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Groc, S., Delabie, J. H. C., Fernandez, F., Petitclerc, F., Corbara, B., Leponce, M., et al. (2017). Litter-dwelling ants as bioindicators to gauge the sustainability of small arboreal monocultures embedded in the Amazonian rainforest. Ecological Indicators, 82, 43–49.
Abstract: One of the greatest threats to biodiversity and the sustainable functioning of ecosystems is the clearing of forests for agriculture. Because litter-dwelling ants are very good bioindicators of man-made disturbance, we used them to compare monospecific plantations of acacia trees, cocoa trees, rubber trees and pine trees with the surrounding Neotropical rainforest (in contrast to previous studies on forest fragments embedded in industrial monocultures). Although the global level of species turnover was weak, species richness decreased along a gradient from the forest (including a treefall gap) to the tree plantations among which the highest number of species was noted for the cocoa trees, which are known to be a good compromise between agriculture and conservation. Species composition was significantly different between natural habitats and the plantations that, in turn, were different from each other. Compared to the forest, alterations in the ant communities were (1) highest for the acacia and rubber trees, (2) intermediate for the cocoa trees, and, (3) surprisingly, far lower for the pine trees, likely due to very abundant litter. Functional traits only separated the rubber tree plantation from the other habitats due to the higher presence of exotic and leaf-cutting ants. This study shows that small monospecific stands are likely sustainable when embedded in the rainforest and that environmentally-friendly strategies can be planned accordingly. © 2017 Elsevier Ltd
Keywords: Ant diversity; Community alteration; Forest species; Functional traits; Human disturbance; Tree monocultures
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Ghislain, B., & Clair, B. (2017). Diversity in the organisation and lignification of tension wood fibre walls – A review. IAWA Journal, 38(2), 245–265.
Abstract: Tension wood, a tissue developed by angiosperm trees to actively recover their verticality, has long been defined by the presence of an unlignified cellulosic inner layer in the cell wall of fibres, called the G-layer. Although it was known that some species have no G-layer, the definition was appropriate since it enabled easy detection of tension wood zones using various staining techniques for either cellulose or lignin. For several years now, irrespective of its anatomical structure, tension wood has been defined by its high mechanical internal tensile stress. This definition enables screening of the diversity of cell walls in tension wood fibres. Recent results obtained in tropical species with tension wood with a delay in the lignification of the G-layer opened our eyes to the effective presence of large amounts of lignin in the G-layer of some species. This led us to review older literature mentioning the presence of lignin deposits in the G-layer and give them credit. Advances in the knowledge of tension wood fibres allow us to reconsider some previous classifications of the diversity in the organisation of the fibre walls of the tension wood. © 2017 International Association of Wood Anatomists.
Keywords: diversity; fibres; G-layer; lignification; multilayered tension wood fibre walls; S1 + S2 + S3 + G; Tension wood
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Ploton, P., Barbier, N., Couteron, P., Antin, C. M., Ayyappan, N., Balachandran, N., et al. (2017). Toward a general tropical forest biomass prediction model from very high resolution optical satellite images. Remote Sensing of Environment, 200, 140–153.
