Agronomist, PhD in vegetation ecology, professional experience in the tropics, mostly in africa, savannas, agricultural landscape, livestock production systems, pastoralism.
A simple grassland process model is tested against ground measurements collected during 15 years ... more A simple grassland process model is tested against ground measurements collected during 15 years in the sahelian zone in Mali. The model uses standard daily meteorological variables and a limited number of site specific parameters to simulate herbage growth and canopy functioning. The model has two calibration parameters. Due probably to the strong interannual variation of both the herbaceous layer
Discusses the aim of studies on vegetation & feed resources in pastoral systems, describing t... more Discusses the aim of studies on vegetation & feed resources in pastoral systems, describing the collection & presentation of data in the descriptive phase; identification of constraints in the diagnostic phase; and analysis of the impact of selected variables or technical innovations on the systems' functioning, and the development of adapted technology in the experimental phase
Introduction: the forage question The forage question is involved in livestock farming practices ... more Introduction: the forage question The forage question is involved in livestock farming practices in the Sahel and also in research conducted on the improvement of its profitability (Lhoste et al., 1993; Klein et al., 2014), animal husbandry development policies (Zoundi and Hitimana, 2008; CORAF/WECARD, 2010; Krätli et al., 2013) and finally discussion of the future of animal husbandry in the Sahel (Peyre de Fabrègue, 1984; Hesse and Thébaud, 2006; Jullien, 2006; Bassett and Turner, 2007). The..
Rappel des objectifs, resultats et methodes du suivi de la vegetation sahelienne du Gourma mis en... more Rappel des objectifs, resultats et methodes du suivi de la vegetation sahelienne du Gourma mis en place depuis juin 1984 au Mali; suivi d'une presentation et d'une analyse sommaire des resultats de la saison 1990 concernant la dynamique de la vegetation apre secheresse; avec ref. partic. sur la baisse d'ensemble des productions herbacees par rapport a 1989, l'evolution plus irreguliere des peuplements ligneux, la composition floristique et ce stock semencier du sol, l'impact de l'expoloitation pastorale, de la densite des plants et des fauches avec ou sans fumure sur la production primaire
ABSTRACT Dynamics of cattle populations in arid and semi-arid tropical Africa are highly influenc... more ABSTRACT Dynamics of cattle populations in arid and semi-arid tropical Africa are highly influenced by droughts, which can create dramatic drops in herd sizes as well as disturbances in sex-and-age structures. The Sahel region is particularly affected by such climate shocks. Successive major droughts are assumed to have effectively decreased the cattle stock and strongly influenced the evolution of pastoral and agro-pastoral systems in the past 40 years and probably before. Demographic resilience, i.e. the ability to recover from significant losses, is a key parameter for the sustainability of livestock populations in systems regularly perturbed by demographic shocks, and thus for prospective studies of the livestock sector, in particular for cattle that are more vulnerable to feed shortage than small ruminants and have a slower biological turnover. Here, a simple mathematical herd growth model is used to simulate the post-drought dynamics of a hypothetical Sahelian cattle population taken as example. A set of scenarios describing the drought severity, herd performances and management practices was considered in a global sensitivity analysis. The resilience was measured by the probability to recover, the recovery time of the population and its annual growth rate during the recovery period. An important finding of the study was the extreme variability of the recovery time. This variability challenges the common postulate according to which 10–15 years are needed for a cattle population to recover after a ‘severe’ drought. This also emphasizes the difficulty of obtaining reliable recovery predictions from inaccurate estimates of demographic parameters. Simulations showed that the proportion of population size decline due to the shock, the calving rate and farmers’ offtake strategy after the drought are overall the most influential factors for recovery dynamics. Simulations also showed that the recovery time can be highly influenced by the transient regime of the herd growth model when the post-drought sex-and-age structure is non-equilibrated. In particular, the sensitivity analysis confirmed that large losses of breeding females during shocks considerably delay herd regeneration.
