Pratiques agricoles et propriétés agro-écologiques des prairies dans un processus d’intensification écologique : le cas de l’élevage bovin dans le Vercors

National audienceL'élevage bovin pour la production laitière est la composante agricole majeure sur le territoire des Quatre Montagnes dans le massif du Vercors. Sur ce territoire, un enjeu fort soulevé par une grande partie des agriculteurs concerne la question de l'autonomie fourragère. Cet aspect de la production est d'autant plus central qu'il est fortement dépendant des caractéristiques des prairies qui permettent d'assurer la production de fourrage en dépit d'aléas de plus en plus contraignants (sécheresses, dégâts de campagnols…). Comprendre comment maintenir un niveau de production suffisant en s'appuyant sur les propriétés écosystémiques des prairies relève du contexte de l'intensification écologique en abordant les relations entre l'organisation des systèmes d'élevage (usages à l'échelle des parcelles, diversité des types de parcelles au sein des exploitations, distribution au sein du paysage) et les valeurs d'usage et services écosystémiques fournis par les prairies. Au sein du projet multi-sites ANR-SYSTERRA MOUVE (Les interactions Elevage et Territoire dans la mise en mouvement de l’intensification écologique), le territoire des Quatre Montagnes constitue l'un des terrains d'approfondissement pour analyser comment l'évolution des pratiques dans le sens de l'intensification écologique peut permettre d'augmenter le niveau des services écologiques et d'améliorer les capacités d'adaptation des élevages. En nous appuyant sur une typologie préétablie des prairies, basée le type d'usage (fauche, pâturage) et la composition simplifiée de la végétation nous avons mesuré un large panel de propriétés écosystémiques sur un échantillon de 50 parcelles représentant la diversité des types d'usage sur le territoire. Les propriétés mesurée couvrent notamment la structure spécifique (diversité, hétérogénéité) et fonctionnelle des communautés (traits foliaires, structuraux, phénologiques), les caractéristiques agronomiques (teneur en N, C, P…) et écologique (biomasse et diversité microbienne) du sol et du fourrage (production, qualité), autant de proxys pour les grands types de services reconnus : (i) services intrants, (ii) services de production fourragère et (iii) services en lien avec la valeur écologique des prairies. Les premiers résultats révèlent le rôle prépondérant de deux facteurs liés aux usages pour les propriétés agro-écologiques des prairies : la date de première fauche ou pâturage et le caractère temporaire ou permanent des prairies (date du dernier retournement). Les prairies temporaires offrent un bon niveau de services intrant (fertilité, matière organique) et de production et qualité fourragère mais une faible valeur écologique (faible diversité). Cette distinction sur la base des propriétés agro-écologiques est d'autant plus intéressante que les entretiens auprès des éleveurs ont souligné l'importance de la place des prairies temporaires comme une des clés pour l'autonomie fourragère. Ces prairies productives étant également les plus sensibles aux aléas et offrant une moindre souplesse d'utilisation. A terme, notre objectif est d'identifier les compromis, synergies et antagonismes entre les différents types de services rendus (agronomiques, écologiques) en fonction de différents scénarios d'intensification écologique à l'échelle du territoire

How would farmers in the French Alps adapt their systems to different drought and socio-economic context scenarios?

International audienceThe French Alps are considered as an area that is particularly vulnerable to climate change. Several droughts have already occurred since 2003. In order to assess the ability of farming systems to adapt to future drought events, we developed prospective scenarios combining different climatic and socio-economic contexts. Four scenarios were defined based on (i) prospective studies conducted at national and international levels, and (ii) a participatory approach with various stakeholders to transcribe these scenarios at a local level. Farmers and shepherds in the Vercors and Oisans massifs were surveyed in order to understand how they had reacted to previous droughts, and how they would plan to react to our scenarios. Results show first that the farmers would strive to continue their activity in each scenario, taking advantage of the flexibility of their farming systems, as in previous years. However, in the most pessimistic climatic scenario, they would also decrease the size of their herds. Depending on the socio-economic hypothesis, they would adopt farm structural changes (farm processing activities, direct selling, etc.), or look for part-time non-agricultural jobs. Three types of strategies were identified, depending on the farmers' objectives and adjustments. Finally, public policies to accompany these changes are considered

