Short-Term Effects on Diversity and Biomass on Grasslands from Artificial Dykes under Grazing and Mowing Treatments

International audienceFew studies document the impacts of conservation management practices such as extensive grazing or mowing on the new ecosystems created by industrial conversions. In southern France, the Rhône channelling led to the construction of dykes to protect the Tricastin industrialized area from floods. Aiming to control plant dynamics for safety reasons and to favour plant biodiversity, mowing or extensive grazing by cattle were recently tested. Monitoring from both permanent plots and aerial photographs shows that three years of extensive grazing and annual mechanical mowing have modified plant composition, significantly increasing plant species richness, evenness and heterogeneity. The increase in evenness and beta-diversity from grazing was significantly higher than from mowing. Only grazing was able to reduce the height and cover of the dominant tussock perennial grass species (Brachypodium phoenicoides), while increasing bare soil cover and thus the contribution of annual species. The Normalized Difference Vegetation Index (NDVI) obtained through aerial photographic analyses confirmed the correlation between NDVI, aboveground biomass and plant species richness for the grazed site alone, allowing the results obtained from quadrats to be generalized to the scale of the grazed site. On the Rhône's artificial dykes, extensive grazing appears to be a better management tool than mowing to enhance plant biodiversity and meet safety objectives

Fire increases the reproduction of the dominant grass Brachypodium retusum and Mediterranean steppe diversity in a combined burning and grazing experiment

International audienceQuestions: What are the effects of fire and grazing on vegetative growth and sexual reproduction of Brachypodium retusum, the dominant species of Mediterranean Thero-Brachypodietea grasslands (“steppes”) and on species composition of the associated plant community?Location: “La Crau”, South-Eastern France.Methods: We set up a split-plot experiment testing the effects of fire season (winter, summer) and grazing on plant cover, inflorescence number, seed set and germination of B. retusum in traditionally grazed grasslands. We further analyzed plant species composition and diversity in vegetation relevés. The same fire treatments were tested in a second experiment in long-term grazing exclosures.Results: B retusum showed a rapid post fire recovery, but other species of the associated plant community, in particular annuals, recovered as fast or even faster. Fire increased B. retusum inflorescence production and seed set per inflorescence and this effect was stronger in the summer fire treatment. At community level, fire significantly increased species richness, evenness and Bray-Curtis dissimilarity in the second post-fire season and again, the summer fire effect was stronger. Grazing exclusion for two seasons had only a small effect on B. retusum and the associated plant community. The effect of both fire treatments on B. retusum was similar in long-term exclosures. In these exclosures, fire resulted in a community shift towards the species composition of traditionally grazed steppes.Conclusions: The concomitant positive effects of experimental burning on B. retusum reproduction and on plant diversity of Mediterranean steppe vegetation suggest that the system is adapted to fire as an important driver of community composition. Annual species surviving as seeds are as successful in post-fire recovery as perennial resprouters. Prescribed burning may be an alternative strategy to restore community structure in abandoned (ungrazed) steppes showing a decline in typical grassland species after several years of grazing abandonment

Grazing in temporary paddocks with hardy breed horses (Konik polski) improved species-rich grasslands restoration in artificial embankments of the Rhône river (Southern France)

International audienceExtensive horse grazing with hardy breeds is largely used in conservation management for restoring species-rich semi-natural grasslands in Europe. As an example, the Donzère-Mondragon Rhône river embankments (south-eastern France) where horse grazing with Konik polski succeeded to maintain high species richness in patches of open and short grassland, but failed for patches of tall grassland dominated by the grass tussock species Brachypodium phoenicoides. In response, an increase of herd density by the creation of temporary paddocks was applied in tall grassland patches. Grazing pressure over time between patches was estimated via GPS fixed to mares, biomass, plant species richness measurements and from multispectral photographs, the normalized Difference Vegetation Index (NDVI) was calculated. Finally, telemetric data were collected. We wondered if the use of extensive horse grazing with temporary paddocks occupation, increase plant species richness. After three years, our results show that the increase in stocking rate enabled a significant increase of plant species richness in the tall grassland patches, with a significant decline of B. phoenicoides in all paddocks. The NDVI was strongly correlated with herbaceous biomass and plant species richness, while the number of GPS points indicating the position of the mares was higher in areas where the NDVI was high. These results are discussed for improving horse grazing conservation systems efficiency on grasslands established in anthropized sites such as embankments and the use of the NDVI as an appropriate tool to help decision-making for large-scale applications

Extensive horse grazing improves grassland vegetation diversity, seed bank and forage quality of artificial embankments (Rhône River - southern France)

