David Etienne

Influence of sample location and livestock numbers on Sporormiella concentrations and accumulation rates in surface sediments of Lake Allos, French Alps

Spores of coprophilous fungi, especially Sporormiella, are often well preserved in lake sediment cores. It has been hypothesized that such spores can be used to quantify past livestock abundance. The quantitative relationship between fungal spore abundance and livestock populations, however, is not well established, nor are the mechanisms of spore transport and deposition in lacustrine systems. Multiple cores from Lake Allos, a large high-elevation lake in the French Alps, were used to map the modern abundance of Sordaria and Sporormiella spores throughout the lake. We observed high spatial heterogeneity with respect to spore numbers. No correlation with the distance from shoreline was found. There was, however, a relation with distance from the two main lake inlets. These results were used to select two fungi-rich sediment cores to investigate grazing pressure over the last two centuries. Comparisons were made between spore influx and historic data on livestock densities in the catchment. A sharp decrease in Sporormiella influx ca. 1894–1895 was associated with a reported reduction in sheep in the Allos catchment at that time. Mean influx of Sporormiella decreased by a factor of three between the nineteenth and twentieth centuries, reflecting a reduction in the reported number of animals in the Lake Allos catchment, from 6,000 to 2,000. This study confirmed that Sporormiella spore abundance in lake sediments can be used as a proxy for catchment herbivore numbers in paleoecological reconstructions. Nevertheless, our data indicate that before spore accumulation can be used to infer past domestic herbivore density, one must understand the processes of coprophilous spore transfer from the catchment to the lake and the influence of core location on spore numbers in the sediment.

Searching for ancient forests: A 2000 year history of land use in northeastern French forests deduced from the pollen compositions of closed depressions

Evidence of the agricultural use, during Roman or Medieval times, of forested areas formerly considered to be ancient, as well as legacies of this former land use on plant biodiversity and soil properties, have encouraged the search for archives of former land use in forests. In central Lorraine (northeastern France), thousands of small closed depressions (CD) on marlstone have been inventoried in forests over the past 150 years, and we hypothesised that these CDs could be used to reconstruct patterns of land use. Closed depressions near the Seille and Sarre valleys were selected and cored for pollen and sediment analyses. Principal Components Analysis (PCA) was used to analyse variations of pollen assemblages during the last two millennia. The history of vegetation changes depicts five main phases. During the Roman period, the region appears to have been primarily covered by grasslands, with some croplands but few forests. All areas were reforested by the end of the Roman period. During the early Medieval period, croplands with grasslands developed in the region, while the late Medieval was characterised by cereal cropping, with especially intense use at sites near the Seille valley, and a lesser extension of grasslands. The present forest cover developed over the past 500 years because of the development of the salt industry in the Seille valley, which required firewood, and the general decrease of agricultural pressure over the past 150 years. Previous investigations had provided evidence of large-scale Roman field systems in the forests covering the limestone plateau and the Vosges foothills on sandstone, areas west and east of the research focus, respectively. These convergent findings suggest that that forests considered to be ‘ancient’ on the basis of historical documents may have been used for pasture or agriculture over extensive periods during the last 2000 years.

Ecological and human land-use indicator value of fungal spore morphotypes and assemblages

The value of non-pollen palynomorphs (NPPs) to complement reconstructions of past communities and environments has led to the identification of an increasing number of microfossil morphotypes. Unfortunately, limited knowledge about their specific ecological indicator values still restricts the interpretation of NPP accumulation rates or assemblage variations. Here, a comparison with classical palaeoecological proxies along a sedimentary sequence has been tested to improve the ecological indicator values of NPP morphotypes. Pollen, geochemical and NPP analyses performed on the same samples all along the Holocene sedimentary sequence of Lac de Moras (France) were compared using principal component analysis to identify statistical relationships and to establish correlations between all these parameters. Ecological indicator values were obtained for some morphotypes such as UG-1097 which is related to specific taxa (Corylus sp.), or Diporotheca rhizophila defined as an indicator of the local presence of alder swamp habitat. However, most of the NPP morphotypes can be combined in two opposite NPP assemblages reflecting the change from natural to managed ecosystems at the drainage basin scale and over the Holocene. It more specifically illustrates a change in the source of organic matter transferred to the lake system provided from the plant debris of woodland cover (litter) to organic matter from animal excreta (dung and manure).