Abstract: Very high spatial resolution (VHSR) optical satellite imagery has shown good potential to provide non-saturating proxies of tropical forest aboveground biomass (AGB) from the analysis of canopy texture, for instance through the Fourier Transform Textural Ordination method. Empirical case studies however showed that the relationship between Fourier texture features and forest AGB varies across forest types and regions of the world, limiting model transferability. A better understanding of the biophysical mechanisms on which canopy texture – forest AGB relation relies is a prerequisite to move toward broad scale applications. Here we simulated VHSR optical canopy scenes in identical sun-sensor geometry for 279 1-ha tropical forest inventory plots distributed across the tropics. Our aim was to assess the respective merits and complementarity of two types of texture analysis techniques (i.e. Fourier and lacunarity) on a set of forests with contrasted structure and geographical origin, and develop a general texture-based approach for tropical forest AGB mapping. Across forests, Fourier texture captured a gradient of stands mean crown size reflecting well the progressive changes in stand structure throughout forest aggradation phase (e.g. Pearson's r = − 0.42 with basal area) while lacunarity texture captured a gradient of canopy openness (, i.e. Pearson's r = − 0.57 with stand gap fraction). Both types of texture indices were highly complementary for predicting forest AGB at the global level (so-called FL-model). The residual error of the FL-model was structured across sites and could be partially captured with a bioclimatic proxy, further improving the performance of the global model (so-called FLE-model) and reducing site-level biases. The FLE model was tested on a set of real Pleiades images covering a mosaic of high-biomass forests in the Congo basin (mean AGB over 49 field plots: 359 ± 98 Mg ha− 1), leading to a significant relationship (R2 = 0.47 on validation data) with reasonable error levels (< 25% rRMSE). The increasing availability of VHSR optical sensors (such as from constellations of small satellite platforms) raises the possibility of routine repeated imaging of the world's tropical forests and suggests that texture-based analyses could become an essential tool in international efforts to monitor carbon emissions from deforestation and forest degradations (REDD +). © 2017 Elsevier Inc.
Keywords: Canopy structure; Forest carbon; Fourier transform; Lacunarity; Passive optical imagery; Redd; Texture; Tropical forests
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Gruhn, G., Dumez, S., Moreau, P. - A., Roy, M., Morreale, O., Schimann, H., et al. (2017). The genus Resinicium in French Guiana and the West Indies: a morphological and molecular survey, revealing Resinicium grandisporum sp. nov. Cryptogamie, Mycologie, 38(4), 1–15.
Abstract: A revision of Resinicium collections (Basidiomycota, Hymenochaetales) from French Guiana and French West Indies is provided, and a new species, Resinicium grandisporum sp. nov., supported by morphological as well as phylogenetic analyses based on ITS DNA sequences, is described and illustrated. An updated key of the genus Resinicium is also provided, which includes species previously described from outside of the studied area.
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Mayer, V. E., Lauth, J., & Orivel, J. (2017). Convergent structure and function of mycelial galleries in two unrelated Neotropical plant-ants. Insectes Sociaux, 64(3), 365–371.
Abstract: The construction process and use of galleries by Azteca brevis (Myrmicinae: Dolichoderinae) inhabiting Tetrathylacium macrophyllum (Salicaceae) were compared with Allomerus decemarticulatus (Myrmicinae: Solenopsidini) galleries on Hirtella physophora (Chrysobalanaceae). Though the two ant species are phylogenetically distant, the gallery structure seems to be surprisingly similar and structurally convergent: both are pierced with numerous holes and both ant species use Chaetothyrialean fungi to strengthen the gallery walls. Al. decemarticulatus is known to use the galleries for prey capture and whether this is also the case for Az. brevis was tested in field experiments. We placed Atta workers as potential prey/threat on the galleries and recorded the behaviour of both ant species. We found considerable behavioural differences between them: Al. decemarticulatus was quicker and more efficient at capture than was Az. brevis. While most Atta workers were captured after the first 5 min by Al. decemarticulatus, significantly fewer were captured by Az. brevis even after 20 min. Moreover, the captured Atta were sometimes simply discarded and not taken to the nest by Az. brevis. As a consequence, the major function of the galleries built by Az. brevis may, therefore, be defense against intruders in contrast to Al. decemarticulatus which uses them mainly for prey capture. This may be due to a higher need for protein in Al. decemarticulatus compared to coccid-raising Az. brevis.
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Epelboin, L., Bourhy, P., Le Turnier, P., Schaub, R., Mosnier, E., Berlioz-Arthaud, A., et al. (2017). La leptospirose en Guyane française et sur le bouclier des Guyanes. État des connaissances en 2016. Bulletin de la Société de pathologie exotique, 110(3), 165–179.
