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991.
A NMR study of water distribution in hardwoods at several equilibrium moisture contents 总被引:1,自引:0,他引:1
The water state of one tropical (Robinia coccinea) and two temperate (Acer saccharum and Fagus grandifolia) hardwoods was determined at different equilibrium moisture contents (EMC) during desorption at 25°C. NMR technique was used
to separate different components of water in wood. The species studied presented different structures, which were apparent
on the spin–spin relaxation T2 values. Three different water components were separated: slow T2 (liquid water in vessel elements), medium T2 (liquid water in fiber and parenchyma elements) and fast T2 (bound or cell wall water). The NMR results showed that even at equilibrated conditions a region exists where loss of liquid
water and bound water takes place simultaneously. This region will vary according to the wood structure. Finally, liquid water
was present at EMC lower than the fiber saturation point, which contradicts the concept of this point when considered as a
bulk property of wood. 相似文献
992.
Shigeru Yamauchi Yoichi Sakai Yasuo Watanabe Michael Kenya Kubo Hideaki Matsue 《Journal of Wood Science》2007,53(4):324-331
The distributions of boron in Japanese cedar (Cryptomeria japonica D. Don) sapwood blocks treated with aqueous or methanolic boric acid [B(OH)3] solutions were explored through Raman spectroscopy and prompt gamma-ray analysis (PGA). B(OH)3 was the sole boron species observed in Raman spectra of the wood blocks treated with either solution. Plots of weight gain
of the treated wood blocks versus boron concentration in treatment solutions were found to be linear. The results indicated
that the methanolic solution makes it possible to impregnate wood with much larger amounts of boron than the aqueous solution.
PGA confirmed that B(OH)3 was highly enriched near the end grains of the treated wood blocks. Raman measurements suggested that boron content in the
bulk of the wood block is not as large as expected from the weight gain of the treated wood blocks when an ordinary air-drying
method is used. It was concluded that the aqueous solution impregnates the cell walls of wood with boron more easily than
the methanolic solution.
Part of this report was presented at the 55th (Kyoto, March 2005) and 56th (Akita, August 2006) Annual Meetings of the Japan
Wood Research Society. This article follows the previous rapid communication “Analysis of boron in wood treated with boric
acid solutions using Doppler broadening method of prompt gamma-rays.” J Wood Sci (2006) 52:279–281 相似文献
993.
The effects of thermo-mechanical refining conditions on the properties of medium density fiberboard (MDF) made from black
spruce (Picea mariana) bark were evaluated. The bark chips were refined in the MDF pilot plant of Forintek Canada Corporation under nine different
refining conditions in which preheating retention time was adjusted from 3 to 5 to 7 min and steam pressure was set at either
0.6, 0.9 or 1.2 MPa. The resulting bark fibers were blended with 12% UF resin (based on oven-dry fiber weight) using a mechanical
blender. The resinated fibers were manually formed into fiber mats and hot-pressed into MDF panels using consistent parameters.
Two panels for each refining condition were produced, resulting in a total of 18 panels. Analysis of variance (ANOVA) was
used to analyze the significance of factors. Regression coefficients and 3D contour plots were used to quantify the relationship
between panel properties and the two test factors. The results from this study indicated that the preheating retention time
was a significant factor for both modulus of rupture (MOR) and modulus of elasticity (MOE), the steam pressure was a significant
factor for internal bond strength (IB), MOR and MOE, whereas both factors were insignificant for thickness swelling, water
absorption and linear expansion. The properties of MDF panels were quadratic functions of retention time and steam pressure.
Compared to the ANSI standard for 120-grade MDF, most panels with a nominal density of 950 kg/m3 had very high IB (>1 MPa) and acceptable MOR, MOE and dimension stabilities. These results suggest that black spruce bark
residues can be considered as a potentially suitable raw material for manufacturing MDF products. 相似文献
994.
