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Fine, P. V. A., Metz, M. R., Lokvam, J., Mesones, I., Zuniga, J. M. A., Lamarre, G. P. A., et al. (2013). Insect herbivores, chemical innovation, and the evolution of habitat specialization in Amazonian trees. Ecology, 94(8), 1764–1775.
Abstract: Herbivores are often implicated in the generation of the extraordinarily diverse tropical flora. One hypothesis linking enemies to plant diversification posits that the evolution of novel defenses allows plants to escape their enemies and expand their ranges. When range expansion involves entering a new habitat type, this could accelerate defense evolution if habitats contain different assemblages of herbivores and/or divergent resource availabilities that affect plant defense allocation. We evaluated this hypothesis by investigating two sister habitat specialist ecotypes of Protium subserratum (Burseraceae), a common Amazonian tree that occurs in white-sand and terra firme forests. We collected insect herbivores feeding on the plants, assessed whether growth differences between habitats were genetically based using a reciprocal transplant experiment, and sampled multiple populations of both lineages for defense chemistry. Protium subserratum plants were attacked mainly by chrysomelid beetles and cicadellid hemipterans. Assemblages of insect herbivores were dissimilar between populations of ecotypes from different habitats, as well as from the same habitat 100 km distant. Populations from terra firme habitats grew significantly faster than white-sand populations; they were taller, produced more leaf area, and had more chlorophyll. White-sand populations expressed more dry mass of secondary compounds and accumulated more flavone glycosides and oxidized terpenes, whereas terra firme populations produced a coumaroylquinic acid that was absent from white-sand populations. We interpret these results as strong evidence that herbivores and resource availability select for divergent types and amounts of defense investment in white-sand and terra firme lineages of Protium subserratum, which may contribute to habitat-mediated speciation in these trees. © 2013 by the Ecological Society of America.
Keywords: Amazonia; Ecological speciation; Ecotypes; Herbivory; Natural enemies; Plant defense; Protium subserratum; Terra firme forests; Tropical rain forests; White-sand forests
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Fisher, J. B., Malhi, Y., Bonal, D., Da Rocha, H. R., De Araujo, A. C., Gamo, M., et al. (2009). The land-atmosphere water flux in the tropics. Glob. Change Biol., 15(11), 2694–2714.
Abstract: Tropical vegetation is a major source of global land surface evapotranspiration, and can thus play a major role in global hydrological cycles and global atmospheric circulation. Accurate prediction of tropical evapotranspiration is critical to our understanding of these processes under changing climate. We examined the controls on evapotranspiration in tropical vegetation at 21 pan-tropical eddy covariance sites, conducted a comprehensive and systematic evaluation of 13 evapotranspiration models at these sites, and assessed the ability to scale up model estimates of evapotranspiration for the test region of Amazonia. Net radiation was the strongest determinant of evapotranspiration (mean evaporative fraction was 0.72) and explained 87% of the variance in monthly evapotranspiration across the sites. Vapor pressure deficit was the strongest residual predictor (14%), followed by normalized difference vegetation index (9%), precipitation (6%) and wind speed (4%). The radiation-based evapotranspiration models performed best overall for three reasons: (1) the vegetation was largely decoupled from atmospheric turbulent transfer (calculated from X decoupling factor), especially at the wetter sites; (2) the resistance-based models were hindered by difficulty in consistently characterizing canopy (and stomatal) resistance in the highly diverse vegetation; (3) the temperature-based models inadequately captured the variability in tropical evapotranspiration. We evaluated the potential to predict regional evapotranspiration for one test region: Amazonia. We estimated an Amazonia-wide evapotranspiration of 1370 mm yr(-1), but this value is dependent on assumptions about energy balance closure for the tropical eddy covariance sites; a lower value (1096 mm yr(-1)) is considered in discussion on the use of flux data to validate and interpolate models.
Keywords: Amazon; eddy covariance; evaporation; evapotranspiration; ISLSCP-II; LBA; model; remote sensing; tropical
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Flores, O., Herault, B., Delcamp, M., Garnier, É., & Gourlet-Fleury, S. (2014). Functional traits help predict post-disturbance demography of tropical trees. PLoS ONE, 9(9), e105022.
