Biomass prediction in tropical forests : the canopy grain approach

18 pagesThe challenging task of biomass prediction in dense and heterogeneous tropical forest requires a multi-parameter and multi-scale characterization of forest canopies. Completely different forest structures may indeed present similar above ground biomass (AGB) values. This is probably one of the reasons explaining why tropical AGB still resists accurate mapping through remote sensing techniques. There is a clear need to combine optical and radar remote sensing to benefit from their complementary responses to forest characteristics. Radar and Lidar signals are rightly considered to provide adequate measurements of forest structure because of their capability of penetrating and interacting with all the vegetation strata. However, signal saturation at the lowest radar frequencies is observed at the midlevel of biomass range in tropical forests (Mougin et al. 1999; Imhoff, 1995). Polarimetric Interferometric (PolInsar) data could improve the inversion algorithm by injecting forest interferometric height into the inversion of P-band HV polarization signal. Within this framework, the TROPISAR mission, supported by the Centre National d'Etudes Spatiales (CNES) for the preparation of the European Space Agency (ESA) BIOMASS program is illustrative of both the importance of interdisciplinary research associating forest ecologists and physicists and the importance of combined measurements of forest properties. Lidar data is a useful technique to characterize the vertical profile of the vegetation cover (e.g. Zhao et al. 2009) which in combination with radar (Englhart et al. 2011) or optical (e.g. Baccini et al. 2008; Asner et al. 2011) and field plot data may allow vegetation carbon stocks to be mapped over large areas of tropical forest at different resolution scales ranging from 1 hectare to 1 km². However, small-footprint Lidar data are not yet accessible over sufficient extents and with sufficient revisiting time because its operational use for tropical studies remains expensive. At the opposite, very-high (VHR) resolution imagery, i.e. approximately 1-m resolution, provided by recent satellite like Geoeye, Ikonos, Orbview or Quickbird as well as the forthcoming Pleiades becomes widely available at affordable costs, or even for free in certain regions of the world through Google Earth®. Compared to coarser resolution imagery with pixel size greater than 4 meters, VHR imagery greatly improves thematic information on forest canopies. Indeed, the contrast between sunlit and shadowed trees crowns as visible on such images (Fig. 1) is potentially informative on the structure of the forest canopy while new promising methods now exist for analyzing these fine scale satellite observations (e.g. Bruniquel-Pinel & Gastellu-Etchegorry, 1998; Malhi & Roman-Cuesta, 2008; Rich et al. 2010). Besides, we believe that there is also a great potential in similarly using historical series of digitized aerial photographs that proved to be useful in the past for mapping large extents of unexplored forest (Le Touzey, 1968; Richards, 1996) for quantifying AGB changes through time. This book chapter presents the advancement of a research program undertaken by our team for estimating high biomass mangrove and terra firme forests of Amazonia using canopy grain from VHR images (Couteron et al. 2005; Proisy et al. 2007; Barbier et al., 2010; 2011). We present in a first section, the canopy grain notion and the fundamentals of the Fourier-based Textural Ordination (FOTO) method we developed. We then introduce a dual experimental-theoretical approach implemented to understand how canopy structure modifies the reflectance signal and produces a given texture. We discuss, for example, the influence of varying sun-view acquisition conditions on canopy grain characteristics. A second section assesses the potential and limits of the canopy grain approach to predict forest stand structure and more specifically above ground biomass. Perspectives for a better understanding of canopy grain-AGB relationships conclude this work

Morphogenetic trends in the morphological, optical and biochemical features of phyllodes in Acacia mangium Willd (Mimosaceae)

A-09-04International audienceEndogenous variations in the annual growth of trees suggest that similar trends would occur in phyllodes. In comparison to leaves, the characteristics of phyllodes are less well known, hence this study examines the effects of architectural position and age of tree on the phyllodes of Acacia mangium. Phyllodes were investigated on 1-, 2-, and 3-year-old trees from three axis positions within the crown. We focused on the morphological, optical and biochemical traits of the phyllodes. The increase in phyllode area and lamina thickness is more pronounced in the older trees. Leaf mass area (LMA), stomatal density, nitrogen and chlorophyll content increase with tree age. The values of these characteristics decrease from the main stem to the lower branches for the older trees. Phyllode light absorptance increased with tree age whereas reflectance was higher for the upper position compared to the lower position within the crown. Carotenoid content and chlorophyll a/b ratio were higher for the younger phyllodes of younger trees. Increasing tree size induced modifications in the phyllode characteristics which are influenced by both morphogenetic and light gradients within the crown. This study demonstrated pronounced changes in terms of morphological and functional indicators of photosynthetic capacity in relation to phyllode position within the crown and to tree age. These morphogenetic effects on the phyllode characteristics should be taken into account in studies on phenotypic plasticity

Flower-scent mimicry masks a deadly trap in the carnivorous plant Nepenthes rafflesiana.

