive critical to grassland and savanna conservation and ecologi- 931 879 farm and rangeland policy since at least the 1930s (Sears, cal restoration. Finally, some argue that ranching should be 932 880 1935; Manning, 1997). A recent integration of communal terminated due to subsidization by the federal government. 933 881 and government land management is the grassbank concept While certainly present, these subsidies amount to a frac- 934 882 developed by the Malpai Borderlands Group. The grass- tion of those provided to other forms of agriculture in the 935 883 bank is an area of rangeland (or a quantity of forage) set US (Starrs, 1998). Industrialized countries have by-en-large 936 884 aside for community use; ranchers are encouraged to utilize determined that subsidizing agriculture to preserve open 937 885 the grassbank while their home range undergoes rest, fire, space in an appropriate use of public funds. Ironically, 938 886 or other restoration treatments. In exchange, the rancher the creation of parks and restoration areas is perhaps the 939 887 donates development rights, conservation easements, or most expensive use of public dollars. For example, initial 940 888 in-kind conservation actions of equal value to the for- estimates from the borderlands indicate even if the Malpai 941 889 age “withdrawn”. In addition to its direct value for range Borderlands Group acquired conservation easements on all 942 890 restoration, grassbanking is a first step toward landscape private lands within their working area, that perpetuating 943 891 level adaptive management. Implicitly, it recognizes that current public/private partnerships costs approximately a 944 892 many ranches are too small to be viable given the patchiness twentieth of the expense of removing local paroralists and 945 893 of rainfall and the variability of other resources in semi-arid instituting public lands management in the form of parks 946 894 and arid landscapes. The high cost of land makes it difficult or wilderness areas (Western, personal communication, 947 895 or impossible for many ranches to expand; grassbanking al- 2000). 948 896 lows for a flexible rescaling of social and economic systems On a more philosophical level, the oppositions posited 949 897 to better accommodate the inherent dynamics of ecological between “protected” and “unprotected”, “natural” and 950 898 systems. “unnatural” warrant critical scrutiny in and of them- 951 selves. Chihuahuan Desert ecosystems, like other arid and 952 semi-arid ecosystems worldwide, are sustained by climate 953 899 5. Conclusion: the Chihuahuan Borderlands and the and its interaction with fire and herbivory (Manning, 1997; 954 900 biosphere reserve concept McPherson and Weltzin, 2000; Curtin and Brown, 2001). 955 None of these factors is purely “natural”; today we know 956 901 The goal of restoring degraded rangelands in the Chi- that even climate is in some measure an artifact of human 957 902 huahuan Desert to their pre-Anglo-settlement conditions is culture, and the structure and composition of grassland and 958 903 as old as range science, and almost as old as commercial savanna ecosystems at the time of European settlement 959 904 ranching itself. For most of the 20th century, the prevailing were partially the result of burning and grazing practices 960 905 model in range science postulated that livestock exclu- by indigenous peoples (Curtis, 1956; Pyne, 1997). The key 961 906 sion would effect such a restoration; management practices to preservation of grassland ecosystems lies not in creating 962 907 and federal policies reflected this assumption, albeit con- more parks, but in preserving the semi-natural matrix that 963 908 strained by economic and political imperatives. Decades of sustains landscapes and human cultural dynamics (Brown 964 909 observations to the contrary have, in recent years, led to and Curtin, 2002). The laudable goals of conservationists 965 910 radically new models—as yet incompletely refined—which cannot be achieved with fences and proscriptions but only 966 911 recognize domestic livestock grazing as only one, rela- with active, adaptive, collaborative management. 