:: F. ISSELIN-NONDEDEU Editorial - Ecologie des communautés végétales: questionnement actuel et approches multiples Editorial - Plant community ecology: current issues and multiple approaches Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 223-232. Français, Anglais Résumé Ce numéro spécial Acta Botanica Gallica. Botany Letters comprend en plus des résumés des actes du colloque, une sélection de sept articles issus de communications orales présentées lors des Neuvième Journées de la conférence sur l’écologie des communautés végétales, ECOVEG9. Au travers de cet éditorial, tout en introduisant des sujets traités dans les articles sélectionnés, je reviendrai sur certains points clefs de définition des communautés végétales, avant de balayer les principaux thèmes actuels en écologie des communautés qui ont été traités lors de ces journées.
Abstract The present issue of Acta Botanica Gallica. Botany Letters includes, in addition to the proceedings, a selection of seven papers that were presented at the 9th International Conference on Plant Community Ecology, ECOVEG9. In this Editorial, I will first cover some basic issues of plant community ecology, and then go through the main issues that were presented during the conference and introduce the selected papers.
:: C. RIBAUDOA, V. BERTRINA & A. DUTARTRE Dissolved gas and nutrient dynamics within an Egeria densa Planch. bed Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 233-241. Anglais Abstract Submerged aquatic weeds may colonize freshwater shallow lakes by forming dense mats: when this occurs, their invasion interferes with human activities and generates several impacts on aquatic processes. In this paper, we present the preliminary results of an investigation concerning the dissolved gas and nutrient dynamics within a bed of Egeria densa Planch. in a bay of Lacanau Lake (southwestern France). Two 24-h cycles were carried out during summer and autumn 2013, for the measurement of dissolved oxygen (O2), carbon dioxide (CO2), methane (CH4) and dissolved inorganic nitrogen (DIN). Our results show that Egeria densa seasonal dynamics might strongly influence the colonized area: during summer, steady levels of O2 (O2 > 0.15 mM) were coupled to the macrophyte photosynthetic activity, while during autumn respiration processes were mostly pronounced (0.02 mM < O2 < 0.25 mM). High concentrations of CH4 (0.6–53.9 μM) and CO2 (0.03–0.83 mM) were measured within the bed during both sampling campaigns, that indicating a potential contribution to greenhouse gas emissions towards the atmosphere. This study suggests that a shallow environment colonized by an elevated biomass of submerged aquatic weeds is most likely subjected to water hypoxia and nutrient mobilization.
:: R. PERRONNE, S. GABA, E. CADET & V. LE CORRE The interspecific and intraspecific variation of functional traits in weeds: diversified ecological strategies within arable fields Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 243-252. Anglais Abstract Arable weeds are a key component of the biodiversity of agroecosystems, but have faced a marked decline due to agricultural intensification. Recently, the crop edge has been considered as a potential refugia for many species. Indeed, weed species richness and abundance are higher in the crop edge than in the field margin and the field core. In this study we question whether weed functional diversity also varies among field elements and whether it is higher in the crop edge. We studied the interspecific and intraspecific variation of three functional traits (specific leaf area, canopy height and above-ground biomass) related to the response of weeds to competition and to agricultural practices, for seven weed species sampled in the crop edge, the field margin and the field core area in four winter-wheat fields. We show that trait values varied significantly with the species, the field element and their interaction. Within the field, all species had high specific leaf area, low canopy height and biomass, suggesting a shade-tolerance syndrome that could be a strategy in response to both competition with the crop and the disturbances induced by agricultural practices. In the crop edge, where the functional variation was the highest, two distinct functional strategies were observed, suggesting a resource partitioning under the predominance of weed–weed competition. In conclusion, the crop edge plays a key role in sustaining weed diversity, mostly because of its intermediate environmental properties that allow the coexistence of weeds with different ecological strategies.
