Pierre Hiernaux

Pierre Hiernaux
Paul Sabatier University - Toulouse III | UPS Toulouse · Laboratoire Géosciences Environnement Toulouse - UM 97 (UMR 5563 / UMRD 234) - GET

PhD Ecology, Agronomy

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265
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Publications

Publications (265)
Article
Full-text available
Strengthening of feed security in the Sahel is urgently needed given the climate change and growing human population. A prerequisite to this is sustainable use of rangeland forage resources for livestock. Many studies have focused on the assessment of rangeland resources during the rainy season, while only a few have focused on the dry season which...
Article
Full-text available
The paradigm of Sahelian desertification, whose roots lie in the colonial period, increased in popularity following the droughts of the 1970s and 1980s. This “desertification narrative” was shaped in the international arena by organizations working in the fields of international cooperation, human rights, regional development, economic regulation a...
Preprint
Full-text available
Transitioning from the expansion of croplands to sustainable agricultural intensification is key to ensuring food and nutrition security. This is particularly the case for small-scale subsistence farmers in drylands, where our current understanding on the sustainability of this transition is however mostly derived from theories based on local obser...
Preprint
Full-text available
The consistent monitoring of trees both inside and outside of forests is key to mitigating climate change. Current monitoring systems either ignore trees outside forests or are too expensive to be applied consistently across countries on a repeated basis. Here we make use of the PlanetScope nanosatellite constellation, which delivers global very hi...
Preprint
Full-text available
The consistent monitoring of trees both inside and outside of forests is key to mitigating climate change. Current monitoring systems either ignore trees outside forests or are too expensive to be applied consistently across countries on a repeated basis. Here we make use of the PlanetScope nanosatellite constellation, which delivers global very hi...
Article
Although a recovery of woody vegetation has been observed throughout the Sahel, western Niger has not followed the overall satellite-derived greening trend. While satellite imagery can be used to study overall patterns and trends, only field observations can provide insights in the dynamics of woody plant populations. Here we used field data from 2...
Preprint
Full-text available
Trees sustain livelihoods and mitigate climate change, but a predominance of trees outside forests and limited resources make it difficult for many developing countries to conduct frequent nation-wide inventories. Here, we propose a rapid and accurate approach to map the carbon stock of each individual tree and shrub at the national scale of Rwanda...
Article
Full-text available
ContextWind erosion plays a major role in land degradation in semi-arid areas, especially in the Sahel. There, wind erosion is as sensitive to land use and land management as to climate factors. Future land use intensification may increase wind erosion and induce regional land degradation.Objective We aimed to estimate wind erosion responses to cha...
Article
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Multipurpose Faidherbia albida trees represent a vital component of agroforestry park-lands in West Africa as they provide resources (fodder for livestock, fruits and firewood) and support water lifting and nutrient recycling for cropping. Faidherbia albida trees are characterized by their inverse phenology, growing leaf flowers and pods during the...
Article
Full-text available
The response of vegetation to variable flood regimes is an important research question for floodplains in semi-arid sub-Saharan Africa experiencing climate change. The Inland Niger Delta (IND), located within the Sahelian zone of Central Mali, is a large floodplain that has experienced a historically-significant period of recurrent drought from 197...
Article
Full-text available
West African Sahelian and Sudanian ecosystems provide essential services to people and also play a significant role within the global carbon cycle. However, climate and land use are dynamically changing, and uncertainty remains with respect to how these changes will affect the potential of these regions to provide food and fodder resources or how t...
Preprint
Full-text available
West African Sahelian and Sudanian ecosystems are providing essential services to people and also play a significant role within the global carbon cycle. However, climate and land use are dynamically changing and it remains uncertain how these changes will affect the potential of these regions for providing food and fodder resources or the biospher...
Article
Full-text available
A large proportion of dryland trees and shrubs (hereafter referred to collectively as trees) grow in isolation, without canopy closure. These non-forest trees have a crucial role in biodiversity, and provide ecosystem services such as carbon storage, food resources and shelter for humans and animals1,2. However, most public interest relating to tre...
Article
Full-text available
Sahel rangelands degradation is prone to many controversies. In Sahel, rangeland forage resources availability is characterized by large spatial heterogeneity and wide seasonal and interannual variations. Pastoral livestock systems adapt to these patchy and variation resources by herd mobility and some supplement feeding that only partially overcom...
Article
Sahel rangelands degradation is prone to many controversies. In Sahel, rangeland forage resources availability is characterized by large spatial heterogeneity and wide seasonal and interannual variations. Pastoral livestock farming systems adapt to these patchy and variation resources by herd mobility and some supplement feeding that only partially...
