Functional attributes: Compacting vs decompacting earthworms and influence on soil structure

A short term field mesocosm experiment was performed in semi-deciduous forest areas of Ivory Coast to assess the impact of a decompacting (Hyperiodrilus africanus, Eudrilidae) and two compacting (Millsonia omodeoi and Dichogaster terraenigrae, Acanthodrilidae) earthworm species on soil properties. These species have been selected for their predominance in the region and their contrasting impact on soil structure. The experimental design consisted of a treatment without worms (control), and treatments with one, two or three species of earthworms. Both compacting and decompacting earthworms increased water infiltration rate in all treatments, with marked impact in H. africanus and M. omodeoi+D. terraenigrae treatments. Interactions between compacting and decompacting species resulted in more large aggregates in comparison to when the compacting species D. terraenigrae was alone. This may be accounted for by their compacting attribute as compacting earthworms are responsible for producing the highest number of large aggregates. The low values of mean weight diameter in treatments combining decompacting and compacting earthworms compared with compacting "M. omodeoi" one also confirmed the trend of decline in soil compaction in the presence of the decompacting species. These results showed positive impact of species richness on soil structure regulation, which is crucial in ecosystem productivity and support consequently the insurance hypothesis. In fact, this study showed that the preservation of earthworm species belonging to these two contrasting functional groups is essential for the maintenance of stable soil structure regulation in agro-tropical ecosystems [Current Zoology 58 (4): 556–565, 2012]

Farmers' preferred tree species and their potential carbon stocks in southern Burkina Faso: Implications for biocarbon initiatives.

The success of terrestrial carbon sequestration projects for rural development in sub-Saharan Africa lies in the (i) involvement of local populations in the selection of woody species, which represent the biological assets they use to meet their daily needs, and (ii) information about the potential of these species to store carbon. Although the latter is a key prerequisite, there is very little information available. To help fill this gap, the present study was undertaken in four pilot villages (Kou, Dao, Vrassan and Cassou) in Ziro Province, south-central Burkina Faso. The objective was to determine carbon storage potential for top-priority woody species preferred by local smallholders. We used (i) participatory rural appraisal consisting of group discussions and key informant interviews to identify priority species and functions, and (ii) landscape assessment of carbon stocks in the preferred woody species. Results revealed 79 priority tree and shrub species grouped into six functions, of which medicine, food and income emerge as the most important ones for the communities. For these functions, smallholders overwhelmingly listed Vitellaria paradoxa, Parkia biglobosa, Afzelia africana, Adansonia digitata, Detarium microcarpum, and Lannea microcarpa among the most important tree species. Among the preferred woody species in Cassou and Kou, the highest quantity of carbon was stored by V. paradoxa (1180 ±209 kg C ha-1 to 2089±522 kg C ha-1) and the lowest by Grewia bicolor (5±1.2 kg C ha-1). The potential carbon stored by the preferred tree communities was estimated at 587.9 Mg C ha-1 (95% CI: 456.7; 719.1 Mg C ha-1) in Kou and256.8 Mg C ha-1 (95% CI: 67.6; 324.4 Mg C ha-1) in Cassou. The study showed that the species that farmers preferred most stored more carbon than species that were less preferred

Ecological changes induced by full-sun cocoa farming in Côte d’Ivoire

AbstractFull-sun cocoa farming is currently the most widespread cocoa cultivation system in humid and sub-humid Côte d’Ivoire. Higher short-term yields from increasing surfaces under cultivation in this farming system have contributed to the country being ranked as top cocoa producer in the world. However the negative consequences including biodiversity loss, soil fertility depletion and soil quality degradation associated with this system, have incredibly received so less attention that the type and magnitude of such agro-ecological consequences within the current context of climate change are worth investigating. The present study was undertaken in the former cocoa belt of Central-Western Côte d’Ivoire, precisely in the Oumé Department. The main objective was to assess the impact of forest conversion to full-sun cocoa plantations on above and below-ground biodiversity along with soil quality by measuring chemical, physical and biological parameters along a chronosequence of different ages (5, 10 and 20 years). The results are summarized as follows: (i) the conversion of semi-deciduous forests to cocoa plantations resulted in plant diversity and species richness loss due to the disappearance of a huge number of native species while earthworm abundance and species richness increased due to the appearance of species adapted to degraded lands, (ii) soil quality was severely impaired by cocoa farming with the worse scenario being found under the 10-year-old cocoa plantations, where SOC, total N, CEC contributed mostly to soil quality degradation. The contribution of these findings to devise options for sustainable tree-based cocoa farming is discussed

