Populations: re-introductions - Restoration Ecology - page 88

have been hampered, in part by predation by goshawk
( Accipiter gentilis ) and pine marten ( Martes martes ;
Kalchreuter & Wagner 1982). Predation may have par-
ticularly severe impacts on very small populations,
especially if a more common primary prey species
is present (prey switching), while at the same time
the number of re-introduced individuals is almost
always small or very small. Only a sufficiently large
re-introduction might overcome predation and succeed
where a smaller one would fail. The minimum viable
population would then, however, be much larger
than that predicted by standard population-viability
analysis. When McCallum et al. (1995) used a simple
stochastic model based upon the bridled nailtail wal-
laby ( Onychogalea fraenata ) to explore this possibil-
ity, even very small amounts of predation (two to four
individuals per 6 months) were sufficient to cause large
re-introductions of up to 50 animals to fail. No clear
threshold population size was found beyond which
re-introductions would succeed. The moral is that if
predation is a serious risk, a single re-introduction of
a given size is preferable to multiple re-introductions
of the same total number of individuals.

munity at a receptor site. The translocation of species
assemblages is used to move communities that would
otherwise be completely destroyed by a change in
land use at the donor site (e.g. civil engineering and
excavation projects; Klötzli 1987). Bullock (1998)
reviewed, among several others, 10 translocation pro-
jects in Britain. Four different techniques were used:
hand turfing, machine turfing, macroturfing (1 m ×

2 m) and spreading (of excavated soil and vegetation).
In most projects, post-translocation management
was similar to the original management at the donor
site. All communities, except the species-poor heath,
showed both losses and gains of species. At some sites,
all translocated communities were becoming more
similar to the original communities at the receptor sites.
Rare plant species were lost on a regular basis. The
associated invertebrate communities showed larger
and more obvious changes than did the plant com-
munities, and often showed losses in rare species of
conservation importance.
The restoration of a former plant community in situ
is quite another issue. If seeds of the target species
(characteristic of the original plant community) are no
longer available in the soil seed bank, they have to
immigrate from elsewhere, for example attached to hay-
making machinery or after deliberate re-introduction.
Somerford Mead is an old flood-meadow along the
River Thames near Oxford, UK, which harboured a
Alopecurus pratensis / Sanguisorba officinalis plant
community in the 1950s. From 1960 to 1982, how-
ever, it was used as grassland for haymaking or
silage cutting and received artificial 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 and set in motion regimes
to create an Alopecurus / Sanguisorba flood-meadow
community again. The possible benefits of removing
the surface soil to reduce fertility was set against the
disadvantage of synchronously removing much of the
seed bank. Therefore, in 1986 the last crop of barley
was grown without any fertilizer in order to start the
reduction of nutrient availability. Further restoration
efforts have been described by McDonald (1992,
1993, 2001) and McDonald et al. (1996). In July 1986
a seed mixture was harvested from the reference site
Oxey Mead, an ancient flood meadow, 2 km down-
stream. Its exploitation has not changed since at least
the 13th century (Baker 1937). It features, therefore,

7.5 Re-introduction techniques

In the majority of cases of animal re-introductions or
translocations, the focus is on populations, rather
than communities, whereas for plants the focus is on
communities. Many techniques are applied to help new
animal populations to get established. Use can be made
of individuals caught in the wild or of individuals kept
and bred in captivity. Choices have to be made con-
cerning which stages in the life cycle of species are
most suitable for translocation activities. Should it be
eggs/seeds, subadults/seedlings, or adults? For plants,
individual plants or whole turfs can be transplanted,
or seed mixtures can be harvested from hay and
spread over the introduction site. A few commonly
applied techniques will be discussed below.

7.5.1 Plants

Community translocation involves the wholesale
removal of an assemblage of species from a site and
the attempt to establish it as a functioning com-