Search

In order to understand the ecophysiology of sub-Sahelian tree species and to optimize their use in agroforestry, studies on tree root distribution are essential. The aim of this study was to investigate the root distribution of three sub-Sahelian tree species, Adansonia digitata, Faidherbia albida and Borassus akeassii, in three sites along a precipitation and soil gradient in Senegal. Root density maps observed on trench walls and soil-coring methods were used to characterize variations in root density of mature trees. Coarse and fine root distribution was strongly influenced by the site conditions, with root density being highest in the humid site for all tree species. B. akeassii had the highest root density compared to the other two species. Fine root biomass was concentrated in the 0–30 cm soil layer for A. digitata and from 30 to 60 cm for B. akeassii and F. albida. Laterally, the fine root biomass decreased substantially with increasing distance from the trees. Understanding the root distribution of sub-Sahelian tree species across climatic conditions could help to reduce competition between crops and perennials in agroforestry parklands.

The recent expansion of Aedes albopictus across continents in both tropical and temperate regions and the exponential growth of dengue cases over the past 50 years represent a significant risk to human health. Although climate change is not the only factor responsible for the increase and spread of dengue cases worldwide, it might increase the risk of disease transmission at global and regional scale. Here we show that regional and local variations in climate can induce differential impacts on the abundance of Ae. albopictus. We use the instructive example of Réunion Island with its varied climatic and environmental conditions and benefiting from the availability of meteorological, climatic, entomological and epidemiological data. Temperature and precipitation data based on regional climate model simulations (3 km × 3 km) are used as inputs to a mosquito population model for three different climate emission scenarios. Our objective is to study the impact of climate change on the life cycle dynamics of Ae. albopictus in the 2070–2100 time horizon. Our results show the joint influence of temperature and precipitation on Ae. albopictus abundance as a function of elevation and geographical subregion. At low-elevations areas, decreasing precipitation is expected to have a negative impact on environmental carrying capacity and, consequently, on Ae. albopictus abundance. At mid- and high-elevations, decreasing precipitation is expected to be counterbalanced by a significant warming, leading to faster development rates at all life stages, and consequently increasing the abundance of this important dengue vector in 2070–2100.

Aim: Elevational gradients are a useful approach to evaluate how environmental factors affect animal diversity. Decades of studies on the elevation-diversity gradient have revealed that this gradient varies greatly with taxa and geographic regions. One potential explanation for this may be the dependence of the relationship on landscape features. We explore the impact of fragmentation, habitat diversity and habitat amount on insect diversity (alpha and beta) and abundance along elevational gradients. We hypothesize that insect diversity and abundance will relate negatively with elevation, but positively with these landscape features. We also hypothesize that landscape features will interact in a way that the positive effect of a given variable on insect diversity may be offset by the others. Location: Reunion Island (Indian Ocean). Taxon: The insect order thrips (Thysanoptera). Methods: Insects were sampled along replicated elevational gradients, and at each sampling plot landscape features and abiotic variables were estimated within buffers surrounding the site. Insect alpha diversity was estimated using abundance-based rarefaction methods, whereas beta diversity was estimated calculating the "Local contributions to beta diversity" metric. The effect of elevation, rainfall, landscape features and their interactions was assessed on insect alpha and beta diversity and abundance during two consecutive seasons using linear mixed effects models. Results: We found that thrips alpha and beta diversity was negatively related with elevation, but the relationship varied between seasons and rainfall regimes. Among the different landscape features considered, we found that habitat amount had the strongest effect on diversity. The effect of habitat amount on diversity, however, was offset in areas of low habitat (or land cover) diversity. Main conclusions: Generalizing the factors that underlie the elevation diversity gradient has become a cornerstone in ecological theory because it can help to understand the impact of human activities on diversity. Here we show that taking landscape information into account may help to fulfil this objective because landscape effects co-vary with elevation with often intricate consequences for diversity.

Major drivers of gains or losses in soil organic carbon (SOC) include land management, land-use change, and climate change. Thousands of original studies have focused on these drivers of SOC change and are now compiled in a growing number of meta-analyses. To critically assess the research efforts in this domain, we retrieved and characterized 192 meta-analyses of SOC stocks or concentrations. These meta-analyses comprise more than 13,200 original studies conducted from 1910 to 2020 in 150 countries. First, we show that, despite a growing number of studies over time, the geographical coverage of studies is limited. For example, the effect of land management, land-use change, and climate change on SOC has been only occasionally studied in North and Central Africa, and in the Middle East and Central Asia. Second, the meta-analyses investigated a limited number of land management practices, mostly mineral fertilization, organic amendments, and tillage. Third, the meta-analyses demonstrated relatively low quality and transparency. Lastly, we discuss the mismatch between the increasing number of studies and the need for more local, reusable, and diversified knowledge on how to preserve high SOC stocks or restore depleted SOC stocks.

