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Auteurs B. Gauzens , E. Thebault , G. Lacroix , S. Legendre

Publication : Journal of The Royal Society Interface

Date : 2015

Volume : 12

Issue : 106

Pages : 20141176-20141176

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#CNRS #ENS #PLANAQUA

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Abstract. The extent to which wood growth is limited by carbon (C) supply (i.e. source control) or by cambial activity (i.e. sink control) will strongly determine the responses of trees to global changes. Nevertheless, the physiological processes that are responsible for limiting forest growth are still a matter of debate. The aim of this study was to evaluate the key determinants of the annual C allocation to wood along large soil and climate regional gradients over France. The study was conducted for five tree species representative of the main European forest biomes (Fagus sylvatica, Quercus petraea, Quercus ilex, Quercus robur and Picea abies).

The drivers of stand biomass growth were assessed on both inter-site and inter-annual scales. Our data set comprised field measurements performed at 49 sites (931 site-years) that included biometric measurements and a variety of stand characteristics (e.g. soil water holding capacity, leaf area index). It was complemented with process-based simulations when possible explanatory variables could not be directly measured (e.g. annual and seasonal tree C balance, bioclimatic water stress indices). Specifically, the relative influences of tree C balance (source control), direct environmental control (water and temperature controls of sink activity) and allocation adjustments related to age, past climate conditions, competition intensity and soil nutrient availability on growth were quantified.

The inter-site variability in the stand C allocation to wood was predominantly driven by age-related decline. The direct effects of temperature and water stress on sink activity (i.e. effects independent from their effects on the C supply) exerted a strong influence on the annual stand wood growth in all of the species considered, including deciduous temperate species. The lagged effect of the past environmental conditions (e.g. the previous year's water stress and low C uptake) significantly affected the annual C allocation to wood. The C supply appeared to strongly limit growth only in temperate deciduous species.

We provide an evaluation of the spatio-temporal dynamics of the annual C allocation to wood in French forests. Our study supports the premise that the growth of European tree species is subject to complex control processes that include both source and sink limitations. The relative influences of the growth drivers strongly vary with time and across spatial ecological gradients. We suggest a straightforward modelling framework with which to implement these combined forest growth limitations into terrestrial biosphere models.

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Auteurs J. Guillemot , N. K. Martin-StPaul , E. Dufrêne , C. François , K. Soudani , J. M. Ourcival , N. Delpierre

Publication : Biogeosciences

Date : 2015

Volume : 12

Issue : 9

Pages : 2773-2790

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#CNRS #FORET Puechabon

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The fire ant Solenopsis saevissima is a major pest frequent in human-disturbed areas of its native range where it forms ‘supercolonies'. We determined that its natural habitat in French Guiana is likely the sporadically flooded riparian forest and aimed to evaluate this ant's impact on the abundance and diversity of other ants by comparing different habitats at two sites. We noted a significant decrease in ant species richness between the rainforest and human-disturbed habitats (but not between the former and the naturally disturbed riparian forest), and between extreme habitats and all others. The number of ant nests per surface unit (i.e., quadrats of equal surface area), a proxy of ant abundance, globally followed this pattern. S. saevissima was absent from pristine rainforest (as expected) and from extreme habitats, showing the limits of its adaptability, whereas some other native ants can develop in these habitats. Ant species richness was significantly lower in the presence of S. saevissima in the riparian forest, forest edges and meadows, illustrating that this ant species has a negative impact on the ant communities in addition to the impact of natural- and man-made disturbances. Only some ant species can develop in its presence, and certain of these can even thrive. Because it has been recorded in Africa, Guadeloupe and the Galápagos Islands, we concluded that, due to the increasing volume of global trade and forest destruction, S. saevissima could become a pantropical invasive species.

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Auteurs Alain Dejean , Régis Céréghino , Maurice Leponce , Vivien Rossi , Olivier Roux , Arthur Compin , Jacques H.C. Delabie , Bruno Corbara

Publication : Biological Conservation

Date : 2015

Volume : 187

Pages : 145–153

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#CIRAD #CNRS #FORET Nouragues #FORET Paracou

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Based on material collected from Rhinella cf. margaritifera (Laurenti) and Rhi. marina (Linnaeus) (Anura: Bufonidae) during a parasite survey of the herpetofauna of French Guiana, updated descriptions of Rhabdias androgyna Kloss, 1971 and R. fuelleborni Travassos, 1926 are presented. In addition to metrical data, which may overlap in closely related species, emphasis is placed on qualitative characters. Rhabdias androgyna is distinguished by the unique presence of an outer and inner cephalic cuticular inflation, a shoulder-like broadening of the body at the anterior end, a wide and shallow buccal capsule (average buccal ratio 0.36) with serrated lumen in apical view, a prominent anterior dilatation of the oesophagus, and the presence of an additional posterior dilatation anterior to the oesophageal bulb. Characters that may help to differentiate R. fuelleborni from closely related species parasitising the Rhi. marina species group are the presence of six relatively uniform lips, and the division of the buccal capsule into an anterior and posterior segment, with differently structured walls. Both the presence of R. androgyna and R. fuelleborni in French Guiana constitute new geographic records. A single specimen of Rhabdias sp. is described from Pristimantis chiastonotus (Lynch et Hoegmood) (Anura: Craugastoridae). This species differs from all its Neotropical congeners by the distinct globular swelling of its head, similar to that seen in only one Palaearctic and one Afrotropical Rhabdias species. A list of species of Rhabdias parasitising amphibians in the Netropical Realm is also provided.

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Auteurs Yuriy Kuzmin , Louis H. du Preez , Kerstin Junker

Publication : Folia Parasitologica

Date : 2015

Volume : 62

Issue : 1

Pages : 31-31

Catégorie(s)

#CNRS #FORET Nouragues

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In contrast to plant-animal interactions, the conceptual framework regarding the impact of secondary metabolites in mediating plant-plant interference is currently less well defined. Here, we address hypotheses about the role of chemically-mediated plant-plant interference (i.e., allelopathy) as a driver of Mediterranean forest dynamics. Growth and defense abilities of a pioneer (Pinus halepensis) and a late-successional (Quercus pubescens) Mediterranean forest species were evaluated under three different plant interference conditions: (i) allelopathy simulated by application of aqueous needle extracts of Pinus, (ii) resource competition created by the physical presence of a neighboring species (Pinus or Quercus), and (iii) a combination of both allelopathy and competition. After 24 months of experimentation in simulated field conditions, Quercus was more affected by plant interference treatments than was Pinus, and a hierarchical response to biotic interference (allelopathy < competition < allelopathy + competition) was observed in terms of relative impact on growth and plant defense. Both species modulated their respective metabolic profiles according to plant interference treatment and thus their inherent chemical defense status, resulting in a physiological trade-off between plant growth and production of defense metabolites. For Quercus, an increase in secondary metabolite production and a decrease in plant growth were observed in all treatments. In contrast, this trade-off in Pinus was only observed in competition and allelopathy + competition treatments. Although Pinus and Quercus expressed differential responses when subjected to a single interference condition, either allelopathy or competition, species responses were similar or positively correlated when strong interference conditions (allelopathy + competition) were imposed.

Auteurs Juan Sebastian Ulloa , Amandine Gasc , Phillipe Gaucher , Thierry Aubin , Maxime Réjou-Méchain , Jérôme Sueur

Publication : Ecological informatics

Date : 2025

Volume : 31

Pages : 91-99

Catégorie(s)

#CNRS #FORET Nouragues

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