Résumé
The primary objective of the European Space Agency's 7th Earth Explorer mission, BIOMASS, is to determine the worldwide distribution of forest above-ground biomass (AGB) in order to reduce the major uncertainties in calculations of carbon stocks and fluxes associated with the terrestrial biosphere, including carbon fluxes associated with Land Use Change, forest degradation and forest regrowth. To meet this objective it will carry, for the first time in space, a fully polarimetric P-band synthetic aperture radar (SAR). Three main products will be provided: global maps of both AGB and forest height, with a spatial resolution of 200 m, and maps of severe forest disturbance at 50 m resolution (where “global” is to be understood as subject to Space Object tracking radar restrictions). After launch in 2022, there will be a 3-month commissioning phase, followed by a 14-month phase during which there will be global coverage by SAR tomography. In the succeeding interferometric phase, global polarimetric interferometry Pol-InSAR coverage will be achieved every 7 months up to the end of the 5-year mission. Both Pol-InSAR and TomoSAR will be used to eliminate scattering from the ground (both direct and double bounce backscatter) in forests. In dense tropical forests AGB can then be estimated from the remaining volume scattering using non-linear inversion of a backscattering model. Airborne campaigns in the tropics also indicate that AGB is highly correlated with the backscatter from around 30 m above the ground, as measured by tomography. In contrast, double bounce scattering appears to carry important information about the AGB of boreal forests, so ground cancellation may not be appropriate and the best approach for such forests remains to be finalized. Several methods to exploit these new data in carbon cycle calculations have already been demonstrated. In addition, major mutual gains will be made by combining BIOMASS data with data from other missions that will measure forest biomass, structure, height and change, including the NASA Global Ecosystem Dynamics Investigation lidar deployed on the International Space Station after its launch in December 2018, and the NASA-ISRO NISAR L- and S-band SAR, due for launch in 2022. More generally, space-based measurements of biomass are a core component of a carbon cycle observation and modelling strategy developed by the Group on Earth Observations. Secondary objectives of the mission include imaging of sub-surface geological structures in arid environments, generation of a true Digital Terrain Model without biases caused by forest cover, and measurement of glacier and icesheet velocities. In addition, the operations needed for ionospheric correction of the data will allow very sensitive estimates of ionospheric Total Electron Content and its changes along the dawn-dusk orbit of the mission.
Auteurs, date et publication :
Auteurs Shaun Quegan , Thuy Le Toan , Jerome Chave , Jorgen Dall , Jean-François Exbrayat , Dinh Ho Tong Minh , Mark Lomas , Mauro Mariotti D'Alessandro , Philippe Paillou , Kostas Papathanassiou , Fabio Rocca , Sassan Saatchi , Klaus Scipal , Hank Shugart , T. Luke Smallman , Maciej J. Soja , Stefano Tebaldini , Lars Ulander , Ludovic Villard , Mathew Williams
Publication : Remote Sensing of Environment
Date : 2019
Volume : 227
Pages : 44-60
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
Understanding the Global Climate Change and the way it will affect the Earth and preserving biodiversity are two major challenges of the 21st century. Forests cover 30% of continental surfaces and are a major contributor to the carbon cycle. Sequestration of carbon in forest biomass appears as an important mechanism - in conjunction with reduced emissions - for mitigating climate change. Adequate management of forest resources could strengthen the action of forests as a carbon sink. Forests also play a key role for biodiversity conservation and energy supply. Sustainable management of forest ecosystems is thus critical for the future of mankind. However, the lack of consistent information on forest structure and biomass and on their dynamics at global scale hampers the development of ecological models and of earth-vegetation-atmosphere interaction global models that are essential to improve knowledge on forest ecosystem functioning and to address the challenge of forest sustainable management. By its ability to measure the vertical structure of land cover, airborne Lidar technology is highly qualified for forest applications. NASA's ICESat1 mission (2003-2009) paved the way for Earth observation from space with Lidar systems. ICESat2, launched in September 2018, although primarily designed for ice monitoring will also provide vegetation height measurements worldwide. Vegetation profiles with high vertical resolution should also become soon available with GEDI (NASA) and MOLI (JAXA) missions that will be installed on the ISS at the end of 2018 and in 2019 or 2020, respectively. Although data coverage will be limited from 52°S to 52°N, both these missions will contribute to ecosystem structure observation from space in conjunction with radar missions, especially the BIOMASS ESA's mission. Combined with Sentinel 2 imagery, which provides spectral information with high spatial and temporal resolutions, they will also