Résumé
textlessptextgreaterThe seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is textless 2000 mm yrtextlesssuptextgreater−1textless/suptextgreater (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall textless 2000 mm yrtextlesssuptextgreater−1textless/suptextgreater.textless/ptextgreater
Auteurs, date et publication :
Auteurs Fabien H. Wagner , Bruno Hérault , Damien Bonal , Clément Stahl , Liana O. Anderson , Timothy R. Baker , Gabriel Sebastian Becker , Hans Beeckman , Danilo Boanerges Souza , Paulo Cesar Botosso , David M. J. S. Bowman , Achim Bräuning , Benjamin Brede , Foster Irving Brown , Jesus Julio Camarero , Plínio Barbosa Camargo , Fernanda C. G. Cardoso , Fabrício Alvim Carvalho , Wendeson Castro , Rubens Koloski Chagas
Publication : Biogeosciences
Date : 2016
Volume : 13
Issue : 8
Pages : 2537–2562
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Cecília Lira Melo de Oliveira Santos , Rubens Augusto Camargo Lamparelli , Dantas Araújo Figueiredo , Gleyce Kelly , Stéphane Dupuy , Julie Boury , Ana Cláudia dos Santos Luciano , Ricardo da Silva Torres , Guerric le Maire
Publication : Remote Sensing
Date : 2025
Volume : 11
Issue : 3
Pages : 334
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
We generalize Ripley's K function to get a new function, M, to characterize the spatial structure of a point pattern relatively to another one. We show that this new approach is pertinent in ecology when space is not homogenous and the size of objects matters. We present how to use the function and test the data against the null hypothesis of independence between points. In a tropical tree data set we detect intraspecific aggregation and inter specific competition
Auteurs, date et publication :
Auteurs Eric Marcon , Florence Puech , Stéphane Traissac
Publication : International Journal of Ecology
Date : 2025
Volume : 2012
Catégorie(s)
#CIRAD #FORET ParacouRésumé
When 2 Mha of Amazonian forests are disturbed by selective logging each year, more than 90 Tg of carbon (C) is emitted to the atmosphere. Emissions are then counterbalanced by forest regrowth. With an original modelling approach, calibrated on a network of 133 permanent forest plots (175 ha total) across Amazonia, we link regional differences in climate, soil and initial biomass with survivors' and recruits' C fluxes to provide Amazon-wide predictions of post-logging C recovery. We show that net aboveground C recovery over 10 years is higher in the Guiana Shield and in the west (21 ±3 Mg C ha-1) than in the south (12 ±3 Mg C ha-1) where environmental stress is high (low rainfall, high seasonality). We highlight the key role of survivors in the forest regrowth and elaborate a comprehensive map of post-disturbance C recovery potential in Amazonia.
Auteurs, date et publication :
Auteurs Camille Piponiot , Plinio Sist , Lucas Mazzei , Marielos Peña-Claros , Francis E Putz , Ervan Rutishauser , Alexander Shenkin , Nataly Ascarrunz , Celso P de Azevedo , Christopher Baraloto , Mabiane França , Marcelino Guedes , Eurídice N.Honorio Coronado , Marcus V.N. D'Oliveira , Ademir R Ruschel , Kátia E da Silva , Eleneide Doff Sotta , Cintia R de Souza , Edson Vidal , Thales Ap West
Publication : eLife
Date : 2025
Volume : 5
Issue : DECEMBER2016
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The objective of this paper is to provide a better understanding of the capabilities of the BIOMASS tomography concerning the retrieval of forest biomass and height in tropical areas. The analysis presented in this paper is carried out on airborne data acquired by Office National d'Etudes et de Recherches Aérospatiales (ONERA) over the site of Paracou, French Guiana, during the European Space Agency campaign TropiSAR. This high-resolution data set (125-MHz bandwidth) was reprocessed in order to generate a new data stack consistent with BIOMASS as for the bandwidth (6 MHz) and the azimuth resolution (about 12 m). To do this, two different processing approaches have been considered. One approach consisted of degrading the resolution of the airborne data through the linear filtering of raw data, followed by standard SAR processing. The other approach consisted of recovering the 3-D distribution of the scatterers at a high resolution, which was then reprojected onto the BIOMASS geometry. The latter procedure allows us to obtain a data stack that is the most realistic emulation of BIOMASS imaging capabilities. In both approaches, neither ionospheric disturbances nor temporal decorrelation has been considered. The connection to the forest biomass has been examined in both cases by investigating the correlation between the backscatter at different forest heights and the above-ground biomass (AGB) values from in situ data. As expected, the reduction of the system bandwidth to 6 MHz resulted in significant vertical resolution losses compared with the original airborne data. Nevertheless, it was possible to retrieve the forest height to within an accuracy of better than 4 m, whereas the backscattered power at the volume height (30 m above the ground) exhibited a correlation higher than 0.8 with the in situ data and no bias phenomena over the AGB values ranging from 250 to 450 t/ha.
