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| Author |
Aubry-Kientz, Mélaine ; Laybros, Anthony ; Weinstein, Ben ; Ball, James G. C. ; Jackson, Toby ; Coomes, David ; Vincent, Grégoire |
| Title |
Multisensor data fusion for improved segmentation of individual tree crowns in dense tropical forests |
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Journal Article |
| Year |
2021 |
Publication |
IEEE Journal of Selected topics in Applied Earth Observations and Remote Sensing |
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| Volume |
14 |
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Pages |
3927-3936 |
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Automatic tree crown segmentation from remote sensing data is especially challenging in dense, diverse, and multilayered tropical forest canopies, and tracking mortality by this approach is even more difficult. Here, we examine the potential for combining airborne laser scanning (ALS) with multispectral and hyperspectral data to improve the accuracy of tree crown segmentation at a study site in French Guiana. We combined an ALS point cloud clustering method with a spectral deep learning model to achieve 83% accuracy at recognizing manually segmented reference crowns (with congruence >0.5). This method outperformed a two-step process that involved clustering the ALS point cloud and then using the logistic regression of hyperspectral distances to correct oversegmentation. We used this approach to map tree mortality from repeat surveys and show that the number of crowns identified in the first that intersected with height loss clusters was a good estimator of the number of dead trees in these areas. Our results demonstrate that multisensor data fusion improves the automatic segmentation of individual tree crowns and presents a promising avenue to study forest demography with repeated remote sensing acquisitions. |
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IEEE |
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EcoFoG @ webmaster @ |
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1008 |
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Essebtey, Salma El Idrissi ; Villard, Ludovic ; Borderies, Pierre ; Koleck, Thierry ; Burban, Benoït ; Le Toan, Thuy |
| Title |
Long-Term Trends of P-Band Temporal Decorrelation Over a Tropical Dense Forest-Experimental Results for the BIOMASS Mission |
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Journal Article |
| Year |
2021 |
Publication |
IEEE Transactions on Geoscience and Remote Sensing |
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60 |
Issue |
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Pages |
1-15 |
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Fostered by the upcoming BIOMASS mission, this article explores long-term trends of P-band temporal decorrelation over a tropical forest due to a time series of 617 days acquired during the TropiScat-2 experiment. The interest in this unique time series is twofold. First, it provides consistent statistics to monitor the yearly evolution of temporal coherences according to specific time scales of the BIOMASS tomographic and interferometric phases. Second, it provides key insights to explore new processing approaches with the combination of data from different orbit directions (ascending/descending) and different mission cycles separated by about seven months according to the current acquisition plan. For the first time, this study shows that 18-day coherences (corresponding to the time interval between the first and last acquisitions of the BIOMASS tomographic processing) can vary significantly according to rainy and dry seasons (medians from 0.3 to 0.9). The extension to time intervals of up to 90 days within both seasons and over two consecutive years puts forward the key role of the typical sporadic rainfalls occurring during dry periods in tropical rainforests, with a stronger impact on temporal coherence evolution compared to the more reproducible rainy seasons. Furthermore, outstanding values significantly above zero have been obtained for the 7- and 14-month coherences (medians of 0.35 and 0.2, respectively), opening the way to new methods of change detection. Overall, this study highlights the role of P-band temporal decorrelation not only as a disturbance factor for coherent applications but also as a relevant indicator of forest changes. |
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Institute of Electrical and Electronics Engineers |
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EcoFoG @ webmaster @ |
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1060 |
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Schmitt, Sylvain ; Raevel, Valérie ; Réjou-Méchain, Maxime ; Ayyappan, Narayanan ; Balachandran, Natesan ; Barathan, Narayanan ; Rajashekar, Gopalakrishnan ; Munoz, François |
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Canopy and understorey tree guilds respond differently to the environment in an Indian rain forest |
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Journal Article |
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2021 |
Publication |
Journal of Végétation Science |
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32 |
Issue |
5 |
Pages |
e13075 |