Estudio de los factores cr?ticos para la reactivaci?n del ecoturismo en el contexto de la Covid-19 en Costa Rica

El turismo se ha visto afectado a nivel mundial por la pandemia. Costa Rica, pionera y l?der del ecoturismo, atraviesa una compleja situaci?n econ?mica derivada de la crisis sanitaria del Covid-19. Todos los actores p?blicos y privados deben encontrar soluciones para reactivar la econom?a y la actividad tur?stica.Como verdadero embajador y modelo del ecoturismo, el pa?s centroamericano, debe continuar con sus esfuerzos y concebir nuevas medidas para reactivar su econom?a a corto y largo plazo y as?, beneficiarse del turismo sostenible en los aspectos: econ?mico, ecol?gico y social. Para cumplir esta meta, hay que analizar la situaci?n pand?mica actual y las consecuencias en el ecoturismo en Costa Rica, que nos permitir?n conocer los factores cr?ticos necesarios para la reactivaci?n del ecoturismo, por parte del sector ecotur?stico y de sus potenciales clientes. Recomendamos propuestas concretas para ofrecer soluciones a corto y largo plazo para el pa?s. As? que, si Costa Rica es capaz de cuidar la salud de sus habitantes como visitantes, tambi?n ser? capaz de cuidar de sus empresas, econom?a, espacios naturales y del medio ambiente, por lo tanto, cuidar? su futuro

On negative higher-order Kerr effect and filamentation

As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence, nor its inversion, nor the intensity at which it is observed, appear to be flawed. Furthermore, we argue that, independently on our values, the principle of including HOKE is straightforward. Due to the different temporal and spectral dynamics, the respective efficiency of defocusing by the plasma and by the HOKE is expected to depend substantially on both incident wavelength and pulse duration. The discussion should therefore focus on defining the conditions where each filamentation regime dominates.Comment: 22 pages, 11 figures. Submitted to Laser physics as proceedings of the Laser Physics 2010 conferenc

High-field quantum calculation reveals time-dependent negative Kerr contribution

The exact quantum time-dependent optical response of hydrogen under strong field near infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schr\"{o}dinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in the weak-field model of polarization. We show that this effect is far from being negligible in particular when closures of ionization channels occur and stems from the interaction of electrons with their parent ions. It provides an interpretation to higher-order Kerr effect recently observed in various gases.Comment: 5 pages, 4 figure

Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning

Combatting global grassland degradation

Grasslands are under severe threat from ongoing degradation, undermining their capacity to support biodiversity, ecosystem services and human well-being. Yet, grasslands are largely ignored in sustainable development agendas. In this Perspective, we examine the current state of global grasslands and explore the extent and dominant drivers of their degradation. Socio-ecological solutions are needed to combat degradation and promote restoration. Important strategies include: increasing recognition of grasslands in global policy; developing standardized indicators of degradation; using scientific innovation for effective restoration at regional and landscape scales; and enhancing knowledge transfer and data sharing on restoration experiences. Stakeholder needs can be balanced through standardized assessment and shared understanding of the potential ecosystem service trade-offs in degraded and restored grasslands. The integration of these actions into sustainability policy will aid in halting degradation and enhancing restoration success, and protect the socio-economic, cultural and ecological benefits that grasslands provide

Functional traits and phenotypic plasticity modulate species coexistence across contrasting climatic conditions

Functional traits are expected to modulate plant competitive dynamics. However, how traits and their plasticity in response to contrasting environments connect with the mechanisms determining species coexistence remains poorly understood. Here, we couple field experiments under two contrasting climatic conditions to a plant population model describing competitive dynamics between 10 annual plant species in order to evaluate how 19 functional traits, covering physiological, morphological and reproductive characteristics, are associated with species’ niche and fitness differences. We find a rich diversity of univariate and multidimensional associations, which highlight the primary role of traits related to water- and lightuse- efficiency for modulating the determinants of competitive outcomes. Importantly, such traits and their plasticity promote species coexistence across climatic conditions by enhancing stabilizing niche differences and by generating competitive trade-offs between species. Our study represents a significant advance showing how leading dimensions of plant function connect to the mechanisms determining the maintenance of biodiversity