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(IF 3.95; Q1); International audience; The rapid expansion of perennial crops is a major threat to biodiversity in Southeast Asia. The biodiversity losses related to the conversion of forest lands to oil palm or rubber plantations (RP) are well documented by recent studies. However, the impact of the conversion from intensively managed annual crops to perennial crops on soil biodiversity has not yet been addressed. This study aims at assessing the impact on soil biodiversity of a) the short-term effect of land use conversion from cassava crop to RP, and b) the long-term effect of RP ageing. Soil biodiversity (bacterial, fungal and macrofaunal), microbial activities and pedoclimatic characteristics were measured over a chronosequence of 1–25 years old of RP compared to cassava fields, the former crop, in Thailand. The conversion from cassava to young RP (1–3 yr) had a significant effect on microbial biomass and activities and fungal composition, but did not impact the bacterial and macrofaunal diversity. This effect of land use conversion could be explained by the change in land management due to the cultivation of pineapple in the inter-row of the young RP. Canopy closure appeared to be the main driver of soil biota shifts, as most of the biotic parameters, composition, abundance and activities were significantly modified after 7 years of RP. The changes of composition in older rubber plantations originated from the dominance of Trichoderma (fungi), Firmicutes (bacteria), and earthworms. Old rubber plantations (23–25 yr) harboured the highest microbial and macrofaunal biomass; however, they were also characterised by a significant decrease in bacterial richness. The change in pedoclimatic conditions across the rubber chronosequence, i.e. increase in soil moisture, litter and organic carbon content, was a stronger driver of soil biota evolution than land use conversion. The macrofaunal composition was more resistant to land use conversion than the bacterial composition, whereas the microbial biomass was sensitive to land use conversion, but showed resilience after 20 years. However, bacterial, fungal and macrofaunal diversity, macrofaunal and microbial biomass and microbial activities were all sensitive to RP ageing.

In Brazilian Amazonia there are 26 million hectares of degraded pastures. One of the causes of degradation is assumed to be alterations in soil structure that is partly determined by a reduction in soil macrofauna diversity. The objective of this case study was to identify the consequences of altered macrofaunal diversity on soil structure and hydrological processes. After forest clearing for pasture establishment, the diversity of soil macroinvertebrates decreased strongly. Tensiometric measurements showed the formation of a superficial groundwater table in a 4-year-old pasture (P4), and a deeper groundwater table in an abandoned pasture (Pa), that was an exceptional situation. The forest soil, in contrast, was almost never water-saturated due to its microaggregate structure. Once the pasture was abandoned, the soil macrofauna was dominated by a single earthworm species, Pontoscolex corethrurus , which may modify, in the course of a few years, the morphology and hydrological functioning of soils. By placing very wet castings on the pasture soil surface, P. corethrurus can form a continuous layer that is relatively impermeable to air and water. Although initially limited to the surface layer, the episodic conditions of water saturation and anoxia may also occur in deeper horizons, favoring the development of hydromorphic conditions, even though the surface soil structure may be regenerating due to the activity of other macrofaunal groups such as termites, after reduction of P. corethrurus populations.

In southern Benin like in other tropical areas, natural fallows, which were traditionally used in order to improve soil fertility, are no longer possible in a context of high population pressure. Many studies have underlined the advantages of legume cover crops to ensure the sustainability of plant productivity: increase in soil organic matter content, increase in crop yields, improvement of the water regime of soils, and decrease in runoff and erosion. Nevertheless the mechanisms responsible for these modifications are not completely understood. The characterisation of biological activity and diversity in a soil can help in understanding the dynamics of soil structure and the flux of nutrients. For this purpose, the density, diversity and functional composition of soil nematodes and soil macroinvertebrates were measured in different treatments under maize cultivation. The three treatments were: (1) a pure traditional maize crop without any fertilisation (T); (2) a maize crop with a mineral fertiliser (NPK); and (3) a maize crop inter-cropped with Mucuna pruriens var. utifs (M). Soil in plot M presented different biological properties when compared with T and NPK: higher macrofauna density (especially termites, earthworms, millipedes, centipedes) and biomass (especially earthworms and termites), higher density of facultative phytophagous, bacterial-feeding and predatory nematodes, and lower density of obligatory phytophagous (Criconemella, Scutellonema and Meloidogyne) nematodes. The modification of the composition and activity of soil biota under Mucuna might partly explain the potential of Mucuna for soil restoration. (c) 2006 Elsevier Masson SAS. All rights reserved.

