Hamadi, A., Borderies, P., Albinet, C., Koleck, T., Villard, L., Ho Tong Minh, D., et al. (2015). Temporal coherence of tropical forests at P-band: Dry and rainy seasons. IEEE Geosci. Remote Sens. Lett., 12(3), 557–561.
Abstract: In this letter, the temporal coherence of tropical forest scattering at P-band is addressed by means of a ground-based experiment. The study is based on the TropiScat campaign in French Guiana, designed to support the Biomass mission, which will be the ESA 7th Earth Explorer mission. For Biomass, temporal coherence is a crucial parameter for coherent processing of polarimetric synthetic aperture radar (SAR) interferometry and SAR tomography in repeat-pass acquisitions. During the experiment, data were continuously collected for six months during both the rainy and dry seasons. For the rain-free days in both seasons, the coherence exhibits a daily cycle showing a high decorrelation during daytime, which is likely due to motion in the canopy. Up to a 20-day baseline, the coherence is much higher in the dry season than in the rainy season (> 0.8). From 20 to 40 days, it presents the same order of magnitude in both seasons [0.6, 0.7]. For larger temporal baselines, it becomes lower in the dry season. The results can be used to assess the long-term coherence of repeat-pass observations over a tropical forest. However, an extension of this study to several years and over other forest spots would be necessary to draw more general conclusions.
Keywords: Biomass mission; forest scattering; ground-based experiment; P-band; range impulse response; temporal coherence
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Khia, A., Ghanmi, M., Satrani, B., Aafi, A., Aberchane, M., Quaboul, B., et al. (2014). Effect of provenance on the chemical and microbiological quality of essential oils of Rosmarinus officinalis L. in Morocco. Phytotherapie, 12(6), 341–347.
Abstract: This study is an assessment of the chemical quality and evaluation of antibacterial and antifungal activity of rosemary’s essential oils from three regions of Morocco (Rchida and Berkine/Eastern Morocco and Aknoul/North East of Morocco. The essential oils obtained by hydrodistillation of the leaves and young twigs of rosemary, were analyzed by GC / FID and GC/ MS. These essential oils are characterized by the presence of α and β-pinene, camphene, 1,8-cineole and camphor compounds. The quality of these essential oils met the AFNOR NF ISO 4730 rosemary Morocco kind (1,8-cineole). The evaluation of the antimicrobial activity of essential oils of Rosmarinus officinalis showed low efficacy against microorganisms tested which were all inhibited from 1/100 v/v except for Penicillium expansum whose growth was stopped at the concentration 1/250 v/v.
Keywords: Antibacterial; Antifungal activity; Chemical composition; Essential Oil; Provenance; Rosmarinus officinalis
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Anouhe, J. - B. S., Adima, A. A., Niamké, F. B., Stien, D., Amian, B. K., Blandinieres, P. - A., et al. (2015). Dicorynamine and harmalan-N-oxide, two new β-carboline alkaloids from Dicorynia guianensis Amsh heartwood. Phytochemistry Letters, 12, 158–163.
Abstract: Abstract 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. © 2015 Published by Elsevier B.V. on behalf of Phytochemical Society of Europe.
Keywords: ABTS antioxidant; Biogenesis; Dicorynia guianensis; Nitrone; Spiroindolone
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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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Morel-Journel, T., Piponiot, C., Vercken, E., & Mailleret, L. (2016). Evidence for an optimal level of connectivity for establishment and colonization. Biol Lett, 12(11), 20160704.
Abstract: Dispersal is usually associated with the spread of invasive species, but it also has two opposing effects, one decreasing and the other increasing the probability of establishment. Indeed, dispersal both slows population growth at the site of introduction and increases the likelihood of surrounding habitat being colonized. The connectivity of the introduction site is likely to affect dispersal, and, thus, establishment, according to the dispersal behaviour of individuals. Using individual-based models and microcosm experiments on minute wasps, we demonstrated the existence of a hump-shaped relationship between connectivity and establishment in situations in which individual dispersal resembled a diffusion process. These results suggest that there is an optimal level of connectivity for the establishment of introduced populations locally at the site of introduction, and regionally over the whole landscape.
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Phillips, O. L., Brienen, R. J. W., Gloor, E., Baker, T. R., Lloyd, J., Lopez-Gonzalez, G., et al. (2017). Carbon uptake by mature Amazon forests has mitigated Amazon nations' carbon emissions. Carbon Balance and Management, 12(1).
Abstract: Background: Several independent lines of evidence suggest that Amazon forests have provided a significant carbon sink service, and also that the Amazon carbon sink in intact, mature forests may now be threatened as a result of different processes. There has however been no work done to quantify non-land-use-change forest carbon fluxes on a national basis within Amazonia, or to place these national fluxes and their possible changes in the context of the major anthropogenic carbon fluxes in the region. Here we present a first attempt to interpret results from ground-based monitoring of mature forest carbon fluxes in a biogeographically, politically, and temporally differentiated way. Specifically, using results from a large long-term network of forest plots, we estimate the Amazon biomass carbon balance over the last three decades for the different regions and nine nations of Amazonia, and evaluate the magnitude and trajectory of these differentiated balances in relation to major national anthropogenic carbon emissions. Results: The sink of carbon into mature forests has been remarkably geographically ubiquitous across Amazonia, being substantial and persistent in each of the five biogeographic regions within Amazonia. Between 1980 and 2010, it has more than mitigated the fossil fuel emissions of every single national economy, except that of Venezuela. For most nations (Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname) the sink has probably additionally mitigated all anthropogenic carbon emissions due to Amazon deforestation and other land use change. While the sink has weakened in some regions since 2000, our analysis suggests that Amazon nations which are able to conserve large areas of natural and semi-natural landscape still contribute globally-significant carbon sequestration. Conclusions: Mature forests across all of Amazonia have contributed significantly to mitigating climate change for decades. Yet Amazon nations have not directly benefited from providing this global scale ecosystem service. We suggest that better monitoring and reporting of the carbon fluxes within mature forests, and understanding the drivers of changes in their balance, must become national, as well as international, priorities. © 2017 The Author(s).
