Managing Habitats for Dragonflies
Habitats: management problems and solutions
I. Lakes (water bodies of more than 1000 m2 and with pH more than 6)
Lakes can be natural or man-made. In southern England nearly all lakes are man-made and are particularly rich in dragonfly species. New lakes in the form of gravel and clay pits, borrow pits and reservoirs are being created continuously and provide great opportunities for management for dragonflies and other wildlife.
In lakes, dragonfly larvae are confined to the warm shallow edges where water plants flourish. Therefore, one large lake contains fewer dragonflies than does a series of small lakes covering the same area.
The management problems presented by lakes and their solutions are as follows:
- Unless controlled, willows etc. can shade out water plants. Therefore, ensure that some stretches of the lake are free of trees and bushes, but see notes on C. aenea and S. metallica (p.7). In newly made lakes and gravel pits control the development of trees and bushes along the shores.
- Steep sides to a lake reduce the zone of shallow water. Therefore, when creating lake habitats, ensure that there is a gradual slope at the margins in at least part of the lake.
- Large lakes are subject to considerable natural wave action and fast-moving boats can also produce similar effects. Vigorous wave action can cause turbulence which reduces the amount of light reaching submerged water plants and can prevent their growth. Waves can also hinder the emergence of dragonflies. Floating booms can be used to reduce wave action in small bays. Boat speeds can be controlled by co-operation with local authorities and boat hire firms. A system of zoning, so that some areas are kept free of boats and their wash, is the best solution.
- Lakes are easily polluted by drains from lakeside dwellings, by boats and particularly by agricultural or industrial waste entering them through streams that drain into the lake. Pollution can only be reduced by co-operation with local landowners, industries, local government and the National Rivers Authority.
- Large numbers of wildfowl or roosting gulls can enrich the water of some lakes so that the lakes cease to be a suitable habitat for dragonflies. Therefore, do not rear mallard or maintain a collection of ornamental waterfowl on lakes where you want dragonflies to be conserved.
- Lakes with unnaturally large populations of fish contain few dragonflies because the fish eat the larvae. Therefore, do not develop fishing lakes with artificial feeding and high stock rates on lakes where you want dragonflies to be conserved.