:: A. ALIGNIERA, D. ALARD, R. CHEVALIER & E. CORCKET Can contrast between forest and adjacent open habitat explain the edge effects on plant diversity? Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 253-259. Anglais Abstract Forest edges are key features in human-dominated landscape. Located between forest and non-forest habitats, edges induce biotic and abiotic changes, which may have profound consequences on vegetation diversity. Recent studies suggest the importance of different edge types in the modulation of edge-related responses. However, edge effect on the spatial dynamic of vegetation, from forest to non-forest habitats, remains unclear. Our aim was to compare the species richness and diversity of vegetation communities between forest and open habitats with their respective edges, in highcontrast versus low-contrast situations. The degree of contrast was defined according to the disturbance regimen of nonforest habitats. We surveyed vascular vegetation along transects in forest and open habitats and in their respective edges, in three regions of France. We showed that edge effects occur on plant diversity, whatever the region, but asymmetrically. Edge effect tends to be greater on the open side than on the forest side of the border. Species richness and diversity were generally higher in open edge than in open habitat, whereas no significant difference was observed between forest edge and forest habitat, whatever the contrast situation encountered. This study shows that the edge effects detected along a forest–edge–exterior habitat gradient may depend in large part on the disturbance regimen in open habitats as well as the vegetation pool size. We highlighted the need to carefully consider the edge types, e.g. their contrast with adjoining non-forest habitat, in further studies to identify the relevant factors and mechanisms behind edge-related response patterns of biodiversity in human-dominated landscapes.
:: S. MASSON, F. MESLÉARD & T. DUTOIT Impacts de différents régimes de perturbations et niveaux de ressource hydrique pour contrôler une espèce proliférante dans un écosystème pseudosteppique : le cas de Rubus ulmifolius Schott. dans la plaine de la Crau (Bouches-du-Rhône, France) Impacts of disturbance regimes and rates of water resource levels in the control of bramble colonization in a pseudo-steppe ecosystem: the case of the plain of la Crau (Bouches-du-Rhône, France) Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 261-275. Français Résumé Depuis des siècles, la pseudo-steppe de la Crau (sud-est de la France) est soumise à de nombreuses perturbations entrainant destruction et fragmentation de cet écosystème unique au monde. Outre une diminution de la richesse spécifique et une banalisation de la végétation, la communauté végétale est menacée par Rubus ulmifolius Schott qui colonise les milieux anciennement cultivés et/ou soumis à des infiltrations hydriques venant de l’irrigation des prairies de foin voisines. L’augmentation de son recouvrement entraine une diminution des surfaces herbacées disponibles pour le pâturage ovin, responsable de l’organisation et de la structure de la formation végétale. Afin de comprendre cette colonisation, des expérimentations in situ testant différents régimes de perturbation (débroussaillage et/ou pâturage) croisés à différents niveaux d’humidité du sol ont été menées de novembre 2010 à septembre 2013. Nos résultats mettent en évidence des changements significatifs de composition et une augmentation de la richesse spécifique entre les placettes débroussaillées et pâturées annuellement et celles qui ne l’étaient pas. Néanmoins l’action unique d’un débroussaillage ou du pâturage n’a pas permis de maintenir le milieu ouvert. Pour contrôler cette dynamique, un débroussaillage annuel couplé à un retour du pâturage ovin est donc recommandé. De plus; la restauration du réseau d’irrigation est à envisager afin de limiter la présence de Brachypodium phoenicoides (L.) Roem. & Schult. qui se développe au dépend des espèces de la steppe.
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.
:: E. BUISSON, P. BRAVET, J. MIEUSSET, N. BAILLOT, C. DUBREUCQ, L. SADONÈS, J. CHENOT & L. BRUN Plant communities of a coastal lagoon foredune: definition of the reference and restoration after compaction Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 277-286. Anglais Abstract Throughout the world, dunes are being altered by human activities. Dunes can be restored to naturally functioning systems to protect human settlements and coastal strips and preserve biotopes. This study took place on the Jaï dunes, on the shore of a coastal lagoon in southeastern France, which were mainly degraded by vehicles. The objectives of this work were (1) to define the reference ecosystem by gathering historical information and exploring other regional sand dunes; (2) to find out about the restoration potential of the site by studying the degraded seed bank; (3) to test the efficacy of a few basic restoration actions. Historical information was of little help in defining the reference ecosystem. The description of EU Habitat Directive habitat types and the selection of regionally less degraded sites allowed us to compile the following list of plant species that we could expect to find in the restored area: Anthemis maritima, Elytrigia juncea, Glaucium flavum and Sporobolus pungens. The seed bank of the road was mainly composed of Juncus acutus, which is not a typical dune species and therefore did not have much potential for restoration. Ploughing can therefore be used to decompact the sand road without hampering colonization from the seed bank. Ploughing was only efficient when the following other conditions were met: environmental conditions adequate for the establishment of dune vegetation, and a sufficient connection between the beach, the foredune and the restored area.