Managing New Risks of and Opportunities for the Agricultural Development of West-African Floodplains: Hydroclimatic Conditions and Implications for Rice Production

International audienceHigh rainfall events and flash flooding are becoming more frequent, leading to severe damage to crop production and water infrastructure in Burkina Faso, Western Africa. Special attention must therefore be given to the design of water control structures to ensure their flexibility and sustainability in discharging floods, while avoiding overdrainage during dry spells. This study assesses the hydroclimatic risks and implications of floodplain climate-smart rice production in southwestern Burkina Faso in order to make informed decisions regarding floodplain development. Statistical methods (Mann-Kendall test, Sen’s slope estimator, and frequency analysis) combined with rainfall-–runoff modeling (HBV model) were used to analyze the hydroclimatic conditions of the study area. Moreover, the spatial and temporal water availability for crop growth was assessed for an innovative and participatory water management technique. From 1970 to 2013, an increasing delay in the onset of the rainy season (with a decreasing pre-humid season duration) occurred, causing difficulties in predicting the onset due to the high temporal variability of rainfall in the studied region. As a result, a warming trend was observed for the past 40 years, raising questions about its negative impact on very intensive rice cultivation packages. Farmers have both positive and negative consensual perceptions of climatic hazards. The analysis of the hydrological condition of the basin through the successfully calibrated and validated hydrological HBV model indicated no significant increase in water discharge. The sowing of rice from the 10th to 30th June has been identified as optimal in order to benefit from higher surface water flows, which can be used to irrigate and meet crop water requirements during the critical flowering and grain filling phases of rice growth. Furthermore, the installation of cofferdams to increase water levels would be potentially beneficial, subject to them not hindering channel drainage during peak flow

Soil macroinvertebrate communities: A world‐wide assessment

International audienceAim: Macroinvertebrates comprise a highly diverse set of taxa with great potential as indicators of soil quality. Communities were sampled at 3,694 sites distributed world-wide. We aimed to analyse the patterns of abundance, composition and network characteristics and their relationships to latitude, mean annual temperature and rainfall, land cover, soil texture and agricultural practices. Location: Sites are distributed in 41 countries, ranging from 55 degrees S to 57 degrees N latitude, from 0 to 4,000 m in elevation, with annual rainfall ranging from 500 to >3,000 mm and mean temperatures of 5-32 degrees C. Time period: 1980-2018. Major taxa studied: All soil macroinvertebrates: Haplotaxida; Coleoptera; Formicidae; Arachnida; Chilopoda; Diplopoda; Diptera; Isoptera; Isopoda; Homoptera; Hemiptera; Gastropoda; Blattaria; Orthoptera; Lepidoptera; Dermaptera; and "others". Methods: Standard ISO 23611-5 sampling protocol was applied at all sites. Data treatment used a set of multivariate analyses, principal components analysis (PCA) on macrofauna data transformed by Hellinger's method, multiple correspondence analysis for environmental data (latitude, elevation, temperature and average annual rainfall, type of vegetation cover) transformed into discrete classes, coinertia analysis to compare these two data sets, and bias-corrected and accelerated bootstrap tests to evaluate the part of the variance of the macrofauna data attributable to each of the environmental factors. Network analysis was performed. Each pairwise association of taxonomic units was tested against a null model considering local and regional scales, in order to avoid spurious correlations. Results: Communities were separated into five clusters reflecting their densities and taxonomic richness. They were significantly influenced by climatic conditions, soil texture and vegetation cover. Abundance and diversity, highest in tropical forests (1,895 +/- 234 individuals/m(2)) and savannahs (1,796 +/- 72 individuals/m(2)), progressively decreased in tropical cropping systems (tree-associated crops, 1,358 +/- 120 individuals/m(2); pastures, 1,178 +/- 154 individuals/m(2); and annual crops, 867 +/- 62 individuals/m(2)), temperate grasslands (529 +/- 60 individuals/m(2)), forests (232 +/- 20 individuals/m(2)) and annual crops (231 +/- 24 individuals/m(2)) and temperate dry forests and shrubs (195 +/- 11 individuals/m(2)). Agricultural management decreased overall abundance by <= 54% in tropical areas and 64% in temperate areas. Connectivity varied with taxa, with dominant positive connections in litter transformers and negative connections with ecosystem engineers and Arachnida. Connectivity and modularity were higher in communities with low abundance and taxonomic richness. Main conclusions: Soil macroinvertebrate communities respond to climatic, soil and land-cover conditions. All taxa, except termites, are found everywhere, and communities from the five clusters cover a wide range of geographical and environmental conditions. Agricultural practices significantly decrease abundance, although the presence of tree components alleviates this effect

