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Thierry Dutoit - One of the best experts on this subject based on the ideXlab platform.

  • Using mechanical clearing and goat grazing for restoring understorey plant diversity of embankments in the Rhône valley (southern France)
    Plant Biosystems, 2020
    Co-Authors: Cannelle Moinardeau, François Mesléard, Hervé Ramone, Thierry Dutoit
    Abstract:

    Consumption by animals remains one of the key points to assess the effectiveness of grazing impacts in woodland for increasing understorey plant diversity. To limit the spread of the Brambles and restore understorey plant diversity on an artificial embankment an original system of clearings connected by paths was created by mechanically crushing Brambles and allowing them to be grazed by rustic goats. The analysis of the indices of consumption of bramble under GIS has been used to provide an estimation of the volume ingested and an estimation of the effectiveness of the goats. The impacts of three different managements (goat grazing, brush clearing and grazing, clearing and exclusion of grazing) and control without management were then tested during a three-year period. The monitoring of the vegetation on permanent plots provided evidence that goat grazing significantly increased in the short term the species-richness and heterogeneity of herbaceous plants communities, in complement with prior clearing. Thus, the objectives of the managers to open up the area and reduce the bramble cover were achieved, but the prior introduction of goats and the installation of mobile enclosures would be advisable in order to ensure the sustainability of these measures on plant diversity in the long term.

  • Impacts of water stress removal and disturbance regimes on Mediterranean dry grasslands diversity and succession
    Plant Ecology, 2015
    Co-Authors: Solène Masson, Matthieu Gauvain, François Mesléard, Thierry Dutoit
    Abstract:

    Our goal was to disentangle the effects of stress removal and disturbance on plant communities of a Mediterranean rangeland, La Crau (southeastern France). We compared undisturbed reference steppe vegetation with vegetation impacted by changes in land use such as earlier phases of cultivation (dating back 20 years) and/or current water infiltrations (revealed by the presence of Brachypodium phœnicoïdes ), since the establishment of adjacent hay meadows. We considered plots with and without Brambles ( Rubus ulmifolius ), an indigenous shrub species that had colonized the area after the land-use changes. We monitored the composition and measured the taxonomic richness and richness of functional groups, evenness and similarities of plant communities. The species richness of the undisturbed community was significantly higher than that of all disturbed plant communities. Although cultivation led to the dominance of ruderal species, the removal of water stress had a stronger negative impact, enabling the establishment of herbaceous competitor species such as B. phœnicoïdes . The dominance of this species resulted in a significant decline in species richness and evenness after water stress removal. The presence of Brambles correlating with former cultivation and/or current water infiltration did not have a significant impact on plant species richness in the vicinity of bramble bushes, although it significantly modified the composition of the adjacent herbaceous vegetation. Our study highlights again the low resilience of Mediterranean dry grasslands after disturbance. While both the disturbance and the water stress removal resulted in changes within the plant community, our findings reveal a stronger impact of the water stress removal. Water infiltration led to decreased plant species richness and evenness because the greater availability of water favored competitor species over the stress-tolerant xeric species. Therefore, for restoring the original steppe species richness, the priority will be to control water infiltrations, even before any scrub-clearing is undertaken to control bramble colonization.

  • Impacts of water stress removal and disturbance regimes on Mediterranean dry grasslands diversity and succession
    Plant Ecology, 2015
    Co-Authors: Solène Masson, Matthieu Gauvain, François Mesléard, Thierry Dutoit
    Abstract:

