Auteurs, date et publication :
Auteurs Sylvain Coq , Jean Weigel , Olaf Butenschoen , Damien Bonal , Stephan Hättenschwiler
Publication : Plant and Soil
Date : 2011
Volume : 343
Issue : 1-2
Pages : 273–286
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Nicolas Fanin , Stephan Hättenschwiler , Nathalie Fromin
Publication : Plant and Soil
Date : 2014
Volume : 379
Issue : 1-2
Pages : 79–91
Catégorie(s)
#CIRAD #FORET ParacouRésumé
We studied the litter sizes of small rodents and opossums caught in the Guianan Region (Brazilian Amapá, French Guiana, Suriname, and Guyana) by pooling the data of animals collected during various field trips conducted primarily between 1990 and 2017. A series of 569 counts of embryos (or of pouch young for marsupials) in 40 species of Didelphidae (N = 12 species), Sigmodontinae (18), Murinae (2), and Echimyidae (8) allowed for a more detailed characterization of the reproductive condition of 14 species known each by more than 10 pregnant females. For eight species with at least 20 pregnant females, an examination of seasonality in breeding occurrence documented that the two months with the lowest percentage of pregnant females are July and August (16.0 and 17.3%, respectively) during the end of the long wet season and beginning of the dry season. By contrast, January and February showed the highest abundance of pregnancies (57.9% and 55.8%, respectively) during the beginning of the long wet season. This timing coincides with most juveniles foraging during the height of the wet season in May when food is presumably most prevalent.
Auteurs, date et publication :
Auteurs François M. Catzeflis , Burton K. Lim , Claudia Regina Da Silva
Publication : Studies on Neotropical Fauna and Environment
Date : 2019
Volume : 54
Issue : 1
Pages : 31-39
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Drought-induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure–functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined optical, laser, and transmission electron microscopy to investigate vessel diameter, vessel grouping, and pit membrane ultrastructure for 26 tropical rainforest tree species across three major clades (magnoliids, rosiids, and asteriids). We then related these anatomical observations to previously published data on drought-induced embolism resistance, with phylogenetic analyses. Vessel diameter, vessel grouping, and pit membrane ultrastructure were all predictive of xylem embolism resistance, but with weak predictive power. While pit membrane thickness was a predictive trait when vestured pits were taken into account, the pit membrane diameter-to-thickness ratio suggests a strong importance of the deflection resistance of the pit membrane. However, phylogenetic analyses weakly support adaptive coevolution. Our results emphasize the functional significance of pit membranes for air-seeding in tropical rainforest trees, highlighting also the need to study their mechanical properties due to the link between embolism resistance and pit membrane diameter-to-thickness ratio. Finding support for adaptive coevolution also remains challenging.
Auteurs, date et publication :
Auteurs Sébastien Levionnois , Steven Jansen , Ruth Tchana Wandji , Jacques Beauchêne , Camille Ziegler , Sabrina Coste , Clément Stahl , Sylvain Delzon , Louise Authier , Patrick Heuret
Publication : New Phytologist
Date : 2025
Volume : 229
Issue : 3
Pages : 1453-1466
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Key message Genetic diversity appears to be unaffected by disturbance in a stand of the light-demanding Neotropical tree V. michelii. Although spatial genetic structure is modified in post-disturbance cohorts, mixing of seeds from different mother trees in canopy gaps appears to efficiently maintain genetic admixture. Context The interplay between genetic and demographic processes has major consequences on population viability. Population size affects demographic trends, while genetic diversity insures viability by reducing risks of inbreeding depression and by maintaining adaptive potential. Yet, the consequences of increases in census size (as opposed to effective size) on genetic diversity of forest populations are poorly known. Aims We have studied the structure of genetic diversity in populations of saplings of the light-responsive tree, Virola michelii (Myristicaceae, the nutmeg family), in two plots having undergone different levels of canopy-gap opening disturbance. This allowed us to test the “intermediate disturbance” hypothesis, which generally applies to species diversity, at the intra-specific scale. Methods Levels and distribution of genetic diversity were compared between plots and between life stages. Sapling parentage was analysed to infer each adult tree's contribution to regeneration. Results Genetic diversity was higher, and spatial genetic structure was stronger in the post-disturbance than in the control seedling population. Parentage analysis suggested that a limited number of parents contributed to most of the regeneration, but that efficient mixing of their progeny may have enhanced the diversity of saplings occupying canopy gaps. Conclusion A mixture of demo-genetic processes may contribute to maintain genetic diversity in spite of, or possibly due to, ecosystem disturbance in V. michelii.
