Henri Dumont achterna – Een verslag over libellenobservaties van 1996-2007 in een natuurreservaat langs de Dender (België – Oost-Vlaanderen)

The article gives a summary of dragonfly observations in the Wellemeersen, a nature reserve of about 100 hectares situated on the left bank of the river Dender near Denderleeuw, in the province of Eastern Flanders (Belgium). The importance of this site as a ‘trap area’ for dragonflies was first discoverd by H. Dumont who published an extended species list in 1971. The area is delimited by linear elements such as railroads and a motorroad which might serve as artificial pathways for dragonfly distribution. The data were collected in the period 1996- 2007 and have been published in a comprehensive report with detailed descriptions of the status, observations and distribution (including maps) of each species. In this article, a short description is given of some specific (but mostly artificial) dragonfly biotopes, like old sandpits, large ponds, former bomb holes, fishing ponds and flooded meadows. Most of the 1840 data records were collected by sight. The area was subdivided into 184 separate inventory units to provide detailed location data. All dubious observations were carefully checked. A total of 34 species were found, of which 23 can be considered as autochthonous. All belong to the Red List category ‘Not threatened’. Nine species are dwellers. Distribution and abundance are discussed. More than 55% of the records originate from 6 species: Ischnura elegans, Aeshna cyanea, Coenagrion puella, Sympetrum sanguineum, Anax imperator and Sympetrum striolatum. The least abundant are Aeshna grandis, Cordulia aenea, Crocothemis erythraea, Enallagma cyathigerum, Erythromma lindenii and Lestes sponsa. The most widespread species within the study area (in more than 50% of the total of 184 inventory blocks) are Ischnura elegans and Sympetrum sanguineum, followed by Aeshna cyanea, Sympetrum striolatum and Aeshna mixta. Within the Flemish context, the Wellemeersen can be considered as a fairly rich dragonfly area. A comparison with Dumont’s list shows that two species, Brachytron pratense and Aeshna isoceles, have not been observed again and have most probably disappeared from the area. On the other hand, new permanent inhabitants are Erythromma viridulum, Crocothemis erythraea and Cordulia aenea. The last two were only occasionaly seen during the former period.