In studies of 25 rangeland sites selected along the S.-N. bioclimatic gradient and on the main so... more In studies of 25 rangeland sites selected along the S.-N. bioclimatic gradient and on the main soil types in the Gourma (Sahel, Mali), herbage cover, standing mass and botanical composition were measured in relation to seasonality of grazing and grazing intensity. When different sites were compared, variability in herbage and spatial heterogeneity were positively correlated. Spatial heterogeneity within a site increased after droughts indicating that compensation between temporal and spatial variations occurred. It was considered that drought-promoted heterogeneity may help the resilience of the vegetation by preserving spots of luxuriant growth. Grazing decreased spatial heterogeneity, however the evenness fostered by grazing did not increase vegetation sensitivity to drought. It is suggested that this was because of the convergence in plant adaptation to grazing and arid conditions
International Journal of Remote Sensing, Jun 1, 1991
... technology, may be more accurate, given the definitional and measurement errors in current es... more ... technology, may be more accurate, given the definitional and measurement errors in current estimates suggested in Allen and Barnes (1985) and ... Penning de Vries and Djiteye 1982, Hiernaux and Cisse 1983), and during drought or poor growing seasons (Diarra and Hiernaux ...
Agriculture, Ecosystems & Environment, Mar 1, 2003
... Soils used for rainfed cereal production in Niger are sandy, deficient in major nutrients (N ... more ... Soils used for rainfed cereal production in Niger are sandy, deficient in major nutrients (N and P), and also low in organic matter content. ... Research by ILRI in west Africa has shown that livestockrecycle about 50% of organic matter (OM), 85% of P, and 48% of N intake via the ...
To date, the interpretation of remote sensing images has not revealed wide-spread degradation of ... more To date, the interpretation of remote sensing images has not revealed wide-spread degradation of the vegetation in the Sahel. However, the interpretation of spectral information depends on a range of assumptions regarding the dynamics of the Sahelian vegetation as a function of rainfall variability and human management. Recent papers have presented diverging views on the vegetation dynamics of the Sahel and how these can be analysed with remote sensing images. We present a further analysis of the vegetation dynamics of semi-arid rangelands, in particular the Sahel, and the subsequent implications for the interpretation of remote sensing images. Specifically, the ecological processes driving the response of the Sahelian vegetation to rainfall variation are re-examined, and a regression analysis of NPP versus rainfall data is carried out. It is shown that the relation between the interannual variation in NPP and rainfall in the Sahel is non-linear and that this relation differs between sites with different average annual rainfall. It has been common practise in remote sensing studies for the Sahel to aggregate data from various Sahelian sites in order to obtain an average relation between rainfall, NPP and Rain Use Efficiency, and to assume these relations to be linear. This paper shows that this approach may lead to a bias in the interpretation of remote sensing images and that further work is required to clarify if wide-spread ecosystem degradation has occurred in the Sahel.
A simple grassland process model is tested against ground measurements collected during 15 years ... more A simple grassland process model is tested against ground measurements collected during 15 years in the sahelian zone in Mali. The model uses standard daily meteorological variables and a limited number of site specific parameters to simulate herbage growth and canopy functioning. The model has two calibration parameters. Due probably to the strong interannual variation of both the herbaceous layer
Discusses the aim of studies on vegetation & feed resources in pastoral systems, describing t... more Discusses the aim of studies on vegetation & feed resources in pastoral systems, describing the collection & presentation of data in the descriptive phase; identification of constraints in the diagnostic phase; and analysis of the impact of selected variables or technical innovations on the systems' functioning, and the development of adapted technology in the experimental phase
Introduction: the forage question The forage question is involved in livestock farming practices ... more Introduction: the forage question The forage question is involved in livestock farming practices in the Sahel and also in research conducted on the improvement of its profitability (Lhoste et al., 1993; Klein et al., 2014), animal husbandry development policies (Zoundi and Hitimana, 2008; CORAF/WECARD, 2010; Krätli et al., 2013) and finally discussion of the future of animal husbandry in the Sahel (Peyre de Fabrègue, 1984; Hesse and Thébaud, 2006; Jullien, 2006; Bassett and Turner, 2007). The..