967 912 tively minor factor in determining the vegetation, habitat The Chihuahuan Borderlands case suggests that advocates 968 913 conditions, and biodiversity of arid and semi-arid range of ecosystem conservation must move away from asking 969 914 ecosystems. how small an area is sufficient to preserve populations of 970 915 Today’s advocates of curtailing or eliminating live- special interest species or their habitats, and instead ask how 971 916 stock grazing have inherited the assumptions of the big an area is needed to preserve the dynamic interaction 972 917 Clements–Sampson model, apparently without critical ex- of natural processes that sustain a functioning ecosystem, 973 918 amination of its origins and limitations. Implicitly or ex- including its human inhabitants. This approach to conserva- 974 919 plicitly, they call for the creation of more “protected” areas tion is similar to UNESCOs biosphere reserves in that a di- 975 920 where human impacts would seemingly be excluded, in verse set of landscapes and cultures are protected within the 976 921 the belief that this would restore pre-settlement conditions context of a matrix of different land ownerships, rather than 977 922 and/or preserve biodiversity. While this may be true in a single government controlled preserve. Community-based 978 923 some areas, it would not likely have the desired ecological efforts in the borderlands area are demonstrating the vi- 979 924 effects in southwestern grasslands where current climatic ability of the biosphere approach in a social, political, 980 925 conditions appear to be driving extensive vegetation change and economic setting where it has not been deployed 981 926 (Brown et al., 1997; Swetnam and Betancourt, 1998; Curtin previously. 982 UNCORRECTED PROOF 12 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

983 Acknowledgements Buffington, L.C., Herbel, C., 1965. Vegetation changes on a semidesert 1041 grassland range from 1858 to 1963. Ecol. Monogr. 35, 139–164. 1042 Burquez, A., Martinez-Yrzar, A., Miller, M., Rojas, K., de los Angeles 1043 984 The proceeding paper represents the outcome of work- Quintana, M., Yetman, D., 1998. Mexican grasslands and the changing 1044 985 shops and meetings connected with the UNESCO/Columbia aridlands of Mexico: an overview and a case study in northwestern 1045 986 University International Conference on Biodiversity and So- Mexico. In: Tellman, B., Finch, D.M., Edminster, C., Hambre, R. 1046 987 ciety and as such represents an integration of the view points (Eds.), Proceedings of the RMRS-P-3 Conference on the Future of Arid 1047 Grasslands: Identifying Issues, Seeking Solutions, Vol. 13. Tucson, 1048 988 of literally dozens of biologists and land management ex- AZ, 9 October 1996, US Department of Agriculture, Forest Service, 1049 989 perts. We thank conference organizers and participants in Rocky Mountain Research Station, Fort Collins, CO. 1050 990 a workshop at the Audubon Research Ranch in Elgin, Ari- Cable, D.R., 1965. Damage to mesquite, Lehmann lovegrass, and black 1051 991 zona and the conference itself at Columbia University in grama by a hot June fire. J. Range Manage. 24, 170–176. 1052 992 New York City for their insights. We also thank numer- Chapline, W.R., 1944. The history of western range research. Agric. 1053 History 18, 127–143. 1054 993 ous individuals who have read and commented on drafts of Chew, R.M., Whitford, W.G., 1992. A long-term positive effect of 1055 994 this manuscript including J. Atchley (World Wildlife Fund), kangaroo rats (Dipodomys spectabilis) on creosote bushes (Larrea 1056 995 K. Havsted (Jornada Experimental Range), and Bill Mc- tridentate). J. Arid Environ. 