Populations: re-introductions - Restoration Ecology - page 89

a notably low-fertility grassland community, the
A. pratensis / S. officinalis association (MG4, according
to Rodwell 1992). The seed mixture was broadcast
over prepared soil on Somerford Mead the following
October. Management included cutting for hay in
early July and grazing the aftermath by cows and/or
sheep. During the first 3 years target species such as
Bromus spp., Cynosurus cristatus , Festuca pratensis ,
Leucanthemum vulgare , Ranunculus spp., Rhinanthus
minor and Trisetum flavescens had become established.
After 6 years, 20 target species were found in the estab-
lished vegetation that had not been re-introduced
from the reference site. They must have spread spon-
taneously or by haymaking machinery. The position
of many re-introduced target species became critical.
Silaum silaus and Leontodon hispidus occurred in the
seed bank and only rarely in the established vegeta-
tion. A. pratensis , Briza media , Hordeum secalinum
and S. officinalis were not found in the seed bank and
were rare in the established vegetation. Species with
short-lived seeds cannot form a seed bank, and hence
cannot survive years when they are absent from the
established vegetation.
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 con-
trol, non-grazed treatment. From 1990 onwards, the
differences between grazed and ungrazed treatments
increased. The ungrazed plots became dominated by
tall grasses such as Arrhenatherum elatius , Dactylis
glomerata , Festuca rubra , Holcus lanatus and Lolium
perenne . At the same time, the frequency of Bromus
hordeaceus , Cirsium arvense , C. cristatus , Ranunculus
bulbosus , Trifolium pratense and Trifolium repens
decreased. The ungrazed plots changed in composi-
tion towards Arrhenatherum elatius grasslands com-
mon on road verges in Britain. Both the cattle- and
sheep-grazed plots became more similar to the com-
munity in the reference site, but were still far from
the species composition of Oxey Mead, even 15 years
after the re-introduction of target species.

important for successful re-introduction of fish and
amphibians. Both translocation from the wild and the
release of captive-bred individuals are commonly
applied techniques. Stocking appropriate life stages
of target species is clearly important for successful
introductions or re-introductions. For fish, 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) monitored the establishment
of large populations of common frogs ( Rana tempor-
aria ) and common toads ( 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.
The Great Lakes ecosystem has changed dramat-
ically in the past 50 years. A review of historical
changes reveals complex interactions of overexploita-
tion of fishery resources, invasion of non-indigenous
species, eutrophication, extensive habitat modifica-
tion and toxic contamination. Native fish species that
required tributary or near-shore habitat for spawning
and nursery areas have declined markedly. Among
surviving native species, such as walleye ( Stizostedion
vitreum ), stock diversity declined with the loss of
tributary-spawning stocks and lake-spawning stocks
became dominant. With the rarefaction of native
species, the abundance of formerly subdominant
species increased. Species such as smelt ( Osmerus
mordax ), gizzard shad ( Dorosoma cepedianum ) and
white perch ( Morone americana ) depend less on
critical tributary and near-shore habitat (Koonce et al.
1996). Invasive species pose a special problem. The
Great Lakes ecosystem is home to at least 139 non-
indigenous species of fauna and flora that have
become established following invasions or intentional
introductions. About 10% of the exotic species have
caused economic or ecological damage to the system.
Despite activities to reduce the causes of decline,
most problems have not yet been solved adequately.
Nevertheless, several re-introduction attempts have been
made with various species. Much attention has been
given to the rehabilitation of the lake trout ( Salvelinus
namaycush ). It seems that a complete restoration of
the Great Lakes is unlikely, due to naturalization of
exotic species, habitat degradation and destruction,

7.5.2 Fish and herpetofauna

The restoration of historical spawning areas, or the
provision of new, suitable spawning habitat, are