Keywords: Amazonia; Carbon balance; Carbon sink; Climate change; Ecosystem service; Land use change; Sequestration; Tropical forests
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Dezecache, C., Faure, E., Gond, V., Salles, J. - M., Vieilledent, G., & Herault, B. (2017). Gold-rush in a forested El Dorado: deforestation leakages and the need for regional cooperation. Environmental Research Letters, 12(3), 034013.
Abstract: Tropical forests of the Guiana Shield are the most affected by gold-mining in South America, experiencing an exponential increase in deforestation since the early 2000’s. Using yearly deforestation data encompassing Guyana, Suriname, French Guiana and the Brazilian State of Amapá, we demonstrated a strong relationship between deforestation due to gold-mining and gold-prices at the regional scale. In order to assess additional drivers of deforestation due to gold-mining, we focused on the national scale and highlighted the heterogeneity of the response to gold-prices under different political contexts. Deforestation due to gold-mining over the Guiana Shield occurs mainly in Guyana and Suriname. On the contrary, past and current repressive policies in Amapá and French Guiana likely contribute to the decorrelation of deforestation and gold prices. In this work, we finally present a case study focusing on French Guiana and Suriname, two neighbouring countries with very different levels of law enforcement against illegal gold-mining. We developed a modelling framework to estimate potential deforestation leakages from French Guiana to Suriname in the border areas. Based on our assumptions, we estimated a decrease in deforestation due to gold-mining of approx. 4300 hectares in French Guiana and an increase of approx. 12 100 hectares in Suriname in response to the active military repression of illegal gold-mining launched in French Guiana. Gold-mining in the Guiana Shield provides challenging questions regarding REDD+ implementation. These questions are discussed at the end of this study and are important to policy makers who need to provide sustainable alternative employment to local populations in order to ensure the effectiveness of environmental policies.
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Grabchak, M., Marcon, E., Lang, G., & Zhang, Z. (2017). The generalized Simpson’s entropy is a measure of biodiversity. Plos One, 12(3), e0173305.
Abstract: Modern measures of diversity satisfy reasonable axioms, are parameterized to produce diversity profiles, can be expressed as an effective number of species to simplify their interpretation, and come with estimators that allow one to apply them to real-world data. We introduce the generalized Simpson’s entropy as a measure of diversity and investigate its properties. We show that it has many useful features and can be used as a measure of biodiversity. Moreover, unlike most commonly used diversity indices, it has unbiased estimators, which allow for sound estimation of the diversity of poorly sampled, rich communities.
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Bastias, C. C., Fortunel, C., Valladares, F., Baraloto, C., Benavides, R., Cornwell, W., et al. (2017). Intraspecific leaf trait variability along a boreal-to-tropical community diversity gradient. PLoS ONE, 12(2), e0172495.
Abstract: Disentangling the mechanisms that shape community assembly across diversity gradients is a central matter in ecology. While many studies have explored community assembly through species average trait values, there is a growing understanding that intraspecific trait variation (ITV) can also play a critical role in species coexistence. Classic biodiversity theory hypothesizes that higher diversity at species-rich sites can arise from narrower niches relative to species-poor sites, which would be reflected in reduced ITV as species richness increases. To explore how ITV in woody plant communities changes with species richness, we compiled leaf trait data (leaf size and specific leaf area) in a total of 521 woody plant species from 21 forest communities that differed dramatically in species richness, ranging from boreal to tropical rainforests. At each forest, we assessed ITV as an estimate of species niche breadth and we quantified the degree of trait overlap among co-occurring species as a measure of species functional similarity. We found ITV was relatively invariant across the species richness gradient. In addition, we found that species functional similarity increased with diversity. Contrary to the expectation from classic biodiversity theory, our results rather suggest that neutral processes or equalizing mechanisms can be acting as potential drivers shaping community assembly in hyperdiverse forests. © This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
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Wagner, F. H., Herault, B., Rossi, V., Hilker, T., Maeda, E. E., Sanchez, A., et al. (2017). Climate drivers of the Amazon forest greening. PLoS ONE, 12(7), e0180932.
Abstract: Our limited understanding of the climate controls on tropical forest seasonality is one of the biggest sources of uncertainty in modeling climate change impacts on terrestrial ecosystems. Combining leaf production, litterfall and climate observations from satellite and ground data in the Amazon forest, we show that seasonal variation in leaf production is largely triggered by climate signals, specifically, insolation increase (70.4% of the total area) and precipitation increase (29.6%). Increase of insolation drives leaf growth in the absence of water limitation. For these non-water-limited forests, the simultaneous leaf flush occurs in a sufficient proportion of the trees to be observed from space. While tropical cycles are generally defined in terms of dry or wet season, we show that for a large part of Amazonia the increase in insolation triggers the visible progress of leaf growth, just like during spring in temperate forests. The dependence of leaf growth initiation on climate seasonality may result in a higher sensitivity of these ecosystems to changes in climate than previously thought.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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