Heavy-metal grassland in Western and Central Europe

This habitat comprises dry, short grasslands on soils with a high natural or anthropogenic content of heavy metals such as zinc, lead, copper, nickel, cobalt, cadmium or chromium, occurring in western and central Europe. The characteristic plant taxa (mostly subspecies or ecotypes) are metallophytes, species that developed various mechanisms for tolerating these heavy metals in the soil. The vegetation often has an open cover of vascular plants and is rich in lichens and mosses. The typical grasslands of the order Violetalia calaminaria are dominated by metallophytes, but on non-optimal sites also grasslands of other types (belonging to the classes Koelerio-Corynephoretea, Festuco-Brometea, Molinio-Arrhenatheretea) may contain lower numbers of metallophytes, and these also are regarded as belonging to this Red List type.

Heavy metal grasslands of this habitat are found in Ireland, England and Scotland, Northeast-Belgium and adjacent Netherlands, Northern France, Germany, Poland, Austria and Slovenia. They occur on natural sites where bedrocks with zinc or lead lie close to or at the surface. Secondary habitats have been created by mining the metal ores, which has resulted in contaminated soils in the vicinity of mines, along transporting routes and in storage areas. Tertiary locations occur where heavy metals have contaminated the soil by air or water transport from other sources. In many places, grazing by wild herbivores such as rabbits helps maintain an open sward and prevents the disappearance of cryptogam-rich early stages in the development of the vegetation and the greater dominance of grasses and dicotyledons.

Exploitation of the heavy metals ores is recorded from Roman times, but has probably occurred since the Bronze Age. Exploitation increased strongly from the Middle Ages, with an optimum industrial exploitation in the 19^th century. In that period, the Belgian area of La Calamine (Kelmis) and Plombières (Bleiberg) was the world centre of zinc mining. Ores were transported to this area from mines in the surrounding to be washed and processed and because of this industry large amounts of zinc have been loaded into the environment, especially into the river Geul (Geulle), resulting in tertiary sites of metallophytes in its floodplain grasslands. The maximum distribution of the habitat type probably occurred in the first half of the 20^th century.

In habitat type E1.B only those heavy metal grasslands are included that have traditionally been placed in the order Violetalia calaminariae.  In several countries, inside and outside the range of this order, other habitats occur on metal-rich soils, like grasslands and scree vegetation on ultramafic soils (serpentine soils and other copper-rich soils). These habitats are not included here, but are considered under other grassland or scree types. According to this definition, the resulting Red List type E1.B is equivalent to the Annex 1 habitat type 6130.

Indicators of good quality:

In good conditions these grasslands are rich in and dominated by metallophytes. In heavily contaminated spots even 100 years after mining no plants may grow at all. In soils with low concentration of heavy metals and where grazing declines, succession slowly leads to overgrowing with taller grasses (for instance Holcus lanatus) or shrubs and trees. In such cases, sites may be managed by mowing, removing trees and shrubs or sod cutting. Eutrophication, manuring and addition of chalk reduces the availability of zinc to the plants, causing a decrease in metallophytes.

The following characteristics are indicators of good quality:

·      High cover of metallophytes

·      Areas with open soil and characteristic lichens

·      Low vegetation structure

·      Low cover of encroaching tall grasses, tall herbs and shrubs

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats