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- PublicationMétadonnées seulementInfluence of tree cover on the diversity of herbaceous communities in subalpine wooded pastures
- PublicationMétadonnées seulement
- PublicationMétadonnées seulementPATUMOD: a compartment model of vegetation dynamics in wooded pasturesA system of wooded pasture can be described by seven biological state variables (trees, shrubs, underwood grasslands, fallows, eutrophic meadows, oligrotrophic lawns and cattle) linked by a network of dynamic interactions, which are controlled by altitude and human activities. PATUMOD is a spatially implicit compartment model designed to simulate vegetation dynamics in such silvopastoral ecosystems at community level and according to an equilibrium paradigm. Computer simulations show that the state variables generally end up on a steady-state (one-point attractor), independent on their initial values but strongly dependent on cattle load. At a given altitude, to each value of the stock density is corresponding a stable equilibrium characterised by a given relative cover of each vegetation component. If the initial values are very far of the attractor, a long succession of intermediate stages is required before leading to the steady-state. A remarkable exception to this rule can occur at low altitude, with a repellor between switching trajectories towards two attractors, corresponding to a threshold between scarcely and densely wooded pastures. PATUMOD can be applied to simulate different management scenarios, which include changing global stock density and cutting trees or shrubs. (C) 2002 Elsevier Science B.V. All rights reserved.
- PublicationMétadonnées seulementToward a general formalism for modelling and simulating ecological hierarchies in constructive dynamical systems
- PublicationAccès libreSituation de la vigne sauvage Vitis vinifera ssp. silvestris en EuropeCette contribution dresse un bilan de la répartition actuelle de la vigne sauvage européenne - Vitis vinifera L. ssp. silvestris (Gmelin) Hegi - sur la base d'une revue bibliographique et d'observations originales effectuées lors de recherches sur son écologie dans les forêts alluviales et colluviales d'Europe. La situation de la vigne sauvage s'avère préoccupante dans la plupart des pays européens, même si elle est souvent mal connue, faute de données récentes fiables. La sous-espèce silvestris se distingue essentiellement des cépages cultivés par sa dioïcité. Les caractères morphologiques végétatifs sont très variables; en particulier, on montre que le dimorphisme sexuel est manifeste dans les populations d'Autriche, alors qu'il n'est pas apparent dans celles du Pays Basque., This paper summarizes the occurrence of the European wild vine - Vitis vinifera L. ssp. silvestris (Gmelin) Hegi – from bibliography and observations made in the framework of research on its ecology in the alluvial and colluvial forests of Europe. The state of the wild vine is disquieting within most of the European countries; in some countries we noticed a lack of recent reliable data. The subspecies silvestris can principally be distinguished from cultivated grapevine by its dioicity. Morphological vegetative criteria are very variable; in particular, we demonstrate that sexual dimorphism occurs in Austrian populations, while it is not found in those of the Basque countries.
- PublicationMétadonnées seulementModeling and simulating hierarchies using an agent-based approach
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- PublicationMétadonnées seulementSeasonal dynamics of plant species at fine scale in wooded pastures
- PublicationAccès libreEffect of cattle activities on gap colonization in mountain pasturesCattle influences gap dynamics in pastures in two ways: (1) by creating gaps and (2) by affecting the colonization process. This effect of cattle activity on gap revegetation can be subdivided in three main factors: herbage removal, trampling and dung and urine deposition. The objective of this study was to assess how these three effects moderate the plant succession following gap creation.
In an exclosure, four controlled treatments simulating cattle activity (repeated mowing, trampling, manuring and untreated control) were applied on plots of 2 x 2 m. In the centre of each plot, one artificial gap of 60 x 60 cm was created. During three years, vegetation changes were monitored in spring and in autumn, with a square grid of 100 cells of 0.01 m2 centred on the gap.
Our experiment confirmed that fine-scale gap creation may have a high impact on relative abundances of species in the community. The gap environment acts on species as a filter and this filtering was described in terms of regenerative attributes. Colonizers were species with small seeds, unspecialized seed dispersal, persistent seed bank and high vegetation spread. However, the role of dung deposition, herbage removal or trampling by cattle did not seem to be of primary importance in the revegetation process, but could moderate vegetation response. Therefore, the different cattle effects act as secondary filters that selectively favoured or disadvantaged different species from the gap-regenerating community. These complex interactions are probably keys to understand plant coexistence in perennial grasslands.
- PublicationAccès libreFunctional responses of multi-taxa communities to disturbance and stress gradients in a restored floodplain1. Trait-based approaches can reveal the mechanisms through which disturbances or stress impact communities, allowing comparisons of the role of different mechanisms in shaping communities among taxonomic groups. Such information can lead to higher comparability, transferability and predictability of the outcome of restoration projects. However, multitaxa trait-based approaches were rarely used in the context of ecosystem restoration. 2. We investigated the responses to environmental gradients of seven taxa (vascular plants, staphylinid and carabid beetles, spiders, isopods, diplopods and earthworms) in a restored floodplain using a species traits approach. We assessed the impact of flood disturbances and soil hydric stress on the functional diversity (FD) and community-weighted mean (CWM) response of traits for each taxon. 3. Ordination of hydrological variables revealed two main gradients. The first was related to the spatiotemporal dynamics of flood disturbances and the second to the average changes in soil hydric conditions. 4. The analysis of CWM revealed that larger, poorly mobile species with narrow ecological tolerances were filtered by regular floods and/or changes in soil hydric conditions. 5. Functional diversity patterns differed between the two gradients: decreasing with increasing flood disturbance, but increasing along the soil hydric stress gradient. This suggests that the mechanisms shaping community composition differ between the two gradients with environmental filtering being dominant with increasing flood disturbances and competition decreasing with more soil hydric stress. 6. Synthesis and applications. Our study shows that the impact of restored flood disturbances and soil hydric stress on plant and invertebrate functional diversity and community- weighted mean can be positive, negative or more complex depending on the taxonomic group and environmental gradient considered. The patterns can to some extent be explained by the specific characteristics of each group. Larger, poorly mobile species with narrow ecological tolerances were particularly vulnerable to changes in disturbance and stress regime following floodplain restoration. These species may therefore be lost in the initial phases of restoration projects, but other more characteristic species of dynamic floodplains will be favoured. Understanding the consequences of these contrasted responses for biodiversity conservation and ecosystem functioning constitutes the next challenge for ecosystem restoration.