    Our goal was to disentangle the effects of stress removal and disturbance on plant communities of a Mediterranean rangeland, La Crau (southeastern France). We compared undisturbed reference steppe vegetation with vegetation impacted by changes in land use such as earlier phases of cultivation (dating back 20 years) and/or current water infiltrations (revealed by the presence of Brachypodium phoenicoides), since the establishment of adjacent hay meadows. We considered plots with and without Brambles (Rubus ulmifolius), an indigenous shrub species that had colonized the area after the land-use changes. We monitored the composition and measured the taxonomic richness and richness of functional groups, evenness and similarities of plant communities. The species richness of the undisturbed community was significantly higher than that of all disturbed plant communities. Although cultivation led to the dominance of ruderal species, the removal of water stress had a stronger negative impact, enabling the establishment of herbaceous competitor species such as B. phoenicoides. The dominance of this species resulted in a significant decline in species richness and evenness after water stress removal. The presence of Brambles correlating with former cultivation and/or current water infiltration did not have a significant impact on plant species richness in the vicinity of bramble bushes, although it significantly modified the composition of the adjacent herbaceous vegetation. Our study highlights again the low resilience of Mediterranean dry grasslands after disturbance. While both the disturbance and the water stress removal resulted in changes within the plant community, our findings reveal a stronger impact of the water stress removal. Water infiltration led to decreased plant species richness and evenness because the greater availability of water favored competitor species over the stress-tolerant xeric species. Therefore, for restoring the original steppe species richness, the priority will be to control water infiltrations, even before any scrub-clearing is undertaken to control bramble colonization.

  • Using Shrub Clearing, Draining, and Herbivory to Control Bramble Invasion in Mediterranean Dry Grasslands
    Environmental management, 2015
    Co-Authors: S. Masson, François Mesléard, Thierry Dutoit
    Abstract:

    For centuries, the dry grassland of the plain of La Crau (south-eastern France) has been subjected to numerous disturbances resulting in the destruction and the fragmentation of this emblematic rangeland ecosystem of the Mediterranean. Today, this ecosystem is facing a new threat from a proliferating native species, the bramble (Rubus ulmifolius Schott), which preferentially colonizes areas that were formerly cultivated and/or exposed to water infiltration. To identify a strategy for effective control of this colonization, in situ experiments testing disturbance regimes (shrub clearing and/or mixed grazing by sheep and goats) combined with the control of access to water resources (with or without drainage trenches) were undertaken between 2010 and 2013. Only clearing and grazing combined over 3 years led to significant changes in vegetation height and bramble cover as well as modifications in the floristic composition, diversity, similarity, and richness of the plant community. Neither a clearing operation carried out in 2010 alone, nor grazing alone, reduced bramble cover, and neither treatment increased the species richness of the plant community. Similarly, digging drainage trenches had no significant impact either on the plant community or on bramble cover. Our study suggests that only annual mechanical clearing coupled with sheep and goats grazing can significantly reduce bramble cover. This combined restoration treatment needs to be applied for at least 3 consecutive years to induce significant changes and enable this ecosystem to return to the dry grassland succession.

  • Impacts de différents régimes de perturbations et niveaux de ressource hydrique pour contrôler une espèce proliférante dans un écosystème pseudo-steppique: le cas de Rubus ulmifolius Schott. dans la plaine de la Crau (Bouches-du-Rhône, France)
    2014
    Co-Authors: Solène Masson, François Mesléard, Thierry Dutoit
    Abstract:

