Auteurs, date et publication :
Auteurs Marilyne Laurans , Olivier Martin , Eric Nicolini , Gregoire Vincent , Hans Cornelissen
Publication : Journal of Ecology
Date : 2012
Volume : 100
Issue : 6
Pages : 1440–1452
Catégorie(s)
#CIRAD #FORET ParacouRésumé
How tropical tree species respond to disturbance is a central issue of forest ecology, conservation and resource management. We define a hierarchical model to investigate how functional traits measured in control plots relate to the population change rate and to demographic rates for recruitment and mortality after disturbance by logging operations. Population change and demographic rates were quantified on a 12-year period after disturbance and related to seven functional traits measured in control plots. The model was calibrated using a Bayesian Network approach on 53 species surveyed in permanent forest plots (37.5 ha) at Paracou in French Guiana. The network analysis allowed us to highlight both direct and indirect relationships among predictive variables. Overall, 89% of interspecific variability in the population change rate after disturbance were explained by the two demographic rates, the recruitment rate being the most explicative variable. Three direct drivers explained 45% of the variability in recruitment rates, including leaf phosphorus concentration, with a positive effect, and seed size and wood density with negative effects. Mortality rates were explained by interspecific variability in maximum diameter only (25%). Wood density, leaf nitrogen concentration, maximum diameter and seed size were not explained by variables in the analysis and thus appear as independent drivers of post-disturbance demography. Relationships between functional traits and demographic parameters were consistent with results found in undisturbed forests. Functional traits measured in control conditions can thus help predict the fate of tropical tree species after disturbance. Indirect relationships also suggest how different processes interact to mediate species demographic response.
Auteurs, date et publication :
Auteurs Olivier Flores , Bruno Hérault , Matthieu Delcamp , Éric Garnier , Sylvie Gourlet-Fleury , Francesco de Bello
Publication : Plos One
Date : 2014
Volume : 9
Issue : 9
Pages : e105022
Catégorie(s)
#CIRAD #FORET ParacouRésumé
We consider competing functional groups of tree species and develop a model of network response dynamics in order to measure the impacts of perturbations on the population distribution and diversity. The analysis of the equilibrium states relies on the connection between mean field game dynamics and replicator dynamics. We simulate our theoretical results from the data inventoried in French Guiana. Our results show that different types of disturbances modify the competitive interactions by affecting the evolutions of group densities. At the high regimes of disturbance, the canopy shade-intolerant species supplant the canopy shade-tolerant species. Tropical forest managers can thus take advantage of the competitive interactions between the functional groups to stimulate the abundance of marketable timber species. We also validate the hypothesis of maximum diversity at the intermediate disturbance levels.
Auteurs, date et publication :
Auteurs Arnaud Z. Dragicevic
Publication : Journal of Bioeconomics
Date : 2016
Volume : 18
Issue : 1
Pages : 1–15
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The relationship between biodiversity and biogeochemical processes gained much interest in light of the rapidly decreasing biodiversity worldwide. In this article, we discuss the current status, challenges and prospects of functional concepts to plant litter diversity and microbial decomposer diversity. We also evaluate whether these concepts permit a better understanding of how biodiversity is linked to litter decomposition as a key ecosystem process influencing carbon and nutrient cycles. Based on a literature survey, we show that plant litter and microbial diversity matters for decomposition, but that considering numbers of taxonomic units appears overall as little relevant and less useful than functional diversity. However, despite easily available functional litter traits and the well-established theoretical framework for functional litter diversity, the impact of functional litter diversity on decomposition is not yet well enough explored. Defining functional diversity of microorganisms remains one of the biggest challenges for functional approaches to microbial diversity. Recent developments in microarray and metagenomics technology offer promising possibilities in the assessment of the functional structure of microbial communities. This might allow significant progress in measuring functional microbial diversity and ultimately in our ability to predict consequences of biodiversity loss in the decomposer system for biogeochemical processes. Dans un contexte mondial de perte de diversité biologique, les relations entre biodiversité et cycles biogéochimiques ont suscité un intérêt croissant auprès de la communauté scientifique. Dans cet article, nous discutons l'état de l'art, les challenges et les perspectives relatifs aux concepts de diversité fonctionnelle des litières végétales et de leurs décomposeurs microbiens. Nous évaluons également si ces concepts permettent de mieux comprendre comment la biodiversité explique la décomposition en tant que processus clef du cycle du carbone et des nutriments dans les écosystèmes terrestres. Une étude bibliographique sur le sujet montre que la diversité des litières végétales et des décomposeurs microbiens est importante pour la décomposition, mais que la diversité basée sur le nombre de taxons présents est peu pertinente et souvent moins informative que leur diversité basée sur des critères fonctionnels. Malgré des traits fonctionnels facilement accessibles et un cadre théorique bien établi en ce qui concerne la diversité des litières végétales, l'impact de la diversité fonctionnelle des litières sur la décomposition n'a été que peu exploré. Une approche fonctionnelle de la diversité microbienne reste, quant à elle, un challenge important pour prendre en compte cette diversité. Dans cette optique, les récents développements méthodologiques (puces à ADN, métagénomique) offrent des perspectives prometteuses pour caractériser la diversité microbienne fonctionnelle et, au final, mieux appréhender les conséquences de pertes de biodiversité sur les processus biogéochimiques qui contrôlent la décomposition.
