Improvement of simple impedance tomography method in RF range for estimating moisture distribution in squared timbers

Improvement of the simple tomography method for estimating moisture distribution in squared timbers was conducted by using impedance measurement in the RF range at 250 kHz. The local impedance in the horizontal and vertical directions was measured during natural drying. An inverse procedure using a trial-and-error method was used to reconstitute the cross-sectional moisture distribution from the surface impedance measurement. Two essential corrections for the spatial heterogeneity of the electric field between electrodes and for the calculation error due to the algorithm of the trial-and-error method were introduced to improve the accuracy of the reconstitution of the moisture distribution. The reconstituted moisture distribution matched well that determined by the oven-dry method.     

Anatomically informed mesoscale electrical impedance spectroscopy in southern pine and the electric field distribution for pin-type electric moisture metres

Abstract

Electrical impedance spectra of wood taken at macroscopic scales below the fibre saturation point have led to inferences that the mechanism of charge conduction involves a percolation phenomenon. The pathways responsible for charge conduction would necessarily be influenced by wood structure at a variety of sub-macroscopic scales – at a mesoscale – but these questions have not yet been addressed. The goal of this work is to explore if mesoscale anatomical features in wood affect impedance spectra. Small (0.5 mm diameter) needles were used as electrodes and were configured such that the line segment between the electrodes could be oriented radially, tangentially, longitudinally and in combinations of those directions in both earlywood and latewood, including comparisons of earlywood–latewood transitions. The spectra were fit to an equivalent circuit model with a constant phase element in parallel with a resistor and Warburg element that describes ionic conduction. Finite element simulations were run to examine the effect of the fringing electric field near the electrodes. The simulations revealed that the current density was concentrated at the electrodes, resulting in a lack of dependence on electrode spacing thus explaining why measurements taken with pin-type electric moisture metres are nearly independent of electrode geometry.     

New monitoring concept of moisture content distribution in wood during RF/vacuum drying

A new method for monitoring moisture content during radio-frequency (RF)/vacuum drying was developed by measurement of temperature and pressure in wood. Temperature and pressure inside the wood were measured simultaneously during RF/vacuum drying at the same point. The relative humidity (RH) and moisture content (MC) below the fiber saturation point (FSP) were calculated based on temperature and pressure, and the relationship between the temperature, RH, and equilibrium moisture content (EMC) at the measurement point. When the moisture content was below the FSP, the calculated MC was slightly greater than the value given by oven drying. The absolute error was within 0.8% near the open cross side, and was within 1.8% at another measurement point. Thus, we concluded that it was practicable to monitor the moisture content below the FSP according to the temperature and pressure inside the wood. Part of this study was presented at the 15th Annual Meeting of the Chugoku Shikoku Branch of the Japan Wood Research Society, Higashi-Hiroshima, Japan, September 2003     

A microwave applicator for on line wood drying: Temperature and moisture distribution in wood

Summary An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy, meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the position of each applicator in a larger scale microwave pilot plant. Received 25 February 1997     

Spatial distribution and influence of large woody debris in an old-growth forest river system, New Zealand

A field survey was undertaken to determine the quantity, spatial distribution and influence of large woody debris (LWD) in a fifth-order river system in old-growth forest in New Zealand. LWD attributes were assessed at 25 sites distributed in the headwaters and along the main stem of the Whirinaki River system (73 km²). LWD volume, number of pieces, piece length and piece size, were positively correlated with bankfull width, whereas the number of pieces/unit area, LWD/unit area, number of pieces suspended across the channel and LWD influence on channel morphology, were negatively correlated. Pieces influencing channel morphology were larger, longer and more stable than average. We identified four key zones in the river system based on LWD spatial distribution patterns and influence on habitat complexity. Zonal boundaries occurred where there were changes in the transport capacity, fluvial processes, channel width and geomorphic structure of the channel. The results of this study highlight the need to understand the characteristics, spatial distribution patterns and influence of LWD at the catchment level when undertaking protective, management or rehabilitation programmes in forested river ecosystems.     