Rappel des objectifs, resultats et methodes du suivi de la vegetation sahelienne du Gourma mis en... more Rappel des objectifs, resultats et methodes du suivi de la vegetation sahelienne du Gourma mis en place depuis juin 1984 au Mali; suivi d'une presentation et d'une analyse sommaire des resultats de la saison 1990 concernant la dynamique de la vegetation apre secheresse; avec ref. partic. sur la baisse d'ensemble des productions herbacees par rapport a 1989, l'evolution plus irreguliere des peuplements ligneux, la composition floristique et ce stock semencier du sol, l'impact de l'expoloitation pastorale, de la densite des plants et des fauches avec ou sans fumure sur la production primaire
ABSTRACT Dynamics of cattle populations in arid and semi-arid tropical Africa are highly influenc... more ABSTRACT Dynamics of cattle populations in arid and semi-arid tropical Africa are highly influenced by droughts, which can create dramatic drops in herd sizes as well as disturbances in sex-and-age structures. The Sahel region is particularly affected by such climate shocks. Successive major droughts are assumed to have effectively decreased the cattle stock and strongly influenced the evolution of pastoral and agro-pastoral systems in the past 40 years and probably before. Demographic resilience, i.e. the ability to recover from significant losses, is a key parameter for the sustainability of livestock populations in systems regularly perturbed by demographic shocks, and thus for prospective studies of the livestock sector, in particular for cattle that are more vulnerable to feed shortage than small ruminants and have a slower biological turnover. Here, a simple mathematical herd growth model is used to simulate the post-drought dynamics of a hypothetical Sahelian cattle population taken as example. A set of scenarios describing the drought severity, herd performances and management practices was considered in a global sensitivity analysis. The resilience was measured by the probability to recover, the recovery time of the population and its annual growth rate during the recovery period. An important finding of the study was the extreme variability of the recovery time. This variability challenges the common postulate according to which 10–15 years are needed for a cattle population to recover after a ‘severe’ drought. This also emphasizes the difficulty of obtaining reliable recovery predictions from inaccurate estimates of demographic parameters. Simulations showed that the proportion of population size decline due to the shock, the calving rate and farmers’ offtake strategy after the drought are overall the most influential factors for recovery dynamics. Simulations also showed that the recovery time can be highly influenced by the transient regime of the herd growth model when the post-drought sex-and-age structure is non-equilibrated. In particular, the sensitivity analysis confirmed that large losses of breeding females during shocks considerably delay herd regeneration.
In studies of 25 rangeland sites selected along the S.-N. bioclimatic gradient and on the main so... more In studies of 25 rangeland sites selected along the S.-N. bioclimatic gradient and on the main soil types in the Gourma (Sahel, Mali), herbage cover, standing mass and botanical composition were measured in relation to seasonality of grazing and grazing intensity. When different sites were compared, variability in herbage and spatial heterogeneity were positively correlated. Spatial heterogeneity within a site increased after droughts indicating that compensation between temporal and spatial variations occurred. It was considered that drought-promoted heterogeneity may help the resilience of the vegetation by preserving spots of luxuriant growth. Grazing decreased spatial heterogeneity, however the evenness fostered by grazing did not increase vegetation sensitivity to drought. It is suggested that this was because of the convergence in plant adaptation to grazing and arid conditions
International Journal of Remote Sensing, Jun 1, 1991
... technology, may be more accurate, given the definitional and measurement errors in current es... more ... technology, may be more accurate, given the definitional and measurement errors in current estimates suggested in Allen and Barnes (1985) and ... Penning de Vries and Djiteye 1982, Hiernaux and Cisse 1983), and during drought or poor growing seasons (Diarra and Hiernaux ...
Agriculture, Ecosystems & Environment, Mar 1, 2003
... Soils used for rainfed cereal production in Niger are sandy, deficient in major nutrients (N ... more ... Soils used for rainfed cereal production in Niger are sandy, deficient in major nutrients (N and P), and also low in organic matter content. ... Research by ILRI in west Africa has shown that livestockrecycle about 50% of organic matter (OM), 85% of P, and 48% of N intake via the ...
To date, the interpretation of remote sensing images has not revealed wide-spread degradation of ... more To date, the interpretation of remote sensing images has not revealed wide-spread degradation of the vegetation in the Sahel. However, the interpretation of spectral information depends on a range of assumptions regarding the dynamics of the Sahelian vegetation as a function of rainfall variability and human management. Recent papers have presented diverging views on the vegetation dynamics of the Sahel and how these can be analysed with remote sensing images. We present a further analysis of the vegetation dynamics of semi-arid rangelands, in particular the Sahel, and the subsequent implications for the interpretation of remote sensing images. Specifically, the ecological processes driving the response of the Sahelian vegetation to rainfall variation are re-examined, and a regression analysis of NPP versus rainfall data is carried out. It is shown that the relation between the interannual variation in NPP and rainfall in the Sahel is non-linear and that this relation differs between sites with different average annual rainfall. It has been common practise in remote sensing studies for the Sahel to aggregate data from various Sahelian sites in order to obtain an average relation between rainfall, NPP and Rain Use Efficiency, and to assume these relations to be linear. This paper shows that this approach may lead to a bias in the interpretation of remote sensing images and that further work is required to clarify if wide-spread ecosystem degradation has occurred in the Sahel.
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