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden.

Faidherbia albida et Balanites aegyptiaca sont deux espèces caractéristiques et emblématiques de la zone semi-aride tchadienne. Elles revêtent une grande importance socio-économique dans toutes leurs zones naturelles de répartition du fait de leurs multiples usages. La présente étude de nature exploratoire a consisté à comprendre le déterminisme des variations des caractéristiques du bois des deux espèces en relation avec leurs variations de conditions de croissance. Sa finalité est de mieux connaitre l'hétérogénéité de comportement technologique des bois de ces deux espèces afin de mieux les valoriser dans les processus de reboisement et d'élargir leur domaine d'utilisation locale. L'étude a été réalisée selon deux approches. La première a consisté à déterminer par des méthodes conventionnelles et normalisées une sélection de caractéristiques physiques, mécaniques et chimiques des bois prélevés dans deux zones climatiques tchadiennes (zone sahélienne et zone soudanienne) et une zone climatique sénégalaise (zone sahélienne), et à étudier leurs variations en fonction des conditions de croissance liées essentiellement aux différences climatiques. La seconde a consisté à étudier les variations radiales de caractéristiques physiques, mécaniques, et de la composition isotopique de carbone 13 (δ13C), ceci en fonction de la croissance des arbres, par des mesures réalisées sur des micro-échantillons prélevés au niveau des cernes. Les résultats du premier volet de l'étude ont mis en évidence pour les deux espèces des tendances variables pour toutes les caractéristiques étudiées. Pour Faidherbia albida, l'infradensité, la masse volumique, les retraits de séchage et les trois caractéristiques mécaniques étudiées sont significativement plus élevés dans la zone sahélienne sénégalaise que dans les deux provenances tchadiennes. Cette même tendance est observée pour les taux d'extractibles et de lignine, mais les taux de cellulose et d'hémicellulose sont significativement plus élevés dans la zone sahélienne tchadienne. Pour Balanites aegyptiaca, les tendances sont variables suivant les propriétés, avec un effet inverse des provenances pour le retrait tangentiel et le retrait radial, et aucune tendance marquée pour le retrait volumique. Le point de saturation des fibres est faible pour les trois provenances (inférieur à 25 %). En zone soudanienne tchadienne, la masse volumique est significativement plus élevée que dans les deux autres zones, alors que la contrainte de rupture en compression et le module d'élasticité longitudinal sont moins élevés. Les taux de lignine et d'hémicellulose sont plus élevés en zone sahélienne tchadienne. Une analyse des extractibles par GC-MS a mis en évidence des différences marquées entre les deux espèces d'une part et les trois provenances d'autre part. Ces différences pourraient être mises en relation avec celles observées entre provenances et espèces pour certaines propriétés physiques et mécaniques du bois telles que les retraits de séchage, le PSF, la masse volumique et le module d'élasticité. L'effet de chaque extractible sur ces propriétés resterait cependant à établir, en tenant compte des probables impacts conjugués de ces différents composés. Le second volet de l'étude a montré que l'accroissement moyen était légèrement supérieur en zone soudanienne qu'en zone sahélienne ce qui reflète les différences de conditions climatiques qui impactent la croissance des arbres. Pour Faidherbia albida, l'absence de différence significative de δ13C entre les deux provenances peut s'expliquer par le fait que cette espèce est une phréatophyte. Pour Balanites aegyptiaca, le δ13C moyen dans la zone sahélienne est significativement inférieur à celui de la zone soudanienne, tendance inverse à celle à laquelle on pouvait s'attendre. Ce résultat tend à montrer que cette espèce présente une bonne efficacité et une bonne stratégie opportuniste d'utilisation de l'eau. L'étude des relations entre les variables prises deux à deux a donné des résultats contrastés. L'absence de relation entre la largeur de cerne et la pluviométrie peut être liée à plusieurs causes : pluviométrie sur les sites de prélèvement des bois différente de celle de la station météorologique éloignée de ces sites, comportement phréatophile avéré de Faidherbia albida et possible pour Balanites aegyptiaca, et délimitation incertaine des cernes liée à leur structure. Les perspectives de recherche à venir sur les deux espèces sont multiples, et concernent aussi bien le protocole d'échantillonnage (utilisation de branches au lieu de troncs), l'étude des rythmes de croissance afin de comprendre le phénomène de disparition/fusion partielle des cernes, que l'élargissement de l'étude à d'autres provenances.