Diurnal and seasonal variability in radial distribution of sap flux density: Implications for estimating stand transpiration

Daily and seasonal patterns in radial distribution of sap flux density were monitored in six trees differing in social position in a mixed coniferous stand dominated by silver fir (Abies alba Miller) and Norway spruce (Picea abies (L.) Karst) in the Alps of northeastern Italy. Radial distribution of sap flux was measured with arrays of 1-cm-long Granier probes. The radial profiles were either Gaussian or decreased monotonically toward the tree center, and seemed to be related to social position and crown distribution of the trees. The ratio between sap flux estimated with the most external sensor and the mean flux, weighted with the corresponding annulus areas, was used as a correction factor (CF) to express diurnal and seasonal radial variation in sap flow. During sunny days, the diurnal radial profile of sap flux changed with time and accumulated photosynthetic active radiation (PAR), with an increasing contribution of sap flux in the inner sapwood during the day. Seasonally, the contribution of sap flux in the inner xylem increased with daily cumulative PAR and the variation of CF was proportional to the tree diameter, ranging from 29% for suppressed trees up to 300% for dominant trees. Two models were developed, relating CF with PAR and tree diameter at breast height (DBH), to correct daily and seasonal estimates of whole-tree and stand sap flow obtained by assuming uniform sap flux density over the sapwood. If the variability in the radial profile of sap flux density was not accounted for, total stand transpiration would be overestimated by 32% during sunny days and 40% for the entire season.     

Land-use system modeling and analysis of shaded cacao production in Belize

Shaded cacao (Theobroma cacao) cultivation is a tropical land-use that has potential to reduce pressure on the forest and provide additional income to smallholder growers. A land-use system (LUS) model was formulated to represent the economic returns derived from shaded cacao production practiced by smallholders in the Toledo district of Belize. Sixty scenarios were tested to elicit response of net-present-value (NPV), returns to labor, and annual returns to land (ARTL) to individual changes in 10 system parameters. Further scenarios tested the combined interactions between hardwood shade tree type, planting density, time to harvest hardwoods, cacao cultivation practice, and expected output. As a modeling exercise, LUS analysis highlights system components that government agencies, donors, NGOs, extension agents, and smallholders should target with policies, agri-silvi- culture projects, and further research. Results identify more favorable credit, labor-saving technology, better shade-management practices, grafting, and incorporating non-hardwood shade trees and laurel (Cordia alliadora) as interventions that could improve cacao financial performance and encourage adoption. At present, the model cannot predict whether smallholders would respond to recommendations and invest in shaded cacao cultivation in lieu of alternative agricultural land-uses or off-farm employment.     

Soil moisture and water use by pastures and silvopastures in a sub-humid temperate climate in New Zealand

Soil moisture content from 0 to 2 m depth was monitored under 2–6 year old radiata pine (Pinus radiata) with three understoreys of bare ground, lucerne (Medicago sativa) and ryegrass/clover (Lolium perenne/Trifolium spp.) and under adjacent open-grown lucerne and ryegrass/clover pastures. By the fifth year soil moisture depletion/recharge pattern under the trees alone was similar to that under open pasture and under trees with pasture understoreys. Maximum plant available moisture storage was 207–223 mm in the top meter of this Templeton silt loam soil but only 69–104 mm at 1–2 m depth where coarse textures often predominated. Lucerne reduced soil moisture content (SMC) to lower levels during drier summers and extracted more water from 1 to 2 m depth than ryegrass/clover. Evapotranspiration (ET) during early summer when soil moisture was high was close to the Penman potential evapotranspiration (E _p ), but the difference increased when SMC in the top meter dropped below 200 mm. The silvopasture treatments had higher ET in winter than pasture alone but this was still less than E _p . Soil moisture deficits (SMD) at the end of each summer were sufficiently large to require slightly higher than normal winter rainfall and ET < E _p to recharge the soil to field capacity before the next summer. The soil moisture results, taken together with root and growth data, suggest that trees and understorey pastures are complementary in the first three or four growing seasons but this balance subsequently declines in favor of the pine trees. Management options, to extend the period that understorey pastures are productive, include reducing tree stockings, more vigorous pruning, using competitive understoreys and changing from pines to deciduous trees. Research on new silvopastoral combinations is suggested.     

Soil properties under a Pinus radiata – ryegrass silvopastoral system in New Zealand. Part I. Soil N and moisture availability, soil C, and tree growth

Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability, soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury, New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9 and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer. No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater in the bare ground treatment, reflecting better soil moisture and N supply conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Root distribution and interactions in jujube tree/wheat agroforestry system

Even though agronomists have considered the spatial root distribution of plants to be important for interspecific interactions in agricultural intercropping, few experimental studies have quantified patterns of root distribution and their impacts on interspecific interactions in agroforestry systems. A field experiment was conducted to investigate the relationship between root distribution and interspecific interactions between intercropped jujube tree (Zizyphus jujuba Mill.) and wheat (Triticum aestivum Linn.) in Hetian, south Xinjiang province, northwest China. Roots were sampled by auger in 2-, 4- and 6-year-old jujube tree/wheat intercropping and in sole wheat and 2-, 4- and 6-year-old sole jujube down to 100 cm depth in the soil profile. The roots of both intercropped wheat and jujube had less root length density (RLD) at all soil depths than those of sole wheat and jujube trees. The RLD of 6-year-old jujube intercropped with wheat at different soil depths was influenced by intercropping to a smaller extent than in other jujube/wheat intercropping combinations. 6-year-old jujube exhibited a stronger negative effect on the productivity of wheat than did 2- or 4-year-old jujube and there was less effect on productivity of jujube in the 6-year-old system than in the 2- or 4-year-old jujube trees grown in monoculture. These findings may partly explain the interspecific competition effects in jujube tree/wheat agroforestry systems.     