Abstract: How tropical tree species respond to disturbance is a central issue of forest ecology, conservation and resource management. We define a hierarchical model to investigate how functional traits measured in control plots relate to the population change rate and to demographic rates for recruitment and mortality after disturbance by logging operations. Population change and demographic rates were quantified on a 12-year period after disturbance and related to seven functional traits measured in control plots. The model was calibrated using a Bayesian Network approach on 53 species surveyed in permanent forest plots (37.5 ha) at Paracou in French Guiana. The network analysis allowed us to highlight both direct and indirect relationships among predictive variables. Overall, 89% of interspecific variability in the population change rate after disturbance were explained by the two demographic rates, the recruitment rate being the most explicative variable. Three direct drivers explained 45% of the variability in recruitment rates, including leaf phosphorus concentration, with a positive effect, and seed size and wood density with negative effects. Mortality rates were explained by interspecific variability in maximum diameter only (25%). Wood density, leaf nitrogen concentration, maximum diameter and seed size were not explained by variables in the analysis and thus appear as independent drivers of post-disturbance demography. Relationships between functional traits and demographic parameters were consistent with results found in undisturbed forests. Functional traits measured in control conditions can thus help predict the fate of tropical tree species after disturbance. Indirect relationships also suggest how different processes interact to mediate species demographic response.
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Flores, O., Rossi, V., & Mortier, F. (2009). Autocorrelation offsets zero-inflation in models of tropical saplings density. Ecol. Model., 220(15), 1797–1809.
Abstract: Modelling the local density of tropical saplings can provide insights into the ecological processes that drive species regeneration and thereby help predict population recovery after disturbance. Yet, few studies have addressed the challenging issues in autocorrelation and zero-inflation of local density. This paper presents Hierarchical Bayesian Modelling (HBM) of sapling density that includes these two features. Special attention is devoted to variable selection, model estimation and comparison. We developed a Zero-Inflated Poisson (ZIP) model with a latent correlated spatial structure and compared it with non-spatial ZIP and Poisson models that were either autocorrelated (Spatial Generalized Linear Mixed, SGLM) or not (generalized linear models, GLM). In our spatial models, local density autocorrelation was modeled by a Conditional Auto-Regressive (CAR) process. 13 explicative variables described ecological conditions with respect to topography, disturbance, stand structure and intraspecific processes. Models were applied to six tropical tree species with differing biological attributes: Oxandra asbeckii, Eperua falcata, Eperua grandiflora, Dicorynia guianensis, Qualea rosea, and Tachigali melinonii. We built species-specific models using a simple method of variable selection based on a latent binary indicator. Our spatial models showed a close correlation between observed and estimated densities with site spatial structure being correctly reproduced. By contrast, the non-spatial models showed poor fits. Variable selection highlighted species-specific requirements and susceptibility to local conditions. Model comparison overall showed that the SGLM was the most accurate explanatory and predictive model. Surprisingly, zero-inflated models performed less well. Although the SZIP model was relevant with respect to data distribution, and more flexible with respect to response curves, its model complexity caused marked variability in parameter estimates. In the SUM, the spatial process alone accounted for zero-inflation in the data. A refinement of the hypotheses employed at the process level could compensate for distribution flaws at the data level. This study emphasized the importance of the HBM framework in improving the modelling of density-environment relationships. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Hierarchical Bayesian Modelling; Conditional Auto-Regressive model; Variable selection; Zero-Inflated Poisson; Posterior predictive; Paracou; French Guiana
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Foken, T., Meixner, F. X., Falge, E., Zetzsch, C., Serafimovich, A., Bargsten, A., et al. (2012). Coupling processes and exchange of energy and reactive and non-reactive trace gases at a forest site – results of the EGER experiment. Atmos. Chem. Phys., 12(4), 1923–1950.
Abstract: To investigate the energy, matter and reactive and non-reactive trace gas exchange between the atmosphere and a spruce forest in the German mountain region, two intensive measuring periods were conducted at the FLUXNET site DE-Bay (Waldstein-Weidenbrunnen) in September/October 2007 and June/July 2008. They were part of the project “ExchanGE processes in mountainous Regions” (EGER). Beyond a brief description of the experiment, the main focus of the paper concerns the coupling between the trunk space, the canopy and the above-canopy atmosphere. Therefore, relevant coherent structures were analyzed for different in- and above canopy layers, coupling between layers was classified according to already published procedures, and gradients and fluxes of meteorological quantities as well as concentrations of non-reactive and reactive trace compounds have been sorted along the coupling classes. Only in the case of a fully coupled system, it could be shown, that fluxes measured above the canopy are related to gradients between the canopy and the above-canopy atmosphere. Temporal changes of concentration differences between top of canopy and the forest floor, particularly those of reactive trace gases (NO, NO2, O-3, and HONO) could only be interpreted on the basis of the coupling stage. Consequently, only concurrent and vertically resolved measurements of micrometeorological (turbulence) quantities and fluxes (gradients) of trace compounds will lead to a better understanding of the forest-atmosphere interaction.
