小径级柞木干燥工艺的试验研究

小径级柞木干燥试验结果表明:在干燥初期干球温度为35℃、干燥末期干球温度为70℃、干燥周期中进行两次中间处理和末期终了处理、干燥周期为15 d的工艺条件下,板材干燥前总平均含水率41.6%,干燥结束后总平均含水率11.7%,板材厚度上含水率偏差<3%;干燥结束后伸长应力和压缩应力甚微,板材表面的颜色轻微变暗,除髓心材和水纹材有少数裂纹和轻微变形外,其余木材并没有发生翘曲、变形、开裂等干燥缺陷,干燥质量满足了GB6491—86《国家锯材干燥质量标准》二级以上的指标要求。本次试验确定的干燥工艺满足了小径级柞木板材的干燥工艺要求。     

常规木材干燥缺陷及产生的原因

在干燥室各部分干燥设备能够保证正常工作状态的情况下,木材干燥工艺条件则是保证木材干燥周期和质量的关键。木材干燥工艺条件的核心内容是木材干燥基准,干燥基准的软硬度基本决定了木材干燥周期和质量。木材干燥过程中出现的开裂、变形和最终含水率不均匀等现象都属于木材在干燥过程中的干燥缺陷。其中开裂也叫干裂,分为端裂、表裂和内裂;变形包括顺弯、横弯和扭曲;最终含水率不均匀包括整体材堆的最终含水率不均匀和单块板材沿厚度方向上的含水率不均匀。在木材干燥生产中,我们希望干燥缺陷出现的越少越好,甚至无干燥缺陷。干燥缺陷一般…     

格木干燥特性及其干燥基准初探

采用百度试验法研究了格木木材干燥特性,拟定了25~30mm厚格木木材的干燥基准。结果表明:格木木材初期开裂初期开裂等级为3级,主要为端裂和端表裂,干燥结束后,未出现内裂,等级为1级;截面变形值弦切板平均0.608mm,径切板平均0.618mm,等级为2级;扭曲值弦切板平均2.7mm,等级为2级,径切板平均1.92mm,低于弦切板;格木干燥质量好,初期开裂是其主要干燥缺陷;弦切板从含水率30%降至5%平均用时26h,平均干燥速度0.96%·h~(-1),径切板平均用时38h,平均干燥速度为0.66%·h~(-1),等级为4级,弦切板干燥速度快于径切板;干燥时可参考本研究制定的25~30mm厚木材干燥基准执行操作,将板材分类摆放,干燥初期干湿球温度差不应太大,升温不宜过快。     

菲律宾桃花芯木锯材干燥工艺初探

以菲律宾桃花芯木为研究对象,探索30 mm厚菲律宾桃花芯木锯材干燥工艺。通过百度试验法得知其初期开裂为3级、内裂为2~3级、截面变形为1级;通过密度测定实验得知其气干密度为0.562 g/cm^3、全干密度为0.517 g/cm^3和基本密度为0.465 g/cm^3。根据该木材密度和干燥特性制定3种30 mm厚菲律宾桃花芯木锯材干燥基准并分别进行常规干燥工艺试验。通过对3次工艺试验结果的综合分析表明：在3次工艺实验所用执行基准均能满足2级干燥指标。其中,第一次工艺实验所用执行干燥基准为本研究中最佳干燥基准。第一次工艺实验的初始温度为60℃,末期温度为80℃、初含水率为66.97%、终含水率为7.79%的锯材干燥周期为185 h。     

金檀干燥工艺的研究

文章采用百度试验法对金檀木材进行干燥特性研究,提出金檀家具用料板材的干燥基准,并进行了工艺试验研究。结果表明,金檀木材初期开裂为5级;内裂为2级;截面变形为3级,干燥速度为4级。初期开裂较严重,干燥速度慢,故金檀为难干燥木材。采用给出的干燥工艺,42 mm厚铁线子地板坯料从初含水率30.66%干燥到12.8%的干燥周期为43d,干燥质量满足家具用料的加工要求。     