The distribution and interrelationship of collapse,volumetric shrinkage,moisture content and density in trees of Eucalyptus regnans F. Muell.

Summary The relationships among collapse, volumetric shrinkage, moisture content and basic density and their distribution within the stem were examined for trees of E. regnans. It was found that collapse and volumetric shrinkage each were significantly related to moisture content (positively), basic density (negatively), and (positively) to the derived values P (per cent of theoretical saturation) and Q (per cent of cell cavity volume containing water). Notwithstanding the inverse association evident between moisture content and density in the living tree, moisture content was shown to be independently related to each of collapse and volumetric shrinkage.Within the stem, collapse and volumetric shrinkage were negatively correlated with height in the tree although the significance of this relationship was qualified by the adjustment for other variables. Samples containing sapwood displayed collapse values significantly lower than heartwood samples. This was reflected in the presence of a positive relationship between collapse and distance from the periphery when all material was considered, but a negative relationship when sapwood-containing samples were omitted. Basic density was positively correlated with height in the tree and negatively correlated with distance from the periphery. Moisture content, P and Q were negatively correlated with both height in the tree and distance from the periphery although the latter relationship for moisture content was dependent on adjustment for density.The highly significant relationship between volumetric shrinkage and collapse suggested that the former could confidently be used in assessing collapse severity. Moisture content was determined to be an independent indirect indicator of collapse whereas basic density, P, Q and green density could all be of indicatory value, especially the last in view of its ease of measurement.     

Comparison of moisture distribution along radial direction in a log cross section of heartwood and mixed sapwood and heartwood during radio-frequency/vacuum drying

The purpose of this study was to compare the distribution of moisture contents (MCs) along the radial direction during radio-frequency/vacuum (RF/V) drying of log cross sections of heartwood (HLC) where sapwood was removed from a green log cross section and log cross section of mixed sapwood and heartwood (MLC) prepared with debarked logs of Japanese larch (Larix leptolepis) and locust (Robinia pseudoacacia). For Japanese larch, an even distribution of MC was observed over the entire cross section in HLC not only at the initial stage of drying but also up to the completion of drying. Furthermore, the moisture gradient between the outermost slice and the adjacent inner slice was more gradual compared with that in MLC. For locust, the moisture gradient between the outermost slice and the adjacent inner slice became severe as drying progressed. It decreased after reaching the maximum during the middle stage of drying but continued until the late stage of drying. Furthermore, despite the fact that the average initial MC of mixed slice within MLC was higher compared with that in heartwood slice, this trend reversed immediately after drying started. It was suggested that the possibility of formation of border checking would be high during drying the MLC, since it would be so complicate that the sapwood and heartwood reach fiber saturation point together because of differences in their green MCs and permeability between them.     

Light distribution,photosynthetic rate and yield in a Paulownia-wheat intercropping system in China

Measurements of photosynthetically active radiation (PAR), leaf photosynthesis, canopy leaf area index (LAI) and crop yield were carried from flowering to maturity to study the effects of tree shading on crop yield in a Paulownia-wheat intercropping system in China. We found that the tree shading reduced the amount of incoming PAR within the intercropping system by 22%, 44% and 56% during flowering, grain-filling and maturing, respectively. The amount of PAR intercepted by the wheat crop inside the intercropping system was 34%, 55% and 68% less than the crop outside the intercropping system during flowering, grain-filling and maturing. Estimates of PAR-saturated leaf photosynthetic rate were not affected by tree shading, and the differences between the wheat yield inside the intercropping system and outside the intercropping system can be explained by the difference in the amount of PAR intercepted. Total grain numbers and grain dry weight per 1000 grains were linearly correlated with the amount of PAR intercepted during 7 days prior to anthesis and during anthesis and grain-filling, respectively. As compared with the wheat crop outside the intercropping system, grain numbers and grain dry weight were reduced by 36% and 25%, respectively. As a result wheat yield inside the intercropping system was 51% lower than that outside the intercropping system. Our results suggest a much higher reduction in crop yield and much smaller economic gain of the Paulownia-wheat intercropping system than previous studies on the similar Paulownia-wheat intercropping systems in China.     