Auteurs, date et publication :
Auteurs Dinh Ho Tong Minh , Stefano Tebaldini , Fabio Rocca , Thuy Le Toan , Ludovic Villard , Pascale C. Dubois-Fernandez
Publication : IEEE Transactions on Geoscience and Remote Sensing
Date : 2015
Volume : 53
Issue : 2
Pages : 965–975
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Quantifying forest biomass is of crucial importance for estimating carbon fluxes on the regional and global scale in climate change studies. Significant relationships have already been established between radar mean intensity and forest biomass, but these relationships show a reduced sensitivity to biomass variations for mature stands (about 80 t/ha and more). On the contrary, recent studies have shown that image texture is significantly related to biomass even for mature stands for a temperate, monospecific, even-aged forest the biomass of which is 140 t/ha at its highest point. The present paper aims at extending these observations to tropical forests which represent a large terrestrial biomass pool with values higher than 450 t/ha. Radar images were acquired during the TropiSAR experiment in 2009, which took place over a tropical rain forest located in French Guiana at P band and cross-polarization with the use of SETHI ONERA airborne instrument. Three sets of treatments applied to 15 forest stands provided biomass values from 268 to 466 t/ha where permanent zones of 6.25 ha each were mapped and regularly measured. Homogeneous patches were selected inside each of the 15 experimental stands. Statistical features were then derived for each patch: a) from grey level statistics; b) from the statistics of pixel pairs on the basis of the gray level co-occurrence matrix. It is shown that linear relationships between texture features and forest biomass are heavily influenced by stand structure and the local topography and soil of the experimental stands. But, when stands are separated on two structural groups using texture descriptors, texture/biomass regressions reveal to be very significant.
Auteurs, date et publication :
Auteurs Isabelle Champion , Jean Pierre , Da Costa , Adrien Godineau , Ludovic Villard
Publication : EARSel eProceedings
Date : 2025
Volume : 12
Issue : 1
Pages : 25–32
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Large tropical trees store significant amounts of carbon in woody components and their distribution plays an important role in forest carbon stocks and dynamics. Here, we explore the properties of a new Lidar derived index, large tree canopy area (LCA) defined as the area occupied by canopy above a reference height. We hypothesize that this simple measure of forest structure representing the crown area of large canopy trees could consistently explain the landscape variations of forest volume and aboveground biomass (AGB) across a range of climate and edaphic conditions. To test this hypothesis, we assembled a unique dataset of high-resolution airborne Light Detection and Ranging (Lidar) and ground inventory data in nine undisturbed old growth Neotropical forests. We found that the LCA for trees greater than 27 m (∼ 25–30 m) in height and at least 100 m2 crown size in a unit area (1 ha), explains more than 75 % of total forest volume variations, irrespective of the forest biogeographic conditions. When weighted by average wood density of the stand, LCA can be used as an unbiased estimator of AGB across all sites (R2 = 0.78, RMSE = 46.02 Mg ha−1, bias = 0.76 Mg ha−1). Unlike other Lidar derived metrics with complex nonlinear relations to biomass, the relationship between LCA and AGB is linear. A comparison with tree inventories across the study sites indicates that LCA correlates best with the crown area (or basal area) of trees with diameter textgreater 50 cm. The spatial invariance of the LCA–AGB relationship across the Neotropics suggests a remarkable regularity of forest structure across the landscape and a new technique for systematic monitoring of large trees for their contribution to AGB and changes associated with selective logging, tree mortality, and other types of forest disturbance and dynamics.
Auteurs, date et publication :
Auteurs Victoria Meyer , Sassan Saatchi , David B. Clark , Michael Keller , Grégoire Vincent , António Ferraz , Fernando Espírito-Santo , Marcus V. N. D'Oliveira , Dahlia Kaki , Jérôme Chave
Publication : Biogeosciences Discussions
Date : 2018
Pages : 1–38
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Abstract Despite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy‐intercepted rainfall) affects the relationship between surface soil water isotopic enrichment (lc‐excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the “drier” season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc‐excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the “drier” season, leading to enhanced rainfall interception and a negative relationship between lc‐excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc‐excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.
Auteurs, date et publication :
Auteurs N. J. Hasselquist , L. Benegas , O. Roupsard , A. Malmer , U. Ilstedt
Publication : Hydrological Processes
Date : 2025
Volume : 32
Issue : 8
Pages : 994-1004
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Mapping tropical forests to a sufficient level of spatial resolution and structural detail is a prerequisite for their rational management, which however remains a largely unmet challenge. We explore the degree to which a forest canopy height model (CHM) derived from airborne laser scanning (ALS) can discriminate between five forest types of similar height but varying structure or composition. We systematically compare various textural features (Haralick, Fourier transform-based, and wavelet- based features) and various classification procedures (linear discriminant analysis (LDA), random forest (RF), and support vector machine (SVM)) applied to two sizes of sampling units (64 m × 64 m and 32 m × 32 m). Simple height distribution statistics achieve at best 70% classification accuracy in our sample set comprising 120 sampling units of 64 m × 64 m. Using wavelet-based features, this accuracy increases to 79% but drops by 10% with smaller sampling units (32 m × 32 m). Classifier performance depends on the texture feature set used, but SVM and RF tend to perform better than LDA. High discrimination rates between forests types of similar height indicate that the ALS-derived CHM provides information suitable for mapping of tropical forest types. Wavelet-based texture features coupled with a SVM classifier was found to be the most promising combination of methods. Ancillary data derived from laser scans and notably topography could be used jointly for an improved segmentation scheme. 1.
Auteurs, date et publication :
Auteurs Pol Kennel , Marie Tramon , Nicolas Barbier , Grégoire Vincent
Publication : International Journal of Remote Sensing
Date : 2025
Volume : 34
Issue : 24
Pages : 8917–8935
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Lore T Verryckt , David S Ellsworth , Sara Vicca , Leandro Van Langenhove , Josep Peñuelas , Philippe Ciais , Juan M Posada , Clément Stahl , Sabrina Coste , Elodie A Courtois
Publication : Biotropica
Date : 2025
Volume : 52
Issue : 6
Pages : 1183-1193