Abstract: La leptospirose est une zoonose cosmopolite causée par les bactéries du genre Leptospira. Si sa répartition est vaste sur le globe, le climat chaud et humide de la zone intertropicale est particulièrement propice à son expansion. Dans la plupart des départements et territoires français d’outremer, la leptospirose est considérée comme un problème de santé publique. En Guyane, département français situé au nord-est de la forêt amazonienne, elle est considérée comme rare. L’objectif de cette revue est de faire l’état des lieux des connaissances sur la leptospirose humaine et animale en Guyane française et dans les pays environnants. Une recherche exhaustive a été conduite, à travers la littérature médicale indexée et informelle en français, anglais, espagnol et portugais. Ainsi, respectivement dix et quatre publications ont pu être identifiées sur la leptospirose humaine et animale en Guyane, publiées entre 1940 et 1995, sous formes de cas cliniques ou de séries de cas. Les publications concernant cette maladie dans les autres pays du plateau des Guyanes, Venezuela oriental, Guyana, Suriname, et État brésilien de l’Amapá, étaient également rares voire inexistantes. En revanche, les données récentes du centre national de la leptospirose français ont montré une augmentation récente et brutale du nombre de cas dans le département, probablement en partie due à la mise en place d’outils diagnostiques tels que la sérologie IgM Elisa. Il est en fait probable que la leptospirose soit une maladie négligée dans la région, du fait de l’absence d’outils diagnostiques rapidement disponibles, de la méconnaissance des cliniciens de cette pathologie et de l’existence de nombreux autres pathogènes à présentation clinique similaire (paludisme, arboviroses, fièvre Q, toxoplasmose amazonienne). La mise en place d’études de plus grande ampleur sur la leptospirose animale et humaine est nécessaire et urgente pour connaître le véritable poids de cette maladie dans notre région.
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Morel, H., Nicolini, E., Bossu, J., Blanc, L., & Beauchene, J. (2017). Qualité et usages du bois de cinq espèces forestières adaptées à la plantation à vocation de bois d’oeuvre et testées en Guyane française. Bois & Forêts des Tropiques, 334, 61–74.
Abstract: Des essais de plantations forestières ont été menés en Guyane française depuis le début des années 1960 sur plus de 138 espèces (70 espèces natives et 68 espèces exotiques). Une étude récente sur la productivité de ces espèces en plantation (projet ForesTreeCulture, 2013-2015) a mis en avant le fort potentieldeproductiondetroisespècesnatives ( Simarouba amara Aubl., Vochysia tomentosa (G. Mey.) DC., Bagassa guianensis ( Aubl.)) et d’une espèce d’Afrique de l’Ouest ( Tarrietia utilis Sprague) avec des volumes de bois produits supérieurs à 20 m3/ha/an. Cependant, les propriétés du bois de ces espèces commerciales ne sont connues qu’au travers d’arbres issus de forêt naturelle. Nous présentons les propriétés du bois de ces espèces en conditions de plantation – densité, retrait, élasticité, angle du fil, durabilité – et discutons de leurs potentiels et de leurs usages respectifs futurs. Une autre espèce, Cordia alliodora ((Ruiz et Pavon) Oken), a également été retenue bien qu’elle n’ait pas encore été plantée en Guyane française. Cette espèce, native de Guyane, est bien connue en Amérique latine pour son bois et son fort potentiel de croissance en milieu anthropisé.
Keywords: propriétés technologiques; qualité du bois; plantation; Guyane française
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Gourlet-Fleury, S., Gazull, L., Bigombe Logo, P., Billand, A., Bolaluembe, P. - C., Boyemba, F., et al. (2017). Are logging concessions a threat to the peatlands in DRC? Bois et Forets des Tropiques, (334), 3–6.
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Dézerald, O., Leroy, C., Corbara, B., Dejean, A., Talaga, S., & Céréghino, R. (2018). Tank bromeliads sustain high secondary production in neotropical forests. Aquatic Sciences, 80(14).