International audienceGrazing by herds of herbivores modifies plant communities in different ways, depending on the herbivore species. Horse grazing is already known to be effective in increasing plant diversity and maintaining herbaceous vegetation, creating different types of patches and thus ensuring spatial heterogeneity. On an artificial embankment at the Donzère-Mondragon hydroelectric facility in the Rhône Valley, extensive grazing by a rustic horse (Konik-Polski) was introduced several years ago to control shrub encroachment and to enhance plant grassland diversity. Vegetation monitoring surveys over a five-year period (2014-2018) showed that horse grazing maintained patches of open and short grasslands and increased species-richness, in particular of annual species, some of which have heritage value. In contrast, overly-low grazing pressure led to the dominance of an unpalatable perennial grass (Brachypodium phoenicoides) at the expense of the annual species that significantly enhance the forage value of the most heavily grazed patches. Horse grazing also had a positive impact on the permanent seed bank of the soil, increasing its heterogeneity and the density of viable seeds. Extensive horse grazing thus appears to be a relevant management tool to preserve the diversity and the forage quality of the most open and short grasslands. Nevertheless, grazing pressure here remained too low to allow restoration of grasslands already colonised by woody species. Combining different livestock species might be a better alternative to pure horse grazing, to increase heterogeneity and diversity. Our results are discussed in relation to extensive horse grazing on artificial ecosystems, such as the embankments bordering rivers and canals

Using mechanical clearing and goat grazing for restoring understorey plant diversity of embankments in the Rhône valley (southern France)

International audienceConsumption 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

Factors limiting early establishment of the Mediterranean grassland species Brachypodium retusum at disturbed sites

International audienceIn Mediterranean dry grasslands, water availability and grazing strongly influence plant establishment. Although higher water availability and lower grazing pressure usually increase seedling recruitment in the beginning, higher competition may reduce seedling survival. In our study, we analysed this trade-off for the dominant species of Western Mediterranean steppes Brachypodium retusum which hardly recolonises restoration sites degraded by soil disturbance such as arable use. A split-plot experiment was set up on an ex-arable site in the "La Crau" steppe in order to test the effects of initial watering and sheep grazing on seedling recruitment, survival and early growth during two years. The watering treatment was applied in the first autumn and spring doubling the usual precipitation during this period and grazing was tested using exclosures. Survival and growth of seedlings established from field-sown seeds were compared to those of transplanted seedlings pre-grown in a growth chamber. Watering did not affect germination whereas the grazing effect was negative. Initial watering had a positive effect on survival only in grazed plots suggesting a compensatory effect under grazing disturbance. Significant main effects of watering on early growth disappeared in the second season. Grazing significantly reduced most measured growth traits whereas the effect on survival was only marginally significant. Planted seedlings (49%) survived better than seedlings emerged from field-sown seeds (36%). In conclusion, initial fencing increases establishment success of B. retusum in ecological restoration. Initial watering may help to mitigate negative grazing effects when fencing is not possible

Why grazing and soil matter for dry grassland diversity: New insights from multigroup structural equation modeling of micro-patterns

International audienceGrazing is recognized as a major process driving the composition of plant communities in grasslands, mostly due to the heterogeneous removal of plant species and soil compaction that results in a mosaic of small patches called micro-patterns. To date, no study has investigated the differences in composition and functioning among these micro-patterns in grasslands in relation to grazing and soil environmental variables at the micro-local scale. In this study, we ask (1) To what extent are micro-patterns different from each other in terms of species composition, species richness, vegetation volume, evenness, and functioning? and (2) based on multigroup structural equation modeling, are those differences directly or indirectly driven by grazing and soil characteristics? We focused on three micro-patterns of the Mediterranean dry grassland of the Crau area, a protected area traditionally grazed in the South-East of France. From 70 plant community relevés carried out in three micro-patterns located in four sites with different soil and grazing characteristics, we performed univariate, multivariate analyses and applied structural equation modeling for the first time to this type of data. Our results show evidence of clear differences among micro-pattern patches in terms of species composition, vegetation volume, species richness, evenness, and functioning at the micro-local scale. These differences are maintained not only by direct and indirect effects of grazing but also by several soil variables such as fine granulometry. Biological crusts appeared mostly driven by these soil variables, whereas reference and edge communities are mostly the result of different levels of grazing pressure revealing three distinct functioning specific to each micro-pattern, all of them coexisting at the micro-local scale in the studied Mediterranean dry grassland. This first overview of the multiple effects of grazing and soil characteristics on communities in micro-patterns is discussed within the scope of the conservation of dry grasslands plant diversity

Utiliser des mélanges artificiels de sol différents pour restaurer des pelouses sèches dans les carrières

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Rétablissement des communautés végétales après éradication des griffes de sorcière (Carpobrotus sp.) dans le cadre du programme de restauration écologique de l'île de Bagaud (Parc national de Port-Cros, France) : résultats 5 ans après éradication