International audience; The rice industry plays an important role in the agricultural economy of Colombia and its success dependents largely on weather conditions. Rice farmers, policymakers and other stakeholders thus need to understand and manage the risks associated with climate variability, including those related to El Nino Southern Oscillation (ENSO) - the most important source of variability affecting Colombian climates. The objectives of this study were to (1) assess the ENSO influence on the spatio-temporal variability of agro-climatic conditions (crop water requirements, dry and wet spells, and heatwaves) and rice yield across the central producing region of Colombia; and (2) identify the main agro-climatic factors driving crop yield variability. Results showed that rice irrigation water requirements under positive ENSO phases (El Nino) increased by up to 14% compared to the long-term average. These increases were associated with less total precipitation, more dry days and longer dry spells, together with a greater number of day-and-night heatwave episodes. During negative phases (La Nina), on the other hand, irrigation requirements decreased by 16% with respect to the long-term average due to longer and more frequent wet spells, and more total precipitation. Analyses of simulated yields indicated that El Nino years reduce crop yield in about 86% of the study region, while La Nina affects 62% of the region positively. The number of heat nights (i.e. nights with minimum temperature > 23 degrees C) during the growing season was the most important agro-climatic factor causing yield losses during ENSO events. Our results represent an important step towards understanding the interaction between climate variability and rice production in Colombia, which is useful for improving climate risk management at local levels.

International audience; In this study, we present an operational methodology for mapping irrigated areas at plot scale, which overcomes the limitation of terrain data availability, using Sentinel-1 (S1) C-band SAR (synthetic-aperture radar) and Sentinel-2 (S2) optical time series. The method was performed over a study site located near Orléans city of north-central France for four years (2017 until 2020). First, training data of irrigated and non-irrigated plots were selected using predefined selection criteria to obtain sufficient samples of irrigated and non-irrigated plots each year. The training data selection criteria is based on two irrigation metrics; the first one is a SAR-based metric derived from the S1 time series and the second is an optical-based metric derived from the NDVI (normalized difference vegetation index) time series of the S2 data. Using the newly developed irrigation event detection model (IEDM) applied for all S1 time series in VV (Vertical-Vertical) and VH (Vertical-Horizontal) polarizations, an irrigation weight metric was calculated for each plot. Using the NDVI time series, the maximum NDVI value achieved in the crop cycle was considered as a second selection metric. By fixing threshold values for both metrics, a dataset of irrigated and non-irrigated samples was constructed each year. Later, a random forest classifier (RF) was built for each year in order to map the summer agricultural plots into irrigated/non-irrigated. The irrigation classification model uses the S1 and NDVI time series calculated over the selected training plots. Finally, the proposed irrigation classifier was validated using real in situ data collected each year. The results show that, using the proposed classification procedure, the overall accuracy for the irrigation classification reaches 84.3%, 93.0%, 81.8%, and 72.8% for the years 2020, 2019, 2018, and 2017, respectively. The comparison between our proposed classification approach and the RF classifier built directly from in situ data showed that our approach reaches an accuracy nearly similar to that obtained using in situ RF classifiers with a difference in overall accuracy not exceeding 6.2%. The analysis of the obtained classification accuracies of the proposed method with precipitation data revealed that years with higher rainfall amounts during the summer crop-growing season (irrigation period) had lower overall accuracy (72.8% for 2017) whereas years encountering a drier summer had very good accuracy (93.0% for 2019).

Bacterial panicle blight (BPB) caused by Burkholderia glumae is one of the main concerns for rice production in the Americas since bacterial infection can interfere with the grain-filling process and under severe conditions can result in high sterility. B. glumae has been detected in several rice-growing areas of Colombia and other countries of Central and Andean regions in Latin America, although evidence of its involvement in decreasing yield under these conditions is lacking. Analysis of different parameters in trials established in three rice-growing areas showed that, despite BPB presence, severity did not explain the sterility observed in fields. PCR tests for B. glumae confirmed low infection in all sites and genotypes, only 21.4% of the analyzed samples were positive for B. glumae. Climate parameters showed that Montería and Saldaña registered maximum temperature above 34°C, minimum temperature above 23°C, and Relative Humidity above 80%, conditions that favor the invasion model described for this pathogen in Asia. Our study found that in Colombia, minimum temperature above 23°C during 10 days after flowering is the condition that correlates with disease incidence. Therefore, this correlation, and the fact that Montería and Saldaña had a higher level of infected samples according to PCR tests, high minimum temperature, but not maximum temperature, seems to be determinant for B. glumae colonization under studied field conditions. This knowledge is a solid base line to design strategies for disease control, and is also a key element for breeders to develop strategies aimed to decrease the effect of B. glumae and high night-temperature on rice yield under tropical conditions.

This work is dedicated to Serge Quilici who has been leading prolific research on the tephritids of Reunion his whole career. This article has been reviewed and recommended by Peer Community in Ecology, https://doi.org/10.24072/pci.ecology.100080. The peer review history for this article is available at https://publo ns.com /publo n/10.1111/ele.13825.; International audience; The relative importance of ecological factors and species interactions for shaping species distributions is still debated. The realised niches of eight sympatric tephritid fruit flies were inferred from field abundance data using joint species distribution modelling and network inference, on the whole community and separately on three host plant groups. These estimates were then confronted the fundamental niches of seven fly species estimated through laboratory-measured fitnesses on host plants. Species abundances depended on host plants, followed by climatic factors, with a dose of competition between species sharing host plants. The relative importance of these factors mildly changed among the three host plant groups. Despite overlapping fundamental niches, specialists and generalists had almost distinct realised niches, with possible competitive exclusion of generalists by specialists on Cucurbitaceae. They had different assembly rules: Specialists were mainly influenced by their adaptation to host plants, while generalist abundances varied regardless of their fundamental host use.

Meeting food demand for the growing population will require an increase to crop production despite climate changes and, more particularly, severe drought episodes. Sorghum is one of the cereals most adapted to drought that feed millions of people around the world. Valorizing its genetic diversity for crop improvement can benefit from extensive phenotyping. The current methods to evaluate plant biomass, leaves area and plants height involve destructive sampling and are not practical in breeding. Phenotyping relying on drone based imagery is a powerful approach in this context. The objective of this study was to develop and validate a high throughput field phenotyping method of sorghum growth traits under contrasted water conditions relying on drone based imagery. Experiments were conducted in Bambey (Senegal) in 2018 and 2019, to test the ability of multi-spectral sensing technologies on-board a UAV platform to calculate various vegetation indices to estimate plants characteristics. In total, ten (10) contrasted varieties of West African sorghum collection were selected and arranged in a randomized complete block design with three (3) replicates and two (2) water treatments (well-watered and drought stress). This study focused on plant biomass, leaf area index (LAI) and the plant height that were measured weekly from emergence to maturity. Drone flights were performed just before each destructive sampling and images were taken by multi-spectral and visible cameras. UAV-derived vegetation indices exhibited their capacity of estimating LAI and biomass in the 2018 calibration data set, in particular: normalized difference vegetative index (NDVI), corrected transformed vegetation index (CTVI), seconded modified soil-adjusted vegetation index (MSAVI2), green normalize difference vegetation index (GNDVI), and simple ratio (SR) (r2 of 0.8 and 0.6 for LAI and biomass, respectively). Developed models were validated with 2019 data, showing a good performance (r2 of 0.92 and 0.91 for LAI and biomass accordingly). Results were also promising regarding plant height estimation (RMSE = 9.88 cm). Regression plots between the image-based estimation and the measured plant height showed a r2 of 0.83. The validation results were similar between water treatments. This study is the first successful application of drone based imagery for phenotyping sorghum growth and development in a West African context characterized by severe drought occurrence. The developed approach could be used as a decision support tool for breeding programs and as a tool to increase the throughput of sorghum genetic diversity characterization for adaptive traits.

Dacryodes edulis (G. Don) H.J. Lam is an underexploited oil-bearing fruit tree highly appreciated in the Central Africa rainforest. To improve horticultural management and provide relevant data to scientists for physiological studies, the reproductive phenology of D. edulis as well as their fruit (safou) development and ripening indexes has been defined and correlated to climatic conditions. Changes in safou were assessed in four production localities in Cameroon. Fruit-set-to-ripening time was evaluated over 2 consecutive production years. Four fruits developmental and ripening stages and their durations were determined as follows: The putative cell division (1–2 weeks); putative elongation (10–14 weeks); pre-ripening (2–7 weeks); and ripening phases (3–5 weeks). Rainfall, average, and cumulative temperatures were found to be correlated with the chronology of reproductive phenophases. The average temperature during the period ranging from the floral bud emergence to the fruit set can be used to predict the thermal time. Similarly, the average ambient temperature during the period from floral bud emergence to anthesis can help to determine the temperature to be cumulated during the ripening phase. These findings are considerable contributions that could help producers to enhance the industrial management of safou sector, reduce fruit perishability, and better control their harvesting time.

International audience; Rubber powdery mildew disease (Oidium heveae) is a serious threat to natural rubber production (Hevea brasiliensis) in some rubber developing regions of the world. Both phenological- and meteorological-related factors have been reported influencing the powdery mildew disease. However, few studies have investigated the effects of both phenological- and meteorological-related factors on the disease. The objective of this study is to quantify the contributions of phenological- and meteorological-related factors to affect the disease. We used the partial least squares (PLS) regression method to comprehensively quantify the effects of thirty-five phenological related factors and six meteorological factors on the infection level of powdery mildew of rubber trees over 9-year records (2003–2011). The relative contributions of significant factors were further investigated by the variation partition analysis. We found that the most influential variables were the mean temperature during winter and the duration of leaf development to maturation which explained 32 and 26% of the variations in the infection level. We found the controlling role of winter mean temperature, for the first time, on the infection level of powdery mildew. The controlling role of winter temperature may have directly increase the infection level when winter temperature is high and indirectly increase the infection level through prolonging the duration of leaf development to maturation, although the duration itself had smaller influences. We detected a warming trend of the winter temperatures from 2003 to 2011, which indicates that the infection level of powdery mildew will be increased if the winter warming continues.

International audience; It is commonly accepted that species should move toward higher elevations and latitudes to track shifting isotherms as climate warms. However, temperature might not be the only limiting factor determining species distribution. Species might move to opposite directions to track changes in other climatic variables. Here, we used an extensive occurrence data set and an ensemble modelling approach to model the climatic niche and to predict the distribution of the seven baobab species (genus Adansonia) present in Madagascar. Using climatic projections from three global circulation models, we predicted species’ future distribution and extinction risk for 2055 and 2085 under two representative concentration pathways (RCPs) and two dispersal scenarios. We disentangled the role of each climatic variable in explaining species range shift looking at relative variable importance and future climatic anomalies. Four baobab species (Adansonia rubrostipa, Adansonia madagascariensis, Adansonia perrieri¸ and Adansonia suarezensis) could experience a severe range contraction in the future (>70% for year 2085 under RCP 8.5, assuming a zero-dispersal hypothesis). For three out of the four threatened species, range contraction was mainly explained by an increase in temperature seasonality, especially in the North of Madagascar, where they are currently distributed. In tropical regions, where species are commonly adapted to low seasonality, we found that temperature seasonality will generally increase. It is, thus, very likely that many species in the tropics will be forced to move equatorward to avoid an increase in temperature seasonality. Yet, several ecological (e.g., equatorial limit, or unsuitable deforested habitat) or geographical barriers (absence of lands) could prevent species to move equatorward, thus increasing the extinction risk of many tropical species, like endemic baobab species in Madagascar.

Climate change is already affecting agro-ecosystems and threatening food security by reducing crop productivity and increasing harvest uncertainty. Mobilizing crop diversity could be an efficient way to mitigate its impact. We test this hypothesis in pearl millet, a nutritious staple cereal cultivated in arid and low-fertility soils in sub-Saharan Africa. We analyze the genomic diversity of 173 landraces collected in West Africa together with an extensive climate dataset composed of metrics of agronomic importance. Mapping the pearl millet genomic vulnerability at the 2050 horizon based on the current genomic-climate relationships, we identify the northern edge of the current areas of cultivation of both early and late flowering varieties as being the most vulnerable to climate change. We predict that the most vulnerable areas will benefit from using landraces that already grow in equivalent climate conditions today. However, such seed-exchange scenarios will require long distance and trans-frontier assisted migrations. Leveraging genetic diversity as a climate mitigation strategy in West Africa will thus require regional collaboration., Replacement of local crops with alternative varieties adapted to future conditions may improve food security under climate change. Here the authors apply landscape genomics and ensemble climate modelling to pearl millet in West Africa, supporting the potential of transfrontier assisted seed exchange.