Abstract: In neotropical landscapes, a substantial fraction of the still waters available is found within tank bromeliads, plants which hold a few milliliters to several litres of rainwater within their leaf axils. The bromeliad ecosystem is integrated into the functioning of rainforest environments, but no study has ever estimated the secondary production, nor the biomass turnover rates of bromeliad macroinvertebrates in relation to other functional traits. We estimated secondary production at invertebrate population to metacommunity level in bromeliads of French Guiana. Coleoptera, Diptera and Crustacea with traits that confer resistance to drought had lower biomass turnover, longer generation times, and slower individual growth than species without particular resistance traits, suggesting convergent life history strategies in phylogenetically distant species. Detritivores and predators accounted for 87% and 13% of the overall annual production, respectively, but had similar production to biomass ratios. An average bromeliad sustained a production of 23.93 g dry mass m−2 year−1, a value which exceeds the medians of 5.0–14.8 g DM m−2 year−1 for lakes and rivers worldwide. Extrapolations to the total water volumes held by bromeliads at our field site yielded secondary production estimates of 226.8 ± 32.5 g DM ha−1 year−1. We conclude that the ecological role of tank bromeliads in neotropical rainforests may be as important as that of other freshwater ecosystems. © 2018, Springer International Publishing AG, part of Springer Nature.
Keywords: Biomass turnover; Epiphytes; Food webs; Functional traits; Invertebrates; Rainforests
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Aguilos, M., Hérault, B., Burban, B., Wagner, F., & Bonal, D. (2018). What drives long-term variations in carbon flux and balance in a tropical rainforest in French Guiana? Agricultural and Forest Meteorology, 253–254, 114–123.
Abstract: A thorough understanding of how tropical forests respond to climate is important to improve ecosystem process models and to reduce uncertainties in current and future global carbon balance calculations. The Amazon rainforest, a major contributor to the global carbon cycle, is subject to strong intra- and interannual variations in climate conditions. Understanding their effect on carbon fluxes between the ecosystem and the atmosphere and on the resulting carbon balance is still incomplete. We examined the long-term (over a 12-year period; 2004–2015) variations in gross primary productivity (GPP), ecosystem respiration (RE) and net ecosystem exchange (NEE) in a tropical rainforest in French Guiana and identified key climatic drivers influencing the changes. The study period was characterized by strong differences in climatic conditions among years, particularly differences in the intensity of the dry and wet seasons, as well as differences in annual carbon fluxes and balance. Annual average GPP varied from 3384.9?g?C?m-2?yr?1 (95% CI [3320.7, 3445.9]) to 4061.2?g?C?m-2?yr?1 (95% CI [3980.1, 4145.0]). RE varied even more than GPP, with a difference of 933.1?C?m-2?yr?1 between the minimum (3020.6?g?C?m-2?yr?1; 95% CI [2889.4, 3051.3]) and maximum (3953.7?g?C?m-2?yr?1; 95% CI [3887.6, 4019.6]) values. Although NEE showed large interannual variability (nine-fold), from ?65.6?g?C?m-2?yr?1 (95% CI [?4.4, ?126.0]) to ?590.5?g?C?m-2 yr?1 (95% CI [?532.3, ?651.6]), the forest remained a carbon sink over the 12-year period. A combination of global radiation (Rg), relative extractable water (REW) and soil temperature (Ts) explained 51% of the daily variations for GPP, 30% for RE and 39% for NEE. Global radiation was always the best predictor of these variations, but soil water content and temperature did also influence carbon fluxes and balance. Seasonally, Rg was the major controlling factor for GPP, RE and NEE during the wet season. During the dry season, variations in carbon fluxes and balance were poorly explained by climate factors. Yet, REW was the key driver of variations in NEE during the dry season. This study highlights that, over the long-term, carbon fluxes and balance in such tropical rainforest ecosystems are largely controlled by both radiation and water limitation. Even though variations in Rg have a greater impact on these fluxes, water limitation during seasonal droughts is enough to reduce ecosystem productivity, respiration and carbon uptake. The reduced precipitation expected in tropical rainforest areas under future climatic conditions will therefore strongly influence carbon fluxes and carbon uptake. This study also highlights the importance for land surface or dynamic global vegetation models to consider the main drivers of carbon fluxes and balance separately for dry and wet seasons.
Keywords: Tropical rainforest; Nee; Gpp; Ecosystem respiration; Radiation; Drought
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