国内外珍贵树种用材林发展动态及其在四川省的发展现状

本文简要介绍了珍贵树种、珍贵用材林的概念、内涵、国内外动态以及省内珍贵用材林发展现状,对四川省认定的73个珍贵树种进行了初步的技术成熟度评估,在评估的基础上提出了四川发展珍贵用材林的长短期建议。     

Effects of early re-spacing on the physical and mechanical properties of Sitka spruce structural timber

The effects of early re-spacing on the physical and mechanical properties of Sitka spruce (Picea sitchensis [Bong.] Carr.) structural-dimensioned timber were studied using material from a fully replicated 57-year-old trial located in Northern Ireland, which had been thinned at age 11 years. Basic density, distortion (spring, twist and bow), modulus of elasticity (MOE) and modulus of rupture (MOR) in bending of structural timber from four different re-spacing treatments (1.83 m × 3.66 m, 3.66 m × 3.66 m, 3.66 m × 5.49 m and 5.49 m × 5.49 m) were compared with those of timber from a control (1.83 m × 1.83 m). Re-spacing intensity had a significant effect on both modulus of elasticity (p = 0.006) and modulus of rupture (p = 0.009), but not on basic density (p = 0.379) or distortion (p > 0.200). Timber from the two widest re-spacing treatments failed to meet the requirements for the C14 strength class, while timber from the control met the requirements for the C16 strength class. Both MOE and MOR were significantly and negatively associated with knot size and frequency, which in turn increased with re-spacing intensity. Overall, re-spacing intensity only explained approximately 10% of the total amount of variation in both MOE and MOR, with most of the variation due to inter- and intra-tree differences within a treatment. Based on these results, re-spacing of Sitka spruce to a residual stand density of less than 900 trees/ha (3.33 m × 3.33 m) is not recommended if the goal of management is to produce C16 structural timber.     

Analysis of trade in illegally harvested timber: Accounting for trade via third party countries

The paper presents a model to analyse trade in illegally harvested timber with a particular focus on trade via third party countries. The model is deduced from the conventional input–output-analysis. In contrast to this type of analysis, inverse export coefficients are introduced to analyse the effect of a certain amount of country-specific supply, e.g., of illegally harvested timber, to the use of wood and wood products of all other countries, based on trade relationships. A database has been compiled especially for application of the model. It comprises data on industrial round-wood production in terms of industrial wood harvested and removed from the forest; recovered wood fibre in the form of recovered paper and waste wood; bilateral trade of 272 wood-based commodities in m³ raw wood equivalent (rwe), and domestic use of those commodities. Two scenarios expressing high and low estimates of illegal harvesting for all countries have been employed in the model. The model reveals the trade linkages between all countries of the world and allows quantification of the global supply and use arising from illegal harvesting. Furthermore it allows calculation of the import of illegally harvested timber for each country of the world. And finally, the model likewise allows the quantification of domestic use of illegally harvested timber for each country of the world.The results show that international trade increases the global domestic supply of illegally harvested timber by more than 70% in each scenario. In particular industrial round-wood from Papua New Guinea, Malaysia, Indonesia and Myanmar passes through many countries until it ends in form of finished wood products in the country of final destination. Not only due to suggested illegally harvested timber in the own country, but also due to strongly developed trade relationships, China holds the lead in total supply and use of illegally harvested timber. However this result must be seen against the background of the large population in China. This aspect also helps to explain the predominant position of China, Brazil and Russia with regard to the domestic use of illegally harvested timber. A comparison of import of illegally harvested timber on the basis of “simple” (covering only bilateral trade) and inverse export coefficients demonstrates the model's merit. The hitherto usually simple approach underestimates the “real” trade by a third up to a half.     

畜禽黑色素及其候选基因研究进展

黑色素对畜禽乌骨及体色的形成起重要的作用,通过近年来在人和鼠上的试验结果表明,与黑色素相关的基因有很多,作者对一些影响畜禽黑色素的主要基因及其研究现状进行了归纳。     

古都国内游客旅游服务质量感知评价研究——以西安市为例

文中以西安市为例,在旅游市场调查的基础上,通过旅游服务质量单要素评价模型,从感知定量化角度定量分析了国内游客对西安旅游服务的感知评价,指出了西安旅游服务的优劣势所在;并通过对比分析不同群体游客的感知评价,揭示了当前西安旅游服务中存在的主要问题,最后针对性地提出了提高旅游服务质量的具体措施,对研究古都类旅游城市旅游服务质量有一定的借鉴意义。     

蒙古栎天然次生林改培大径级材技术研究

在吉林蛟河地区开展蒙古栎天然次生林改培育大径级材林试验,结果表明:松江林场的天然次生蒙古栎林改培效果最为明显,其每年胸径增长量为0.44cm,平均增长率为5.59%,材积每年平均增长率为6.73%;不同立地条件及不同间伐强度对培育大径级材林影响差异显著,最佳间伐强度为28%,最佳立地条件为西南坡或南坡,胸径生长量最佳的为坡下,坡度为4°的长势良好,郁闭度为0.9的改培育效果最好。     

竹材密度测定方法及变异规律研究进展

文中介绍了常见的竹材密度测定方法及其特点, 阐述了竹材密度变异规律及产生密度变异的主要机理, 并简要探讨了密度变异对竹材及竹基复合材料力学性质的影响。这些成果对竹材密度的深入研究及其加工利用具有重要的参考价值。     

ANSYS在木结构构件中的应用

介绍了大型通用有限元软件ANSYS的特点和进行有限元分析的一般步骤。通过在木桁架、木结构剪力墙和木结构楼板3种结构中应用得知,ANSYS可以用于对木结构构件的建模和应力分析以及进行相应的力学性能预测,且研究精度高、速度快,可节约大量的产品试制和试验经费,同时还可以实现对结构的优化。     

2005—2014年国际原木贸易格局的社会网络分析

采用社会网络分析方法,利用2005—2014年世界120个国家（地区）原木进出口贸易数据,对国际原木贸易网络的网络密度、中心性及核心节点等指标进行计算,对国际原木贸易网络核心—边缘结构进行分析。研究结果表明:国际原木贸易的发展受到世界经济形势和政府原木进出口政策的显著影响;大部分国家（地区）原木贸易伙伴少、贸易量小,只有少数贸易伙伴较多、贸易量大;美国一直是原木进出口贸易的核心国家,德国是后加入的核心国家,属于金砖国家的中国、印度发展迅速,中国在2011年跻身核心国家行列。     

篌竹林经营技术研究进展

篌竹广泛分布于长江流域及以南我国各省(区),是重要的中小型笋材兼用竹种之一,其栽培及经营技术研发历来为业界关注。本研究收集了篌竹近40年国内外研究文献100余篇,系统分析了篌竹分布、生物生态学特性、苗木培育、人工造林、病虫害防治、幼林和成林抚育,以及材用林、笋用林和笋材兼用林经营关键技术,以期为篌竹林培育利用及林下经济发展提供科学依据。