Auteurs, date et publication :

Auteurs Diarietou Sambakhe , Mathieu Fortin , Jean-Pierre Renaud , Christine Deleuze , Philippe Dreyfus , Nicolas Picard

Publication : Forest Science

Date : 2014

Volume : 60

Issue : 6

Pages : 1050–1059

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Synthetic Aperture Radar (SAR) texture has been demonstrated to have the potential to improve forest biomass estimation using backscatter. However, forests are 3D objects with a vertical structure. The strong penetration of SAR signals means that each pixel contains the contributions of all the scatterers inside the forest canopy, especially for the P-band. Consequently, the traditional texture derived from SAR images is affected by forest vertical heterogeneity, although the influence on texture-based biomass estimation has not yet been explicitly explored. To separate and explore the influence of forest vertical heterogeneity, we introduced the SAR tomography technique into the traditional texture analysis, aiming to explore whether TomoSAR could improve the performance of texture-based aboveground biomass (AGB) estimation and whether texture plus tomographic backscatter could further improve the TomoSAR-based AGB estimation. Based on the P-band TomoSAR dataset from TropiSAR 2009 at two different sites, the results show that ground backscatter variance dominated the texture features of the original SAR image and reduced the biomass estimation accuracy. The texture from upper vegetation layers presented a stronger correlation with forest biomass. Texture successfully improved tomographic backscatter-based biomass estimation, and the texture from upper vegetation layers made AGB models much more transferable between different sites. In addition, the correlation between texture indices varied greatly among different tomographic heights. The texture from the 10 to 30 m layers was able to provide more independent information than the other layers and the original images, which helped to improve the backscatter-based AGB estimation.

Auteurs, date et publication :

Auteurs Zhanmang Liao , Binbin He , Xingwen Quan

Publication : International Journal of Applied Earth Observation and Geoinformation

Date : 2020

Volume : 88

Pages : 102049

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

Tropical rainforests host exceptional biodiversity and provide important ecosystem services, but they are facing anthropogenic and climatic threats. Preserving the genetic diversity of forest tree populations is essential for their capacity to adapt and exhibit resilience to environmental changes and anthropogenic pressures. Here, we collected conservation genetic baseline information for the heavily exploited timber tree Dicorynia guianensis Amshoff (Fabaceae) at the regional and local levels in French Guiana. Based on genotyping at five microsatellite loci in 1566 individuals collected in 23 forest locations, we documented the genetic differentiation of locations from the West of French Guiana and identified distinctive genetic diversity patterns with higher genetic diversity and some bottlenecked sites in the East and inland. The regional population genetic structure is likely the result of past population isolation in distinct Pleistocene refuges and different demographic histories potentially influenced by Holocene drought periods or palaeofires. Assessment of spatial genetic structure (Sp from 0 to 0.028) in five intensively sampled locations yielded estimates of Wright’s neighborhood size of 35 to 313, indicative of restricted dispersal and local metapopulation dynamics, and useful as baseline information to assess the effects of selective logging for conservation management. These results support the current management strategies with low impact extraction of D. guianensis in three zones of the French Guiana permanent forest domain and allow us to make recommendations for further research and management to best preserve its genetic diversity and adaptive potential.

Auteurs, date et publication :

Auteurs Julien Bonnier , Niklas Tysklind , Valérie Troispoux , Ivan Scotti , Stéphanie Barthe , Olivier Brunaux , Stéphane Guitet , Stéphane Traissac , Myriam Heuertz

Publication : Tree Genetics & Genomes

Date : 2025

Volume : 20

Issue : 1

Pages : 2

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

The biodiversity-productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, showing that continued biodiversity loss would result in an accelerating decline in forest productivity worldwide. The value of biodiversity in maintaining commercial forest productivity alone-US$166 billion to 490 billion per year according to our estimation-is more than twice what it would cost to implement effective global conservation. This highlights the need for a worldwide reassessment of biodiversity values, forest management strategies, and conservation priorities.

