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.     

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     

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 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.     

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.     

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。     

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.     

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。     

Poplar leaf biomass distribution and nitrogen dynamics in a poplar-barley intercropped system in southern Ontario, Canada

The effect of hybrid poplar (Populus spp. clone DN 177) leaf biomass distribution on soil nitrification was investigated in two experiments during the 1993, 1994 and 1995 growing seasons in a poplar-barley (Hordeum vulgare cv. OAC Kippen) intercropping experiment established at Guelph, Ontario, Canada. In experiment 1, poplar was intercropped with barley during all three years and the poplar leaves shed during the fall season were removed from the soil surface during 1993 and 1994. In experiment 2, poplar was intercropped with barley in 1993 and with corn (Zea mays cv. Pioneer 3917) in 1994 an 1995, respectively, and the shed poplar leaves were not removed. In experiment 1, the nitrification rates were lower during 1994 and 1995 when the dropped leaves were removed from the field. The total above-ground biomass of barley within 2.5 m of the tree row was 517, 500 and 450 g×m⁻², respectively during the three years, whereas in the middle of the crop row (4–11 m), the corresponding figures were 491, 484 and 464 g×m–2. Mean nitrification rates, N availability and carbon content were higher in soils close to the poplar tree rows (2.5 m) compared to the corresponding values in the middle of the crop alley (4–11 m from the tree row). In experiment 2, where poplar leaves were not removed from the field, nitrification rates in soils within 2.5 m distance from the poplar row were fairly constant (range 100 to 128 μg 100 g⁻¹ dry soil day⁻¹) during the three years. Results suggest that soil nitrification rates, soil carbon content and plant N uptake adjacent to the poplar tree rows are influenced by poplar leaf biomass input in the preceding year. This revised version was published online in June 2006 with corrections to the Cover Date.     

Early growth and quality of radiata pine in a silvopastoral system in New Zealand

The effect of different understoreys on the early growth and quality of radiata pine (Pinus radiata) in a silvopastoral system was evaluated in Canterbury, New Zealand. Fitted models successfully represented the effect of understorey on the growth (basal area and height) and a quality of trees (diameter over stubs). Basal area, diameter, height and volume growth were affected by understorey competition. Trees growing with no-understorey had 34%and 29% higher volume than trees growing with lucerne (Medicagosativa) and cocksfoot (Dactylis glomerata)understoreys, respectively. However, the height of trees at age 10 grown without understorey competition was only 9% and 15% more than trees grown with grass and lucerne understorey, respectively. Understorey competition effects on growth became more evident during the summer and early autumn months when water deficits occurred. The quality of trees was also affected by understorey competition. While trees grown in bare ground had higher growth than trees grown with understorey competition, they had the poorest stem quality with higher diameters over stubs, branch size, sweep and proportion of stem defects. This will have an impact on the agroforestry system profitability by affecting the net harvest revenue. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth, herbivore distribution, and herbivore damage of timber trees in a tropical silvopastoral reforestation system

Context

The reforestation of degraded tropical pastures requires innovative tree planting systems that consider land user needs.

Aim

We established a silvopastoral reforestation system and assessed the effects of companion trees on the native timber tree Tabebuia rosea in Panama. Timber tree individuals were established in (1) solitary plantings (TSol) or in companion plantings with (2) Guazuma ulmifolia (TGua) or (3) the nitrogen-fixing Gliricidia sepium (TGli).

Methods

We quantified growth characteristics and herbivory of T. rosea, and analyzed leaf chemistry (including the stable isotopes ??¹⁵N and ??¹³C) and structure (leaf mass per area).

Results

Companion trees significantly affected stem diameter growth of T. rosea. Stem diameter growth was as high in TGli trees as in TSol trees but was reduced in TGua trees. Furthermore, TGua trees had higher leaf water content, and lower ??¹³C and lower leaf mass-to-area ratio than TGli trees, suggesting there were effects of shading by G. ulmifolia on T. rosea. Herbivory was high but not affected by planting regimes. Leafing phenology did not differ between planting regimes and G. sepium did not increase nitrogen content in T. rosea leaves.

