Résumé

Tropical forest mortality is controlled by both biotic and abiotic processes, but how these processes interact to determine forest structure is not well understood. Using long‐term demography data from permanent forest plots at the Paracou Tropical Forest Research Station in French Guiana, we analysed the relative influence of competition and climate on tree mortality. We found that self‐thinning is evident at the stand level, and is associated with clumped mortality at smaller scales (textless2 m) and regular spacing of living trees at intermediate (2.5–7.5 m) scales. A competition index (CI) based on spatial clustering of dead trees was used to build predictive mortality models, which also accounted for climate interactions. The model that most closely fitted observations included both the CI and climatic variables, with climate‐only and competition‐only models less informative than the full model. There was strong evidence for U‐shaped size‐specific mortality, with highest mortality for small and very large trees, as well as sensitivity of trees to drought, especially when temperatures were high, and when soils were water saturated. The effect of the CI was more complex than expected a priori: a higher CI was associated with lower mortality odds, which we hypothesize is caused by gap‐phase dynamics, but there was also evidence for competition‐induced mortality at very high CI values. The strong signature of competition as a control over mortality at the stand and individual scales confirms its important role in determining tropical forest structure. The complexity of the competition‐mortality relationship and its interaction with climate indicates that a thorough consideration of the scale of analysis is needed when inferring the role of competition in tropical forests, but demonstrates that climate‐only mortality models can be significantly improved by including competition effects, even when ignoring species‐specific effects. Synthesis. Empirical models such as the one developed here can help constrain and improve process‐based vegetation models, serving both as a benchmark and as a means to disentangle mortality processes. Tropical vegetation dynamic models would benefit greatly from explicitly considering the role of competition in stand development and self‐thinning while modelling demography, as well as its interaction with climate.

Auteurs, date et publication :

Auteurs Michiel Pillet , Emilie Joetzjer , Camille Belmin , Jérôme Chave , Philippe Ciais , Aurélie Dourdain , Margaret Evans , Bruno Hérault , Sebastiaan Luyssaert , Benjamin Poulter , Shurong Zhou

Publication : Journal of Ecology

Date : 2018

Volume : 106

Issue : 3

Pages : 1165–1179

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

1. The potential for competition is highest among species in close association. Despite net benefits for both parties, mutualisms can involve costs, including food competition. This might be true for the two neotropical ants Camponotus femoratus and Crematogaster levior, which share the same nest in a presumably mutualistic association (parabiosis). 2. While each nest involves one Crematogaster and one Camponotus partner, both taxa were recently found to comprise two cryptic species that show no partner preferences and seem ecologically similar. Since these cryptic species often occur in close sympatry, they might need to partition their niches to avoid competitive exclusion. 3. Here, we investigated first, is there interference competition between parabiotic Camponotus and Crematogaster, and do they prefer different food sources under competition? And second, is there trophic niche partitioning between the cryptic species of either genus? 4. Using cafeteria experiments, neutral lipid fatty acid and stable isotope analyses, we found evidence for interference competition, but also trophic niche partitioning between Camponotus and Crematogaster. Both preferred protein- and carbohydrate-rich baits, but at protein-rich baits Ca. femoratus displaced Cr. levior over time, suggesting a potential discovery-dominance trade-off between parabiotic partners. Only limited evidence was found for trophic differentiation between the cryptic species of each genus. 5. Although we cannot exclude differentiation in other niche dimensions, we argue that neutral dynamics might mediate the coexistence of cryptic species. This model system is highly suitable for further studies of the maintenance of species diversity and the role of mutualisms in promoting species coexistence.

Auteurs, date et publication :

Auteurs Philipp P. Sprenger , Christian Müsse , Juliane Hartke , Barbara Feldmeyer , Thomas Schmitt , Gerhard Gebauer , Florian Menzel

Publication : Ecological Entomology

Date : 2025

Volume : n/a

Issue : n/a

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Tropical soils are a major contributor to the balance of greenhouse gas (GHG) fluxes in the atmosphere. Models of tropical GHG fluxes predict that both the frequency of drought events and changes in atmospheric deposition of nitrogen (N) will significantly affect dynamics of soil carbon dioxide (CO2) and methane (CH4) production and consumption. In this study, we examined the combined effect of a reduction in precipitation and an increase in nutrient availability on soil CO2 and CH4 fluxes in a primary French Guiana tropical forest. Drought conditions were simulated by intercepting precipitation falling through the forest canopy with tarpaulin roofs. Nutrient availability was manipulated through application of granular N and / or phosphorus (P) fertilizer to the soil. Soil water content (SWC) below the roofs decreased rapidly and stayed at continuously low values until roof removal, which as a consequence roughly doubled the duration of the dry season. After roof removal, SWC slowly increased but remained lower than in the control soils even after 2.5 months of wet-season precipitation. We showed that drought-imposed reduction in SWC decreased the CO2 emissions (i.e CO2 efflux), but strongly increased the CH4 emissions. N, P and N × P (i.e. NP) additions all significantly increased CO2 emission but had no effect on CH4 fluxes. In treatments where both fertilization and drought were applied, the positive effect of N, P and NP fertilization on CO2 efflux was reduced. After roof removal, soil CO2 efflux was more resilient in the control plots than in the fertilized plots while there was only a modest effect of roof removal on soil CH4 fluxes. Our results suggest that a combined increase in drought and nutrient availability in soil can locally increase the emissions of both CO2 and CH4 from tropical soils, for a long term.

