Auteurs, date et publication :
Auteurs Elisa Adriano , Jean-Paul Laclau , João Domingos Rodrigues
Publication : Trees
Date : 2025
Volume : 31
Issue : 1
Pages : 285-297
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Understanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observation scales (1-m2 sampling point vs. 2,500-m2 plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance−decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales.
Auteurs, date et publication :
Auteurs Guille Peguero , Miquel Ferrín , Jordi Sardans , Erik Verbruggen , Irene Ramírez-Rojas , Leandro Van Langenhove , Lore T. Verryckt , Jerome Murienne , Amaia Iribar , Lucie Zinger , Oriol Grau , Jerome Orivel , Clément Stahl , Elodie A. Courtois , Dolores Asensio , Albert Gargallo-Garriga , Joan Llusià , Olga Margalef , Romà Ogaya , Andreas Richter
Publication : Ecology
Date : 2025
Volume : 103
Issue : 2
Pages : e03599
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET NouraguesRésumé
Measuring functional or phylogenetic diversity is the object of an active literature. The main issues to address are relating measures to a clear conceptual framework, allowing unavoidable estimation‐bias correction and decomposing diversity along spatial scales. We provide a general mathematical framework to decompose measures of species‐neutral, phylogenetic or functional diversity into α and β components. We first unify the definitions of phylogenetic and functional entropy and diversity as a generalization of HCDT entropy and Hill numbers when an ultrametric tree is considered. We then derive the decomposition of diversity. We propose a bias correction of the estimates allowing meaningful computation from real, often undersampled communities. Entropy can be transformed into true diversity, that is an effective number of species or communities. Estimators of α‐ and β‐entropy, phylogenetic and functional entropy are provided. Proper definition and estimation of diversity is the first step towards better understanding its underlying ecological and evolutionary mechanisms.
Auteurs, date et publication :
Auteurs Eric Marcon , Bruno Hérault , Robert Freckleton
Publication : Methods in Ecology and Evolution
Date : 2015
Volume : 6
Issue : 3
Pages : 333–339
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Unlike Eucalyptus monocultures, nitrogen fixing trees are likely to improve the soil nutrient status through the decomposition of N-enriched litter. The Home Field Advantage (HFA) hypothesis states that plants can create conditions that increase the decomposition rates of their own litter. However, there may not be any HFA when most of the decomposers are generalists. A reciprocal transplant decomposition experiment of fine roots and leaves of Acacia mangium and Eucalyptus grandis was undertaken in monocultures of these two species to test the HFA hypothesis using a complete randomized design with three blocks. Three litterbags containing leaf or fine root residues of each species were collected every 3 months from each plot over 12 months for fine roots and 24 months for leaves. The litter mass and C, N and P concentrations were measured at each sampling date. The concentrations of C-compounds were measured 0, 12 and 24 months from the start of the experiment. There was no evidence of HFA for either the leaves or the fine roots of either species. The decomposition rates were slower for Acacia litter than for Eucalyptus litter even though initial N concentrations were 1.9–2.9 times higher and P concentrations were 1.5–3.3 times higher in the Acacia residues. N:P ratios were greater than 20–30 for the residues of both species, with the highest values for Acacia. Litter decomposition depended partly on the C quality of the litter, primarily in terms of water soluble compounds and lignin content. As shown recently in tropical rainforests, these results suggest that the activity of decomposers is limited by energy starvation in tropical planted forests. Decomposer activity may also have been limited by P availability which may not have been directly related to the P concentrations or C:P ratios in the residues. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs J.-R. Bachega Feijo Rosa , J.-P. Bouillet , M. De Cassia Piccolo , L. Saint André , J.-M. Bouvet , Y. Nouvellon , J.-L. De Moraes Gonçalves , A. Robin , J.-P. Laclau
Publication : Forest Ecology and Management
Date : 2025
Volume : 359
Pages : 33-43
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Clumping index (CI) is a measure of foliage aggregation relative to a random distribution of leaves in space. The CI can help with estimating fractions of sunlit and shaded leaves for a given leaf area index (LAI) value. Both the CI and LAI can be obtained from global Earth Observation data from sensors such as the Moderate Resolution Imaging Spectrometer (MODIS). Here, the synergy between a MODIS-based CI and a MODIS LAI product is examined using the theory of spectral invariants, also referred to as photon recollision probability ('p-theory'), along with raw LAI-2000/2200 Plant Canopy Analyzer data from 75 sites distributed across a range of plant functional types. The p-theory describes the probability (p-value) that a photon, having intercepted an element in the canopy, will recollide with another canopy element rather than escape the canopy. We show that empirically-based CI maps can be integrated with the MODIS LAI product. Our results indicate that it is feasible to derive approximate p-values for any location solely from Earth Observation data. This approximation is relevant for future applications of the photon recollision probability concept for global and local monitoring of vegetation using Earth Observation data.
