Amazonian Rainforest Canopy Research Articles

Coordination and trade-offs among hydraulic safety, efficiency and drought avoidance traits in Amazonian rainforest canopy tree species.

Predicting responses of tropical forests to climate change-type drought is challenging because of high species diversity. Detailed characterization of tropical tree hydraulic physiology is necessary to evaluate community drought vulnerability and improve model parameterization. Here, we measured xylem hydraulic conductivity (hydraulic efficiency), xylem vulnerability curves (hydraulic safety), sapwood pressure-volume curves (drought avoidance) and wood density on emergent branches of 14 common species of Eastern Amazonian canopy trees in Paracou, French Guiana across species with the densest and lightest wood in the plot. Our objectives were to evaluate relationships among hydraulic traits to identify strategies and test the ability of easy-to-measure traits as proxies for hard-to-measure hydraulic traits. Xylem efficiency was related to capacitance, sapwood water content and turgor loss point, and other drought avoidance traits, but not to xylem safety (P50 ). Wood density was correlated (r=-0.57 to -0.97) with sapwood pressure-volume traits, forming an axis of hydraulic strategy variation. In contrast to drier sites where hydraulic safety plays a greater role, tropical trees in this humid tropical site varied along an axis with low wood density, high xylem efficiency and high capacitance at one end of the spectrum, and high wood density and low turgor loss point at the other.

Influence of meteorology and anthropogenic pollution on chemical flux divergence of the NO–NO<sub>2</sub>–O<sub>3</sub> triad above and within a natural grassland canopy

Abstract. The detailed understanding of surface–atmosphere exchange fluxes of reactive trace gases is a crucial precondition for reliable modelling of processes in atmospheric chemistry. Plant canopies significantly impact the atmospheric budget of trace gases. In the past, many studies focused on taller forest canopies or crops, where the bulk plant material is concentrated in the uppermost canopy layer. However, within grasslands, a land-cover class that globally covers vast terrestrial areas, the canopy structure is fundamentally different, as the main biomass is concentrated in the lowest part of the canopy. This has obvious implications for aerodynamic in-canopy transport, and consequently also impacts on global budgets of key species in atmospheric chemistry such as nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3). This study presents for the first time a comprehensive data set of directly measured in-canopy transport times and aerodynamic resistances, chemical timescales, Damköhler numbers, trace gas and micrometeorological measurements for a natural grassland canopy (canopy height = 0.6 m). Special attention is paid to the impact of contrasting meteorological and air chemical conditions on in-canopy transport and chemical flux divergence. Our results show that the grassland canopy is decoupled throughout the day. In the lowermost canopy layer, the measured transport times are fastest during nighttime, which is due to convection during nighttime and a stable stratification during daytime in this layer. The inverse was found in the layers above. During periods of low wind speed and high NOx (NO+NO2) levels, the effect of canopy decoupling on trace gas transport was found to be especially distinct. The aerodynamic resistance in the lowermost canopy layer (0.04–0.2 m) was around 1000 s m−1, which is as high as values determined previously for the lowest metre of an Amazonian rain forest canopy. The aerodynamic resistance representing the bulk canopy was found to be more than 3–4 times higher than in forests. Calculated Damköhler numbers (ratio of transport and chemical timescales) suggest a strong flux divergence for the NO–NO2–O3 triad within the canopy during daytime. During that time, the timescale of NO2 uptake by plants ranged from 90 to 160 s and was the fastest relevant timescale, i.e. faster than the reaction of NO and O3. Thus, our results reveal that grassland canopies of similar structure exhibit a strong potential to retain soil-emitted NO due to oxidation and subsequent uptake of NO2 by plants. Furthermore, photo-chemical O3 production was observed above the canopy, which was attributed to a deviation from the NO–NO2–O3 photostationary state by a surplus of NO2 due to oxidation of NO, by e.g. peroxy radicals. The O3 production was one order of magnitude higher during high NOx than during low NOx periods and resulted in an underestimation of the O3 deposition flux measured with the EC method.

