POZNAŃSKIE TOWARZYSTWO PRZYJACIÓŁ NAUK
since 1857
For. Lett. No 109: 7-10, 2016
ORIGINAL ARTICLE
Damages caused by European beaver (Castor fiber L., 1758)
in broadleaved stands
Jacek Kamczyc1, Michał Bielachowicz1, Emilia Pers-Kamczyc2
1
2
Poznań University of Life Sciences, Department of Game Management and Forest Protection,email – [email protected]
Institute of Dendrology Polish Academy of Science
Abstract: The main aims of the study were: (1) to describe the various types of damage caused by European beavers in young
broadleaved stands; and (2) to check whether a steel fence built parallel to the river and laterally (both sides 40 m long) can protect the
stands from these animals. The chain-link fencing (mesh size: 6 cm) was buried in the ground to the depth of 50 cm and the
aboveground part of the fence was 1 m high. Our results indicate that beavers mainly cut the trees down (the dominant type of
damage), most frequently close to the river. Overall, 76-99% of the damaged trees were identified in the vicinity of the river. We also
found that the fence effectively protected the stands, as beavers did not pass through this barrier.
Key words: European beaver, Castor fiber, tree protection against wildlife, damage by wildlife
INTRODUCTION
European beaver (Castor fiber L.) is the largest
Eurasian rodent, characterized by a high ecological
plasticity (Wajdzik et al. 2013). Currently it inhabits not
only primeval and undisturbed forests, but more and more
often also the habitats transformed by human activity
(Jamrozy et al. 2001, Bereszyński, Hofman 2007,
Czyżowski et al. 2009). The large numbers of beavers in
Poland, currently estimated at about more than one
hundred thousand individuals, result from their successful
reintroduction in the 1960s and protection of this species
(Leśnictwo 2015).
Beavers strongly affect wetlands and aquatic
ecosystems, and results of their activity are noticeable
much further than the habitats penetrated by them. The
impact of beavers on the environment depends on their
population density and dynamics as well as duration of
the presence of beavers in the given area (Wajdzik et al.
2013). Most often, the damages caused by beavers are
linear and are found along watercourses and edges of
water bodies (Borowski et al. 2005). The negative
influence of this species is associated with the losses
connected with the building of dams and destruction of
levees, which lead to flooding. Besides, the damages
caused by beavers in forests and orchards result in tree
injuries (Dzięciołowski 1996), while in farmlands they
sometimes feed on cultivated crops (Jamrozy et al. 2001).
The positive influence of beavers on the environment is
associated with improvement of hydrological conditions,
initiation of paludification, and increase in biodiversity
(Czech 2000).
The negative effects of beavers can be alleviated by
financial compensation for the damages or catching and
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resettlement of beaver families and disassembling of the
dams, as well as proper protection of roads, culverts,
embankments, and levees. Recently, apart from the
technical solutions, repellents were tested on various plant
species, but the results were discouraging (Borowski et al.
2005). Besides, single valuable trees or particularly
valuable crops can be protected by steel chain-link
fencing (Czech 2000).
The aims of this study were: (1) to assess the various
kinds of damage caused by beavers in selected
broadleaved stands; (2) to determine the effectiveness of
fencing of forest stands from the watercourse and laterally
(side length: 40 m). In relation to the second question, we
determined if beavers tend to skirt the fence and cause
further damage in the forest stand.
MATERIALS AND METHODS
1. STUDY SITES
Field research was conducted in Nowa Sól Forest
District, located in Lubuskie Province (administered by
the Regional Directorate of State Forests in Zielona
Góra). Land relief within the Forest District is not highly
varied. The area is dominated by lowlands, up to 200 m
a.s.l. The climate in the valley of the Oder (Odra) is
characterized by higher humidity than the neighbouring
regions. The annual mean temperature is +8.1°C and the
growing season lasts 220-240 days. The Forest District
lies within the Oder catchment area. The direct Oder
catchment accounts for the largest proportion of the
Forest District, while the Bóbr catchment is much smaller,
very much like the Obrzyca catchment (Plan urządzania
lasu, 2011).
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2. EXPERIMENTAL DESIGN
Within the Forest District, 4 forest stands were
selected, located near watercourses or wetlands. Our
research plots were located in the 4 forest stands, where
beavers cause substantial damages. Two experimental
forest stands (forest sections 107h and 111g) were partly
protected by steel chain-link fencing along the
watercourse and laterally (both sides 40 m long), while
the other forest stands (forest sections 181m and 222g)
were used as control plots and were not fenced. The
chain-link fencing (mesh size: 6 cm) was buried in the
ground to the depth of 50 cm and the aboveground part of
the fence was 1 m high. Its construction took place in
April 2014.
Field research consisted in the counting of trees
damaged by beavers in individual plots, identification of
tree species/genus, marking of the tree with paint (to
avoid re-counting of the tree), and classification according
to a scale of tree damage: class 1 = only stump left (Fig.
1a); class 2 = root collar injured but tree not fallen or
fallen but remaining undetached (Fig. 1b); class 3 =
nibbled bark and injured trunk (Fig. 1c); class 4 = flooded
tree (Fig. 1d). The damages were surveyed twice: before
the partial fencing (4 April 2014) and after the fencing (4
June 2014).
Table 1. Description of the study sites.
Age
Plot type
(forest sections)
Surface area (ha)
Fenced (107h)
2.32
10-35
Fenced (111g)
8.52
40-70
Control (181m)
0.56
13
pedunculate oak, European ash
very dense
Control (222g)
1.32
15-60
pedunculate oak
very dense
(years)
Dominant tree species
pedunculate oak (Quercus robur), black alder (Alnus
glutinosa), European ash (Fraxinus excelsior)
European hornbeam (Carpinus betulus), pedunculate oak,
small-leaved linden (Tilia cordata)
Herbaceous cover
dense
dense
Fig. 1. Damages to the trees in young broadleaved forests: class 1 (A); class 2 (B); class 3 (C); class 4 (D).
RESULTS
The analysis based on the data collected before
fencing (April) has revealed that the damages caused by
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beavers are most severe within a distance of 20 m from
the watercourse. In the experimental forest stands, which
had not been fenced yet, in total 87 trees were subject to
beaver damage, and the damages, depending on the
distance, were as follows: 36.8% at a distance of 0-10 m,
62.1% at a distance of 10-20 m, and 1.1% at a distance of
30-40 m. In the control forest stands, 47 trees were found
in total. At a distance of 10 m from the watercourse, 16
trees were recorded (34.0% of the trees subject to beaver
damage), compared to 22 trees at a distance of 10-20 m
(46.8%), and 9 trees at a distance of 30-40 m (19.2%).
The results indicate that the damages caused by beavers in
younger broadleaved stands reach up to 40 m from the
watercourse but mostly in its vicinity and consist
primarily in tree felling (Table 2).
The analysis of data collected after partial fencing
(June) revealed that trees were damaged by beavers in the
meantime only in the control plots (no fence). In the plots
that were fenced on 3 sides, no new damages caused by
beavers were found. In total, in the control plots, 75
newly damaged trees were recorded. At the various
distances, different numbers of trees were subject to
damage: at 0-10 m, 33 trees (44% of trees subject to
beaver damage), at 10-20 m, 24 trees (32%), while at a
distance of 30-40 m, 18 trees in total (24%). The damages
observed in June consisted in flooding of trees in the
immediate vicinity of the watercourse and felling them at
a distance of up to 40 m from the watercourse (Table 3).
