Abstract
A 1.70 m core extracted from the Lac des Lauzons, Haut Champsaur, French Alps, at 2180 m altitude, provided a detailed Holocene record of beetles, pollen and plant macrofossils, enabling the reconstruction of local palaeoenvironmental changes during the last 10 000 years. After an early phase of colonization by plants and insects, corresponding to the Lateglacial interstadial, a long phase of relative stability of the ecosystems (at least in the vicinity of the lake) is recorded. Strikingly, there is no evidence from beetle and plant macrofossils that the treeline reached the altitude of Lauzons during the Holocene climate optimum, although this period is characterized by major forest expansion in many high-altitude sites in the southern French Alps. The uppermost part of the record is blurred by the infilling of the lake, progressively turning into a peat bog. This sequence also provides an opportunity to compare the records of coprophilous fungal spores and coprophilous beetles and to improve the interpretation of these proxies in terms of their significance as proxies for pastoralism.
Highlights
Reconstructing high-altitude palaeoenvironments from fossil biological material preserved in lakes and peat bogs is problematic
It is necessary to keep in mind that the volume of sediment analysed per sample is small; the absence of certain taxa in the fossil record cannot be firmly interpreted as their absence in the past communities
The most significant feature in the beetle record is the regular occurrences in significant numbers of Aphodius mixtus throughout the sequence
Summary
Reconstructing high-altitude palaeoenvironments from fossil biological material preserved in lakes and peat bogs is problematic. The complex taphonomic history that results from the combined action of many factors are difficult to interpret since a significant part of the assemblages is often build up with allochthonous elements corresponding to long-distance transportation. Such phenomena primarily affect the smaller and lighter wind-blown elements, such as pollen grains, especially those of Pinus and other conifers (Andrieu et al, 1997; de Beaulieu, 1977; Brugiapaglia et al, 1998; Court-Picon, 2007; Ortu, 2002), and, to a lesser extent, plant macroremains (leaves, seeds, samarae, etc.). As a rule, the knowledge concerning the modern ‘rain’ of insects (and plant macroremains) is still in infancy (Smith et al, 2010), contrary to that of pollen (Andrade Olalla et al, 1994; Caseldine and Pardoe, 1994; CourtPicon et al, 2005, 2006; Frits et al, 1994; Ruffaldi, 1994)
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