El Pinacate and Gran Desierto de Altar Biosphere Reserve

The construction of the border wall between the United States and Mexico, which forms the northern boundary of the site presents significant challenges to the ecological connectivity between the site and other protected areas in the US including the Organ Pipe Cactus National Monument and Biosphere Reserve, Cabeza Prieta National Wildlife Refuge, and the Barry M. Goldwater Range which supports key elements of the site's OUV, most notably migratory ungulates such as Sonoran pronghorn sheep and bighorn sheep (IUCN Consultation, 2020; UNESCO, 2024). Of the 140 km of border between Mexico and the US along the northern boundary of the property, the border wall extends 109 km (according to the USA figures) or 128.7 km (according to Mexican figures), with the only gaps remaining in the mountainous areas (UNESCO, 2024). The border wall consists of a solid metal wall, parallel barbed wire mesh fence, as well as parallel roads. The infrastructure represents a barrier that disrupts free movement of wildlife, which can result in negative impacts on populations of several species, restricting their access to critical feeding and breeding areas, with likely consequences for genetic variability. There are only small wildlife openings along the Organ Pipe Cactus National Monument (UNESCO, 2024). Furthermore, alterations to the flow and disposal of surface water were also observed as a result of the construction (State Party of Mexico, 2020).

Although the border wall is located outside the formal boundaries of the World Heritage property, its effects on the site’s values are direct. The physical and road infrastructure associated with the wall—including metal fences, parallel roads, and barbed wire—disrupts key ecological processes by blocking the movement of wide-ranging species such as the Sonoran pronghorn (Antilocapra americana sonoriensis) and the desert bighorn sheep (Ovis canadensis mexicana), affecting their access to critical feeding, breeding, and genetic dispersal areas within the site. This type of impact represents a direct alteration of the ecological functionality of the transboundary ecosystem. Surface runoff has also been affected due to topographic modifications caused by the construction. Despite binational monitoring and conservation efforts—such as the Sonoran Pronghorn Recovery Plan and studies promoted by the USGS—ecological connectivity between the site and the protected area of southern Arizona remains seriously compromised. An urgent mitigation strategy based on effective binational cooperation and the restoration of wildlife corridors is needed to restore the ecological connectivity across the transboundary landscape (UNESCO, 2024). Binational collaboration is ongoing: The Sonoran Pronghorn Recovery Plan has been prepared and includes a captive breeding programme, water and forage supply improvement project, pronghorn translocation programme, census and aerial monitoring; In addition, the National Park Service has initiated a study to be conducted by scientists from the US Geological Survey and the University of Arizona to assess the impacts of the US-Mexico border barrier on mammal communities in the Sonoran Desert, with initial results expected by 2025 and a final report in early 2026 (UNESCO, 2024; State Party of Mexico, 2025).

The main invasive alien species affecting the property are Tamarix ramosissima (saltcedar), Brassica tournefortii (Sahara mustard), and Gambusia affinis (western mosquitofish). Saltcedar (Tamarix ramosissima) is primarily found along the Sonoyta River channel, within the Agua Dulce Ramsar site. This species competes aggressively with native riparian vegetation, alters soil salinity, and can disrupt the local hydrological regime (State Party of Mexico, 2023). Sahara mustard (Brassica tournefortii) has a broader distribution. Although its germination depends on rainfall events, its invasive behaviour is concerning, as it displaces native species and contributes to fire risk by altering the native fuel load. The mosquitofish (Gambusia affinis) poses a threat to native aquatic species in temporary water bodies. The presence of buffelgrass (Cenchrus ciliaris) and feral burros (Equus asinus) has also been reported. Although currently found at lower densities and mostly in areas with higher human use, such as those near roads, these species have historically had negative impacts on vegetation structure, soil compaction, and the hydrological balance of the desert ecosystem (El Pinacate and GDA Biosphere Reserve, n.d.). These alien species represent a direct and growing threat to the Outstanding Universal Value of the property, affecting the composition and dynamics of unique desert ecosystems, the natural landscape, and the viability of endemic and threatened species.

