Zone de Protection Naturelle, Agricole et Forestière du plateau de Saclay: A Protected Peri-Urban Landscape

The ZPNAF is best known for protecting a vast perimeter of open farmland on the edge of Greater Paris, resisting the urban spread that surrounds it on all sides. It also stands out for encompassing the historic hydraulic network of rigoles, ponds and aqueducts originally designed by Colbert and Le Nôtre to feed the fountains of the Château de Versailles. The plateau's forested ridges and the Étangs de Saclay, with their reedbeds and heronries, give the zone a recognisable ecological profile. It is equally valued as a landscape where cereal plains, broadleaf woodland, engineered waterways and protected species co-exist within an urban region.

The protection of the Saclay Plateau has a longer administrative history than the ZPNAF itself. In 1976, the Schéma Directeur d'Aménagement et d'Urbanisme de la Région Île-de-France imposed a freeze on urbanisation across the plateau, following recommendations from a group of experts commissioned by the Prime Minister. This early planning decision laid the groundwork for later legal safeguards.

During the 1990s, local elected representatives from fifteen communes proposed a development scheme to protect 2,000 hectares of farmland, while the regional authority acquired roughly 300 hectares of agricultural land to keep it from being developed. In 2008, the prefiguration mission for the Opération d'Intérêt National envisaged a contiguous protected area of at least 1,800 hectares dedicated to preserving the natural, agricultural, landscape and rural character of the plateau.

The decisive step came with the Grand Paris law of 3 June 2010, which formally created the ZPNAF and set a minimum target of 2,300 hectares. A public inquiry subsequently refined the boundaries, and the zone was officially delimited by decree on 27 December 2013, with annexed maps published by the Établissement Public d'Aménagement Paris-Saclay. Management of the zone is overseen by a steering committee of institutional bodies chaired by the prefect of Essonne.

The Saclay Plateau is a wide, relatively flat limestone surface sitting above the valleys of the Yvette to the east and the Bièvre to the south. Its open core is dominated by expansive cereal fields that give the plateau its characteristic horizontal horizon, broken only by scattered farm buildings, research facilities and patches of woodland. The slopes that descend toward the surrounding towns are typically cloaked in mixed deciduous forest, creating a green belt that visually frames the agricultural plain.

The most distinctive physical features of the zone are its water elements. Six rigoles, including the rigole de Saint-Aubin, the rigole de Châteaufort and the rigole de Corbeville, channel runoff across the plateau and into the Étangs de Saclay, notably the Étang Vieux and the Étang Neuf. Two successive buried aqueducts, the aqueduc de Villedombe and the aqueduc du Plessis, once carried water onward through the now-lost Étang du Trou Salé beneath the Toussus-le-Noble aerodrome, then across the Bièvre valley via the Aqueduc des Arcades de Buc to reach the reservoirs designed by architect Thomas Gobert and ultimately the gardens of Versailles. This rare combination of engineered waterways and natural ponds shapes much of the plateau's scenery.

Ecologically, the ZPNAF is defined by the contrast between its large open farmland and its forested and wetland margins. The plateaux host the cultivated matrix, with hedges, field margins and small ecological features providing refuge for species adapted to agricultural landscapes. The forests ringing the cultivated areas are predominantly broadleaf, with chestnut and sessile oak among the dominant species, while the slopes add structural diversity to the ecological mosaic.

The wetland complex is the zone's most ecologically sensitive element. The Étangs de Saclay, surrounded by reedbeds, shrubs and poplar stands, offer habitat for nesting waterbirds, foraging herons and amphibians. Ecological engineering initiatives led by the public development agency have created new ponds within the zone to host protected species, including amphibians such as the great crested newt and aquatic plants such as étoile d'eau (Damasonium), strengthening the area's value as a refuge in a densely populated region.

The Étangs de Saclay are the most important wildlife component of the ZPNAF, supporting an estimated sixty bird species that nest in the surrounding reedbeds, shrubs and poplar banks. Grey herons and great cormorans have established breeding colonies in the area, and the little bittern, a scarce and localised species in France, has been observed and recorded breeding occasionally in 2014 and 2018. An ornithological observatory has been built on the ponds to facilitate observation of these populations.

The plateau's agricultural landscape also supports wildlife typical of large cultivated plains in the Paris Basin, while its forests provide habitat for forest-dwelling birds, mammals and invertebrates. The deliberate creation of new ponds within the zone has expanded opportunities for amphibians, including reintroduction efforts for the great crested newt, and for aquatic flora, reinforcing the area's biological diversity in a regional context otherwise dominated by urban and suburban environments.

The ZPNAF represents a major conservation instrument in the Île-de-France region, embedding more than 4,000 hectares of farmland, forest and wetland into a permanently protected status. Its principal conservation value lies in maintaining a coherent agricultural and ecological wedge within the highly urbanised southwestern fringe of Paris, safeguarding species, habitats and ecological functioning that would otherwise be lost to suburban expansion.

The zone's protection regime also extends to specific threatened species. Targeted interventions, including the creation of breeding ponds, are designed to support protected amphibians such as the great crested newt and protected aquatic plants including étoile d'eau. The conservation effort complements broader work to restore the historic hydraulic network overseen by intercommunal syndicates, combining habitat preservation with the rehabilitation of a unique cultural and ecological water system.

The cultural significance of the plateau is inseparable from 17th-century royal ambition. The rigoles, ponds, buried aqueducts and aqueduct bridges that crisscross the landscape were built to supply water to the fountains of the Château de Versailles at the request of Louis XIV, under the direction of Colbert and with hydraulic planning influenced by Le Nôtre. The system, attributed architecturally in part to Thomas Gobert, is widely regarded as a singular achievement in early modern European water engineering.

Today the plateau remains a hub of agricultural identity in the region, with working farms, equestrian centres and nurseries embedded within the protected area. The combination of historic royal infrastructure and living rural economy gives the ZPNAF a distinctive cultural character, linking contemporary land use to one of the most iconic landscapes of French national heritage.

The ZPNAF stands out for the sheer scale of contiguous protected farmland it preserves within the Paris metropolitan region. Its plateaus of cereal fields, ringed by the broadleaf forests of the Versailles, Port-Royal, Palaiseau and Verrières state forests, create a landscape that is rare for its location so close to a major European capital.

Equally distinctive is the historical hydraulic network that threads through the zone: six rigoles feeding the Étang Vieux and Étang Neuf, two buried aqueducts, the lost Étang du Trou Salé, and the Arcades of Buc. Combined with the Étangs de Saclay's birdlife and the zone's ecological restoration projects, this network defines a protected landscape of national historical and ecological importance.

The plateau's rural and wetland landscapes are accessible year-round, with the agricultural core changing character through the seasons. Late spring and early summer bring the most active cereal growth and the peak of pondside bird activity around the Étangs de Saclay, including breeding heron and cormorant colonies. Autumn offers the most vivid forest colour on the wooded slopes surrounding the plateau, and the reedbed-fringed ponds remain productive for waterbird observation through migration periods.

Winter draws species to open water on the ponds and reveals the open horizons of the cereal plateau, while the rigoles and historic aqueducts are most easily read as a continuous landscape when surrounding vegetation is low. Because the ZPNAF is a working agricultural zone rather than a fenced nature reserve, visits reflect rural conditions and seasonal use of the land.