Ejidos de Xochimilco y San Gregorio Atlapulco

Ejidos de Xochimilco y San Gregorio Atlapulco is an ecological conservation zone within Mexico City, protecting the remaining chinampa agricultural landscape and associated lacustrine ecosystem of Xochimilco—the southern chinampas that were designated a UNESCO World Heritage Site in 1987 as part of 'Historic Centre of Mexico City and Xochimilco.' The conservation zone encompasses the working chinampa plots, interconnected canal systems, and remnant wetland habitats of the ejidos of Xochimilco and San Gregorio Atlapulco in the Xochimilco borough of Mexico City. This area is ecologically critical as one of the last surviving fragments of the Aztec-era lake system of the Valley of Mexico, which was once the world's most extensive urban wetland before Spanish-era drainage beginning in the seventeenth century reduced it to a fraction of its original extent. The zone harbors the axolotl (Ambystoma mexicanum), a critically endangered salamander endemic to the Xochimilco lakes that has become a global symbol of biodiversity conservation.

The Xochimilco conservation zone is famous worldwide as the last stronghold of the axolotl (Ambystoma mexicanum), the neotenic salamander that retains larval features throughout its adult life and has extraordinary regenerative capabilities studied by biomedical researchers. Wild axolotl populations have declined dramatically in recent decades due to introduced predatory fish, water quality degradation, and reduced canal connectivity, and the species is classified as Critically Endangered by the IUCN. Migratory and resident waterbirds make extensive use of the chinampa canal system and remaining open water areas, with species including great blue heron, black-crowned night heron, various egrets, cormorants, and numerous duck species in winter. The canals support diverse aquatic invertebrates including native freshwater shrimp, insects, and mollusks that form the base of the aquatic food web. Carp and tilapia introduced in the twentieth century have dramatically altered the native aquatic community.

The chinampa system supports a unique combination of cultivated and wild plants maintained through centuries of indigenous agricultural practice. Chinampas—raised garden beds constructed from lake sediment and organic material—support a diverse range of vegetables, flowers, and herbs cultivated for Mexico City's markets. Ahuejote willows (Salix bonplandiana), a distinctive tree planted along chinampa borders to stabilize edges and mark boundaries, create the iconic visual character of the Xochimilco landscape. Aquatic macrophytes including water hyacinth (Eichhornia crassipes, invasive), tule (Scirpus lacustris), water lilies, and native Nymphaea species occupy canal margins and open water. Restored areas in the conservation zone support patches of native aquatic vegetation managed to improve habitat for axolotl and native fish. The area also preserves remnant populations of native plants displaced by urban expansion.

Xochimilco sits in the southern portion of the Valley of Mexico, an ancient lake bed formed in a volcanic basin surrounded by the Trans-Mexican Volcanic Belt. The underlying substrate consists of lacustrine sediments—clay, silt, and organic material—deposited over thousands of years in the shallow lakes that once covered the valley floor. These sediments are deep and compressible, contributing to Mexico City's well-documented problem of differential subsidence as groundwater is extracted from underlying aquifers. The Xochimilco area has experienced significant land surface subsidence over the past century, with some areas sinking by several meters. The chinampa structures themselves represent a remarkable engineering achievement, built up from lake bottom material over centuries to create stable agricultural platforms above the lake surface. Volcanic springs (manantiales) historically supplied fresh water to the lake system.

Xochimilco experiences Mexico City's temperate highland climate, influenced by its elevation of approximately 2,240 m above sea level. The wet season runs from May to October, when afternoon convective thunderstorms deliver the majority of the approximately 700–900 mm of annual precipitation. The dry season from November to April brings clear skies, cool nights, and occasional frost risk during December and January. Mean annual temperature is approximately 16°C, with little seasonal variation in temperature compared to the dramatic wet-dry seasonality. The lacustrine environment moderates local temperature extremes somewhat, maintaining higher humidity near the canal system. Hail storms are not uncommon during the wet season convective events and can damage chinampa crops. Air quality in the conservation zone is influenced by Mexico City's urban pollution, particularly during thermal inversion events in winter.