enable to evaluate the complementarity between information on 3D structure, composition and phenology for a comprehensive monitoring of forest ecosystem conditions. LEAF (Lidar For Earth and Forests) mission has been under study at CNES since 2008 and could contribute in the future to the international effort to sustain global carbon and biodiversity monitoring systems. The system under study combines a NIR full-waveform Lidar profiler and a very high resolution multispectral imager. CNES has supported scientific projects in order to refine instrument specifications and design a system that will meet user requirements. Due to the high cost associated with the development of an airborne prototype, priority has been given to simulation approaches. The aim of this contribution is to present LEAF mission concept and to focus on the recent "LEAF ExpeVal" experiment, designed to consolidate and validate the simulation approaches developed to model a realistic Lidar signal on various forest types, including complex tropical forests. These approaches rely on DART, a radiative transfer model developed at CESBIO. A Lidar module was introduced into DART in the early 2010s and has undergone constant improvement since then. However, simulating a realistic signal also requires to work on model inputs and to develop methods to build detailed forest scenes. The objective of the LEAF-Expeval experiment was twofold: first, to validate the simulations by comparing simulated and experimental Lidar waveforms on a tropical forest; second, to develop a new approach to simulate spaceborne Lidar data from small footprint airborne Lidar data (ALS data). Achieving the first objective is a key step to refine LEAF system specifications in order to ensure that the system will provide accurate height measurements and vegetation profiles on tropical forests, which are the most constraining environment for a space Lidar. Field and airborne data were collected in Paracou experimental forest in French Guiana. The processing and analysis steps include (1) the construction of forest scenes from TLS (Terrestrial Lidar Scanner) and reflectance measurements on a dense forest plot, (2) the estimation of the calibration coefficient of the airborne system, coefficient that is used to convert digital count into physical units, (3) the simulation of airborne Lidar data on the forest scene using DART and (4) the comparison of simulated and real waveforms. As ALS data are now widely available, achieving the second objective would enable the simulation and evaluation of LEAF data on a variety of forest ecosystems. This part of the study relies on Lidar simulations realized on temperate broadleaved forest scenes created using Allostand (Amap) and Genesis software. Small footprint lidar point clouds were simulated using DART and were in turn used to simulate large footprint lidar waveforms. The resulting waveforms were compared to reference data, i.e. large footprint waveforms obtained directly with DART on the same forest scenes. First results are encouraging and showed that large footprint waveforms obtained from the processing of small footprint data were very similar to reference waveforms, even with a change of waveband between lidar point clouds and large footprint waveform.
Auteurs, date et publication :
Auteurs S. Durrieu , F. de Boissieu , J. P. Gastellu Etchegorry , G. Vincent , C. Lavalley , G. Couderc , S. Mpili , F. Heuschmidt , J. Costeraste , J. B. Feret , D. Ebengo , N. Lauret , M. J. Lefèvre Fonollosa , T. Yin
Date : 2019
Pages : 21
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Increasing evidence shows that the functioning of the tropical forest biome is intimately related to the climate variability with some variables such as annual precipitation, temperature or seasonal water stress identified as key drivers of ecosystem dynamics. How tropical tree communities will respond to the future climate change is hard to predict primarily because several demographic processes act together to shape the forest ecosystem general behavior. To overcome this limitation, we used a joint individual-based model to simulate, over the next century, a tropical forest community experiencing the climate change expected in the Guiana Shield. The model is climate dependent: temperature, precipitation and water stress are used as predictors of the joint growth and mortality rates. We ran simulations for the next century using predictions of the IPCC 5AR, building three different climate scenarios (optimistic RCP2.6, intermediate, pessimistic RCP8.5) and a control (current climate). The basal area, above-ground fresh biomass, quadratic diameter, tree growth and mortality rates were then computed as summary statistics to characterize the resulting forest ecosystem. Whatever the scenario, all ecosystem process and structure variables exhibited decreasing values as compared to the control. A sensitivity analysis identified the temperature as the strongest climate driver of this behavior, highlighting a possible temperature-driven drop of 40% in average forest growth. This conclusion is alarming, as temperature rises have been consensually predicted by all climate scenarios of the IPCC 5AR. Our study highlights the potential slow-down danger that tropical forests will face in the Guiana Shield during the next century.