    The plain of la Crau, located in South Eastern France, is a unique pseudo-steppe ecosystem, characterized by the presence of a Mediterranean climate, stony soil and limestone conglomerate at 40cm depth, and a traditional sheep grazing dating back to 6,000 years. Nevertheless, for many decades, this ecosystem has been subjected to numerous exogenous disturbance regimes. Indeed, during the 16th century, the construction of channels led to the transformation of the dry grasslands into hay meadows. Moreover, during the last century, agriculture intensification and the industrial development of military activities have significantly altered the steppe. Now, the plain of la Crau is a fragmented landscape where steppe habitats are connected directly with irrigated orchards or hay meadows. The effects on plant communities have been a decrease of species richness, a trivialization of plant composition and also the colonization of disturbed areas by pioneer invasive species such as Rubus ulmifolius Schoot, the elm leaf bramble. Absent from the original plant composition, this species can colonize areas formerly cultivated and/or subjected to water infiltrations coming from the mismanagement of the irrigation of hay meadows nearby. The increase of bramble cover is a threat to the Crau, because it causes the reduction of herbaceous community available for traditional sheep grazing, which is responsible for the organization and the structure of the steppe plant communities. To better understand this phenomenon and to discriminate the factors responsible for this colonization, an experimentation in situ based on the implementation of different disturbance regimes (shrub clearing and/or grazing) crossed with two levels of water resources has been carried out during three years (between November 2010 to September 2013). During this period, we have performed a monitoring of the vegetation each spring and measured the photosynthetically active radiation at different times to a year (at the moment of clearing, before and after grazing, and after the summer drought).Our results evidence significant changes in the composition and a drastic increase of species richness between plots that were cleared and grazed each year and those that were not. These differences can be explained by a significant reduction in the area occupied by the bramble (increase of photosynthetically active radiation). However, the action of a single clearing or grazing alone did not succeed in maintaining an open environment. No significant action of the drying plots could be detected on the plant community and on the dynamics of Brambles. In order to perform a potential ecological restoration, an annual clearing coupled with a return of sheep grazing is recommended. In addition, the restoration of the irrigation system is considered in the discussion to limit the presence of Brachypodium phoenicoides (L.) Roem. & Schult that develops probably at the expense of typical steppe species.

Arie M. C. A. Koster - One of the best experts on this subject based on the ideXlab platform.

  • Wiley Encyclopedia of Operations Research and Management Science - Treewidth, Tree Decompositions, and Brambles
    Wiley Encyclopedia of Operations Research and Management Science, 2011
    Co-Authors: Arie M. C. A. Koster
    Abstract:

    The notions of tree decomposition and treewidth play an important role in the design and analysis of algorithms for combinatorial optimization problems. The notion of a bramble can be used to find a lower bound on the treewidth of a graph. In this article we review the most important results for treewidth, tree decompositions, and Brambles, both from a theoretical and practical point of view. Keywords: treewidth; tree decomposition; fixed parameter complexity; bramble; tree decomposition–based algorithm; pathwidth; branchwidth

  • treewidth tree decompositions and Brambles
    Wiley Encyclopedia of Operations Research and Management Science, 2011
    Co-Authors: Arie M. C. A. Koster
    Abstract:

    The notions of tree decomposition and treewidth play an important role in the design and analysis of algorithms for combinatorial optimization problems. The notion of a bramble can be used to find a lower bound on the treewidth of a graph. In this article we review the most important results for treewidth, tree decompositions, and Brambles, both from a theoretical and practical point of view. Keywords: treewidth; tree decomposition; fixed parameter complexity; bramble; tree decomposition–based algorithm; pathwidth; branchwidth

  • treewidth lower bounds with Brambles
    European Symposium on Algorithms, 2005
    Co-Authors: Hans L. Bodlaender, Alexander Grigoriev, Arie M. C. A. Koster
    Abstract:

    In this paper we present a new technique for computing lower bounds for graph treewidth. Our technique is based on the characterisation of the treewidth as the maximum order of a bramble of the graph. We give two algorithms: one for general graphs, and one for planar graphs. The algorithm for planar graphs is shown to give a lower bound for the treewidth that is at most a constant factor away from the exact treewidth. For both algorithms, we report on extensive computational experiments that show that the algorithms give often excellent lower bounds, in particular when applied to (close to) planar graphs.

  • Treewidth Lower Bounds with Brambles
    2005
    Co-Authors: Hans L. Bodlaender, Alexander Grigoriev, Arie M. C. A. Koster
    Abstract:

    In this paper we present a new technique for computing lower bounds for graph treewidth. Our technique is based on the fact that the treewidth of a graph G is the maximum order of a bramble of G minus one. We give two algorithms: one for general graphs, and one for planar graphs. The algorithm for planar graphs is shown to give a lower bound for both the treewidth and branchwidth that is at most a constant factor away from the optimum. For both algorithms, we report on extensive computational experiments that show that the algorithms give often excellent lower bounds, in particular when applied to (close to) planar graphs.

