Abstract: Accurate CO2 concentration gradient measurements are needed for the computation of advective flux terms, which are part of the full Net Ecosystem Exchange (NEE) budget equation. A typical draw back of current gradient measurement designs in advection research is the inadequate sampling of complex flow phenomena using too few observation points in space and time. To overcome this draw back, a new measurement design is presented which allows the parallel measurement of several sampling points at a high frequency. Due to the multi-analyzer nature of the design, inter-instrument bias becomes more of a concern compared to conventional setups. Therefore a statistical approach is presented which allows for accurate observations of concentration gradients, which are typically small in relation to analyzer accuracy, to be obtained. This bias correction approach applies a conditional, time dependent signal correction. The correction depends on a mixing index based on cross correlation analysis, which characterizes the degree of mixing of the atmosphere between individual sample points. The approach assumes statistical properties of probability density functions (pdf) of concentration differences between a sample point and the field average which are common to the pdf's from several sample points. The applicability of the assumptions made was tested by Large Eddy Simulation (LES) using the model PALM and could be verified for a test case of well mixed conditions. The study presents concentration time series before and after correction, measured at a 2 m height in the sub-canopy at the FLUXNET spruce forest site Waldstein-Weidenbrunnen (DE-Bay), analyzes the dependence of statistical parameters of pdf's from atmospheric parameters such as stratification, quantifies the errors and evaluates the performance of the bias correction approach. The improvements that are achieved by applying the bias correction approach are one order of magnitude larger than possible errors associated with it, which is a strong incentive to use the correction approach. In conclusion, the presented bias correction approach is well suited for – but not limited to – horizontal gradient measurements in a multi-analyzer setup, which would not have been reliable without this approach. Finally, possible future improvements of the bias correction approach are outlined and further fields of application indicated.

Abstract: Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization of wood fibres cell wall structure.

Abstract: Because of their ecological characteristics, slow growth rates and the presence of contaminants, Chaetothyriales fungi associated with structures built by tropical plant-ants can be difficult to isolate with standard procedures. Here, we describe an easy-to-use protocol for obtaining pure cultures by using cotton as a first substrate. We have further found by means of fluorescent stains that nuclei concentrate either in young hyphae or in the tips of the hyphae. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract: Selective logging applied in tropical forests is based on one universal criterion: a minimum diameter cutting limit for all commercial timber species. Minimum diameter cutting limits in mixed dipterocarp forests of the Malesia region lead to high felling intensities (10-20+ trees ha(-1)). Such extraction rates create massive stand damage (> 50% of the remaining tree population), which has a negative impact on the regeneration and growth of many harvested dipterocarp, species. As such, the minimum diameter cutting limit approach is seldom compatible with sustainable forest management. Where basic ecological characteristics of the commercial species are considered in timber harvesting prescriptions, mixed dipterocarp, forests appear capable of sustained timber yields, habitat conservation, and providing other goods and services. This paper first presents the main silvicultural systems developed in mixed dipterocarp, forests of Western Malesia and then reviews current knowledge of dipterocarp, biology to finally develop guidelines aimed at improving the ecological sustainability of production forests of Western Malesia. These guidelines, a pragmatic reflection of science and 'best guess' judgement, include: (1) integration of reduced-impact logging practices into normal management operations; (2) cutting of eight trees ha(-1) or less (with a felling cycle of 40-60 years to be determined according to local conditions); (3) defining minimum diameter cutting limits according to the structure, density and diameter at reproduction of target species; (4) avoiding harvesting species with less than one adult tree ha(-1) (diameter at breast height [dbh] greater than or equal to 50 cm over an area of 50-100 ha); (5) minimizing the size and connectivity of gaps (< 600 m(2) whenever possible); (6) refraining from treatments such as understorey clearing; and (7) providing explicit protection for key forest species and the ecological processes they perform. Further refinement is encouraged to allow for local conditions, and for other forest types.

Abstract: Reduced-impact logging (RIL) and conventional techniques (CNV) were compared in a mixed dipterocarp hill forest in East Kalimantan in three blocks of about 100 ha each. Damage was evaluated using pre- and post-harvesting assessments in 24 one-hectare sample plots. RIL techniques nearly halved the number of trees destroyed (36 vs 60 trees/ha). RIL's main benefit was in the reduction of skidding damage (9.5% of the original tree population in RIL vs 25% in CNV). Before logging, mean canopy openness in CNV (three plots only) and RIL (9 plots) was similar (3.6 and 3.1%) and not significantly different (x(2) = 2.73, P = 0.254). After logging, the mean canopy openness was 19.2% in CNV (n = 9 plots) and 13.3% in RIL (n = 8 plots), and the distributions of the canopy class in RIL and CNV significantly different x(2) = 43.56, P < 0.001). CNV plots showed a higher proportion of measurements in the most open class greater than or equal to30% than in RIL. At a larger scale, the area of skidtrail per unit timber volume extracted was halved in the RIL compartment (15 m(2) vs 27 m(2) m(-3) for CNV). However, under high felling intensity (>8 trees/ha), both stand damage and canopy disturbance in RIL approached those recorded in CNV under low or moderate felling regime. Over this felling intensity threshold the effectiveness of RIL in reducing tree damage is limited. In mixed dipterocarp forest where harvestable timber density generally exceeds 10 trees/ha, a minimum diameter felling limit is clearly insufficient to keep extraction rates below 8 trees/ha. Based on these new results and previous studies in Borneo, we suggest three silvicultural rules: (1) to keep a minimum distance between stumps of ca. 40 m, (2) to ensure only single tree gaps using directional felling, (3) to harvest only stems with 60-100 cm dbh. Foresters, policy makers and certifiers should consider these as criteria for sustainable forest management. We emphasise the need to expand harvesting studies to look at impacts and trade-offs across larger forest landscapes, to expand RIL beyond silvicultural concepts and to include the maintenance of other forest goods and services. (C) 2002 Elsevier Science B.V. All rights reserved.