Papers by Sébastien Barot
... 2), Nicolas Florsch (3), Jean-Louis Janeau (1), David Ward (4), Sébastien Barot (5), Pascal P... more ... 2), Nicolas Florsch (3), Jean-Louis Janeau (1), David Ward (4), Sébastien Barot (5), Pascal Podwojewski (1), Simon Lorentz (6 ... of gully initiation (threshold determination) and gully evolution (driving factors) is still debated due to methodological advances (Vandekerckhove et al ...
PloS one, 2007
Soil ecology has produced a huge corpus of results on relations between soil organisms, ecosystem... more Soil ecology has produced a huge corpus of results on relations between soil organisms, ecosystem processes controlled by these organisms and links between belowground and aboveground processes. However, some soil scientists think that soil ecology is short of modelling and evolutionary approaches and has developed too independently from general ecology. We have tested quantitatively these hypotheses through a bibliographic study (about 23000 articles) comparing soil ecology journals, generalist ecology journals, evolutionary ecology journals and theoretical ecology journals. We have shown that soil ecology is not well represented in generalist ecology journals and that soil ecologists poorly use modelling and evolutionary approaches. Moreover, the articles published by a typical soil ecology journal (Soil Biology and Biochemistry) are cited by and cite low percentages of articles published in generalist ecology journals, evolutionary ecology journals and theoretical ecology journal...
Theoretical population biology, 2004
In terrestrial plants the segregation of male and female reproductions on different individuals r... more In terrestrial plants the segregation of male and female reproductions on different individuals results in the seed-shadow handicap: males do not disperse any seed so that the number of local patches reached by seeds is potentially reduced in dioecious populations in comparison to hermaphrodite populations. An analytical model, incorporating a lottery-based recruitment and dispersal stochasticity, was built. The spatially mediated cost of the seed-shadow handicap has been assessed considering the criterions for the invasion of a resident hermaphrodite species by a dioecious species and the reverse invasion, both species having the same demographic parameters but assuming a likely higher fecundity for dioecious females. The reciprocal invasion of a dioecious and hermaphrodite species differing only by their fecundity is never possible. The seed-shadow handicap disappears when the dispersal or survival rate is high enough. This latter point is due to dispersal stochasticity, which all...
We investigated the impact of perennial and annuals grass species on nitrogen cycling in a Sudani... more We investigated the impact of perennial and annuals grass species on nitrogen cycling in a Sudanian savanna of Burkina Faso. We also analysed how the local context in terms of grazing and soil properties modifies these impacts. We selected four plots differing both by the intensity of grazing by cattle and soil depth, and used soil and grass biomass 15 N as integrative indicators of N cycle. If perennials are able to foster a more efficient nitrogen cycling there should be lower 15 N abundances in their biomass and soil. If soil depth and cattle pressure significantly modify nitrogen fluxes, soil depth and cattle pressure should influence 15 N signatures. Our results suggest that perennial grasses are more conservative for nitrogen (inhibition of nitrification, less leaching via a perennial root system, slower cycling). The increase in leaf d 15 N with N concentration is steeper in Loudetia togoensis than in the three other grasses. No significant difference was found between the 15 N signatures of the four plots. Our results on 15 N signatures and the fact that perennial grasses are much more abundant in the plots that are less grazed and have deeper soils, confirm that the switch from perennial to annual grasses is linked to a degradation in soil fertility and pasture quality. This suggests that 15 N signatures can be used as indicators of fertility.
Savanna trees often display significant hollows due to the combined action of fire and termites (... more Savanna trees often display significant hollows due to the combined action of fire and termites (N'Dri et al., J Trop Ecol 27:269-278, 2011). Observations have shown that internal cavities caused by termites in tree stems often result in external hollows under annual fire regimes, and it is quite possible that such hollows/fire interaction may increase the probability of trunk or big branch breakage and/or tree mortality. A study of individual tree and branch mortality as a function of prior termite and fire damage was undertaken in a West African savanna (Lamto, Côte d'Ivoire) where most of the trees naturally have hollows in their stems due to termite and fire interaction. Our goal was to examine the dynamics of hollowing and to determine whether hollowing significantly affected tree mortality. Branch and whole plant mortality were quantified for dominant tree species according to their initial hollow state and height. Four different responses were obtained depending on tree species: (1) mortality increased with cavity severity and tree size (Piliostigma thonningii), (2) mortality depended on tree size only (Bridelia ferruginea), (3) no mortality even after being hollowed by termites and externally damaged by fire (Crossopteryx febrifuga, the species with the highest proportion of individuals with hollows yet the greatest background survival time, 14 ± 2 years) and (4) high mortality, but few hollow trees suggesting a weak resistance to hollowing (Cussonia arborea which was insensitive to all the factors examined in this study). For species resistant to hollowing, tree mortality was rare; alternatively, for species prone to hollowing, whole trees died quickly and before the most severe hollow classes could be observed. Long-term demographic data yielded population-level mortality estimates of adult trees at least four times lower in fire-exclusion zones than that in fire-prone areas. Because hollow dynamics interact with fire in affecting adult mortality of some dominant tree species, fire management is important for a sustainable woody component of these savannas.
Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soi... more Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soil microflora and nutrient mineralization. The properties of earthworm casts should depend both on earthworm species or ecological group and on soil properties. Interactions between earthworm species and soil types have been suggested, but only poorly demonstrated. In order to better understand those interactions, two hypotheses led our study: (1) Soil type has a greater influence on cast properties than earthworm; (2) Earthworms from different species influence cast properties differently; (3) The intensity and direction of the impact of each earthworm species on cast properties vary with soil properties. Fifteen physical and chemical variables (N-NH 4 + , N-NO 3 − , total organic C and N, C/N ratio, CaCO 3 , pH, P, K + , Mg 2+ , Mn 2+ , Na + , CEC, moisture, wettability) were measured in casts of three earthworm species (Lumbricus terrestris, Allolobophora chlorotica and Aporrectodea rosea) produced in three temperate soils. Univariate and multivariate analyses showed that earthworm species and soil types significantly impacted cast properties. pH, N t , K and Mg contents were interactively altered by both factors. Multivariate analysis showed that a difference of soil type had a major impact on casts properties (62%) compared to the impact of a difference of earthworm species (10%). Cast properties were most impacted by L. terrestris, then by A. chlorotica and last by A. rosea. The response ratio (ratio of the properties of the casts to the properties of the bulk soil) was used to quantify the effect of earthworm species compared to the control soil. It showed a higher response of variables in casts in nutrient-rich soils, especially in casts of L. terrestris. The interactions between earthworm species and soil types on cast properties were discussed with regards to earthworm ecology, properties of the soil, and earthworm modifications of cast microflora.
Because of technical difficulties in measuring soil properties at a large scale, little is known ... more Because of technical difficulties in measuring soil properties at a large scale, little is known about the effect of soil properties on the spatial distribution of trees in grasslands. We were interested in the associations of soil properties with the phenomenon of tree encroachment, where trees increase in density at the expense of grasses. The spatial variation of soil properties and especially soil texture may modify the properties of hydraulic conductivity, and the availability of soil water and mineral nutrients, which in turn may affect the spatial distribution of encroaching trees. Through the development of a geophysical method (Slingram) using an electromagnetic device EM38 and Bayesian inversion, we were able to accurately map soil electrical conductivity (EC) of a Luvisol in a grassland of South Africa. EC measured at the 0·8 to 2 m depth on a 1·5 ha area is a proxy for clay content and was correlated with the spatial distribution of four size classes of the encroaching Acacia sieberiana. Tree location (all sizes considered) was significantly correlated with EC. Tall acacias (>3m height) were totally absent from patches with EC >24 mS m À1 . For all other size classes from medium trees to seedlings, tree density decreased with increasing EC. This suggests that high clay contents at depth associated with high EC values may prevent the establishment and/or survival of trees and influence the spatial distribution of A. sieberiana. This result also shows that geophysical tools may be useful for demonstrating important ecological processes. Figure 2. Photography of a gully side on the left and a typical electrical conductivity profile against depth (continuous curve) together with the fitted model used in this study (dotted lines) on the right. (S) surface; (U) upper limit of the transition layer; (L) lower limit of the transition layer; (B) conventional model bottom (=practical device sensitivity limit).
Dispersal Earthworms Feedback Intraand inter-specific interactions Soil structure A B S T R A C T... more Dispersal Earthworms Feedback Intraand inter-specific interactions Soil structure A B S T R A C T By burrowing galleries and producing casts, earthworms are constantly changing the structure and properties of the soils in which they are living. These changes modify the costs and benefits for earthworms to stay in the environment they modify. In this paper, we measured experimentally how dispersal behaviour of endogeic and anecic earthworms responds to the cumulative changes they made in soil characteristics. The influence of earthworm activities on dispersal was studied in standardised mesocosms by comparing the influence of soils modified or not modified by earthworm activities on earthworm dispersal rates.
Intensive agriculture is often criticized for negative impacts on environment and human health. T... more Intensive agriculture is often criticized for negative impacts on environment and human health. This issue may be solved by a better management of organisms living in crop fields. Here, we review the benefits of earthworms for crops, and we present techniques to increase earthworm abundance. The major points are the following: (1) Earthworms usually improve soil structural stability and soil porosity and reduce runoff.
Earthworms provide key soil functions that favour many positive ecosystem services. These service... more Earthworms provide key soil functions that favour many positive ecosystem services. These services are important for agroecosystem sustainability but can be degraded by intensive cultural practices such as use of pesticides. Many literature reports have investigated the effect of pesticides on earthworms. Here, we review those reports to assess the relevance of the indicators of earthworm response to pesticides, to assess their sensitivity to pesticides, and to highlight the remaining knowledge gaps. We focus on European earthworm species and products authorised in Europe, excluding natural compounds and metals. We consider different organisation levels: the infra-individual level (gene expression and physiology), the individual and population levels (life-history traits, population density and behaviour) and the community level: community biomass and density. Our analysis shows that earthworms are impacted by pesticides at all organisation levels. For example, pesticides disrupt enzymatic activities, increase individual mortality, decrease fecundity and growth, change individual behaviour such as feeding rate and decrease the overall community biomass and density.
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Papers by Sébastien Barot