Résumé
textlessptextgreaterAdvances in forest carbon mapping have the potential to greatly reduce uncertainties in the global carbon budget and to facilitate effective emissions mitigation strategies such as REDD+. Though broad scale mapping is based primarily on remote sensing data, the accuracy of resulting forest carbon stock estimates depends critically on the quality of field measurements and calibration procedures. The mismatch in spatial scales between field inventory plots and larger pixels of current and planned remote sensing products for forest biomass mapping is of particular concern, as it has the potential to introduce errors, especially if forest biomass shows strong local spatial variation. Here, we used 30 large (8–50 ha) globally distributed permanent forest plots to quantify the spatial variability in aboveground biomass (AGB) at spatial grains ranging from 5 to 250 m (0.025–6.25 ha), and we evaluate the implications of this variability for calibrating remote sensing products using simulated remote sensing footprints. We found that the spatial sampling error in AGB is large for standard plot sizes, averaging 46.3% for 0.1 ha subplots and 16.6% for 1 ha subplots. Topographically heterogeneous sites showed positive spatial autocorrelation in AGB at scales of 100 m and above; at smaller scales, most study sites showed negative or nonexistent spatial autocorrelation in AGB. We further show that when field calibration plots are smaller than the remote sensing pixels, the high local spatial variability in AGB leads to a substantial "dilution" bias in calibration parameters, a bias that cannot be removed with current statistical methods. Overall, our results suggest that topography should be explicitly accounted for in future sampling strategies and that much care must be taken in designing calibration schemes if remote sensing of forest carbon is to achieve its promise.textless/ptextgreater
Auteurs, date et publication :
Auteurs M. Rejou-Mechain , H. C. Muller-Landau , M. Detto , S. C. Thomas , T. Toan , S. S. Saatchi , J. Barreto-Silvia , N. A. Bourg , S. Bunyavejchewin , N. Butt , W. Y. Brockelman , M. Cao , D. Cardenas , J.-M. Chiang , G. B. Chuyong , K. Clay , R. Condit , H. S. Dattaraja , S. J. Davies , A. Duque
Publication : Biogeosciences Discussions
Date : 2014
Volume : 11
Issue : 4
Pages : 5711–5742
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Species living in sympatry and sharing a similar niche often express parallel phenotypes as a response to similar selection pressures. The degree of parallelism within underlying genomic levels is often unexplored, but can give insight into the mechanisms of natural selection and adaptation. Here, we use multi-dimensional genomic associations to assess the basis of local and climate adaptation in two sympatric, cryptic Crematogaster levior ant species along a climate gradient. Additionally, we investigate the genomic basis of chemical communication in both species. Communication in insects is mainly mediated by cuticular hydrocarbons (CHCs), which also protect against water loss and, hence, are subject to changes via environmental acclimation or adaptation. The combination of environmental and chemical association analyses based on genome-wide Pool-Seq data allowed us to identify single nucleotide polymorphisms (SNPs) associated with climate and with chemical differences. Within species, CHC changes as a response to climate seem to be driven by phenotypic plasticity, since there is no overlap between climate- and CHC-associated SNPs. The only exception is the odorant receptor OR22c, which may be a candidate for population-specific CHC recognition in one of the species. Within both species, climate is significantly correlated with CHC differences, as well as to allele frequency differences. However, associated candidate SNPs, genes and functions are largely species-specific and we find evidence for minimal parallel evolution only on the level of genomic regions (J = 0.04). This highlights that even closely related species may follow divergent evolutionary trajectories when expressing similar adaptive phenotypes.
Auteurs, date et publication :
Auteurs Juliane Hartke , Ann-Marie Waldvogel , Philipp P. Sprenger , Thomas Schmitt , Florian Menzel , Markus Pfenninger , Barbara Feldmeyer
Publication : Journal of Evolutionary Biology
Date : 2025
Volume : n/a
Issue : n/a
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, 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