Article
Full-text available
RESUME La forte variation du régime des pluies au Sahel est reconnue par tous. La phénologie de la strate herbacée dominée par des plantes annuelles suit ce cycle annuel en faisant alterner une courte saison de croissance et une longue saison morte. Le Gourma situé dans la bande sahélienne au Mali est une zone pastorale soumise à cette variabilité...
Article
Remote sensing-derived cropland products have depicted the location and extent of agricultural lands with an ever increasing accuracy. However, limited attention has been devoted to distinguishing between actively cropped fields and fallowed fields within agricultural lands, and in particular so in grass fallow systems of semi-arid areas. In the Sa...
Chapter
Full-text available
This book contains 18 chapters that describes the evolving and multi-faceted roles of ILRI in addressing these and other global challenges in nearly a half century of research. ILRI researchers and partners took leading roles, for example, in the following. This volume can serve as a reference and resource for all interested in the role of livestoc...
Article
Full-text available
The Sahel (semi-arid fringe south of the Sahara) experienced a long and prolonged drought from the 1970s to the mid-1990s, with a few extremely severe episodes that strongly affected ecosystems and societies. Long-term observations showed that surface runoff has increased during this period, despite the rainfall deficit. This paradox stems from the...
Article
Full-text available
The leaf area index, LAI, of Sahelian rangelands and related variables such as the vegetation cover fraction, fCover, the fraction of absorbed photosynthetically active radiation, fAPAR, and the clumping index, λo, were measured in the Gourma region (Mali) during 13 successive rainy seasons, between 2005 and 2017. These variables, known as climate...
Article
Full-text available
The leaf area index of Sahelian rangelands and related variables such as the vegetation cover fraction, the fraction of absorbed photosynthetically active radiation and the clumping index were measured between 2005 and 2017 in the Gourma region of northern Mali. These variables, known as climate essential variables, were derived from the acquisitio...
Article
Changing woody plant density across agricultural landscapes of the Sudano-Sahelian region is a debated issue. This paper reports the results of an investigation on the contribution of field hedges to overall woody plant density. Hedges separating individual cropped parcels were studied within village agropastoral territories in the Dantiandou distr...
Article
Full-text available
Dryland ecosystems comprise a balance between woody and herbaceous vegetation. Climate change impacts rainfall timing, which may alter the respective contributions of woody and herbaceous plants on the total vegetation production. Here, we apply 30 years of field-measured woody foliage and herbaceous mass from Senegal and document a faster increase...
Conference Paper
Full-text available
The West African Sahel experienced a long drought from the 1970s to the 1990s during which runoff has paradoxically increased, as a response to human and climate-induced changes in surface conditions. Despite the vegetation recovery (re-greening) observed at regional scale over the past 30 years, surface runoff is still increasing, suggesting that...
Article
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Echinochloa stagnina (Retz) P. Beauv., a widespread semi-aquatic perennial grass, is a key species for the sustainability of many African wetlands. In an effort to assess interactions between hydrological regimes and management strategies targeting conservation, this study focuses on characterizing the growth of a typical East African wet grassland...
Article
During the last few decades, ‘desertification’ has reached the status of a global environmental issue. The African Sahel is often seen as the world region worst hit by this process. The idea that deserts are spreading, mainly due to local land-use practices, is, however, not new. It already existed early in the colonial period in tropical Africa. T...
Article
This paper explores an original approach in which greenhouse gas (GHG) emissions and carbon (C) accumulation are assessed monthly and at landscape scale to account for the highly seasonal monsoon climate and the mobility of pastoral herds that characterize West African pastoral ecosystems. The study was conducted in northern Senegal, in the service...
Conference Paper
Full-text available
The Sahel witnessed a climatic drought from the 1970s to the 2000s. During this period, vegetation cover decreased and surface runoff increased in many places. While annual rainfall has partly recovered since the begining of this century, runoff has not reacted accordingly. The state of the ecohydrological system changed, and it responds in a new w...
Poster
Full-text available
The semi-arid Sahelian region is particularly prone to wind erosion due to low and variable annual precipitation producing low vegetation cover with a high interannual variability. Surfaces traditionally devoted to livestock grazing are used as croplands, increasing the proportion of bare surface unprotected from wind erosion. Wind erosion could si...
Article
This study (i) presents a coupled vegetation-soil model adapted to perennial C4 seasonally flooded semi-arid grasslands; and (ii) applies the model to evaluate changes in the annual productivity of the grasslands of the Tana River Delta, Kenya, under changing flooding conditions. Main plant growth processes are modelled within coupled plant carbon...
Article
It has been widely asserted that a high grazing pressure has led to a reduction in vegetation production at decadal time scales, implying land degradation, in African drylands, and in the Sahel in particular. We test this hypothesis by analyzing spatio‐temporal patterns of vegetation production in the north‐western Ferlo in Senegal. Normalized Diff...
