Résumé

Forest aboveground biomass is a key variable in remote sensing based forest monitoring. Active sensor systems, such as lidar, can generate detailed canopy height products. Relationships between canopy height and biomass are commonly established via regression analysis using information from ground-truth plots. In this way, many site-specific height-biomass relationships have been proposed in the literature and applied for mapping in regional contexts. However, such relationships are only valid within the specific forest type for which they were calibrated. A generalized relationship would facilitate biomass estimation across forest types and regions. In this study, a combination of lidar-derived and ancillary structural descriptors is proposed as an approach for generalization between forest types. Each descriptor is supposed to quantify a different aspect of forest structure, i.e., mean canopy height, maximum canopy height, maximum stand density, vertical heterogeneity and wood density. Airborne discrete return lidar data covering 194 ha of forest inventory plots from five different sites including temperate and tropical forests from Africa, Europe, North, Central and South America was used. Biomass predictions using the best general model (nRMSE = 12.4%, R2 = 0.74) were found to be almost as accurate as predictions using five site-specific models (nRMSE = 11.6%, R2 = 0.78). The results further allow interpretation about the importance of the employed structure descriptors in the biomass estimation and the mechanisms behind the relationships. Understanding the relationship between canopy structure and aboveground biomass and being able to generalize it across forest types are important steps towards consistent large scale biomass mapping and monitoring using airborne and potentially also spaceborne platforms.

Auteurs, date et publication :

Auteurs Nikolai Knapp , Rico Fischer , Victor Cazcarra-Bes , Andreas Huth

Publication : Remote Sensing of Environment

Date : 2020

Volume : 237

Pages : 111597

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Background and aims – The evolutionary history of Amazonia’s hyperabundant tropical tree species, also known as “hyperdominant” species, remains poorly investigated. We assessed whether the hyperdominant Eschweilera coriacea (DC.) S.A.Mori (Lecythidaceae)
represents a single genetically cohesive species, and how its genetic constitution relates to other species from the same clade with which it occurs sympatrically in French Guiana. Methods – We sampled 152 individuals in nine forest sites in French Guiana, representing
11 species of the genus Eschweilera all belonging to the Parvifolia clade, with emphasis on E. coriacea. Samples were genotyped at four simple sequence repeat (SSR) markers. We delimited gene pools, i.e., genetically coherent putative taxa, using STRUCTURE software and principal
component analysis. We compared the genetic assignment of individuals with their morphological species determination and estimated genetic diversity and differentiation for gene pools and species. We also estimated genome size using flow cytometry. Key results – SSR
profiles commonly displayed up to four alleles per genotype, suggesting that the investigated Eschweilera species bear a paleopolyploid signature. Flow cytometry suggested that the studied species are diploid with haploid genome sizes of 871–1046 Mbp. We detected five gene pools
and observed a good correspondence between morphological and genetic delimitation for Eschweilera sagotiana Miers and the undescribed morphospecies E. sp. 3 (which resembles E. grandiflora (Aubl.) Sandwith), and to a lesser extent for E. decolorans Sandwith and
E. micrantha (O.Berg) Miers. Eschweilera coriacea was the most genetically diverse species and included individuals assigned to each gene pool. Conclusions – We found no conclusive evidence for cryptic species within E. coriacea in French Guiana.
SSRs detected fewer gene pools than expected based on morphology in the Parvifolia clade but discriminated evolutionary relationships better than available plastid markers. A positive trend between demographic abundance of species and allelic richness illustrates that hyperdominants may have
a high evolutionary potential. This hypothesis can be tested using more powerful genomic data in combination with tree phenotypic trait variation and characterization of niche breadth, to enhance our understanding of the causes of hyperdominance in Amazonian trees.

Auteurs, date et publication :

Auteurs Myriam Heuertz , Henri Caron , Caroline Scotti-Saintagne , Pascal Pétronelli , Julien Engel , Niklas Tysklind , Sana Miloudi , Fernanda A. Gaiotto , Jérôme Chave , Jean-François Molino , Daniel Sabatier , João Loureiro , Katharina B. Budde

Publication : Plant Ecology and Evolution

Date : 2020

Volume : 153

Issue : 1

Pages : 67-81

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha−1 year−1), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha−1 year−1) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha−1 year−1) and canopy leaching (22 kg ha−1 year−1) were three times larger than internal nutrient recycling via litterfall (11 kg ha−1 year−1). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest.

