From Black Mountains to Green Lungs: The Remarkable Transformation of Mining Heaps

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The slag heaps, remnants of the mining industry, are more alive than one might think when they were first constructed. Several decades after the mines closed, a guide reveals the rich diversity of wildlife and plant life they now support.

Loos-en-Gohelle (Pas-de-Calais), report

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Imagine a landscape reminiscent of Zola’s Germinal, immortalized forever by Claude Berri’s 1993 film. Picture smoke and metallic noises, men, poverty, and exploitation, alongside solidarity. And the mineshafts, around which entire working-class lives revolved, were used to extract coal—a cheap but polluting energy source.

In Loos-en-Gohelle (Pas-de-Calais), mining at shaft 11 began in 1894, followed by shaft 19 in 1960. These two shafts led to the creation of the famous twin slag heaps, emblems of the Nord-Pas-de-Calais region, and somewhat shameful symbols of labor exploitation.

The 11/19 site ceased operations in 1986, yet from its past, a sense of pride has been reclaimed, greatly aided by the mining basin’s designation as a UNESCO World Heritage site in 2012. Since then, perceptions of these black mountains have shifted. Previously thought to be barren rock piles, they have blossomed into biodiversity hotspots, becoming vital refuge zones. Decatur Metro explored this fauna and flora with a guide from the permanent center for environmental initiatives, Chaîne des terrils.

“The slag heap is a man-made environment,” explains Orane Wojtyna, a naturalist study officer at Chaîne des terrils. “It resembles a dune environment, or even limestone hills. It’s very dry and hot, and the habitat is diverse. Many species from the dunes, now struggling in their original habitats, find refuge on the slag heaps and manage to persist.”

After earning a master’s degree in naturalist expertise and biodiversity management, Orane Wojtyna started at Chaîne des terrils in 2025. “I do a lot of fieldwork, and I enjoy it. I didn’t realize there were so many different species on the slag heaps. Working to protect this environment is crucial; everything here could have been razed.” Established in 1989, Chaîne des terrils already envisioned that “the remnants of coal mining would form the basis for new developments.”

In 2003, the public land authority of Nord-Pas-de-Calais purchased 129 slag heaps over 1,750 hectares from Charbonnages de France, which operated the mines. The goal was to create a regional green network and plant trees. “There is now an excessive density of trees, little room for undergrowth. This is problematic for wildlife and plants,” notes Orane Wojtyna. “About one in five trees need to be cut down to recreate an open environment conducive to more life.”

The Japanese knotweed (Reynoutria japonica), a highly invasive species, is found at the base of the slag heaps. “It was brought here by humans. If a piece gets stuck under a shoe, it spreads. Together with the CPIE and an integration association, we try to contain it by mowing, then placing a textile over it to smother regrowth,” explains Orane Wojtyna. Other invasive species present include Virginia creeper and tree-of-heaven (Ailanthus altissima).

The challenging environment for plants on the slag heap consists mainly of shale and also sandstone. It’s a dry, hot soil with little organic matter. Horned poppy (Glaucium flavum), recognized by its horn-shaped stems, can also be found here, similar to those on the slopes of Vesuvius.

“The blue-winged grasshopper [Oedipoda caerulescens] is an emblematic species of the slag heap fauna. It is recognized by its turquoise wings. The aquamarine locust [Sphingonotus caerulans] also inhabits this environment. This type of grasshopper prefers shale because it lays its eggs there. A bare soil is very conducive to their development, as they are nearly invisible against the gray. And rabbits help maintain this bare soil,” details Orane Wojtyna.

The bryo-lichen carpet surrounding the slag heaps consists mainly of lichen. It’s a lawn on shale, a mix of small-sized vegetation adapted to these arid conditions.

Hawkbit (Leontodon saxatilis) can be mistaken for a dandelion. It is a mountainous rock plant that thrives in poor, dry soils and grows here on the lichen carpet.

At the base of slag heap 74 is a schlamms bath, these mining residues consist of fine coal dust and water. When it was in use, the water evaporated, and the schlamms were collected in this settling basin. Over time, ponds have formed, attracting amphibians. Common reed thrives here, as well as woody species like birches, a pioneer species here, and brambles, which grow in these now dried-up former ponds.

Perfoliate yellow-wort (Blackstonia perfoliata) is not very common on a slag heap. It primarily grows in dunes but also thrives here. It is not protected, unlike other species such as the overlooked orchid (Dactylorhiza praetermissa) or round-leaved sorrel (Rumex scutatus). Over 300 species of plants have been observed on the 11/19 site.

Since 2025, rare instances of the overlooked orchid, a protected species, have been found. “Its presence is not necessarily linked to the natural environment of the slag heap,” notes Orane Wojtyna. “It grows in wastelands, but here, it’s exceptional. In terms of site ecology, it’s very positive.”

For the past two years, eighteen ditch goats, a mountain species, have been grazing on the slopes of slag heap 74A. “The goal is for them to graze on woody species, those that grow tall and can destabilize the slopes,” explains Orane Wojtyna. “We also hope they will graze on the tree-of-heaven, an invasive species present on the summits.”

The Loos-en-Gohelle site consists of three slag heaps. The 74 and 74A are conical, and the 74B is flat, or table-like. There were also two other conical slag heaps that have been exploited over time, and are still currently being mined for their shale. To the right of the image, you can see the schlamms bath.

View from slag heap 74A of the 11/19 mining site. The typical metal headframe of the mining landscape is visible: it’s shaft 11. The concrete tower—shaft 19—was a second shaft brought into service in 1960. The site now houses the Culture commune theater, a regional center for ecotransition, and the Chaîne des terrils, which works to preserve and enhance the landscapes associated with coal mining.

Slag heap 74 is off-limits to visitors, as it is too unstable. On its side remains the wooden ramp for dumping mining residues. Slag heaps 74 and 74A measure 146 meters from the ground, but their elevation above sea level is 187.50 meters, making them the tallest in Europe. The three slag heaps have a volume of 24 million cubic meters, over 90 hectares.

The slag heap is a dynamic landscape. A man-made environment, it can shift. Some still emit heat due to the combustion of the materials comprising them, attracting crickets. Here, you can see gullies, crevices that form from trampling or the runoff of rainwater. To contain these and maintain terrain stability, the CPIE constructs fascines, types of dams made with willow branches.

The wasp spider (Argiope bruennichi) is a typical spider of meadows and wastelands. “It’s quite abundant around here. It uses the vegetation to make its web. The stabilimentum, a characteristic white zig-zag pattern,” notes Orane Wojtyna. Its function is less clear, but it might help attract prey.

The gatekeeper butterfly (Pyronia tithonus) is very common and found in all environments. “Generally, a butterfly operates with a host plant. On the slag heaps, it’s quite diverse,” observes Orane Wojtyna. Many butterfly species are present, like the swallowtail (Papilio machaon), whites, speckled wood (Pararge aegeria), and the rare burnet (Zygaena filipendulae).

“The common wall lizard is another emblematic species here. So is the natterjack toad, which is kind of the star everyone wants to see,” but which we couldn’t observe during our report. The CPIE has placed ground plates to shelter reptiles and amphibians, allowing them to be counted. You can hear them rustling between the stones during walks. In total, 550 animal species have been observed at Loos-en-Gohelle.