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Decaens T.,CNRS Biodiversity Studies Laboratory
Global Ecology and Biogeography | Year: 2010

Aim To review published evidence regarding the factors that influence the geographic variation in diversity of soil organisms at different spatial scales. Location Global. Methods A search of the relevant literature was conducted using the Web of Science and the author's personal scientific database as the major sources. Special attention was paid to include seminal studies, highly cited papers and/or studies highlighting novel results. Results Despite their significant contribution to global biodiversity, our taxonomic knowledge of soil biota is still poor compared with that of most aboveground organisms. This is particularly evident for small-bodied taxa. Global patterns of soil biodiversity distribution have been poorly documented and are thought to differ significantly from what is reported above-ground. Based on existing data, it appears that microorganisms do not respond to large-scale environmental gradients in the same way as metazoans.Whereas soil microflora seem to be mainly represented by cosmopolitan species, soil animals respond to altitudinal, latitudinal or area gradients in the same way as described for above-ground organisms. At local scales, there is less evidence that local factors regulate above- and below-ground communities in the same way. Except for a few taxa, the humpbacked response to stress and disturbance gradients doesn't seem to apply underground. Soil communities thus appear weakly structured by competition, although competitive constraints may account for assembly rules within specific taxa. The main factor constraining local soil biodiversity is the compact and heterogeneous nature of soils, which provides unrivalled potential for niche partitioning, thus allowing high levels of local biodiversity. This heterogeneity is increased by the impact of ecosystem engineers that generate resource patchiness at a range of spatio-temporal scales. © 2010 Blackwell Publishing Ltd. Source

Le Bagousse-Pinguet Y.,University of Konstanz | Le Bagousse-Pinguet Y.,University of Bordeaux 1 | Forey E.,CNRS Biodiversity Studies Laboratory | Touzard B.,University of Bordeaux 1 | Michalet R.,University of Bordeaux 1
Journal of Vegetation Science | Year: 2013

Questions: What is the relative role of water vs nutrients in driving changes in plant interactions in a dry and nutrient-poor dune system, where facilitation has been shown to highly contribute to the diversity and composition of plant communities? Location: Atlantic coastal sand dune system, Aquitaine region, France. Methods: We manipulated water (water addition) and nutrient (fertilizer addition) availabilities in a full-factorial experiment that lasted from September 2005 to September 2006. The responses of plants to neighbours were assessed through transplanting six target species within each experimental plot in the presence or absence (removal procedure) of the dominant shrub Helichrysum stoechas. We also measured changes in H. stoechas biomass among treatments. Results: Watering mainly affected survival of the target species without neighbours and the direction of their responses to the shrub, whereas fertilization strongly increased the biomass of the shrub and intensity of the responses of the targets to the effects of the shrub. We did not observe any occurrence of biotic interactions (either positive or negative) for most of the target species in the unfertilized plots. In contrast, three of the six species exhibited significant facilitation in fertilized and un-watered plots, and significant competition in fertilized and watered plots. Conclusions: Our results highlight the co-limitation of water and nutrients in coastal sand dunes. Nutrient availability mainly drove the neighbour effect of the shrub, whereas water availability affected the responses of the target species. Although further measurements of resource modifications by the shrub are needed to firmly conclude neighbour effects, our results provide new insights to the contrasting results in the literature on plant-plant interactions in unproductive communities. We propose that, depending on the system, changes in a given direct stress factor may either induce a collapse of interactions by decreasing neighbour performances and their effects, or a shift in the direction of interactions by affecting target species responses. © International Association for Vegetation Science. Source

Forey E.,CNRS Biodiversity Studies Laboratory | Dutoit T.,University of Avignon
Community Ecology | Year: 2012