  • ESA - Treewidth lower bounds with Brambles
    Algorithms – ESA 2005, 2005
    Co-Authors: Hans L. Bodlaender, Alexander Grigoriev, Arie M. C. A. Koster
    Abstract:

    In this paper we present a new technique for computing lower bounds for graph treewidth. Our technique is based on the characterisation of the treewidth as the maximum order of a bramble of the graph. We give two algorithms: one for general graphs, and one for planar graphs. The algorithm for planar graphs is shown to give a lower bound for the treewidth that is at most a constant factor away from the exact treewidth. For both algorithms, we report on extensive computational experiments that show that the algorithms give often excellent lower bounds, in particular when applied to (close to) planar graphs.

Bohumil Trávníček - One of the best experts on this subject based on the ideXlab platform.

  • Ploidy level variation in the genus Rubus in the Pannonian Basin and the northern Balkans, and evolutionary implications
    Plant Systematics and Evolution, 2019
    Co-Authors: Michal Sochor, Bohumil Trávníček, Gergely Király
    Abstract:

    Ploidy can serve as an excellent diagnostic character and proxy for evolutionary and reproductive behaviour, particularly in taxonomically complicated apomictic genera. In Rubus , ploidy level has so far been established for 230 European species (ca 30% of the total), mainly from Western or central Europe. We present the first DNA ploidy data for 25 described species and 22 undescribed stable morphotypes from the Pannonian Basin and the northern Balkans (8 countries). We also review previously published ploidy data covering the entire bramble flora of the studied area (78 recognized species in total). The most common ploidy level is tetraploid, which is the only ploidy level in most series (e.g. Micantes , Rhamnifolii , Sylvatici ). This likely reflects elevated sexuality and the higher probability of new species formation via hybridization in tetraploids compared to other ploidy levels. As in central Europe but unlike in other regions, we also recorded many triploid species, namely in ser. Discolores (19 species) and ser. Rubus (four species). The diversity of triploid Discolores in the region may be linked to the occurrence of diploid R. canescens , making the region a hot spot of triploid Rubus diversity. Six pentaploid and a single hexaploid species, all from sect. Corylifolii , were recorded. Ploidy proved to be a good diagnostic character for several species that are difficult to distinguish morphologically, confirming its importance in inventories of Brambles. One of these species is described here as R. praecocifrons Király & Trávn.

  • Melting pot of biodiversity: first insights into the evolutionary patterns of the Colchic bramble flora (Rubus subgenus Rubus, Rosaceae)
    Botanical Journal of the Linnean Society, 2016
    Co-Authors: Michal Sochor, Bohumil Trávníček
    Abstract:

    The Caucasus is a biodiversity hotspot of global significance, containing a number of highly diverse and species-rich plant taxa. The region is also thought to be an important evolutionary hotspot for Rubus subgenus Rubus (Brambles). However, Caucasian Brambles have only been poorly studied to date and our knowledge of their evolutionary mechanisms, systematics and taxonomic variability remains rudimentary. Therefore, the objectives of this study were to shed light on the evolution, diversity and reproduction modes of Rubus in one of the two Caucasian glacial refugia, Colchis. Flow cytometry measurements were used to estimate DNA ploidy, a flow cytometric seed screen was conducted to determine reproduction mode and Sanger sequencing of two non-coding plastid regions was used to reveal phylogenetic patterns. The most common ploidy level was tetraploid, followed by diploid and (rarely) triploid. Intra-individual variation in reproduction mode was low, as the morphoseries Glandulosi and Radula exhibited strict sexuality and other taxa were mostly apomictic. A few exceptions were observed that deserve further attention, e.g. sexuality induced hypothetically by haploid pollen or by environmental conditions, a high proportion of triploid embryos or polyspermy. Plastid haplotype variability revealed specific, ancient evolutionary patterns with limited involvement of extant diploid taxa and recent isolation from European Brambles. We provide the first insight into the variability and evolution of Colchic Brambles, which serves as a starting point for further systematic and evolutionary studies.

