130925-studie-wildlife-comeback-in-europe

% change
20,000
16,000
12,000
200
100
0
Figure 2.
Change in Eurasian
beaver population
abundance by
decade and overall
change between
1960 and 2005. Please
note that due to the
way change was
calculated, decadal
change does not sum
to overall change.
1960s 1970s 1980s 1990s 2000–05 1960–2005
Drivers of recovery
Although none of the factors tested explained the
resurgence of Eurasian beaver observed in our
data set, a number of possible reasons for these
trends have been discussed in the literature. The
most important of these are undoubtedly legal
protection and the restriction of hunting, reintroductions
and translocations, and natural recolonisation
following initial recovery (Table 3).
Legal protection of the five populations
remaining at the beginning of the 20 th century [5]
was key in enabling the species to persist in Europe.
In addition to merely preserving genetic material,
some of these final five also acted as source populations
for many of the extensive reintroduction
and translocation programmes that have taken
place in at least 25 European countries [5] . Initially,
these efforts were motivated by the fur trade,
comprised hard releases and lacked habitat suitability
assessments, but latterly they became more
conservation-focused and better researched [5] .
Viable populations have been established in all
countries where reintroductions have occurred [5]
because the species is robust and will succeed in
most river systems if left alone [2] . As part of legal
protection, the cessation of hunting, which had
driven the species to near extinction, has resulted
in population growth, e.g. in Belarus [5] .
A robust species, the beaver expands rapidly
within a watershed of occurrence to occupy
available optimum habitat [20] . However, in medium
to large-sized watersheds [2] this reduces beaver
density, and the critical threshold for encountering
a mate is usually only reached after 10–25
years, leading to an explosion in numbers [20] . In
smaller rivers, for example the River Tay in the
United Kingdom, this phase of rapid increase
occurs almost immediately [2] . The following 10
or so years are marked by population decline as
marginal habitats become exhausted, and this is
followed by rough stability [20] . While the species
can easily spread between watersheds – as has
been the case in eastern Norway, which was repopulated
from Sweden, the islands of Saaremaa and
Hiiumaa from mainland Estonia [5] , and Slovenia
from Croatian watersheds [2] – natural and artificial
barriers can strongly hinder expansion [5] .
While legal protection, reintroductions and
recolonisation are the key drivers of beaver
recovery in Europe, habitat protection and restoration
have also played a role in its resurgence.
Unsuitable habitat is believed to be the reason for
reintroduction failures in Switzerland, and poor
habitat quality is limiting reproductive output in
the Biesbosch National Park in the Netherlands [5] .
On the other hand, the conservation and regeneration
of riparian zones around rivers for flood
control has created suitable beaver habitat around
the continent [5] , and has certainly contributed to
the observed recoveries. In addition to changes
in the way that man is managing the Eurasian
beaver, the species’ resilience and ability to spread
swiftly within a watershed following introduction
or colonisation, will also have been beneficial in
the increase and expansion observed throughout
most of its historic range. Populations have now
been established in all former range countries
except Portugal, Italy and the southern Balkans [11] .
Recent developments
Despite the impressive recovery in abundance
and range, the Eurasian beaver still occurs at
low densities in some locations, and large areas
of suitable habitat remain unused [11] , suggesting
plenty of opportunity for further spread. Considerable
growth in range and numbers is expected,
particularly in western Europe and the Danube
watershed [11] . This would make the species
common in much of Europe within the next few
decades [10] . In addition, reintroduction efforts
are continuing with an ambitious programme to
recolonise the entire Danube basin, with other
successful recent reintroductions (or spread) in
Denmark, Belgium and Scotland [21] . As a result,
many populations are now considered to be at
a mature stage of development [5] . There are also
proposals to re-establish the beaver in Wales [7]
and England [22] . The species is expected to spread
from the Tay watershed in Scotland, where the
population was discovered in 2010 and increased
by around 20% since 2012, to other watersheds
such as the Dee, Spey and Forth in the United
Kingdom [2] . Although the population was established
“illegally”, it is unlikely that there will be
the resources and public support to eradicate
it [2] . In Luxembourg, newly established beavers
were found to be North American escapees from
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