Résumé
Natural disturbance is a fundamental component of the functioning of tropical rainforests let to natural dynamics, with tree mortality the driving force of forest renewal. With ongoing global (i.e. land-use and climate) changes, tropical forests are currently facing deep and rapid modifications in disturbance regimes that may hamper their recovering capacity so that developing robust predictive model able to predict ecosystem resilience and recovery becomes of primary importance for decision-making: (i) Do regenerating forests recover faster than mature forests given the same level of disturbance? (ii) Is the local topography an important predictor of the post-disturbance forest trajectories? (iii) Is the community functional composition, assessed with community weighted-mean functional traits, a good predictor of carbon stock recovery? (iv) How important is the climate stress (seasonal drought and/or soil water saturation) in shaping the recovery trajectory? Paracou is a large scale forest disturbance experiment set up in 1984 with nine 6.25 ha plots spanning on a large disturbance gradient where 15 to 60% of the initial forest ecosystem biomass were removed. More than 70,000 trees belonging to ca. 700 tree species have then been censused every 2 years up today. Using this unique dataset, we aim at deciphering the endogenous (forest structure and composition) and exogenous (local environment and climate stress) drivers of ecosystem recovery in time. To do so, we disentangle carbon recovery into demographic processes (recruitment, growth, mortality fluxes) and cohorts (recruited trees, survivors). Variations in the pre-disturbance forest structure or in local environment do not shape significantly the ecosystem recovery rates. Variations in the pre-disturbance forest composition and in the post-disturbance climate significantly change the forest recovery trajectory. Pioneer-rich forests have slower recovery rates than assemblages of late-successional species. Soil water saturation during the wet season strongly impedes ecosystem recovery but not seasonal drought. From a sensitivity analysis, we highlight the pre-disturbance forest composition and the post-disturbance climate conditions as the primary factors controlling the recovery trajectory. Highly-disturbed forests and secondary forests because they are composed of a lot of pioneer species will be less able to cope with new disturbance. In the context of increasing tree mortality due to both (i) severe droughts imputable to climate change and (ii) human-induced perturbations, tropical forest management should focus on reducing disturbances by developing Reduced Impact Logging techniques.
Auteurs, date et publication :
Auteurs Bruno Hérault , Camille Piponiot
Publication : Forest Ecosystems
Date : 2018
Volume : 5
Issue : 1
Pages : 2
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Stable isotope variations are extremely useful for flow partitioning within the hydrologic cycle but remain poorly understood throughout the tropics, particularly in watersheds with rapidly infiltrating soils, such as Andisols in Central America. This study examines the fluctuations of stable isotope ratios ( delta O-18 and delta H-2) in the hydrologic components of a tropical coffee agroforestry watershed (similar to 1 km(2)) with Andisol soils in Costa Rica. Samples were collected in precipitation, groundwater, springs, and stream water over 2 years. The local meteoric water line for the study site was delta H-2 = 8.5 delta O-18 + 18.02 (r(2) = 0.97, n = 198). The isotope ratios in precipitation exhibited an enriched trend during the dry season and a notable depletion at the beginning of the wet season. The delta O-18 compositions in groundwater (average = -6.4 parts per thousand, sigma = 0.7) and stream water (average = -6.7 parts per thousand, sigma = 0.6) were relatively stable over time, and both components exhibited more enriched values in 2013, which was the drier year. No strong correlation was observed between the isotope ratios and the precipitation amount at the event or daily time-step, but a correlation was observed on a monthly scale. Stream water and base flow hydrograph separations based on isotope end-member estimations showed that pre-event water originating from base flow was prevalent. However, isotope data indicate that event water originating from springs appears to have been the primary driver of initial rises in stream flow and peak flows. These results indicate that isotope sampling improves the understanding of water balance components, even in a tropical humid location, where significant variations in rainfall challenge current modelling efforts. Further research using fine-scale hydrometric and isotopic data would enhance understanding the processes driving spring flow generation in watersheds.
Auteurs, date et publication :
Auteurs K. Welsh , J. Boll , R. Sanchez-Murillo , O. Roupsard
Publication : Hydrological Processes
Date : 2018
Volume : 32
Issue : 13
Pages : 1965-1977
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs Daniel Mika-Nsimbi Poultney , Mathias Christina , Antoine Versini
Publication : Plant and Soil
Date : 2025
Volume : 453
Issue : 1-2
Pages : 597-613
Catégorie(s)
#CIRAD #INRAE #PRO #PRO ReunionAuteurs, date et publication :
Auteurs D. Epron , Y. Nouvellon , L. Mareschal , L. S. Koutika , B. Geneste , J. S. Delgado Rojas , J. P. Laclau , G. Sola , J. L. De Moraes Gonçalves , J. P. Bouillet
Publication : Forest Ecology and Management
Date : 2025
Volume : 301
Pages : 102-111
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent.
