Etienne Dambrine

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 These convergent findings suggest that that forests considered to be ‘ancient’ on the basis of historical documents may have been used for pasture or agriculture over extensive periods during the last 2000 years.

Magnesium Isotope Variations to Trace Liming Input to Terrestrial Ecosystems: A Case Study in the Vosges Mountains.

Liming with Ca and Mg carbonates is commonly used to reduce soil and stream acidity and to improve vegetation growth and nutrition in forests. Ten years ago, dolomite lime was experimentally applied to a forest catchment on granite in the Vosges Mountains (northeast France), which is characterized by acid soils and drained by an acid stream. The average Mg isotope composition of the dolomite lime (-1.75‰) was low compared with that of tree foliage (-0.70‰), granite and deep soil layers (-0.40‰), and stream water (-0.80‰) in the control catchment. After liming, the exchangeable Mg concentrations in surface soil layers, which were initially very low, increased, and the Mg isotope composition decreased (up to -0.60‰). The decrease was smaller in deeper layers but not in proportion to the increase in exchangeable Mg content, suggesting contributions from mineralization of organic matter and/or displacement of exchangeable Mg from surface layers. Before application, Mg concentration in beech and fir leaves was low, and that of 1-yr-old fir needles was lower than that in current needles. Internal Mg translocation within fir needles also resulted in a lower δMg of older needles. Three years after dolomite application, the Mg isotope composition of plant leaves was lower than that in the control catchment; this decrease (up to -1.00‰) was attributed to direct uptake of Mg from dissolving dolomite. Liming doubled the concentration of Mg in the stream, whereas the Mg isotope composition decreased correspondingly from -0.80 to -1.20‰, indicating a fast transfer of dolomite Mg to the stream. Our findings indicate that monitoring of δMg may be a promising tool to study the fate of dolomitic inputs in terrestrial and aquatic ecosystems.

Two thousand–year reconstruction of livestock production intensity in France using sediment-archived fecal Bacteroidales and source-specific mitochondrial markers

The reconstruction of past pastoral activities based on microscopic methods (pollen and coprophilous fungal ascospores) does not accurately identify the domestic species involved. In contrast, source-specific DNA markers, commonly employed in water quality microbial source tracking (MST) studies, may represent a promising tool for retrospectively identifying species-specific fecal contamination in sediment deposition. In the present study, molecular methods were used to quantify Bacteroidales and identify ovine and bovine mitochondrial DNA extracted from sediment cores from two forest hollows comprising 2000 years of deposition. The DNA marker abundance was contrasted with the abundance of ascospores and plant-specific pollen throughout the sediment chronosequence. The distribution of DNA markers indicated an agro-pastoral practice transition from pasture/crop production to forested landscape from the second Iron Age/classical Antiquity to the end of the Roman period/modernity, in correlation with microscopic markers. During the second Iron Age/classical Antiquity, hollows were likely used to water herds, whereas during the late Antiquity, low Bacteroidales abundances and the sporadic detection of bovine and ovine DNA markers confirm the progressive afforestation observed using pollen data. For the end of the Roman period and modern times, reforested areas are characterized by the absence of ovine and bovine DNA markers while low Bacteroidales abundances suggest the presence of wild herbivores. The present study has established that in tandem with microscopic methods, sediment-archived fecal-specific bacterial and mitochondrial DNA are extremely useful for reconstructing agricultural practice over timeframes of millennia.

NutsFor a process-oriented model to simulate nutrient and isotope tracer cycling in forest ecosystems

Abstract We developed a process-oriented model called NutsFor that simulates nutrient cycling of major cations (Ca, Mg, K, Al, NH 4 , Na) and anions (NO 3 , SO 4 , Cl) and the stable isotope tracers for each of the respective elements at the scale of an ecosystem (isotopic fractionation are not simulated). We tested the ability of NutsFor to reproduce major element and stable isotope tracer ( 26 Mg and 44 Ca) cycling with the data from 35-yr old beech stand in France. NutsFor correctly reproduced the measured trends in soil solution chemistry for most major elements. The high similarity between modeled and measured distribution of 26 Mg and 44 Ca tracers in the ecosystem provided a unique and robust way to evaluate the hypotheses grounding the model and study the efficiency of Mg and Ca cycling at this very nutrient-poor site.