Reserva ecológica Arenillas: A Comprehensive Map and Geographic Portrait of a Vital Nature Reserve

Arenillas is best known as one of Ecuador's largest and most intact remnants of Tumbes-Piura dry forest, a naturally dry and deciduous ecosystem that is increasingly rare and fragmented along the Pacific coast. The reserve is a stronghold for endemic birds of the Tumbesian region, including globally threatened species such as the grey-cheeked parakeet. The reserve is also distinguished by the combination of its dry forest interior with coastal mangroves, creating a transition between terrestrial dry habitats and tidally influenced shoreline that supports both resident and migratory species. Its dual role as an ecological reserve and a military-restricted area has helped keep large portions of the habitat in unusually good condition for this part of Ecuador.

The area now known as Arenillas Ecological Reserve was originally declared as a protected area more than sixty years before its modern designation, reflecting an early recognition of the ecological value of Ecuador's southwestern dry forests. A foundational interministerial agreement in 1994 (Acuerdo Interministerial N.º 1646) initiated the formal steps toward recognizing the area's conservation significance.

The reserve's modern identity dates to 2001, when it was officially incorporated into Ecuador's National System of Protected Areas through Registro Oficial N.º 342 of June 7, 2001. A subsequent modification, recorded in Registro Oficial N.º 787 of September 12, 2012, refined its official status. Throughout this period, the Federal Foundation for Environmental Research and Management (FEDIMA) played a central role in producing the technical studies that justified the area's transition from a military reserve to a formally recognized Ecological Reserve.

The reserve's overlap with a military zone continues to shape its administration and access policies. Visitors must request permission to enter, and management responsibility rests with Ecuador's Ministry of Defense rather than its environmental ministry. In parallel, nongovernmental organizations such as Fundación Cerro Verde have worked with local communities in the buffer zone to build a local management committee representing thirty-six communities, supporting conservation through environmental education initiatives.

The Arenillas Ecological Reserve occupies lowland terrain in the Pacific coastal region of southwestern Ecuador, with elevations ranging from sea level to around three hundred meters above sea level. This relatively gentle topography creates a setting where vegetation transitions smoothly from inland dry formations to coastal systems, allowing distinct habitat zones to develop close together.

The interior of the reserve is dominated by lowland deciduous forest and tropical dry shrubland typical of the Tumbes-Piura ecoregion. Trees here tend to be relatively short and adapted to long dry seasons, with thorny legumes, cacti, and bromeliads contributing to a distinctive dry-forest structure. Although the original stands of commercially valuable timber have largely been removed, the broader vegetation patterns have persisted, and the habitats are described as being in good overall condition.

As the terrain nears the coast, vegetation becomes shorter and more shrubby, eventually giving way to mangrove systems that extend along roughly twenty-eight hundred hectares of shoreline. The mean annual temperature is around twenty-four degrees Celsius, consistent with the warm, semi-arid conditions that define this stretch of the Ecuadorian coast. Together, these characteristics give the reserve a landscape profile quite distinct from the wetter cloud forests and Andean ecosystems more commonly associated with Ecuador.

Ecologically, Arenillas represents one of the most significant surviving blocks of tropical dry forest in Ecuador, a habitat type that has been heavily reduced across the Tumbes-Piura region. The reserve's vegetation combines deciduous lowland forest, dry thorny shrubland, mangrove, and successional growth, creating a patchwork of habitats that supports both forest-interior species and coastal-edge fauna.

Approximately one hundred and eleven plant species have been documented within the reserve, distributed across around fifty families. Of these, seventy-six are native and twenty-five are endemic to the Tumbesian region, while ten are introduced. The Mimosaceae family stands out for its species richness, with nine recorded species, followed by cacti and bromeliads as notable components of the dry plant community.

Juvenile populations of important forest species such as Tabebuia chrysantha, Ziziphus thysiflora, and Albizia guachapele are recovering in the reserve, along with mature individuals of large trees like Ceiba trischistandra and Ficus species. The mangroves along the coast contribute additional plant diversity and play a particularly important role in supporting marine and bird life. The combination of these habitats gives the reserve a particularly high ecological value for its size.