22, 375–386. 1057 996 Donald (Malpai Borderlands Group) and two anonymous Clements, F.E., 1916. Plant Succession: An Analysis of the Development 1058 of Vegetation. Publication 242, Carnegie Institution of Washington, 1059 997 reviewers. This work was supported in part by the Forest Washington, DC. 1060 998 Service Rocky Mountain Research Station, the Jornada Ex- Connell, J.H., 1978. Diversity in tropical rain forest and coral reefs. 1061 999 perimental Range, Audubon Research Ranch, Udall Center, Science 199, 1302–1310. 1062 1000 UNESCO and through grants from the Claiborne-Ortenberg Cooke, R.U., Reeves, R.W., 1976. Arroyos and Environmental Change in 1063 1001 Foundation, Hewlett Foundation, Thaw Charitable Trust, the American Southwest. Clarendon Press, Oxford, UK. 1064 Crawford, C.S., 1986. The role of invertebrates in desert ecosystems. 1065 1002 The Nature Conservancy, and the Wallace Research Fund. In: Whitford, W.G. (Ed.), Pattern and Process in Desert Ecosystems. 1066 University of New Mexico Press, Albuquerque, pp. 73–91. 1067 Curtin, C.G., 2002a. Integration of science and community-based 1068 1003 References conservation in the Mexico–US Borderlands. Conserv. Biol. in press. 1069 Curtin, C.G., 2002b. Cattle grazing, rest, and restoration in arid lands. 1070 1004 Abruzzi, W.S., 1995. The social and ecological consequences of early Conservation Biology, in press. 1071 1005 cattle ranching in the little Colorado river basin. Hum. Ecol. 23 (1), Curtin, C.G., 2002c. Fire as a landscape restoration and maintenance tool 1072 1006 75–98. in the Mexico–US Borderlands. In: Proceedings of the First National 1073 1007 Atherton, L., 1961. The Cattle Kings. Indiana University Press, Congress on Fire Ecology, Prevention, and Management (Review). Tall 1074 1008 Bloomington. Timbers Research Station, Tallahasee, FL. 1075 1009 Atlas of the New West, 1997. Center of the American West—University Curtin, C.G., Brown, J.H., 2001. Climate and herbivory in structuring 1076 1010 of Colorado at Boulder, W.W. Norton & Company, New York. the vegetation of the Malpai Borderlands. In: Bahre, C.J., Webster, G. 1077 1011 Bahre, C.J., 1991. A Legacy of Change: Historic Human Impact on (Eds.), Changing Plant Life of La Frontera: Observations of Vegetation 1078 1012 Vegetation in the Arizona Borderlands. The University of Arizona Change in the United States–Mexico Borderlands. University of New 1079 1013 Press, Tucson. Mexico Press, Albuquerque, pp. 84–94. 1080 Curtin, C.G., Kelt, D.A., Frey, T.C., Brown, J.H., 2000. On the role of 1081 1014 Bahre, C.J., Shelton, M.L., 1996. Rangeland destruction: cattle and drought small animals in mediating climatically driven vegetation change. Ecol. 1082 1015 in southeastern Arizona at the turn of the century. J. Southwest 38 (1), Lett. 3, 309–317. 1083 1016 1–22. Curtis, J.T., 1956. The modification of mid-latitude grasslands and forests 1084 1017 Bentley, H.L., 1898. Cattle Ranges of the Southwest: A History of the by man. In: Thomas Jr., W.L. (Ed.), Man’s Role in Changing the Face 1085 1018 Exhaustion of the Pasturage and Suggestions for its Restoration. US of the Earth. Chicago University Press, Chicago, IL, USA, pp. 721–736. 1086 1019 Department of Agriculture, Farmer’s Bulletin No. 72, Government Dinerstein, E., Olson, D., Atchley, J., Loucks, C., Contreras-Balderas, 1087 1020 Printing Office, Washington, DC. S., Abell, R., Inigo, E., Enkerlin, E., Williams, C.E., Castilleja, G., 1088 1021 Bentley, H.L., 1902. Experiments in Range Improvement in Central Texas. 2000. Ecoregion-based conservation of the Chihuahuan Desert: a 1089 1022 US Department of Agriculture, Bureau of Plant Industry, Bulletin No. biological assessment. The Nature Conservancy. World Wildlife Fund, 1090 1023 13, Government Printing Office, Washington, DC. Commission National para el Conocimiento y Uso de la Biodiversidad 1091 1024 Bock, C.E., Bock, J.H., 2000. The View from Bald Hill: 30 Years in an (CONBIO), PRONATURA Noreste, Instituto Tecnologico y de 1092 1025 Arizona Grassland. University of California Press, Berkeley. Estudios Superiores de Monterrey (ITESM). 