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Questions Changes in the functional composition of tree communities along resource availability gradients have received attention, but it is unclear whether understorey and canopy guilds respond similarly to different light, biomechanical, and hydraulic constraints. Location An anthropically undisturbed, old-growth wet evergreen dipterocarp forest plot located in Karnataka State, India. Methods We measured leaf and wood traits of 89 tree species representing 99% of all individuals in a 10-ha permanent plot with varying topographic and canopy conditions inferred from Light Detection And Ranging (LiDAR) data. We assigned tree species to guilds of canopy and understorey species and assessed the variation of the guild-weighted means of functional-trait values with canopy height and topography. Results The functional-trait space did not differ between canopy and understorey tree species. However, environmental filtering led to significantly different functional composition of canopy and understorey guild assemblages. Furthermore, they responded differently along environmental gradients related to water, nutrients, light, and wind exposure. For example, the canopy guild responded to wind exposure while the understorey guild did not. Conclusions The pools of understorey and canopy species are functionally similar. However, fine-scale environmental heterogeneity impacts differently on these two guilds, generating striking differences in functional composition between understorey and canopy guild assemblages. Accounting for vertical guilds improves our understanding of forest communities' assembly processes. |
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International Association for Vegetation Science |
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EcoFoG @ webmaster @ |
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1038 |
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Mirabel, Ariane ; Marcon, Eric ; Hérault, Bruno |
| Title |
30 Years of postdisturbance recruitment in a Neotropical forest |
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Journal Article |
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2021 |
Publication |
Ecology and Evolution |
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11 |
Issue |
21 |
Pages |
14448-14458 |
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John Wiley & Sons, Ltd (10.1111) |
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EcoFoG @ webmaster @ |
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1043 |
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Gargallo-Garriga, Albert ; Sardans, Jordi ; Alrefaei, Abdulwahed Fahad ; Klem, Karel ; Fuchslueger, Lucia ; Ramirez-Rojas, Irène ; Donald, Julian ; Leroy, Celine ; Van Langenhove, Leandro ; Verbruggen, Erik ; Janssens, Ivan A. ; Urban, Otmar ; Penuelas, Josep |
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Tree Species and Epiphyte Taxa Determine the “Metabolomic niche” of Canopy Suspended Soils in a Species-Rich Lowland Tropical Rainforest |
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Journal Article |
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2021 |
Publication |
Metabolites |
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11 |
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11 |
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Bacteria, Canopy soils, Epiphyte, French Guiana, Metabolomics |
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Tropical forests are biodiversity hotspots, but it is not well understood how this diversity is structured and maintained. One hypothesis rests on the generation of a range of metabolic niches, with varied composition, supporting a high species diversity. Characterizing soil metabolomes can reveal fine-scale differences in composition and potentially help explain variation across these habitats. In particular, little is known about canopy soils, which are unique habitats that are likely to be sources of additional biodiversity and biogeochemical cycling in tropical forests. We studied the effects of diverse tree species and epiphytes on soil metabolomic profiles of forest floor and canopy suspended soils in a French Guianese rainforest. We found that the metabolomic profiles of canopy suspended soils were distinct from those of forest floor soils, differing between epiphyte-associated and non-epiphyte suspended soils, and the metabolomic profiles of suspended soils varied with host tree species, regardless of association with epiphyte. Thus, tree species is a key driver of rainforest suspended soil metabolomics. We found greater abundance of metabolites in suspended soils, particularly in groups associated with plants, such as phenolic compounds, and with metabolic pathways related to amino acids, nucleotides, and energy metabolism, due to the greater relative proportion of tree and epiphyte organic material derived from litter and root exudates, indicating a strong legacy of parent biological material. Our study provides evidence for the role of tree and epiphyte species in canopy soil metabolomic composition and in maintaining the high levels of soil metabolome diversity in this tropical rainforest. It is likely that a wide array of canopy microsite-level environmental conditions, which reflect interactions between trees and epiphytes, increase the microscale diversity in suspended soil metabolomes |
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MDPI |
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EcoFoG @ webmaster @ |
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1041 |
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Agrawal, Anurag A. ; Boroczky, Katalin ; Haribal, Meena ; Hastings, Amy P. ; White, Ronald, A. ; Jiang, Ren-Wang ; Duplais, Christophe |
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Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds |
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Journal Article |
