Éditeur(s) : HAL CCSD
Résumé : This paper develops a two-way director-firm fixed effect model to study the relationship between independent directors’ individual heterogeneity and firm operating performance, using French data. This strategy allows considering and differentiating in a unified empirical framework mechanisms related to board functioning and mechanisms related to director selection. We first show that the independence status, netted out unobservable individual heterogeneity, is negatively related to performance. This result suggests that independent board members experience a strong informational gap that outweighs other monitoring benefits. However, we show that industry-specific expertise as well as informal connections inside the boardroom may help to bridge this gap. Second, we provide evidence that independent directors have higher intrinsic ability as compared to affiliated board members, consistent with a reputation-based selection process.
https://hal.archives-ouvertes.fr/hal-01060211

hal-01060211
https://hal.archives-ouvertes.fr/hal-01060211
https://hal.archives-ouvertes.fr/hal-01060211v2/document
https://hal.archives-ouvertes.fr/hal-01060211/file/cahier%202014-29.pdf

Éditeur(s) : HAL CCSD
Résumé : While often criticized, independence remains the ultimate criterion for evaluating board composition, whether for regulators or shareholder activists. In this study, we examine the relationship between board independence and firm operating performance in a panel of French listed companies, paying particular attention to heterogeneity and endogeneity concerns. We take advantage of an original database, with a time-series dimension that can be used to mitigate heterogeneity and dynamic endogeneity issues through GMM estimators. In addition, this database can be disaggregated at the individual (director) level. This design enables us to introduce firm fixed effects and individual fixed effects in (firm) performance equations, thereby controlling for heterogeneity at the firm and individual levels. To our knowledge, this is the first paper so far to provide a systematic account on this issue for France. Our main result is to document a significant negative relationship between accounting performance and the independence status (irrespective of the person). This result supports the argument of an information gap suffered by independent board members, as developed by Adams and Ferreira (2007).
https://hal.archives-ouvertes.fr/hal-00919408

hal-00919408
https://hal.archives-ouvertes.fr/hal-00919408
https://hal.archives-ouvertes.fr/hal-00919408v2/document
https://hal.archives-ouvertes.fr/hal-00919408/file/cahier_de_recherche_2014-01.pdf

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : We investigated the relationship between habitat association and physiological performance in four congeneric species pairs exhibiting contrasting distributions between seasonally flooded and terra firme habitats in lowland tropical rain forests of French Guiana, including Virola and Iryanthera (Myristicaceae), Symphonia (Clusiaceae), and Eperua (Caesalpiniaceae). We analyzed 10-year data sets of mapped and measured saplings (stems 150 cm in height and <10 cm diameter at breast height [dbh]) and trees (stems 10 cm dbh) across 37.5 ha of permanent plots covering a 300-ha zone, within which seasonally flooded areas (where the water table never descends below 1 m) have been mapped. Additionally, we tested the response of growth, survival, and leaf functional traits of these species to drought and flood stress in a controlled experiment. We tested for habitat preference using a modification of the torus translation method. Strong contrasting associations of the species pairs of Iryanthera, Virola, and Symphonia were observed at the sapling stage, and these associations strengthened for the tree stage. Neither species of Eperua was significantly associated with flooded habitats at the sapling stage, but E. falcata was significantly and positively associated with flooded forests at the tree stage, and trees of E. grandiflora were found almost exclusively in nonflooded habitats. Differential performance provided limited explanatory support for the observed habitat associations, with only congeners of Iryanthera exhibiting divergent sapling survival and tree growth. Seedlings of species associated with flooded forest tended to have higher photosynthetic capacity than their congeners at field capacity. In addition, they tended to have the largest reductions in leaf gas exchange and growth rate in response to experimental drought stress and the least reductions in response to experimental inundation. The corroboration of habitat association with differences in functional traits and, to a lesser extent, measures of performance provides an explanation for the regional coexistence of these species pairs. We suggest that specialization to seasonally flooded habitats may explain patterns of adaptive radiation in many tropical tree genera and thereby provide a substantial contribution to regional tree diversity.
ISSN: 0012-9658

