Unkenpfuhle Marzahn: A Critical Protected Nature Reserve and Amphibian Sanctuary in Berlin

The geological foundation of the Unkenpfuhle area was laid during the Weichselian glaciation, when ground moraine deposits of glacial till accumulated to form a gently undulating plateau. The present-day soils are dominated by loamy sand and loam over poorly permeable clay and till layers, which is why water can collect on the surface and sustain ponds.

In the 1980s, the Marzahn housing estate was built, and the area that would eventually become the nature reserve was used as a construction site. In 1985, the first two ponds (Unkenpfuhl I and II) were formed within former building pits. A drainage channel (Unkenpfuhlgraben) was later dug north of the cemetery in the 1990s, although in practice it contributes little or no water to the ponds.

By the mid-1990s, the local environment office had recognised the ecological value of the unintentional ponds and their surroundings. In 1996, soil probing confirmed an impermeable clay layer that helped retain water in the basins. A third pond, Unkenpfuhl III, was deliberately created in the mid-1990s to bolster amphibian populations, with a shallow profile and sealed base.

The area received formal protection through an ordinance dated 25 October 2001, taking legal effect on 10 February 2002. This made Unkenpfuhle Marzahn a fully recognised Naturschutzgebiet under Berlin law, with its full official title being Naturschutzgebiet Unkenpfuhle Marzahn.

The physical landscape of Unkenpfuhle Marzahn is shaped by the legacy of the Weichselian glaciation. Beneath the reserve, a ground moraine plateau composed largely of glacial till provides a substrate of loamy sand and loam over heavier, poorly permeable layers. It is this natural sealing that allows the ponds to hold water without significant inflow.

The surface topography is gentle and undulating, with low embankments around the smallest pond and a shallow excavated basin for the largest. Natural stone blocks were placed around Unkenpfuhl III as part of its 1990s construction, becoming permanent landscape features.

Surrounding land use is essentially urban. To the south lies the Parkfriedhof Marzahn, a park cemetery, and elsewhere the reserve is bordered by commercial and industrial zones. Within this tight urban envelope, the ponds and their immediate fringing habitats form a small but pronounced natural depression in an otherwise built landscape.

Ecologically, Unkenpfuhle Marzahn combines several distinct habitat types in a very small area. Open water in the three ponds is fringed by reedbeds of common reed and bulrush, and on the shallower margins by low marsh communities of rushes, sedges, and amphibious herbs. Hornwort, water knotweed, and various pondweeds grow submerged or floating in the waterbodies.

Landward of the wet zones, the reserve has retained patches of dry and semi-dry grassland communities typical of sandy, calcium-influenced soils in the Berlin region. Wild carrot and white melilot flourish in these dry swards, and surveys have recorded around 220 fern and flowering plant species within the small site.

Vegetation management is essential here. Continuous succession would otherwise convert the open habitats to scrub and woodland; conversely, unchecked expansion of reed would silt up the ponds. Periodic removal of broad-leaved cattail and other interventions are used to keep the balance between open water, marsh, grassland, and shrub.

Unkenpfuhle Marzahn is most celebrated as an amphibian breeding refuge. The reserve provides spawning habitat for endangered species including the European green toad, the garlic toad, the moor frog, the smooth newt, and the common water frog. Historically it also hosted the fire-bellied toad, the species for which the reserve is named, though that species is now locally extinct; individuals were still documented in 1996 but disappeared in the years following protection.

Reptiles and invertebrates round out the wildlife profile. Sand lizards and grass snakes use the dry and damp edges depending on the season, while at least 34 butterfly species have been recorded across the reserve, taking advantage of the diverse flora. Small refuges distributed across the reserve serve as overwintering and retreat sites for amphibians, helping populations persist through cold months.

The combination of rare amphibians, reptiles, and pollinators gives Unkenpfuhle Marzahn an ecological importance that is unusually high for such a small site embedded in an urban district.

The core conservation purpose of Unkenpfuhle Marzahn is the long-term protection of breeding habitat for endangered amphibians and the preservation of rare plant communities. Protection status under Berlin nature reserve law, combined with IUCN Category IV designation, gives the area a strong legal framework for habitat management.

Active measures reflect this priority. Water levels in Unkenpfuhl I and II have been stabilised through engineering work, including a 1992 lining intervention in the southern part of the smaller pond. Construction debris, old shafts, and unnecessary fencing from the site's earlier life as a building site have been cleared. Periodic mowing, selective clearing, and partial renewal of the perimeter fence keep habitats in suitable condition.

The reserve is also heavily dependent on volunteer engagement. Local honorary caretakers carry out much of the practical conservation work, an arrangement that gives the site sustained care but also constrains how intensively it can be managed. The fenced and non-accessible character is itself a deliberate conservation choice, designed to limit disturbance to sensitive species.

Unkenpfuhle Marzahn sits within Marzahn, a district strongly shaped by late twentieth-century large-scale housing construction. The reserve emerged from the very processes that defined modern Marzahn: large estates, construction activity, and infrastructure development. Its ponds were essentially accidental products of building pits from the 1980s, before being deliberately turned into a nature reserve.

This origin gives the reserve a particular local cultural meaning. Rather than being an untouched patch of countryside, it represents a successful transformation of a residual urban construction site into a valued habitat. The neighbouring Parkfriedhof Marzahn reinforces this sense of green infrastructure shaped by careful planning rather than natural wilderness.

The reserve's relationship with the Hönower Weg, a long-distance walking trail that runs along its edge, ties it into the wider regional network of recreational paths that connect eastern Berlin's green spaces.

The strongest points of distinction at Unkenpfuhle Marzahn are its three protected ponds, the contrasting dry and wet habitats compressed into a minuscule area, and the unusual concentration of threatened amphibian species within a dense Berlin neighbourhood. Despite being only about 3.3 hectares, the reserve supports more than two hundred plant species and dozens of butterfly species in addition to its herpetological fauna.

The site's origin story, where construction debris and former building pits were turned into officially designated wildlife habitat, is also a highlight in itself. Active management, including targeted control of reed expansion and ongoing water-level stabilisation, keeps the protected habitats in ecologically valuable condition.

For visitors, the main highlight is the experience of encountering a fenced, protected nature reserve tucked between commercial zones and a major Berlin cemetery, a tangible example of how small, well-managed urban reserves can carry real ecological weight.

Unkenpfuhle Marzahn itself is fenced and not accessible to visitors, so appreciation of the site is largely tied to surrounding paths such as the Hönower Weg. These paths can be walked at any time of year, but late spring and early summer tend to bring the most active amphibian and reptile movements and the richest display of dry grassland wildflowers.

Late summer can also be rewarding visually, when reedbeds and flowering plants reach their peak biomass and butterfly activity around the reserve margins is high, though many of these species occur just outside the fence. Winter visits offer quieter, more contemplative walking, with the dormant marsh and grassland landscape visible from the perimeter.

Because the reserve itself is closed to entry, weather considerations matter mainly for comfortable walking along the adjacent trails rather than for any specific wildlife viewing condition inside the protected area.