Détermination du Potentiel Pastoral Herbacé dans le Bioclimat Soudanien Nord au Mali : Cas de la Commune Rurale de Dièma

L’élevage contribue environ à 15% du produit intérieur brut de l’ensemble des pays sahéliens de l’Afrique de l’ouest. Au Mali, il est la deuxième activité socioéconomique après l’agriculture. Il est pratiqué de façon extensive avec des mobilités saisonnières des troupeaux à la recherche du disponible fourrager, dans le contexte du changement climatique. Paradoxalement, la production herbacée, dans ces parcours sahéliens, qui équivaut à des milliards de francs, est annuellement consumée par les feux de brousse. C’est dans ce contexte que la présente étude a été initiée pour améliorer la gestion des pâturages naturels dans la commune rurale de Diéma dans la région de Kayes. La méthode de transect a été utilisée dans les parcours naturels suivant les quatre points cardinaux du district de la commune. Les relevés phytoécologiques et des coupes de biomasse herbacée ont été effectués dans les parcelles échantillons. Il a été recensé au total 71 espèces appartenant à 18 familles avec la dominance des Poaceae, Fabaceae et Convolvulaceae. La production de biomasse des parcours est d’environ 3t.ha-1. Une différence significative (P=0,042) a été observée pour la valeur pastorale des parcours et cela en fonction de leur orientation par rapport au District de la Commune.  Pour une meilleure gestion de l’environnement et de production animale, il importe de connaitre les caractéristiques de nos parcours naturels.   Livestock contributes about 15% of the gross domestic product of all the Sahelian countries of West Africa. In Mali, it is the second socioeconomic activity after agriculture. It is practiced extensively with seasonal movements of herds in search of available fodder, in the context of climate change. Paradoxically, the herbaceous production in these Sahelian rangelands, which is equivalent to billions of francs, is consumed annually by bush fires. It is in this context that the present study was initiated to improve the management of natural pastures in the rural commune of Diéma in the Kayes region. The transect method was used in the natural routes following the four cardinal points of the district of the commune. Phytoecological surveys and herbaceous biomass cuts were carried out in the sample plots. 71 species belonging to 18 families have been identified with the dominance of Poaceae, Fabaceae and Convolvulaceae. The biomass production of rangelands is about 3t.ha-1. A significant difference (P=0.042) was observed for the pastoral value of the rangelands and this according to their orientation in relation to the District of the Commune. For better management of the environment and animal production, it is important to know the characteristics of our natural rangelands

Détermination du Potentiel Pastoral Herbacé dans le Bioclimat Soudanien Nord au Mali : Cas de la Commune Rurale de Dièma

L’élevage contribue environ à 15% du produit intérieur brut de l’ensemble des pays sahéliens de l’Afrique de l’ouest. Au Mali, il est la deuxième activité socioéconomique après l’agriculture. Il est pratiqué de façon extensive avec des mobilités saisonnières des troupeaux à la recherche du disponible fourrager, dans le contexte du changement climatique. Paradoxalement, la production herbacée, dans ces parcours sahéliens, qui équivaut à des milliards de francs, est annuellement consumée par les feux de brousse. C’est dans ce contexte que la présente étude a été initiée pour améliorer la gestion des pâturages naturels dans la commune rurale de Diéma dans la région de Kayes. La méthode de transect a été utilisée dans les parcours naturels suivant les quatre points cardinaux du district de la commune. Les relevés phytoécologiques et des coupes de biomasse herbacée ont été effectués dans les parcelles échantillons. Il a été recensé au total 71 espèces appartenant à 18 familles avec la dominance des Poaceae, Fabaceae et Convolvulaceae. La production de biomasse des parcours est d’environ 3t.ha-1. Une différence significative (P=0,042) a été observée pour la valeur pastorale des parcours et cela en fonction de leur orientation par rapport au District de la Commune.  Pour une meilleure gestion de l’environnement et de production animale, il importe de connaitre les caractéristiques de nos parcours naturels.   Livestock contributes about 15% of the gross domestic product of all the Sahelian countries of West Africa. In Mali, it is the second socioeconomic activity after agriculture. It is practiced extensively with seasonal movements of herds in search of available fodder, in the context of climate change. Paradoxically, the herbaceous production in these Sahelian rangelands, which is equivalent to billions of francs, is consumed annually by bush fires. It is in this context that the present study was initiated to improve the management of natural pastures in the rural commune of Diéma in the Kayes region. The transect method was used in the natural routes following the four cardinal points of the district of the commune. Phytoecological surveys and herbaceous biomass cuts were carried out in the sample plots. 71 species belonging to 18 families have been identified with the dominance of Poaceae, Fabaceae and Convolvulaceae. The biomass production of rangelands is about 3t.ha-1. A significant difference (P=0.042) was observed for the pastoral value of the rangelands and this according to their orientation in relation to the District of the Commune. For better management of the environment and animal production, it is important to know the characteristics of our natural rangelands