1093 1026 Brown, J.H., 1998. The desert granivory system at Portal. In: Resetaritis Dobyns, H.F., 1981. From Fire to Flood: Historic Human Destruction 1094 1027 Jr., W.L., Bernardo, J. (Eds.), Issues and Perspectives in Experimental of Sonoran Desert Riverine Oases. Anthropological Papers No. 20, 1095 1028 Ecology. Oxford University Press, Oxford, UK. Ballena Press, Socorro, New Mexico. 1096 1029 Brown, J.H., Curtin, C.G., 2002. Management of the semi-natural matrix. Donahue, D.L., 1999. The Western Range Revisited: Removing Livestock 1097 1030 In: Marquet, P.A., Bradshaw, G., Mooney, H.A. (Eds.), Disruptions from Public Lands to Conserve Native Biodiversity. University of 1098 1031 and Variability: The Dynamics of Climate, Human Disturbance and Oklahoma Press, Norman, OK, USA. 1099 1032 Ecosystem in the Americas. in press. Dyksterhuis, E.J., 1949. Condition and management of range land based 1100 1033 Brown, J.H., Kodric-Brown, A., 1995. Biodiversity in the borderlands. on quantitative ecology. J. Range Manage. 2 (3), 104–115. 1101 1034 Nat. History 105, 58–61. Fleischner, T.L., 1994. Ecological costs of livestock grazing in western 1102 1035 Brown, D.E., Lowe, C.H., 1980. Biotic communities of the Southwest. North America. Conserv. Biol. 8 (3), 629–644. 1103 1036 General Technical Report RM—70, USDA Forest Service Rocky Frank, D.A., McNaughton, S.J., Tracy, B.F., 1998. The ecology of the 1104 1037 Mountain Research Station. earth’s grazing ecosystems. Bioscience 48, 513–521. 1105 1038 Brown, J.H., Valone, T.J., Curtin, C.G., 1997. Reorganization of an arid Fredrickson, E., Havstad, K.M., Estell, R., Hyder, P., 1998. Perspectives 1106 1039 ecosystem in response to local climate change. Proc. Natl. Acad. Sci. on desertification: southwestern United States. J. Arid Environ. 39, 1107 1040 U.S.A. 94, 9729–9733. 191–207. 1108 UNCORRECTED PROOF C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14 13

1109 Gehlbach, F.G., 1981. Mountain islands and desert seas: a natural history Martin, P.S., 1984. Pleistocene overkill: the global model. In: Martin, 1176 1110 of the US–Mexico Borderlands. Texas A&M Press, Austin, TX, USA. P.S., Klein, R.G. (Eds.), Quaternary Extinctions. University of Arizona 1177 1111 Gentner, B., 1999. Characteristics of Public Land Grazing Permittees. Press, Tucson, pp. 354–403. 1178 1112 Unpublished Master’s Thesis, Oregon State University, Oregon. Martin, W.E., Jefferies, G.L., 1966. Relating ranch prices and grazing 1179 1113 Gibbons, R.P., Havstad, K.H., Billhiemer, D.D., Herbel, C.H., 1993. permit values to ranch productivity. J. Farm Econ. 48 (2), 233–242. 1180 1114 Creosote vegetation after 50 years of lagomorph exclusion. Oecologia McAuliffe, J.R., 1998. Rangeland water developments: conservation 1181 1115 94, 210–217. solution or illusion? In: Proceedings of a Symposium on Environmental, 1182 1116 Glendening, G.E., 1952. Some quantitative data on the increase of Economic, and Legal Issues Related to Rangeland Water Developments, 1183 1117 mesquite and cactus on a desert grassland range in southern Arizona. Vol. 335. The Center for the Study of Law, Science, and Technology, 1184 1118 Ecology 33, 319–328. Arizona State University College of Law, Tempe, Arizona, 13–15 1185 1119 Griffiths, D., 1901. Range Improvement in Arizona. US Department of November 1997, p. 310. 1186 1120 Agriculture, Bureau of Plant Industry, Bulletin No. 4, Government McClaran, M.P., Van Devender, T.R., 1995. The Desert grassland. The 1187 1121 Printing Office, Washington, DC. University of Arizona Press, Tucson. 