Article
Full-text available
West Africa is a region in fast transition from climate, demography, and land use perspectives. In this context, the African Monsoon Multidisciplinary Analysis (AMMA)–Couplage de l’Atmosphère Tropicale et du Cycle eco-Hydrologique (CATCH) long-term regional observatory was developed to monitor the impacts of global change on the critical zone of We...
Article
The feeding behavior and fodder intake of cattle, sheep and goats grazing semi-arid sub-Saharan Africa rangelands in Senegal was studied over a one-year cycle. The objective of the study was to improve the assessment of fodder intake by livestock grazing rangelands in semi-arid sub-Saharan Africa. The study was conducted in the service area of a bo...
Article
Full-text available
In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968–1990s ‘Great Drought’ period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which th...
Article
Full-text available
Woody vegetation in farmland acts as a carbon sink and provides ecosystem services for local people, but no macroscale assessments of the impact of management and climate on woody cover exist for drylands. Here we make use of very high spatial resolution satellite imagery to derive wall-to-wall woody cover patterns in tropical West African drylands...
Chapter
Feed and grazing management affect both the quantity and quality of animal manure and consequently nutrient cycling in the mixed crop-livestock systems in West Africa Sahel. Dietary measures can significantly influence the composition of manure and hence it’s agricultural value. High nutrient feed will generally result in higher nutrient content of...
Article
Full-text available
Following a 25 years of below average annual rainfall in Sahel during the 1970-1995 period , the return to more humid conditions led to a rapid post-droughts recovery of the woody cover. However, the increase of the woody cover is not spatially homogeneous raising questions about the resilience of some woody vegetation types. Based on the analysis...
Article
Full-text available
Au Sahel, la végétation se compose d’une strate herbacée principalement composée de plantes annuelles et d’une strate ligneuse peu dense dominée par des épineux. Dans cette région, l’essentiel de la production fourragère a lieu entre juillet et septembre. Le disponible fourrager constitué au cours de cette courte période décroît durant les neuf moi...
Article
Full-text available
West Africa is a region in fast transition from climate, demography, and land use perspectives. In this context, the African Monsoon Multidisciplinary Analysis (AMMA)-Couplage de l'Atmosphere Tropicale et du Cycle eco-Hydrologique (CATCH) long-term regional observatory was developed to monitor the impacts of global change on the critical zone of We...
Conference Paper
Full-text available
Greenhouse gas (GHG) emissions in agricultural systems are usually calculated at year level. This study puts forward, in an original way, a dynamic and spatialized GHG balance, to account for the strong seasonality of the monsoon climate, and the spatial heterogeneity of forage resources and livestock mobility. The study is conducted over the servi...
Conference Paper
Full-text available
Pastoralism in the sahel, refers to the extensive production of livestock in rangelands, in which managed herd mobility (transhumance and nomadism) are necessary for the productivity and the sustainability of pastoral system. However, in this region, impact assessment and adaptation solutions face several methodological limitations and lack of data...
Conference Paper
Full-text available
Les parcours sahéliens sont peuplés d’une communauté d’herbacées principalement annuelles en interaction avec une communauté de ligneux. Le lien statistique entre la composition botanique des communautés ligneuses et celle des herbacés est étudié. Les observations analysées sur la région du Ferlo de 1970 à 1981 sont extraites de la base de données...
Article
La commune de Djougou témoigne d’importantes modifications liées à l’exploitation forestière, aux défrichements agricoles et à l’extension de l’élevage. La dynamique paysagère est analysée à partir d’une série temporelle d’images-satellite Landsat (1984- 2012). Une approche régressive, exploitant les missions de terrain et les entretiens semi-direc...
Article
Full-text available
In recent decades, the Sahel has witnessed a paradoxical increase in surface water despite a general precipitation decline. This phenomenon, commonly referred to as the Sahelian paradox, is not completely understood yet. The role of cropland expansion due to the increasing food demand by a growing population has been often put forward to explain th...
Article
Full-text available
L'élevage pastoral représente la principale activité économique de nombreux ménages au nord du Sahel. Malgré la qualité des pâturages au cours de la saison des pluies, cet élevage est soumis à de nombreuses contraintes liées à l'irrégularité de la disponibilité fourragère, aux difficultés d'accès aux compléments alimentaires et aux soins vétérinair...
Article
In the Sahel, climate change and demographic growth are raising major concerns about the ability of crop yields to support the local population. Agro-pastoral management affects wind erosion (e.g. through crop residue management and tillage practices, which modify surface characteristics), which itself substantially affects the soil fertility, and...