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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.

The objective of this study was to investigate the impact of soil management on soil biofunctioning in the highlands of Madagascar. Direct seeding Mulch-based Cropping systems (DMC) were compared to conventional tillage (CT) and the natural fallow (NF) on the rate of decomposition and mineralization of residues as well as on the abundance, biomass and activity of litter- and soilmicroorganisms and macrofauna. Long term experimentation was used in Bemasoandro and Andranomanelatra. Contrasted cropping systems were studied, DMC on crop residues and on living mulches, CT and the NF. Results showed that the NF soil had the highest C and N content, however DMCs increased microbial biomass, soil respiration and nutrient cycling except for urease activity which was very high in NF (P, L'impact du mode de gestion du sol sur son biofonctionnement a été étudié sur les hauts plateaux de Madagascar. Le semis direct sur couverture végétale (SCV) est comparé au labour traditionnel (LB) et à la jachère naturelle (JN) concernant la minéralisation des résidus, l'abondance et les activités des microorganismes et de la macrofaune de la litière et du sol. L’étude a été menée à Bemasoandro et Andranomanelatra sur des systèmes contrastés de longue durée, SCV sur résidus et couverture vive, LB et la JN. Le sol sous la JN a les teneurs en C et N les plus élevées. Mais les SCV augmentent la biomasse microbienne, la respiration du sol et certaines activités enzymatiques du sol plus que la JN (P

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.

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

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.

La pratique d'écobuage, appelée "maala" en langue locale Bembé, est l'un des nombreux systèmes de culture traditionnels pratiqués dans la vallée du Niari, dans le Sud-Ouest du Congo en Afrique centrale. Ce système consiste à former des buttes de sol, ou de longs billons, dans lesquels les herbes enfouies sont brûlées par étouffement. Cette technique est pratiquée sur des sols ferrallitiques, argileux, désaturés et acides. On a mesuré dans ce travail l'incidence de cette pratique sur les peuplements de macroinvertébrés en général, et les vers de terre en particulier, et l'influence que ces derniers peuvent avoir sur la structure micromorphologique, les propriétés physico-chimiques de ces sols et la production agricole. La densité du peuplement de macroinvertébrés du sol dans les divers types d'utilisation traditionnelle du sol de la région varie de 456 à 1907 ind/m2 ; la biomasse de 16 à 75 g/m2. La densité des vers de terre varie de 68 à 738 ind/m2 et la biomasse de 16 à 50 g/m2. L'enfouissement des débris végétaux permet une recolonisation du milieu par les peuplements de macroinvertébrés, et surtout les vers de terre. Les transformations provoquées par l'élévation de la température se manifestent par une coagulation des particules argileuses qui est à l'origine de la formation d'agrégats très cohérents et très peu dispersables avec les méthodes classiques. On observe une augmentation des sables grossiers (pseudosables) et une diminution du taux d'argile granulométrique. L'activité des vers de terre a pour effet visible un certain tassement de ces sols très aérés en profondeur ce qui influe favorablement sur leur capacité à retenir l'eau. La fraction organique s'appauvrit tandis que l'apport d'éléments minéraux, contenus dans les cendres, provoque une augmentation du pH, des cations échangeables et une saturation du complexe adsorbant... (D'après résumé d'auteur)

An encompassing view of coral reef ecosystems needs to extend beyond the prominent and attractive hard substrata to include soft-sediment habitats associated with the reefs. Focusing on the soft-sediment assemblages within the lagoon of the Great Astrolabe Reef (Fiji), we quantified pat- terns, clines and variability of community structure across space and evaluated models for marine bio- diversity conservation based on the spatial distribution and rarity of benthic species. Water depth sam- pled ranged from 17 to 42 m over a spatial sampling scale of 18 x 11 km with 25 localities on average 2.4 km apart. Both plant diversity and biomass were poor predictors of zoobenthic diversity. In contrast to the commonly held view that sediment characteristics are the prime factors in structuring benthic assemblages, spatial variability of the benthos was overriding the generally weak relationships between sedimentary features and the biota. High spatial heterogeneity in community structure is a key feature of the benthic biota in the lagoon. Part of this pronounced spatial heterogeneity stems from the marked patchiness in individual species distributions, here operationally coined 'spot endemism'. Out of a total of 211 recorded taxa, 42% were rare, being restricted to a single site. No species' range spanned the entire lagoon; in fact, the maximum species range was 16 out of 25 sites sampled. Fur- thermore, the number of taxa common to any 2 localities was not strongly linked to spatial distance, with adjoining sites having no more taxa in common than more distant localities. The commonness of rarity, prevalence of highly compressed species' range sizes, and patchiness in benthic diversity all combine to have profound implications for conservation strategies of these marine benthic habitats.