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2021 |
Publication |
PNAS |
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118 |
Issue |
16 |
Pages |
e2024463118 |
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For highly specialized insect herbivores, plant chemical defenses are often co-opted as cues for oviposition and sequestration. In such interactions, can plants evolve novel defenses, pushing herbivores to trade off benefits of specialization with costs of coping with toxins? We tested how variation in milkweed toxins (cardenolides) impacted monarch butterfly ( Danaus plexippus ) growth, sequestration, and oviposition when consuming tropical milkweed ( Asclepias curassavica ), one of two critical host plants worldwide. The most abundant leaf toxin, highly apolar and thiazolidine ring–containing voruscharin, accounted for 40% of leaf cardenolides, negatively predicted caterpillar growth, and was not sequestered. Using whole plants and purified voruscharin, we show that monarch caterpillars convert voruscharin to calotropin and calactin in vivo, imposing a burden on growth. As shown by in vitro experiments, this conversion is facilitated by temperature and alkaline pH. We next employed toxin-target site experiments with isolated cardenolides and the monarch’s neural Na + /K + -ATPase, revealing that voruscharin is highly inhibitory compared with several standards and sequestered cardenolides. The monarch’s typical >50-fold enhanced resistance to cardenolides compared with sensitive animals was absent for voruscharin, suggesting highly specific plant defense. Finally, oviposition was greatest on intermediate cardenolide plants, supporting the notion of a trade-off between benefits and costs of sequestration for this highly specialized herbivore. There is apparently ample opportunity for continued coevolution between monarchs and milkweeds, although the diffuse nature of the interaction, due to migration and interaction with multiple milkweeds, may limit the ability of monarchs to counteradapt. |
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National Academy of Sciences |
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EcoFoG @ webmaster @ |
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1014 |
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Seibold, Sebastien ; Rammer, Werner ; Hothorn, Torsten ; Seidl, Rupert ; Ulyshen, Michael ; Lorz, Janina ; Cadotte, Marc ; Lindenmayer, David ; Adhikari, Yagya ; Aragón, Roxana ; Bae, Soyeon ; Baldrian, Petr ; Barimani Varandi, Hassan ; Barlow, Jos ; Bässler, Clauss ; Beauchêne, Jacques ; and all ................... |
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The contribution of insects to global forest deadwood decomposition |
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Journal Article |
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2021 |
Publication |
Nature |
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597 |
Issue |
7874 |
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77-81 |
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The amount of carbon stored in deadwood is equivalent to about 8 per cent of the global forest carbon stocks1. The decomposition of deadwood is largely governed by climate2-5 with decomposer groups-such as microorganisms and insects-contributing to variations in the decomposition rates2,6,7. At the global scale, the contribution of insects to the decomposition of deadwood and carbon release remains poorly understood7. Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effect-including the direct consumption by insects and indirect effects through interactions with microorganisms-insects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9 per cent and -0.1 per cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9 ± 3.2 petagram of carbon per year released from deadwood globally, with 93 per cent originating from tropical forests. Globally, the net effect of insects may account for 29 per cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle. |
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NATURE PUBLISHING GROUP |
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EcoFoG @ webmaster @ |
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1046 |
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Migliavacca, Mirco ; Musavi, Talie ; Mahecha, Miguel D. ; Nelson, Jacob A. ; Knauer, Jurgen ; Baldocchi, Dennis D. ; Perez-Priego, Oscar ; Christiansen, Rune ; Peters, Jonas ; Anderson, Karen ; Bahn, Michael ; Black, T. Andrew ; Blanken, Peter D. ; and all .................. |
| Title |
The three major axes of terrestrial ecosystem function |
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Journal Article |
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2021 |
Publication |
Nature |
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598 |
Issue |
7881 |
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468-472 |
