Limburg's coal mining waste heaps foster unique Mediterranean ecosystem

The coal mining waste heaps of Limburg, Belgium, have unexpectedly transformed into a unique haven for Mediterranean flora. These "terrils," formed from the stony residue of coal extraction, have created a distinct microclimate that supports plants usually found in warmer, southern European regions.

The key to this phenomenon lies in the composition of the waste material. It is dark, absorbing significant amounts of sunlight and thus becoming exceptionally warm, especially on steep, south-facing slopes. Furthermore, the rock is rich in salts, and the steep terrain causes water to drain quickly. This combination of heat, salinity, and dryness mimics the conditions of Mediterranean hillsides.

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So, 300 to 350 million years ago, Belgium was located on the equator. Our areas were covered with tropical swamp forests where giant trees grew.

This unique ecosystem's origins trace back millions of years. Professor Emeritus Jacob Vangronsveld of UHasselt explains that around 300 to 350 million years ago, Belgium was situated near the equator. The land was covered in tropical swamp forests, and the decomposition of plant matter in oxygen-poor conditions led to the formation of peat. Over eons, this peat was buried, compressed, and heated, eventually transforming into coal.

When coal was mined, approximately 50% of the extracted material was not coal but shale and other calcareous rocks. These were piled up, forming the terrils. Today, these human-made hills host an unusual array of plants, creating a striking contrast with the surrounding, greener landscape of the Hoge Kempen. The visual resemblance to southern European landscapes, like the rocks near Palermo in Sicily, is notable, especially on warm summer days.

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You must understand that only 50 percent of what was brought up was coal. The rest was shale and other calcareous rocks. These were piled up on a waste heap, the terrils.