Con el propósito de desarrollar un índice multimétrico para evaluar la calidad biológica de los ríos de la Cuenca Chipiriri (Bolivia), tomamos muestras de macroinvertebrados bentónicos y medidas ambientales en dos grupos de sitios distribuidos uniformemente en toda la cuenca, 38 sitios con mínima perturbación antropogénica y 29 sitios perturbados. Usando los datos del primer grupo de sitios, desarrollamos modelos estadísticos sencillos de modo que expliquen adecuadamente los patrones observados de 12 diferentes variables biológicas tomadas en cuenta; posteriormente, seleccionamos las varialbes biológicas más efectivas qe respondieron de forma significativa a efectos de perturbación. Finalmente, sumando los valores de las variables biológicas seleccionadas obtuvimos el índice final que distinguió claramente la variación de la calidad biológica de las condiciones naturales y perturbadas. Los métodos y consideraciones descritas en este trabajo podrían emplearse para desarrollar un índice de integridad ecológica en otras regiones, incluyendo nuevos parámetros a esta escala.

International audience; As primary forest is cleared, pastures and secondary forest occupy an increasing space in the Amazonian landscape. We evaluated the effect of forest clearing on a soil macrofauna (invertebrate) community in a smallbolder farming system of southeastern Amazonia. We sampled the soil macrofauna in 22 plots of forest, upland rice fields, pastures, and fallows of different ages. In total, we collected 10, 728 invertebrates. In cleared plots the species richness per plot of the soil macrofauna fell from 76 to 30 species per plot immediately after forest clearance, and the composition of the new community was different. Ants, termites, and spiders were most affected by the disturbance. In plots deforested several years before, the effect of forest clearance was highly dependent on the type of land use (pasture or fallow). In fallows, the community was similar to the initial state. The species richness per plot in old fallows rose to 66, and the composition was closer to the primary forests than to the other types of land use. On the contrary, in the pastures the species richness per plot remained low at 47. In fallows, all the groups showed a richness close to that in primary forest, whereas in the forest only the richness of earthworms and Coleoptera recovered. Our results show that forest clearing constitutes a major disturbance for the soil macrofauna and that the recovery potential of the soil macrofauna after 6 or 7 years is much higher in fallows than in pastures. Thus, fallows may play a crucial role in the conservation of soil macrofauna; A medida que el bosque es talado, los pastizales y la vegetación secundaria cada vez ocupan más espacio en el paisaje Amazónico. Evaluamos el efecto de la tala del bosque sobre una comunidad de macrofauna (invertebrados) del suelo en un sistema agrícola de pequeña propiedad en el sureste de la Amazonía. Muestreamos la macrofauna en 22 parcelas de bosque campos de arroz, pastizales y barbechos de diferentes edades. En total, recolectamos 10,728 invertebrados. En parcelas taladas, la riqueza de especies de macrofauna del suelo por parcela disminuyó de 76 a 30 especies por parcela inmediatamente después de que el bosque fue talado, y la composición de la comunidad nueva fue diferente. Las hormigas, termitas y arañas fueron las más afectadas por la perturbación. El efecto de la tala del bosque fue altamente dependiente del tipo de uso de suelo (pastizal o barbecho) en las parcelas deforestadas varios años antes. En los barbechos, la comunidad fue similar al estado inicial. La riqueza de especies por parcelas en los barbechos viejos se elevó a 66, y la composición fue más cercana a la de bosques primarios que a la de los otros tipos de uso de suelo. Por el contrario, la riqueza de especies por parcela en pastizales permaneció baja en 47. En los barbechos, todos los grupos mostraron una riqueza similar a la del bosque primario, mientras que en el bosque solo se recuperó la riqueza de lombrices y Coleópteros. Nuestros resultados sugieren que la tala de bosques constituye una perturbación mayor para la macrofauna del suelo y que el potencial de recuperación de la macrofauna del suelo después de 6 o 7 años es mucho mayor en los barbechos que en los pastizales. Por lo tanto, los barbechos pueden jugar un papel crucial en la conservación de la macrofauna del suelo

International audience; Soil macrofauna was surveyed in six sites characterised by different vegetation types on five occasions in the Western Ghats, India. Sampling sites included a primary forest, a weakly disturbed forest (slightly logged in the past), a highly disturbed forest (intensively logged), an Acacia auriculiformis plantation (8 years old), a pasture with high density of Phoenix humilis and a pasture without P. humilis. We showed that both land management and temporal variability induced significant changes in the soil macrofauna. Forest sites hosted larger densities of soil macroorganisms. The effect of seasons was apparent as some clear modifications in the fauna composition occurred. Some groups like earthwonns mainly exhibited temporal variability whereas others like millipedes were chiefly affected by land management options. The seasonal rhythms of soil macrofauna were poorly expressed in the pasture plots and the Acacia plantation, but were particularly clear in the forest sites. This interaction between land management and temporal patterns may be explained by some changes in the species composition associated with certain land-uses. Our approach was based on a between-within classes PCA that proved particularly useful by providing statistical tests and a hierarchy of land management and temporal rhythm effects