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The leaf economics spectrum1,2 and the global spectrum of plant forms and functions3 revealed fundamental axes of variation in plant traits, which represent different ecological strategies that are shaped by the evolutionary development of plant species2. Ecosystem functions depend on environmental conditions and the traits of species that comprise the ecological communities4. However, the axes of variation of ecosystem functions are largely unknown, which limits our understanding of how ecosystems respond as a whole to anthropogenic drivers, climate and environmental variability4,5. Here we derive a set of ecosystem functions6 from a dataset of surface gas exchange measurements across major terrestrial biomes. We find that most of the variability within ecosystem functions (71.8%) is captured by three key axes. The first axis reflects maximum ecosystem productivity and is mostly explained by vegetation structure. The second axis reflects ecosystem water-use strategies and is jointly explained by variation in vegetation height and climate. The third axis, which represents ecosystem carbon-use efficiency, features a gradient related to aridity, and is explained primarily by variation in vegetation structure. We show that two state-of-the-art land surface models reproduce the first and most important axis of ecosystem functions. However, the models tend to simulate more strongly correlated functions than those observed, which limits their ability to accurately predict the full range o |
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Nature Publishing Group |
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EcoFoG @ webmaster @ |
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1044 |
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Duplais, Christophe ; Sarou-Kanian, Vincent ; Massiot, Dominique ; Hassan, Alia ; Perrone, Barbara ; Estevez, Yannick ; Wertz, John; Martineau, Estelle ; Farjon, Jonathan ; Giraudeau, Patrick, Moreau, Carrie S. |
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Gut bacteria are essential for normal cutile development in herbivorous turtle ants |
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Journal Article |
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2021 |
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Nature Communication |
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12 |
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1-6 |
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Across the evolutionary history of insects, the shift from nitrogen-rich carnivore/omnivore diets to nitrogen-poor herbivorous diets was made possible through symbiosis with microbes. The herbivorous turtle ants Cephalotes possess a conserved gut microbiome which enriches the nutrient composition by recycling nitrogen-rich metabolic waste to increase the production of amino acids. This enrichment is assumed to benefit the host, but we do not know to what extent. To gain insights into nitrogen assimilation in the ant cuticle we use gut bacterial manipulation, 15N isotopic enrichment, isotope-ratio mass spectrometry, and 15N nuclear magnetic resonance spectroscopy to demonstrate that gut bacteria contribute to the formation of proteins, catecholamine cross-linkers, and chitin in the cuticle. This study identifies the cuticular components which are nitrogen-enriched by gut bacteria, highlighting the role of symbionts in insect evolution, and provides a framework for understanding the nitrogen flow from nutrients through bacteria into the insect cuticle. |
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NATURE PUBLISHING GROUP |
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Anglais |
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EcoFoG @ webmaster @ |
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1005 |
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Bréchet, Laëtitia M.; Daniel Warren; Stahl, Clément; Burban, Benoït; Goret, Jean-Yves; Salomon, Roberto L.; Janssens, Ivan A.o |
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Simultaéneous tree stem and soil greenhouse gas (CO2, CH4, N2O) flux measurements: a novel design for continuous monitoring towards improving flux estimates and temporal resolution |
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Journal Article |
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2021 |
Publication |
New Phytologist |
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230 |
Issue |
6 |
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2487-2500 |
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système de chambre automatisé ; efflux de dioxyde de carbone ; flux de méthane ; flux d'oxyde nitreux ; tige d'arbre ; forêt tropicale |
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Tree stems and soils can act as sources and sinks for the greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Since both uptake and emission capacities can be large, especially in tropical rainforests, accurate assessments of the magnitudes and temporal variations of stem and soil GHG fluxes are required. We designed a new flexible stem chamber system for continuously measuring GHG fluxes in a French Guianese rainforest. Here, we describe this new system, which is connected to an automated soil GHG flux system, and discuss measurement uncertainty and potential error sources. In line with findings for soil GHG flux estimates, we demonstrated that lengthening the stem chamber closure time was required for accurate estimates of tree stem CH4 and N2O flux but not tree stem CO2 flux. The instrumented stem was a net source of CO2 and CH4 and a weak sink of N2O. Our experimental setup operated successfully in situ and provided continuous tree and soil GHG measurements at a high temporal resolution over an 11-month period. This automated system is a major step forward in the measurement of GHG fluxes in stems and the atmosphere concurrently with soil GHG fluxes in tropical forest ecosystems. |
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New Phytologist Foundation |
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EcoFoG @ webmaster @ |
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1004 |
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