The mapping was achieved by recording all the species seen in a tetrad, which is a 2km x 2km square on the Ordnance Survey map. There are 450 such tetrads in Hertfordshire, hence the need for a six-year study, to allow sufficient time for the recorders to pay multiple visits to each of the tetrads over the entire dragonfly flight season. A longer period would not be viable, as it would mask trends in changes to the dragonfly distribution.
One of the main problems with any Atlas Project is coverage. Inadequate coverage resulting from too few recorders or insufficient time leads to misleading distribution maps, which are more a statement on the distribution of recorders rather than the dragonflies themselves. In an attempt to overcome this problem, I acted as central coordinator. This entailed producing coverage maps at the end of each season and coordinating the efforts of the recorders to minimise duplication.
Clearly the census work could only be carried out during the dragonfly flight season. However , it was possible to visit some of the more barren tetrads during the winter months, to confirm that there is no suitable dragonfly habitat, and that further visits during the flight season would not be worthwhile.
In this way these tetrads could be regarded as " covered " without wasting valuable recording time during the summer months.
If you require more information, please contact :
Alan Reynolds
32 Mandeville Road
Hertford
Herts SG13 8JQ
Tel : 01992 586150
Email : apreynolds22@hotmail.com