Forest-floor temperatures and soil moisture across riparian zones on first- to third-order headwater streams in southern New England,USA

Riparian zones along forest streams in the western United States have been repeatedly shown to be floristically and climatically different from adjacent upland forest, and to be important contributors to forest biodiversity. Similar evidence for the presence or function of riparian zones is lacking for forests of the northeastern U.S. We conducted seasonal surveys of forest-floor temperature and soil moisture across 30-m riparian transects on first- to third-order streams in southern New England. We were unable to detect any effect of distance from the stream channel on either temperature or soil moisture. These preliminary results indicate the absence of a unique riparian forest-floor microclimate within 30 m of low-order streams in southern New England. While this study failed to identify a distinctive riparian microclimatic zone, protection of a riparian buffer during forestry operations or other disturbance is essential for the protection of forest streams and their resources and the maintenance of forest biodiversity.     

金沙江干热河谷不同土壤水分对台湾青枣根系生长的影响

通过田间试验研究了不同水分处理下台湾青枣根系的分布状况,调查分析了不同径级根系数量、根系含水率、根系密度等项目。结果表明:台湾青枣根系主要分布在0-60 cm的土壤中,根系数量随土壤含水量的降低而增加,但根系含水率则是随着土壤含水量的增加而增加,而根系数量则随着土壤含水量的减少而增多的特征。因此,A处理(土壤含水量为田间持水量的40%-55%)是台湾青枣生长的最适水量,通过人为控制土壤含水量,以此调节根系生长与空间分布,最终达到调控作物生长和产量。     

林业有害生物危害状分类及在网络森林医院系统中的应用

概述了林业有害生物危害状分类现状及进展,分析了网络森林医院系统中林业有害生物危害状分类存在的问题,对林业有害生物危害状分类提出了改进建议,并对林业有害生物危害状编码化管理提出了设想.     

Fine root distribution of pruned trees and associated crops in a parkland system in Burkina Faso

Besides aboveground interactions, pruning of trees may also modify their rooting pattern for which a better understanding is needed for the optimisation of agroforestry systems. Thus, variation in fine root (d 2 mm) distribution of pruned trees and crops were assessed during three cropping seasons by sampling soil layers at 10 cm intervals up to 50 cm and at four distances from tree trunk. Three crown pruning treatments (totally-pruning, half-pruning and no-pruning) were applied to karité (Vitellaria paradoxa) and néré (Parkia biglobosa). In 1999, 59% (0.477 cm cm^–3) and 69% (0.447 cm cm^–3) of fine roots for karité and néré respectively occurred in the upper 20 cm with a significant decrease in root length density with soil depth. However, in 2000, totally-pruned trees of néré and karité showed 32% (0.051 cm cm^–3) and 34% (0.078 cm cm^–3) of their density in the upper 20 cm whereas root distribution in 2001 was similar to that of 1999. Thus, pruning to reduce belowground competition for the benefit of associated crops can be recommended in the light of the temporary reduction of root density in crop rooting zone and consequently the increase in crop production.This revised version was published online in November 2005 with corrections to the Cover Date.     

Spatial and temporal distribution of earthworms in a temperate intercropping system in southern Ontario, Canada

Earthworms are known to increase soil bulk density, soil porosity, mixing of organic matter, and to strengthen aggregation of soil particles. They perform important functions in the maintenance and stabilization of the soil matrix. Historically, temperate intercropping research has focused on the above-ground benefits of adding trees into the agricultural landscape. Earthworm research in temperate intercropping systems has been non-existent to date. More emphasis on studying below-ground components, such as earthworms, is required in order to better understand the mechanisms of intercropping ecosystem function. The purpose of this study was to examine seasonal changes in distribution and abundance of earthworms under a temperate intercropping system in southwestern Ontario, Canada. Sampling occurred during the spring and summer of 1997 at the University of Guelph's Agroforestry Research Station, Guelph, Ontario. Earthworm samples were collected at various distances from the tree rows. Significant variation in both earthworm biomass and density were found between the three tree species sampled. Total mean earthworm density was 182 m^-2 within the poplar rows, 71 m^-2 within the silver maple rows, and 90 m^-2 within the white ash rows. A marked difference was also observed in the distribution of earthworms within the tree rows and the field area. For example, total mean density within the tree rows for poplar was 182 individuals m^-2, as compared to total mean densities of 117 and 95 individuals m^-2, two metres and six metres into the field from the tree, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

城镇污水处理厂供配电系统分析

污水处理已成为城市建设中必不可少的环节,所以对相应的配套工程也提出了更高的要求,本文将对污水处理厂的供配电系统进行简要的分析。