Viewpoint Nature Divided, Scientists United: US–Mexico Border Wall Threatens Biodiversity and Binational Conservation

ROBERT PETERS, WILLIAM J. RIPPLE, CHRISTOPHER WOLF, MATTHEW MOSKWIK, GERARDO CARREÓN-ARROYO, GERARDO CEBALLOS, ANA CÓRDOVA, RODOLFO DIRZO, PAUL R. EHRLICH, AARON D. FLESCH, RURIK LIST, THOMAS E. LOVEJOY, REED F. NOSS, JESÚS PACHECO, JOSÉ K. SARUKHÁN, MICHAEL E. SOULÉ, EDWARD O. WILSON, JENNIFER R. B. MILLER, AND 2556 SCIENTIST SIGNATORIES FROM 43 COUNTRIES (INCLUDING 1472 FROM THE UNITED STATES AND 616 FROM MEXICO)

ences and walls erected the Endangered Species Act (ESA) and Borderlands Conservation Hotspots Falong international boundaries in the National Environmental Policy Act identified by Defenders of Wildlife the name of national security have (NEPA). With these laws sidelined, represent top-priority areas of high unintended but significant conse- wall construction proceeds without biological diversity and binational­ quences for biodiversity (Trouwborst the necessary depth of environmen- investment in conservation that are et al. 2016). In North America, along tal impact analysis, development of threatened by border wall construc- the 3200-kilometer US–Mexico bor- less-damaging alternative strategies, tion (figure 1; Peters and Clark 2018). der, fence and wall construction over postconstruction environmental mon- Like any large-scale development, the past decade and efforts by the itoring, mitigation, public input, and construction of the wall and associated Trump administration to complete pursuit of legal remedies. Since 2005, infrastructure, such as roads, lights, a continuous border “wall” threaten the DHS has issued eight waivers in and operating bases, eliminates or some of the continent’s most biologi- all four US border states, including degrades natural vegetation, kills ani- cally diverse regions. Already-built three by the Trump administration mals directly or through habitat loss, sections of the wall are reducing the in 2017 for construction in California fragments habitats (thereby subdivid- area, quality, and connectivity of plant and New Mexico. ing populations into smaller, more and animal habitats and are compro- vulnerable units), reduces habitat con- mising more than a century of bina- (2) The border wall harms wildlife nectivity, erodes soils, changes fire tional investment in conservation. populations by eliminating, regimes, and alters hydrological pro- Political and media attention, however, degrading, and fragmenting cesses (e.g., by causing floods). As of often understate or misrepresent the habitats 2017, the DHS had constructed 1050 harm done to biodiversity. The US–Mexico borderlands traverse kilometers of “primary” pedestrian We call on fellow scientists to join six ecoregions (figure 1) containing and vehicle barriers serviced by 8000 us in expressing unified concern over vegetation types that include desert kilometers of roads, as well as many the border wall’s negative impacts on scrub, temperate forests and wood- thousands of kilometers of undesig- wildlife, habitat, and binational collab- lands, semidesert and plains grasslands, nated routes created by off-road patrol oration in conservation and ­scientific subtropical scrublands, freshwater vehicles. Human activity, light, and research. Below, we describe three wetlands, and salt marshes. These noise associated with the wall further ways in which border infrastructure environments span portions of a broad displace wildlife, making additional and security operations (hereafter “the Nearctic–Neotropical transition zone habitat unavailable. border wall”) threaten biodiversity, and support extraordinary biological The border wall threatens some and we outline actions to minimize diversity. Our analysis shows that the populations by degrading landscape these threats. border bisects the geographic ranges of connectivity. Physical barriers prevent 1506 native terrestrial and freshwater or discourage animals from accessing (1) The border wall bypasses animal (n = 1077) and plant (n = 429) food, water, mates, and other critical environmental laws species, including 62 species listed as resources by disrupting annual or sea- In 2005, the US Congress passed Critically Endangered, Endangered, or sonal migration and dispersal routes. the Real ID Act, which gives the Vulnerable by the International Union For example, continuous walls could Department of Homeland Security for Conservation of Nature (IUCN) constrain endangered Peninsular big- (DHS) authority to waive any laws that Red List (supplemental appen- horn sheep (Ovis canadensis nelsoni) slow the wall’s construction, including dix S1, supplemental table S1). Five from moving between California and

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United States

Sonoran Desert San Diego! ! ! Mexicali Tijuana !Tucson !Sonoyta !El Paso Nogales ! ! Agua Prieta The Californias

!Del Rio Sky Islands !Chihuahua

Mexico McAllen ! Brownsville Reynosa ! ! Big Bend Saltillo ! ! Monterrey Matamoros ¯

Lower Rio Ecoregions Conservation hotspots Grande Valley California Coastal Existing border barrier Sonoran Desert Pedestrian Madrean Archipelago Vehicle Chihuahuan Desert 0 40 80 120 160 Southern Texas Plains Miles Western Gulf Coastal Plain

Figure 1. The five Borderlands Conservation Hotspots identified by Defenders of Wildlife, which highlight areas of high biological diversity and significant investment in conservation land and projects. See Peters and Clark (2018) for more information.

