共查询到20条相似文献,搜索用时 31 毫秒
1.
南斯拉夫共有杨柳树林地15万公顷,仅占森林面积的1.5%,但其木材产量却占全国木材总产量的8%。杨木产量由1950年的10立方米,提高到1985年的120万立方米,增加了11倍,成为当今国际杨树委员会的重要成员国之一。该国杨树发展速度之所以快,与其有一支稳定的科研队伍密切相关。本文较详细地介绍了南斯拉夫杨树育种的成就和经验,并结合我国的实际情况,提出了作者的看法和建议。 相似文献
2.
美洲黑杨及其杂种在世界和我国杨树栽培中的地位与作用 总被引:2,自引:0,他引:2
本文介绍了美洲黑杨的天然分布, 生长状况。西欧各国对其珍贵基因资源的重视和利用, 我国引种美洲黑杨的现状及其作用等, 并对我国进一步利用美洲黑杨的基因资源, 促进我国杨树栽培的发展提出了一些看法。 相似文献
3.
由于特殊的地理和气候特征。使甘孜州高丘区阳坡,半阳坡以及金沙江,雅砻江,大渡河等“两江-河”河谷及其干流的绿化成为全州,全省,全国乃至全世界造林难题之一。目前甘孜州造林已经由立地条件较好的深沟采伐迹地更新全面转向上述难造林地区。通过多年的摸索。认为甘孜州造林要依靠科技,充分挖掘,利用州内丰富多样的植物资源,从解决四大问题入手,一是绿化思路(先灌,草绿化覆盖,后乔,灌结合造林;突破常规的投入和设计,实行稀树造林,宽带造林和多种围栏造林)的突破与创新,二是造林树草种(乡土地草种的选择和全光照营养袋培育雨季造林)选育,三是造林后期管护(落实专人,村组农户,专业队),四是进一步密切造林本身与广大农牧民增收的关系(发展名特优干果,地道药材的人工,半人工抚育和种植,造林绿化与环境美化,香化,服务生态旅游事业),逐步解决林牧矛盾,林农问题,不断提升林业在社会,经济发展中的地位和作用。 相似文献
4.
实施西部大开发,再造祖国秀美山川,是以江泽民同志为核心的党的第三代领导集体高举邓小平理论伟大旗帜,把握历史,面向未来,高瞻远瞩,审时度势,总揽全局,站在跨世纪我国经济发展的战略高度作出的决策,是加快西部地区经济发展,逐步缩小东西部地区差距,确保国家长治久安,人民安居乐业,促进共同繁荣,实现中华民族伟大复兴的重要举措。在实施西部大开发中,人力资源的开发与利用至关重要。 相似文献
5.
6.
Forest cover change is one of the defining contemporary environmental changes that validate the proposition of the Anthropocene narrative. Forest transition is a well-recognized global phenomenon, which has been studied and explained in well elaborated forest transition theory. Forest transition has been observed in over 30 countries, and it has been a trend in multiple countries in Asia. Forest transition is most relevant for the Anthropocene narrative, as it suggests that forest cover decline may eventually be followed by a forest cover increase at the global scale. The paper reviews evidence of forest transition in eight Asian countries and juxtaposes this with global forest cover trends. In Asia countries like China, India, Japan, Philippines, South Korea, and Japan and Vietnam are among the countries that have experienced an increase in the area under some kind of tree cover. Complex interplays of forest cover, population growth, economic development, demand for forest goods and services and governance effectiveness are the driving forces of forest transition. While it is not possible to extrapolate Asia's forest transition to the global scale, the Asian experience makes it possible to make statements on possible global forest cover scenarios. Ultimately, forest transition theory in general, and the experience of forest transition in Asia also support the concept and related narrative of the Anthropocene. 相似文献
7.
Mir Mozaffar FALLAHCHAI 《中国林学(英文版)》2012,14(2):131-136
In this study the regeneration diversity of Syahkal forests afforestated and natural stands in north of Iran was studied and compared from the point of view of evenness and diversity index.In order to accomplish this study two natural and man-made stands that almost are located in the same height above the sea level were chosen.The area of each stand was 30 ha and the inventory was done by the random-systematic method with a 5R land measurement(500 m2)selected.Also,in order to study the regeneration in the center of each sample piece 125 square meters micro plots were formed.The results show that regeneration diversity index in natural stands is more than that in man-made stands which in this case Mc-Arthur index with 2.41 has the most amount while Simpson index with 0.543 has the least amount.But the evenness indexes in man-made stands are more than that in natural stand which the main reason is the purity of the man-made stand. 相似文献
8.
森林病虫害防治是国家减灾工程的重要组成部分,对保护森林资源,改善生态环境,促进国民经济和社会可持续发展具有十分重要的意义。 相似文献
9.
10.
我国桉树木材性质及其变异规律研究进展 总被引:1,自引:0,他引:1
概述了国内桉树木材解剖性质、物理力学性质、化学性质及其变异规律的研究现状,对桉树木材性质变异的影响因子及其材性遗传相关性研究进行了总结,最后分析其存在的问题,并展望了桉树材性遗传改良的研究前景。 相似文献
11.
以德国南部小城镇加米施-帕滕基兴(Garmisch-Partenkirchen)市为例,在介绍该市园林绿化概况的基础上,重点介绍其民居庭院绿化与阳台绿化的特色;并对如何更好地发展中国小城镇绿化进行了探讨。
相似文献
12.