This study identifies the long lasting impacts of former cultivation on soils, seed banks and above-ground vegetation of limestone grasslands. We compared the resilience of three crop fields cultivated in the 19th century and abandoned (Abandoned Fields) with three grasslands which have never been cultivated (Old Grasslands). Grasslands were located in the Nature reserve of Grand-Pierre and Vitain valleys in France. Sites were identified using historical sources. Chemical and physical soil properties, above-ground vegetation and soil seed bank (0-10 cm and 10-20 cm) were studied. Data were analysed using a multivariate and univariate analyses to detect the effects/impacts of ancient cultivation. Our results clearly show that soil properties (e.g., calcium, carbonate, clay contents), above-ground vegetation (species diversity, moss and lichen cover) and seed bank (floristic composition, species-richness and diversity) are still impacted more than one century after their abandonment. Species richness of both above ground vegetation and seed bank are higher in old grasslands than in formerly cultivated fields. In the seed bank of the formerly cultivated soils we also found the presence of a very rare arable weed species (Althaea hirsuta) which has not been inventoried for a long time in the above-ground vegetation of the nature reserve. The resilience of formerly cultivated limestone grasslands might be influenced by the present management regime (site effect). Nevertheless, the resilience period of limestone grasslands is very long-more than one century-and return to an initial state might be difficult or impossible to reach. © Akadémiai Kiadó, Budapest. Source

Trap J.,IRD Montpellier | Hattenschwiler S.,CNRS Center of Evolutionary and Functional Ecology | Gattin I.,Laboratoire Biosol | Aubert M.,CNRS Biodiversity Studies Laboratory
Forest Ecology and Management | Year: 2013

The role of forest age as a potential driver of intraspecific variation in leaf litter quality, that is a key plant trait determining ecosystem functioning, has largely been neglected. Using a set of fully replicated pure beech (Fagus sylvatica) forest stands differing in age (15, 65, 95 and 130. years), we quantified the forest stand age related variability of twelve leaf litter quality traits. Litter Mg, N and K showed significantly higher concentrations in litter from 15-yrs-old stands and decreased with increasing stand age. Mn was the only nutrient analyzed that was highest in the oldest stands. Hemicellulose and cellulose were lowest, and lignin and lignin/N ratio were highest in stands of intermediate age. The amount of N within the litter lignin fraction was highest in the 95-yrs-old stands (51% of total N) and lowest in the oldest stands (34% of total N). The amount of N associated within the hemicellulose fraction (<3%) showed the opposite pattern along the forest stand age gradient compared to lignin. Using Partial Least Squares regressions, we showed that litter N, C/N, lignin/N, K, Mn and Mg were the most important predictors of litter decomposition along the chronosequence. In contrast the proportions of C fractions and the amount of N within these C fractions were the most significant variables explaining the variation in final litter N content after one year of decomposition. N mineralization in ground litter was highly related to the proportion of total N within lignin and humus N mineralization was mostly explained by Mn and the lignin/N ratio. We showed that forest age is an important driver of litter quality variation and contributed considerably to the overall variation of F. sylvatica leaf litter quality traits observed from a reviewed data of published studies conducted at the continental scale. Furthermore, intraspecific litter quality variation greatly impacted belowground processes. Accounting for forest age related litter trait variation, and for the crucial role of the distribution of N within different litter C fractions, may improve the mechanistic understanding of ecosystem functioning. © 2013 Elsevier B.V. Source

Huste A.,CNRS Biodiversity Studies Laboratory | Boulinier T.,CNRS Center of Evolutionary and Functional Ecology
Biological Conservation | Year: 2011

The ecological processes responsible for the spatial assemblages of breeding bird communities in urban landscapes are more and more investigated. Indeed, understanding these processes is imperative to plan relevant management policies. We investigated breeding bird communities on 67 patches in the suburbs of Paris, France. We examined the role of patch characteristics and geographic distance between patches in determining similarity between bird assemblages. To do this, we proposed a new SØrensen similarity index based on estimators of change in community composition taking into account the detection probability of species. The patch occupancy by sedentary and migratory species was also estimated to compare their sensitivity to urbanization. Patches close to each other supported more similar bird assemblages, suggesting an effect of the spatial distribution of patches on bird dispersal and a posteriori on local community composition. Accounting for spatial location of patches, bird assemblage similarity was related to the similarity of the surrounding level of urbanization but not to the similarity of patch size or to the similarity of patch vegetation. The mean estimated occupancy rate of sedentary species was higher than that of migratory species in the whole study area. While sedentary species occupied patches surrounded by both moderate and high levels of urbanization, migratory ones primarily occupied patches surrounded by moderate levels of urbanization. Human choices in degrees, styles, and extent of urbanization, including designation and design of patches within an urban matrix, affect the composition of local bird communities. © 2010 Elsevier Ltd. Source

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