Modeling the influence of thermal modification on the electrical conductivity of wood

A model has been developed aiming at the description of the effect of thermal modification on the electrical conductivity of wood. The intention was to calculate the moisture content (MC) of thermally modified timber (TMT) through the parameters electrical resistance R, wood temperature T, and CIE L*a*b* color data, which are known to correlate well with the intensity of a heat treatment. Samples of Norway spruce (Picea abies Karst.) and beech (Fagus sylvatica L.) samples were thermally modified in laboratory scale at 11 different heat treatment intensities and the resistance characteristics of the samples were determined. Within the hygroscopic range, a linear relationship between the resistance characteristics and the mass loss (ML) through the heat treatment was established. Based on this, a model was developed to calculate MC from R, T, and ML. To validate this model, color values of 15 different TMTs from industrial production were determined for estimation of their ML and fed into the model. MC of the 15 arbitrarily heat-treated TMTs was calculated with an accuracy of ±3.5% within the hygroscopic range. The material-specific resistance characteristics based on experimental data led to an accuracy of ±2.5%.

Light absorption by organic carbon from wood combustion

Carbonaceous aerosols affect the radiative balance of the Earth by absorbing and scattering light. While black carbon (BC) is highly absorbing, some organic carbon (OC) also has significant absorption, especially at near-ultraviolet and blue wavelengths. To the extent that OC absorbs visible light, it may be a non-negligible contributor to positive direct aerosol radiative forcing. Quantification of that absorption is necessary so that radiative-transfer models can evaluate the net radiative effect of OC. In this work, we examine absorption by primary OC emitted from solid fuel pyrolysis. We provide absorption spectra of this material, which can be related to the imaginary refractive index. This material has polar character but is not fully water-soluble: more than 92% was extractable by methanol or acetone, compared with 73% for water and 52% for hexane. Water-soluble OC contributes to light absorption at both ultraviolet and visible wavelengths. However, a larger portion of the absorption comes from OC that is extractable only by methanol. Absorption spectra of water-soluble OC are similar to literature reports. We compare spectra for material generated with different wood type, wood size and pyrolysis temperature. Higher wood temperature is the main factor creating OC with higher absorption; changing wood temperature from a devolatilizing state of 210 °C to a near-flaming state of 360 °C causes about a factor of four increase in mass-normalized absorption at visible wavelengths. A clear-sky radiative transfer model suggests that, despite the absorption, both high-temperature and low-temperature OC result in negative top-of-atmosphere radiative forcing over a surface with an albedo of 0.19 and positive radiative forcing over bright surfaces. Unless absorption by real ambient aerosol is higher than that measured here, it probably affects global average clear-sky forcing very little, but could be important in energy balances over bright surfaces.

Aquatic arthropods and forestry: effects of large-scale land use on aquatic systems in Nearctic temperate regions

Aquatic arthropods can be affected by forest management through increased amounts of light, discharge, and sediment runoff, alteration of the supply of basal resources, changes in the supply of large wood, temperature modifications, and food-web effects. This syndrome of alterations varies geographically in magnitude, and the specific details depend on initial biotic and abiotic conditions, local topography, climate, and the particular management practices used. Impacts on standing water appear to be subtle, and most attention has focussed on streams, where changes are often more obvious. The intensity of any changes in processes affecting aquatic arthropods depends, in part, on the proximity of logging to the shoreline and the proportion of watershed harvested, and also on the condition and frequency of forest access roads crossing or near water bodies. Some groups of species are particularly vulnerable, but others, particularly generalist species such as some Baetis Leach (Ephemeroptera: Baetidae) and some Chironomidae (Diptera), appear to benefit from harvesting. In general, outcomes of harvesting near streams are temporary increases in production and abundance but reductions in diversity. Impacts on all trophic levels, especially in streams, can occur from forest harvesting. The primary tool for mitigating these impacts is the use of riparian buffers, but there are still major uncertainties about the effectiveness of specific widths and configurations of buffers and their use for additional types of disturbance.