Soil macroinvertebrate communities: A world‐wide assessment

International audienceAim Macroinvertebrates comprise a highly diverse set of taxa with great potential as indicators of soil quality. Communities were sampled at 3,694 sites distributed world-wide. We aimed to analyse the patterns of abundance, composition and network characteristics and their relationships to latitude, mean annual temperature and rainfall, land cover, soil texture and agricultural practices. Location Sites are distributed in 41 countries, ranging from 55 degrees S to 57 degrees N latitude, from 0 to 4,000 m in elevation, with annual rainfall ranging from 500 to >3,000 mm and mean temperatures of 5-32 degrees C. Time period 1980-2018. Major taxa studied All soil macroinvertebrates: Haplotaxida; Coleoptera; Formicidae; Arachnida; Chilopoda; Diplopoda; Diptera; Isoptera; Isopoda; Homoptera; Hemiptera; Gastropoda; Blattaria; Orthoptera; Lepidoptera; Dermaptera; and "others". Methods Standard ISO 23611-5 sampling protocol was applied at all sites. Data treatment used a set of multivariate analyses, principal components analysis (PCA) on macrofauna data transformed by Hellinger's method, multiple correspondence analysis for environmental data (latitude, elevation, temperature and average annual rainfall, type of vegetation cover) transformed into discrete classes, coinertia analysis to compare these two data sets, and bias-corrected and accelerated bootstrap tests to evaluate the part of the variance of the macrofauna data attributable to each of the environmental factors. Network analysis was performed. Each pairwise association of taxonomic units was tested against a null model considering local and regional scales, in order to avoid spurious correlations. Results Communities were separated into five clusters reflecting their densities and taxonomic richness. They were significantly influenced by climatic conditions, soil texture and vegetation cover. Abundance and diversity, highest in tropical forests (1,895 +/- 234 individuals/m(2)) and savannahs (1,796 +/- 72 individuals/m(2)), progressively decreased in tropical cropping systems (tree-associated crops, 1,358 +/- 120 individuals/m(2); pastures, 1,178 +/- 154 individuals/m(2); and annual crops, 867 +/- 62 individuals/m(2)), temperate grasslands (529 +/- 60 individuals/m(2)), forests (232 +/- 20 individuals/m(2)) and annual crops (231 +/- 24 individuals/m(2)) and temperate dry forests and shrubs (195 +/- 11 individuals/m(2)). Agricultural management decreased overall abundance by <= 54% in tropical areas and 64% in temperate areas. Connectivity varied with taxa, with dominant positive connections in litter transformers and negative connections with ecosystem engineers and Arachnida. Connectivity and modularity were higher in communities with low abundance and taxonomic richness. Main conclusions Soil macroinvertebrate communities respond to climatic, soil and land-cover conditions. All taxa, except termites, are found everywhere, and communities from the five clusters cover a wide range of geographical and environmental conditions. Agricultural practices significantly decrease abundance, although the presence of tree components alleviates this effect