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  • Publication
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    Factors modulating cottongrass seedling growth stimulation to enhanced nitrogen and carbon dioxide: compensatory tradeoffs in leaf dynamics and allocation to meet potassium-limited growth
    (2013)
    Siegenthaler, Andy
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    Buttler, Alexandre
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    Grosvernier, Philippe
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    Nilsson, Mats B.
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    Eriophorum vaginatum is a characteristic species of northern peatlands and a keystone plant for cutover bog restoration. Understanding the factors affecting E. vaginatum seedling establishment (i.e. growth dynamics and allocation) under global change has practical implications for the management of abandoned mined bogs and restoration of their C-sequestration function. We studied the responses of leaf dynamics, above- and belowground biomass production of establishing seedlings to elevated CO2 and N. We hypothesised that nutrient factors such as limitation shifts or dilutions would modulate growth stimulation. Elevated CO2 did not affect biomass, but increased the number of young leaves in spring (+400 %), and the plant vitality (i.e. number of green leaves/total number of leaves) (+3 %), both of which were negatively correlated to [K+] in surface porewater, suggesting a K-limited production of young leaves. Nutrient ratios in green leaves indicated either N and K co-limitation or K limitation. N addition enhanced the number of tillers (+38 %), green leaves (+18 %), aboveground and belowground biomass (+99, +61 %), leaf mass-to-length ratio (+28 %), and reduced the leaf turnover (-32 %). N addition enhanced N availability and decreased [K+] in spring surface porewater. Increased tiller and leaf production in July were associated with a doubling in [K+] in surface porewater suggesting that under enhanced N production is K driven. Both experiments illustrate the importance of tradeoffs in E. vaginatum growth between: (1) producing tillers and generating new leaves, (2) maintaining adult leaves and initiating new ones, and (3) investing in basal parts (corms) for storage or in root growth for greater K uptake. The K concentration in surface porewater is thus the single most important factor controlling the growth of E. vaginatum seedlings in the regeneration of selected cutover bogs.
  • Publication
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    Etude sur la purification des eaux de gravité passant à travers le sol forestier
    (2012)
    Scherrer, Luc
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    Le monde sylvicole franco-suisse souhaite connaître son impact sur la qualité des eaux souterraines. Le projet Interreg Alpeau réunit ingénieurs forestiers, gérants des ressources en eau et scientifiques afin de mesurer cette influence. La répartition géographique du projet rayonne autour de l'Arc jurassien entre Chambéry (F) et Neuchâtel (CH).
    Cette étude réalisée sur deux sites de terrain, le Gibloux dans le Canton de Fribourg et la Côte de Champ-du-Moulin dans la République et Canton de Neuchâtel, se focalise sur les propriétés des eaux atmosphériques et de gravité percolant à travers le sol. Après un suivi complet d'une année de ces eaux, des essais en laboratoire sur des paramètres ciblés permettent de mieux saisir l'importance de la gestion forestière sur le blocage de micropolluants. Les récoltes des eaux sur le terrain ne présentent pas de polluants organiques mais contiennent, en revanche, une faible concentration en éléments traces métalliques que le sol ne filtre pas, qu'importe sa nature. Les essais en laboratoire sur le benzène (polluant du trafic routier), le tétrachloréthène (produit par l'activité industrielle) et la cyperméthrine (insecticide utilisé pour le traitement des bois) illustrent notamment que la forme d'humus influence le taux de filtration et que l'épisolum humifère est directement en lien avec le travail de l'ingénieur forestier. Les principaux résultats montrent que le pH influence peu la fixation de ces molécules ; le calcaire est antagoniste à l'adsorption du benzène et du tétrachloréthène ; un sol fi filtre moins bien qu'un sol épais ; l'épisolum humifère acide et accumulant retient moins bien la cyperméthrine mais, globalement, tous ces polluants sont retenus à près de 90% dans les sols testés.
    Il est donc possible d'affirmer que les choix des praticiens sylvicoles peuvent influencer positivement ou négativement la qualité des eaux souterraines. Ce travail met en avant également le rôle essentiel de la structure, mais aussi, à un degré moindre, celui de la texture sur la conductivité hydraulique. Finalement, il présente un nouvel outil, la carte des unités écosystémiques, qui permet, par l'intégration des groupements végétaux, du peuplement, des formes d'humus et des sols, un suivi temporel de la forêt du sol à la cime des arbres., French-Swiss silvicultural people wishes to know its impact on the quality of groundwater. The Interreg Alpeau project combines forest engineers, managers of water resources and scientists to measure this influence. The geographical distribution of the project shines around the Jura mountains between Chambéry (F) and Neuchâtel (CH).
