Late‐glacial and Holocene high‐altitude environmental changes in Vallée des Merveilles (Alpes–Maritimes, France): insect evidence

Abstract

A series of sedimentary profiles derived from the Lac Long Inférieur peat-bog (2090 m altitude, southern Alps) enabled the tracing of the evolution of successive fossil insect assemblages (Coleoptera, Hymenoptera Formicidae, Diptera Bibionidae, Trichoptera, Megaloptera and Nevroptera) from the Würm deglaciation to the present in this part of Vallée des Merveilles. This evolution reflects the climatic changes and hence the vegetation changes, as well as the human impact on the environment since neolithic times. During deglaciation, an episode marked by very poor fossil insect assemblages was followed by one with abundant boreo-alpine Coleoptera dependent on melting snow and steppe Coleoptera. This episode corresponds to the Younger Dryas climatic deterioration (10 970 ± 210 yr BP; 10 430 ± 210 yr BP) during which a steppe vegetation prevailed. The sudden fall in the number of insects belonging to cold environments marks the beginning of the Holocene warming. During the Preboreal and the Boreal period (8801 ± 54 yr BP; 8692 ± 53 yr BP) these insects disappear almost totally. On the other hand, Coleoptera mostly living at the tree-line and at forest margins increase and reach a maximum at the end of the Boreal. Thereafter (Atlantic, 8087 ± 58 yr BP; 5678 ± 50 yr BP) they decrease to the benefit of forest insects. This development corresponds to an elevation of the tree-line during the Atlantic and the Sub-boreal (4770 ± 300 yr BP; 3740 ± 160 yr BP) and to a thicker forest cover. Coleoptera dependent on Abies and Larix appear at this time. The final entomological event occurs at the end of the Sub-boreal and in the Subatlantic (2660 ± 190 yr BP): it is characterised by a regular decrease of tree-dependent taxa. This development is attributed to human action.

Holocene environmental history of a small Mediterranean island in response to sea-level changes, climate and human impact

“…The beetle data alone should be interpreted with caution -and therefore compared with pollen data. Previous multiproxy studies have demonstrated a good agreement between both records (e.g., Hughes et al, 2000;Ponel et al, 2001Ponel et al, , 2014: monophagous or oligophagous beetles may confirm the local presence of plant taxa (e.g., Phytobius leucogaster) or reveal the presence of plant not indicated in the pollen record (e.g., Ficus carica), and both proxy may provide original information concerning local past human activities (e.g., dung dependent beetles and coprophilous spores).…”

“…This highlights the limits of pollen analysis alone to reconstruct the structure and the state of maturity of the woody vegetation: was it composed of relatively low Erica shrubs or old trees and decaying trunks in a mature forest with a notable amount of dead wood? As emphasized by Ponel (1995) and Ponel et al (1992Ponel et al ( , 2001, fossil beetles could help to answer this difficult question. Concerning Cavallo Island, the saproxylic beetles recorded during the maximum of Erica arborea frequencies could bring part of an answer (Fig.…”

“…5), could correspond to an early presence of domestic cattle 2500 years before the first archaeological evidence of human presence in the Lavezzi archipelago. Co-occurrences of these bio-indicators have often been used as markers of pastoralism but it is necessary to interpret dung beetle fossils carefully: these specialized insects could be associated with domestic mammals and pastoralism but they could also reveal the local presence of wild animals as shown in the Alps (Lemdahl 2000;Ponel et al, 2001Ponel et al, , 2011 cal. yr B.P.)…”

“…Many species are specific to very narrow ecological niches, they respond quickly to ecosystem shifts and disturbances, and they are relatively easy to identify to species or species-group level. Recent multidisciplinary studies including pollen and coleopteran analyses provide original and independent data concerning forest dynamics, human activities and climate (Ponel et al, 1992(Ponel et al, , 2001(Ponel et al, , 2011Gustavsson et al, 2009;Tessier et al, 1993). This study is the first multidisciplinary analysis including Coleoptera carried out in the Corso-Sardinian region.…”

Timing of glaciation in the Mediterranean mountains during the last cold stage

“…Lacustrine sediments at the glacial Lac Long Inférieur (2090 m a.s.l.) indicate that deglaciation had begun by 14.19 AE 0.13 14 C ka BP (Ponel et al, 2001).…”