Auteurs, date et publication :
Auteurs Stephan Hättenschwiler , Nathalie Fromin , Sandra Barantal
Publication : Comptes Rendus Biologies
Date : 2011
Volume : 334
Issue : 5-6
Pages : 393–402
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Forest aboveground biomass (AGB), which plays an important role in the study of global carbon cycle, is one of the most important indicators in forest resource monitoring. Thus, how to estimate and map regional forest AGB quickly and accurately attracts more interests of researchers. Tomographic SAR (TomoSAR) is an advanced SAR technique developed in recent years, which has a wide range application in forest AGB estimation. In this paper, we proposed a multi-feature-based modeling method to estimate forest AGB by fitting backscattered power of TomoSAR vertical profile. The procedure of the proposed method includes four parts: (1) Processing TomoSAR data to obtain the backscattered power of vertical profile. (2) Fitting the backscattered power of the vertical profile. (3) Analyzing the fitted backscattered power distribution characteristic of the vertical profile. (4) Extracting the TomoSAR vertical profile features according to the forest AGB measurement factors based on the dendrometry theory. In this paper, we proposed two new features like the forest average height weighted by backscattered power (BPFAH) and the total length of the backscattered power curve (LBPC) as supplement features to estimate forest AGB by TomoSAR technique. We also used the traditional TomoSAR features including backscattered power at specific height layer of vertical power profile (BPV) and forest average height (FAH) for AGB estimation. After the feature selection, the selected features and the ground field data of the forest AGB were used for regression and modeling. Then the forest AGB was estimated and the accuracy was validated. The results showed that the accuracy of proposed method is 90.73%, and RMSE is 42.45 t/ha. Finally, we discussed the performance of our proposed method compared with traditional methods.
Auteurs, date et publication :
Auteurs Xiangxing Wan , Zengyuan Li , Erxue Chen , Lei Zhao , Wangfei Zhang , Kunpeng Xu
Publication : Remote Sensing
Date : 2021
Volume : 13
Issue : 2
Pages : 186
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The European Space Agency (ESA) is currently implementing the BIOMASS mission as 7th Earth Explorer satellite. BIOMASS will provide for the first time global forest aboveground biomass estimates based on P-band synthetic aperture radar (SAR) imagery. This paper addresses an often overlooked element of the data processing chain required to ensure reliable and accurate forest biomass estimates: accurate identification of forest areas ahead of the inversion of radar data into forest biomass estimates. The use of the P-band data from BIOMASS itself for the classification into forest and non-forest land cover types is assessed in this paper. For airborne data in tropical, hemi-boreal and boreal forests we demonstrate that classification accuracies from 90 up to 97% can be achieved using radar backscatter and phase information. However, spaceborne data will have a lower resolution and higher noise level compared to airborne data and a higher probability of mixed pixels containing multiple land cover types. Therefore, airborne data was reduced to 50m, 100m and 200m resolution. The analysis revealed that about 50–60% of the area within the resolution level must be covered by forest to classify a pixel with higher probability as forest compared to non-forest. This results in forest omission and commission leading to similar forest area estimation over all resolutions. However, the forest omission resulted in a biased underestimated biomass, which was not equaled by the forest commission. The results underline the necessity of a highly accurate pre-classification of SAR data for an accurate unbiased aboveground biomass estimation.