Table 2. Damages to the trees in broadleaved forests due to beavers before the fence was built (4 April 2014)
Plot type
Distance from watercourse (m) Number of trees subject to beaver damage Class of damage
0-10
29 oaks, 3 lindens
1
10-20
52
oaks,
2
maples
1
Experimental
Control
30-40
1 oak
3
0-10
10-20
30-40
12 oaks, 3 alders, 1 maple
22 oaks
9 oaks
1
1
1
Table 3. Damages of the trees in broadleaved forests due to beavers after the fence building (4 June 2014), excluding the marked trees that were
damaged before fencing
Plot type
Experimental
Control
Distance from watercourse (m) Number of ‘new’ trees subject to beaver damage Class of damage
0-10
0
-
10-20
0
-
30-40
0
-
0-10
33 oaks
4
10-20
24 oaks
1
30-40
18 oaks
1
DISCUSSION
European beavers affect much larger areas than their
territories. The damages caused by beavers are found
mostly along the edges of water bodies and watercourses,
within a narrow belt, less than 100 m wide (Borowski et
al. 2005). The initial data collected in our study, before
the fencing of broadleaved stands indicate that the
greatest damages were observed at a distance of up to 20
m from the watercourse. In the experimental plots that
had not been fenced yet, nearly 99% of trees damaged by
beavers were within this distance from the watercourse. In
the control plots, 76% of all the trees damaged by beavers
were up to 20 m away from the watercourse.
Results of research on the food preferences of European
beavers indicate that they use the available food base but
prefer some tree species (Czyżowski et al. 2009). The
cited authors report that some species are subject to
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beaver damage proportionally to their abundance in the
area. In our study, beavers used mostly young oak trees,
while damages to lindens, alders, and maples were rare
(Table 2), proportionally to their contribution to the forest
stands.
The damages caused by beavers in the forest
ecosystem result from the biology of this species. It
consists in flooding of the area as a result of water
impoundment by the dams constructed by them and in
felling or injuring of trees while feeding and collecting
food reserves for winter (Czyżowski et al. 2009). In our
study, most of the trees subject to beaver damage were
felled (class 1, Table 2).
The losses caused by beavers may be reduced e.g. by
fencing of single trees or valuable forest stands (Czech
2005). The activity of beavers is generally observed
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mostly at a distance of up to 35 m from the watercourse
(Szczepański and Janiszewski 1997; Czech 2002;
Żurowski and Kasperczak 1996), but in some cases even
up to 60-100 m from the watercourse (Brzuski and
Kulczycka 1999). In our study, in broadleaved stands
fenced on 3 sides (along the watercourse and laterally, to
a distance of 40 m), the fencing completely protected the
forest stands, as no new damages were detected there,
although in the control plots new beaver damages
appeared (Table 3). Damages in the control plots
consisted in flooding of the area and waterlogging of trees
at a distance of up to 10 m and felling of trees at a
distance of up to 40 m from the watercourse. Felling of
younger trees, observed in our study, is consistent with
the findings of Kubacki and Wajdzik (2002), who showed
that younger trees growing at a distance of up to 35 m
from the watercourse were most frequently felled by
beavers.
CONCLUSIONS
In younger broadleaved stands, beavers cause
damages to trees mostly at a distance of up to 20 m from
the watercourse, which is reflected in the highest
proportion of trees subject to beaver damage within this
distance from the watercourse. The damages caused by
beavers in younger forest stands consist primarily in tree
felling. The fencing of valuable broadleaved stands along
the watercourse and laterally to a distance of 40 m seems
sufficient to reduce the damages caused by beavers.
ACKNOWLEDGEMENTS
We express sincere thanks to the Manager of Nowa
Sól Forest District, who allowed us to make the
observations and provided us with the necessary
materials. The manuscript was partly translated into
English by Sylwia Ufnalska.
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For citations
Kamczyc J., Bielachowicz M., Pers-Kamczyc E. 2016.
Damages caused by European beaver (Castor fiber L.,
1758) in broadleaved stands. For. Lett. 109: 7-10.
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