Abstract: Although tropical forests harbour most of the terrestrial carbon and biological diversity on Earth they continue to be deforested or degraded at high rates. In Amazonia, the largest tropical forest on Earth, a sixth of the remaining natural forests is formally dedicated to timber extraction through selective logging. Reconciling timber extraction with the provision of other ecosystem services (ES) remains a major challenge for forest managers and policy-makers. This study applies a spatial optimisation of logging in Amazonian production forests to analyse potential trade-offs between timber extraction and recovery, carbon storage, and biodiversity conservation. Current logging regulations with unique cutting cycles result in sub-optimal ES-use efficiency. Long-term timber provision would require the adoption of a land-sharing strategy that involves extensive low-intensity logging, although high transport and road-building costs might make this approach economically unattractive. By contrast, retention of carbon and biodiversity would be enhanced by a land-sparing strategy restricting high-intensive logging to designated areas such as the outer fringes of the region. Depending on management goals and societal demands, either choice will substantially influence the future of Amazonian forests. Overall, our results highlight the need for revaluation of current logging regulations and regional cooperation among Amazonian countries to enhance coherent and trans-boundary forest management.

Abstract: Arboreal ant mosaics have been intensively investigated, but what generates these mosaics remains poorly understood. In this paper, we hypothesize that the dynamics of arboreal ant mosaics could be better understood by examining the ontogenetic succession of ants in tropical trees. We used three African pioneer tree species as biological models. Lophira alata (Ochnaceae) is a long-lived species that does not furnish any reward (i.e., extra-floral nectaries [EFNs], shelter) to ants, Anthocleista vogelii (Gentianaceae) bears extremely well-developed EFNs, and Barteria fistulosa (Passifloraceae) is a long-lived myrmecophyte providing both EFNs and domatia. For both L. alata and A. vogelii, we noted a succession of different associated ants as the plants grew and aged. Ground-nesting, arborealforaging ant species were the first associates, followed by arboreal species that build nests with the leaves of their host trees, together with some species nesting opportunistically in pre-existing cavities. Carton-building Crematogaster species were the last in this succession. The presence of EFNs on A. vogelii slows species turnover, demonstrating that the plant exerts some control over its ant associates. The comparison with B. fistulosa, which generally remains associated with the same plant-ant species during its entire ontogeny, highlights the importance of the selective attractiveness of the trees for their associated ants – or, perhaps, the existence of plant filters that screen arriving ants. (C) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

Abstract: The exchanges of carbon, water and energy between the atmosphere and the Amazon basin have global implications for the current and future climate. Here, the global atmospheric inversion system of the Monitoring of Atmospheric Composition and Climate (MACC) service is used to study the seasonal and interannual variations of biogenic CO<inf>2</inf> fluxes in Amazonia during the period 2002-2010. The system assimilated surface measurements of atmospheric CO<inf>2</inf> mole fractions made at more than 100 sites over the globe into an atmospheric transport model. The present study adds measurements from four surface stations located in tropical South America, a region poorly covered by CO<inf>2</inf> observations. The estimates of net ecosystem exchange (NEE) optimized by the inversion are compared to an independent estimate of NEE upscaled from eddy-covariance flux measurements in Amazonia. They are also qualitatively evaluated against reports on the seasonal and interannual variations of the land sink in South America from the scientific literature. We attempt at assessing the impact on NEE of the strong droughts in 2005 and 2010 (due to severe and longer-than-usual dry seasons) and the extreme rainfall conditions registered in 2009. The spatial variations of the seasonal and interannual variability of optimized NEE are also investigated. While the inversion supports the assumption of strong spatial heterogeneity of these variations, the results reveal critical limitations of the coarse-resolution transport model, the surface observation network in South America during the recent years and the present knowledge of modelling uncertainties in South America that prevent our inversion from capturing the seasonal patterns of fluxes across Amazonia. However, some patterns from the inversion seem consistent with the anomaly of moisture conditions in 2009. © Author(s) 2015.

Abstract: Tropical forests store large amounts of biomass despite they generally grow in nutrient-poor soils, suggesting that the role of soil characteristics in the structure and dynamics of tropical forests is complex. We used data for >34 000 trees from several permanent plots in French Guiana to investigate if soil characteristics could predict the structure (tree diameter, density and aboveground biomass), and dynamics (growth, mortality, aboveground wood productivity) of nutrient-poor tropical forests. Most variables did not covary with site-level changes in soil nutrient content, indicating that nutrient-cycling mechanisms other than the direct absorption from soil (e.g. the nutrient uptake from litter, the resorption, or the storage of nutrients in the biomass), may strongly control forest structure and dynamics. Ecosystem-level adaptations to low soil nutrient availability and long-term low levels of disturbance may help to account for the lower productivity and higher accumulation of biomass in nutrient-poor forests compared to nutrient-richer forests.

Abstract: One of the most advanced ant–plant mutualisms is represented by myrmecophytes sheltering colonies of some plant-ant species in hollow structures called domatia. In turn, the myrmecophytes benefit from biotic protection and sometimes nutrient provisioning (myrmecotrophy). Furthermore, over the course of evolution, some ant species have become social parasites of others. In this general context, we studied the relationship between its host trees and Azteca andreae (Dolichoderinae), a temporary social parasite of the plant-ant Azteca ovaticeps, and, as such, obligatorily associated with myrmecophytic Cecropia obtusa trees (Urticaceae). A first experiment showed that the δ15N values of the young leaves of Cecropia sheltering a mature A. andreae colony were very similar to those for trees sheltering Azteca alfari or A. ovaticeps, two typical Cecropia mutualists for which myrmecotrophy is known. In a second experiment, by injecting a 15N-labelled glycine solution into locusts given as prey to A. andreae colonies, we triggered an increase in δ15N in the young leaves of their host Cecropia. Thus, 15N passed from the prey to the host trees, explaining the outcomes of the first experiment. We discuss these results in light of the notion of ‘by-product benefits’.