Xochimilco is one of the cradles of Aztec civilization, where the Xochimilca people—predecessors to the Mexica (Aztec)—developed the chinampa agricultural system over more than a millennium beginning around 1200 CE. Chinampas enabled intensive food production in shallow lake environments by creating fertile raised beds from accumulated vegetation and lake mud, allowing multiple harvests per year in a climate where rain-fed agriculture was seasonal and unreliable. The Aztec Triple Alliance absorbed Xochimilco into the empire in the fifteenth century, and the chinampa system supplied a substantial portion of the food for Tenochtitlán (present-day Mexico City). After the Spanish conquest in 1521, chinampa agriculture continued but drainage schemes progressively reduced the lake area. Xochimilco's designation as a UNESCO World Heritage Site in 1987 recognized the cultural and historical significance of this living archaeological landscape.

The designation of Ejidos de Xochimilco y San Gregorio Atlapulco as an ecological conservation zone represents Mexico City's recognition of the urgent need to protect the last functioning chinampa ecosystem within the metropolis. This designation established formal conservation status over ejido-held lands that had been under community management since the post-revolutionary land reform but were increasingly threatened by illegal urban expansion, landfill, and infrastructure encroachment from surrounding colonias. CORENA (Mexico City's environmental authority, now SEDEMA) administers the conservation zone and has implemented programs to restore degraded canal areas, combat invasive species, and support chinampa farmers in maintaining traditional agricultural practices. The Proyecto de Conservación y Restauración del Axolotl, based in the conservation zone, has become internationally recognized.

Xochimilco is one of Mexico City's most visited ecological and cultural destinations, famous for the trajineras—colorful flat-bottomed canal boats—that ferry visitors through the chinampa canal system. Weekend and holiday boat tours from the Embarcadero Cuemanco and Embarcadero Fernando Celada provide access to areas within and adjacent to the conservation zone. The floating gardens visited during trajinera tours showcase active chinampa cultivation, and vendors in boats sell food and flowers typical of the Xochimilco market tradition. The ecological conservation zone itself has less formal tourist infrastructure than the commercial embarcadero areas, but permits visits from researchers, educators, and ecotourism groups. Birdwatching from canal-edge walkways is productive, particularly in early morning when wading birds are active. The Dolores Olmedo Patiño Museum, adjacent to the canal system, houses significant muralist art alongside chinampa gardens.

Xochimilco is accessible from central Mexico City via the light rail (Tren Ligero) to Xochimilco station, bus routes, and private vehicles. The commercial embarcadero areas near the town of Xochimilco are the primary visitor entry points, with numerous trajinera rental operations, restaurants, and services. Within the ecological conservation zone proper, access is more restricted and primarily via canal boat. SEDEMA coordinates guided ecological tours of the conservation zone focusing on chinampa agriculture, axolotl habitat, and native plant restoration for educational groups. The weekend and holiday 'floating market' atmosphere of the commercial Xochimilco canal areas provides a festive cultural experience that complements the ecological significance of the protected area. Several community chinampa farms within the conservation zone offer direct-sale organic produce and educational farm visits.

Xochimilco faces an interconnected set of conservation challenges rooted in Mexico City's urbanization dynamics. Illegal settlement on ejido land within and adjacent to the conservation zone progressively reduces the ecological area. Water quality in the canals is severely degraded by wastewater inputs, agricultural runoff, and solid waste dumping, creating conditions hostile to axolotl and native aquatic species. The axolotl now survives in very low densities in a small fraction of the original canal system, and a captive breeding program maintains insurance populations at UNAM's biology institute. Invasive species—particularly tilapia, carp, and water hyacinth—have fundamentally altered the aquatic ecosystem. SEDEMA's Xochimilco conservation program coordinates canal restoration, native species reintroduction, community involvement in monitoring, and enforcement of protected area boundaries. Sustainable chinampa agriculture is promoted as both a conservation tool and an economic livelihood for ejido members.