:: A. BULOT, E. PROVOST & T. DUTOIT Transférer le sol pour restaurer des communautés végétales: quelles leçons pour mesurer la résilience des pelouses sèches ? (Plaine de La Crau, Sud-Est de la France). Transfer of soil as a toll to restore plant communities: lessons drawn to measure xeric grassland resilience (Crau plain, south east France) Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 287-300. Français Résumé La restauration écologique peut accélérer la résilience des pelouses sèches dégradées. Parmi les techniques utilisées, le transfert de sol a, ainsi, déjà permis d’obtenir des résultats encourageants pour rétablir des communautés végétales riches en espèces. En revanche, il s’agit d’une méthode non durable, car destructrice du site donneur. Le 07 août 2009, une importante fuite d’un oléoduc est survenue au milieu de la steppe de La Crau. En 2010, plus de 5,5 ha de végétation ont été détruits par excavation et évacuation en décharge du sol pollué par les hydrocarbures. La restauration de ce site a, alors, été associée à différentes expérimentations in situ de remise en place du sol, en l’absence du pâturage ovin traditionnel (exclos), pour tester l’importance du respect de l’organisation verticale des principaux horizons pédologiques. Après trois années de suivi, nos premiers résultats montrent une forte résilience de la végétation en termes de composition et de richesse spécifique. De plus, peu d’espèces rudérales ont réussi à coloniser le site après transfert du sol. Cependant, aucune des modalités de remise en place du sol n’a pas permis de restaurer l’intégrité de la communauté végétale steppique de référence. Il semble, alors, maintenant nécessaire de remettre en place le système de pâturage ovin ancestral pour permettre la restauration de la structuration spatiale et de la diversité de la végétation steppique.
Abstract Ecological restoration can accelerate the resilience of degraded dry grasslands. Among the ecological restoration techniques used, soil transfer has already given promising results for restoring species-rich plant communities by providing the ability to recreate rapidly a habitat that corresponds to the reference ecosystem (the non disturbed dry grasslands). However, soil transfer is a destructive method, since it involves the use of non-renewable resources such as grassland soils of the donor sites that are the produce of centuries of interactions between climate, plants and animals. In south-eastern France, the plain of La Crau is an example of Mediterranean dry grasslands where the resilience of the steppe vegetation is extremely slow after land use changes which have impacted soil and vegetation. On 7th August 2009, a major oil leak occurred in the steppe center, destroying more than 13 acres of steppe vegetation. As a consequence, in 2010, the polluted soil was excavated and evacuated in a specialised dump. This operation was, then, combined with various in situ experiments of soil transfer, with exclusion of traditional sheep grazing management, to test (i) the importance of respecting the vertical organization of the main soil horizons and (ii) some opportunities to save this non-renewable resource. In May 2011, just after the soil transfer (72,000 tons) was achieved in April 2011 from a nearby quarry which extension had been authorised prior to the oil leak, different quadrats were materialized in the reference steppe vegetation around and in the restored site, with at the soil surface: the organic layer (top-soil, treatment ABC) with or without compaction (treatment ABCnc), the mineral layer (sub-soil, treatment BC) or the altered bedrock only (treatment C). After three years of vegetation monitoring, all the different treatments of soil transfer resulted in a rapid resilience of steppe vegetation in terms of floristic composition and plant species richness. Indeed, in 2013, the treatment with the transfer of mineral layer only at the soil surface, showed no significant difference in terms of plant species richness with the reference steppe plant community. Furthermore, there was a significant higher species richness for the treatments with the transfer of organic layer, compacted or not, in comparison with the reference steppe plant community. In addition, between 2011 and 2013, the natural colonisation by some ruderal opportunistic species was very low. Nevertheless, the reference steppe plant community organization was not restored for none of the different soil transfer treatments, as revealed by the calculation of the Bray-Curtis index. In addition, species abundances in the uncompacted organic layer, mean vegetation height and plant cover were significantly higher, than in the reference steppe plant community. Our results show that after only 3 years, the results of the different soil transfer treatments seem very promising. It appears from this three year monitoring that soil transfer of a mixture of the organic (top soil) and mineral (sub soil) layers, without final compaction, could be sufficient to boost the natural resilience of the typical plants of the reference steppe plant community. It might also be possible to increase the surface where the soil will be spread according to ratios of 1 to 2 or 1 to 3, instead of 1 to 1. This method will allow the protection of the steppe soil that is still a non-renewable resource. Because none of the different soil transfer treatments has allowed for the restoration of the integral steppe plant community, it seems now necessary to reinstall the traditional sheep grazing system with the aim to increase the restoration of the reference steppe plant community spatial organization.