1188 1122 Griffiths, D., 1904. Range Investigations in Arizona. US Department of McDonald, B., 1996. Fire and the Malpai Borderlands Group: one 1189 1123 Agriculture, Bureau of Plant Industry, Bulletin No. 67, Government Rancher’s perspective. In: Ffolliot, P.F., Debano, L., Baker, M.B., 1190 1124 Printing Office, Washington, DC. Gottfried, G.J., Solis-Garza, G., Edminster, C.B., Neary, D.G., 1191 1125 Griffiths, D., 1907. The Reseeding of Depleted Range and Native Pastures. Allen, L.S., Hhamre, R.H. (Eds), Effects of Fire on Madrean 1192 1126 US Department of Agriculture, Bureau of Plant Industry, Bulletin No. Province Ecosystems. USDA Forest Service General Technical Report 1193 1127 117, Government Printing Office, Washington, DC. RM-GTR-289, pp. 175–177. 1194 1128 Griffiths, D., 1910. A Protected Stock Range in Arizona. US Department McKenzie, E., 1994. Privatopia: Homeowners’ Associations and the Rise 1195 1129 of Agriculture, Bureau of Plant Industry, Bulletin No. 177, Government of Private Government. Yale University Press, New Haven. 1196 1130 Printing Office, Washington, DC. McPherson, G.R., 1995. The role of fire in desert grasslands. In: McClaran, 1197 1131 Grover, H.D., Musick, H.B., 1990. Shrubland encroachment in New M.P., Van Devender, T.R., (Eds.), The Desert Grassland. University of 1198 1132 Mexico. Climate Change 17, 305–330. Arizona Press, Tucson, pp. 130–151. 1199 1133 Guo, Q., Thompson, D.B., Valone, T.J., Brown, J.H., 1995. The effects McPherson, G.R., Weltzin, J.F., 2000. Disturbance and Climate 1200 1134 of vertebrates, granivores and folivores on plant community structure Change in United States–Mexico Borderland Plant Communities: 1201 1135 in the Chihuahan Desert. Oikos 73, 251–259. A State-of-the-Knowledge Review. USDA Forest Service, Rocky 1202 1136 Hardin, G., 1968. The tragedy of the commons. Science 162, 1243–1248. Mountain Research Station General Technical Report RMRS-GTR-50. 1203 1137 Hastings, R.J., Turner, R.M., 1965. The Changing Mile: An Ecological Melville, E., 1994. A Plague of Sheep: Environmental Consequences of 1204 1138 Study of Vegetation Change With Time in the Lower Mile of an Arid the Conquest of Mexico. Cambridge University Press, New York, USA. 1205 1139 and Semi-Arid Region. University of Arizona Press, Tucson, Arizona, Milchunas, D.G., Lauenroth, W.K., 1993. Quantitative effects of grazing 1206 1140 USA. on vegetation and soils over a global range of environments. Ecol. 1207 1141 Havstad, K.M., Coffin Peters, D.P., 1999. People and rangeland Monogr. 63, 327–366. 1208 1142 biodiversity—North America. In: Proceedings of the Sixth International Morrisey, R.J., 1950. The early range cattle industry in Arizona. Agric. 1209 1143 Rangeland Congress, Vol. 2. Townsville, Australia, pp. 634–638. History 24, 151–156. 1210 1144 Hawkins, L.K., Nicoletto, P.F., 1992. Kangaroo rat burrows structure and National Research Council, 1994. Rangeland Health: New Methods to 1211 1145 spatial organization of ground dwelling animals in semidesert grassland. Classify, Inventory, and Monitor Rangelands. National Academy Press, 1212 1146 J. Arid Environ. 23, 199–208. Washington, DC. 1213 1147 Hobbs, R.J., Huenneke, L.F., 1992. Disturbance, diversity, and invasion: Neilson, R.P., 1986. High-resolution climatic analysis of southwestern 1214 1148 implications for conservation. Conserv. Biol. 6 (3), 324–337. biogeography. Science 232, 27–34. 1215 1149 Humphrey, R.R., 1958. The Desert Grassland. Bot. Rev. 24, 193–252. Odell, E., Knight, R., 2001. Songbird and medium-sized mammal 1216 1150 Jackson, W.T., 1956. British interests in the range cattle industry. In: communities associated with ex-urban development in Pitkin County, 1217 1151 Frink, M., Jackson, W.T., Spring, A.W. (Eds.), When Grass Was King? Colorado. Conserv. Biol., in press. 1218 1152 University of Colorado Press, Boulder, pp. 135–334. Olson, D.M., Dinerstein, E., 1998. The global 2000: a representative 1219 1153 Jardine, J.T., 1917. Increased Cattle Production on Southwestern Ranges. approach to conserving the earth’s most biologically valuable 1220 1154 USDA Bulletin No. 588, Government Printing Office, Washington, DC. ecoregions. Conserv. Biol. 3, 502–512. 1221 1155 Jensen, M.N., 2001. Can cows and conservation mix. Bioscience 51, 85– 1156 90. Osgood, E.S., 1929. The Day of the Cattleman. University of Chicago 1222 1157 Jones, A., 2000. Effects of cattle grazing on North American arid Press, Chicago. 1223 1158 ecosystems: a quantitative review. West. N. Am. Nat. 60, 155–164. Potter, A.F., Coville, F.V., 1905. Grazing on Public Lands: Extracts from 1224 1159 Kelt, D.A., Valone, T.J., 1995. Effects of grazing on the abundance the Report of the Public Lands Commission. USDA Forest Service 1225 1160 and diversity of annual plants in Chihuahuan Desert scrub habitat. Bulletin No. 62, Government Printing Office, Washington, DC. 1226 1161 Oecologica 103, 191–195. Pyne, S.J., 1982. Fire in America. Princeton University Press, Princeton, 1227 1162 Knight, R.L., Gilgert, W., Marston, E., 2002. Ranching West of the 100th NJ. 1228 1163 Meridian. Island Press, Washington, DC. Pyne, S.J., 1997. World Fire. University of Washington Press, Seattle, WA. 1229 1164 Landsberg, J., James, C.D., Morton, S.R., Hobbs, T.J., Stol, J., Drew, Quo, Q., Thompson, D.B., Valone, T.J., Brown, J.H., 1995. The effects 1230 1165 A., Tongway, H., 1997. The effects of artificial sources of water on of vertebrate granivores and folivores on plant community structure in 1231 1166 rangel and biodiversity. Environment. Final Report to the Biodiversity the Chihauhuan Desert. Oikos 73, 251–259. 1232 1167 Convention and Strategy Section of the Biodiversity Group, Australia. Reisner, M., 1986. Cadillac Desert: The American West and Its 1233 1168 Laycock, W.A., 1994. Implications of grazing versus no grazing on Disappearing Water. Viking Press, New York. 1234 1169 today’s rangelands. In: Vavra, M., Laycock, W.A., Pieper, R.D. (Eds.), Remley, D., 2000. Bell Ranch: Cattle Ranching in the Southwest, 1235 1170 Ecological Implications of Livestock Herbivory in the West. Society 1824–1947. Yucca Tree Press, Las Cruces, NM, USA. 1236 1171 for Range Management, Denver, pp. 250–280. Reynolds, H.G., Bohning, J.W., 1956. Effects of burning on a desert 1237 1172 Liffmann, R.H., Huntsinger, L., Forero, L.C., 2000. To ranch or not to grass-shrub range in southern Arizona. Ecology 37, 769–777. 1238 1173 ranch: home on the urban range. J. Range Manage. 53, 362–370. Rich, K.M., Muldavin, E., Valone, T.J., 1999. Historical Vegetation of 1239 1174 Manning, R., 1997. Grassland: the History, Biology, and Promise of the the Borderlands Ecosystem Management Area. Unpublished Report to 1240 1175 American Prairie. Penguin Books, Middlesex, UK. US Forest Service and Malpai Borderlands Group. 1241 UNCORRECTED PROOF 14 C.G. Curtin et al. / Environmental Science & Policy 218 (2002) 1–14

1242 Rowe, H.I., Bartlett, E.T., Swanson Jr., L.E., 2001. Ranching motivations Tobey, R.C., 1981. Saving the Prairies: the Life Cycle of the Funding 1284 1243 in two Colorado counties. J. Range Manage. 54, 314–321. School of American plant ecology, 1895–1955. University of California 1285 1244 Sampson, A.W., 1919. Plant Succession in Relation to Range Management. Press, Berkeley, CA. 1286 1245 USDA Bulletin No. 791, Government Printing Office, Washington, USDI BLM, 1997. Working Together for the Health of America’s Public 1287 1246 DC. Lands. US Department of Interior, Bureau of Land Management, 1997 1288 1247 Sayre, N.F., 1999. The cattle boom in southern Arizona: towards a critical Annual Report, Washington, DC. 1289 1248 political ecology. J. Southwest 41 (2), 239–271. Veslany, K. (Ed.), 2001. Purchase of Development Rights: Conserving 1290 1249 Sayre, N.F., 2001. The New Ranch Handbook: A Guide to Restoring Lands, Preserving Western Livelihoods. Western Governors’ 1291 1250 Western Rangelands. Quivira Coalition, Santa Fe. Association, Trust for Public Land, and National Cattlemen’s Beef 1292 1251 Sayre, N.F., 2002. Ranching, Endangered Species, and Urbanization in the Association, Denver. 