Projets tutorés

Impact of forest management on Araceae communities and influences of other environmental factors.

Flavio DIAS FERREIRA, Jules-Maurice MADKAUD, Pierre FREYRE under the supervision of Alex TOUCHARD

The tropical ants’ world is vast and remains largely unexplored especially in French Guiana where few myrmecological studies have been conducted. A total of 136 samples were collected from dead trees fallen on the ground, in five selected sites, according to the degree of disturbance and the variation of average annual rainfall of these sites. This present work aims to observe the ant communities present in the dead wood of French Guiana and to evaluate the impact of disturbances on the diversity of these communities. 55 different species have been found, mainly belonging to three subfamilies: Myrmicinae, Formicinae and Ponerinae. Comparison of diversity indexes between the sampled sites revealed variations that could be linked with the degree of disturbance of the rain forest. Despite the lack of sampling efforts and low sample coverage, our results show that ant diversity from dead logs is lower in secondary and disturbed rain forests parts than in other more preserved areas.

Surface area growth in relation to crown structure in Dicorynia guianensis: an architectural approach to quantifying tree reiteration.

Chloé BOURDEN, Anais-Pasiphaé GOREL, Katherine JOHNSON, under the supervision of Vivien ROSSI, Eric NICOLINI

Background and Aims. We aim to continue investigating the link between surface area growth rates and architectural changes, which occur during tree development, and are likely to affect tropical forest dynamics. The objectives of this study are to (1) propose a method of quantifying the crown structure of adult trees by examining their degree of reiteration, and (2) establish a link between the degree of an individual’s reiteration and its radial growth.
Methods. This study was conducted on a canopy emergent, Dicorynia guianensis (Caesalpinioideae), at the Paracou field station in French Guiana. Field descriptions included (1) reiterative stage of crown architecture, (2) tree height and diameter (3) surface trunk growth recorded over a 25-year survey period (4) environmental parameters. Statistical analyses with quantitative variables describing trees such as diameter or surface area growth related to crown stages were performed.
Key Results. Analyses showed that crown architecture could be quantified through a number of branches exhibiting a reiteration process. Moreover, the study showed a strong relationship between the duplicative stage of the trees and their respective diameter at breast height (dbh).

Using a soil water index for upscaling soil respiration on an area of tropical rainforest in French Guiana.

Camille DEZECACHE, Virgile SCHEMLA under the supervision of Lukas SIEBICKE

This study provides a first set of analyses in order to estimate soil respiration (Rsoil) on an area of neotropical rain-forest in Paracou field station, French Guiana, based on Rsoil and soil moisture (SM) data obtained during a field campaign in dry season and with automatic chambers measurements along the year. The Saga Wetness Index (SWI) calculated for more than 100’000 points on the whole area of interest was then used as a proxy for SM to allow Rsoil upscaling on this large area. We used an exponential regression to model the relationship between SWI and SM, and a polynomial regression for the relationship between SM and Rsoil. The mean Rsoil measurement from the field campaign was approximately 4.9 μmolCO2.m-2.s-1 and the average Rsoil given by the model for the whole area of interest was 0.93 tC.ha-1.y-1. These values are consistent with the literature, but the model developed in this study needs improvements in order to take into account calculation uncertainties and discern more precisely Rsoil temporal and spatial variability.

Morphometric and morphological analyses of leaves in two species of Araceae : Montrichardia linifera and Montrichardia arborescens among different French Guiana populations.

Emmanuelle MIROUZE, Adrien STAQUET, Remi VEZY, under the supervision of Marc GIBERNAU

In French Guiana, Araceae represents one of the most important monocots family. Montrichardia is one of its 117 genera and it is represented by two species, M. arborescens and M. linifera. Currently, the two species can be found meanly in diverse sites of the region. Recent studies on the species have failed to establish clear geographical patterns between the two species and among their populations. Here, the morphological variations of leaves were studied in the two species of Montrichardia using classical measurements of leaf outlines shape. In order to identify intra-populational variabilities and interspecific differences of their leaves, the Elliptic Fourier Analysis and multivariate statistical analyses were performed. The results obtained showed that the morphological variables were more discriminating at interspecific level. At the intra-populational level, there are two parameters to consider. Firstly, in M. arborescens, morphological variables had a more important part in the population discrimination than morphometric variables. Secondly, in M. linifera, the populations were better discriminated by morphometrics variables than for M. arborescens. Moreover, it was highlighted that even if differences could be observed between both species within each site, one population of one species from one site could be morphometrically and/or morphologically similar to another population of the other species in another site. This result suggests that the variation of the leaf studied traits was as important within site between the two species as among sites within a given species.

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