:: J. CHENOT, L. AFFRE, A. PASSETTI & E. BUISSON Consequences of iceplant (Carpobrotus) invasion on the vegetation and seed bank structure on a Mediterranean island: response elements for their local eradication Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 301-308. Anglais Abstract Biological invasions are one of the world’s leading causes of biodiversity loss. Islands are particularly good models for studying the impact of invasive species. Bagaud island (58 ha), which is part of Port-Cros National Park (southeastern France), is currently suffering an invasion of Carpobrotus. A restoration project has been established with the aim of eradicating these species to protect native ecosystems. The objective of the present study was to examine the plant composition of the local vegetation and seed bank (in litter and soil) focusing on (i) Carpobrotus patches and (ii) native plant communities, with the ultimate goal of determining whether Carpobrotus removal is followed by native plant community colonization. A further objective of this study was to help identify the most effective protocol for adequate ecological restoration. Native plant communities found around Carpobrotus patches can vary depending on whether the patch is located on the coast or inland; we can therefore expect a variety of plant communities to form following Carpobrotus removal. Even though Carpobrotus litter can frequently contain seeds of native species, such Atriplex prostrata, Frankenia sp. and Sonchus asper, it also contained many more Carpobrotus seeds (77.6%). Therefore, it is important to remove Carpobrotus litter to prevent large numbers of Carpobrotus seeds from recolonizing after eradication. We conclude that the most effective ecological restoration protocol consists of the following: (i) the removal of living Carpobrotus plants and (ii) the removal of Carpobrotus litter. This protocol can be made even more effective by following it up in the near and mid-term by periodic and thorough checks for Carpobrotus reinvasion.
:: J. SAWTSCHUK, M. DELISLE, X. MESMIN & I. BERNEZ How past riparian management practices can affect composition and structure of vegetation for headwater ecological restoration projects Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 309-320. Anglais Abstract Ecological restoration of river networks, especially of headwaters, is a key issue to improve water ecological, chemical and physical qualities and ecological functioning of aquatic ecosystems. Ecological restoration of degraded riparian vegetation is commonly considered as an efficient way to improve headwater habitats. This study aims to describe past management dynamics and their effect on current riparian vegetation structure and composition. We focused on two headwater brooks surrounded by traditional pasture in the rural catchment of the river Oir, a salmonid nursery of the river Sélune, Normandy, France. Historical riparian vegetation dynamic has been characterized thanks to interpretation of ortho-photographs from 1947 to 2010. GIS analyses allowed us to distinguish five types of management practices from stable vegetation (maintained open or maintained woody) to heterogeneous dynamic vegetation (alternation of clear-cutting, coppice management and recolonization by ligneous species). To measure their impact on the riparian ecosystem, past management practices were linked with field data describing current structure and composition of riparian vegetation. Results show that structure of riparian plant communities depends mainly on recent management practices, while floristic composition depends both on recent and past management practices. Knowledge of the past dynamics of riparian landscapes proves to be a relevant indicator of the ecological status of headwater ecosystems that could be used to improve ecological restoration instead of classical management practices of riparian vegetation.
:: F. ISSELIN Actes du 9ème Colloque d’Ecologie des Communautés Végétales, ECOVEG9 Tours 3-5 avril 2013 (Proceedings of the 9th Plant Community Ecology conference, Tours April 3–5, 2013, France) : résumés Paru dans Acta Botanica Gallica, 2014, 161 (3), pp. 321-342. Anglais