D. G. Hunt 《Wood Science and Technology》1989,23(4):323-333
Summary Non-linearity of softwood in axial mechano-sorptive creep during moisture cycling can be characterised as departure from linear behaviour. Linear behaviour is shown by experimental measurement to be a gradual approach to a creep limit with exponentially decreasing increments of compliance, Ji, per moisture cycle, when tested under a constant stress. On the other hand, when the stress is progressively increased by a small increment after each moisture cycle, the compliance increments will progressively increase, having a value of
, where n is the cycle number. By subtracting one compliance increment from the succeeding one, the value of Ji can be obtained. Analysis of experimental results in bending tension and compression showed that the compression test pieces departed from linearity at total strains around 0.14% to 0.15%, the bending test pieces showed slight evidence of non-linearity at about the same strain, whilst the tensile pieces were approximately linear up to 0.18% strain.This project was supported by the U.K. Science and Engineering Research Council and by the European Commission 相似文献
13.
文章简要地分析了围垦湖沼、上游截流、过度利用及工艺技术落后等人为因素对湿地资源的破坏情况与负面影响,给人们赖以生存的湿地生态环境带来严重的不可逆转的后果,并有针对性地提出了几点建议。 相似文献
14.
Changes in susceptibility to wind and snow damage due to thinningand fertilization were examined in even aged Norway spruce (Piceaabies (L.) Karst.) stands in southern Sweden. The stands arepart of a nationwide experiment to investigate growth and yieldfollowing different thinning and fertilization regimes establishedbetween 1966 and 1983. The material used in this study included16 replications of seven treatments. The treatments were: threelevels of thinning from below (2070 per cent); 20 percent thinning from above; thinning from below in combinationwith N and NP fertilization (thinning percentage 2528per cent); and unthinned control. The stands have been censusedtwice for damage during an average period of 12 years. The degree of wind and snow induced damage varied between 9and 20 per cent of the basal area increment produced duringthe observation period. For treatments with high basal arearemoval, the highest relative number of trees damaged by windoccured during the first period after thinning. The denseststands (i.e. unthinned controls and stands thinned from above)showed a high proportion of snow damage throughout the observationperiod. The block effect was in general more significant thanthe effect of treatments on damage level. When analysing theinfluence of the block effect (i.e. of site and stand characteristics)on damage level, wind damage was best predicted by stand basalarea left after thinning and stand age, while snow damage wasbest predicted by latitude, altitude, site index, and standage. On average the tested site and stand characteristics explained17 per cent of the variation in wind damage and 36 per centin snow damage. 相似文献
15.
森林分类区划是为了解决天然林的修养生息和恢复发展而提出的,但禁伐区、限伐区、商品林经营区划分在实施过程中存在一些问题。文章主要针对其存在的问题,提出一些可行性的建议和对策。 相似文献
16.
Ginkgo (Ginkgo biloba L.) is a multi-value deciduous tree species grown for the production of nuts, timber and foliage for medicinal products. Understanding
the ecological and biological basis for Ginkgo agroforestry systems is essential for the design of optimum Ginkgo-crop species
combinations. We established two greenhouse replacement series to examine interactions between Ginkgo and wheat (Triticum aestivum L.); and Ginkgo and broad bean (Vicia faba L.). The results showed that crop species were more competitive than Ginkgo at low Ginkgo density, but less competitive than
Ginkgo at high Ginkgo density. Ginkgo: wheat ratio 5:1 and Ginkgo: broad bean ratio 5:1 had relative yield total (RYT) and
relative land output (RLO) values of more than one and the largest total land output (TLO) values in respective mixtures.
Therefore, these two ratios might be considered optimum Ginkgo: crop ratio for enhancing the combined biomass of the Ginkgo
and crop in respective mixtures. Broad bean and wheat were more competitive than Ginkgo, which was less affected by wheat
than by broad bean. However, there were compensatory interactions between Ginkgo and wheat, and Ginkgo and broad bean. There
was significant belowground competition for soil N between Ginkgo and the two crop species in the Ginkgo/crop mixtures. The
two mixtures outperformed monocultures of the individual species when comparing the mixtures with the crop monoculture system. 相似文献
17.
18.
Diurnal and seasonal variations in leaf hydraulic conductance in evergreen and deciduous trees 总被引:1,自引:0,他引:1
We studied changes in the hydraulic conductance of leaves (K(leaf)) between dawn and dusk during the growth period (July) and at midday at the beginning of autumn in four tree species. The main objectives of the study were to check the extent of diurnal and seasonal changes in K(leaf) and the relationships between K(leaf), irradiance and leaf gas exchange. Two evergreen (Aleurites moluccana and Persea americana) and two deciduous trees (Platanus orientalis and Quercus rubra) were studied. Leaf hydraulic conductance was measured every 2 h between 0700 and 1900 h in July and compared with values measured between 0900 and 1300 h in October. Other variables measured were photosynthetically active radiation (PAR), leaf conductance to water vapor (gL) and water potential (psiL). In July, K(leaf) varied by up to 75% in Pe. americana on a diurnal basis and by at least 44% in Q. rubra. The diurnal time course of K(leaf) showed a distinct increase between dawn and late morning (1100 h) and a subsequent decrease in the evening in A. moluccana and Pl. orientalis, whereas in the other two species, K(leaf) was highest just after dawn and lowest in the evening. In October, K(leaf) of all the species studied was lower than in July, with differences of 20 to 28% for A. moluccana and Pl. orientalis and of 66 to over 70% in Pe. americana and Q. rubra, respectively. Significant correlations were found between PAR and K(leaf) (in all species) as well as between gL and K(leaf) (in three out of four species). Leaf habit (evergreen or deciduous) did not influence absolute values of K(leaf) or its diurnal variation. 相似文献
19.