Wildlife at Arenillas reflects the broader importance of the Tumbes-Piura ecoregion as a center of endemism on the Pacific coast. Around one hundred and fifty-nine animal species have been recorded in total across multiple classes, with birds making up the most species-rich and conservation-significant group.

The reserve hosts roughly one hundred and fifty-three bird species, of which approximately thirty-five percent are endemic to the Tumbesian region. It supports globally threatened species such as the grey-cheeked parakeet (Brotogeris pyrrhoptera), the slate-colored becard (Pachyramphus spodiurus), and the blackish-headed spinetail (Synallaxis tithys). The mangrove areas serve as important gathering sites for both resident and migratory congregatory bird species, contributing to seasonal diversity.

Twenty-six mammal species have been documented across fifteen families, including the Sechuran fox, the lesser anteater, the nine-banded armadillo, the jaguarundi, the tayra, and the crab-eating raccoon. A high number of these mammals, fifteen of the twenty-six recorded, fall within some category of conservation concern, highlighting the regional pressures on dry-forest mammal populations. Reptile and amphibian registrations together involve around nineteen species, including several Tumbesian endemics such as the Arenillas lizard (Callopistes flavipunctatus) and the Tumbes toad (Ceratophrys stolzmanni).

Arenillas Ecological Reserve is a cornerstone of dry-forest conservation in southwestern Ecuador, where natural vegetation has been heavily transformed by agriculture, timber extraction, and coastal development. By protecting more than thirteen thousand hectares of Tumbes-Piura dry forest, dry shrubland, and mangrove, the reserve maintains ecological processes and habitat connectivity that would otherwise have been lost in this region.

The reserve receives particular conservation attention because of its high concentration of endemic species. Roughly a third of its recorded bird species are endemic to the Tumbesian region, and a significant proportion of its mammals, reptiles, amphibians, and plants are similarly restricted in range or considered threatened. Its designation as an Important Bird and Biodiversity Area by BirdLife International reflects this global significance.

Its inclusion in Ecuador's National System of Protected Areas gives the reserve a formal conservation framework, while its administration as a military zone has, in practice, also contributed to the preservation of its habitats by limiting public access and large-scale human pressure. Conservation efforts extend beyond the reserve boundaries through the work of organizations such as Fundación Cerro Verde, which supports a local management committee of thirty-six communities in the buffer zone and runs environmental education activities grounded in field ecology.

The reserve is situated within El Oro Province in a region shaped by Ecuadorian coastal livelihoods, including agriculture, ranching, and cross-border commerce with neighboring Peru. The cantons of Arenillas and Huaquillas, in which the reserve lies, have long-standing local communities that interact with the surrounding landscape in traditional ways, including dry-forest land use and coastal resource harvesting.

In the buffer zone, organizations working around the reserve have helped organize thirty-six local communities into a participatory management committee, linking conservation action with regional social structure. This kind of community-based environmental governance is part of the broader cultural context in which the reserve operates, integrating conservation planning with local identity and stewardship traditions of the southwestern Ecuadorian coast.

Arenillas stands out for protecting one of the largest remaining blocks of Tumbes-Piura dry forest on the Ecuadorian coast, a habitat type that is disappearing quickly elsewhere in the region. Its dry-forest interior and coastal mangroves together support a remarkable concentration of endemic Tumbesian species, especially birds, mammals, and reptiles.

The reserve also stands out for its unusual administrative context: although it is part of Ecuador's national system of protected areas, it is managed by the Ministry of Defense because of its overlap with a military zone. This combination of legal protection and restricted access has helped keep habitats in unusually good condition, making the reserve an important benchmark for understanding intact dry-forest ecosystems of the Pacific coast.

Because Arenillas lies in a coastal dry-forest region with a relatively stable warm climate averaging around twenty-four degrees Celsius, the experience of visiting the reserve shifts mainly with the wet and dry seasons that characterize the Tumbes-Piura ecoregion. The dry season typically offers clearer skies, easier trail access, and more concentrated wildlife viewing around water sources, while the wet season brings lusher vegetation and heightened bird activity, particularly among migrant and breeding species.

Visitors should also keep in mind that the reserve is administered as a military zone, and access requires advance permission from the relevant authorities. Planning around this requirement, rather than around weather alone, is often the most important step for a successful and responsible visit.