As primary forest is cleared, pastures and secondary forest occupy an increasing space in the Amazonian landscape. We evaluated the effect of forest clearing on a soil macrofauna (invertebrate) community in a smallholder farming system of southeastern Amazonia. We sampled the soil macrofauna in 22 plots of forest, upland rice fields, pastures, and fallows of different ages. In total, we collected 10,728 invertebrates. In cleared plots the species richness per plot of the soil macrofauna fell from 76 to 30 species per plot immediately after forest clearance, and the composition of the new community was different. Ants, termites, and spiders were most affected by the disturbance. In plots deforested several years before, the effect of forest clearance highly depended on the type of land use (pasture or fallow). In fallows, the community was most similar to the initial state. The species richness per plot diversity in old fallows rose to 66 species per plot, and the composition was closer to the primary forests than to the other types of land use. On the contrary, in the pastures the species richness per plot diversity remained low, with 47 species per plot. In fallows, all the groups showed a species richness close to that in primary forest, whereas in the forest only the species richness of earthworms and coleoptera recovered. Our results suggest that forest clearing constitutes a major disturbance for the soil macrofauna and that the recovery potential of the soil macrofauna after 6 or 7 years is much higher in fallows than in pastures. Thus, fallows may play a crucial role in the conservation of soil macrofauna., Les communautés de macrofaune du sol en Amazonie du sud-est demeurent très peu décrites, malgré leur importance primordiale pour la compréhension du fonctionnement des sols, particulièrement ceux des milieux tropicaux. En effet, dans ces derniers, les conditions édaphiques sont souvent défavorables au cycle des nutriments, ce qui pose des problèmes de gestion dans les zones de déforestation.Parmi les facteurs potentiels structurant les communautés de la macrofaune du sol, la diversité de la végétation et la structure du paysage sont de plus en plus souvent proposées, mais peu d’études appuient ces hypothèses. Nous avons abordé ces questions par une étude multi échelle, avec un plan d’échantillonnage emboîté de 270 blocs TSFB, ce qui a permis d’étudier l’effet des différents facteurs selon l’échelle considérée. La zone géographique choisie est la localité de Benfica, une zone de déforestation par l’agriculture familiale, représentative de l’Amazonie du sud-est.Nos résultats montrent qu’au niveau du paysage, la richesse spécifique de macrofaune du sol peut être en bonne partie prédite par 3 variables, dont 2 paysagères : le type d’occupation du sol, la densité en lisière, et le nombre de type d’occupation du sol. La communauté de la macrofaune du sol est très appauvrie en rizière et en pâturage, alors qu’elle est plus élevée en forêt et jachère.Au niveau de la parcelle, le type de sol et la couverture végétale en pâturage influencent significativement la macrofaune du sol. En milieu arboré, la diversité de la macrofaune du sol est corrélée avec celle de la diversité de la litière, mais pas avec sa biomasse. D’autre part, la densité de la macrofaune de litière ne présente pas de structure spatiale significative sur des échelles de 2 à 10 m.Nous n’avons pas pu mettre évidence une relation entre le milieu de prédilection et les activités enzymatiques exprimées, mais cela peut être dû à une inadaptation du protocole.En testant plusieurs modèles statistiques, nous montrons que l’évaluation de la relation entre la structure du paysage et la richesse spécifique locale de la macrofaune peut être améliorée par l’utilisation d’un réseau de neurones (perceptron) au lieu de l’approche habituelle d’un modèle basé sur les GLM. Les 2 modèles s’avèrent performants, mais le perceptron apporte des résultats meilleurs en prenant en compte 10% de variance supplémentaire. D’un point de vue méthodologique, les analyses a posteriori que nous avons menées, montrent qu’une dizaine de points par type d’occupation du sol auraient été suffisant pour les analyses. Nous montrons également que les quadrats TSBF ont tendance à surestimer la densité réelle de la macrofaune de litière.Notre étude apporte donc des résultats inédits en montrant l’existence de relations entre la structure du paysage, la diversité de la litière, le type de sol, la structure du couvert végétal à fine échelle, et la communauté de la macrofaune du sol.Selon l’échelle considérée, nous avons identifié des facteurs différents qui influencent la macrofaune du sol, ce qui démontre l’intérêt de notre approche multi-scalaire. Afin d’approfondir ces résultats, il serait nécessaire de les conforter en étudiant ces relations dans d’autres systèmes pédologiques présents en Amazonie, d’approfondir les modalités de dispersion spatiale des organismes à l’échelle du paysage, et d’identifier les mécanismes conditionnant la relation entre la diversité de la macrofaune et celle de la litière.

