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Laybros, A., Aubry-Kientz, M., Féret, J. - B., Bedeau, C., Brunaux, O., Derroire, G., et al. (2020). Quantitative airborne inventories in dense tropical forest using imaging spectroscopy. Remote Sens., 12(10), 1577.
Abstract: Tropical forests have exceptional floristic diversity, but their characterization remains incomplete, in part due to the resource intensity of in-situ assessments. Remote sensing technologies can provide valuable, cost-effective, large-scale insights. This study investigates the combined use of airborne LiDAR and imaging spectroscopy to map tree species at landscape scale in French Guiana. Binary classifiers were developed for each of 20 species using linear discriminant analysis (LDA), regularized discriminant analysis (RDA) and logistic regression (LR). Complementing visible and near infrared (VNIR) spectral bands with short wave infrared (SWIR) bands improved the mean average classification accuracy of the target species from 56.1% to 79.6%. Increasing the number of non-focal species decreased the success rate of target species identification. Classification performance was not significantly affected by impurity rates (confusion between assigned classes) in the non-focal class (up to 5% of bias), provided that an adequate criterion was used for adjusting threshold probability assignment. A limited number of crowns (30 crowns) in each species class was sufficient to retrieve correct labels effectively. Overall canopy area of target species was strongly correlated to their basal area over 118 ha at 1.5 ha resolution, indicating that operational application of the method is a realistic prospect (R2 = 0.75 for six major commercial tree species). © 2020 by the authors.
Keywords: Hyperspectral; LiDAR; Species diversity; Tropical forest; Cost effectiveness; Discriminant analysis; Infrared devices; Infrared radiation; Logistic regression; Remote sensing; Tropics; Classification accuracy; Classification performance; Linear discriminant analysis; Operational applications; Regularized discriminant analysis; Remote sensing technology; Short wave infrared bands; Visible and near infrared; Forestry
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Yguel, B., Piponiot, C., Mirabel, A., Dourdain, A., Hérault, B., Gourlet-Fleury, S., et al. (2019). Beyond species richness and biomass: Impact of selective logging and silvicultural treatments on the functional composition of a neotropical forest. Forest Ecology and Management, 433, 528–534.
Abstract: Tropical forests harbor the greatest terrestrial biodiversity and provide various ecosystem services. The increase of human activities on these forests, among which logging, makes the conservation of biodiversity and associated services strongly dependent on the sustainability of these activities. However the indicators commonly used to assess the impact of forest exploitation, namely species richness and biomass, provide a limited understanding of their sustainability. Here, we assessed the sustainability of common forest exploitation in the Guiana Shield studying the recovery of two ecosystem services i.e. carbon storage and wood stock, and an ecosystem function i.e. seed dispersal by animals. Specifically, we compared total and commercial biomass, as well as functional composition in seed size of animal-dispersed species in replicated forest plots before and 27 years after exploitation. Species richness is also studied to allow comparison. While species richness was not affected by forest exploitation, total and commercial biomass as well as seed size of animal-dispersed species decreased 27 years after exploitation, similarly to forests affected by hunting. These results show that ecosystem services and function likely did not recover even at the lowest intensity of forest exploitation studied, questioning the sustainability of the most common rotation-cycle duration applied in the tropics.
Keywords: Selective logging; Humid tropical forest; Functional composition; Seed dispersal; Carbon storage; Commercial stock; Anthropogenic pressure; Sustainability
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Poorter, L., Craven, D., Jakovac, C. C., van der Sande, M. T., Amissah, L., Bongers, F., et al. (2021). Multidimensional tropical forest recovery. Science, 374(6573), 1370–1376.
Abstract: Tropical forests disappear rapidly because of deforestation, yet they have the potential to regrow naturally on abandoned lands. We analyze how 12 forest attributes recover during secondary succession and how their recovery is interrelated using 77 sites across the tropics. Tropical forests are highly resilient to low-intensity land use; after 20 years, forest attributes attain 78% (33 to 100%) of their old-growth values. Recovery to 90% of old-growth values is fastest for soil (<1 decade) and plant functioning (<2.5 decades), intermediate for structure and species diversity (2.5 to 6 decades), and slowest for biomass and species composition (>12 decades). Network analysis shows three independent clusters of attribute recovery, related to structure, species diversity, and species composition. Secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration, climate change mitigation, and biodiversity conservation.
