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Doris Hölling

Forschungsanstalt WSL

Swiss Federal Research Institute WSL
Swiss Forest Protection
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CH - 8903 Birmensdorf

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Article

Author(s): Doris Hölling
Editorial office: WSL, Switzerland
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Beavers – landscapers with potential for conflict

In the 19th Century the beaver was wiped out in Switzerland and in 1956 re-introduced. Due to its long absence a large amount of knowledge about how to coexist along side this animal was lost. Now both interested and affected parties have once again to deal with the question of the beaver. They have to find a way for a conflict free coexistence.

Nagender Biber
Fig. 1 - In summer beavers feed mainly on young tree shoots and water and river bank plants. In winter on alder, poplar, hazelnut, birch and species of willow.
Photo. Christof Angst

 
Aufgestauter Bachlauf
Fig. 2 - The entrance to the beaver lodge must be below the water line. If the water is not deep enough beavers will dam the river.
Photo. Christof Angst
 
Biberspur am Ufer
Fig. 3 - A beaver’s imprint in mud on a river bank.
Photo. Christof Angst
 
Verbreitung des Bibes in der Schweiz
Fig. 4 - The actual spread of beavers is limited to the lower laying lands. 90-95% of the animals live at heights between 400 und 500 m. Click to enlarge.
Photo: © Biberfachstelle/CSCF, Map background: swisstopo
 
Fällplatz
Fig. 5 - Within the shortest of time beavers bring dynamic into a water landscape by felling trees and damming running water.
Photo: Doris Hölling (WSL)
 
Benagter Stamm
Fig. 6 - Beavers fell trees for food in winter: branches and bark. Oak trees are felled only for building.
Photo: Doris Hölling (WSL)
 
Stamm mit abgenagter Rinde
Fig. 7 - The availability of food in winter is necessary for survival: a beaver eats 900g of bark per night.
Photo: Doris Hölling (WSL)
 
Bachlauf - eingegrenzt von landwirtschaftlichen Flächen und Wegen
Fig. 8 - In a suitable habitat 500m of river bank are adequate to support a beaver family. In an unsuitable habitat, where little wood is available, several kilometres of river bank are required to feed a family.
Photo: Christof Angst
 
Tief eingegrabender Biberausstieg aus dem Bachlauf
Fig. 9 - If natural food resources are not available beavers will search for alternatives: e.g. in fields and in doing so clearly point out the mistakes made in river bank planning. Much frequented water exits become deep trenches.
Photo: Doris Hölling (WSL)

Since its return the beaver has once again brought dynamic and life back into the Swiss waterways. For more than 100 years humans had often totally prevented this dynamic. Thanks to its damming of rivers, the keeping open of vegetation and its active dead wood promotion Master Bockert – as the beaver is know in fables – makes a mosaic of new structures and habitats from which other animals, in some cases rare animals, also profit.

The beaver then and now

The beaver was driven to extinction in Switzerland at the end of the 19th Century. The animal was hunted mainly for its thick fur and because of the purported healing properties of castoreum, a gland secretion smelling of musk, used for marking territory. Beaver meat was eaten during periods of fasting, as the beaver, thanks to its scaly tail, was declared to be fish by the Catholic Church.

Today many place and field names bear witness to former beaver settlements. Biber, Biberbrugg, Bibern, Biberist, Bebrelèque. The beavers in existence today are descendents of the 141 animals released into the wild in western Switzerland and in the Canton of Thurgau between 1956 and 1977. In 1962 they were placed under protection in Switzerland. Since 1966 they have been on the red list of endangered species. Various government laws and regulations also protect beaver dams and habitats (watermeadow regulations, parliamentary laws on water management and river engineering.)

On the trail of the beaver

The beaver is a dusk and night active animal resting during the day in its lodge. It is therefore rarely sighted. However, the animals leave typical tracks: ranging from dams, to footprints, scenting hills and feeding and felling spots. From these the size of the beaver family, as well as its territory, can be deducted.

In the winter of 2007 / 2008 the Beaver Service, on behalf of the Federal Office for the Environment (FOEN), carried out a nationwide census. 250 volunteers, game keepers and other experts from 16 Cantons searched over 6500 km of river banks for signs of beavers, as direct sightings are rarely possible.

