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

Résumé

The recovery of soil conditions is crucial for successful ecosystem restoration and, hence, for achieving the goals of the UN Decade on Ecosystem Restoration. Here, we assess how soils resist forest conversion and agricultural land use, and how soils recover during subsequent tropical forest succession on abandoned agricultural fields. Our overarching question is how soil resistance and recovery depend on local conditions such as climate, soil type and land-use history. For 300 plots in 21 sites across the Neotropics, we used a chronosequence approach in which we sampled soils from two depths in old-growth forests, agricultural fields (i.e. crop fields and pastures), and secondary forests that differ in age (1–95 years) since abandonment. We measured six soil properties using a standardized sampling design and laboratory analyses. Soil resistance strongly depended on local conditions. Croplands and sites on high-activity clay (i.e. high fertility) show strong increases in bulk density and decreases in pH, carbon (C) and nitrogen (N) during deforestation and subsequent agricultural use. Resistance is lower in such sites probably because of a sharp decline in fine root biomass in croplands in the upper soil layers, and a decline in litter input from formerly productive old-growth forest (on high-activity clays). Soil recovery also strongly depended on local conditions. During forest succession, high-activity clays and croplands decreased most strongly in bulk density and increased in C and N, possibly because of strongly compacted soils with low C and N after cropland abandonment, and because of rapid vegetation recovery in high-activity clays leading to greater fine root growth and litter input. Furthermore, sites at low precipitation decreased in pH, whereas sites at high precipitation increased in N and decreased in C : N ratio. Extractable phosphorus (P) did not recover during succession, suggesting increased P limitation as forests age. These results indicate that no single solution exists for effective soil restoration and that local site conditions should determine the restoration strategies.This article is part of the theme issue ‘Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Auteurs, date et publication :

Auteurs Masha T. van der Sande , Jennifer S. Powers , Thom W. Kuyper , Natalia Norden , Beatriz Salgado-Negret , Jarcilene Silva de Almeida , Frans Bongers , Diego Delgado , Daisy H. Dent , Géraldine Derroire , Mario Marcos do Espirito Santo , Juan Manuel Dupuy , Geraldo Wilson Fernandes , Bryan Finegan , Mayra E. Gavito , José Luis Hernández-Stefanoni , Catarina C. Jakovac , Isabel L. Jones , Maria das Dores Magalhães Veloso , Jorge A. Meave

Publication : Philosophical Transactions of the Royal Society B: Biological Sciences

Date : 2025

Volume : 378

Issue : 1867

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from $sim$1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers.

Auteurs, date et publication :

Auteurs Jingjing Liang , Javier G P Gamarra , Nicolas Picard , Mo Zhou , Bryan Pijanowski , Douglass F Jacobs , Peter B Reich , Thomas W Crowther , Gert-Jan Nabuurs , Sergio De-Miguel , Jingyun Fang , Christopher W Woodall , Jens-Christian Svenning , Tommaso Jucker , Jean-Francois Bastin , Susan K Wiser , Ferry Slik , Bruno Hérault , Giorgio Alberti , Gunnar Keppel

Publication : Nature Ecology & Evolution

Date : 2025

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Production, emission, and absorption of biogenic volatile organic compounds (BVOCs) in ecosystem soils and associated impacts of nutrient availability are unclear; thus, predictions of effects of global change on source-sink dynamic under increased atmospheric N deposition and nutrition imbalances are limited. Here, we report the dynamics of soil BVOCs under field conditions from two undisturbed tropical rainforests from French Guiana. We analyzed effects of experimental soil applications of nitrogen (N), phosphorus (P), and N + P on soil BVOC exchanges (in particular of total terpenes, monoterpenes, and sesquiterpenes), to determine source and sink dynamics between seasons (dry and wet) and elevations (upper and lower elevations corresponding to top of the hills (30 m high) and bottom of the valley). We identified 45 soil terpenoids compounds emitted to the atmosphere, comprising 26 monoterpenes and 19 sesquiterpenes; of these, it was possible to identify 13 and 7 compounds, respectively. Under ambient conditions, soils acted as sinks of these BVOCs, with greatest soil uptake recorded for sesquiterpenes at upper elevations during the wet season (-282 μg m-2 h-1). Fertilization shifted soils from a sink to source, with greatest levels of terpene emissions recorded at upper elevations during the wet season, following the addition of N (monoterpenes: 406 μg m-2 h-1) and P (sesquiterpenes: 210 μg m-2 h-1). Total soil terpene emission rates were negatively correlated with total atmospheric terpene concentrations. These results indicate likely shifts in tropical soils from sink to source of atmospheric terpenes under projected increases in N deposition under global change, with potential impacts on regional-scale atmospheric chemistry balance and ecosystem function.

