Environmental Engineering Reference
In-Depth Information
which the majority were lost to predation by wolves.
The fate of these 33 introductions is consistent with
the view that predation (natural and hunting) is a
major factor in the decline of caribou in eastern North
America following European settlement. In Europe,
meanwhile, attempts to reintroduce black grouse
(
Lyrurus tetrix
) and capercaillie (
Tetrao urogallus
) have
been hampered, in part by predation by goshawk
(
Accipiter gentilis
) and pine marten (
Martes martes
; Kal-
chreuter & 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 reintroduced individuals is almost always
small or very small. If predation is a serious risk, a
single reintroduction of a given size class is preferable
to multiple reintroductions of the same total number
of individuals.
8.5.1
Plants
Strategies for the reintroduction of
endangered
plants, that is, at the level of species populations, have
been extensively dealt with in the volume edited by
Falk
et al
. (1996), and several examples will be shown
in Chapters 9, 14 and 15. Here we focus on the re-
establishment of plant communities. If seeds of target
species (characteristic of a reference plant community)
are no longer available in the soil seed bank, they have
to immigrate from elsewhere, or be deliberately reintro-
duced. In a recent review, Kiehl
et al
. (2010) evaluates
a number of techniques for the establishment of
semi-
natural grasslands
that have been applied in restora-
tion projects in central and northwestern Europe. The
techniques include, among others, (1) seeding of com-
mercially produced site-specifi c seed mixtures, (2)
transfer of fresh seed-containing hay and (3) transfer
of turves and seed-containing soil. The establishment
of species-rich grasslands with habitat-specifi c species
composition appeared to be most successful when
seeds, seed-containing plant material or soil are spread
on bare soil of ex-arable fi elds after tilling or topsoil
removal, or on raw soils such as in mined areas, pro-
vided that an appropriate follow-up management (e.g.
hydrological measures, grazing and cutting) can be
assured in the long run. The fi nal establishment rates
were lower than 40% when restoration sites were dom-
inated by grasslands with dense swards. One of the
classic examples of
in situ
restoration of a degraded
meadow by hay transfer from a reference site is pre-
sented in Box 8.1, showing that hay transfer is a useful
starting point but only partly results in a community
similar to the reference site. Transfer of blocks of turf
- including vegetation and soil - of, for example,
0.5 m × 0.5 m with a minimum depth of 0.3 - 0.5 m,
has been successfully applied as a method of environ-
mental mitigation (reviewed by Bullock 1998).
There are many parallels between the causes for
success and failure of plant and animal reintroduction
attempts. Godefroid
et al
. (2011) examined 249 plant
species reintroductions. They found that survival, fl ow-
ering and fruiting rates were generally low. Even more
problematic was that the data showed a downward
trend over time After 4 years, fl owering percentage was
only 6% on average. A statistical treatment of the data
revealed a number of variables associated with success.
Reintroduction success is increased when using mate-
rial originating from multiple populations. There was
also a clear positive relationship between the number
8.5
REINTRODUCTION TECHNIQUES
In the majority of cases of reintroductions or translo-
cations of animals, the focus is on populations of a
single species, and choices have to be made concerning
which stages in the life cycle of species are most suit-
able for translocation activities. Should it be eggs, sub-
adults, or adults? For plants, reintroductions can also
aim at re-establishing a viable population of a single
species, but the focus tends to be on communities,
either sown or transplanted.
If no targets have been set, as is frequently the case,
success can not be measured. But more often, there is
an array of possible targets, that cannot always be met
simultaneously. For example, if the aim is to re-establish
a plant community similar to the
reference
commu-
nity, does this imply that species richness, species com-
position or relative abundance of various species
should be favoured? Are rare species more important
than 'common' species? These and similar questions
can be asked in case of re-establishment of populations
of a single species as well: does a viable population
imply the number of individuals, or also a minimum of
genetic variability (see Chapter 7)? Pavlik (1996) clari-
fi ed the discussion by distinguishing between project
success (according to goals and objectives) and biolo-
gical success (dealing with the performance of a popu-
lation or a community). A few commonly applied
techniques will be discussed below, for plants and a
number of vertebrate groups.