Auteurs, date et publication :

Auteurs Jingjing Liang , Thomas W Crowther , Nicolas Picard , Susan Wiser , Mo Zhou , Giorgio Alberti , Ernst-Detlef Schulze , A David McGuire , Fabio Bozzato , Hans Pretzsch , Sergio De-Miguel , Alain Paquette , Bruno Hérault , Michael Scherer-Lorenzen , Christopher B Barrett , Henry B Glick , Geerten M Hengeveld , Gert-Jan Nabuurs , Sebastian Pfautsch , Helder Viana

Publication : Science

Date : 2016

Volume : 354

Issue : 6309

Pages : 196

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Frédéric Mortier , Vivien Rossi , Gilles Guillot , Sylvie Gourlet-Fleury , Nicolas Picard , Olivier Gimene Z

Publication : Methods in Ecology and Evolution

Date : 2013

Volume : 4

Issue : 4

Pages : 316–326

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

The spatial distribution of biomass is key to optimize forest inventory designs to estimate forest aboveground biomass. Point process theory sets an appropriate mathematical framework to model the spatial distribution of trees, then to derive analytical expressions for the relationship between the variance of biomass in plots and the characteristics (size and shape) of plots, possibly accounting also for plot autocorrelation in biomass. Models derived from point process theory provided a better fit to data from twenty spatially homogeneous sites in tropical rain forests than the commonly used Taylor power model for biomass variance. The model CV = $ømega$+κ/|A| with CV the coefficient of variation of biomass, |A| the plot area, and $ømega$ and κ parameters to estimate, provided in particular a better fit than the power model when the range of autocorrelation in biomass was greater than the plot width. The twenty tropical forest sites greatly differed in the observed relationship between biomass variance and plot size, reflecting differences in the spatial pattern of biomass according to the fitted point process. Accordingly, optimized forest inventory designs also greatly differed between forest sites, with positive biomass autocorrelation favouring cluster sampling design with a distance between subplots in the order of the range of the biomass autocorrelation. In a spatially heterogeneous context consisting of different homogeneous forest strata, large-scale heterogeneity prevailed upon local biomass autocorrelation in determining the optimized plot size and shape. If uncontrolled through stratification, large-scale heterogeneity resulted in much smaller (approximately 0.1–0.2 ha) optimized plot sizes than the homogeneous case (approximately 1–2 ha).

Auteurs, date et publication :

Auteurs Nicolas Picard , Javier G.P. Gamarra , Luca Birigazzi , Anne Branthomme

Publication : Forest Ecology and Management

Date : 2018

Volume : 430

Pages : 10–20

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Embolism spreading in xylem is an important component of plant drought resistance. Since embolism resistance has been shown to be mechanistically linked to pit membrane characters in stem xylem, we speculate that similar mechanisms account for leaf xylem. We conducted transmission electron microscopy to investigate pit membrane characters in leaf xylem across 18 Neotropical tree species. We also conducted gold perfusion and polar lipid detection experiments on three species covering the full range of leaf embolism resistance. We then related these observations to previously published data on embolism resistance of leaf xylem. We also incorporated previously published data on stem embolism resistance and stem xylem pit membranes to investigate the link between vulnerability segmentation (i.e. difference in embolism resistance) and leaf–stem anatomical variation. Maximum pit membrane thickness (Tpm,max) and the pit membrane thickness-to-diameter ratio (Tpm,max/Dpm) were predictive of leaf embolism resistance, especially when vestured pits were taken into account. Variation in Tpm,max/Dpm was the only trait predictive of vulnerability segmentation between leaves and stems. Gold particles of 5- and 10-nm infiltrated pit membranes in three species, while the entry of 50-nm particles was blocked. Moreover, polar lipids were associated with inner conduit walls and pits. Our results suggest that mechanisms related to embolism spreading are determined by Tpm, pore constrictions (i.e. the narrowest bottlenecks along pore pathways), and lipid surfactants, which are largely similar between leaf and stem xylem and between temperate and tropical trees. However, our mechanistic understanding of embolism propagation and the functional relevance of Tpm,max/Dpm remains elusive.

Auteurs, date et publication :

Auteurs Sèbastien Levionnois , Lucian Kaack , Patrick Heuret , Nina Abel , Camille Ziegler , Sabrina Coste , Clèment Stahl , Steven Jansen

Publication : Plant Physiology

Date : 2022

Volume : 190

Issue : 1

Pages : 371–386

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Amazonia’s floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region’s floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon’s tree diversity and its function.