Mango is one of the most economically important fruit crop in the north of Côte d’Ivoire. However, its production and productivity are limited by various biotic and abiotic factors. Amongst fungal disease, mango anthracnose is recorded to be the most important disease in the northern districts. This study assessed the incidence and severity of pre- and post-harvest anthracnose to compare the level of orchard infestation in the seven mango producing districts in the north of Côte d’Ivoire. Anthracnose disease incidence and severity varied from locality to locality both in dry and rainy season. Disease intensity was higher in rainy season than dry season. In dry and rainy seasons, the highest disease incidence (19.08% and 32.25%) was recorded in Bèrèdougou and the least in Zèguèrè. Pre and post-harvest anthracnose correlated significantly indicating that infection initiated in field and remained latent until fruits repining. The disease was also more severe on fruits than leaves. On fruits disease incidence and severity were higher in Dianra village (90% and 100%) and Bèrèdougou (36% and 40%). The lowest disease incidence (7.5%) and severity (1.5%) on fruits were observed in Zèguèrè. This study showed that anthracnose disease is one the most important threat to production and marketing of fresh mango fruits in the north of Côte d’Ivoire.Keywords: Anthracnose, incidence, severity, mango, symptoms.

This chapter focuses on protected cultivation (PC), defined as the protection of crops against adverse climatic and biological factors using physical means. As natural resources become scarcer, farm inputs become more expensive and consumers more attentive to the sanitary and nutritious aspects of food produced, PC has become one promising yet improvable way to address these challenges. As the global demand for high value crops, such as vegetables, increases, PC appears an opportunity for farmers to increase their income, improve their working conditions and secure their production, thereby attracting youth to enter the crucial but aging farming sector. In Sub-Saharan Africa, farmers constantly face the threat of losing their crops due to pests, diseases or harsh climatic conditions, with no insurance to cover their loss. A case study, comparing PC of tomatoes in Benin and Tanzania, showed that PC is profitable despite high initial investments, provided there is a market for high quality produce. Favourable policies, farmers' training and agronomic research are prerequisites to the adoption and development of PC technologies and techniques in Sub-Saharan Africa. PC has the potential to enhance bioeconomy in the region and at the same time achieve some of the SDGs.

Understanding evapotranspiration and its long-term trends is essential for water cycle studies, modeling and for water uses. Spatial and temporal analysis of evapotranspiration is therefore important for the management of water resources, particularly in the context of climate change. The objective of this study is to analyze the trend of reference evapotranspiration (ET0) as well as its sensitivity to climatic variables in the Senegal River basin. Mann-Kendall&rsquo, s test and Sen&rsquo, s slope were used to detect trends and amplitude changes in ET0 and climatic variables that most influence ET0. Results show a significant increase in annual ET0 for 32% of the watershed area over the 1984&ndash, 2017 period. A significant decrease in annual ET0 is observed for less than 1% of the basin area, mainly in the Sahelian zone. On a seasonal scale, ET0 increases significantly for 32% of the basin area during the dry season and decreases significantly for 4% of the basin during the rainy season. Annual maximum, minimum temperatures and relative humidity increase significantly for 68%, 81% and 37% of the basin, respectively. However, a significant decrease in wind speed is noted in the Sahelian part of the basin. The wind speed decrease and relative humidity increase lead to the decrease in ET0 and highlight a &ldquo, paradox of evaporation&rdquo, in the Sahelian part of the Senegal River basin. Sensitivity analysis reveals that, in the Senegal River basin, ET0 is more sensitive to relative humidity, maximum temperature and solar radiation.