初含水率对白橡锯材热压干燥特性的影响

以白橡锯材为研究对象,采用平板热压机对其进行干燥处理,系统研究了初含水率对木材温变特性、干燥速率、干缩特性、干燥缺陷和微观构造的影响规律,探明白橡锯材的热压干燥特性。结果表明:热压干燥是一种高效快速的干燥方法,将初含水率为14%~75%的木材在温度为140℃、压力为0.1MPa的条件下干燥到2%以下终了含水率仅需120~210 min,木材干燥速率随着初含水率的增加而增加;初含水率较高的木材在热压后会产生严重内裂和皱缩缺陷,当木材初含水率降至15%以下时,热压后无内裂缺陷产生,截面变形也明显减小;随着初含水率的增加,木材厚度干缩系数呈增加趋势,而宽度干缩系数则呈下降趋势。通过观察木材的横切面微观结构发现,高初含水率试件的内裂沿木射线生成,其早材大管孔部位可观察到明显压缩。     

铁线子地板坯料的干燥工艺

采用百度试验法,进行铁线子木材干燥特性和干燥工艺的试验。结果表明,铁线子木材初期开裂较严重,为5级,内裂为2级,截面变形为3级;干燥速度较慢,为4级。按照试验拟定的干燥基准,进行22 mm厚铁线子地板坯料干燥试验。从初含水率30.7%到终含水率12.3%,干燥周期为28 d,干燥质量满足实木地板的加工要求。     

大花序桉干燥特性与干燥工艺研究

通过百度试验法研究了25年生大花序桉木材的干燥特性,制定其干燥基准,进行干燥工艺优化试验。结果表明:大花序桉初期开裂等级为4级,内裂等级为2级,截面变形等级为2级,干燥速度等级为5级,属中等难干材;采用百度试验法制定的干燥工艺,40 mm厚大花序桉从初含水率48.89%降至9.45%,干燥周期为26天,干燥均匀度较好,厚度上含水率偏差为3.22%,除纵裂外,其他可见干燥缺陷指标均达到国家标准GB/T 6491-2012《锯材干燥质量》规定的一级要求。     

青冈锯材常规干燥工艺探讨

青冈属木材材质好,在我国具有一定数量的蓄积量。木材加工企业在生产中通常将其分为白青冈、红青冈类,但其树种间材性存在差异,部分树种自身变异也较大,干燥时易开裂。青冈是白青冈类中的一种,至今未得到充分利用。针对30mm厚青冈锯材,采用3种干燥基准分别对其进行干燥工艺的初步研究,旨在探讨合理的青冈锯材干燥工艺,为其加工利用提供理论依据和实践指导。结果表明：干燥初期锯材含水率下降速度快,前期干燥温度不宜过高,应采用低温预热并保持一段时间,干球温度不应高于40℃,干湿球差需控制在1℃。风速控制在1.0~1.2m/s,甚至更低为宜。研究证明采用合理的多阶段干燥基准,控制各含水率阶段的干燥速度,可以有效减少青冈锯材干燥过程中的开裂等干燥缺陷,满足二级干燥锯材质量的要求,可应用于地板基材、家具用材。     

基于百度试验法制定29年生杉木木材干燥基准的研究

以广西融安县西山林场1.5代种子园29年生杉木(Cunninghamia lanceolata)为样本,采用百度试验法,分析杉木木材的干燥特性,编制出杉木木材的干燥基准,结果表明:杉木属于易干燥树种,百度试验时出现的主要干燥缺陷为初期开裂和扭曲变形。初期开裂等级为3级;扭曲等级为3级;内裂等级为1级;截面变形等级为1级。根据29年生杉木木材的干燥特性,得出29年生杉木木材的干燥初期温度为60℃,干湿球温度差3～4℃,末期温度为90℃,拟制定25～30 mm厚29年生杉木木材的软(硬)干燥基准。实际干燥生产中使用软基准可减少干燥缺陷。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.