Agroecology and global change

The intensive farming practices that have been developed over the past 60 years are based mainly on the use of chemical inputs such as fertilisers and pesticides, mechanical tillage and monoculture. The limitations of these methods are now clear: long-term degradation of soil fertility, impacts on the environment and human health, high consumption of fossil fuels, low efficiency of inputs and threats to food security in a context of climate change. Would farming practices that rely on the activation of ecological processes be an alternative to achieve a balance between high productivity and environmental preservation? While many studies suggest a positive relationship between soil biodiversity and ecosystem services, there is considerable debate on the form such agricultural systems should take. This study reviewed the state of current knowledge and identified aspects requiring further research to achieve the aim of sustainable intensification of agriculture. The following major points emerged : Most studies focused on the evaluation of individual practices. However, changes in farmers’ cropping practices to take advantage of soil biodiversity services would need to manage not only the interactions between various practices but also the trade-off between the technical and socio economic constraints of cropping systems. Advances in agricultural system design approaches may help to ensure appropriate trade-offs. More attention should be given to drawing on knowledge from different sources: laboratory studies focusing on the ecological functions of soil biodiversity, experimental surveys on farmers’ fields to rank the farming practices and processes to be included in site-specific models, and on- station experiments to test hypotheses and acquire additional reference material. Whereas advances in technical and scientific knowledge provide an increasing number of relevant indicators for characterizing biodiversity and ecological functions, studies are rarely targeted at the development of indicators that are accessible to farmers or their technical advisors. The lack of indicators accessible to grassroots players for evaluating the impacts of their decisions on soil biodiversity remains a serious obstacle to the development of innovative agro-ecological systems

Factors affecting spatial occupancy and local abundance of the Forest Thrush, Turdus lherminieri, in Guadeloupe forests.

International audienceThe Forest Thrush (FT), Turdus lherminieri , is a secretive, ground-dwelling forest bird species of conservation concern, endemic to only four Caribbean islands. Factors influencing habitat selection and abundance by FT have been seldom documented so far. We assessed variation in the presence and abundance of FT in various forested habitats in Guadeloupe. To that end, we deployed 5-camera-trap arrays over 14 days on 24 different survey stations resulting in 1680 trap days. We observed FT more frequently at camera trap stations where rainforest dominated, with local abundance declining with increasing canopy openness. Furthermore, temperature was the most important factor affecting the presence of FT at our study sites. FT was essentially diurnal, with some activity at dawn and dusk. We document for the first-time spatial co-occurrence between FT and potential mammal predators. FT co-occurred positively with rats and negatively with cats. Although FT is globally listed as near threatened by IUCN, the species the species appeared to be relatively abundant in Guadeloupe, possibly as a consequence of the suspension of hunting since 2014 and/or the almost total protection of the Guadeloupe tropical rainforest. We recommend the use of camera traps to improve knowledge for the conservation status of the species in other part of its area of distribution and to provide additional information on the potential impact of exotic predatory mammals

Soil fauna abundance and diversity in a secondary semi-evergreen forest in Guadeloupe (Lesser Antilles) : influence of soil type and dominant tree species

International audienceThe importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species' litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols)

How earthworm activities affect banana plant response to nematodes parasitism

The burrowing nematode Radopholus similis and the lesion nematodes Pratylenchus spp. are considered as major constraints to banana cultivation worldwide. As an alternative to the use of chemical pesticides in commercial banana plantations, the possible role of the earthworm Pontoscolex corethrurus was studied regarding the reducing harmfulness of the main plant-feeding nematodes of banana. The interactions among banana plants, plant-feeding nematodes and earthworms have been tested in a controlled experiment combining treatments including or not earthworms and nematodes, over a complete vegetative banana development cycle. The aim of the work was to evaluate how earthworm activity can affect the pathogenicity of the three main plant-feeding nematodes associated with dessert banana (Musa spp. AAA group, cv. Cavendish) in Guadeloupe (French West Indies), R. similis, Pratylenchus coffeae and Helicotylenchus multicinctus. Results showed that damages caused by plant-feeding nematodes were lowered in the presence of the earthworm P. corethrurus; the population of plant-feeding nematodes did not decrease whereas root damage induced by nematodes was significantly reduced (50% reduction of root necrosis in the presence of earthworms). Moreover, in the presence of P. corethrurus, we observed a change of soil porosity. On the one hand, the burrowing activity of earthworms destroyed most of the initial structural porosity (mesobiotic pores, 3-300 mu m) and on the other hand, they increased the volume of the finest structural pores diameter class (microbiotic pores, 0.3-3 mu m). P. corethrurus also stimulated phosphorus mineralization. Soil bioturbation carried out by P. corethrurus could have enhanced the efficiency of microbial community that is involved in phosphorus bioavailability. This observation was corroborated by a higher phosphorus availability in earthworm casts (1386 +/- 38 mg 13 kg(-1) of dry matter in cast versus 778 +/- 61 mg P kg(-1) of dry matter in the soil compartment not influenced by earthworm activity), and a better plant phosphorus nutrition in the presence of earthworms. Phosphorus uptake resulted in a better plant nutrition and a better tolerance to plant-feeding nematodes. Besides, the reduction of the mesobiotic porosity by bioturbation could also have disturbed the nematodes activities during their soil phase and contributed to the reduction of their damage