Auteurs, date et publication :

Auteurs John Ethan Householder , Florian Wittmann , Jochen Schöngart , Maria Teresa Fernandez Piedade , Wolfgang J. Junk , Edgardo Manuel Latrubesse , Adriano Costa Quaresma , Layon O. Demarchi , Guilherme de S. Lobo , Daniel P. P. de Aguiar , Rafael L. Assis , Aline Lopes , Pia Parolin , Iêda Leão do Amaral , Luiz de Souza Coelho , Francisca Dionízia de Almeida Matos , Diógenes de Andrade Lima Filho , Rafael P. Salomão , Carolina V. Castilho , Juan Ernesto Guevara-Andino

Publication : Nature Ecology & Evolution

Date : 2024

Volume : 8

Issue : 5

Pages : 901-911

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Both the Canadian Land Surface Scheme (CLASS) and the Soil, Vegetation, and Snow (SVS) land surface models employ a potentially problematic discretization of Richards equation for unsaturated vertical flow in the soil column. It is shown here that this discretization will always overestimate the vertical moisture gradient compared to a better-constructed first-order scheme, which under some circumstances could lead to erroneous moisture drawdown. The problem stems from an interpolation calculation on the irregularly spaced grids traditionally used by these models. While vanishing on uniform grids, this numerical error progressively worsens with increasing layer thickness differences. In this brief technical note a systematic method for developing first and higher order schemes on irregular, staggered grids is presented. To demonstrate the potential impact of the new first–order scheme, multi-year simulations of five FLUXNET sites are presented and discussed. A dramatic improvement in first layer soil moisture is found for two of the sites, which contributes to potentially significant differences in evapotranspiration. Higher order schemes are also possible but must be constructed carefully, in concert with a judicious choice of soil layer spacing in order to minimize discretization error. Given the extensive use of CLASS and SVS in Canadian environmental prediction systems, and the freedom with which users can specify soil layer thicknesses, it is recommended that modellers consider this issue carefully in their applications.

Auteurs, date et publication :

Auteurs Murray D. MacKay , Gesa Meyer , Joe R Melton

Publication : Atmosphere - Ocean

Date : 2025

Volume : 61

Issue : 1

Pages : 1–11

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Soil fauna is a key control of the decomposition rate of leaf litter, yet its interactions with litter quality and the soil environment remain elusive. We conducted a litter decomposition experiment across different topographic levels within the landscape replicated in two rainforest sites providing natural gradients in soil fertility to test the hypothesis that low nutrient availability in litter and soil increases the strength of fauna control over litter decomposition. We crossed these data with a large dataset of 44 variables characterizing the biotic and abiotic microenvironment of each sampling point and found that microbe-driven carbon (C) and nitrogen (N) losses from leaf litter were 10.1 and 17.9% lower, respectively, in the nutrient-poorest site, but this among-site difference was equalized when meso- and macrofauna had access to the litterbags. Further, on average, soil fauna enhanced the rate of litter decomposition by 22.6%, and this contribution consistently increased as nutrient availability in the microenvironment declined. Our results indicate that nutrient scarcity increases the importance of soil fauna on C and N cycling in tropical rainforests. Further, soil fauna is able to equalize differences in microbial decomposition potential, thus buffering to a remarkable extent nutrient shortages at an ecosystem level.

Auteurs, date et publication :

Auteurs Guille Peguero , Jordi Sardans , Dolores Asensio , Marcos Fernández-Martínez , Albert Gargallo-Garriga , Oriol Grau , Joan Llusià , Olga Margalef , Laura Márquez , Romà Ogaya , Ifigenia Urbina , Elodie A. Courtois , Clément Stahl , Leandro Van Langenhove , Lore T. Verryckt , Andreas Richter , Ivan A. Janssens , Josep Peñuelas

Publication : Proceedings of the Royal Society B: Biological Sciences

Date : 2019

Volume : 286

Issue : 1910

Pages : 20191300

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou