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 ParacouRésumé
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 ParacouRésumé
Eucalyptus plantations are commonly fertilized at planting to sustain high biomass production over successive rotations in nutrient-poor soils. However, the dynamics of nutrient uptake by tree roots in the early stages of stand development, depending on the lateral distance from the trees and the depth in the soil, are poorly documented. We assessed the potential uptake of N, K and Ca, from 6 to 18 months after planting, by Eucalyptus grandis trees depending on: i) the lateral distance from the tracer injection point and ii) the depth in the soil. At 6 months after planting, we injected 15NO3-, Rb+, Sr2+ and Cs+ tracers at depths of 1, 3, 5, and 7 m, respectively. Recently expanded leaves were then sampled monthly on 16 target E. grandis trees located at lateral distances ranging from 0.75 to 11.1 m from the injection points, and on 4 more distant E. grandis control trees; 15N contents (atom %) and concentrations of Rb, Cs and Sr in the leaves were determined at each sampling date, and compared to those of control trees to detect the dates of tracer uptake for each individual. A LOESS model was applied to account for the temporal trend and inter-tree variability among the control trees. Tracer uptake by a target tree was detected if the measurements exceeded the upper limit of the prediction interval (alpha = 0.005) generated by the model. Only the 6 target trees located within 2.0 m from the injection point took up the 15NO3- tracer. However, Rb+, Sr2+ and Cs+ tracers were taken up to lateral distances of approx. 11 m from the injection point. Tracer uptake occurred as early as 9, 7, 8 and 9 months after planting for 15NO3-, Rb+, Sr2+ and Cs+, respectively. Four trees located within 2.8 m from the injection point took up the 3 cation tracers, injected between the depths of 3 m and 7 m. All but one of the target trees took up at least one cation tracer. The potential of Eucalyptus trees to take up nutrients early, at long distance and at depth, can be promoted by silvicultural practices enhancing rapid root development after planting, as subsoiling in commercial plantations and large planting holes in smallholder plantations. Our results also suggest that fertilization could be applied only once at planting in Eucalyptus stands established on deep tropical soils, with low risks of nutrient losses by deep drainage.
Auteurs, date et publication :
Auteurs J. P. Bouillet , B. Bordron , J. P. Laclau , A. Robin , J. L. M. Goncalves , C. H. Abreu-Junior , P. C. O. Trivelin , Y. Nouvellon , G. le Maire
Publication : FOREST ECOLOGY AND MANAGEMENT
Date : 2023
Volume : 550
Catégorie(s)
#ANR-Citation #CIRAD #FORET ItatingaRésumé
Reconstructing past ecological population dynamics and demographic events is crucial for understanding the dynamics of ecological processes, evaluating the impact of environmental changes and making informed conservation decisions. In forest ecosystems, retrodiction (i.e. the backward projection of ecological populations) plays a pivotal role in understanding historical forest carbon levels and the factors that have influenced their variation over time, because forest demography is a major determinant of the amount of carbon stored in forest ecosystems. The persistent lack of quantitative methods has been a significant obstacle in retrodicting forest demography, especially in applications of a broad geographical scale. While there is a wealth of models for predicting future forest conditions, models that can project these conditions backward in time are scarce. This study presents reverse matrix model (RMM), an innovative retrodiction modelling approach grounded in the principles of transition matrix models. RMM is designed to deduce past demographic characteristics of ecological populations using current data, making it one of the first models capable of projecting the fine-scale dynamics of forest demography into the past. We assessed the retrodictive performance of RMM by fitting it to a dataset of a disturbed tropical rainforest in French Guiana in 2001–2023, then comparing the retrodictions to observations back to 1983 when the disturbance occurred. We further empirically evaluated the viability of retrodiction over a defined duration by inverting the density-dependent matrix model by Lin et al. (1996), which predicts the dynamics of northern hardwoods in the United States. The case studies demonstrate significant potential for RMM application in various domains of forestry and conservation, including ecosystem management and conservation planning, global change impact assessment and biodiversity monitoring.
Auteurs, date et publication :
Auteurs Nicolas Picard , Jack Andrew Hansen , Nancy Harris , Jingjing Liang
Publication : Methods in Ecology and Evolution
Date : 2025
Volume : 15
Issue : 11
Pages : 2024-2037
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Climate extremes and biotic interactions at the neighbourhood scale affect tropical forest dynamics with long-term consequences for biodiversity, global carbon cycling and climate change mitigation. However, forest disturbance may change crowding intensity, and thus the relative contribution of climate extremes and neighbourhood interactions on tree growth, thereby influencing tropical forest resistance and resilience to climate change. Here, we aim to evaluate the separate and interactive effects of climate and neighbours on tree growth in old-growth and disturbed tropical forests. We used 30 years of growth measurements for over 300 tropical tree species from 15 forest plots in French Guiana to investigate the separate and interactive effects of climate anomalies (in solar radiation, maximum temperature, vapour pressure deficit and climatic water deficit) and neighbourhood crowding on individual tree growth. Contrasting old-growth and selectively logged forests, we also examined how disturbance history affects tree growth sensitivity to climate and neighbours. Finally, for the most abundant 100 species, we evaluated the role of 12 functional traits pertaining to water relations, light and carbon use in mediating tree growth sensitivity to climate anomalies, neighbourhood crowding and their interactions. Climate anomalies tied to heat and drought stress and neighbourhood crowding independently reduced tree growth, and showed positive interactive effects which attenuated their separate effects on tree growth. Their separate and interactive effects were stronger in disturbed than undisturbed forests. Fast-growing species (i.e. higher intrinsic growth rates) were more abundant in disturbed forests and more sensitive to climate anomalies and neighbourhood crowding. Traits related to water relations, light and carbon use captured species sensitivities to different climate anomalies and neighbourhood crowding levels but were weak predictors of their interactions. Synthesis: Our results demonstrate that climate anomalies and neighbourhood crowding can interact to shape tropical tree growth, suggesting that considering the biotic context may improve predictions of tropical forest dynamics facing altered climate regimes. Furthermore, species traits can capture tree growth sensitivity to the separate effects of climate and neighbours, suggesting that better representing leading functional dimensions in tropical tree strategies offers a promising way towards a better understanding of the underlying ecological mechanisms that govern tropical forest dynamics.
Auteurs, date et publication :
Auteurs Daniela Nemetschek , Géraldine Derroire , Eric Marcon , Mélaine Aubry-Kientz , Johanna Auer , Vincyane Badouard , Christopher Baraloto , David Bauman , Quentin Le Blaye , Marion Boisseaux , Damien Bonal , Sabrina Coste , Elia Dardevet , Patrick Heuret , Peter Hietz , Sébastien Levionnois , Isabelle Maréchaux , Sean M. McMahon , Clément Stahl , Jason Vleminckx
Publication : Journal of Ecology
Date : 2025
Volume : 112
Issue : 3
Pages : 590-612
Catégorie(s)
#CIRAD #FORET ParacouRésumé
One foundational assumption of trait-based ecology is that traits can predict species demography. However, the links between traits and demographic rates are, in general, not as strong as expected. These weak associations may be due to the use of traits that are distantly related to performance, and/or the lack of consideration of size-related variations in both traits and demographic rates. Here, we examined how wood traits were related to demographic rates in 19 tree species from a lowland forest in eastern Amazonia. We measured 11 wood traits (i.e. structural, anatomical and chemical traits) in sapling, juvenile and adult wood; and related them to growth and mortality rates (MR) at different ontogenetic stages. The links between wood traits and demographic rates changed during tree development. At the sapling stage, relative growth rates (RGR) were negatively related to wood specific gravity (WSG) and total parenchyma fractions, while MR decreased with radial parenchyma fractions, but increased with vessel lumen area (VA). Juvenile RGR were unrelated to wood traits, whereas juvenile MR were negatively related to WSG and axial parenchyma fractions. At the adult stage, RGR scaled with VA and wood potassium concentrations. Adult MR were not predicted by any trait. Overall, the strength of the trait-demography associations decreased at later ontogenetic stages. Our results indicate that the associations between traits and demographic rates can change as trees age. Also, wood chemical or anatomical traits may be better predictors of growth and MR than WSG. Our findings are important to expand our knowledge on tree life-history variations and community dynamics in tropical forests, by broadening our understanding on the links between wood traits and demography during tree development.
