Changes in the dragonfly communities at the twenty ponds at Woodwalton Fen, Cambridgeshire, United Kingdom, since the study of 1962-1988

The pattern of the number of spp. per pond changed completely between 1988 and 2000. The growth of scrub on the edges of the ponds caused a decline in the number of dragonfly spp. when more than 50% of pond edge was shaded by bushes. When the ponds were completely shaded they lost all their dragonfly spp. The decline in spp. appeared to be caused by shading rather than changes in the aquatic flora caused by shading. When the scrub was not controlled the ponds were inhabited by dragonflies from 26 to at least 39 yr. In ponds where no scrub developed, or where it was controlled, Coenagrion paella, Ischnura elegans, Libellula quadrimaculata. Aeshna cyanea, Sympetrum striolatum and Sympetrum sanguineum were still continuing to inhabit the ponds after 39 yr. Aeshna grandis, which had occurred most yr. in the 1962-1988 period, was still present in 2000. Pyrrhosoma nymphula and Brachytron pratense, which had bred from 1964 to 1972 and 1968 to 1973 respectively, both reappeared after 20 yr. absence. Their return to the ponds appeared to be connected with their increase in adjacent habitats at Woodwalton Fen in the 1989-2000 period. Anax imperator and Libellula fulva, which had also increased at Woodwalton Fen, were seen for the first time at the ponds during this period. The reason for the recent disappearance of Lestes sponsa firm the ponds and adjacent habitats is not known. This study yet further emphasises the need to conserve large core populations of dragonflies, and it reiterates the need for really long term monitoring.