Auteurs, date et publication :
Auteurs Michael Schlund , Klaus Scipal , Malcolm W.J. Davidson
Publication : International Journal of Applied Earth Observation and Geoinformation
Date : 2017
Volume : 56
Pages : 65–76
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The objective of this work is to provide an experimental assessment of the accuracy to retrieve forest height in tropical areas by using P-band multibaseline SAR data. Two different approaches are considered for retrieving forest height: i) parametric inversion based on the assumption of RVoG model, and ii) direct assessment by thresholding the estimated tomographic intensities. Both approaches are tested based on P-band data from the ESA campaigns: TropiSAR, flown in French Guiana in 2009. Validations are carried out by performing pixel-by-pixel comparisons against the canopy height model (CHM) derived from LiDAR measurements. Results show that at a resolution of 25 m×25 m, both of the two approaches are able to retrieve forest height to within an accuracy of about 3.5 m or better over the interval of forest height between 20 to 40 m.
Auteurs, date et publication :
Auteurs X. Yang , M. Liao , L. Zhang , S. Tebaldini
Date : 2019
Pages : 1-5
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Cronbach's alpha is an estimate of the reliability of a test score if the items are essentially tau-equivalent. Several authors have derived results that provide al-ternative interpretations of alpha. These interpretations are also valid if essential tau-equivalency does not hold. For example, alpha is the mean of all split-half reliabilities if the test is split into two halves that are equal in size. This note presents several con-nections between Cronbach's alpha and the Spearman-Brown formula. The results provide new interpretations of Cronbach's alpha, the stepped down alpha, and stan-dardized alpha, that are also valid in the case that essential tau-equivalency or parallel equivalency do not hold. The main result is that the stepped down alpha is a weighted average of the alphas of all subtests of a specific size, where the weights are the de-nominators of the subtest alphas. Thus, the stepped down alpha can be interpreted as an average subtest alpha. Furthermore, we may calculate the stepped down alpha without using the Spearman-Brown formula.
Auteurs, date et publication :
Auteurs
Publication : Journal of Classification
Date : 2023
Volume : 32
Issue : March
Pages : 46–62
Catégorie(s)
#FORET ParacouRésumé
To recover verticality after disturbance, angiosperm trees produce ‘tension wood' allowing them to bend actively. The driving force of the tension has been shown to take place in the G-layer, a specific unlignified layer of the cell wall observed in most temperate species. However, in tropical rain forests, the G-layer is often absent and the mechanism generating the forces to reorient trees remains unclear. A study was carried out on tilted seedlings, saplings and adult Simarouba amara Aubl. trees—a species known to not produce a G-layer. Microscopic observations were done on sections of normal and tension wood after staining or observed under UV light to assess the presence/absence of lignin. We showed that S. amara produces a cell-wall layer with all of the characteristics typical of G-layers, but that this G-layer can be observed only as a temporary stage of the cell-wall development because it is masked by a late lignification. Being thin and lignified, tension wood fibres cannot be distinguished from normal wood fibres in the mature wood of adult trees. These observations indicate that the mechanism generating the high tensile stress in tension wood is likely to be the same as that in species with a typical G-layer and also in species where the G-layer cannot be observed in mature cells.
Auteurs, date et publication :
Auteurs Jean-Romain Roussel , Bruno Clair , Chung-Jui Tsai
Publication : Tree Physiology
Date : 2015
Volume : 35
Issue : 12
Pages : 1366–1377
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Lucy Rowland , Timothy Charles Hill , Clement Stahl , Lukas Siebicke , Benoit Burban , Joana Zaragoza-Castells , Stephane Ponton , Damien Bonal , Patrick Meir , Mathew Williams
Publication : Global Change Biology
Date : 2014
Volume : 20
Issue : 3
Pages : 979–991