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Guitet, S., Pélissier, R., Brunaux, O., Jaouen, G., & Sabatier, D. (2015). Geomorphological landscape features explain floristic patterns in French Guiana rainforest. Biodiversity and Conservation, 24(5), 1215–1237.
Abstract: Geomorphic landscape features have been suggested as indicators of forest diversity. However, their explanatory power has not yet been explicitly tested at a regional scale in tropical rainforest. We used forest inventories conducted according to a stratified sampling design (3,132 plots in 111 transects at 33 sites) and holistic multi-scale geomorphological mapping derived from a Shuttle Radar Topography Mission digital elevation model to describe and explain spatial patterns in floristic composition across French Guiana (80,000 km2). We measured and identified 123,906 trees with DBH ≥20 cm and used constrained and unconstrained ordinations to analyze variations in the abundance of 221 taxa and 51 families. Variance partitioning and variograms were used to detect spatial patterns in species composition, compare the explanatory power of spatial and environmental factors, and select the variables that best explain forest composition. Strong floristic patterns corresponded to a major latitudinal gradient and significant sub-regional floristic structure. Geomorphological landscapes shaped by historic climate fluctuations and major geological events successfully captured these patterns and explained the variation in abundance of 80 taxa, corresponding to 65 % of the inventoried trees. Our findings suggest that long-term forest dynamics are under substantial “geomorphographic control”. A geomorphological perspective on landscapes that incorporates current and past environmental filters and historical biogeographical processes could thus be used more systematically in tropical regions for regional planning and forest conservation. © 2014, Springer Science+Business Media Dordrecht.
Keywords: Geodiversity; Geomorphology; Landscapes; Species distribution; Tree community
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Lambs, L., Bompy, F., Imbert, D., Corenblit, D., & Dulormne, M. (2015). Seawater and freshwater circulations through coastal forested wetlands on a Caribbean Island. Water, 7(8), 4108–4128.
Abstract: Structure and composition of coastal forested wetlands are mainly controlled by local topography and soil salinity. Hydrology plays a major role in relation with tides, seaward, and freshwater inputs, landward. We report here the results of a two-year study undertaken in a coastal plain of the Guadeloupe archipelago (FWI). As elsewhere in the Caribbean islands, the study area is characterized by a micro-tidal regime and a highly seasonal climate. This work aimed at understanding groundwater dynamics and origin (seawater/freshwater) both at ecosystems and stand levels. These hydrological processes were assessed through 18O/16O and 2H/1H isotopic analyses, and from monthly monitoring of water level and soil salinity at five study sites located in mangrove (3) and swamp forest (2). Our results highlight the importance of freshwater budget imbalance during low rainfall periods. Sustained and/or delayed dry seasons cause soil salinity to rise at the mangrove/swamp forest ecotone. As current models on climate change project decreasing rainfall amounts over the inner Caribbean region, one may expect for this area an inland progression of the mangrove forest to the expense of the nearby swamp forest. © 2015 by the authors.
Keywords: 18O/2H stable isotope; Hydrology; Mangrove; Salinity; Swamp forest; Water level
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Rivalland, C., Madhkour, S., Salvin, P., & Robert, F. (2015). Electrochemical and microbial monitoring of multi-generational electroactive biofilms formed from mangrove sediment. Bioelectrochemistry, 106, 125–132.
Abstract: Electroactive biofilms were formed from French Guiana mangrove sediments for the analysis of bacterial communities' composition. The electrochemical monitoring of three biofilm generations revealed that the bacterial selection occurring at the anode, supposedly leading microbial electrochemical systems (MESs) to be more efficient, was not the only parameter to be taken into account so as to get the best electrical performance (maximum current density). Indeed, first biofilm generations produced a stable current density reaching about 18A/m2 while second and third generations produced current densities of about 10A/m2. MES bacterial consortia were characterized thanks to molecular biology techniques: DGGE and MiSeq® sequencing (Illumina®). High-throughput sequencing data statistical analysis confirmed preliminary DGGE data analysis, showing strong similarities between electroactive biofilms of second and third generations, but also revealing both selection and stabilization of the biofilms. © 2015 Elsevier B.V.
Keywords: Dissimilarity; High-throughput sequencing; Mes; Microbial diversity; Syntrophism
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Dejean, A., Groc, S., Herault, B., Rodriguez-Pérez, H., Touchard, A., Céréghino, R., et al. (2015). Bat aggregation mediates the functional structure of ant assemblages. Comptes Rendus – Biologies, 338(10), 688–695.
