共查询到20条相似文献,搜索用时 218 毫秒
1.
气候、地貌、土壤等自然因素和森林植被遭破坏,坡耕地面积逐年增加等人为因素是云南省沙化土地形成的主要原因。根据沙化土地的特点,将其划分为河漫滩沙化、淤积沙化、风沙化、沙石化和土林等5个沙化土地类型。沙化土地造成土地生产力退化,生态环境恶化,制约了当地经济和社会的可持续发展,全省现有沙化土地面积6425.2hm2经过近5年的治理,各类土地面积有明显变化,对今后沙化土地的治理提出了综合治理与开发相结合、生物措施与工程措施相结合的各项措施。 相似文献
2.
赖兴会 《云南林业调查规划设计》2001,26(1):45-50
气候,地貌,土壤等自然因素和森林植被遭破坏,坡耕地面积逐年增加等人为因素是云南省沙化土地形化的主要原因,根据沙化土地的特点,将其划分为河漫滩沙化,淤积沙化,风沙化,沙石化和土林等5个化土地类型,沙化土地造成土地产生力退化,生态环境恶化,制约当地经济和社会的可持续发展,全省现有沙化土地面积6425.2hm^2,经过折5年的治理,各类土地面积有明显变化,对今后沙化土的治理提出了综合治理与开发相结合,生物措施与工程措施相结合的各项措施。 相似文献
3.
山高坡陡,切割强烈;降水丰富,降水年内分配不均;土层深厚,土体疏松等是盈江县沙化土地形成的主要自然因素。森林植被遭到破坏,坡耕地面积逐年增加等是盈江县沙化土地形成的主要人为因素。盈江县现有沙化土地面积2520.5hm^2,有流动沙地、兰固定沙地、固定沙地、沙改田4个沙化土地类型。通过长期的治理,沙化土地各类型面积及利用状况发生明显变化,总体发展趋势呈现逆转,沙化土地得到有效利用。今后需以治理水土流失为中心,采取生物措施、工程措施、农业措施相结合,开发利用并举的综合治理措施。 相似文献
4.
5.
6.
关于洞庭湖区土地沙化与治理对策的探讨 总被引:1,自引:0,他引:1
土地沙(漠)化是全球性的环境问题,我国是一个土地沙(漠)化较严重的国家之一。洞庭湖沙区由于其成因与北方沙区有明显不同、特点迥异,属“沙化”而非“沙漠化”。本文根据洞庭湖区土地沙化现状和危害,从分析成因入手,对治理对策和措施进行初探。 相似文献
7.
河南省沙化土地的变化趋势及治理技术路线 总被引:1,自引:0,他引:1
通过对河南省沙化土地的成因、分布、自然和社会经济条件的全面分析,在近20年连续亢进对比的基础上,结合沙区实际,提出了河南省沙化土地的变化动态与发展趋势,提出了进一步治理的原则和技术措施。 相似文献
8.
9.
西藏沙化动态及其原区 总被引:1,自引:0,他引:1
西藏自治区是我国沙化最严重的地区之一。2004年调查结果表明,西藏沙化面积为216842.7km^2其中重度以上的沙化面积占总沙化面积的91.53%;沙化类型以戈壁占绝对优势:草地、未利用地是主要的沙化土地利用类型。全区沙化总体上呈恶化趋势,沙化土地面积增加,沙化程度加剧,但拉萨、山南等地沙化土地有所减少。西藏土地沙化变化是受自然因素与人为因素共同作用的结果。 相似文献
10.
11.
1990~1993年连续4a,对马尾松球果和种子的生长发育与养分动态,进行了比较系统的分析研究。结果表明:(1)马尾松球果系2年成熟,授粉(4月上旬)后当年为幼球果形成期;第2年受精前的6月至以后的9月中旬为球果迅速生长期,9月下旬至10月为球果成熟期。(2)在2年生球果生长期间,球果干物质不断增加,而水分含量逐渐减少,10月底干物质与水分的含量达到平衡点。(3)球果养分的含量,l年生球果幼期N>K>P,三者变化趋势近乎一致,2年生球果含N量明显下降。种子内的N、K含量在7月中两者相当,此后N含量上升直至成熟期,到10中K与P的含量相近。(4)胚胎发育进程中,球果和种子的体积与养分含量在原胚和幼胚阶段(7月至9月中旬)的变化最大,以后渐趋平缓。 相似文献
12.
介绍云南省近年来干旱灾情发生、发展情况及其原因,阐述天然降水的时间分布规律,对森林保持水土和涵养水源的生态功能进行分析和评估,说明森林在涵养水源、保持水土方面有着重要作用,并与森林的数量和质量成正比。建议在今后的抗旱工作中重视和加强生态公益林建设和管理。 相似文献
13.
