Zbigniew Borowski
Forest Research Institute
Poland
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Beaver population in Poland like in many other countries
during last 40 years increased rapidly from 270 to over 80
000 ind.
This unexpected success in species reintroduction was
partly caused by special program for reintroduction
(Program for Active Protection of the European Beaver).
However, we still do not know what mechanisms stay
behind this success.
The return of beaver, although beneficial from a wildlife
standpoint, has created problems for many landowners.
Damage caused by beaver usually consists of flooded
timber and agricultural land, girdling and cutting valuable
trees and interference with drainage systems.
Whereas locally damages caused by beavers are very
important there is no information about their intensity on
the country level.
The objective of the study was to answer to the following
questions:
•What is the pattern of distribution of beaver population in
Poland and its density?
What is the spatial pattern of damages caused by beavers in
Polish forests and their intensity?
• When damages caused by beavers are the most numerous
and what tree species are the most preferred?
•How important is beaver’s impact on forest economy?
The Eurasian beaver (Castor fiber)
is the continent’s largest rodent
characterised by:
• A semi-aquatic life-style,
inhabitant of all kinds of freshwater
systems
• Strictly herbivorous
• Monogamous species living in
small family groups
• Produce 1-3 young per year, lifespan 7-8 years
Beavers are agents of landscape
change, altering the structure and
species composition of vegetative
communities thought herbivory
and water impoundment
Beaver’s status in Poland:
• Until 1994 – strictly protected
species
• From 1994 – protected with
some exceptions
The level of compensation:
2011 - 2,5 mln EUR
2008 – 1 mln EUR
68993
Number of beavers [ind.]
90 000
80 000
70 000
60 000
50 000
43499
40 000
30 000
24464
20 000
10 000
0
7600
0
130
270
1000
1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Years
80 000
over 14 000 ind.
8 001 - 14 000 ind.
4 001 - 8 000 ind.
1 001 - 4 000 ind.
< 1 000 ind.
First record
Number of beaver colonies
Tree species damaged by beaver
Mean percent of damages
50
mean percentage of damages per tree species
40
30
20
10
0
Poplar Willow
Lime
Larch
Ash
Elm
Fir
Birch Beech Maple
Number of forest districts
300
250
Alder Scotch
Pine
Oak
Norway
Spruce
Elm
Fir
number of forest districts [out of n=4] where damages
of consequitive tree species were recorded
200
150
100
50
0
Poplar Alder Willow
Oak
Birch Scotch Beech
Pine
Ash
Norway Larch Maple
Spruce
Lime
Seasonal dynamics of tree damages caused by beavers
300
Cutting
250
Tree numbers
200
150
100
50
0
Debarking
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Birch
Oak
Elm
Rowan
Poplar
Cutted
Bird
cherry
Alder
Scotch
Pine
Debarked
Norway
Spruce
100
r = -0,73
%of cutted trees
80
60
40
20
0
0
5
10
15
Mean diametes of tree species [cm]
20
2,5
Cutted
Debarked
2
1,5
Jacobs' electivity index
1
0,5
0
-0,5
<6
6-10
10-14
14-18
-1
-1,5
-2
-2,5
Diameter [cm]
18-22
22-26
26-30
>30
Beaver preferences in relation to tree species
1,5
Napiwodzko-Ramuckie Forests
Jacobs’ electivity index
1
0,5
0
-0,5
-1
-1,5
-2
-2,5
Jacobs' electivity index
2
-3
1
0
-1
-2
-3
-4
Knyszyńska Forest
Distance from water to tree species damaged by beavers in two locations:
Knyszyńska Forest and Napiwodzko-Ramuckie Forests
Distance from the water [m]
Napiwodzko-Ramuckie Forests
100
Knyszyńska Forest
100
80
80
60
60
40
40
20
20
0
Birch
Bird Norway
cherry Spruce
Oak
Scotch Rowan Willow
Pine
Hazel
Poplar
0
Alder
Hazel
Birch HornbeamWillow Larch Scotch Pine Oak
Birch
18
17
16
cutted
debarked
14
13
12
11
10
9
8
7
6
Spring
Summer
Autumn - Winter
Seasons
Bird cherry
18
16
14
Diameter [cm]
Diameter [cm]
15
12
10
8
6
4
2
wiosna
lato
Sezony
jesień-zima
Mean (±SD) diameter of felling trees which were taken or left by
beavers in Napiwodzko-Ramuckie Forests ***-p<0.001, *-p<0.05.
35
Taken
***
Left
***
30
***
Diameter [cm]
25
***
***
20
*
15
10
5
0
Birch
Oak
Hornbeam
Alder
Scotchpine Willow
 Estimated
number of beaver population in
Poland amounted to 80 000 animals
 In the local scale beaver’s impact on forest
stands was small; in places of beavers’ forage
damages averaged 28% (Knyszyńska Forest)
and 31% (Napiwodzko-Ramuckie Forests) of
available trees
 Tree species the most preferred by beavers
were: poplar, oak, willow, birch whereas the less
preferred were: alder, Scotch pine and lime
The distance of beaver operation was not bigger
than 40 m from water (except poplar – 62m).
 Autumn and Winter (from October to March) are
the periods with the highest intensity of beavers
damages.
 Trees with lower diameter most often were cut
whereas bigger trees were debarked. Moreover,
among felling trees beavers were taking thinner
trees.
 Scale and intensity of beaver’s damages was low,
therefore in the majority of cases there was no
significant conflict with forest economy.

Thank you for your attention