Environmental Engineering Reference
In-Depth Information
Silene paradoxa, S. vulgaris (Caryophyllaceae), Alyssum spp., Arabidopsis halleri,
Biscutella laevigata, Cochlearia pyrenaica and all Thlaspi spp. (Brassicaceae) on
heavy-metal-enriched soils (Regvar et al.
2003
). Metalliferous soils are extremely
restricted habitats, posing a strong Darwinian challenge to candidates for
survival. This combination of intense selection with restricted location pro-
motes microevolution and speciation processes on sites (Antonovics et al.
1971
).
Metallophytes are typically endemic to their native metalliferous sites and, as a
result, have a very restricted geographical distribution (Baker & Brooks
1989
).
Conservation and management of metallophyte communities
in Europe
Threats
A species can be considered rare when it meets one or more of the following
three criteria: restricted geographical distribution; a habitat with restricted
ecological conditions; or small population size (Olivieri & Vitalis
2001
), though
rarity in itself does not constitute a threat of extinction. Soils with elevated
metal concentrations, however, are extremely fragmented and dispersed habi-
tats in Europe, often forming small geographically isolated 'islands' in areas
of background vegetation with non-elevated metal concentrations (Baker &
Proctor
1990
). Because of their restricted geographical distribution and very
limited ecological amplitude, metallophytes are prone to extinction due to
habitat destruction. This results in genetic drift, demographic stochasticity and
inbreeding (Bizoux et al.
2004
). Rare endemic metallophyte species or ecotypes
are, therefore, priority targets in biodiversity conservation programmes.
Heavy-metal vegetation is a fragile community type and frequently faces a
severe threat of extinction leading to absolute rather than local extinction of
metallophytes. The main threats to metallophyte vegetation include: (1) agri-
cultural reclamation, application of herbicides, and application of fertilisers
and lime, causing eutrophication in the nutrient-poor metallophyte commu-
nities; (2) vegetation succession due to lack of active ecological management;
(3) soil remediation enforced by regulatory agencies and (4) site destruction
due to mining, gravel extraction, landscape development or tree-planting.
Decline
The designation of metallophyte habitats as 'wastelands' or 'derelict land' in
need of rehabilitation has been largely responsible for the disappearance of
most metallophyte communities in the last decades. Metallophyte habitats are
variously regarded as ecologically degraded sites, derelict brownfields, environ-
mental problems, wastelands and pollution threats. This has resulted in an
unambiguous European-wide effort for site rehabilitation and remediation. Sites
were either made suitable for agriculture, levelled, used as waste dumps or for
gravel and aggregate production, or built upon with industrial developments.