Auteurs, date et publication :
Auteurs Mélaine Aubry-Kientz , Vivien Rossi , Guillaume Cornu , Fabien Wagner , Bruno Hérault
Publication : Scientific Reports
Date : 2019
Volume : 9
Issue : 1
Pages : 10235
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Synthetic aperture radar (SAR) tomography (TomoSAR) is an emerging technology to image the 3D structure of the illuminated media. TomoSAR exploits the key feature of microwaves to penetrate into vegetation, snow, and ice, hence providing the possibility to see features that are hidden to optical and hyper-spectral systems. The research on the use of P-band waves, in particular, has been largely propelled since 2007 in experimental studies supporting the future spaceborne Mission BIOMASS, to be launched in 2022 with the aim of mapping forest aboveground biomass (AGB) accurately and globally. The results obtained in the frame of these studies demonstrated that TomoSAR can be used for accurate retrieval of geophysical variables such as forest height and terrain topography and, especially in the case of dense tropical forests, to provide a more direct link to AGB. This paper aims at providing the reader with a comprehensive understanding of TomoSAR and its application for remote sensing of forested areas, with special attention to the case of tropical forests. We will introduce the basic physical principles behind TomoSAR, present the most relevant experimental results of the last decade, and discuss the potentials of BIOMASS tomography.
Auteurs, date et publication :
Auteurs Stefano Tebaldini , Dinh Ho Tong Minh , Mauro Mariotti d’Alessandro , Ludovic Villard , Thuy Le Toan , Jerome Chave
Publication : Surveys in Geophysics
Date : 2019
Volume : 40
Issue : 4
Pages : 779-801
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouRésumé
In this work we investigate the role of volume scattering obtained from tomography and ground/volume decomposition in retrieving AGB (Above Ground Biomass). Results here presented originate from the BIOMASS L2 study, aimed at defining and implementing the tomographic and interferometric processors of the BIOMASS mission. In particular we aim at discussing whether, and to what extent, ground/volume decomposition can provide a valid alternative to tomography. To do this, both are tested based on the P-Band data collected at the forest site of Paracou, French Guiana, during the TropiSAR campaign, and validated against in-situ AGB measurements in terms of correlation and sensitivity of the retrievals. Quite surprisingly, results indicate that volumebackscattered power as obtained by ground/volume decomposition is almost unsensitive to AGB, notwithstanding different solutions for volume scattering are tested, and lead to conclusion that forest structure actually plays a non-negligible role in AGB retrieval in tropical areas.
Auteurs, date et publication :
Auteurs F. Banda , M. M. d’Alessandro , S. Tebaldini , D. Giudici
Date : 2019
Pages : 1073-1076
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The architecture (here, the size distribution combined with the spatial pattern of individuals) of natural forest at demographic equilibrium can be used to infer the demographic processes that drive the forest dynamics. In particular, a constant growth rate and a constant mortality rate for all trees would generate an exponential distribution of their size, whereas the metabolic scaling theory predicts a power distribution. In an undisturbed tropical rainforest in French Guiana, the diameter distribution was significantly steeper than the best-fit exponential distribution and significantly flatter than the best-fit power distribution. A simple individual-based model of forest dynamics with asymmetric competition between trees, where the strength of competition was regulated by a single parameter, was able to predict the observed distribution. Competition drove the forest into a self-organized state with stronger inequalities of size among trees, a lower mean competition index, and a spatial pattern of trees that deviated from complete spatial randomness.