This study describes the impact on soil fauna populations after conversion of native vegetation to pastures. The invertebrate edaphic macrofauna was evaluated in areas where pastures are being introduced and renewed in the Cerrado, savannah biome. Five sites were considered in a Ferralsol area: a native vegetation area of Cerrado (CE), the deforested Cerrado (DC) and three areas involving pastures:9-years old pasture of Brachiaria brizantha (Pa9), a renewed pasture with the same plant (PaB), and a renewed pasture with Brachiaria associated with a legume, Stylosanthes guianensis (PaS). Thirty-six samples, at random, spaced 20 m apart, were removed from each site. A soil volume of 25 × 25 × 10 cm was delimited at each sampling point. The macrofauna was separated from the soil manually and then identified and weighed. The old pasture presents a higher biomass than the Cerrado area. Mechanical tilling, in both the old pasture and the Cerrado, caused a marked decrease in macrofauna populations. The renewed pastures PaB and PaS showed less diversity, population density and biomass than the deforested Cerrado. Termites were more abundant in the old pasture than in the other areas, however, the Cerrado (CE) showed greater diversity of termite genera and a greater number of predators (Araneae, Scorpions and Pseudoscorpions).

International audience; The influence of three spatially hierarchical factors upon soil macrofauna biodiversity was studied in four pasture plots in eastern Amazonia. The first factor was the local depth of the soil. The second factor was the ground cover type on the soil samples (bare ground, grass tufts, dead trees lying on the ground). The third factor was the dimensions of the grass tufts sampled (size and shape). The effect of each factor upon the morphospecies richness and density of total soil macrofauna was analysed. Detailed results are given for earthworms, termites, ants, beetles and spiders. All factors significantly affected the morphospecies richness and/or density of the soil macrofauna. The type of ground cover had the strongest influence, affecting the total richness and density of the soil macrofauna and of almost all the groups represented. The soil depth affected only the density of the termites and the global morphospecies richness. Interactions between soil depth and ground cover type affected the total macrofauna morphospecies richness and the density of the earthworms. The dimensions of the grass tuft influenced the global morphospecies richness, the morphospecies richness of the ants and the density of the spiders

The impact of sediemnt releases due to road construction on water chemistry and invertebrate communities was studied in a clear water river system in the tropical humid Bolivian Andes. Eight sites (2 references, 1 source and 5 impacted along the main river) were sampled during the 1997 low flow season. Suspended sediment concentrations exhibited a 500-fold increase downstream form the source of pollution compared to the reference site, but recovered to natural levels within 90km in the main river. Suspended soids had only a minor influence on other chemical parameters, but had a clear negative effect on invertebrate density (200-fold decrease in abundance) and diversity (6-fold decrease in number of taxa) in the main river. The most affected insects were epibenthic gatherers (e.g. Ephemeroptera: Leptohyphidae, Coleoptera: Elmidae), swimmers (Ephemeroptera: Leptophlebiidae) and scrapers (Coleoptera: Psephenidae, Trichoptera: Hydroptilidae). These families are therefore considered to be the best potential bio-indicators of sediment release impact in clear-water Andean rivers., L'impact de rejets de sédiments dus à la construction d'une route sur la chimie de l'eau et les communautés d'invertébrés benthiques a été étudié dans un système de rivières d'eaux claires dans les Andes tropicales humides de Bolivie. Huit sites (2 références, 1 sur la source de pollution et 5 sites impactés sur le cours principal) ont été échantillonnés en 1997 pendant la saison sèche. La teneur en matières en suspension (MES) était multipliée par 500 dans le ruisseau recevant les rejets de sédiments, mais retrouvait son niveau naturel après 90 km sur le cours principal. Les MES avaient une influence faible sur les autres paramètres chimiques, mais un impact négatif très marqué sur la densité des invertébrés (abondance réduite d'un facteur 200) et sur leur diversité (nombre de taxons réduit d'un facteur 6) dans le cours principal. Les insectes les plus affectés étaient les collecteurs épibenthiques (Ephemeroptera : Leptohyphidae, Coleoptera : Elmidae), les nageurs (Ephemeroptera : Leptophlebiidae) et les racleurs (Coleoptera : Psephenidae, Trichoptera : Hydroptilidae). Ces familles sont donc considérées comme les meilleurs bioindicateurs potentiels de l'impact des rejets de sédiments dans les rivières andines d'eaux claires.

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From April to September 1994, micofauna density, total biomass, and species diversity of earthworms were measured across a range of land use types in the Cabuyal River watershed. The methodology recommended by the Tropical Soil Biology and Fertility Program (TSBF) was used. Macrofauna density, biomass, and diversity of earthworm species varied considerably across land use types, and depths. Principal component analysis yielded three factors that accounted for 71.8% of the total variance in macrofauna density. High taxonomic units values occur in the Andean forest (98 observed), decreasing dramatically in pastures (ranging from 28 to 13) and farm lands (ranging from 31 to 18). (Résumé d'auteur)