Signs of beavers are:

  • All sorts of lodges (even abandoned ones)
  • Feeding and felling places, signs of gnawing, winter supplies
  • Water exits, canal fluctuation
  • Dams (in Switzerland only in shallow water zones)
  • Scenting hills
  • Tracks
  • Families / colonies

The re-introduction of beavers took place slowly at first – which according to Christof Angst from the Beaver Service Office is quite normal. Since the middle of the 1990’s the beaver population has greatly increased. Today, there are around 1600 animals spread over 472 well connected territories. Whereas in 1993 beavers had only permanently settled along around 280 km of river banks in 2008 they had had already colonized 1400 km. At first the beavers lived along the larger rivers, the Aare, the Rhine, the Rhone and the Thur. Later however they moved into the tributaries and into cultivated land, as long as these did not provide any obstacles such as weirs, dam walls or culverting.

Essential timber harvesting

The ecological needs of a beaver are important criteria for the definition of its potential habitat:

  • As a semi-aquatic animal the beaver requires not only water but also river banks.
  • Food in the immediate vicinity of the water (max. 20m from the waters edge).
  • Slow flowing water and banks in which to dig their lodges.

All of this is generally available in unbuilt, close to nature river banks, water meadow areas and below 700 m in lakes. Running water at higher altitudes which has too strong a current or too steep a course or too much debris are usually avoided by beavers as are bodies of water at lower altitudes where they cannot have an influence on sudden and exceptional flooding.

Beavers search for food or building materials along a 20m wide strip of river bank. Its “timber harvesting” slightly resembles the forestry femel felling because the beaver establishes small felling areas where he intensively uses the forest or thins it out.

In the following winter it moves its felling place to another part of its territory so the vegetation is able to regenerate. Beavers do not just act as lumber jacks but also help with the spread of trees through dragging plant material, or felling willows, which re-sprout.

Only rarely do beavers find near-to-nature habitats with site specific riverbank vegetation. There are usually only a few site specific trees around on the river banks and these then mainly fall prey to their timber use. However if there is a wider, well structured river bank available then damage caused by beavers is hardly visible. Therefore, according to Ulrich Messlinger from Bayern, beavers are indicators that river banks are being wrongly used. Can Christmas tree plantations along river banks be considered natural vegetation?

Often the size of an animal’s territory is determined by the quality of habitat. This also applies to the beaver. In territories with an adequate natural food supply the beaver uses shorter lengths of river than in those with a meagre food supply. If the habitat is over used the animals move on and the softwoods can recover and regenerate until they once again, several years later, become a food supply source for the beavers. The main potential for conflict between beavers and man therefore occurs in suboptimal habitats. For beavers it is becoming increasingly difficult to find conflict free habitats.

The sunny side and the dark side of beaver occurrence

From an ecological and conservationist point of view beavers bring great advantages: hardly any other animal forms its habitat as intensely as the beaver thanks to all its digging, damming and felling activities. In the shortest of time it introduces a dynamic into the waterways which would otherwise only occur during exceptional natural catastrophes such as flooding, storm, snow breakage or fire.

Where there is wilderness there is also room for collapsing lodges, felled trees and dammed streams. However, in intensively cultivated areas, which the majority of our landscape is today, there is no place for such things. The further an animal ventures into cultivated land the more conflict arises with humans. And the majority of these conflicts occur within a distance of less than 10 meters from the river’s edge. According to Christof Angst a 10- 15 m wide strip of river bank would be more than enough to reduce this conflict or to stop it all together. But here lies the problem, because 75% of agricultural areas have a path or a road running along the river’s edge.

The dynamic and diversity introduced by beavers in structure, light and current provides ideal habitat conditions for many plants and animals. So in time biodiversity increases in beaver waters. The beaver in forming its habitat allows the wilderness to return to heavily cultivated landscapes.

Is conflict free cohabitation possible?

Annoyances such as undermined roads and fields, blocked drainage or gnawed trees along paths can often be avoided through preventative measures:

  • Protect valuable trees near beaver territories with cylinders made out of galvanised fencing or Wöbra paste
  • Protect beet and maize fields with electric fences
  • Protect roads and river banks from undermining e.g. by the intensification of river bank strips; river bank protection using wire mesh; the provision of artificial lodges
  • Prevent water logging in nearby fields by inserting drainage pipes into beaver dams
  • Make more room for water so that it can fulfil its ecological function and at times of flooding slow down runoff.

If it still came to damage on cultivated agricultural land or to forests the owners would be compensated by the state and cantons, but only if prevention measures had previously been taken. According to Christof Angst damage caused to forests results in lower costs than that caused to cultivated land. Even if beavers did cause unacceptable damage to forests or cultivated land then they could, as an exception, be shot or captured with the permission of the Federal Office for the Environment (BAFU). In Bavaria, where today 12,000 beavers live, 500 are removed yearly to avoid greater conflict.

