AN INSECT RECORD OF THE LAST 12 KA IN PYRÉNÉES, FRANCE: COMPARISON WITH POLLEN DATA
- Unlike pollen data which indicates a pioneer Pinus forest at the onset of the Holocene (10 - 9 ka), the abundance of cold-adapted insect species suggests that no forest cover was present. Tmax were probably below 10°C. High Pinus pollen percentages should be attributed to extra local apport, however some scarce occurrences of Pinus stomata suggest that isolated trees were possibly present on the sunny slopes.
- At the onset of the Holocene, the disappearance of cold-adapted species of Coleoptera is dramatic. This event is synchronous with a sharp peak of Drusus discolor that lives today in cold and rapid streams of mountaneous regions. In his turn this taxa disappears quickly, suggesting a rapid evolution of the environment induced by the Holocene warming.
- This warming is followed by a long period (from 9000 to 4700 BP) characterized by regular occurrences of arboreal Coleoptera. The presence of deciduous and coniferous trees in pollen assemblages indicate that the site of La Restanque was possibly situated in an ecotone zone. Surprisingly few forest-dependent ground Coleoptera were identified, this suggests that the forest cover was light. High temperatures are marked by several taxa including the tree dependent ant Dolichoderus quadripunctatus.
- During the Subboreal (4700 - 2700 BP) the human impact on the forest cover is suggested by a decrease in conifer dependent Coleoptera, the reappearance of open environment Coleoptera and a peak of Camponotus, dependent on dead wood. At the same time the Fagus forest become established nearby as recorded in the pollen diagramme and also attested by the weevil Rhynchaenus fagi exclusively dependent on beech. Orobitis cyanea that feeds on Viola in the underwood suggests that a true forest environment prevailed then. The Restanque site was obviously located at that time at the limit between a ruined pine forest and an expanding beech forest.
- At the last recorded stage the arboreal cover is eradicated to the benefit of a heath land with Ericaceae community as proved by the oligophagous weevil Micrelus ericae.