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Barantal, S., Schimann, H., Fromin, N., & Hattenschwiler, S. (2012). Nutrient and Carbon Limitation on Decomposition in an Amazonian Moist Forest. Ecosystems, 15(7), 1039–1052.
Abstract: Tropical forests determine global biogeochemical cycles to a large extent, but control factors for key ecosystem processes such as decomposition remain poorly understood. With a full-factorial C (cellulose), N (urea), and P (phosphate) fertilization experiment, we tested the relative importance of C and nutrient limitation on litter decomposition in a mature lowland moist forest of French Guiana. Despite the previously demonstrated litter C quality control over decomposition and the very low soil P content (0. 1 mg g -1 of soil) at our study site, fertilization with C or P alone did not increase the decomposition of a wide range of litter types (N:P ratios between 20 and 80). Nitrogen fertilization alone also had no effect on decomposition. However, the combined fertilization with N and P resulted in up to 33. 5% more initial litter mass lost, with an increasing effect with wider litter N:P ratios. Soil fauna strongly stimulated litter mass loss and enhanced nutrient fertilization effects. Moreover, nutrient effects on decomposition increased with additional C fertilization in the presence of fauna. Our results suggest that increased N availability is required for a positive P effect on decomposition in the studied P-poor tropical forest. Further stimulation of decomposition by C amendment through priming indicates energy limitation of decomposers that is co-determined by nutrient availability. The demonstrated intricate control of the key resources C, N, and P on decomposition calls for an intensified research effort on multiple resource limitation on key processes in tropical forests and how they change under multiple human impacts. © 2012 Springer Science+Business Media, LLC.
Keywords: energy limitation; labile carbon; litter quality; nitrogen; phosphorus; priming effect; soil fauna; tropical forest
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Baraloto, C., Rabaud, S., Molto, Q., Blanc, L., Fortunel, C., Herault, B., et al. (2011). Disentangling stand and environmental correlates of aboveground biomass in Amazonian forests. Glob. Change Biol., 17(8), 2677–2688.
Abstract: Tropical forests contain an important proportion of the carbon stored in terrestrial vegetation, but estimated aboveground biomass (AGB) in tropical forests varies two-fold, with little consensus on the relative importance of climate, soil and forest structure in explaining spatial patterns. Here, we present analyses from a plot network designed to examine differences among contrasting forest habitats (terra firme, seasonally flooded, and white-sand forests) that span the gradient of climate and soil conditions of the Amazon basin. We installed 0.5-ha plots in 74 sites representing the three lowland forest habitats in both Loreto, Peru and French Guiana, and we integrated data describing climate, soil physical and chemical characteristics and stand variables, including local measures of wood specific gravity (WSG). We use a hierarchical model to separate the contributions of stand variables from climate and soil variables in explaining spatial variation in AGB. AGB differed among both habitats and regions, varying from 78 Mg ha(-1) in white-sand forest in Peru to 605 Mg ha(-1) in terra firme clay forest of French Guiana. Stand variables including tree size and basal area, and to a lesser extent WSG, were strong predictors of spatial variation in AGB. In contrast, soil and climate variables explained little overall variation in AGB, though they did co-vary to a limited extent with stand parameters that explained AGB. Our results suggest that positive feedbacks in forest structure and turnover control AGB in Amazonian forests, with richer soils (Peruvian terra firme and all seasonally flooded habitats) supporting smaller trees with lower wood density and moderate soils (French Guianan terra firme) supporting many larger trees with high wood density. The weak direct relationships we observed between soil and climate variables and AGB suggest that the most appropriate approaches to landscape scale modeling of AGB in the Amazon would be based on remote sensing methods to map stand structure.
Keywords: carbon stocks; climate; flooded forest; forest structure; French Guiana; Peru; REDD; soil properties; tropical rainforest; white-sand forest; wood specific gravity
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Cecilia Blundo, Julieta Carilla, Ricardo Grau, Agustina Malizia, Lucio Malizia, Oriana Osinaga-Acosta, et al. (2021). Taking the pulse of Earth’s tropical forests using networks of highly distributed plots. Biological Conservation, 260.