Auteurs, date et publication :
Auteurs Fabien Wagner , Vivien Rossi , Mélaine Aubry-Kientz , Damien Bonal , Helmut Dalitz , Robert Gliniars , Clément Stahl , Antonio Trabucco , Bruno Hérault , Morag Mcdonald
Publication : Plos One
Date : 2014
Volume : 9
Issue : 3
Pages : e92337
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Although ongoing research has revealed some of the main drivers behind global spatial patterns of microbial communities, spatio-temporal dynamics of these communities still remain largely unexplored. Here, we investigate spatio-temporal variability of both bacterial and eukaryotic soil microbial communities at local and intercontinental scales. We compare how temporal variation in community composition scales with spatial variation in community composition, and explore the extent to which bacteria, protists, fungi and metazoa have similar patterns of temporal community dynamics. All soil microbial groups displayed a strong correlation between spatial distance and community dissimilarity, which was related to the ratio of organism to sample size. Temporal changes were variable, ranging from equal to local between-sample variation, to as large as that between communities several thousand kilometers apart. Moreover, significant correlations were found between bacterial and protist communities, as well as between protist and fungal communities, indicating that these microbial groups change in tandem, potentially driven by interactions between them. We conclude that temporal variation can be considerable in soil microbial communities, and that future studies need to consider temporal variation in order to reliably capture all drivers of soil microbiome changes.
Auteurs, date et publication :
Auteurs Johan De Gruyter , James T Weedon , Stéphane Bazot , Steven Dauwe , Pere-Roc Fernandez-Garberí , Stefan Geisen , Louis Gourlez De La Motte , Bernard Heinesch , Ivan A Janssens , Niki Leblans , Tanguy Manise , Romà Ogaya , Mikaell Ottosson Löfvenius , Josep Peñuelas , Bjarni D Sigurdsson , Gaëlle Vincent , Erik Verbruggen
Publication : FEMS Microbiology Ecology
Date : 2020
Volume : 96
Issue : fiaa018
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
Unoccupied aerial vehicle laser scanning (UAV-LS) has been increasingly used for forest structure assessment in recent years due to the potential to directly estimate individual tree attributes and availability of commercial solutions. However, standardised procedures for campaign planning are still largely missing. This study investigated scanner properties and flight planning to provide recommendations on minimising forest canopy occlusion and thereby maximise exploration of canopy volume. A flight campaign involving two UAV-LS systems was conducted over a dense, wet tropical forest at the Paracou research station (French Guiana). Four experiments on scanner properties and flight planning were conducted, analysed and recommendations derived. First, the scanner pulse repetition rate (PRR) should be at least 100 kHz per 1 m s−1 flight speed based on 360° FOV for exploration of middle canopy strata (5 m to 20 m). Higher PRR are beneficial for exploration of lower canopy (<5 m) but would need to be increased exponentially to achieve linear improvement. Alternatively, flight speed could be reduced within the constraints given by the inertial measurement unit (IMU), but would increase flight time. Second, the scanner maximum range was identified as a proxy for the laser pulse power, which positively impacts canopy exploration. This was particularly the case when using multi-return capabilities. No saturation could be observed when increasing the laser power, suggesting that this is currently a limiting factor. Additionally, a smaller laser beam divergence and pulse width were plausible reasons for better exploration of the upper canopy just below the top of canopy. Third, off-nadir scanning angles up to 20° were found to result in similar occlusions, suggesting a practical FOV of 40° in the investigated dense forest. This number might be larger for open canopies. UAV-LS systems with viewing geometries that focus laser pulses downwards and within optimal ranges should be preferred. Fourth, using different horizontal flight directions in the mission planning favours minimisation of occlusion. A minimum of two different flight directions is suggested. However, specific optimal yaw angles were not possible to predict before flight. Therefore, including multiple directions ensures coverage of all possible configurations. Many of these investigated features can be optimised independently from each other, and should be considered before acquisition of new UAV-LS systems and flight mission planning. These results support the establishment of general guidelines for the investment in UAV-LS systems and optimal mission planning for forest structure assessment.
Auteurs, date et publication :
Auteurs Benjamin Brede , Harm M. Bartholomeus , Nicolas Barbier , François Pimont , Grégoire Vincent , Martin Herold
Publication : International Journal of Applied Earth Observation and Geoinformation
Date : 2022
Volume : 114
Pages : 103056
Catégorie(s)
#CIRAD #FORET ParacouRésumé
There is increasing evidence to suggest that soil nutrient availability can limit the carbon sink capacity of forests, a particularly relevant issue considering today’s changing climate. This question is especially important in the tropics, where most part of the Earth’s plant biomass is stored. To assess whether tropical forest growth is limited by soil nutrients and to explore N and P limitations, we analyzed stem growth and foliar elemental composition of the five stem widest trees per plot at two sites in French Guiana after 3 years of nitrogen (N), phosphorus (P), and N + P addition. We also compared the results between potential N-fixer and non-N-fixer species. We found a positive effect of N fertilization on stem growth and foliar N, as well as a positive effect of P fertilization on stem growth, foliar N, and foliar P. Potential N-fixing species had greater stem growth, greater foliar N, and greater foliar P concentrations than non-N-fixers. In terms of growth, there was a negative interaction between N-fixer status, N + P, and P fertilization, but no interaction with N fertilization. Because N-fixing plants do not show to be completely N saturated, we do not anticipate N providing from N-fixing plants would supply non-N-fixers. Although the soil-age hypothesis only anticipates P limitation in highly weathered systems, our results for stem growth and foliar elemental composition indicate the existence of considerable N and P co-limitation, which is alleviated in N-fixing plants. The evidence suggests that certain mechanisms invest in N to obtain the scarce P through soil phosphatases, which potentially contributes to the N limitation detected by this study.
Auteurs, date et publication :
Auteurs Helena Vallicrosa , Laynara F. Lugli , Lucia Fuchslueger , Jordi Sardans , Irene Ramirez‐Rojas , Erik Verbruggen , Oriol Grau , Laëtitia Bréchet , Guille Peguero , Leandro Van Langenhove , Lore T. Verryckt , César Terrer , Joan Llusià , Romà Ogaya , Laura Márquez , Pere Roc‐Fernández , Ivan Janssens , Josep Peñuelas
Publication : Ecology
Date : 2025
Volume : 104
Issue : 6
Pages : e4049
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouAuteurs, date et publication :
Auteurs Mauro Mariotti D'Alessandro , Stefano Tebaldini , Fabio Rocca
Publication : IEEE Transactions on Geoscience and Remote Sensing
Date : 2013
Volume : 51
Issue : 8
Pages : 4430–4437
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Synthetic aperture radar (SAR) data collected over a 2-D synthetic aperture can be processed to focus the illuminated scatterers in the 3-D space, using a number of signal processing techniques generally grouped under the name of SAR tomography (TomoSAR). A fundamental requirement for TomoSAR processing is to have precise knowledge of the platform position along the 2-D synthetic aperture. This requirement is not easily met in the case where the 2-D aperture is formed by collecting different flight lines (i.e., 1-D apertures) in a repeat-pass fashion, which is the typical case of airborne and spaceborne TomoSAR. Subwavelength platform position errors give rise to residual phase screens among different passes, which hinder coherent focusing in the 3-D space. In this paper, we propose a strategy for calibrating repeat-pass tomographic SAR data that allows us to accurately estimate and remove such residual phase screens in the absence of reference targets and prior information about terrain topography and even in the absence of any point- or surface-like target within the illuminated scene. The problem is tackled by observing that multiple flight lines provide enough information to jointly estimate platform and target positions, up to a roto-translation of the coordinate system used for representing the imaged scene. The employment of volumetric scatterers in the calibration process is enabled by the phase linking algorithm, which allows us to represent them as equivalent phase centers. The proposed approach is demonstrated through numerical simulations, in order to validate the results based on the exact knowledge of the simulated scatterers, and using real data from the ESA campaigns AlpTomoSAR, BioSAR 2008, and TropiSAR. A cross-check of the results from simultaneous P- and L-band acquisitions from the TropiSAR data set indicates that the dispersion of the retrieved flight trajectories is limited to a few millimeters.
Auteurs, date et publication :
Auteurs Stefano Tebaldini , Fabio Rocca , Mauro Mariotti d'Alessandro , Laurent Ferro-Famil
Publication : IEEE Transactions on Geoscience and Remote Sensing
Date : 2016
Volume : 54
Issue : 3
Pages : 1775–1792