Abstract: In the Guianese rainforest, we examined the impact of the presence of guano in and around a bat roosting site (a cave). We used ant communities as an indicator to evaluate this impact because they occupy a central place in the functioning of tropical rainforest ecosystems and they play different roles in the food web as they can be herbivores, generalists, scavengers or predators. The ant species richness around the cave did not differ from a control sample situated 500m away. Yet, the comparison of functional groups resulted in significantly greater numbers of detritivorous fungus-growing and predatory ant colonies around the cave compared to the control, the contrary being true for nectar and honeydew feeders. The role of bats, through their guano, was shown using stable isotope analyses as we noted significantly greater δ15N values for the ant species captured in and around the cave compared to controls. © 2015 Académie des sciences.
Keywords: Ant functional groups; Bat roosts; Biogeochemical hotspots; Bioindicators; Stable isotopes
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Rutishauser, E., Herault, B., Baraloto, C., Blanc, L., Descroix, L., Sotta, E. D., et al. (2015). Rapid tree carbon stock recovery in managed Amazonian forests. Current Biology, 25(18), R787–R788.
Abstract: Summary While around 20% of the Amazonian forest has been cleared for pastures and agriculture, one fourth of the remaining forest is dedicated to wood production [1]. Most of these production forests have been or will be selectively harvested for commercial timber, but recent studies show that even soon after logging, harvested stands retain much of their tree-biomass carbon and biodiversity [2,3]. Comparing species richness of various animal taxa among logged and unlogged forests across the tropics, Burivalova et al.[4] found that despite some variability among taxa, biodiversity loss was generally explained by logging intensity (the number of trees extracted). Here, we use a network of 79 permanent sample plots (376 ha total) located at 10 sites across the Amazon Basin [5] to assess the main drivers of time-to-recovery of post-logging tree carbon (Table S1). Recovery time is of direct relevance to policies governing management practices (i.e., allowable volumes cut and cutting cycle lengths), and indirectly to forest-based climate change mitigation interventions. © 2015 Elsevier Ltd.
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Talaga, S., Dezerald, O., Carteron, A., Petitclerc, F., Leroy, C., Céréghino, R., et al. (2015). Tank bromeliads as natural microcosms: A facultative association with ants influences the aquatic invertebrate community structure. Comptes Rendus – Biologies, 338(10), 696–700.
Abstract: Many tank bromeliads have facultative relationships with ants as is the case in French Guiana between Aechmea aquilega (Salib.) Griseb. and the trap-jaw ant, Odontomachus haematodus Linnaeus. Using a redundancy analysis, we determined that the presence of O. haematodus colonies is accompanied by a greater quantity of fine particulate organic matter in the water likely due to their wastes. This increase in nutrient availability is significantly correlated with an increase in the abundance of some detritivorous taxa, suggesting a positive bottom-up influence on the aquatic macroinvertebrate communities living in the A. aquilega wells. On the other hand, the abundance of top predators is negatively affected by a lower number of available wells due to ant constructions for nesting, releasing a top-down pressure that could also favor lower trophic levels. © 2015 Académie des sciences.
Keywords: Aechmea; Ant-bromeliad associations; Aquatic communities; Odontomachus; Phytotelm
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Nirma, C., Eparvier, V., & Stien, D. (2015). Reactivation of antibiosis in the entomogenous fungus Chrysoporthe sp. SNB-CN74. Journal of Antibiotics, 68(9), 586–590.
Abstract: Chrysoporthe sp. SNB-CN74 was isolated from a Nasutitermes corniger nest, and its ethyl acetate extract was found to exhibit very strong antibacterial activity. Two antibacterial metabolites were isolated, (-)-R-skyrin (2) and (+)-rugulosin A (3). Eventually, the fungus lost its antibiotic potential when subcultured, and the use of yeast extract induced the re-expression of these two antibiotics. Yeast extract possibly activated a cryptic pathway by mimicking the presence of an ecological competitor. © 2015 Japan Antibiotics Research Association All rights reserved.
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Maréchaux, I., Bartlett, M. K., Sack, L., Baraloto, C., Engel, J., Joetzjer, E., et al. (2015). Drought tolerance as predicted by leaf water potential at turgor loss point varies strongly across species within an Amazonian forest. Functional Ecology, 29(10), 1268–1277.
Abstract: Amazonian droughts are predicted to become increasingly frequent and intense, and the vulnerability of Amazonian trees has become increasingly documented. However, little is known about the physiological mechanisms and the diversity of drought tolerance of tropical trees due to the lack of quantitative measurements. Leaf water potential at wilting or turgor loss point (π<inf>tlp</inf>) is a determinant of the tolerance of leaves to drought stress and contributes to plant-level physiological drought tolerance. Recently, it has been demonstrated that leaf osmotic water potential at full hydration (π<inf>o</inf>) is tightly correlated with π<inf>tlp</inf>. Estimating π<inf>tlp</inf> from osmometer measurements of π<inf>o</inf> is much faster than the standard pressure-volume curve approach of π<inf>tlp</inf> determination. We used this technique to estimate π<inf>tlp</inf> for 165 trees of 71 species, at three sites within forests in French Guiana. Our data set represents a significant increase in available data for this trait for tropical tree species. Tropical trees showed a wider range of drought tolerance than previously found in the literature, π<inf>tlp</inf> ranging from -1·4 to -3·2 MPa. This range likely corresponds in part to adaptation and acclimation to occasionally extreme droughts during the dry season. Leaf-level drought tolerance varied across species, in agreement with the available published observations of species variation in drought-induced mortality. On average, species with a more negative π<inf>tlp</inf> (i.e. with greater leaf-level drought tolerance) occurred less frequently across the region than drought-sensitive species. Across individuals, π<inf>tlp</inf> correlated positively but weakly with leaf toughness (R2 = 0·22, P = 0·04) and leaf thickness (R2 = 0·03, P = 0·03). No correlation was detected with other functional traits (leaf mass per area, leaf area, nitrogen or carbon concentrations, carbon isotope ratio, sapwood density or bark thickness). The variability in π<inf>tlp</inf> among species indicates a potential for highly diverse species responses to drought within given forest communities. Given the weak correlations between π<inf>tlp</inf> and traditionally measured plant functional traits, vegetation models seeking to predict forest response to drought should integrate improved quantification of comparative drought tolerance among tree species. © 2015 British Ecological Society.
Keywords: Climate change; French Guiana; Functional traits; Plant-water relations; Tropical trees; Wilting
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Paine, C. E. T., Baraloto, C., & Díaz, S. (2015). Optimal strategies for sampling functional traits in species-rich forests. Functional Ecology, 29(10), 1325–1331.
Abstract: Functional traits provide insight into a variety of ecological questions, yet the optimal sampling method to estimate the community-level distribution of plant functional trait values remains a subject of debate, especially in species-rich forests. We present a simulation analysis of the trait distribution of a set of nine completely sampled permanent plots in the lowland rain forests of French Guiana. Increased sampling intensity consistently improved accuracy in estimating community-weighted means and variances of functional trait values, whereas there was substantial variation among functional traits and minor differences among sampling strategies. Thus, investment in intensified sampling yields a greater improvement in the accuracy of estimation than does an equivalent investment in sampling design complication. Notably, 'taxon-free' strategies frequently had greater accuracy than did abundance-based strategies, which had the additional cost of requiring botanical surveys. We conclude that there is no substitute for extensive field sampling to accurately characterize the distribution of functional trait values in species-rich forests. © 2015 British Ecological Society.
Keywords: French Guiana; Functional traits; Plant traits; Sampling design; Specific leaf area; Tropical forest; Wood density
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Aubry-Kientz, M., Rossi, V., Wagner, F., & Herault, B. (2015). Identifying climatic drivers of tropical forest dynamics. Biogeosciences, 12(19), 5583–5596.
Abstract: In the context of climate change, identifying and then predicting the impacts of climatic drivers on tropical forest dynamics is becoming a matter of urgency. To look at these climate impacts, we used a coupled model of tropical tree growth and mortality, calibrated with forest dynamic data from the 20-year study site of Paracou, French Guiana, in order to introduce and test a set of climatic variables. Three major climatic drivers were identified through the variable selection procedure: drought, water saturation and temperature. Drought decreased annual growth and mortality rates, high precipitation increased mortality rates and high temperature decreased growth. Interactions between key functional traits, stature and climatic variables were investigated, showing best resistance to drought for trees with high wood density and for trees with small current diameters. Our results highlighted strong long-term impacts of climate variables on tropical forest dynamics, suggesting potential deep impacts of climate changes during the next century. © Author(s) 2015.
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