Interannual variability of photosynthesis across Africa and its attribution

Africa is thought to be a large source of interannual variability in the global carbon cycle, only vaguely attributed to climate fluctuations. This study uses a biophysical model, Simple Biosphere, to examine in detail what specific factors, physiological (acute stress from low soil water, temperature, or low humidity) and biophysical (low vegetation radiation use), are responsible for spatiotemporal patterns of photosynthesis across the African continent during the period 1982-2003. Acute soil water stress emerges as the primary factor driving interannual variability of photosynthesis for most of Africa. Southern savannas and woodlands are a particular hot spot of interannual variability in photosynthesis, owing to high rainfall variability and photosynthetic potential but intermediate annual rainfall. Surprisingly low interannual variability of photosynthesis in much of the Sudano-Sahelian zone derives from relatively low vegetation cover, pronounced humidity stress, and somewhat lower rainfall variability, whereas perennially wet conditions diminish interannual variability in photosynthesis across much of the Congo Basin and coastal West Africa. Though not of focus here, the coefficient of variation in photosynthesis is notably high in drylands and desert margins (i.e., Sahel, Greater Horn, Namib, and Kalahari) having implications for supply of food and fiber. These findings emphasize that when considering impacts of climate change and land surface feedbacks to the atmosphere, it is important to recognize how vegetation, climate, and soil characteristics may conspire to filter or dampen ecosystem responses to hydroclimatic variability. Copyright 2008 by the American Geophysical Union

Détermination du Potentiel Pastoral Herbacé de la Commune Rurale de Dièma dans le Bioclimat Soudanien Nord au Mali

L’élevage contribue à environ 15% du produit intérieur brut de l’ensemble des pays sahéliens de l’Afrique de l’ouest. Au Mali, il est la deuxième activité socioéconomique après l’agriculture. Il est pratiqué de façon extensive avec des mobilités saisonnières des troupeaux à la recherche du disponible fourrager, dans le contexte du changement climatique. Malheureusement, la production herbacée, dans ces parcours sahéliens, qui équivaut à des milliards de francs, est annuellement consumée par les feux de brousse. C’est dans ce contexte que la présente étude a été initiée pour caractériser les pâturages naturels dans la commune rurale de Diéma en vue d’améliorer leur gestion. La méthode de transect a été utilisée dans les parcours naturels suivant les quatre points cardinaux du district de la commune. Les relevés phytoécologiques et des coupes de biomasse herbacée ont été effectués dans les parcelles échantillons. La valeur pastorale des parcours a été calculée. Il a été recensé au total 80 espèces appartenant à 18 familles avec la dominance des Poaceae, des Fabaceae et des Convolvulaceae. La production de biomasse des parcours est d’environ 3tMS.ha-1. Une différence significative (P=0,042) a été observée pour la valeur pastorale avec une moyenne générale de 38,15% entre les orientations. Pour une meilleure gestion de l’environnement et de production animale, il importe de connaitre les caractéristiques de nos parcours naturels.   Livestock contributes about 15% of the gross domestic product of all the Sahelian countries of West Africa. In Mali, it is the second socioeconomic activity after agriculture. It is practiced extensively with seasonal movements of herds in search of available fodder, in the context of climate change. Paradoxically, the herbaceous production in these Sahelian rangelands, whichis equivalent to billions of francs, is consumed annually by bush fires. It is in this context that the present study was initiated to improve the management of natural pastures in the rural commune of Diéma in the Kayes region. The transect method was used in the natural routes following the four cardinal points of the district of the commune. Phytoecological surveys and herbaceous biomass cuts were carried out in the sample plots. 80 species belonging to 18 families have been identified with the dominance of Poaceae, Fabaceae and Convolvulaceae. The biomass production of rangelands is about 3t.ha-1. A significant difference (P=0.042) was observed for the pastoral value of the rangelands and this according to their orientation in relation to the District of the Commune. For better management of the environment and animal production, it is important to know the characteristics of our natural rangelands

Constraints on shrub cover and shrub-shrub competition in a U.S. southwest desert

The cover of woody perennial plants (trees and shrubs) in arid ecosystems is at least partially constrained by water availability. However, the extent to which maximum canopy cover is limited by rainfall and the degree to which soil water holding capacity and topography impacts maximum shrub cover are not well understood. Similar to other deserts in the U.S. southwest, plant communities at the Jomada Basin Long-Term Ecological Research site in the northern Chihuahuan Desert have experienced a long-term state change from perennial grassland to shrubland dominated by woody plants. To better understand this transformation, and the environmental controls and constraints on shrub cover, we created a shrub cover map using high spatial resolution images and explored how maximum shrub cover varies with landform, water availability, and soil characteristics. Our results indicate that when clay content is below similar to 18%, the upper limit of shrub cover is positively correlated with plant available water as mediated by surface soil clay influence on water retention. At surface soil day contents >18%, maximum shrub cover decreases, presumably because the amount of water percolating to depths preferentially used by deep-rooted shrubs is diminished. In addition, the relationship between shrub cover and density suggests that self-thinning occurs in denser stands in most landforms of the Jomada Basin, indicating that shrub-shrub competition interacts with soil properties to constrain maximum shrub cover in the northern Chihuahuan Desert.National Science Foundation [1235828]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Comment on "The extent of forest in dryland biomes"