Auteurs, date et publication :
Auteurs Andrés González-Melo , Juan Manuel Posada , Jacques Beauchêne , Romain Lehnebach , Sébastian Levionnois , Géraldine Derroire , Bruno Clair , Juliana Medeiros
Publication : AoB PLANTS
Date : 2024
Volume : 16
Issue : 1
Pages : plad090
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
Understanding the effect of planting densities and species proportions on light absorption and light use efficiency can help to improve the management of mixed-species forest plantations. Our study aimed to disentangle the role of light interception and light use efficiency (LUE) on the biomass production of Eucalyptus grandis (E), a highly productive species in tropical conditions, and Acacia mangium (A), a N2-fixing species, in monocultures and mixed-species plantations for contrasting planting densities. A randomized block experiment set up over 4 ha in southern Brazil was intensively monitored for 14 months at mid rotation. The absorbed photosynthetically active radiation (APAR) was simulated for each tree of the experiment using the tri-dimensional MAESPA model parameterized with detailed in situ measurements of tree and foliage. LUE for stem wood production was estimated as the ratio of measured stem biomass production (SBP) and simulated APAR. The APAR of Eucalyptus trees did not significantly differ between monocultures and mixed plantations, the reduction of Eucalyptus density being compensated by an increase in light absorption of Eucalyptus individuals. The LUE of Eucalyptus trees in monoculture and mixed-species stands was found to be comparable only at low planting densities. The replacement of Eucalyptus trees with Acacia trees resulted in a reduction in Eucalyptus LUE only at high planting density. The SBP of Eucalyptus trees was mainly explained by differences in APAR, while both APAR and LUE explained the SBP of Acacia trees. The maximum stand production was obtained with monoculture of Eucalyptus at high density and no mixture reached this productivity. Reducing the proportion of Eucalyptus in mixture lead to a substantial decrease in stand production at high planting density due to a decrease in LUE, while this stand production reduction was offset at low planting density, underlying a higher diversity effect at low planting density. In the perspective of increasing diversity in forest plantations to foster multifunctionality, mixed plantations of Acacia and Eucalyptus at low planting density can be an interesting option to maintain a relatively high productivity, which is similar to Eucalyptus monocultures at the same low planting density.
Auteurs, date et publication :
Auteurs I. R. Oliveira , J. P. Bouillet , J. Guillemot , C. B. Brandani , B. Bordron , C. B. Frayret , J. P. Laclau , A. V. Ferraz , J. L. M. Goncalves , G. le Maire
Publication : FOREST ECOLOGY AND MANAGEMENT
Date : 2024
Volume : 554
Catégorie(s)
#ANR-Citation #CIRAD #FORET ItatingaRésumé
Predictions of climate change over land indicate drying trends in the form of ecological and agricultural droughts over many regions (1-6), and increased flooding in others (7). Globally, evapotranspiration (ET) from vegetated areas consumes about 63% of annual precipitation8, which is expected to increase with global warming (9,10), and can approach 100% in drylands (11) beyond which ecosystems are unsustainable. As global climate change progresses, it remains unknown what fraction of the precipitation will remain available for runoff, recharge of aquifers and consumption, or prevent ecosystems’ collapse in dry regions (7,12). Here, we show using a global dataset that evapotranspiration from ecosystems displays a conservative ‘saturation effect’ at ~460 mm across climates with a precipitation range of ~4000 mm. This implies that changes in precipitation are preferentially reflected in ecosystem water yield (WY; the residual between precipitation and evapotranspiration). Consequently, changes in WY are greatly enhanced compared with precipitation changes, both in observations and model-based future projections. In dry regions, ecosystems will reach the unsustainable state (negative WY) faster than expected based on predicted changes in precipitation alone, imposing land cover changes and impacting water availability for ecological and societal needs.