  • How just a few makes a lot: Speciation via reticulation and apomixis on example of European Brambles (Rubus subgen. Rubus, Rosaceae)
    Molecular phylogenetics and evolution, 2015
    Co-Authors: Michal Sochor, Radim J. Vašut, Timothy F. Sharbel, Bohumil Trávníček
    Abstract:

    New species are generated by many means, among which hybridization plays an important role. Interspecific hybrids can form isolated evolutionary units, especially when mechanisms increasing viability and fertility, like polyploidy and apomixis, are involved. A good model system to study reticulate evolution in plants is Rubus subgen. Rubus (Brambles, blackberries), which only in Europe includes 748 accepted species, out of which only four are sexual diploids and all others are polyploid apomicts. We employed two molecular markers (ITS and cpDNA) to shed light on the evolutionary history of European bramble flora and main processes generating such high species diversity. We distinguished just six ancestral diploids (including two extinct ones) for both markers, which gave rise to all European polyploid accessions, and revealed an extreme reticulation in bramble evolution. We furthermore detected hybridogenous origins and identified putative parents for several taxa (e.g. ser. Nessenses), while in other groups (e.g. ser. Discolores) we could also infer the direction of hybridization. By comparing different cp haplotypes having clear geographic patterns, we hypothesize that the origin of European Brambles can be attributed to both Holocene species range expansion and Pleistocene climate fluctuations.

  • new insights into the variability of reproduction modes in european populations of rubus subgen rubus how sexual are polyploid Brambles
    Sexual Plant Reproduction, 2012
    Co-Authors: Petra Sarhanova, Radim J. Vašut, Martin Dancak, Petr Bures, Bohumil Trávníček
    Abstract:

    Rubus subgen. Rubus includes common European species with highly complicated taxonomy, ongoing hybridisation and facultative apomixis. Out of approximately 750 species recognised in Europe, only 3 diploid sexual species are known, along with numerous apomictic Brambles that are highly connected to polyploidy. One exception of a tetraploid taxon is R. ser. Glandulosi, which is known for prevalent sexuality. This taxon highly hybridises with tetraploid members of R. ser. Discolores and leads to the origin of many hybridogenous populations and individuals. In this study, we verify reproduction modes in different diploid, triploid and tetraploid species of subgen. Rubus, with focus on taxa putatively involved in such hybridisation by applying flow cytometric seed screen analysis. We found 100 % sexuality of diploid species, whereas triploid species had obligate unreduced embryo sac development. In contrast, tetraploid plants had varying degrees of sexuality. Additionally, we discovered that R. bifrons has the ability to undergo a reproduction mode switch as a reaction to environmental conditions. These results provide insight into reproductive modes of European Brambles and shed light on their reticulate evolution and speciation.

François Mesléard - One of the best experts on this subject based on the ideXlab platform.

  • Using mechanical clearing and goat grazing for restoring understorey plant diversity of embankments in the Rhône valley (southern France)
    Plant Biosystems, 2020
    Co-Authors: Cannelle Moinardeau, François Mesléard, Hervé Ramone, Thierry Dutoit
    Abstract:

    Consumption by animals remains one of the key points to assess the effectiveness of grazing impacts in woodland for increasing understorey plant diversity. To limit the spread of the Brambles and restore understorey plant diversity on an artificial embankment an original system of clearings connected by paths was created by mechanically crushing Brambles and allowing them to be grazed by rustic goats. The analysis of the indices of consumption of bramble under GIS has been used to provide an estimation of the volume ingested and an estimation of the effectiveness of the goats. The impacts of three different managements (goat grazing, brush clearing and grazing, clearing and exclusion of grazing) and control without management were then tested during a three-year period. The monitoring of the vegetation on permanent plots provided evidence that goat grazing significantly increased in the short term the species-richness and heterogeneity of herbaceous plants communities, in complement with prior clearing. Thus, the objectives of the managers to open up the area and reduce the bramble cover were achieved, but the prior introduction of goats and the installation of mobile enclosures would be advisable in order to ensure the sustainability of these measures on plant diversity in the long term.