Food Habits of the Harpy Eagle, a Top Predator from the Amazonian Rainforest Canopy

The Harpy Eagle (Harpia harpyja), the heaviest and the most powerful bird of prey in the canopy of the Neotropical rainforests, is critically endangered in some parts of its range, mainly due to hunting pressure and habitat loss by deforestation. In this study, we found that the diet of five breeding pairs of Harpy Eagles in the central Amazonian rainforest over three years was dominated by two species of sloths (Bradypus variegatus and Choloepus didactylus) in terms of number of individuals and biomass consumed. Twelve other species, including primates, rodents, carnivores, and birds, also contributed to the Harpy Eagle diet in central Amazonia; there was no evidence of Harpy Eagle predation on livestock or domestic animals. Throughout the Harpy Eagle's entire range, 69 prey species have been documented, indicating that it can use a wide range of food resources. However, in our study, there was an evident diet specialization, resulting in a niche breadth which was relatively low (Bsta = 0.171). Conservation of Harpy Eagles should include protection of nesting trees, territories, and prey species to maintain the variability and availability of resources and its ecological functions throughout its geographic range.Harpia harpyja, el ave de presa más pesada y poderosa del dosel de los bosques lluviosos neotropicales, está en peligro crítico en algunas partes de su distribución, principalmente debido a la presión de caza y la pérdida de hábitat por deforestación. En este estudio encontramos que la dieta de cinco parejas reproductivas de H. harpyja en los bosques lluviosos amazónicos centrales estuvo dominada a lo largo de tres años por dos especies de perezosos (Bradypus variegatus y Choloepus didactylus) en términos de número de individuos y biomasa consumidos. Otras doce especies, incluyendo primates, roedores, carnívoros y aves también contribuyeron a la dieta de H. harpyja en la Amazonía central; no hubo evidencia de depredación de ganado o animales domésticos por parte de H. harpyja. A lo largo de la distribución completa de H. harpyja se documentaron 69 especies de presa, indicando que la misma puede utilizar un amplio rango de fuentes de alimento. Sin embargo, en nuestro estudio hubo una evidente especialización de la dieta, resultando en un ancho de nicho relativamente estrecho (Bsta = 0.171). La conservación de H. harpyja debería incluir la protección de árboles nido, de territorios y de especies de presas para mantener la variabilidad y disponibilidad de recursos y sus funciones ecológicas a través de su distribución geográfica.

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Next article FreeAnnouncementsPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMore2008 President's AwardThe President's Award of the American Society of Naturalists is given to the paper that, in the president's judgment, was the best paper to appear in The American Naturalist in the preceding calendar year. The President's Award for 2008 was given to Nathan J. B. Kraft, William K. Cornwell, Campbell O. Webb, and David D. Ackerly for their article, “Trait evolution, community assembly, and the phylogenetic structure of ecological communities” (American Naturalist170:271–283).2008 Edward Osborne Wilson Naturalist AwardThe Edward Osborne Wilson Naturalist Award was established in 1997 on the occasion of Professor Wilson's retirement in recognition of his lifetime of outstanding contributions in the areas of ecology and evolutionary biology. The award is given annually to an active investigator in midcareer who has made significant contributions to the knowledge of a particular ecosystem or group of organisms. The 2008 award of an honorarium and an especially appropriate work of art (see fig. 1), a drawing by George Venable of Agra eowilsoni Erwin, a carabid beetle species endemic to the Amazonian rain forest canopy, went to Ulrich Mueller.Figure 1: Agra eowilsoni Erwin (drawing by George Venable). Erwin, T. L. 1996. Evolution at the equator: arboreal and alticolous beetles and their taxon pulses with descriptions of a new Agra subclade and its species (Coleoptera: Carabidae). In G. E. Ball, A. Casale, and A. Vigna Taglianti, eds. Phylogeny and classification of Caraboidea (Coleoptera: Adephaga). Proceedings of a symposium (August 28, 1996, Florence, Italy), XX International Congress of Entomology. Museo Regionale Scienze Naturali–Torino, Atti, Torino.View Large ImageDownload PowerPoint2008 Sewall Wright AwardThe Sewall Wright Award, established in 1991, is given annually to honor a senior but still active investigator who is making fundamental contributions to the goals of the American Society of Naturalists, namely, promoting the conceptual unification of the biological sciences. The 2008 award and an honorarium of $1,000 went to Spencer Barrett.2008 Young Investigators' PrizesThe Young Investigators' Prizes recognize outstanding and promising work by investigators who received their doctorates in the three years preceding the application deadline or are in their final year of graduate school. Prizewinners are invited to present their work at the Young Investigators' Symposium at the annual meetings of the American Society of Naturalists. The prizes for 2008 went to Jennifer Lau, Judith Mank, Volker Rudolf, and Mark Urban. Next article DetailsFiguresReferencesCited by The American Naturalist Volume 172, Number 6December 2008 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/595522 Views: 28 PDF download Crossref reports no articles citing this article.