Conclusion

Companion tree planting can support timber tree growth in silvopastoral reforestations, but adequate species selection is crucial for successful implementation of this planting system. Tree?Ctree interactions seem to be more relevant for timber tree growth than herbivory in the studied system.     

Biomass production and root distribution of Gmelina arborea under an agrisilviculture system in subhumid tropics of Central India

A study of an agrisilviculture system comprising Gmelina arborea and soybean (Glycine max) was conducted in the subhumid region of Central India. Above- and below-ground biomass production and distribution of coarse and fine roots were studied in 4-year-old G. arborea, planted at a spacing of 2 × 2 m, 2 × 3 m, 2 × 4 m and 2 × 5 m. The total biomass varied from 10.89 Mg ha^–1 to 3.65 Mg ha^–1 depending on the tree density. Among the different tree components, stemwood contributed maximum biomass (54.3–79.4%), followed by branches and leaves. Root distribution pattern showed that most of the coarse roots were distributed in the top 40 cm of soil, whereas fine roots were concentrated in the top 20 cm. Coarse root biomass decreased with an increase in spacing. The spread of roots was asymmetrical in trees planted at 2 × 2 m and 2 × 3 m spacings, while it was symmetrical in trees planted at wide spacings. No significant difference was observed in the fine root biomass in different stands. The root:shoot ratio increased with an increase in spacing. Crop (soybean) growth and productivity varied significantly and it increased with a decrease in tree density. Soybean yield varied between 1.5 Mg ha^–1 to 2.1 Mg ha^–1. The role of root architecture of G. arborea trees on productivity of crops under agri-silviculture system is discussed.     

The relationship between shelterwood cuts and crown thinnings and the abundance and distribution of birds in a southern New England forest

Forest regeneration methods such as shelterwood treatments have been shown to substantially increase the diversity of bird species, specifically of species that prefer early seral forests, now rare in the eastern United States. Stand improvement techniques such as thinnings have also been found to increase avian diversity under some conditions. A sustainably managed forest, however, must simultaneously apply regenerative harvesting with stand improvements, and the effect of such treatment combinations on bird community composition is not clear. We compared bird distribution and abundance on shelterwood cuts, crown thinnings, and unmanaged stands at the Yale Myers Forest, a large privately owned and actively managed forest in southern New England. Bird abundance and species diversity was highest in shelterwood cuts and lowest in unmanaged forest, with thinnings being intermediary. Different suites of species inhabited the three treatments, with 18 of 49 common species differing significantly in their abundances between treatments. Characteristics of the vegetation that were directly influenced by silvicultural intervention, including canopy openness, seedling regeneration and vertical structural diversity, appeared to be the dominant drivers of bird abundance. The abundances of some species or groups of species were correlated with the number of trees retained in the implementation of the forestry practices. In conjunction with the conservation of a variety of mature forest habitats, regenerative cuts and stand improvement techniques can be used together to sustain a diverse assemblage of bird species.     

Effects of flow rate and chamber position on measurement of stem respiration rate with an open flow system in a Japanese red pine

The effects of air flow rate and chamber position on measuring stem respiration rate (R_stem) were examined using an open flow system on six Japanese red pine (Pinus densiflora Sieb. and Zucc) trees. R_stem was more closely correlated with stem temperature observed 2–6 h earlier than with current stem temperature. R_stem was not affected by the air flow rate passing through the stem chamber. Although there were no differences in stem temperatures between azimuth angles, there were significant differences in R_stem between azimuth angles (except for only one case) of each sample stem. The distance from below the bark to the stem centre varied at each azimuth in the samples, and was significantly positively correlated with R₀ (p < 0.01). The chamber type did not affect the measurement of stem respiration, because the mean R_stem of four azimuth angles measured with in a rectangular chamber was almost the same as R_stem measured with in a circular chamber. From these results, we suggest that a whole circumference estimate made by either:

(1) measuring stem respiration at each azimuth separately with a rectangular chamber, or

(2) measuring the total CO₂ efflux from the whole radial circumference with a circular chamber,

must be conducted for scaling-up chamber measurements to individual or stand level.