Auteurs, date et publication :

Auteurs Leandro Van Langenhove , Lore T. Verryckt , Laëtitia Bréchet , Elodie A. Courtois , Clement Stahl , Florian Hofhansl , Marijn Bauters , Jordi Sardans , Pascal Boeckx , Erik Fransen , Josep Peñuelas , Ivan A. Janssens

Publication : Biogeochemistry

Date : 2020

Volume : 149

Issue : 2

Pages : 175-193

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Despite their low contribution to forest carbon stocks, lianas (woody vines) play an important role in the carbon dynamics of tropical forests. As structural parasites, they hinder tree survival, growth and fecundity; hence, they negatively impact net ecosystem productivity and long-term carbon sequestration. Competition (for water and light) drives various forest processes and depends on the local abundance of resources over time. However, evaluating the relative role of resource availability on the interactions between lianas and trees from empirical observations is particularly challenging. Previous approaches have used labour-intensive and ecosystem-scale manipulation experiments, which are infeasible in most situations. We propose to circumvent this challenge by evaluating the uncertainty of water and light capture processes of a process-based vegetation model (ED2) including the liana growth form. We further developed the liana plant functional type in ED2 to mechanistically simulate water uptake and transport from roots to leaves, and start the model from prescribed initial conditions. We then used the PEcAn bioinformatics platform to constrain liana parameters and run uncertainty analyses. Baseline runs successfully reproduced ecosystem gas exchange fluxes (gross primary productivity and latent heat) and forest structural features (leaf area index, aboveground biomass) in two sites (Barro Colorado Island, Panama and Paracou, French Guiana) characterized by different rainfall regimes and levels of liana abundance. Model uncertainty analyses revealed that water limitation was the factor driving the competition between trees and lianas at the drier site (BCI), and during the relatively short dry season of the wetter site (Paracou). In young patches, light competition dominated in Paracou but alternated with water competition between the wet and the dry season on BCI according to the model simulations. The modelling workflow also identified key liana traits (photosynthetic quantum efficiency, stomatal regulation parameters, allometric relationships) and processes (water use, respiration, climbing) driving the model uncertainty. They should be considered as priorities for future data acquisition and model development to improve predictions of the carbon dynamics of liana-infested forests. Synthesis. Competition for water plays a larger role in the interaction between lianas and trees than previously hypothesized, as demonstrated by simulations from a process-based vegetation model.

Auteurs, date et publication :

Auteurs Félicien Meunier , Hans Verbeeck , Betsy Cowdery , Stefan A. Schnitzer , Chris M. Smith‐Martin , Jennifer S. Powers , Xiangtao Xu , Martijn Slot , Hannes P. T. De Deurwaerder , Matteo Detto , Damien Bonal , Marcos Longo , Louis S. Santiago , Michael Dietze

Publication : Journal of Ecology

Date : 2025

Volume : 109

Issue : 1

Pages : 519-540

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Roberto Cazzolla , Peter B Reich , Javier G P Gamarra , Tom Crowther , Cang Hui , Angelica Maria , Almeyda Zambrano , Esteban Alvarez-davila , Alejandro Araujo-murakami , Valerio Avitabile , Gerardo A Aymard , Radomir Balazy , Chris Baraloto , Jorcely G Barroso , Meredith L Bastian , Philippe Birnbaum , Robert Bitariho , Jan Bogaert , Frans Bongers , Olivier Bouriaud

Publication : PNAS

Date : 2025

Volume : 119

Issue : 6

Pages : 1–11

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Plant-associated microorganisms have been shown to aid plants in coping with drought. However, the underlying mechanisms are poorly understood and there is uncertainty regarding which microbial taxa and functions are mostly involved. We explored these issues in Neotropical rainforests and identified foliar microorganisms that may play a role in drought tolerance of trees. Our objectives were to (i) test the relationship between drought tolerance traits in Neotropical trees and the diversity and composition of their foliar fungal and bacterial communities and (ii) identify leaf microbial taxa positively or negatively associated with drought tolerance traits. Our results showed that the composition of leaf fungal communities but not bacterial communities was related to drought tolerance. We identified 27 fungal amplicon sequence variants whose relative abundance covaried with drought tolerance traits. Most variants were assigned to fungal clades often described as plant pathogens and increased in abundance with drought susceptibility. This greater relative abundance of leaf pathogens in the most drought-susceptible trees might increase their vulnerability to climate change. Moreover, we identified the Strelitziana and Ochroconis fungal genera as potential candidates for future culture-dependent studies aimed at understanding and improving drought tolerance in Neotropical forests.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Auteurs, date et publication :

Auteurs Marine C Cambon , Dinïa Cartry , Emilie Chancerel , Camille Ziegler , Sebastien Levionnois , Sabrina Coste , Clément Stahl , Sylvain Delzon , Marc Buée , Benoit Burban , Jocelyne Cazal , Tania Fort , Jean-Yves Goret , Patrick Heuret , Patrick Léger , Elianne Louisanna , Yves Ritter , Damien Bonal , Mélanie Roy , Heidy Schimann