Auteurs, date et publication :

Auteurs Joan Llusià , Dolores Asensio , Jordi Sardans , Iolanda Filella , Guille Peguero , Oriol Grau , Romà Ogaya , Albert Gargallo-Garriga , Lore T. Verryckt , Leandro Van Langenhove , Laëtitia M. Brechet , Elodie Courtois , Clément Stahl , Ivan A. Janssens , Josep Peñuelas

Publication : Science of The Total Environment

Date : 2022

Volume : 802

Pages : 149769

Catégorie(s)

#ANR-Citation #CIRAD #CNRS #FORET Nouragues

Résumé

Abstract
Biogeochemical niche (BN) hypothesis aims to relate species/genotype elemental composition with its niche based on the fact that different elements are involved differentially in distinct plant functions. We here test the BN hypothesis through the analysis of the 10 foliar elemental concentrations and 20 functional‐morphological of 60 tree species in a French Guiana tropical forest. We observed strong legacy (phylogenic + species) signals in the species‐specific foliar elemental composition (elementome) and, for the first time, provide empirical evidence for a relationship between species‐specific foliar elementome and functional traits. Our study thus supports the BN hypothesis and confirms the general niche segregation process through which the species‐specific use of bio‐elements drives the high levels of α‐diversity in this tropical forest. We show that the simple analysis of foliar elementomes may be used to test for BNs of co‐occurring species in highly diverse ecosystems, such as tropical rainforests. Although cause and effect mechanisms of leaf functional and morphological traits in species‐specific use of bio‐elements require confirmation, we posit the hypothesis that divergences in functional‐morphological niches and species‐specific biogeochemical use are likely to have co‐evolved.

Auteurs, date et publication :

Auteurs Jordi Sardans , Joan Llusià , Romà Ogaya , Helen Vallicrosa , Iolanda Filella , Albert Gargallo‐Garriga , Guille Peguero , Leandro Van Langenhove , Lore T. Verryckt , Clément Stahl , Elodie A. Courtois , Laëtitia M. Bréchet , Akash Tariq , Fanjiang Zeng , Abdulwahed Fahad Alrefaei , Weiqi Wang , Ivan A. Janssens , Josep Peñuelas

Publication : Ecology

Date : 2025

Volume : 104

Issue : 11

Pages : e4118

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

Estimating consistent large-scale tropical forest height using remote sensing is essential for understanding forest-related carbon cycles. The Global Ecosystem Dynamics Investigation (GEDI) light detection and ranging (LiDAR) instrument employed on the International Space Station has collected unique vegetation structure data since April 2019. Our study shows the potential value of using remote-sensing (RS) data (i.e., optical Sentinel-2, radar Sentinel-1, and radar PALSAR-2) to extrapolate GEDI footprint-level forest canopy height model (CHM) measurements. We show that selected RS features can estimate vegetation heights with high precision by analyzing RS data, spaceborne GEDI LiDAR, and airborne LiDAR at four tropical forest sites in South America and Africa. We found that the GEDI relative height (RH) metric is the best at 98% (RH98), filtered by full-power shots with a sensitivity greater than 98%. We found that the optical Sentinel-2 indices are dominant with respect to radar from 77 possible features. We proposed the nine essential optical Sentinel-2 and the radar cross-polarization HV PALSAR-2 features in CHM estimation. Using only ten optimal indices for the regression problems can avoid unimportant features and reduce the computational effort. The predicted CHM was compared to the available airborne LiDAR data, resulting in an error of around 5 m. Finally, we tested cross-validation error values between South America and Africa, including around 40% from validation data in training to obtain a similar performance. We recommend that GEDI data be extracted from all continents to maintain consistent performance on a global scale. Combining GEDI and RS data is a promising method to advance our capability in mapping CHM values.

Auteurs, date et publication :

Auteurs Yen-Nhi Ngo , Dinh Ho Tong Minh , Nicolas Baghdadi , Ibrahim Fayad

Publication : Remote Sensing

Date : 2023

Volume : 15

Issue : 4

Pages : 975

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

In a time of rapid global change, the question of what determines patterns in species abundance distribution remains a priority for understanding the complex dynamics of ecosystems. The constrained maximization of information entropy provides a framework for the understanding of such complex systems dynamics by a quantitative analysis of important constraints via predictions using least biased probability distributions. We apply it to over two thousand hectares of Amazonian tree inventories across seven forest types and thirteen functional traits, representing major global axes of plant strategies. Results show that constraints formed by regional relative abundances of genera explain eight times more of local relative abundances than constraints based on directional selection for specific functional traits, although the latter does show clear signals of environmental dependency. These results provide a quantitative insight by inference from large-scale data using cross-disciplinary methods, furthering our understanding of ecological dynamics.

Auteurs, date et publication :

Auteurs Edwin Pos , Luiz de Souza Coelho , Diogenes de Andrade Lima Filho , Rafael P. Salomão , Iêda Leão Amaral , Francisca Dionízia de Almeida Matos , Carolina V. Castilho , Oliver L. Phillips , Juan Ernesto Guevara , Marcelo de Jesus Veiga Carim , Dairon Cárdenas López , William E. Magnusson , Florian Wittmann , Mariana Victória Irume , Maria Pires Martins , Daniel Sabatier , José Renan da Silva Guimarães , Jean François Molino , Olaf S. Bánki , Maria Teresa Fernandez Piedade

Publication : Scientific Reports

Date : 2023

Volume : 13

Issue : 1

Pages : 1–11

Catégorie(s)

#CIRAD #FORET Paracou