The Puerto Peñasco Photovoltaic Power Plant, located 7 km east of the property’s buffer zone, commenced construction in 2022 with a substation located in the buffer zone (State Party of Mexico, 2023a; UNESCO, 2024). Although it is located outside the buffer zone of the property, due to its large footprint on limited desert habitat, it has a direct impact on wide-ranging fauna species, particularly the Sonoran pronghorn (Antilocapra americana sonoriensis), whose natural distribution includes seasonal movements into the property (State Party of Mexico, 2023a; UNESCO, 2024). The power transmission network associated with the project extends from the plant and crosses approximately 7.75 km within the property, following the route of the Puerto Peñasco–Gulf of Santa Clara state highway. However, the remainder of the transmission line runs through both the eastern and western buffer zones of the property, as well as the Upper Gulf of California and Colorado River Delta Biosphere Reserve, located to the south. This direct and immediate overlap with the property’s boundary and other protected areas poses a risk to landscape integrity and regional ecological connectivity. Although technical inputs on the distribution and habitat of the pronghorn have been submitted to the environmental authorities (SEMARNAT), the actual scope and effectiveness of the mitigation measures implemented remain unclear (State Party of Mexico, 2023b). Therefore, it is urgent to ensure that these actions are aligned with the site's management objectives and to implement rigorous adaptive monitoring to identify and prevent negative impacts on the property's Outstanding Universal Value (World Heritage Committee, 2024). It is important to highlight that among the 19 specific environmental programs established by the environmental authority in the resolution issued to the proponent and executor of the project (CFE), the “Monitoring and Application Program on the State of Conservation of the Property” stands out. Its objective is to “develop a scientifically and technically sound procedure that allows for the spatially explicit assignment of values to the natural elements that define the Outstanding Universal Value of the World Heritage Site 'El Pinacate and Gran Desierto de Altar Biosphere Reserve,' and to establish an accounting system for the property's value with the capacity to integrate environmental, regulatory, or land-use changes that may affect it. This monitoring system must be developed by incorporating the value perceptions of different social sectors.” The program is scheduled to begin implementation in 2025.

Gold mining further east in the state of Sonora is a growing threat due to the scale of the projects and their strategic location within the last viable habitat of the Sonoran pronghorn (Antilocapra americana sonoriensis), a key species for the property's Outstanding Universal Value (State Party of Mexico, 2023b; Búrquez & Martínez-Yrízar, 2006). Although there is no direct physical connection or adjacency to the property or its buffer zone, the presence of large open-pit mining projects in functional pronghorn habitats has the potential to indirectly affect the site through habitat fragmentation, landscape alteration, noise generation, heavy vehicle traffic, and changes in soil structure and productivity. These impacts may hinder the natural movement of wildlife between key areas and reduce long-term population viability. Additionally, the visual and topographic impacts of mining affect the integrity of the desert and volcanic landscape characteristic of the property's surroundings. Indeed, mining outside the property affects the landscape and alters soil properties, and other extractive activities may alter the habitat of wildlife species and produce noise (State Party of Mexico, 2023b). Prior to the establishment of the Reserve, rock and sand extraction was one of the most productive activities (Brusca et al 2001). It seemed that commercial extraction of sand, gravel and cinder in certain locations within the buffer zone is allowed.

Although there is a regulatory framework governing mineral extraction in the state of Sonora, it is unclear whether these instruments adequately consider the indirect impacts on the World Heritage property. In this regard, it is necessary to strengthen environmental monitoring and establish inter-institutional coordination to assess and mitigate potential cumulative effects on the site's values (State Party of Mexico, 2023b).

Unregulated harvesting of wild plants has been documented within the World Heritage property, primarily by residents of nearby dispersed settlements. The most frequently extracted species include mesquite (Prosopis spp.), ironwood (Olneya tesota), and ocotillo (Fouquieria splendens), which are used for firewood, charcoal, and, to a lesser extent, rustic construction. Although these activities appear to be on a domestic or subsistence scale, the lack of regulation, monitoring, and quantitative data makes it difficult to assess their true ecological impact. Species such as ironwood are extremely slow-growing and form an essential part of the structure and functionality of the Sonoran Desert ecosystem. The selective harvesting of these plants can lead to changes in vegetation structure, promote erosion, and reduce the availability of habitat for associated species. Additionally, it can have cumulative impacts on the scenic beauty of the desert landscape, particularly in areas near access routes or zones of tourist or scientific interest. Therefore, it is considered necessary to carry out an updated assessment of native plant harvesting within the property, including both ecological and social analysis, and to establish clear guidelines within the framework of the management plan, incorporating criteria for conservation, sustainable use (if applicable), and ecological restoration.

The coastal highway Puerto Peñasco–Gulf of Santa Clara (completed in 2009) and Federal Highway 2 (completed in 2012) cross the surroundings of the property. Although they do not constitute recent infrastructure, their heavy use and subsequent complementary works have generated cumulative impacts on the site and its buffer zone. These impacts include the extraction of rock materials and water, the opening of auxiliary roads, dust and noise generation, and an increased risk of pollution.
One of the most significant effects has been habitat fragmentation caused by roadside fencing, which is legally required along many sections. This fencing disrupts ecological connectivity, particularly for species such as the Sonoran pronghorn, whose presence declines sharply in areas near high-traffic roads (Grageda García, 2023).

