Environmental Engineering Reference
In-Depth Information
Box 8.1
In situ
restoration of a degraded meadow: Somerford Mead
A particularly well-studied example of restoration of a
plant community is the case of Somerford Mead, an
old fl ood-meadow along the River Thames near
Oxford, United Kingdom (e.g. McDonald
et al
. 1996;
McDonald 2001). In the 1950s, it harboured an
Alo-
pecurus pratensis
/
Sanguisorba offi cinalis
plant com-
munity. From 1960 to 1982, however, it was used as
grassland for haymaking or silage cutting and received
artifi cial fertilizers. From 1982 to 1985, it was ploughed
and used for barley. In 1985, it was agreed to take
Somerford Mead out of this high productivity scenario
and set in motion regimes to re-create an
Alopecurus
/
Sanguisorba
fl ood-meadow plant community. In July
1986, a seed mixture was harvested from the refer-
ence site Oxey Mead, an ancient fl ood meadow, 2 km
downstream. Its exploitation had not changed since at
least the thirteenth century. As a result, it featured a
notably low-fertility grassland community, the
A.
pratensis
/
S. offi cinalis
association (MG4, according to
Rodwell 1992). The seed mixture was broadcast over
prepared soil on Somerford Mead the following
October. In 1989, a management experiment began
in Somerford Mead consisting of an annual hay cut
at the end of June followed by 4 weeks of grazing
in October - by sheep or cattle - in comparison to
a control, nongrazed treatment. Both the cattle-
and sheep-grazed plots became more similar to
the community in the reference site, but were still far
from the species composition of Oxey Mead, even 15
years after the reintroduction of target species. So,
while the project has been considered successful, the
reference ecosystem was used more as a source of
inspiration than as a living system to be copied or
emulated.
of introduced individuals and their survival. Success
was also much higher when seedlings were used
instead of seeds. The problem with seeds is that they
only rarely will germinate and grow into new plants in
the wild, and that the seedling stage is the most vulner-
able part of a plant's life cycle. The source population
also proved to to be important. The survival of prop-
agules from stable source populations was twice as
high as that from declining populations. A possible
reason for this could be that declining populations
already have a lower genetic diversity (and may have
lost some rare alleles). Finally, proper management of
the out-planting site increased reintroduction success.
monitored the establishment of large populations of
the European common frog (
Rana temporaria
) and
common toad (
Bufo bufo
) for 6 years in a newly created
reserve following stocking with spawn of both species
and with toads rescued from a site to be destroyed.
Transfer of spawn proved to be more effective as a
means of establishing a new population of toads than
transfer of adults.
Most reintroduction projects involving amphibians
and reptiles have not been very successful (Dodd &
Seigel 1991), but efforts undertaken for the natterjack
toad (
Bufo calamita
) represent an interesting exception.
The species is endangered in Britain and has been
legally protected since 1975. This amphibian suffered
a major decline during the fi rst half of the twentieth
century, due partly to
habitat
destruction but mostly
to
successional changes
in its specialized biotopes
and anthropogenic
acidifi cation
of breeding sites.
Extensive autecological research over the past 25
years has provided the foundations for an intensive,
3-year species-recovery programme funded by statu-
tory nature - conservation organizations (Denton
et al
.
1997). Management of heath and dune habitats
focused on restoration and maintenance of early stages
of serial succession, initially through physical clear-
ance of invasive scrub and woodland vegetation, fol-
lowed by applying grazing regimes similar to those
prevalent in earlier centuries. In some cases, extra
8.5.2
Fish and herpetofauna
For successful reintroduction of fi sh and amphibians,
the restoration of historical spawning areas, or the pro-
vision of new, suitable spawning habitats, are impor-
tant. Both translocation from the wild and the release
of captive-bred individuals are commonly applied tech-
niques. Stocking appropriate life stages of target species
is clearly important for successful introductions or
reintroductions. For fi sh, using older/larger individuals
has been more successful than using spawn (Noakes &
Curry 1995), whereas the reverse seems to have been
the case for amphibians. Cooke and Oldham (1995)