International audience; Understanding the processes driving plant phenology is crucial for assessing how shifts in climate affect plant productivity and species’ distribution. Despite the key role of fine roots in carbon and nutrient cycling, root phenology is less well characterized than shoot phenology, due largely to methodological problems when measuring root systems at depths > 1.0 m. Fine root demography is also poorly related to the better established patterns of aboveground primary and secondary growth. We examined the influence of climatic factors on the dynamics of fine root elongation rate (RER), to a depth of 4.7 m, and assessed relationships with shoot phenology of walnut trees (Juglans nigra × J. regia) in a Mediterranean agroforestry system. Rhizotrons and minirhizotrons were installed for 21 months to monitor RER. Dendrometers were used to measure trunk and lateral root radial growth during the same period. Results showed that RER was not synchronous with budbreak and leaf unfolding (occurring from April to May) at any soil depth. However, during phase 2 of the growing season (June–November), daily RER in the upper soil (0.00–1.70 m) was synchronous with both trunk and lateral root radial growth, which were themselves positively correlated with the mean monthly soil and air temperatures and the mean monthly solar irradiance. Mean daily RER was not correlated to mean monthly soil and air temperatures at any soil depth during phase 2 of the growing season. However, during this period, mean daily RER of very shallow roots (0.00–0.85 m) was significantly and positively correlated with both mean monthly soil water content and solar irradiance. Maximal daily RER occurred during phase 2 of the growing season for the three upper soil layers (June–October), but peaked during the aerial dormant season (December) in the deepest soil layer (4.00–4.70 m). We conclude that drivers of phenology for different tree organs and between shallow and deep roots are not the same. This spatial plasticity in growth throughout a tree enables it to maximize resource uptake, even throughout the winter months, and thus is a highly useful mechanism for increasing tree resistance to abiotic stresses.

This study set out to determine which environmental factors of growth and silvicultural practices can affect the properties of Eucalyptus robusta coppice wood and also to study variability in those properties depending on the factors. Hundred and thirty-five coppice logs aged 2 to 10 years were collected from five zones in the Highlands of Madagascar. Wood density at 12% moisture content was measured by X-ray microdensitometry. Chemical properties, such as the total extractives, Klason lignin and holocellulose contents were predicted using near infrared spectrometry prediction models. The results significantly showed (p-value

SummaryAlthough several studies have underlined the advantages of using insect-proof nets to improve yields while reducing the use of pesticides, one obstacle to the diffusion of this technique in tropical conditions is the associated increase in temperature in the tunnel. The aim of this work was to assess the interest of combining the physical protection provided by nets against insect pests with the beneficial impacts of using shade nets to grow cabbages. A two-season experiment was set up to compare temperature conditions, insect pest populations, yields, and the quality of cabbage crops grown in the open field and in low tunnels covered with nets providing different degrees of shading, 17.2% by white and 50.1% by silver nets. During the day, the temperature under the white and silver nets was 10.4 °C and 6.3 °C higher, respectively, than in the open field in the first season, and 6.5 °C and 5.9 °C higher in the second season. Both insect-proof nets significantly reduced insect pest populations and hence the need for insecticide treatments. The white nets increased marketable yield by 45.4% in the first season and by 16.4% in the second compared to yields in the open field, whereas silver nets reduced yield by 18.6% and 15.0%, respectively. The reduction in yield under silver nets was attributed to excessive shading that prevented the light requirements of cabbage crops from being fulfilled. Economic analysis raised some concerns about the profitability of the use of netting to grow cabbage due to investment costs and the lack of premium prices for vegetables produced with fewer pesticides in local markets.

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

International audience; Fruit abscission facilitates the optimal conditions and timing of seed dispersal. Environmental regulation of tropical fruit abscission has received little attention, even though climate change may have its strongest impacts in tropical regions. In this study, oil palm fruit abscission was monitored during multiple years in the Benin Republic to take advantage of the climatic seasonality and the continuous fruit production by this species. An innovative multivariable statistical method was used to identify the best predictors of fruit abscission among a set of climate and ecophysiological variables, and the stage of inflorescence and fruit bunch development when the variables are perceived. The effects of climate scenarios on fruit abscission were then predicted based on the calibrated model. We found complex regulation takes place at specific stages of inflorescence and bunch development, even long before the fruit abscission zone is competent to execute abscission. Among the predictors selected, temperature variations during inflorescence and fruit bunch development are major determinants of the fruit abscission process. Furthermore, the timing of ripe fruit drop is determined by temperature in combination with the trophic status. Finally, climate simulations revealed that the abscission process is robust and is more affected by seasonal variations than by extreme scenarios. Our investigations highlighted the central function of the abscission zone as the sensor of environmental signals during reproductive development. Coupling ecophysiological and statistical modeling was an efficient approach to disentangle this complex environmental regulation. K E Y W O R D S climate change, Elaeis guineensis, environmental regulation, fruit abscission, multivariable models