Auteurs, date et publication :
Auteurs Ivan Scotti , William Montaigne , Klára Cseke , Stéphane Traissac
Publication : Annals of Forest Science
Date : 2015
Volume : 72
Issue : 8
Pages : 1035–1042
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Stemwood productivity in forest ecosystems depends on the amount of light absorbed by the trees (APAR) and on the Light Use Efficiency (LUE), i.e. the amount of stemwood produced per amount of absorbed light. In fertilized Eucalyptus plantations of Brazil, growth is expected to be strongly limited by light absorption in the first years after planting, when trees can benefit from high soil water stocks, recharged after clearcutting the previous stand. Other limiting factors, such as water or nutrient shortage are thought to increase in importance after canopy closure, and changes in allocation patterns are expected, affecting the LUE. Studying changes in APAR and LUE along a complete rotation is paramount for gaining insight into the mechanisms that drive the inter- and infra-genotype variabilities of productivity and stemwood biomass at the time of harvest. Here, we present a 6-year survey of productivity, APAR and LUE of 16 Eucalyptus genotypes of several species used in commercial plantations and planted in 10 randomized replications in the Sao Paulo Region, Brazil. APAR was estimated using the MAESTRA tridimensional model parameterized at tree scale for each tree in each plot (a total of 16,000 trees) using local measurements of leaf and canopy properties. Stand growth was estimated based on allometric relationships established through successive destructive biomass measurements at the study site. Allometric relationships predicting biomass of tree components, leaf surface, crown dimension and leaf inclination angle distribution throughout the rotation for the 16 productive genotypes are shown. Results at stand scale showed that (1) LUE increased with stand age for all genotypes, from 0.15 at age 1 yr to 1.70 g MJ(-1) at age 6 yrs on average; (2) light absorption was a major limiting factor over the first year of growth (R-2 between APAR and stand biomass ranging from 0.5 to 0.95), explaining most of the inter- and infra-genotype growth variability; (3) at rotation scale, the variability of final stemwood biomass among genotypes was in general attributable to other factors than average APAR; (4) differences in stemwood productions among genotypes remained large throughout the rotation; (5) LUEs over the second half of the rotation, rather than initial growth or APAR, was the major driver of stemwood biomass at the time of harvest.
Auteurs, date et publication :
Auteurs Guerric le Maire , Joannes Guillemot , Otavio C. Campoe , Jose-Luiz Stape , Jean-Paul Laclau , Yann Nouvellon
Publication : FOREST ECOLOGY AND MANAGEMENT
Date : 2019
Volume : 449
Catégorie(s)
#ANR-Citation #CIRAD #FORET ItatingaAuteurs, date et publication :
Auteurs Hannes De Deurwaerder , Pedro Hervé-Fernández , Clément Stahl , Benoit Burban , Pascal Petronelli , Bruce Hoffman , Damien Bonal , Pascal Boeckx , Hans Verbeeck
Publication : Tree Physiology
Date : 2018
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Tropical forests are a critical component of the Earth system, storing half of the global forest carbon stocks and accounting for a third of terrestrial photosynthesis. Lianas are structural parasites that can substantially reduce the carbon sequestration capacity of these forests. Simulations of this peculiar growth form have only recently started and a single vegetation model included lianas so far. In this work we present a new liana implementation within the individual based model Formind. Initial tests indicate high structural realism both horizontal and vertical. In particular, we benchmarked the model against empirical observations of size distribution, mean liana cluster size and vertical leaf distribution for the Paracou site in French Guiana. Our model predicted a reduction of above-ground biomass between 10% for mature stands to 45% for secondary plots upon inclusion of lianas in the simulations. The reduced biomass was the result of a lower productivity due to a combination of lower tree photosynthesis and high liana respiration. We evaluated structural metrics (LAI, basal area, mean tree-height) and carbon fluxes (GPP, respiration) by comparing simulations with and without lianas. At the equilibrium, liana productivity was 1.9tC ha−1 y−1, or 23% of the total GPP and the forest carbon stocks were between 5% and 11% lower in simulations with lianas. We also highlight the main strengths and limitations of this new approach and propose new field measurements to further the understanding of liana ecology in a modelling framework.