Auteurs, date et publication :

Auteurs Laëtitia Bréchet , Elodie A. Courtois , Thomas Saint-Germain , Ivan A. Janssens , Dolores Asensio , Irene Ramirez-Rojas , Jennifer L. Soong , Leandro Van Langenhove , Erik Verbruggen , Clément Stahl

Publication : Frontiers in Environmental Science

Date : 2025

Volume : 7

Catégorie(s)

#CIRAD #FORET Paracou

Résumé

Volatile terpenes are among the most diverse class of defensive compounds in plants, and they are implicated in both direct and indirect defense against herbivores. In terpenes, both the quantity and the diversity of compounds appear to increase the efficiency of defense as a diverse blend of compounds provides a more efficient protection against a broader range of herbivores and limits the chances that an enemy evolves resistance. Theory predicts that plant defensive compounds should be allocated differentially among tissues according to the value of the tissue, its cost of construction and the herbivore pressure on it. We collected volatile terpenes from bark and leaves of 178 individual tree belonging to 55 angiosperm species in French Guiana and compare the kind, amount, and diversity of compounds in these tissues. We hypothesized that in woody plants, the outermost part of the trunk should hold a more diverse blend of volatile terpenes. Additionally, as herbivore communities associated with the leaves is different to the one associated with the bark, we also hypothesized that terpene blends should be distinct in the bark vs. the leaves of a given species. We found that the mixture of volatile terpenes released by bark is different and more diverse than that released by leaves, both in monoterpenes and sesquiterpenes. This supports our hypothesis and further suggests that the emission of terpenes by the bark should be more important for trunk defense than previously thought.

Auteurs, date et publication :

Auteurs Elodie A. Courtois , Christopher Baraloto , C.E. Timothy Paine , Pascal Petronelli , Pierre-Alain Blandinieres , Didier Stien , Emeline Höuel , Jean-Marie Bessière , Jérôme Chave

Publication : Phytochemistry

Date : 2012

Volume : 82

Pages : 81–88

Catégorie(s)

#CIRAD #CNRS #FORET Nouragues #FORET Paracou

Résumé

Tropical rainforests harbor a particularly high plant diversity. We hypothesize that potential causes underlying this high diversity should be linked to distinct overall functionality (defense and growth allocation, anti-stress mechanisms, reproduction) among the different sympatric taxa. In this study we tested the hypothesis of the existence of a metabolomic niche related to a species-specific differential use and allocation of metabolites. We tested this hypothesis by comparing leaf metabolomic profiles of 54 species in two rainforests of French Guiana. Species identity explained most of the variation in the metabolome, with a species-specific metabolomic profile across dry and wet seasons. In addition to this “homeostatic” species-specific metabolomic profile significantly linked to phylogenetic distances, also part of the variance (flexibility) of the metabolomic profile was explained by season within a single species. Our results support the hypothesis of the high diversity in tropical forest being related to a species-specific metabolomic niche and highlight ecometabolomics as a tool to identify this species functional diversity related and consistent with the ecological niche theory.

Auteurs, date et publication :

Auteurs Albert Gargallo-Garriga , Jordi Sardans , Victor Granda , Joan Llusià , Guille Peguero , Dolores Asensio , Romà Ogaya , Ifigenia Urbina , Leandro Van Langenhove , Lore T. Verryckt , Jérome Chave , Elodie A. Courtois , Clément Stahl , Oriol Grau , Karel Klem , Otmar Urban , Ivan A. Janssens , Josep Peñuelas

Publication : Scientific Reports

Date : 2020

Volume : 10

Issue : 1

Pages : 6937

Catégorie(s)

#ANR-Citation #CIRAD #FORET Paracou

Résumé

The chemical investigations of Dicorynia guianensis heartwood led to the isolation of four new indole alkaloids for the first time in this plant. Compound (1) identified as spiroindolone 2′,3′,4′,9′-tetrahydrospiro [indoline-3,1′pyrido[3,4-b]-indol]-2-one, and compound (3) described as nitrone 1-methyl-4,9-dihydro-3H-pyrido [3,4-b] indole 2-oxide and were isolated for the first time as natural products. ABTS antioxidant activity guided their isolation.

Auteurs, date et publication :

Auteurs Jean-Baptiste Say Anouhe , Augustin Amissa Adima , Florence Bobelé Niamké , Didier Stien , Brise Kassi Amian , Pierre-Alain Blandinières , David Virieux , Jean-Luc Pirat , Seraphin Kati-Coulibaly , Nadine Amusant

Publication : Phytochemistry Letters

Date : 2015

Volume : 12

Pages : 158–163

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Sanna Olsson , Pedro Seoane-Zonjic , Rocío Bautista , M. Gonzalo Claros , Santiago C. González-Martínez , Ivan Scotti , Caroline Scotti-Saintagne , Olivier J. Hardy , Myriam Heuertz

Publication : Molecular Ecology Resources

Date : 2017

Volume : 17

Issue : 4

Pages : 614–630

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs J.-P. Laclau , J.-L. de Moraes Gonçalves , R. Moreira e Moreira , J.-P. Bouillet , Y. Nouvellon

Publication : Série Técnica IPEF

Date : 2025

Volume : 18

Issue : 39

Pages : 19625

Catégorie(s)

#CIRAD #FORET Itatinga #INRAE

Auteurs, date et publication :

Auteurs Barbara R. V. Meyer-Sand , Celine Blanc-Jolivet , Malte Mader , Kathelyn Paredes-Villanueva , Niklas Tysklind , Alexandre M. Sebbenn , Erwan Guichoux , Bernd Degen

Publication : Conservation Genetics Resources

Date : 2017

Pages : 1–3

Catégorie(s)

#CIRAD #FORET Paracou

Auteurs, date et publication :

Auteurs Clément Stahl , Bruno Hérault , Vivien Rossi , Benoit Burban , Claude Bréchet , Damien Bonal

Publication : Oecologia

Date : 2013

Volume : 173

Issue : 4

Pages : 1191–1201

Catégorie(s)

#CIRAD #FORET Paracou