Abstract: Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and monitor them have been largely disconnected. Networking is essential to discover the answers to questions that transcend borders and the horizons of funding agencies. Here we show how a global community is responding to the challenges of tropical ecosystem research with diverse teams measuring forests tree-by-tree in thousands of long-term plots. We review the major scientific discoveries of this work and show how this process is changing tropical forest science. Our core approach involves linking long-term grassroots initiatives with standardized protocols and data management to generate robust scaled-up results. By connecting tropical researchers and elevating their status, our Social Research Network model recognises the key role of the data originator in scientific discovery. Conceived in 1999 with RAINFOR (South America), our permanent plot networks have been adapted to Africa (AfriTRON) and Southeast Asia (T-FORCES) and widely emulated worldwide. Now these multiple initiatives are integrated via ForestPlots.net cyber-infrastructure, linking colleagues from 54 countries across 24 plot networks. Collectively these are transforming understanding of tropical forests and their biospheric role. Together we have discovered how, where and why forest carbon and biodiversity are responding to climate change, and how they feedback on it. This long-term pan-tropical collaboration has revealed a large long-term carbon sink and its trends, as well as making clear which drivers are most important, which forest processes are affected, where they are changing, what the lags are, and the likely future responses of tropical forests as the climate continues to change. By leveraging a remarkably old technology, plot networks are sparking a very modern revolution in tropical forest science. In the future, humanity can benefit greatly by nurturing the grassroots communities now collectively capable of generating unique, long-term understanding of Earth's most precious forests.
Keywords: parcelle, forêt tropicale, biodiversité forestière, Écosystème forestier, Écologie forestière, Changement de couvert végétal, Couvert forestier
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Lamarre, G. P. A., Molto, Q., Fine, P. V. A., & Baraloto, C. (2012). A comparison of two common flight interception traps to survey tropical arthropods. ZooKeys, 216, 43–55.
Abstract: Tropical forests are predicted to harbor most of the insect diversity on earth, but few studies have been conducted to characterize insect communities in tropical forests. One major limitation is the lack of consensus on methods for insect collection. Deciding which insect trap to use is an important consideration for ecologists and entomologists, yet to date few study has presented a quantitative comparison of the results generated by standardized methods in tropical insect communities. Here, we investigate the relative performance of two flight interception traps, the windowpane trap, and the more widely used malaise trap, across a broad gradient of lowland forest types in French Guiana. The windowpane trap consistently collected significantly more Coleoptera and Blattaria than the malaise trap, which proved most effective for Diptera, Hymenoptera, and Hemiptera. Orthoptera and Lepidoptera were not well represented using either trap, suggesting the need for additional methods such as bait traps and light traps. Our results of contrasting trap performance among insect orders underscore the need for complementary trapping strategies using multiple methods for community surveys in tropical forests.
Keywords: Flight interception trap; French Guiana; Malaise trap; Performance; Sampling strategies; Tropical forest; Windowpane trap
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Ter Steege, H., Henkel, T. W., Helal, N., Marimon, B. S., Marimon-Junior, B. H., Huth, A., et al. (2019). Rarity of monodominance in hyperdiverse Amazonian forests. Scientific reports, 9(1), 13822.
Abstract: Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees over 10cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.
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Sullivan, M. J. P., Talbot, J., Lewis, S. L., Phillips, O. L., Qie, L., Begne, S. K., et al. (2017). Diversity and carbon storage across the tropical forest biome. Sci. Rep., 7, 39102.
Abstract: Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-Tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity. © The Author(s) 2017.
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Van Langenhove, L., Verryckt, L. T., Stahl, C., Courtois, E. A., Urbina, I., Grau, O., et al. (2021). Soil nutrient variation along a shallow catena in Paracou, French Guiana. Soil Research, 59(2), 130.
Abstract: Tropical forests are generally considered to stand upon nutrient-poor soils, but soil nutrient concentrations and availabilities can vary greatly at local scale due to topographic effects on erosion and water drainage. In this study we physically and chemically characterised the soils of 12 study plots situated along a catena with a shallow slope in a tropical rainforest in French Guiana both during the wet and the dry season to evaluate seasonal differences. Soils along the catena were all Acrisols, but differed strongly in their water drainage flux. Over time, this differential drainage has led to differences in soil texture and mineral composition, affecting the adsorption of various nutrients, most importantly phosphorus. The more clayey soils situated on the slope of the catena had higher total concentrations of carbon, nitrogen, phosphorus and several micronutrients, while extractable nutrient concentrations were highest in the sandiest soils situated at the bottom of the catena. We found that carbon, nitrogen and extractable nutrients all varied seasonally, especially in the surface soil layer. These results are interesting because they show that, even at the local scale, small differences in topography can lead to large heterogeneity in nutrient concentrations, which can have large impacts on plant and microbial community organisation at the landscape level.
Keywords: French Guiana, lowland tropical forest, Paracou, phosphorus, topography, water drainage.
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