Publication : Phytobiomes Journal

Date : 2025

Issue : 1

Pages : 1–61

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Estimating tropical forests' vertical structure using remote sensing is a challenge. Active sensors such as low-frequency synthetic aperture radar (SAR) operating at the P-band, with a wavelength of 69 cm, and light detection and ranging (LiDAR) are able to penetrate thick vegetation layers. While NASA's Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne LiDAR data, the ESA's next Earth Explorer BIOMASS mission will acquire multiple acquisitions over the same areas to form 3-D images through the SAR tomography (TomoSAR) technique. Our study shows the potential value of GEDI and TomoSAR acquisitions in producing accurate estimates of forests' vertical structure. By analyzing the airborne P-band TomoSAR, airborne LiDAR, and spaceborne GEDI LiDAR at a tropical forest site in Paracou, French Guiana, South America, we show that both GEDI and P-band TomoSAR can directly measure surface, vegetation heights, and vertical profiles with high resolution and precision. Airborne TomoSAR is of higher quality than GEDI due to better penetration properties and precision. However, GEDI vegetation height root-mean-square error (RMSE) is less than 5 m, for an average forest height value around 30 m at the Paracou site, which is similar to the expected performance of the future spaceborne BIOMASS mission. These results suggest that GEDI measurements, i.e., shots with sensitivity greater than 98%, will provide a good reference of forest structure to calibrate the BIOMASS mission algorithms.

Auteurs, date et publication :

Auteurs Yen Nhi Ngo , Yue Huang , Dinh Ho Tong Minh , Laurent Ferro-Famil , Ibrahim Fayad , Nicolas Baghdadi

Publication : IEEE Geoscience and Remote Sensing Letters

Date : 2025

Volume : 19

Pages : 1

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

The dry and wet seasons in the Neotropics have strong effects on soil water and nutrient availability, as well as on forest dynamics. Despite these major effects on forest ecology, little is known on how leaf traits vary throughout the seasons in tropical rainforest trees. Here, we investigated the influence of seasonal variations in climate and soil characteristics on leaf trait variation in two tropical tree species. We measured two leaf traits, thickness and water mass per area, in 401 individuals of two species of Symphonia (Clusiaceae) in the Paracou research station in French Guiana tropical lowland rainforest. We found a significant effect of seasonal variation on these two leaf traits. Soil relative extractable water was a strong environmental predictor of leaf trait variation in response to seasonal variation. Reduced soil water availability during the dry season was associated with increased leaf thickness and water mass per area, possibly as a result of stomatal closure. Our findings advocate the need to account for environmental seasonality when studying leaf traits in seasonal ecosystems such as tropical forests.

Auteurs, date et publication :

Auteurs Sylvain Schmitt , Santiago Trueba , Sabrina Coste , Ducouret , Niklas Tysklind , Myriam Heuertz , Damien Bonal , Benoît Burban , Bruno Hérault , Géraldine Derroire

Publication : Plant Biology

Date : 2025

Volume : 24

Issue : 3

Pages : 458–463

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Forests that regrow naturally on abandoned fields are important for restoring biodiversity and ecosystem services, but can they also preserve the distinct regional tree floras? Using the floristic composition of 1215 early successional forests (≤20 years) in 75 human-modified landscapes across the Neotropic realm, we identified 14 distinct floristic groups, with a between-group dissimilarity of 0.97. Floristic groups were associated with location, bioregions, soil pH, temperature seasonality, and water availability. Hence, there is large continental-scale variation in the species composition of early successional forests, which is mainly associated with biogeographic and environmental factors but not with human disturbance indicators. This floristic distinctiveness is partially driven by regionally restricted species belonging to widespread genera. Early secondary forests contribute therefore to restoring and conserving the distinctiveness of bioregions across the Neotropical realm, and forest restoration initiatives should use local species to assure that these distinct floras are maintained.

Auteurs, date et publication :

Auteurs Catarina C Jakovac , Jorge A Meave , Frans Bongers , Susan G Letcher , Juan Manuel Dupuy , Daniel Piotto , Danaë M.A. Rozendaal , Marielos Peña-Claros , Dylan Craven , Braulio A Santos , Alexandre Siminski , Alfredo C Fantini , Alice C Rodrigues , Alma Hernández-Jaramillo , Alvaro Idárraga , André B Junqueira , Angelica María Almeyda Zambrano , Ben H.J. De Jong , Bruno Ximenes Pinho , Bryan Finegan

Publication : Science Advances

Date : 2025

Volume : 8

Issue : 26

Pages : eabn1767

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Sylvain Schmitt , Niklas Tysklind , Myriam Heuertz , Bruno Hérault

Publication : Molecular Ecology

Date : 2025

Catégorie(s)

#CIRAD #FORET Paracou