hal-01031746
https://hal.archives-ouvertes.fr/hal-01031746

Éditeur(s) : HAL CCSD Wiley
Résumé : Wood specific gravity (WSG) is a strong predictor of tree performance across environmental gradients. Yet it remains unclear how anatomical elements linked to different wood functions contribute to variation in WSG in branches and roots across tropical forests. [br/][br/]We examined WSG and wood anatomy in white sand, clay terra firme and seasonally flooded forests in French Guiana, spanning broad environmental gradients found throughout Amazonia. We measured 15 traits relating to branches and small woody roots in 113 species representing the 15 most abundant species in each habitat and representative species from seven monophyletic lineages occurring in all habitats. [br/][br/]Fiber traits appear to be major determinants of WSG, independent of vessel traits, in branches and roots. Fiber traits and branch and root WSG increased from seasonally flooded species to clay terra firme species and lastly to white sand species. Branch and root wood traits were strongly phylogenetically constrained. Lineages differed in wood design, but exhibited similar variation in wood structure across habitats. [br/][br/]We conclude that tropical trees can invest differently in support and transport to respond to environmental conditions. Wind disturbance and drought stress represent significant filters driving tree distribution of Amazonian forests; hence we suggest that biophysical explanations should receive more attention.
ISSN: 0028-646X

hal-01195075
https://hal.archives-ouvertes.fr/hal-01195075
PRODINRA : 269680
PUBMED : 24329812

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3.We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20%of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our 'every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.
ISSN: 0269-8463

hal-00594009
https://hal.archives-ouvertes.fr/hal-00594009

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé :  
1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3.We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20%of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our 'every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.
Functional Ecology

hal-01032175
https://hal.archives-ouvertes.fr/hal-01032175
DOI : 10.1111/j.1365-2435.2009.01600.x

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
This study aims to assess the evidence on adverse pregnancy outcome associated with living close to polluted industrial sites, and identify the strengths and weaknesses of published epidemiological studies. A systematic literature search has been performed on all epidemiological studies published in developed countries since 1990, on the association between residential proximity to industrial sites (hazardous waste sites, industrial facilities and landfill sites) and adverse pregnancy outcome (low birth weight, preterm birth, small for gestational age, intrauterine growth retardation, infant mortality, congenital malformation). Based on 41 papers, our review reveals an excess risk of reproductive morbidity. However, no studies show significant excess risk of mortality including fetal death, neonatal or infant mortality and stillbirth. All published studies tend to show an increased risk of congenital abnormalities, yet not all are statistically significant. All but two of these studies revealed an excess risk of low birth weight. Results for preterm birth, small for gestational age and intrauterine growth retardation show the same pattern. There is suggestive evidence from the post-1990 literature that residential proximity to polluted sites (including landfills, hazardous waste sites and industrial facilities) might contribute to adverse reproductive outcomes, especially congenital malformations and low birth weight—though not mortality. This body of evidence has limitations that impede the formulation of firm conclusions, and new, well-focused studies are called for. The review findings suggest that continued strengthening of rules governing industrial emissions as well as industrial waste management and improved land use planning are needed.
ISSN: 1476-072X

Droits : http://creativecommons.org/licenses/by/
hal-01547817
http://hal.upmc.fr/hal-01547817
http://hal.upmc.fr/hal-01547817/document
http://hal.upmc.fr/hal-01547817/file/s12942-017-0091-y.pdf
DOI : 10.1186/s12942-017-0091-y

Éditeur(s) : HAL CCSD Wiley
Résumé : Understanding the mechanisms generating species distributions remains a challenge, especially in hyperdiverse tropical forests. We evaluated the role of rainfall variation, soil gradients and herbivory on seedling mortality, and how variation in seedling performance along these gradients contributes to habitat specialisation. In a 4-year experiment, replicated at the two extremes of the Amazon basin, we reciprocally transplanted 4638 tree seedlings of 41 habitat-specialist species from seven phylogenetic lineages among the three most important forest habitats of lowland Amazonia. Rainfall variation, flooding and soil gradients strongly influenced seedling mortality, whereas herbivory had negligible impact. Seedling mortality varied strongly among habitats, consistent with predictions for habitat specialists in most lineages. This suggests that seedling performance is a primary determinant of the habitat associations of adult trees across Amazonia. It further suggests that tree diversity, currently mostly harboured in terra firme forests, may be strongly impacted by the predicted climate changes in Amazonia.
ISSN: 1461-023X

hal-01531751
https://hal.archives-ouvertes.fr/hal-01531751
DOI : 10.1111/ele.12661
PRODINRA : 387284