    This study carried out on two sites of ground, Gibloux in the Canton of Fribourg and the Côte de Champ-du-Moulin in the Republic and Canton of Neuchâtel, focuses on the properties of atmospheric and percolant water through the humus forms and the soil. After a complete water's follow-up of one year, essays in laboratory on targeted parameters allow to seize better the importance of the forest management on the blocking of micropollutants.
    The collected waters on the soil do not present organic pollutants but contain, a low concentration in elements metallic tracks which the soil doesn't filter, it doesn't matter to its nature. The essays in laboratory on the benzene (pollutant of the road traffic), the tetrachlorethylene (produced by the industrial activity) and the cypermethrin (insecticide used for the treatment of wood) illustrate that the humus form influences the rate of filtration and that the humifer episolum is directly in connection with the work of the forest engineer. The main results show that the pH influences little the binding of these molecules ; the limestone is conflicting in the adsorption of the benzene and the tetrachlorethylene ; a thin soil leaks out although a thick soil ; the acid and accumulating humus form retains less well the cypermethrin but, globally, all these pollutants are retained about 90 % in the tested soils. It is possible to assert that the choices of the silvicultural practitioners can influence positively or negatively the quality of ground waters. This work also puts forward the essential role of the structure, but also, in a lesser degree, that of the texture on the hydraulic conductivity. Finally, it presents a new tool, the map of the ecosystematic units, which allows, by the integration of forest compartiment, a temporal follow-up.
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  • Publication
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    Ecological conditions for Saxifraga hirculus in Central Europe: A better understanding for a good protection
    (2006)
    Vittoz, Pascal
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    Wyss, Tania
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    Saxifraga hirculus is a postglacial relict in Central Europe, whose populations suffered a dramatic decrease in the 19th and 20th centuries. However, few researchers have been interested in its ecological requirements in Central Europe. This article synthesizes previous knowledge supplemented by original data from the last large population (Switzerland). S. hirculus is a weak competitor which needs precise ecological conditions. It grows on bryophyte carpets in neutral to slightly acid wetlands, with stable water table close to the soil surface (optimum between 8 and 14 cm) but does not stand long flooding. However, it requires a good oxygen supply, with roots 2-3 cm under the soil surface, generally not reached by water, with running, cold water through loose, fibric peat. Its optimal conditions are in spring fens, but it grows in other types of wetlands as well. However, overgrowing by shrubs, sedges or Sphagnum in natural successions may threaten the species with extinction, as did drainage and peat extraction previously. Now, its survival in Central Europe depends on an adequate management of the ecosystems. Moderate grazing (cattle or sheep) or mowing help to limit competition with taller Carex species. Reintroduction of disappeared populations or creation of new ones from cultivation in botanical garden is possible, but appropriate sites are rare. in some cases, substrate management could improve the conditions in somewhat inadequate situations. This management in four directions can be flexibly applied in different situations to progress to optimal conditions for the conservation of this valuable species. (c) 2006 Elsevier Ltd. All rights reserved.
  • Publication
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    Erfolgskontrolle der Vegetationskynamik
    (2006)
    Vadi, Gaëlle
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    Roulier, Christian
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  • Publication
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    Spatial and seasonal patterns of cattle habitat use in a mountain wooded pasture
    (2006)
    Kohler, Florian
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    Reust, Stéphanie
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    Wagner, Helene
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    Gadallah, Fawziah
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    Buttler, Alexandre
    Management-oriented models of cattle habitat use often treat grazing pressure as a single variable summarizing all cattle activities. This paper addresses the following questions: How does the spatial pattern of cattle effects vary between cattle activities in a highly heterogeneous landscape? Do these patterns change over the grazing season as forage availability decreases? What are the respective roles of natural and management-introduced structures? We estimated the intensity of herbage removal, dung deposition and trampling after each of three grazing periods on a grid of 25 m x25 m cells covering an entire paddock in the Swiss Jura Mountains. We found no significant positive correlations between cattle effects. Spatial patterns weakened through the season for grazing and trampling, whereas dunging patterns changed little between grazing periods. Redundancy analysis showed that different cattle effects were correlated with different environmental variables and that the importance of management-introduced variables was highest for herbage removal. Autocorrelograms and partial redundancy analyses using principal coordinates of neighbour matrices suggested that dunging patterns were more coarse-grained than the others. Systematic differences in the spatial and seasonal patterns of cattle effects may result in complex interactions with vegetation involving feedback effects through nutrient shift, with strong implications for ecosystem management. In heterogeneous environments, such as pasture-woodland landscapes, spatially explicit models of vegetation dynamics need to model cattle effects separately.
  • Publication
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