Auteurs, date et publication :
Auteurs Manfredo di Porcia e Brugnera , Rico Fischer , Franziska Taubert , Andreas Huth , Hans Verbeeck
Publication : Ecological Modelling
Date : 2020
Volume : 431
Pages : 109159
Catégorie(s)
#CIRAD #FORET ParacouRésumé
High-density Airborne Laser Scanning was used to derive the Canopy Height Model (CHM) of an experimental forest site in the neotropics (Paracou, French Guiana). Individual tree heights were computed by manually segmenting tree crowns on the CHM and then extracting the local maximum canopy height. Three hundred and ninety-six (396) height estimates were matched from dominant or emergent trees with the corresponding ground records of stem diameters sampled in two plots with different mean canopy heights (28.1 m vs. 31.3 m). Tree slenderness was found to be positively and very significantly correlated with mean canopy height at the plot level. The same correlation was observed at the species population level for the three species adequately sampled. It can therefore be concluded that stratification by canopy height is to be recommended when deriving allometric relationships in order to avoid bias in Above Ground Biomass estimations. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Grégoire Vincent , F. Caron , Damien Sabatier , Lilian Blanc
Publication : Bois et Forêts des Tropiques
Date : 2025
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Key message Forest disturbance affects the within-population distribution of genetic diversity, but not its overall levels, in a tropical pioneer tree species. In particular, clumps of related saplings with impoverished diversity are found in canopy gaps but not under forest cover. Context Forest disturbances can have long-term consequences on the genetic structure of tree populations, because they can alter the demographic properties of the regeneration process and favour some subpopulations/genotypes, both by stochastic processes and by selection. Intermediate disturbances tend to favour species diversity, at least in highly diverse communities, but their effect on intra-specific diversity is unknown. Aims In this study, we have looked at the genetic consequences of forest disturbance in a stand of the long-lived Neotropical pioneer species, Jacaranda copaia. Methods The study site was experimentally logged in 1984, and the canopy gaps generated by the logging were mapped. Seedlings of J. copaia colonised the gaps, as expected, at a higher density than in the surrounding forest. In 2006, we exhaustively sampled all saplings and adult trees available in a 25-ha area. The samples were genotyped at nine microsatellite loci, and the distribution of genetic diversity was inspected by analyses of spatial autocorrelation, automated Bayesian assignment and comparisons of diversity between cohorts by bootstrap (RaBoT). Results Spatial autocorrelation was found to extend farther in post-disturbance saplings than in the undisturbed population (100 m and beyond versus less than 50 m), and divergent clumps (F ST = 0.05) of related genotypes were found; genetic diversity was found to be impoverished in each clump relative to the global population at about half of the loci. Conclusion Overall, our results suggest that forest disturbance has changed the patterns of distribution of genetic diversity, with potential consequences on long-term population viability.
Auteurs, date et publication :
Auteurs Thomas Leclerc , Ruppert Vimal , Valérie Troispoux , Sophie Périgon , Ivan Scotti
Publication : Annals of Forest Science
Date : 2015
Volume : 72
Issue : 5
Pages : 509–516