Bastin et al (Reports, 12 May 2017, p. 635) infer forest as more globally extensive than previously estimated using tree cover data. However, their forest definition does not reflect ecosystem function or biotic composition. These structural and climatic definitions inflate forest estimates across the tropics and undermine conservation goals, leading to inappropriate management policies and practices in tropical grassy ecosystems

Connectivity: insights from the U.S. Long Term Ecological Research Network

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of “populations and communities.” The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the “connectivity” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies

Complexity in water and carbon dioxide fluxes following rain pulses in an African savanna

The idea that many processes in arid and semi-arid ecosystems are dormant until activated by a pulse of rainfall, and then decay from a maximum rate as the soil dries, is widely used as a conceptual and mathematical model, but has rarely been evaluated with data. This paper examines soil water, evapotranspiration (ET), and net ecosystem CO2 exchange measured for 5 years at an eddy covariance tower sited in an Acacia–Combretum savanna near Skukuza in the Kruger National Park, South Africa. The analysis characterizes ecosystem flux responses to discrete rain events and evaluates the skill of increasingly complex “pulse models”. Rainfall pulses exert strong control over ecosystem-scale water and CO2 fluxes at this site, but the simplest pulse models do a poor job of characterizing the dynamics of the response. Successful models need to include the time lag between the wetting event and the process peak, which differ for evaporation, photosynthesis and respiration. Adding further complexity, the time lag depends on the prior duration and degree of water stress. ET response is well characterized by a linear function of potential ET and a logistic function of profile-total soil water content, with remaining seasonal variation correlating with vegetation phenological dynamics (leaf area). A 1- to 3-day lag to maximal ET following wetting is a source of hysteresis in the ET response to soil water. Respiration responds to wetting within days, while photosynthesis takes a week or longer to reach its peak if the rainfall was preceded by a long dry spell. Both processes exhibit nonlinear functional responses that vary seasonally. We conclude that a more mechanistic approach than simple pulse modeling is needed to represent daily ecosystem C processes in semiarid savannas

Global application of an unoccupied aerial vehicle photogrammetry protocol for predicting aboveground biomass in non‐forest ecosystems

P. 1-15Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely sensed biomass products and are undersampled by in situ monitoring. Current global change threats emphasize the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we developed and deployed a new protocol for photogrammetric height using unoccupied aerial vehicle (UAV) images to test its capability for delivering standardized measurements of biomass across a globally distributed field experiment. We assessed whether canopy height inferred from UAV photogrammetry allows the prediction of aboveground biomass (AGB) across low-stature plant species by conducting 38 photogrammetric surveys over 741 harvested plots to sample 50 species. We found mean canopy height was strongly predictive of AGB across species, with a median adjusted R2 of 0.87 (ranging from 0.46 to 0.99) and median prediction error from leave-one-out cross-validation of 3.9%. Biomass per-unit-of-height was similar within but different among, plant functional types. We found that photogrammetric reconstructions of canopy height were sensitive to wind speed but not sun elevation during surveys. We demonstrated that our photogrammetric approach produced generalizable measurements across growth forms and environmental settings and yielded accuracies as good as those obtained from in situ approaches. We demonstrate that using a standardized approach for UAV photogrammetry can deliver accurate AGB estimates across a wide range of dynamic and heterogeneous ecosystems. Many academic and land management institutions have the technical capacity to deploy these approaches over extents of 1–10 ha−1. Photogrammetric approaches could provide much-needed information required to calibrate and validate the vegetation models and satellite-derived biomass products that are essential to understand vulnerable and understudied non-forested ecosystems around the globe.S

Africa and the global carbon cycle

The African continent has a large and growing role in the global carbon cycle, with potentially important climate change implications. However, the sparse observation network in and around the African continent means that Africa is one of the weakest links in our understanding of the global carbon cycle. Here, we combine data from regional and global inventories as well as forward and inverse model analyses to appraise what is known about Africa's continental-scale carbon dynamics. With low fossil emissions and productivity that largely compensates respiration, land conversion is Africa's primary net carbon release, much of it through burning of forests. Savanna fire emissions, though large, represent a short-term source that is offset by ensuing regrowth. While current data suggest a near zero decadal-scale carbon balance, interannual climate fluctuations (especially drought) induce sizeable variability in net ecosystem productivity and savanna fire emissions such that Africa is a major source of interannual variability in global atmospheric CO(2). Considering the continent's sizeable carbon stocks, their seemingly high vulnerability to anticipated climate and land use change, as well as growing populations and industrialization, Africa's carbon emissions and their interannual variability are likely to undergo substantial increases through the 21st century