Auteurs, date et publication :
Auteurs Fedor Tatrinov , Jonathan Müller , Eyal Rotenberg
Date : 2024
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Tropical forests play a key role in the global carbon balance and in natural climate change mitigation, as they account for 68% of global forest carbon stocks and represent up to 30% of global soil carbon stocks. However, major uncertainties remain regarding the long-term sustainability of their carbon sink capacity when considering the full greenhouse gas exchange, including methane (CH4) and nitrous oxide (N2O) fluxes, and accurately identifying and quantifying all sources and sinks.In this line, we present here original continuous high-frequency ecosystem (eddy covariance) and soil (automated chamber) CH4 and N2O flux data from a 2.5-year study in a seasonally wet tropical forest at the Guyaflux experimental site, French Guiana. The main objective of our study was to assess the seasonal patterns of CH4 and N2O exchange at the ecosystem and soil levels, and to identify the environmental drivers. Seasonal variations in ecosystem and soil CH4 and N2O fluxes were tremendous, with generally higher CH4 and N2O emissions in the wettest than in the driest season. Global radiation, soil water content and soil temperature were the main drivers of seasonal variation in ecosystem and soil CH4 and N2O fluxes. Furthermore, based on eddy covariance measurements of all greenhouse gases, i.e. CH4, N2O and CO2, the forest was overall a significant carbon sink (-1,875 ± 813 kgC ha-1 y-1, i.e. cumulative net ecosystem exchange), although the ecosystem shifted from a small sink to a small source of CH4 during the wettest season, and remained a more or less small but constant source of N2O. In contrast, soil fluxes in the upper part of the forest within the tower footprint were consistently a CH4 sink, while soil N2O fluxes shifted depending on the season, from a small N2O sink in the driest season to a small source in the wettest season.Our study shows that the carbon sink potential of the Guyaflux forest is not yet compromised by CH4 and N2O emissions. However, under the more frequent extreme conditions of contrasting soil water content and global radiation expected in the future, CH4 and N2O emissions may increase and thus reduce the forest carbon sink.
Auteurs, date et publication :
Auteurs Laëtitia Brechet , Mercedes Ibáñez , Benoît. Burban , Jean-Yves Goret , Clément Stahl , Damien Bonal , Rob Jackson , Ivan Janssens
Date : 2024
Pages : 9235
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Background The availability of soil phosphorus (P) often limits the productivities of wet tropical lowland forests. Little is known, however, about the metabolomic profile of different chemical P compounds with potentially different uses and about the cycling of P and their variability across space under different tree species in highly diverse tropical rainforests.
Results We hypothesised that the different strategies of the competing tree species to retranslocate, mineralise, mobilise, and take up P from the soil would promote distinct soil 31P profiles. We tested this hypothesis by performing a metabolomic analysis of the soils in two rainforests in French Guiana using 31P nuclear magnetic resonance (NMR). We analysed 31P NMR chemical shifts in soil solutions of model P compounds, including inorganic phosphates, orthophosphate mono- and diesters, phosphonates, and organic polyphosphates. The identity of the tree species (growing above the soil samples) explained > 53% of the total variance of the 31P NMR metabolomic profiles of the soils, suggesting species-specific ecological niches and/or species-specific interactions with the soil microbiome and soil trophic web structure and functionality determining the use and production of P compounds. Differences at regional and topographic levels also explained some part of the the total variance of the 31P NMR profiles, although less than the influence of the tree species. Multivariate analyses of soil 31P NMR metabolomics data indicated higher soil concentrations of P biomolecules involved in the active use of P (nucleic acids and molecules involved with energy and anabolism) in soils with lower concentrations of total soil P and higher concentrations of P-storing biomolecules in soils with higher concentrations of total P.
Conclusions The results strongly suggest “niches” of soil P profiles associated with physical gradients, mostly topographic position, and with the specific distribution of species along this gradient, which is associated with species-specific strategies of soil P mineralisation, mobilisation, use, and uptake.
Auteurs, date et publication :
Auteurs Albert Gargallo-Garriga , Jordi Sardans , Joan Llusià , Guille Peguero , Marta Ayala-Roque , Elodie A. Courtois , Clément Stahl , Otmar Urban , Karel Klem , Pau Nolis , Miriam Pérez-Trujillo , Teodor Parella , Andreas Richter , Ivan A. Janssens , Josep Peñuelas
Publication : BMC Plant Biology
Date : 2024
Volume : 24
Issue : 1
Pages : 278