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How plants shape the ant community in the Amazonian rainforest canopy: the key role of extrafloral nectaries and homopteran honeydew

Ant-plant interactions in the canopy of a lowland Amazonian rainforest of the upper Orinoco, Venezuela, were studied using a modified commercial crane on rails (Surumoni project). Our observations show a strong correlation between plant sap exudates and both abundance of ants and co-occurrence of ant species in tree canopies. Two types of plant sap sources were compared: extrafloral nectaries (EFNs) and honeydew secretions by homopterans. EFNs were a frequent food source for ants on epiphytes (Philodendron spp., Araceae) and lianas (Dioclea, Fabaceae), but rare on canopy trees in the study area, whereas the majority of trees were host to aggregations of homopterans tended by honeydew-seeking ants (on 62% of the trees examined). These aggregations rarely occurred on epiphytes. Baited ant traps were installed on plants with EFNs and in the crowns of trees from three common genera, including trees with and without ant-tended homopterans: Goupia glabra (Celastraceae), Vochysia spp. (Vochysiaceae), and Xylopia spp. (Annonaceae). The number of ant workers per trap was significantly higher on plants offering one of the two plant sap sources than on trees without such resources. Extrafloral nectaries were used by a much broader spectrum of ant species and genera than honeydew, and co-occurrence of ant species (in traps) was significantly higher on plants bearing EFNs than on trees. Homopteran honeydew (Coccidae and Membracidae), on the other hand, was mostly monopolised by a single ant colony per tree. Homopteran-tending ants were generally among the most dominant ants in the canopy. The most prominent genera were Azteca, Dolichoderus (both Dolichoderinae), Cephalotes, Pheidole, Crematogaster (all Myrmicinae), and Ectatomma (Ponerinae). Potential preferences were recorded between ant and homopteran species, and also between ant-homopteran associations and tree genera. We hypothesize that the high availability of homopteran honeydew provides a key resource for ant mosaics, where dominant ant colonies and species maintain mutually exclusive territories on trees. In turn, we propose that for nourishment of numerous ants of lower competitive capacity, Philodendron and other sources of EFNs might be particularly important.

Stomatal and surface conductance of tropical rainforest

Although the absolute values of stomatal conductance of tropical rainforest vary greatly, there is some similarity in the response to humidity deficit and radiation. Stomatal conductance decreases downward through the canopy of Amazonian rainforest. Using a multi-layer approach and measured profiles of stomatal conductance and weather variables through the canopy, good agreement can be obtained between calculated and observed values of dry canopy evaporation. The relationship between the biological response of stomata to radiation at the leaf level and the response of surface conductance to radiation above the canopy is derived by relating the profile of stomatal conductance through the canopy to the attenuation of radiation. Simple use of responses derived at leaf level will greatly overestimate surface conductance if used with above-canopy radiation measurements. Three models of surface conductance of the same Amazonian forest, varying in their degree of complexity, were tested against measured evaporation data for the Reserva Ducke forest in Brazil. A simple model with surface conductance varying only with time of day was found to model the observed data slightly better than a more complex environmental model. Using a constant value of surface conductance gave a poorer fit to the data, although the average evaporation can be calculated accurately. It is recommended that the more complex environmental model be used when estimates of evaporation are required under any conditions substantially different from those of the central Amazonian forest where the data were collected.