International audience1. Nepenthes rafflesiana is a carnivorous vine from Borneo characterized by an ontogenetic pitcher dimorphism with aerial (upper) and ground (lower) pitchers of different morphologies. Previous studies have shown that fragrant upper pitchers of climbing parts of the plant are more effective in trapping flying insects than non-fragrant lower pitchers, which are essentially restricted to an ant diet. We tested the hypotheses that odours are effective cues for prey attraction in this carnivorous plant and that upper pitchers biochemically mimic flowers in their olfactory cues. 2. The visitor diversity and the scent composition of each pitcher type were determined for different sites and periods during field studies in Borneo. Olfactometer bioassays were conducted using fruit flies and ants as models for flying flower-visitors and non-flying visitors, respectively. 3. Fifty-four volatile compounds were identified and the analysis of their relative quantities in the blends showed significant differences between pitcher types. The blends of lower pitchers contained some aliphatics and terpenoids but were poor in benzenoids. Upper pitchers differed from lower ones in that they attracted a greater quantity and diversity of insects, including a guild of flower-visitors absent from the visitor spectrum of lower pitchers. Upper pitchers also emitted a greater quantity of odours and a larger spectrum of volatiles, including some terpenoids and benzenoids that often characterize the sweet scents classically found in flower blends. Choice bioassays showed that, in absence of any visual cue, the scents of the nectariferous pitcher rim (peristome) were particularly attractive to ants and flies, and those of upper pitchers were more attractive to flies than those of lower pitchers. 4. Synthesis. This study demonstrates the use of scent by Nepenthes carnivorous plants to mediate prey attraction. The climbing part of the plant produces pitcher-modified leaves that mimic flower olfactory cues and suggest an evolutionary convergent strategy with that of generalist pollination systems

Pith: A new criterion for monitoring the architecture in Mediterranean pines

Plant architecture can be used to study plant development retrospectively thanks to time-dependent morphological markers, particularly those corresponding to the winter break in temperate regions. The Aleppo Pine and the Turkish Pine are polycyclic species, thus they usually develop several consecutive growth units per year, making it sometimes difficult to date them. In this study, we show that keeping track of the pith diameter profile, to date each shoot, is an efficient method. The pith diameter is larger on the first growth unit than on the last growth unit of the year. Moreover, a pairwise comparison showed that the pith diameter undergoes a decrease along the annual shoot from the first growth unit to the last. As pith diameter decreases upwards the annual shoot, it can be used for dating. Pith diameter progresses from 1 year to another too: there is an increase in the early years of life, corresponding to the tree's establishment phase. Lastly, we found a positive relationship between the basal pith diameter of an annual shoot and its length. The variability around this relationship could reflect environmental conditions, especially climate conditions. (Résumé d'auteur

Advantages and limitations of online communities of patients for research on health products

International audienc

Advantages and limitations of online communities of patients for research on health products

International audienc

ANISEED 2017: extending the integrated ascidian database to the exploration and evolutionary comparison of genome-scale datasets

International audienceANISEED (www.aniseed.cnrs.fr) is the main model organism database for tunicates, the sister-group of vertebrates. This release gives access to annotated genomes, gene expression patterns, and anatomical descriptions for nine ascidian species. It provides increased integration with external molecular and taxonomy databases, better support for epigenomics datasets, in particular RNA-seq, ChIP-seq and SELEX-seq, and features novel interactive interfaces for existing and novel datatypes. In particular, the cross-species navigation and comparison is enhanced through a novel taxonomy section describing each represented species and through the implementation of interactive phylogenetic gene trees for 60% of tunicate genes. The gene expression section displays the results of RNA-seq experiments for the three major model species of solitary ascidians. Gene expression is controlled by the binding of transcription factors to cis-regulatory sequences. A high-resolution description of the DNA-binding specificity for 131 Ciona robusta (formerly C. intestinalis type A) transcription factors by SELEX-seq is provided and used to map candidate binding sites across the Ciona robusta and Phallusia mammillata genomes. Finally, use of a WashU Epigenome browser enhances genome navigation, while a Genomicus server was set up to explore microsynteny relationships within tunicates and with vertebrates, Amphioxus, echinoderms and hemichordates