Mexico to access water and birth- A continuous border wall could Border barriers could also hinder­ ing sites. It will be likely impossi- disconnect more than 34% of US some low-flying species, like the ble for endangered animals such as nonflying native terrestrial and ­ESA-listed endangered Quino check- the Mexican gray wolf (Canis lupus freshwater animal species (n = 346) erspot butterfly (Euphydryas editha baileyi) and Sonoran pronghorn from the 50% or more of their range quino) and the ESA-candidate ferru- (Antilocapra americana sonoriensis) to that lies south of the border (figure ginous pygmy-owl (Glaucidium brasil- disperse across the border to reestab- 2; appendix S1). If cut off by a bor- ianum; Flesch et al. 2010). Over long lish recently extirpated populations or der wall, 17% of the 346 species we periods, degradation of landscape bolster small existing populations. As analyzed, including jaguar (Panthera connectivity can also drive genetic climate change and increasingly warm, onca) and ocelot (Leopardus par- discontinuities in plants and animals. dry conditions redistribute resources dalis), would have residual US Although the influence of barriers on and shift habitats in the borderlands, populations covering 20,000 square populations depends on both a species’ the wall may prevent some popula- kilometers or less (Table S1). This movement ability and the quantity, tions from tracking these changes. would elevate their risk of extirpa- quality, and spatial arrangement of Fragmented populations may suffer tion within the United States accord- habitats, for many species, the biologi- from reduced genetic diversity and ing to IUCN Red List criteria (table cal impacts of a “wall” are comparable face greater extinction risks. S1; appendix S1). to those of a “fence.” What matters

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The wall places such investments at risk by undermining their objectives and diverting funds away from con- servation projects and toward barrier construction. The wall and associated security operations also obstruct scientific research. US and Mexican scientists have shared distressing stories of being intimidated, harassed, and delayed by border security officers (Peters and Clark 2018). Binational meetings and other collaborative activities become inconvenient and constrained by the hours required to pass border security checkpoints. These factors diminish the amount of much-needed scientific work conducted in the borderlands. This is especially concerning given that the waiving of environmental laws means independent research may pro- vide the best source of scientific insight into the wall’s impacts on biodiversity.

Scientists’ call for action As informed stewards of biodiversity, we urgently advise the following: First, the US Congress should Figure 2. The percentage of species ranges that may become inaccessible to US ensure that the DHS follows the sound species after construction of a US–Mexico border wall. The number of species scientific and legal frameworks of US ranked in the IUCN Red List as Endangered (“EN”) or Vulnerable (“VU”) are environmental laws, including the ESA shown by taxonomic group. Species include nonflying native terrestrial and and NEPA. Any future appropriations freshwater animal species with spatial range data available in the IUCN Red for border barrier construction and List (n = 346). The percentages represent the amount of species’ total ranges operations should require adherence located south of the US–Mexico border. to all environmental laws and preclude their waiver. In areas where the DHS has already issued waivers, we call on the DHS to carry out analysis, mitiga- is whether the barrier is passable, managed for biodiversity conserva- tion, and opportunities for public par- and from a jaguar’s point of view, an tion (comparable to IUCN Protected ticipation as prescribed by all relevant uncrossable fence has the same effect Areas Categories I–IV) in addition to environmental laws. as a wall. 2.6 million hectares managed for sus- Second, for any barrier construction tainable multiuse (IUCN Categories or security operations, the DHS should (3) The border wall devalues V–VI; supplemental appendix S2). In complete rigorous preplanning and conservation investment and total, 18% of the borderlands contain preimplementation surveys to iden- scientific research protected lands. This includes four tify species, habitats, and ecological The US and Mexican governments, clusters of protected lands that sand- resources at risk, and they should work tribes, nongovernmental organiza- wich a total of 400 border kilometers closely with pertinent Mexican and US tions, and private landowners have to create contiguous binational habi- government agencies, tribes, private set aside many millions of acres of tat corridors through the Sonoran landowners, the scientific community, protected land and invested mil- Desert, Sky Islands, Big Bend, and other stakeholders to gather such lions of dollars in conservation, often and Lower Rio Grande (figure 1). information. binationally coordinated (Peters and Numerous binational collaborations Third, the DHS should mitigate as Clark 2018). Within 80 kilometers have also targeted specific species, completely as possible any environ- of the border, 4.5 million hectares of such as the binational aerial census mental harm resulting from projects. US and Mexican protected areas are of endangered Sonoran pronghorn. Mitigation should include forgoing

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physical barriers in places with high by scientists in border countries. The and Washington, DC. William J. Ripple and ecological sensitivity, such as cross- broader, global representation of sci- Christopher Wolf are with the Global Trophic Cascades Program in the Department of border corridors or critical habitat entist signatories from 43 countries Forest Ecosystems and Society at Oregon State for endangered species. Wherever (and counting) speaks to the world- University, in Corvallis, Oregon. Gerardo possible, border barriers should be wide impacts of border barriers on Carreón-Arroyo is with Naturalia, AC, in the designed for maximum wildlife per- biodiversity and to scientists’ unified Ecosystems and Wildlife Conservation Program, meability, including the use of vehicle call for political leaders to consider in Sonora, México. Gerardo Ceballos and Jesús Pacheco are affiliated with the Instituto de barriers instead of pedestrian barriers. wildlife when making national secu- Ecologia at the Universidad Nacional Autonoma When harm to biological resources rity decisions. In recognizing that the de Mexico, in Mexico City, Mexico. Ana Córdova is inevitable, the DHS should imple- threat of border barriers to biodiver- is affiliated with the Department of Urban ment mitigation measures to ensure sity is long term and widespread, we and Environmental Studies at El Colegio de la no net environmental loss, such as by continue to welcome signatories to Frontera Norte, in Ciudad Juárez, Chihuahua, Mexico. Rodolfo Dirzo and Paul R. Ehrlich are purchasing or restoring replacement join and further strengthen our united with the Department of Biology at Stanford habitats. voice of concern. Visit www.defenders. University, in Palo Alto, California. Aaron D. Fourth, the DHS should facilitate org/border-wall to sign and to view Flesch is affiliated with the School of Natural scientific research in the borderlands the updated signatory numbers and Resources and the Environment and The Desert to complement and assist environmen- names. A Spanish version of the article Laboratory – Tumamoc Hill at the University of Arizona, in Tucson, Arizona. Rurik List is tal evaluation and mitigation efforts. is available in supplemental file 3. affiliated with the Área de Investigación en This should include training Border Biología de la Conservación at the Universidad Patrol agents to be sensitive to the Supplemental material Autónoma Metropolitana–Lerma, in Lerma presence of researchers and briefing Supplementary data are available at de Villada, Mexico. Thomas E. Lovejoy is with Border Patrol agents when indepen- BIOSCI online. the Department of Environmental Science and Policy at George Mason University, in dent scientists will be working near Fairfax, Virginia. Reed F. Noss is affiliated the border. References cited with the Southeastern Grasslands Initiative at We urge the US government to Flesch AD, Epps CW, Cain JW, Clark M, Austin Peay State University, in Clarksville, recognize and give high priority to Krausman PR, Morgart JR. 2010. Potential Tennessee, and with the Florida Institute for effects of the United States–Mexico border conserving the ecological, economic, Conservation Science, in Sarasota, Florida. José fence on wildlife. Conservation Biology 24: K. Sarukhán is affiliated with CONABIO and political, and cultural value of the US– 171–181. the Department of Natural Resources at the Mexico borderlands. National security Peters, RL, Clark, M. 2018. In the shadow Instituto de Ecologia at the Universidad Nacional can and must be pursued with an of the wall: Borderlands conservation Autonoma de Mexico, in Mexico City, Mexico. approach that preserves our natural hotspots on the line. Defenders of Wildlife. Michael E. Soulé is professor emeritus in the (16 May 2018; https://newsroom.defenders. heritage. Department of Environmental Studies at the org/in-the-shadow-of-the-wall) University of California, Santa Cruz. Edward O. Trouwborst A, Fleurke F, Dubruelle J. 2016. Wilson is professor emeritus in the Museum of Epilogue Border fences and their impacts on large Comparative Zoology at Harvard University, in We are immensely grateful to the carnivores, large herbivores and biodi- Cambridge, Massachusetts. 2500+ scientist signatories across the versity: An international wildlife law per- spective. Review of European Community Earth who endorsed this article. In and International Environmental Law 25: the continuing spirit of binational col- 291–306. laboration, we received 1470+ scien- tist signatories from the United States Robert Peters, Matthew Moskwik, and Jennifer and 610+ from Mexico, demonstrat- R. B. Miller ([email protected]) are affiliated ing in real-time the deep concern felt with Defenders of Wildlife, in Tucson, Arizona, doi:10.1093/biosci/biy063

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