Weston F. Mwase Åsmund Bjørnstad James M. Bokosi Moses B. Kwapata Brita Stedje 《New Forests》2007,33(3):297-307
Biodiversity is declining throughout southern African miombo woodlands due to poor land use practices that are detrimental
to soil, vegetation and habitat. We aimed at examining tree and shrub species diversity and distribution in Uapaca kirkiana-dominated woodlands under three land tenure types; forest reserves, customary and leasehold land. The study was conducted
at different forest sites within similar agroecological zone in southern Malawi. Study sites were located at a range of altitudes
between 900 and 1,200 m a.s.l. Three circular plots each with 32.60 m radius were established at each study site to sample
tree and shrub species composition, structure and distribution under three land tenure types. We found that forest reserves
had higher species diversity with an average of 16 tree families, 27 genera and 34 species as compared to only 10 tree families,
6 genera and 6 species on customary forest lands. Comparisons of diameter at breast height size class distributions showed
that customary land had significantly low numbers of small (5.0–10.0 cm) and very large (≥30 cm) diameter classes suggesting
lower levels of regeneration and high rate of anthropogenic activities. The high species diversity and richness in forest
reserves and leasehold land indicate high potential for protected lands to restore tree species diversity. It is concluded
that levels of human activities as influenced by land tenure type reduce tree species diversity, composition and distribution
at the different sites, and this confirms the hypothesis that open access lands are not compatible with conservation of tree
and shrub species diversity because of high anthropogenic activities. 相似文献
995.
Sanding is a common practice required in order to prepare wood surfaces for coating. Little literature is available regarding the effect of sanding parameters on the quality of surfaces. Sugar maple wood surfaces were evaluated in samples that had been sanded using two types of abrasive minerals, three grit sizes and four feed speeds. Roughness, wetting properties and cell damage were used to assess surface quality. Both abrasives decreased roughness and cell damage from 100- to 120-grit sanding stage. Addition of a 150-grit stage did not further reduce the roughness, whereas the cell damage continued to decrease. Increasing feed speed led to rougher surfaces due to higher fibrillation. Surfaces produced by silicon carbide were smoother and less damaged than those obtained with aluminum oxide. However, the surfaces sanded with aluminum oxide were more wettable and showed no significant difference in wetting time as a function of grit size. For these surfaces, the wetting time was reduced as feed speed increased.An erratum to this article is available at .An erratum to this article can be found at 相似文献
996.
Lili Zhou Addo-Danso Daniel Shalom Pengfei Wu Zongming He Chunhua Liu Xiangqing Ma 《林业研究》2016,27(2):357-368
Biomass production and nutrient (N, P, K, Ca and Mg) accumulation, distribution and cycling were quantified in young, mature and over-mature (10-, 22-, and 34-year old) Chinese fir [Cunninghamia lanceolate (Lamb.) Hook] plantations in southern China. Total stand biomass of young, mature and over-mature stands was 38, 104 and 138 t ha?1 respectively. Biomass production increased significantly with age. Stem wood represented the highest percentage of stand biomass, accounting for 41, 55 and 63 % in the young, mature and over-mature plantations respectively. Nutrients concentration was highest in live needles and branches, and lowest in stem wood. The plantations accumulated more N, followed by K, Ca, Mg, and P. Nutrient return amount, nutrient utilization efficiency, nutrient turnover time, the ratio of nutrient return and uptake increased with stand age, which implies that young Chinese fir deplete soil nutrients to maintain growth, and efficiently utilize nutrients to decrease dependence on soil nutrients as they age. Harvesting young Chinese fir plantations would therefore lead to high nutrient loss, but prolonging the rotation length could improve soil recovery, and help sustain productivity in the long-term. Improved nutrient return through litterfall as stands get older may also be beneficial to nutrient pool recovery. 相似文献
997.