  • Impacts of water stress removal and disturbance regimes on Mediterranean dry grasslands diversity and succession
    Plant Ecology, 2015
    Co-Authors: Solène Masson, Matthieu Gauvain, François Mesléard, Thierry Dutoit
    Abstract:

    Our goal was to disentangle the effects of stress removal and disturbance on plant communities of a Mediterranean rangeland, La Crau (southeastern France). We compared undisturbed reference steppe vegetation with vegetation impacted by changes in land use such as earlier phases of cultivation (dating back 20 years) and/or current water infiltrations (revealed by the presence of Brachypodium phœnicoïdes ), since the establishment of adjacent hay meadows. We considered plots with and without Brambles ( Rubus ulmifolius ), an indigenous shrub species that had colonized the area after the land-use changes. We monitored the composition and measured the taxonomic richness and richness of functional groups, evenness and similarities of plant communities. The species richness of the undisturbed community was significantly higher than that of all disturbed plant communities. Although cultivation led to the dominance of ruderal species, the removal of water stress had a stronger negative impact, enabling the establishment of herbaceous competitor species such as B. phœnicoïdes . The dominance of this species resulted in a significant decline in species richness and evenness after water stress removal. The presence of Brambles correlating with former cultivation and/or current water infiltration did not have a significant impact on plant species richness in the vicinity of bramble bushes, although it significantly modified the composition of the adjacent herbaceous vegetation. Our study highlights again the low resilience of Mediterranean dry grasslands after disturbance. While both the disturbance and the water stress removal resulted in changes within the plant community, our findings reveal a stronger impact of the water stress removal. Water infiltration led to decreased plant species richness and evenness because the greater availability of water favored competitor species over the stress-tolerant xeric species. Therefore, for restoring the original steppe species richness, the priority will be to control water infiltrations, even before any scrub-clearing is undertaken to control bramble colonization.

  • Impacts of water stress removal and disturbance regimes on Mediterranean dry grasslands diversity and succession
    Plant Ecology, 2015
    Co-Authors: Solène Masson, Matthieu Gauvain, François Mesléard, Thierry Dutoit
    Abstract:

    Our goal was to disentangle the effects of stress removal and disturbance on plant communities of a Mediterranean rangeland, La Crau (southeastern France). We compared undisturbed reference steppe vegetation with vegetation impacted by changes in land use such as earlier phases of cultivation (dating back 20 years) and/or current water infiltrations (revealed by the presence of Brachypodium phoenicoides), since the establishment of adjacent hay meadows. We considered plots with and without Brambles (Rubus ulmifolius), an indigenous shrub species that had colonized the area after the land-use changes. We monitored the composition and measured the taxonomic richness and richness of functional groups, evenness and similarities of plant communities. The species richness of the undisturbed community was significantly higher than that of all disturbed plant communities. Although cultivation led to the dominance of ruderal species, the removal of water stress had a stronger negative impact, enabling the establishment of herbaceous competitor species such as B. phoenicoides. The dominance of this species resulted in a significant decline in species richness and evenness after water stress removal. The presence of Brambles correlating with former cultivation and/or current water infiltration did not have a significant impact on plant species richness in the vicinity of bramble bushes, although it significantly modified the composition of the adjacent herbaceous vegetation. Our study highlights again the low resilience of Mediterranean dry grasslands after disturbance. While both the disturbance and the water stress removal resulted in changes within the plant community, our findings reveal a stronger impact of the water stress removal. Water infiltration led to decreased plant species richness and evenness because the greater availability of water favored competitor species over the stress-tolerant xeric species. Therefore, for restoring the original steppe species richness, the priority will be to control water infiltrations, even before any scrub-clearing is undertaken to control bramble colonization.

