Environmental Engineering Reference
In-Depth Information
Heavy-metal sites and their vegetation in Europe
Evolution and distribution of metallophytes
After the last Quaternary Ice Age, forest developed on nearly all soils in Europe,
except on those with extreme climatic or edaphic conditions. In the latter group
are soils with elevated concentrations of heavy metals, too toxic for trees. In such
situations, shadow-sensitive xerophytes were able to survive when they had the
genetic advantages in metal tolerance (Ernst et al.
1992
). Heavy-metal-tolerant
vegetation was originally restricted to natural outcrops of metal ores, scattered
as a relic of the Late Glacial epoch over Europe. Most of these habitats were
destroyed or modified by mining activities from the Bronze Age onwards. How-
ever, metal mining has considerably enlarged the potential habitat range by
creating further areas of metal-contaminated soils (Ernst
1990
;Ernstet al.
2004
).
In Europe, sparsely distributed sites with metal-enriched soils form residual
sanctuaries for metallophyte communities. Most sites are disconnected spatially
and are of very limited extent. The UK has many sites in Wales (Davies & Roberts
1978
), the Peak District (Barnatt & Penny
2004
) and the North Pennines, and
some isolated sites in Cornwall and in the Mendips (Ernst
1974
;JNCC
2002
). The
central part of Germany is well-known for its heavy-metal vegetation (Schubert
1953
,
1954
;Ernst
1964
,
1974
;Beckeret al.
2007
). Alluvial heavy-metal vegetation
occurs along the rivers Innerste and Oker in the Harz Mountains. In the Mansfeld
area, several hundreds of large Cu-Pb-Zn-mine spoil heaps are scattered with metal-
lophyte communities (Schubert
1953
; Ernst&Nelissen
2000
). In the EuropeanAlps in
Austria, Slovenia and Italy, in the French Pyrenees, and several small sites are known
in the Spanish Picos de Europa. The most studied and extensive communities are
those of the three-border area of Belgium, the Netherlands and Germany, the Harz
Mountains area and the Pennine orefield in the UK. Metallophyte vegetation makes
up an important component of the biodiversity of Europe (Whiting et al.
2004
).
Thalius (
1588
) was the first to recognise a relationship between the plant
Minuartia verna and heavy-metal-enriched soils in the Harz Mountains, Germany.
Subsequently, the association of the plant with lead-mine wastes in the Pennine
orefield, UK, gave rise to its local name 'leadwort'. Schulz (
1912
) speculated that
M. verna is in fact a glacial relict species surviving on heavy-metal soils as an
isolated population; this was later confirmed by genetic analysis (Baumbach
2005
). Libbert (
1930
) then defined the Armerietum halleri as a plant association
specific to metalliferous soils, and the Violetum calaminariae was described from
the Breiniger Berg near Aachen by Schwickerath in
1931
. Plant associations
specific to metal-enriched soils were thus recognised.
Types of heavy-metal sites
The history of metal sites determines the species composition of the vegetation.
Three types of heavy-metal vegetation can be distinguished on syntaxonomy
and on their occurrence: primary, secondary and tertiary.
