Is sensitivity to xylem cavitation a relevant physiological trait for fodder production in dry season?

In the Sahel parklands, trees can provide fodder during the dry season if they keep functional foliage. In such conditions, the xylem vessels sustain high tension which can induce cavitation, decrease the conduction of sap and lead to branch mortality. Therefore, xylem resistance to cavitation is a good index of tree tolerance to water stress. However, information about this parameter remains scarce in Sahel tree species. Moreover, its measurement is difficult and requires equipment limiting its feasibility in field conditions. To measure the vulnerability to xylem cavitation in 10 tree species with fodder potential in North Senegal and to assess if this ecophysiological trait can be correlated to morphological traits that are easier to measures: wood density, xylem anatomy, and vessel length. Branch samples were collected in parklands in Louga region, Northern Senegal. Wood density and xylem anatomy were determined. Branch sections were wrapped to keep wet and sent to France within 1 week. The Cavitron spinning technique was used to construct cavitation vulnerability curves and to compute the P50 (water potential inducing 50 % loss of conductivity). Vessel length was assessed by flushing air at low pressure through gradually shortened branch sections. The Cavitron spinning technique was not relevant on nine out of ten species. Most vulnerability curves had a sharp increase in loss of conductivity, starting at low water stress. The resulting P50 which were not consistent with water potential measured in the field. All this species but Tamarindus indica had xylem elements longer than the device rotor. They were severed during measurement, inducing artificial loss of conductivity. Only Boscia senegalensis showed correct curves, and revealed very resistant to cavitation (P50 = ?7.9 Mpa). Wood densities ranged between 0.41 - Adansonia digitata - to 0.71 - Acacia tortilis. P50 estimated from these densities were between - 2 and - 6 MPa. Vulnerability to xylem cavitation could not be assessed by the spinning technique 'Cavitron', due to long xylem vessels elements in most the species. The probable low vulnerabilities estimated from high wood densities could be corroborated by xylem anatomy. (Texte intégral

Crosstalk Statistics via Collocation Method

A probabilistic model for the evaluation of transmission lines crosstalk is proposed. The geometrical parameters are assumed to be unknown and the exact solution is decomposed into two functions, one depending solely on the random parameters and the other on the frequency. The stochastic collocation method is used to estimate the crosstalk statistical moments. The results are obtained from a limited number of carefully-chosen values of the random geometrical parameters. The estimated statistical moments are then used to build the probability density function of the crosstalk parameters. A Monte Carlo validation demonstrates the accuracy and efficiency of the advocated method.\ud \u

A remote sensing based approach for optimizing sampling strategies in tree monitoring and agroforestry systems mapping

Characterizing agroforestry systems (AFS) at landscape scale is of a great importance for development planning at regional scale in Africa. Therefore, the major constraint to effective AFS mapping with remote sensing is the high diversity within landscapes. To have a robust and representative sample of training data, this study proposes an optimized sampling strategy guided by the AFS functioning and allowing to take into account the landscape diversity. A simple and reproducible approach based on unsupervised classification of remote sensing data and an a priori knowledge on the environment functioning is developed. The study is conducted on AFS of the Senegalese Peanut Basin. Assuming that AFS landscapes with similar trees and crop cover composition will have similar phenological development, a multiresolution segmentation was performed on Sentinel-2 NDVI time series to obtain homogeneous landscape units. Then for each unit, landscape diversity proxies were derived from various geospatial data sources, namely vegetation productivity and its temporal dynamic, actual evapotranspiration, woody cover rates and soil type. Using a hierarchical clustering, four classes of typical unit of the landscape heterogeneity gradient were obtained. On this basis an optimized sampling plan was produced and used to carry out an inventory campaign of tree biodiversity (figure). The results showed a well-defined landscape diversity gradient, confirmed by the field inventory of tree species

Tamarind (Tamarindus indica L.) parkland mycorrhizal potential within three agro-ecological zones of Senegal

Introduction. Tamarind (Tamarindus indica L.) belongs to the Fabaceae family; it is a multipurpose tree with slow growth. In order to help improve its growth and development, we assessed mycorrhizal diversity of tamarind parklands in Senegal. Materials and methods. Three sites of tamarind populations were sampled for each agro-ecological zone in Senegal: the Sahelian zone (i), Sahelo-Sudan zone (ii) and Sudan zone (iii). Soil and root samples were collected in each site and used for arbuscular mycorrhizal (AM) spore isolation and root colonization assessment. We identified the mycorrhizal fungi from spore collections and evaluated the root mycorrhization rate, defined as percentage of roots colonized according to agro-ecological zones. Results and discussion. The results did not reveal a specific AM fungal strain associated with tamarind plants. Three arbuscular mycorrhizal fungi (AMF) were identified from spores on the genus level: Glomus, Scutellospora and Acaulospora. Tamarind sites with sandy soil texture (70-90%) and located in dry areas (Sahel and Sudano-Sahel zones) were shown to be rich in mycorrhizal propagules. High densities of soil AM propagules evaluated with the Most Probable Number method (MPN) were found in Niokhoul (1100 propagules per 50 g of soil), Sakal (790 propagules per 50 g of soil) and Mbassis (780 propagules per 50 g of soil). However, higher mycorrhizal colonization (11%) was observed in the Sahel agro-ecological zone compared with the Sudano-Sahelian and Sahelian zones (3%) of Senegal. Conclusion. Our study explored natural AMF diversity as a starting point to develop inocula to be used in commercial nursery production of tamarinds

Versatile surrogate models for IC buffers

In previous papers [1,2] the authors have investigated the use of Volterra series in the identification of IC buffer macro-models. While the approach benefited from some of the inherent qualities of Volterra series it preserved the two-state paradigm of earlier methods (see [3] and its references) and was thus limited in its versatility. In the current paper the authors tackle the challenge of going beyond an application or device-oriented approach and build versatile surrogate models that mimic the behavior of IC buffers over a wide frequency band and for a variety of loads thus achieving an unprecedented degree of generality. This requires the use of a more general system identification paradig

Rapport Annuel de PerformanceActivité de l’USAID/CINSERE (1er avril-30 septembre 2016)

Ce rapport resume les activités meneées par les projet USAID/CINSERE d'avril à Septembre 2016. CINSERE est un projet de trois (3) ans (2016-2019) financé par l'USAID/Sénégal et mis en œuvre par l'ICRISAT/CCAFS en collaboration avec ANACIM. USAID/CINSERE vise à accroître l'accès et l'utilisation des services d'information climatique (SIC) pour encourager une meilleure prise de décision face aux changements climatiques et à la variabilité du climat. Les principaux bénéficiaires de l'USAID/CINSERE sont des acteurs qui vivent dans la zone d’intervention de l'USAID/Naatal Mbay, USAID/COMFISH, l'USAID/Yaajeende et de l'USAID/ERA. Ces quatre projets ont investi des ressources importantes dans la création et le renforcement des groupes d'agriculteurs et de pêcheurs artisanaux, et les institutions concernées. L'objectif de l'USAID/CINSERE est d'accroître la résilience et la productivité des communautés d’agriculteurs, pêcheurs artisanaux et éleveurs sénégalais ciblés, hommes et femmes, dans la zone d’intervention du FtF, en matière de la variabilité et le changement du climat, à travers l'amélioration de la fourniture, la communication et l'utilisation des services d’information climatiques. Cet objectif sera atteint à travers (i) le renforcement des capacités au niveau national dans la production, fourniture et l'utilisation de SIC et (ii) l'élaboration d'un cadre durable pour la vulgarisation et l’utilisation à grande échelle des SIC