INSECTES AQUATIQUES D'UNE TOURBIÈRE 



531 



SUMMARY 



1. The peat bog of Le Cachot is situated at an altitude of 1050 m, in the valley 

 of La Brévine. The author has studied the ecology of the insects bound to the 

 aquatic habitat of this peat bog (ponds and channels). 



2. The climate of the valley of La Brévine (macroclimate) is rainy (annual 

 average rainfall: 1446 mm) and cold (annual average température: +4,7°C). 

 Winter lasts about 6 months. Nocturnal mists occupy the bottom of the valley 

 from the end of Summer, through Autumn and into Winter. 



3. In the peat bog, température fluctuations, air humidity and dryness are 

 accentuated with regard to the macroclimate during the period of fine 

 weather. 



4. The peat bog contains a phreatic water table which surfaces in its centre. 

 The water level in the ponds indicates the level of the water table. The channels 

 represent the minimum level of the latter. Précipitations represent the only 

 source of water. 



5. When the ponds dry up, the vegetable deposits harden on the bottom and 

 form a protective crust which retards evaporation of the subjacent peat layer. 

 The périphérie channels are permanently filled with water. 



6. The humid centre of the peat bog is occupied by the Sphagnetum-medii- 

 This plant association is surrounded by the Sphagno-Mugetum. The pine 

 forest is itself separated from the edge of the peat bog by degraded moors. 

 The ponds belong to the Scheuzerietum in various degrees of évolution. The 

 author has classified the ponds on the basis of their floristic composition 

 by adopting the method proposed by Mountford. The végétation of the 

 high bog is evolving gradually towards its climax (Sphagno-Mugetum ) . This 

 implies that the ponds are being filled by Sphagnum. 



The channels contain chiefly a floating végétation (bladderwort and fila- 

 mentous algae). 



7. The author has established an almost complète list of insects bound to the 

 aquatic habitat and has studied their distribution in the various stations. 

 He also establishes a list of insect communities which occur constantly in 

 the chosen biotopes. 



8. The insects appear in large numbers in Spring and disappear just as rapidly 

 when the cold weather sets in. 



9. The surface of the stations détermines the variety of the species and the 

 abundance of the populations of the surface living insects. In smaller stations, 

 one species tends to supplant the others. 