Although the current extent of these threats within the property is considered scattered (5–15%), their impact on endangered species and on the integrity of the landscape is considerable. Therefore, it is necessary to implement corrective measures such as wildlife crossings on Highways Mexico 2 and 8, as well as regional connectivity strategies to mitigate the barrier effect caused by infrastructure, in conjunction with that of the border wall (IUCN, 2013; Castillo-Sánchez, 1999). Avoiding the development of new highways within the pronghorn range should be considered.

Despite its vast area and low level of human occupation, water availability and quality represent a significant and growing threat to the property. Currently, the number of permanent residents within the site does not exceed 20 people, distributed among very dispersed settlements. However, pressure on water resources originates primarily from the surrounding area, particularly in the northeastern region of the buffer zone near the city of Sonoyta and Federal Highways 2 and 8, where domestic and intensive agricultural use—such as asparagus cultivation—is concentrated (IUCN Consultation, 2025).

The Agua Dulce Ramsar site, an integral part of the property, is particularly vulnerable as it depends on the availability of both surface water (Sonoyta River) and groundwater. Excessive extraction and agricultural and industrial pollution—on both the Mexican and U.S. sides—directly affect riparian habitats, aquatic species, and landscape integrity (State Party of Mexico, 2023b; IUCN, 2013). Pollution of the Sonoyta River—resulting from agricultural runoff in Arizona and wastewater from the city of Sonoyta—has been a documented problem for decades and continues to this day. At the regional level, the transformation of the Colorado River system has drastically reduced the flow of water to the delta and the Gulf of California, altering fundamental ecological processes that sustain the functionality of the Altar Desert ecosystem. Although monitoring efforts have been initiated and a participatory water management strategy is being developed for the region, it is urgent to advance its effective implementation, prioritizing an integrated watershed approach and binational coordination to prevent cumulative and irreversible impacts on the property's Outstanding Universal Value.

In the buffer zone of the property there are large agricultural fields, mainly related to asparagus cultivation, that use controlled burning as a harvesting method. This practice produces large smoke plumes, visible from long distances, that, depending on the direction of the wind, can drift into the property, affecting both residents and visitors (State Party of Mexico, 2023b). In addition to its impact on air quality, this activity has direct negative effects on the site's landscape values, particularly the scenic perception of the desert environment—one of the key elements of its Outstanding Universal Value. The contrast between the polluted atmosphere and the desert’s typically clear horizon alters the aesthetic and natural experience of the protected area. Efforts have been initiated to encourage local authorities to prohibit or strictly regulate the use of agricultural burning in the vicinity of the property. However, fully implemented legal mechanisms and adequate control measures are still lacking. It is necessary to strengthen inter-institutional coordination and promote sustainable alternatives to agricultural burning, with the participation of the local agricultural sector (IUCN Consultation, 2025).

Following the site's inscription as a World Heritage property in 2013, the number of visitors to the Reserve and the Visitor Center increased temporarily, reaching approximately 12,000 people per year. However, in recent years, visitation has returned to levels like those prior to the designation, with an estimated average of 3,000 visitors annually (State Party of Mexico, 2023b). Although these figures are low compared to the theoretical capacity of up to 120,000 visitors per year, the main risk lies not in the current situation but in the potential for uncontrolled tourism growth in the future, particularly in connection with regional coastal development. Tourism-related impacts have already been observed, including:
– Vehicle traffic generating noise, solid waste, and wildlife roadkill.
– Off-road use of all-terrain vehicles, causing damage to vegetation, soil, and habitats.
– Illegal harvesting of flora and fauna by some visitors.
– Pressure on water resources due to demand from coastal tourism developments in adjacent areas.
– Incentives to expand road infrastructure, increasing the risk of habitat fragmentation and the introduction of invasive alien species.

Effective tourism management must take these potential risks into account, even if the current volume of visitors remains low. It is a priority to implement access control systems, ecological monitoring, environmental education, and inter-institutional coordination to prevent cumulative impacts on the site's Outstanding Universal Value (State Party of Mexico, 2023b).
However, the most critical long term management issues to address are potential problems derived from tourism-related water consumption (State Party of Mexico, 2023b; IUCN, 2013; Burquez y Martinez-Yrizar, 2006).