Abstract: Micrometeorological measurements of night time ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397-403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (F-C) and change in storage (F-S) of CO2 in the few hours after sundown. The sum of F-C and F-S reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration R-Rmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of F-c + F-s extrapolated to zero light, R-LRC, and (3) with a detailed process-based forest ecosystem model, R-cast. At most sites respiration rates estimated using the u*-filter, R-ust, were smaller than R-Rmax, and R-LRC. Agreement of our approach with independent measurements indicates that R-Rmax, provides an excellent estimate of nighttime ecosystem respiration. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Knowledge of the jaguar population is needed in French Guiana that faces an increase of human-jaguar conflicts. We carried out a camera trap survey to assess jaguar local density and home range size in a preserved coastal area of French Guiana. We ran spatially explicit capture recapture (SECR) models. In our model, the scale parameter σ, that is linked to the home range size, was larger for males (σ=3.87±0.59 SE km) than for females (σ=2.33±0.30 SE km). The assessed jaguar density was 3.22±0.87 SE ind. 100 km â '2, which should be considered as an optimal density in a French Guiana coastal area.

Abstract: The accuracy of a ThetaProbe (Delta-T Devices Ltd, UK) to obtain repeated measures of soil water content in pot plants was tested. This alternative to balance determinations led to a large underestimation of water content, varying from 12.2 to 21.8% of the total water content, depending on soil type.

Abstract: Microbial organisms support the high species diversity associated with tropical forests, and likely drive functional processes, but microorganisms found in rainforest canopies are not well understood. We quantified the microbial diversity of suspended soils from two classical epiphytic model systems (bromeliads & bird's nest ferns) across two localities: the Nouragues Reserve in French Guiana and Danum Valley in Malaysian Borneo. Non-epiphytic suspended soils were also collected as controls at the Nouragues Reserve. Effects of epiphyte type and sample location on microbial community composition were determined using Phospholipid Fatty Acid (PLFA) analysis. Total microbial biomass remained constant across the suspended soil types, but PLFA peaks denoting the relative abundance of different microbes varied between bromeliads, bird's nest ferns and non-epiphytic control soils. Suspended soils associated with bird's nest ferns from Borneo contained a microbial community significantly different in composition from those of congeneric bird's nest ferns from Amazonia, due to shifts in the relative abundance of fungi and bacteria. Our findings reveal that epiphytes create convergent niches for microorganisms in tropical canopies, while highlighting the sensitive nature of suspended soil microbial communities. © 2020 Elsevier Masson SAS

Abstract: 1.Regional above-ground biomass estimates for tropical moist forests remain highly inaccurate mostly because they are based on extrapolations from a few plots scattered across a limited range of soils and other environmental conditions. When such conditions impact biomass, the estimation is biased. The effect of soil types on biomass has especially yielded controversial results. 2.We investigated the relationship between above-ground biomass and soil type in undisturbed moist forests in the Central African Republic. We tested the effects of soil texture, as a surrogate for soil resources availability and physical constraints (soil depth and hydromorphy) on biomass. Forest inventory data were collected for trees ≥20cm stem diameter in 2754 0.5ha plots scattered over 4888km2. The plots contained 224 taxons, of which 209 were identified to species. Soil types were characterized from a 1:1000000 scale soil map. Species-specific values for wood density were extracted from the CIRAD's data base of wood technological properties. 3.We found that basal area and biomass differ in their responses to soil type, ranging from 17.8m2ha-1 (217.5tha-1) to 22.3m2ha-1 (273.3tha-1). While shallow and hydromorphic soils support forests with both low stem basal area and low biomass, forests on deep resource-poor soils are typically low in basal area but as high in biomass as forests on deep resource-rich soils. We demonstrated that the environmental filtering of slow growing dense-wooded species on resource-poor soils compensates for the low basal area, and we discuss whether this filtering effect is due to low fertility or to low water reserve. 4.Synthesis. We showed that soil physical conditions constrained the amount of biomass stored in tropical moist forests. Contrary to previous reports, our results suggest that biomass is similar on resource-poor and resource-rich soils. This finding highlights both the importance of taking into account soil characteristics and species wood density when trying to predict regional patterns of biomass. Our findings have implications for the evaluation of biomass stocks in tropical forests, in the context of the international negotiations on climate change. © 2011 The Authors. Journal of Ecology © 2011 British Ecological Society.