Contributions of a global network of tree diversity experiments to sustainable forest plantations

status: publishe

Essence coloniale d’une politique contemporaine: pour une approche fanonienne de la discrimination positive en France

The purpose of this article is to consider the trans-historic dimension of the discussions around positive discrimination in France with the aim to emphasize the origins and continuities of the phenomenon. Firstly, I consider how this practice of differentiation has a dialectic and contradictory relationship with the universalist and republican principles of France. I then demonstrate that some of the historical basis for this relatively recent policy are found in colonialism and slavery. Ultimately, I will face these issues from the vantage point of the concept of "reconnaissance" in Fanonian proposing an analysis through which positive discrimination is inscribed within a dynamic, not at all anachronistic, that insidiously reinforces and perpetuates the cultural and social hegemony of the traditional elites.[fr] Cet article a pour objectif de considérer la dimension transhistorique des discours qui entourent la discrimination positive en France afin de mettre l’accent sur les origines et continuités du phénomène. Il s’agira premièrement d’évoquer le rapport dialectique et contradictoire que cette pratique différentialiste entretient avec les principes universalistes et républicains de la France. Je montrerai par la suite que le colonialisme et l’esclavage constituent certains des fondements historiques de cette politique, pourtant relativement récente dans l’Hexagone. En dernière instance, cette problématique sera envisagée au prisme du concept de « reconnaissance » — dans son acception fanonienne — afin de proposer l’analyse selon laquelle la discrimination positive s’inscrit dans une dynamique — nullement anachronique — qui renforce et perpétue insidieusement l’hégémonie culturelle et sociale des élites traditionnelles

Advancing biodiversity-ecosystem functioning science using high-density tree-based experiments over functional diversity gradients

Increasing concern about loss of biodiversity and its effects on ecosystem functioning has triggered a series of manipulative experiments worldwide, which have demonstrated a general trend for ecosystem functioning to increase with diversity. General mechanisms proposed to explain diversity effects include complementary resource use and invoke a key role for species' functional traits. The actual mechanisms by which complementary resource use occurs remain, however, poorly understood, as well as whether they apply to tree-dominated ecosystems. Here we present an experimental approach offering multiple innovative aspects to the field of biodiversity-ecosystem functioning (BEF) research. The International Diversity Experiment Network with Trees (IDENT) allows research to be conducted at several hierarchical levels within individuals, neighborhoods, and communities. The network investigates questions related to intraspecific trait variation, complementarity, and environmental stress. The goal of IDENT is to identify some of the mechanisms through which individuals and species interact to promote coexistence and the complementary use of resources. IDENT includes several implemented and planned sites in North America and Europe, and uses a replicated design of high-density tree plots of fixed species-richness levels varying in functional diversity (FD). The design reduces the space and time needed for trees to interact allowing a thorough set of mixtures varying over different diversity gradients (specific, functional, phylogenetic) and environmental conditions (e.g., water stress) to be tested in the field. The intention of this paper is to share the experience in designing FD-focused BEF experiments with trees, to favor collaborations and expand the network to different conditions

Functional identity is the main driver of diversity effects in young tree communities

Two main effects are proposed to explain biodiversity–ecosystem functioning relationships: niche complementarity and selection effects. Both can be functionally defined using the functional diversity (FD) and functional identity (FI) of the community respectively. Herein, we present results from the first tree diversity experiment that separated the effect of selection from that of complementarity by varying community composition in high-density plots along a gradient of FD, independent of species richness and testing for the effects of FD and community weighted means of traits (a proxy for FI) on stem biomass increment (a proxy for productivity). After 4 years of growth, most mixtures did not differ in productivity from the averages of their respective monocultures, but some did overyield significantly. Those positive diversity effects resulted mostly from selection effects, primarily driven by fast-growing deciduous species and associated traits. Net diversity effect did not increase with time over 4 years

Surface litter decomposition, soil respiration as a function of Taxonomic diversity, functional diversity and functional identity

No.Sp – number of species CO2 – rates of soil respiration in µmolCO2m-2s-1 K – decomposition rate of home litter in d-1 ComsubK – decomposition rate of common substrate (“Common litter experiment”) Pred.CO2 – soil respiration rates predicted from those in monospecific plots Pred.K – decomposition rates of home litter predicated from those in monospecific plots Pred.ComsubK – decomposition rates of the common substrate predicted from the same common substrate decomposition in monoculture plots Dev.pred – (observed – predicted) CWM – community-weighted mean FD- functional Diversity Traits maxH – max height GR – growth rate LS – leaf size WD – wood density WDR – wood decay resistence Sem – seed mass RoH – root habut AM - Arbuscular mycorrhizas (Endomycorrhiza ) EM - Ectomycorrhizas Rdiam – root diameter Llo – lead longevity Lma – leaf mass per area Nleaf – leaf nitrogen content C – litter carbon content N – litter carbon content LDMC – leaf dry matter content SLA – specific leaf are

Partitioning the effect of composition and diversity of tree communities on leaf litter decomposition and soil respiration

The decomposition of plant material is an important ecosystem process influencing both carbon cycling and soil nutrient availability. Quantifying how plant diversity affects decomposition is thus crucial for predicting the effect of the global decline in plant diversity on ecosystem functioning. Plant diversity could affect the decomposition process both directly through the diversity of the litter, and/or indirectly through the diversity of the host plant community and its affect on the decomposition environment. Using a biodiversity experiment with trees in which both functional and taxonomic diversity were explicitly manipulated independently, we tested the effects of the functional diversity and identity of the living trees separately and in combination with the functional diversity and identity of the decomposing litter on rates of litter decomposition and soil respiration. Plant traits, predominantly leaf chemical and physical traits, were correlated with both litter decomposition and soil respiration rates. Surface litter decomposition, quantified by mass loss in litterbags, was best explained by abundance-weighted mean trait values of tree species from which the litter was assembled (functional identity). In contrast, soil respiration, which includes decomposition of dissolved organic carbon and root respiration, was best explained by the variance in trait values of the host trees (functional diversity). This research provides insight into the effect of loss of tree diversity in forests on soil processes. Such understanding is essential to predicting changes in the global carbon budget brought on by biodiversity loss

Nicolas Sarkozy's Africa policy: Change, continuity or confusion?

Three years after inviting Colonel Ghadafi on a state visit, the French president, Nicolas Sarkozy, was spearheading NATO's campaign against the Libyan regime. This dramatic volte face pointed to a new approach to North Africa, while also highlighting the immobility of French policy towards black Africa. Before being elected, Sarkozy had promised to break with Françafrique. But did he deliver? This article does not confine itself to the usual debate about rupture/continuity but also assesses the extent to which Sarkozy's Africa policy was marked by uncertainty, inconsistency and confusion. It looks for evidence of rupture, continuity and confusion during the Sarkozy era. It then identifies the factors driving and constraining change, as well as the causes of policy incoherence. It ends by exploring the wider implications of this case and identifying future policy directions