Auteurs, date et publication :
Auteurs Nicolas Picard
Publication : Forest Science
Date : 2019
Volume : 65
Issue : 5
Pages : 562-569
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Secondary forests are a prominent component of tropical landscapes, and they constitute a major atmospheric carbon sink. Rates of carbon accumulation are usually inferred from chronosequence studies, but direct estimates of carbon accumulation based on long-term monitoring of stands are rarely reported. Recent compilations on secondary forest carbon accumulation in the Neotropics are heavily biased geographically as they do not include estimates from the Guiana Shield. We analysed the temporal trajectory of aboveground carbon accumulation and floristic composition at one 25-ha secondary forest site in French Guiana. The site was clear-cut in 1976, abandoned thereafter, and one large plot (6.25 ha) has been monitored continuously since. We used Bayesian modeling to assimilate inventory data and simulate the long-term carbon accumulation trajectory. Canopy change was monitored using two aerial lidar surveys conducted in 2009 and 2017. We compared the dynamics of this site with that of a surrounding old-growth forest. Finally, we compared our results with that from secondary forests in Costa Rica, which is one of the rare long-term monitoring programs reaching a duration comparable to our study. Twenty years after abandonment, aboveground carbon stock was 64.2 (95% credibility interval 46.4, 89.0) Mg C/ha, and this stock increased to 101.3 (78.7, 128.5) Mg C/ha 20 yr later. The time to accumulate one-half of the mean aboveground carbon stored in the nearby old-growth forest (185.6 [155.9, 200.2] Mg C/ha) was estimated at 35.0 [20.9, 55.9] yr. During the first 40 yr, the contribution of the long-lived pioneer species Xylopia nitida, Goupia glabra, and Laetia procera to the aboveground carbon stock increased continuously. Secondary forest mean-canopy height measured by lidar increased by 1.14 m in 8 yr, a canopy-height increase consistent with an aboveground carbon accumulation of 7.1 Mg C/ha (or 0.89 Mg C·ha−1·yr−1) during this period. Long-term AGC accumulation rate in Costa Rica was almost twice as fast as at our site in French Guiana. This may reflect higher fertility of Central American forest communities or a better adaptation of the forest tree community to intense and frequent disturbances. This finding may have important consequences for scaling-up carbon uptake estimates to continental scales.
Auteurs, date et publication :
Auteurs Jérôme Chave , Camille Piponiot , Isabelle Maréchaux , Hubert de Foresta , Denis Larpin , Fabian Jörg Fischer , Géraldine Derroire , Grégoire Vincent , Bruno Hérault
Publication : Ecological Applications
Date : 2025
Volume : 30
Issue : 1
Pages : e02004
Catégorie(s)
#ANR-Citation #CIRAD #FORET ParacouRésumé
Tropical forests shelter the highest species diversity worldwide, although genus diversity is lower than expected. In the species-rich genera, species complexes are composed of closely-related species that share large amounts of genetic variation. Despite the key role of species complexes in diversification, evolution and functioning of ecological communities, little is known on why species complexes arise and how they are maintained in Neotropical forests. Examining how individual phenotypes vary along environmental gradients, within and among closely-related species within species complexes, can reveal processes allowing species coexistence within species complexes. We examined leaf functional trait variation with topography in a hyperdiverse tropical forest of the Guiana Shield. We collected leaf functional traits from 766 trees belonging to five species in two species complexes in permanent plots encompassing a diversity of topographic positions. We tested the role of topography on leaf functional trait variation with a hierarchical Bayesian model, controlling for individual tree diameter effect. We show that, mirroring what has been previously observed among species and communities, individual leaf traits covary from acquisitive to conservative strategy within species. Moreover, decreasing wetness from bottomlands to plateaus was associated with a shift of leaf traits from an acquisitive to a conservative strategy both across and within closely-related species. Our results suggest that intraspecific trait variability widens species’ niches and converges at species’ margins where niches overlap, potentially implying local neutral processes. Intraspecific trait variability favors local adaptation and divergence of closely-related species within species complexes. It is potentially maintained through interspecific sharing of genetic variation through hybridization.