Auteurs, date et publication :
Auteurs J. Pisek , H. Buddenbaum , F. Camacho , J. Hill , J. L. R. Jensen , H. Lange , Z. L. Liu , A. Piayda , Y. H. Qu , O. Roupsard , S. P. Serbin , S. Solberg , O. Sonnentag , A. Thimonier , F. Vuolo
Publication : Remote Sensing of Environment
Date : 2018
Volume : 215
Pages : 1-6
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs Eric Nicolini , Jacques Beauchêne , Benjamin Leudet de la Vallée , Julien Ruelle , Thomas Mangenet , Patrick Heuret
Publication : Annals of Forest Science
Date : 2012
Volume : 69
Issue : 5
Pages : 543–555
Catégorie(s)
#CIRAD #FORET ParacouRésumé
This article presents the effects of logging on the dynamics of above-ground biomass from the results of the post-logging study within two forests: Cikel in Eastern Pará, Brazil and Paracou in French Guiana. The main objective is to compare the impact of commercial logging on the regeneration of the aboveground biomass in these forests whose characteristics differ in terms of structure and growth. In both sites, the intensity of exploitation is a key factor in determining the loss of biomass and the time required for its regeneration. In Paracou, the regeneration of biomass lost during conventional logging of 10 trees per hectare takes 45 years and more than 100 years when operating with higher intensity (21 trees/ha ). In Cikel the forest biomass regenerates after 49 years harvesting 6 trees/ha and that takes 87 years after removal of 8 trees/ha. This regeneration needs similar time on both sites but with lower logging intensity at Cikel, in which felled trees are larger with a greater biomass than those of Paracou. This post-logging study has established a direct correlation of the dynamics of the biomass with the initial structure of the forest, as well as with the parameters of forest dynamics: mortality, growth and recruitment. The accumulation of biomass by the tree growth of the two remaining stands is a key parameter for the net carbon storage, while the contribution of recruitment in Paracou becomes significant only after 10 years after felling. Therefore in view to improve the growth of residual trees, it is compulsory to apply adequate silvicultural treatments such as selective thinning or removal of vines. While the two forests are geographically close enough, their regenerative abilities differ and because of the significant difference in size of the trees, the forest could tolerate more intensive harvesting in French Guiana. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Plinio Sist , Lilian Blanc , Lucas Mazzei , Christopher Baraloto , Raphaël Aussenac
Publication : Bois et Forêts des Tropiques
Date : 2025
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Upon advances in sequencing techniques, more and more morphologically identical organisms are identified as cryptic species. Often, mutualistic interactions are proposed as drivers of diversification. Species of the neotropical parabiotic ant association between Crematogaster levior and Camponotus femoratus are known for highly diverse cuticular hydrocarbon (CHC) profiles, which in insects serve as desiccation barrier but also as communication cues. In the present study, we investigated the association of the ants’ CHC profiles with genotypes and morphological traits, and discovered cryptic species pairs in both genera. To assess putative niche differentiation between the cryptic species, we conducted an environmental association study that included various climate variables, canopy cover, and mutualistic plant species. Although mostly sympatric, the two Camponotus species seem to prefer different climate niches. However in the two Crematogaster species, we could not detect any differences in niche preference. The strong differentiation in the CHC profiles may thus suggest a possible role during speciation itself either by inducing assortative mating or by reinforcing sexual selection after the speciation event. We did not detect any further niche differences in the environmental parameters tested. Thus, it remains open how the cryptic species avoid competitive exclusion, with scope for further investigations.
Auteurs, date et publication :
Auteurs Juliane Hartke , Philipp P. Sprenger , Jacqueline Sahm , Helena Winterberg , Jérôme Orivel , Hannes Baur , Till Beuerle , Thomas Schmitt , Barbara Feldmeyer , Florian Menzel
Publication : Ecology and Evolution
Date : 2025
Volume : 9
Issue : 16
Pages : 9160-9176
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
Decreasing growth rate (Feeley et al., 2007) and large die-back due to drought (Phillips et al., 2009) suggest that tropical forests are suffering recent climate changes. Forest vulnerability to external factors (e.g. air pollution, acid rain) is widely studied in northern countries, while only a few attempts have investigated crown integrity in the Tropics. The method needs to be generic enough to account for the large number of species and crown shapes encountered in tropical forests. In the present study, we developed and tested a novel field method that estimates crown fragmentation (main branch mortality (MB) and secondary branch mortality (SB)), liana infestation (LI) and crown position (CP) in the canopy. The relationship between crown fragmentation and annual growth rate (agr) was investigated through multiple regression. Six out of eight canopy tree species showed significant growth decline with increasing crown fragmentation. Higher probability of death was also found in trees with severe crown fragmentation. The capacity of such crown assessment to depict tree vitality in a forest stand is discussed along with potential applications in both forest science and management.
Auteurs, date et publication :
Auteurs Ervan Rutishauser , Daniel Barthélémy , Lilian Blanc , Nicolini Eric-André
Publication : Forest Ecology and Management
Date : 2011
Volume : 261
Issue : 3
Pages : 400–407
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Louis S. Santiago , Mark E. De Guzman , Christopher Baraloto , Jacob E. Vogenberg , Max Brodie , Bruno Hérault , Claire Fortunel , Damien Bonal
Publication : New Phytologist
Date : 2025