Litter N-content influences soil millipede abundance, species richness and feeding preferences in a semi-evergreen dry forest of Guadeloupe (Lesser Antilles)

Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations

Changes in soil biological quality under legume- and maize-based farming systems in a humid savanna zone of Côte d’Ivoire

Studying the impact of farming systems on soil status is essential in determining the most relevant for a given agroecological zone. A trial was conducted in a West Africa humid savanna, aiming at assessing the short-term effects of farming systems on soil (0-10 cm) organic carbon (SOC) content and some soil microbiological properties. A randomized complete block experimental design with three replications, and the following treatments were used: Mucuna pruriens (Mucuna), Pueraria phaseoloides (Pueraria), Lablab purpureus (Lablab), a combination of these three legumes (Mixed-legumes), maize + urea (Maize-U), maize + triple super phosphate (Maize-Sp), maize + urea + triple super phosphate (Maize-USp), fertilizer-free maize continuous cropping (Maize-Tradi). Results indicated that SOC content was improved over time under legume-based systems. The relative increase was the highest with the legume association and Lablab, where SOC varied from 7.5 to 8.6 g.kg-1 (i.e. 14.7%) and from 7.2 to 8.3 g.kg-1 (i.e. 15.3%) respectively, between the start and the end of the trial. Besides, applying grass and maize residues as mulch on the ground, in association with inorganic fertilizers may be a way of improving SOC content in the short-term. Although legume-based systems exhibited highest values, microbial biomass carbon (MBC) did not show any statistical significant differences between treatments. However, soil C mineralization and soil specific respiration were influenced by the farming systems, with higher mean values under legume-based systems (42 ± 7.6 mg C-CO2.g-1 Corg and 0.4 mg C-CO2.g-1 biomass C, respectively), compared to maize continuous cropping systems (33.1 ± 1.6 mg C-CO2.g-1 Corg and 0.3 mg C-CO2.g-1 biomass C, respectively). Thus, these parameters can be used as sensitive indicators of the early changes in soil organic matter quality. The integration of legumes cover crops in farming systems may contribute to improve soil quality that would lead to sustainable agriculture in Côte d'Ivoire humid savannas

Coastal dune topography as a determinant of abiotic conditions and biological community restoration in northern KwaZulu-Natal, South Africa

Topography is rarely considered as an independent goal of restoration. However, topography determines microenvironmental conditions and hence living conditions for species. Restoring topography may therefore be an important first step in ecological restoration. We aimed at establishing the relative importance of topography where coastal dunes destroyed by mining are rebuilt as part of a rehabilitation program. We assessed the response of (1) microclimatic and soil conditions, and (2) woody plant and millipede species richness and density, to locationspecific topographic profiles. We enumerated the topographic profile using variables of dune morphology (aspect, elevation, and gradient) as well as relative position on a dune (crest, slope, and valley). Temperature, relative humidity, and light intensity varied with aspect, elevation, gradient, and position. However, regeneration age was a better predictor of soil nutrient availability than these topographic variables. Age also interacted with topographic variables to explain tree canopy density and species richness, as well as millipede species richness. The density of keeled millipedes (forest specialists) was best explained by topographic variables alone. The transient nature of these new-growth coastal dune forests likely masks topography-related effects on communities because age-related succession (increasing structural complexity) drives the establishment and persistence of biological communities, not habitat conditions modulated by topography. However, our study has shown that the microhabitats associated with topographic variability influence specialist species more than generalists.Department of Trade and Industry and Richards Bay Minerals and the National Research Foundationhttp://link.springer.com/journal/11355hb2014ab201