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Fontaine, S., Stahl, C., Klumpp, K., Picon-Cochard, C., Grise, M. M., Dezécache, C., et al. (2018). Response to Editor to the comment by Schipper and Smith to our paper entitled 'Continuous soil carbon storage of old permanent pastures in Amazonia'. Global Change Biology, 24(3), e732–e733.
Keywords: chronosequence study; continuous C accumulation; deep soil C; eddy covariance; grassland
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Fonty, E., Molino, J. F., Prevost, M. F., & Sabatier, D. (2011). A new case of neotropical monodominant forest: Spirotropis longifolia (Leguminosae-Papilionoideae) in French Guiana. J. Trop. Ecol., 27(6), 641–644.
Keywords: French Guiana; layering; monodominance; sprouting; supporting strategy; suppressive strategy; tropical rain forests
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Fortunel, C., Fine, P. V. A., & Baraloto, C. (2012). Leaf, stem and root tissue strategies across 758 Neotropical tree species. Funct. Ecol., 26(5), 1153–1161.
Abstract: 1. Trade-offs among functional traits reveal major plant strategies that can give insight into species distributions and ecosystem processes. However, current identification of plant strategies lacks the integration of root structural traits together with leaf and stem traits. 2. We examined correlations among 14 traits representing leaf, stem and woody root tissues. Traits were measured on 1084 individuals representing 758 Neotropical tree species, across 13 sites representative of the environmental variation encompassed by three widespread habitats (seasonally flooded, clay terra firme and white-sand forests) at opposite ends of Amazonia (French Guiana and Peru). 3. Woody root traits were closely aligned with stem traits, but not with leaf traits. Altogether leaf, stem and woody root traits delineated two orthogonal axes of functional trade-offs: a first axis defined by leaf traits, corresponding to a 'leaf economics spectrum', and a second axis defined by covarying stem and woody root traits, corresponding to a 'wood economics spectrum'. These axes remained consistent when accounting for species evolutionary history with phylogenetically independent contrasts. 4. Despite the strong species turnover across sites, the covariation among root and stem structural traits as well as their orthogonality to leaf traits were strongly consistent across habitats and regions. 5. We conclude that root structural traits mirrored stem traits rather than leaf traits in Neotropical trees. Leaf and wood traits define an integrated whole-plant strategy in lowland South American forests that may contribute to a more complete understanding of plant responses to global changes in both correlative and modelling approaches. We suggest further meta-analyses in expanded environmental and geographic zones to determine the generality of this pattern. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.
Keywords: French Guiana; Functional trade-offs; Leaf economics; Peru; Plant traits; Tropical forest; Wood economics
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Fortunel, C., Garnier, E., Joffre, R., Kazakou, E., Quested, H., Grigulis, K., et al. (2009). Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe. Ecology, 90(3), 598–611.
Abstract: Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors ( disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices ( litter lignin concentration, lignin : nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors ( disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites.
Keywords: climate; community functional parameters; disturbance; leaf traits; litter decomposability; litter quality
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Fortunel, C., Paine, C. E. T., Fine, P. V. A., Kraft, N. J. B., & Baraloto, C. (2014). Environmental factors predict community functional composition in Amazonian forests. J. Ecol., 102(1), 145–155.
Abstract: The consequences of biodiversity loss for ecosystem services largely depend on the functional identities of extirpated species. However, poor descriptions of spatial patterns of community functional composition across landscapes hamper accurate predictions, particularly in highly diverse tropical regions. Therefore, understanding how community functional composition varies across environmental gradients remains an important challenge. We sampled 15 functional traits in 800 Neotropical tree species across 13 forest plots representative of the broad climatic and soil gradients encompassed by three widespread lowland forest habitats (terra firme forests on clay-rich soils, seasonally flooded forests and white-sand forests) at opposite ends of Amazonia (Peru and French Guiana). We combined univariate and multivariate approaches to test the magnitude and predictability of environmental filtering on community leaf and wood functional composition. Directional shifts in community functional composition correlated with environmental changes across the 13 plots, with denser leaves, stems and roots in forests occurring in environments with limited water and soil-nutrient availability. Critically, these relationships allowed us to accurately predict the functional composition of 61 additional forest plots from environmental data alone. Synthesis. Environmental filtering consistently shapes the functional composition of highly diverse tropical forests at large scales across the terra firme, seasonally flooded and white-sand forests of lowland Amazonia. Environmental factors drive and allow the prediction of variation in community functional composition among habitat types in Amazonian forests. © 2013 British Ecological Society.
Keywords: Amazonian landscape; Climatic and soil gradients; Determinants of plant community diversity and structure; Environmental filtering; Functional traits; Tree communities; Tropical forests
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