Auteurs, date et publication :
Auteurs Sylvain Schmitt , Bruno Hérault , Émilie Ducouret , Anne Baranger , Niklas Tysklind , Myriam Heuertz , Éric Marcon , Saint Omer Cazal , Géraldine Derroire
Publication : Oikos
Date : 2025
Volume : 129
Issue : 10
Pages : 1521-1530
Catégorie(s)
#CIRAD #FORET ParacouRésumé
BIOMASS is ESA’s seventh Earth Explorer mission, scheduled for launch in 2022. The satellite will be the first P-band SAR sensor in space and will be operated in fully polarimetric interferometric and tomographic modes. The mission aim is to map forest above-ground biomass (AGB), forest height (FH) and severe forest disturbance (FD) globally with a particular focus on tropical forests. This paper presents the algorithms developed to estimate these biophysical parameters from the BIOMASS level 1 SAR measurements and their implementation in the BIOMASS level 2 prototype processor with a focus on the AGB product. The AGB product retrieval uses a physically-based inversion model, using ground-canceled level 1 data as input. The FH product retrieval applies a classical PolInSAR inversion, based on the Random Volume over Ground Model (RVOG). The FD product will provide an indication of where significant changes occurred within the forest, based on the statistical properties of SAR data. We test the AGB retrieval using modified airborne P-Band data from the AfriSAR and TropiSAR campaigns together with reference data from LiDAR-based AGB maps and plot-based ground measurements. For AGB estimation based on data from a single heading, comparison with reference data yields relative Root Mean Square Difference (RMSD) values mostly between 20% and 30%. Combining different headings in the estimation process significantly improves the AGB retrieval to slightly less than 20%. The experimental results indicate that the implemented retrieval scheme provides robust results that are within mission requirements.
Auteurs, date et publication :
Auteurs Francesco Banda , Davide Giudici , Thuy Le Toan , Mauro Mariotti d’Alessandro , Kostas Papathanassiou , Shaun Quegan , Guido Riembauer , Klaus Scipal , Maciej Soja , Stefano Tebaldini , Lars Ulander , Ludovic Villard
Publication : Remote Sensing
Date : 2020
Volume : 12
Issue : 6
Pages : 985
Catégorie(s)
#CIRAD #FORET ParacouRésumé
We observed strong positive relationships between soil properties and forest dynamics of growth and mortality across twelve primary lowland tropical forests in a phosphorus-poor region of the Guiana Shield. Average tree growth (diameter at breast height) increased from 0.81 to 2.1mmyr(-1) along a soil texture gradient from 0 to 67% clay, and increasing metal-oxide content. Soil organic carbon stocks in the top 30cm ranged from 30 to 118 tons C ha(-1), phosphorus content ranged from 7 to 600mgkg(-1) soil, and the relative abundance of arbuscular mycorrhizal fungi ranged from 0 to 50%, all positively correlating with soil clay, and iron and aluminum oxide and hydroxide content. In contrast, already low extractable phosphorus (Bray P) content decreased from 4.4 to <0.02mgkg(-1) in soil with increasing clay content. A greater prevalence of arbuscular mycorrhizal fungi in more clayey forests that had higher tree growth and mortality, but not biomass, indicates that despite the greater investment in nutrient uptake required, soils with higher clay content may actually serve to sustain high tree growth in tropical forests by avoiding phosphorus losses from the ecosystem. Our study demonstrates how variation in soil properties that retain carbon and nutrients can help to explain variation in tropical forest growth and mortality, but not biomass, by requiring niche specialization and contributing to biogeochemical diversification across this region.
Auteurs, date et publication :
Auteurs Jennifer L. Soong , Ivan A. Janssens , Oriol Grau , Olga Margalef , Clement Stahl , Leandro Van Langenhove , Ifigenia Urbina , Jerome Chave , Aurelie Dourdain , Bruno Ferry , Vincent Freycon , Bruno Herault , Jordi Sardans , Josep Penuelas , Erik Verbruggen
Publication : SCIENTIFIC REPORTS
Date : 2020
Volume : 10
Issue : 1