  • Using Shrub Clearing, Draining, and Herbivory to Control Bramble Invasion in Mediterranean Dry Grasslands
    Environmental management, 2015
    Co-Authors: S. Masson, François Mesléard, Thierry Dutoit
    Abstract:

    For centuries, the dry grassland of the plain of La Crau (south-eastern France) has been subjected to numerous disturbances resulting in the destruction and the fragmentation of this emblematic rangeland ecosystem of the Mediterranean. Today, this ecosystem is facing a new threat from a proliferating native species, the bramble (Rubus ulmifolius Schott), which preferentially colonizes areas that were formerly cultivated and/or exposed to water infiltration. To identify a strategy for effective control of this colonization, in situ experiments testing disturbance regimes (shrub clearing and/or mixed grazing by sheep and goats) combined with the control of access to water resources (with or without drainage trenches) were undertaken between 2010 and 2013. Only clearing and grazing combined over 3 years led to significant changes in vegetation height and bramble cover as well as modifications in the floristic composition, diversity, similarity, and richness of the plant community. Neither a clearing operation carried out in 2010 alone, nor grazing alone, reduced bramble cover, and neither treatment increased the species richness of the plant community. Similarly, digging drainage trenches had no significant impact either on the plant community or on bramble cover. Our study suggests that only annual mechanical clearing coupled with sheep and goats grazing can significantly reduce bramble cover. This combined restoration treatment needs to be applied for at least 3 consecutive years to induce significant changes and enable this ecosystem to return to the dry grassland succession.

  • Impacts de différents régimes de perturbations et niveaux de ressource hydrique pour contrôler une espèce proliférante dans un écosystème pseudo-steppique: le cas de Rubus ulmifolius Schott. dans la plaine de la Crau (Bouches-du-Rhône, France)
    2014
    Co-Authors: Solène Masson, François Mesléard, Thierry Dutoit
    Abstract:

    The plain of la Crau, located in South Eastern France, is a unique pseudo-steppe ecosystem, characterized by the presence of a Mediterranean climate, stony soil and limestone conglomerate at 40cm depth, and a traditional sheep grazing dating back to 6,000 years. Nevertheless, for many decades, this ecosystem has been subjected to numerous exogenous disturbance regimes. Indeed, during the 16th century, the construction of channels led to the transformation of the dry grasslands into hay meadows. Moreover, during the last century, agriculture intensification and the industrial development of military activities have significantly altered the steppe. Now, the plain of la Crau is a fragmented landscape where steppe habitats are connected directly with irrigated orchards or hay meadows. The effects on plant communities have been a decrease of species richness, a trivialization of plant composition and also the colonization of disturbed areas by pioneer invasive species such as Rubus ulmifolius Schoot, the elm leaf bramble. Absent from the original plant composition, this species can colonize areas formerly cultivated and/or subjected to water infiltrations coming from the mismanagement of the irrigation of hay meadows nearby. The increase of bramble cover is a threat to the Crau, because it causes the reduction of herbaceous community available for traditional sheep grazing, which is responsible for the organization and the structure of the steppe plant communities. To better understand this phenomenon and to discriminate the factors responsible for this colonization, an experimentation in situ based on the implementation of different disturbance regimes (shrub clearing and/or grazing) crossed with two levels of water resources has been carried out during three years (between November 2010 to September 2013). During this period, we have performed a monitoring of the vegetation each spring and measured the photosynthetically active radiation at different times to a year (at the moment of clearing, before and after grazing, and after the summer drought).Our results evidence significant changes in the composition and a drastic increase of species richness between plots that were cleared and grazed each year and those that were not. These differences can be explained by a significant reduction in the area occupied by the bramble (increase of photosynthetically active radiation). However, the action of a single clearing or grazing alone did not succeed in maintaining an open environment. No significant action of the drying plots could be detected on the plant community and on the dynamics of Brambles. In order to perform a potential ecological restoration, an annual clearing coupled with a return of sheep grazing is recommended. In addition, the restoration of the irrigation system is considered in the discussion to limit the presence of Brachypodium phoenicoides (L.) Roem. & Schult that develops probably at the expense of typical steppe species.

Bruce A. Smith - One of the best experts on this subject based on the ideXlab platform.