Guangyu Wang Tongli Wang Haijun Kang Shari Mang Brianne Riehl Brad Seely Shirong Liu Futao Guo Qinglin Li John L. Innes 《林业研究》2016,27(3):469-488
Climate change is a threat to the stability and productivity of forest ecosystems throughout the Asia-Pacific region. The loss of forests due to climate-induced stress will have extensive adverse impacts on biodiversity and an array of ecosystem services that are essential for the maintenance of local economies and public health. Despite their importance, there is a lack of decision-support tools required to evaluate the potential effects of climate change on Asia-Pacific ecosystems and economies and to aid in the development of regionally appropriate adaptation and mitigation strategies. The project Adaptation of Asia-Pacific Forests to Climate Change, summarized herein, aims to address this lack of knowledge and tools and to provide support for regional managers to develop effective policy to increase the adaptive capacity of Asia-Pacific forest ecosystems. This objective has been achieved through the following activities: (1) development of a high-resolution climate downscaling model, ClimateAP, applicable to any location in the region; (2) development of climate niche models to evaluate how climate change might affect the distribution of suitable climatic conditions for regionally important tree species; (3) development and application of forest models to assess alternative management strategies in the context of management objectives and the projected impacts of climate change; (4) evaluation of models to assess forest fire risk and the relationship between forest fire and climate change; (5) development of a technique to assess ecosystem carbon storage using LiDAR; and (6) evaluation of how vegetation dynamics respond to climate change using remote sensing technology. All project outputs were developed with a focus on communication and extension to facilitate the dissemination of results to regional forest resource managers to support the development of effective mitigation and adaptation policy. 相似文献
998.
Extracts are important components of fuels.Fatty-extracts with high heating value(HV) are hypothesized by researchers as positively related to the HV of fuels.The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings,including long processing time(8–10 h) and the requirement for large amounts of organic solvent.Supercritical extraction is an alternate and useful technique for extraction of natural products.However,published studies rarely discuss the relationship between extracts and HV.In this study,we assessed the supercritical extracts(Su E) of forest fuels in the Great Xing'an Mountains.Our results indicated that the optimum conditions for extraction of Su Es were40–60 mesh,40–50 MPa,45 °C,80 min and a CO_2 flow rate of 1.5–2.0 dm~3/min.The Soxhlet extracts contents and the Su E contents were all related to HV.However,R~2 of the coniferous samples(0.8499) and needle samples(0.9722) demonstrated that the correlation between HV and the Su E content was closer.We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels,especially coniferous fuels.Su E data can be used in fire management,for example to estimate the rate of fire spread or fire intensity. 相似文献
999.
Within a research project on quality of plants for forestation of agricultural lands, we studied the aetiology of a late seedling rot affecting holm oak (Quercus ilex ssp. ballota) in two forest nurseries in southern Spain. Major disease symptoms were foliage wilting and necrosis of feeder roots. Phytophthora cinnamomi, Phytophthora cryptogea and Phytophthora drechsleri were isolated from necrotic roots of holm oaks. Selected isolates of the three Phytophthora species were pathogenic to Quercus ilex ssp. ballota and Quercus suber seedlings in artificial inoculations. Soil flooding conditions were essential for infection and root rot development. There was no host specificity among the species, the isolates of P. cinnamomi being the most virulent in all inoculated plants. In these inoculations, Q. ilex ssp. ballota plants were more susceptible than those of Q. suber. This work is the first report of P. cinnamomi, P. drechsleri and P. cryptogea affecting Q. ilex ssp. ballota in forest nurseries. 相似文献
1000.
This study investigates the optimal conditions for the vegetative propagation of the multipurpose leguminous shrub Colutea istria from leafy stem cuttings. The conditions examined included 1) the origin of the cutting (apical, medial or basal), 2) indole-3-butyric
acid (IBA) treatment (0, 50, 200 or 400 mg/l), 3) the relative humidity of the propagation environment (high or low), 4) wounding
base of cutting, and 5) the season in which the cutting was taken. The rooting ability of the cuttings was significantly influenced
by all these factors. Winter cuttings obtained from the middle and base of the branch showed a greater rooting capacity than
those harvested from the apical area, while autumn cuttings harvested from the middle and apical areas of the branch showed
a greater rooting capacity than those harvested from the base. Winter cuttings showed the best rooting capacity than autumn
cuttings. IBA treatment (200 mg/l), high humidity (98-100%), and wounding increased the rooting capacity of the cuttings. The sprout
of new leaves was higher in basal cuttings, while IBA and wounding also significantly enhanced the root number of rooted cuttings.
A method for vegetatively propagating C. istria plants is given. 相似文献