Beavers as a driving force for species diversity

Prachtlibelle
Fig. 10 - The banded demoiselle damselfly also populates slow running streams, smaller rivers and canals rich in vegetation. Pollution, canalisation, straightening and the development of riverbanks have greatly limited their habitats.
Photo: Doris Hölling (WSL)
 
Schwimmender Biber
Fig. 11 - The beaver’s nose, eyes and ears are aligned in row along the top of its head. Therefore, they can be optimally used whilst the remainder of its body stays submerged.
Photo: Christof Angst

At a conference organised by the BAFU and the Centre Suisse de la Cartographie de la Faune Neuchâtel (CSCF) in Bern in December 2009 Ulrich Messlinger showed that pioneer species can spread despite beavers gnawing them. He has registered a large increase in species diversity in beaver habitats. For many animals and plant species, even rare ones such as the tree frog, dragonfly or various reed species, a suitable habitat becomes available after beaver activity. For example, waters rich in amphibians and fish are a source of food for the black stork and dead wood provides perches for kingfishers. As beavers seem to play an important role for rare animal species they must therefore also play an important role in species and habitat protection. Even in extremely dry years beavers manage to create open areas of water. This can, for instance, be important for areas with a large percentage of spruces, because these are then less susceptible to bark beetle infestation.

Armin Peter from the EAWAG Kastaninebaum points out that dead wood in bodies of water has a positive effect on the fish fauna and increases its biodiversity. His conclusion is: wood is good”. Dead wood in bodies of water provides cover for fish, reduces competition between species and not only increases the fish population, but also the number of smaller creatures. Therefore, in revitalising bodies of water not only should dead wood be used for erosion protection in the area of the river bank, but also as structured elements in the river bed itself – of course always with safety during flooding in mind. Beavers increase this input of wood noticeably and without cost.

The re-naturalisation fund of the canton of Bern is in favour of such measures. They also support plans for land purchase which would permit a re-settlement of beavers.

During the course of the conference Rolf-Jürgen Gebler presented some of the many technical measures available for small scale development of bodies of water. However, these are usually bound to considerable costs and it takes more than 50 years until regulated waterways once again become naturalised. Messlinger’s research points out that beavers manage to achieve this re-naturalisation more successfully, more quickly and more cheaply. This habitat networking also establishes good migratory corridors for other animal species. So the beaver can also be called a door opener for small bodies of water. There are hardly any losers, but many winners!

According to Christof Angst and other experts the most sustainable solution is to give bodies of water more room so that once again on both sides of the river natural strips of river bank, around 10-15m wide, can develop. In Switzerland around one percent of agriculturally cultivated land would be enough to provide a habitat for beavers whilst at the same time greatly reducing the potential for conflict. In any case, these strips along river banks will become less valuable over time because it will take more effort to up keep them after every flooding that occurs. The best solution would be to leave them to the water and the beavers.

According to a survey in Germany (Spessart) beaver activity, measured in terms of re-naturalisation carried out by humans, is worth 10,500 Euro per year. It was also proved that there was less flooding in areas with beaver dams and wetlands because the dams slowed down the pace of the water. Several dams, one behind the other, interrupt flooding by way of cascades. At the same time beaver dams filter nitrate out of the water: a beaver dam breaks down 40KgN/year. The amount it puts into the water is negligible as it utilises its food optimally.

Interesting facts about the beaver and its way of life

  • Beavers are the largest rodents in Europe and are pure vegetarians.
  • Pairs stay together for a life time. They have permanent territories which are marked with castoreum from the rectal scent glands. A family consists of the young from two generations which then look for their own territories in the third year.
  • The life of these tree fellers is spent mainly in water. Webbed feet on their back legs and a scaly tail used for steering make beavers excellent swimmers and divers. On land they are very clumsy.
  • Their thick fur is optimal protection against the cold and the wet.
  • They have a jaw musculature which is twice as strong as that of humans. The strong incisors grow constantly.
  • Beavers do not go into hibernation.

Measures to protect and promote the beaver as well as establish new habitats:

  • Promotion of sources of food by planting site appropriate trees.
  • Improvement of sub-optimal territories e.g. by naturalising river banks and digging out silted-up side arms of rivers.
  • The buying up of areas or paying compensation when relinquishing use; reducing agricultural or forestry usage on attractive river bank areas in the favour of beavers
  • Leaving fallen or felled trees.
  • Establishing compensation areas as near to rivers as possible.
  • Public information campaigns and individual advice on the spot.
  • Removal of migration barriers (beavers cannot climb over 50cm)
  • Protection from migration dangers (e.g. roads)

According to research carried out by the Zentrum für Fisch- und Wildtiermedizin of the University of Bern these last two points are the main causes of beaver deaths in Switzerland.

  • Translation: Dawn Meister (Affoltern a. A.)

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