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Beavers great for dragonflies and damselflies!

News / 27th October 2012

The effect of the Eurasian Beaver on Dragonflies and Damselflies (Odonata)
by Sara Schloemer, Lutz Dalbeck and Andreé Hamm. Institute of crop Science and Resource Conservation (INRES).

***Download the scientific poster from the download page***

Introduction
As a result of a reintroduction project in 1981 the Eurasian Beaver returned to the Hürtgenwald, a large woodland area in the Eifel mountain range in the extreme west of Germany. The study looked at the effects of the large-scale changes to dragonfly and damselfly communities in the narrow, originally wooded, mountain valleys of the northern Eifel area.

Method
In order to compare beaver ponds with woodland streams representative of large areas north of the Alps, but yet not influenced by the beaver, we studied the following habitat types:

1. Natural springs (definite woodland springs)
2. Streams (natural – semi-natural in woodland, not influenced by the beaver)
3. Beaver ponds (some 10 -15 years old, up to 2000 m², sunny to half-shaded).
4. Beaver ponds abandoned for 1 to 3 years.

All areas were searched for dragonflies and damselflies, their larvae and exuvia throughout the season in 2011 and 2012.

In addition chemical and physical parameters such as pH-value, temperature, and water speed were measured at all sample sites, and makrozoobenthos collected, in order to gather information on the water quality in both the presence and absence of the beaver.

Results
With a total of 29 species, the number of species in beaver ponds is markedly higher than in ponds without beavers (4 species). Even in abandoned beaver ponds the number of species is higher than in the streams (7 species).

If species typical of the streams are considered, these also profited from the influence of the beaver. This is due on the one hand to the dams, which are clearly very suitable habitat and on the other to the increased exposure to sunlight, even on stretches of running water, caused by the beaver’s activities.

Conclusion
Despite the relatively short period of time since the return of the beaver, and the rather small number of beaver ponds, the ponds already now make a remarkable contribution to the conservation and spread of rare dragonfly and damselfly species.

Beavers contribute markedly to nature and species conservation in the densely settled countryside of Central Europe. The species should therefore be more greatly integrated into plans to implement conservation measures and renaturisation of water bodies than it has been to date.

Particularly notable are:
- The extraordinary combinations of species (boreal alongside sub-Mediterranean species)
- The extremely different habitat requirements of the species
- The increase in typical stream dragonflies and damselflies in spite of damming by the beaver
- The increase in part of highly endangered species

List of Dragonflies and Damselflies associated with beaver modified habitat (the usual habitat these species are found within is shown underneath):

Libellula depressa
Still waters, small, sunny and bare

Libellula quadrimaculata
Still waters with well developed vegetation

Cordulia aenea
Standing waters

Anax imperator
Standing waters, well-vegetated

Somatochlora metallica
Standing and slow-flowing waters

Aeshna cyanea
Preferring small and shaded ponds

Aeshna juncea
Acidic heathy lakes and bogs

Aeshna mixta
Still and slowflowing waters

Orthethrum coerulescens
mainly runnels in boggy areas

Orthethrum brunneum
Small streams, preferring scantily vegetated sites

Cordulegaster boltonii
Streams, in forests, open moors and heaths

Gomphus pulchellus
All kinds of slow-flowing and standing waters

Sympetrum striolatum
Pioneer of newly created ponds

Sympetrum danae
Mostly acidic waters, bogs, moorland and heathy lakes

Leucorrhinia rubicund
Acidic, oligotrophic lakes, tarns and bogs, also richly vegetated habitats

Leucorrhinia pectoralis
Less acidic, mesotrophic bogs, forest lakes, marshy ditches and oxbows

Brachyton pretense
Reedy canals, marshes, oxbows

Calopteryx splendens
Running waters, avoiding shade

Calopteryx virgo
Running water, classic habitat forest streams

Coenagrion puella
Running and standing water, favours the presence of aquatic vegetation

Ischnura elegans
Running and especially standing waters

Ischnura pumilio
Small or temporary ponds

Platycnemis pennipes
Running and still water

Enallagma cyathigerum
Lestes sponsa

Any standing water, numerous at recent shallow or acidic sites

Lestes virens
Heath and bog lakes with peatmoss

Lestes viridis
Standing or slow flowing water with bordering trees and bushes

Ceriagrion tenellum
Small streams, bogs and heathy lakes with peatmoss

Pyrrhosoma nymphula
Well-vegetated standing and running waters