Structures d’exploitation et exercice de l’activité agricole : continuités, changements ou ruptures ?

Ce numéro est issu des échanges qui se sont tenus lors du colloque organisé par la SFER en février 2015 à Rennes et consacré à l’évolution des structures d’exploitation et des formes d’exercice de l’activité agricole. À l’heure où des changements structurels importants continuent de s’opérer au sein de l’agriculture française, il a semblé utile de prendre le temps de la réflexion pour analyser les tendances à l’œuvre, en étudier les facteurs explicatifs et les conséquences, identifier les élé..

Présentation générale des lésions de deux individus du site de Sainte-Tulle et plus particulièrement d’un cas de SLAC

International audienc

Présentation générale des lésions de deux individus du site de Sainte-Tulle et plus particulièrement d’un cas de SLAC

International audienc

Présentation générale des lésions de deux individus du site de Sainte-Tulle et plus particulièrement d’un cas de SLAC

International audienc

Aerosol/Cloud Measurements Using Coherent Wind Doppler Lidars

The accurate localization and characterization of aerosol and cloud layers is crucial for climate studies (aerosol indirect effect), meteorology (Planetary Boundary Layer PBL height), site monitoring (industrial emissions, mining,…) and natural hazards (thunderstorms, volcanic eruptions). LEOSPHERE has recently developed aerosol/cloud detection and characterization on WINDCUBE long range Coherent Wind Doppler Lidars (CWDL). These new features combine wind and backscatter intensity informations (Carrier-to-Noise Ratio CNR) in order to detect (aerosol/cloud base and top, PBL height) and to characterize atmospheric structures (attenuated backscatter, depolarization ratio). For each aerosol/cloud functionality the method is described, limitations are discussed and examples are given to illustrate the performances

Introduction. Structures d’exploitation et exercice de l’activité agricole : continuités, changements ou ruptures ?

National audienceCe numéro est issu des échanges qui se sont tenus lors du colloque organisé par la SFER en février 2015 à Rennes et consacré à l’évolution des structures d’exploitation et des formes d’exercice de l’activité agricole. A l’heure où des changements structurels importants continuent de s’opérer au sein de l’agriculture française, il a semblé utile de prendre le temps de la réflexion pour analyser les tendances...(...

Introduction. Structures d’exploitation et exercice de l’activité agricole : continuités, changements ou ruptures ?

National audienceCe numéro est issu des échanges qui se sont tenus lors du colloque organisé par la SFER en février 2015 à Rennes et consacré à l’évolution des structures d’exploitation et des formes d’exercice de l’activité agricole. A l’heure où des changements structurels importants continuent de s’opérer au sein de l’agriculture française, il a semblé utile de prendre le temps de la réflexion pour analyser les tendances...(...

Structures d'exploitation et exercice de l'activité agricole: Introduction du dossier

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Piezoelectric tantalum pentoxide studied for optical tunable applications

International audiencePiezoelectric transparent thin films are of great interest for use in tunable filters. We present experimental results on Ta2O5 single layers coated on fused-silica substrates with an electron-beam deposition process. Above 450 °C, coatings change from an amorphous to a polycrystallized structure. When this structure shows a preferred orientation matching the piezoelectric tensor of the Ta2O5 crystal and the external electric field, variation in the piezoelectric layer thickness is expected. We detail experimental results in terms of optical (spectrophotometric and scattering measurements) and nonoptical characterizations (x-ray diffraction and scanning electron microscopy). Then the resultant thickness variation under oscillating applied voltage is measured with an extrinsic Fabry-Perot interferometer setup

The within-population variability of leaf spring and autumn phenology is influenced by temperature in temperate deciduous trees

Leaf phenology is a major driver of ecosystem functioning in temperate forests and a robust indicator of climate change. Both the inter-annual and inter-population variability of leaf phenology have received much attention in the literature; in contrast, the within-population variability of leaf phenology has been far less studied. Beyond its impact on individual tree physiological processes, the within-population variability of leaf phenology can affect the estimation of the average budburst or leaf senescence dates at the population scale. Here, we monitored the progress of spring and autumn leaf phenology over 14 tree populations (9 tree species) in six European forests over the period of 2011 to 2018 (yielding 16 site-years of data for spring, 14 for autumn). We monitored 27 to 512 (with a median of 62) individuals per population. We quantified the within-population variability of leaf phenology as the standard deviation of the distribution of individual dates of budburst or leaf senescence (SDBBi and SDLSi, respectively). Given the natural variability of phenological dates occurring in our tree populations, we estimated from the data that a minimum sample size of 28 (resp. 23) individuals, are required to estimate SDBBi (resp. SDLSi) with a precision of 3 (resp. 7) days. The within-population of leaf senescence (average SDLSi = 8.5 days) was on average two times larger than for budburst (average SDBBi = 4.0 days). We evidenced that warmer temperature during the budburst period and a late average budburst date were associated with a lower SDBBi, as a result of a quicker spread of budburst in tree populations, with a strong species effect. Regarding autumn phenology, we observed that later senescence and warm temperatures during the senescence period were linked with a high SDLSi, with a strong species effect. The shares of variance explained by our models were modest suggesting that other factors likely influence the within-population variation in leaf phenology. For instance, a detailed analysis revealed that summer temperatures were negatively correlated with a lower SDLSi