Réserve naturelle régionale du bois d'Encade: Mapping a Protected Biodiversity Island in Hauts-de-France

The protection story of the Bois d'Encade begins with private initiative. In November 1999, the site's owner prepared and submitted the first application for designation as a voluntary nature reserve (Réserve naturelle volontaire, RNV) to the prefecture of the Nord. The RNV was formally approved by prefectoral order on 6 February 2001, and early management of the site was entrusted to the CPIE Bocage de l'Avesnois.

In 2002, France's loi "démocratie de proximité" (proximity democracy law) declassified all existing RNVs nationwide. This required the Bois d'Encade to go through an entirely new classification procedure. That reclassification process concluded on 30 June 2008, when the Conseil régional Nord - Pas-de-Calais formally created the present Réserve naturelle régionale (RNR169).

Day-to-day administration is handled by the Conservatoire d'espaces naturels du Nord et du Pas-de-Calais, which has since been reorganized into the broader Conservatoire d'espaces naturels des Hauts-de-France, ensuring continuity of stewardship across the region's network of small protected natural sites.

Ecologically, the reserve is best understood as a habitat island defined by its combination of woodland, rocky habitats, and riverside vegetation. Mature forest and ancient coppice occupy the steeper slopes, while the lower valley hosts alluvial terraces and a corridor of riverside woodland along the Hogneau. The mosaic structure means that shade-loving woodland species, light-demanding clearing species, and rock-crevice specialists all occur within a short distance of each other.

Two habitat types of European Community interest (listed under Annex I of the EU Habitats Directive) have been formally identified within the reserve, based on a botanical study by Bruno de Foucault (1995). The first is a tall-herb megaphorb community (Phalario arundinaceae - Petasitetum hybridi) characterized by large, nutrient-demanding herbs such as Cirsium oleraceum, Filipendula ulmaria, and Petasites hybridus. The second is a chasmophyte community (Asplenio trichomanis - Phyllitidetum scolopendrii) that colonizes the humid crevices of the site's walls and rock faces.

The varied microhabitats also support a striking range of supporting vegetation patterns, including woodland understory flora along the alluvial terrace of the Hogneau, rock-face and ruin flora in the damp quarry zones, and disturbed-ground vegetation in the post-poplar clearing. This layered botanical character gives the reserve an ecological depth that is unusual for its size and is the main reason for its protection.

The reserve supports a rich fauna for its size, reflecting both its woodland cover and its river corridor. More than 80 species of birds have been observed, with roughly half of these confirmed as nesting on the site. Forest and edge species, including European Kingfisher along the Hogneau, contribute significantly to this diversity.

Mammals include small woodland mammals, micromammifères, and bats such as Brandt's bat (Myotis brandtii), which roosts in the area's mature trees. Amphibians are present in the damper habitats along the stream and in shaded forest pools. The site is also rich in invertebrates, particularly insects associated with dead wood and with the river margin, where fallen timber and humid microclimates sustain specialized communities.

Lepidoptera are particularly well documented. Around twenty species of day-flying butterflies have been recorded at the site, including three taxa considered regionally rare: the Purple Emperor (Apatura ilia), the Lesser Purple Emperor (Apatura iris), and the Bath White (Pieris napi). Autumn also brings a flush of fungi, with several species associated with dead wood and mature forest conditions.

The conservation significance of the Bois d'Encade is twofold. It preserves a habitat mosaic that has largely disappeared from the surrounding cereal plain, and it does so at a scale that allows the site to act as a stepping stone in the reconstruction of biological corridors along the Hogneau valley.

The reserve is classified under IUCN Category IV as a habitat and species management area. This designation is used in France to support targeted interventions against specific threats rather than to impose strict wilderness preservation. Active management here focuses on three pressures: over-use by visitors, eutrophication driven by agricultural runoff and visitor impacts, and biological invasion, most notably by Japanese knotweed (Reynoutria japonica / Fallopia japonica), which is expanding along the Hogneau's banks and threatening sensitive riparian species such as Chrysosplenium alternifolium. Stream bank trampling from visitors is a parallel concern, particularly for plant species growing close to the water.

By bringing these pressures under coordinated management, the reserve serves both a local function, safeguarding rare plants, bats, woodland birds, and dead-wood invertebrates, and a landscape-scale function, providing a key node in regional connectivity for forest species in an otherwise heavily modified agricultural setting.

The Bois d'Encade is intimately linked with the marble-working heritage of its valley. The broader landscape is known as the Vallée du Marbre, and the reserve itself contains the ruins of a former marbrerie (marble works), along with numerous small quarries cut into the valley sides. These structures are not just historical curiosities; they have become integrated into the reserve's ecological identity, providing shaded rock habitats that harbor specialized ferns and other crevice plants.

Local interpretive infrastructure reflects this dual heritage. The Sentier des Carriers, a roughly 4.5-kilometer loop trail made up of three connected circuits, runs through the area and links the natural and industrial history of the valley, allowing visitors to experience both the abandoned quarry landscape and its recovery into habitat. The reserve is part of the broader identity of the Avesnois bocage region and sits within the Communauté de communes du Bavaisis, anchoring a sense of place tied to small-scale industry, rural landscape, and woodland refuges.

Despite its tiny surface area, the Bois d'Encade Regional Nature Reserve stands out for the concentration and diversity of habitats it packs into a short stretch of the Hogneau valley. Its combination of mature woodland, sunlit clearings, shaded quarry ruins, and a flowing stream produces an ecological richness out of scale with its size, making it a textbook example of a small biodiversity island embedded in an agricultural matrix.

Highlights include two Annex I habitats of the EU Habitats Directive, more than 325 recorded plant species, over 80 bird species with about half breeding on site, notable bat presence including Brandt's bat, and a regionally important butterfly assemblage. The reserve is also a standout destination along the Sentier des Carriers, where industrial-archaeological heritage and natural recovery are visible within a few hundred meters of each other.

Because the reserve is a small valley woodland and riparian site, its character shifts significantly with the seasons. Late spring is particularly rewarding for woodland ground flora, when flowering species such as Myosotis sylvatica and Corydalis solida are visible along the alluvial terrace of the Hogneau. Summer brings full canopy cover, active birdlife along the river, and the strongest visibility for the quarry-rock flora and open clearing vegetation. Early autumn is the most reliable period for fungi associated with dead wood, which form a notable component of the site's biodiversity.

Visiting should be timed outside the wettest conditions, as the quarry rocks and riverside ground are sensitive to trampling and the reserve's small size means pressure is easily concentrated. Light, dry days are ideal both for ecological appreciation and for walking the Sentier des Carriers loop.