Elmeros, M., Berthelsen, J.P., Hald, A.B., Andersen, P.N., Øverland, L.K. & Therkildsen, O.R. 2009: Overvågning af bæver Castor fiber i Danmark 2007. Danmarks Miljøundersøgelser, Aarhus Universitet. 82 s. – Arbejdsrapport fra DMU nr. 247.
summary
The beaver was reintroduced to Denmark in 1999, when 18 individuals from a population in Germany were released in lakes and streams on Klosterheden State Forest. Population development, distribution and the effects of beaver activity on various nature and environment factors have been monitored by National Environmental Research Institute and the Danish Forest and Nature Agency Regional Office, West Jutland (SNSV).
Population development and distribution of beavers
Population development and size was estimated in the spring from simultaneous sight observations at all active lodges and core areas. The beavers were counted at dawn and dusk in two days primarily to record number of beaver kits born in the previous summer to estimate annual population recruitment. A total of 16 kits born in the summer of 2007 were observed at 11 different colonies. The population size is estimated to more than 100 beavers.
The distribution of beavers was determined by regular observations and identification of beaver lodges and core areas by SNSV. In total, 28 occupied territories were recorded; 11 inside the state forest area and 17 in streams and lakes on private lands. The density of territories is highest in the catchment where the beavers were reintroduced. The beavers have dispersed to several streams surrounding the brackish Nissum Fjord, which is situated 25 km downstream from the reintroduction area, and they have established colonies more than 30 km upstream the fjord.
Status and mapping of beaver territories
Positions of beaver huts, dams, foraging areas, size of territories, surface area of beaver ponds, and areas affected by raised water levels in selected territories were registered in spring 2007 and digitized in a GIS-environment. The average size of areas affected by raised water levels was 4.6 ha/territory. Beaver colony size and area of affected vegetation, length of waterways and areas affected with raised water level showed no correlations.
Vegetation survey in beaver habitats
In 2007 the effects of beavers on the vegetation was described in eight active territories. As anticipated at the reintroduction the beavers’ foraging and construction of dams have opened the landscape by cutting down willow (Salix sp.) and bog myrtle (Myrica gale), created a mosaic of small new wetland habitats and initiated re-growth of Sphagnum spp., and created a dynamic network of small brooks. On the down side the changes induced by the beavers have promoted growth of large reedbeds and vegetation indicating more nutrient rich conditions. Some of the new wetlands have also flooded valuable nutrient poor vegetation, e.g. mires with bog asphodel (Narthecium ossifragum) and bog sedge (Carex limosa).
Survey of breeding birds
The occurrence of breeding birds in areas affected by beavers was recorded in the late spring of 2007. A total of 63 species were recorded, of which 55 species were breeding or assumed to be breeding in the study area. The different bird species are living in a wide range of habitats, e.g. coniferous and deciduous forests, heather, meadow, reed beds, lakes and streams, which reflects the high diversity of habitats in the beaver territories and adjacent areas. An increasing number of observations of water birds were assumed to be a result of the creation of more wetlands by the beavers. However, a late study period was not optimal for registration of breeding activity of water birds.
Impact on production areas and contact with private landowners
All beaver lodges are registered and supervised by SNSV, also on private lands outside the state forest. Private landowners with beaver activity on their land were contacted by SNSV staff. If problems occurred the staff undertook the required mitigating measures in consultation with the landowners. Overall 8 incidents and complaints were registered in 2007 regarding problems with blocking of spawning migration for fish and passage for boats, flooding of riparian areas and felling of trees in a garden. Dams were removed totally or partially in 3 instances, a tube was inserted in two dams to regulate upstream water level and trees were fenced in one garden.
Communication to the public
The beaver still receives huge attention from the public and the species is a key element in the public orientated activities at SNSV. Easy accessibility to see the beavers or tracks and signs of the animals has resulted in an increasing interest from naturalists visiting the forest. 76 volunteers and landowners participated in dawn and dusk beaver counts to estimate population development in the spring of 2007. A total of 380 tours with more than 13.000 participants were carried out in 2007. Among these were 109 guided hiking tours with the beaver as the focus species and 93 tours with a specially equipped bus.
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