1293 1252 Southwest: Species of Capital. University of Arizona Press, Tucson, Wagoner, J.J., 1961. Overstocking of the ranges in southern Arizona 1294 1253 in press. during the 1870s and 1880s. Arizoniana 2 (1), 23–27. 1295 1254 Schlesinger, W.H., Reynolds, J.F., Cunningham, G.L., Huenneke, L.F., Webb, W.P., 1931. The Great Plains. University of Nebraska Press, Lincoln 1296 1255 Jarrell, W.M., Virginia, R.A., Whitford, W.G., 1990. Biological (reprinted 1981). 1297 1256 feedback in global desertification. Science 247, 1043–1048. Webster, G.L., Bahre, C.J., 2001. Changing Plant Life of La Frontera. 1298 1257 Sears, P.B., 1935. Deserts on the March. Island Press, Washington, DC. University of New Mexico Press, Albuquerque. 1299 1258 Sheridan, T.E., 2001. Cows, condos, and the contested commons: the Weltzin, J.E., Archer, S., Heitchmidt, R.K., 1997. Small mammal 1300 1259 political ecology of ranching on the Arizona–Sonora Borderlands. regulation of vegetation structure in a temperate savanna. Ecology 78, 1301 1260 Hum. Org. 60 (2), 141–152. 751–763. 1302 1261 Smith, J.G., 1899. Grazing Problems in the Southwest and How to Meet Western, D., 2000. Conservation in a human-dominated world. Issues in 1303 1262 Them. USDA Division of Agrostology Bulletin No. 16, Government Science and Technology (on-line). Spring. 1304 1263 Printing Office, Washington, DC. Western, D., Wright, R.M., Strum, S.C., 1994. Natural Connections: 1305 1264 Smith, A.H., Martin, W.E., 1972. Socioeconomic behavior of cattle Perspectives in Community-based Conservation. Island Press, 1306 1265 ranchers, with implications for rural community development in the Washington, DC. 1307 1266 west. Am. J. Agric. Econ. 54 (2), 217–225. Westoby, M., Walker, B.H., Noy-Meir, I., 1989. Opportunistic management 1308 1267 Starrs, P.F., 1998. Let the Cowboy Ride: Cattle Ranching in the American for rangelands not at equilibrium. J. Range Manage. 42, 266–274. 1309 1268 West. The Johns Hopkins University Press, Baltimore. Wilson, E.O., 1988. Biodiversity. National Academy Press, Washington, 1310 1269 Stegner, W., 1954. Beyond the Hundredth Meridian. Houghton Mifflin, DC. 1311 1270 Boston. Winder, J., 1999. The Quivira Coalition and the New Ranch. Range 1312 1271 Stohlgren, T.J., Schell, L.D., Vanden Heuvel, B., 1999. How grazing and Magazine, Winter, pp. 13–15. 1313 1272 soil quality affect native and exotic plant diversity in rocky mountain Wooton, E.O., 1908. The Range Problem in New Mexico. New Mexico 1314 1273 grasslands. Ecol. Appl. 9, 45–64. Agricultural Experiment Station Bulletin No. 66, Albuquerque Morning 1315 1274 Swetnam, T.W., Betancourt, J.L., 1998. Mesoscale disturbance and Journal Press, Albuquerque. 1316 1275 ecological response to decadal climatic variability in the American Wooton, E.O., 1916. Carrying Capacity of Grazing Ranges in Southern 1317 1276 southwest. J. Climate 11, 3128–3147. Arizona. USDA Bulletin No. 367, Government Printing Office, 1318 1277 Swetnam, T.W., Baisan, C.H., Kaib, J.M., 2001. Forest fire histories of Washington, DC. 1319 1278 the sky islands of La Frontera. In: Bahre, C.J., Webster, G. (Eds.), Worster, D., 1977. Nature’s Economy: The History of Ecological Ideas. 1320 1279 Changing plant life of La Frontera: Observations of Vegetation Change Cambridge University Press, New York, USA. 1321 1280 in the United States–Mexico Borderlands. University of New Mexico Wu, J., Loucks, O.L., 1995. From balance of nature to hierarchical patch 1322 1281 Press, Albuquerque, pp. 95–119. dynamics: a paradigm shift in ecology. Q. Rev. Biol. 70, 439–466. 1323 1282 Thornber, J.J., 1910. The Grazing Ranges of Arizona. Bulletin No. 65, Wuerthner, G., 1994. Subdivisions versus agriculture. Conserv. Biol. 8, 1324 1283 University of Arizona Agricultural Experiment Station, Tucson. 905–908. 1325

UNCORRECTED PROOF