Rapport scientifique du Parc National de Port-CrosInternational audienceBagaud island (Hyères Island Archipelago, Var, France), was submitted to two major disturbances during the last centuries: the invasions of the black rat (Rattus rattus) and iceplant (Carpobrotus sp.). An eradication program of these two taxa was launched in 2010 by the Port-Cros National Park. This project involves a 10-year monitoring of animal and plant communities, including a preeradication monitoring in 2010 and 2011. Temporal changes of plant communities (i.e., plant cover and similarity between native vegetation and vegetation in areas where Carpobrotus sp. was removed) were analyzed in permanent plots (100 m² and 16 m²) before (2010-2011) and after (2013-2014) Carpobrotus sp. eradication. Native plant cover significantly increased since 2013. On coastal sites, the recovery of native flora is fast and matches with the haloresistant reference plant community. On the other hand, on inland sites, the recovered native flora includes some low matorral species as well as halo-nitrophilous species. This monitoring from 2010 to 2017 is important to understand plant community recovery after the eradication of 2 invasive taxa.L'île de Bagaud (archipel des îles d'Hyères, Var, France) a été soumise à deux perturbations majeures d'origine anthropique au cours des derniers siècles : l'invasion du rat noir (Rattus rattus) et des griffes de sorcière (Carpobrotus sp.). Un programme d'éradication de ces deux taxons a été lancé en 2010 par le Parc national de Port-Cros. Ce projet prévoit un suivi des communautés animales et végétales sur 10 ans, précédé d'un «état zéro» pré-éradications de 2 ans. Les changements temporels des communautés végétales (i.e., recouvrement végétal et similarité entre la végétation autochtone et la végétation sur les zones où Carpobrotus sp. a été retiré) ont été analysés au sein de placettes permanentes (100 m² et 16 m²) avant (2010-2011) et après éradication (2013-2014) de Carpobrotus sp. Le recouvrement végétal de la flore autochtone augmente considérablement à partir de 2013. En zone littorale, la reprise de la flore autochtone, comprenant des communautés halo-résistantes, semble plus rapide que dans l'intérieur de l'île, comprenant certaines espèces de matorral bas et des espèces halo-nitrophiles. Ce suivi floristique 2010-2017 donne des informations primordiales sur les capacités de rétablissement d'un écosystème insulaire suite à l'éradication locale de deux taxa invasifs

Rétablissement des communautés végétales après éradication des griffes de sorcière (Carpobrotus sp.) dans le cadre du programme de restauration écologique de l'île de Bagaud (Parc national de Port-Cros, France) : résultats 5 ans après éradication

Rapport scientifique du Parc National de Port-CrosInternational audienceBagaud island (Hyères Island Archipelago, Var, France), was submitted to two major disturbances during the last centuries: the invasions of the black rat (Rattus rattus) and iceplant (Carpobrotus sp.). An eradication program of these two taxa was launched in 2010 by the Port-Cros National Park. This project involves a 10-year monitoring of animal and plant communities, including a preeradication monitoring in 2010 and 2011. Temporal changes of plant communities (i.e., plant cover and similarity between native vegetation and vegetation in areas where Carpobrotus sp. was removed) were analyzed in permanent plots (100 m² and 16 m²) before (2010-2011) and after (2013-2014) Carpobrotus sp. eradication. Native plant cover significantly increased since 2013. On coastal sites, the recovery of native flora is fast and matches with the haloresistant reference plant community. On the other hand, on inland sites, the recovered native flora includes some low matorral species as well as halo-nitrophilous species. This monitoring from 2010 to 2017 is important to understand plant community recovery after the eradication of 2 invasive taxa.L'île de Bagaud (archipel des îles d'Hyères, Var, France) a été soumise à deux perturbations majeures d'origine anthropique au cours des derniers siècles : l'invasion du rat noir (Rattus rattus) et des griffes de sorcière (Carpobrotus sp.). Un programme d'éradication de ces deux taxons a été lancé en 2010 par le Parc national de Port-Cros. Ce projet prévoit un suivi des communautés animales et végétales sur 10 ans, précédé d'un «état zéro» pré-éradications de 2 ans. Les changements temporels des communautés végétales (i.e., recouvrement végétal et similarité entre la végétation autochtone et la végétation sur les zones où Carpobrotus sp. a été retiré) ont été analysés au sein de placettes permanentes (100 m² et 16 m²) avant (2010-2011) et après éradication (2013-2014) de Carpobrotus sp. Le recouvrement végétal de la flore autochtone augmente considérablement à partir de 2013. En zone littorale, la reprise de la flore autochtone, comprenant des communautés halo-résistantes, semble plus rapide que dans l'intérieur de l'île, comprenant certaines espèces de matorral bas et des espèces halo-nitrophiles. Ce suivi floristique 2010-2017 donne des informations primordiales sur les capacités de rétablissement d'un écosystème insulaire suite à l'éradication locale de deux taxa invasifs