14.
以白杨派和黑杨派杨树的盆栽苗为试材,分析了不同干旱胁迫程度对5个杨树的气体交换参数与荧光参数(Fv/Fm、Fmv/Fms)的影响,并对不同树种的耐旱性进行了综合评价。结果表明:①5种杨树净光合速率与蒸腾速率均随苗木叶水势的下降而呈明显下降趋势;在水分胁迫初期,欧洲黑杨和银白杨的净光合速率呈现明显的上升趋势。②在中度干旱胁迫前,5个供试杨树的水分利用效率大部分随叶水势的下降有增大现象。③不同树种的Fv/Fm随叶水势降低总体上呈逐渐下降趋势。④与Fv/Fm相比,Fmv/Fms能更直接地反映光合机构的实际光能捕获能力。⑤当苗木叶水势为-1.5 MPa时,5个树种耐旱性的综合评价结果为:转Bt基因欧洲黑杨>欧洲黑杨>银白杨>银灰杨为欧洲山杨,综合指数评价结果与采用单一指标中的水分利用效率完全一致,与净光合速率相近;水分利用效率证明是一种较为可靠的树种耐旱性评价指标。 相似文献
15.
介绍了国内外温室测控技术的发展历史、现状、发展趋势及研究动向,提出了进一步发展我国温室测控技术、提高我国温室现代化程度所亟待研究和解决的问题. 相似文献
16.
温室测控技术的发展及我国温室测控面监的问题 总被引:2,自引:0,他引:2
介绍了国内外温室测控技术的发展历史、现状、发展趋势及研究动向,提出了进一步发展我国温室测控技术、提高我国温室现代化程度所亟待研究和解决的问题。 相似文献
17.
Stem cuttings of Eucalyptus globulus are used within tree improvement programs and for mass deployment. To be successful, cuttings must perform as well or better than seedlings. The root systems of cuttings are fundamentally different from those of seedlings. If these differences influence growth, the differences and their consequences must be identified and the propagation system manipulated to improve performance of the propagules.Cuttings are only a viable alternative to seedlings as planting stock if the method of propagation does not affect their growth and development adversely. Full-sibling cuttings and seedlings of Eucalyptus globulus were compared under controlled environmental conditions to minimise extraneous sources of variation, and to establish whether changes in growth or development were induced by propagation. On three occasions over a period of eight weeks root-collar diameter, shoot height, leaf and stem weight, shoot/root ratios and root system morphology were measured on cuttings and seedlings. Seedlings were taller than cuttings throughout the experiment, but both plant types had similar height growth rates. Diameter growth rates were lower in cuttings than seedlings, and there were differences in both height and diameter growth rates between families. Root system configuration differed between the plant types. Seedlings had strongly gravitropic tap-roots, with two types of primary roots from which secondary roots emerged. Cuttings had no tap roots, and the main structural components of their root systems were adventitious roots formed during propagation. Cuttings did not develop further structural roots during the experiment, whereas seedlings continued to develop primary roots. Individual primary roots of cuttings were longer and had larger mid-point diameters than those of seedlings, but the total length of primary roots was greater in seedlings. Seedlings also had a greater number and total length of secondary roots. Shoot/root ratios, calculated from a range of functional measures, were higher in cuttings than seedlings. 相似文献
18.
CHEN Peng ZHAO Guangjie College of Material Science Technology Beijing Forestry University Beijing P.R.China 《中国林业科技(英文版)》2007,(2)
There are many advantages of bended wood,such as good-looking shape,simple process and low cost.The product,however,is easy to get recovery,which is urgent to be dealt with.This paper concludes the features of deformation and recovery of bended wood and wood-based composites and summarizes four treating methods to keep dimensional stability.Compared to bended solid wood,some elementary perspectives on the research of bended wood-based composites are presented.The purpose of this paper is to suggest:1)to investigate the optimum heating time and temperature that bended wood and wood-based composites need from the formation of deformation to the recovery and to the permanent fixation,according to its changes of dimensional stability such as curvature radius;2)to measure the composites comprised of wood and adhesives on the changes of stress relaxation,dynamic viscoelasticity and crystal1ization field;3)to quantitatively analyze changes of the major components in wood cell wall polymers as well as the composites under heat/steam treatment and untreated conditions.It will be helpful for subsequent research to clarify on the mechanisms of permanent fixation of bended wood and also contribute to that of wood-based composites. 相似文献
19.
水土流失的危害与森林的作用 总被引:20,自引:0,他引:20
“水”和“土”是人类生息的重要资源,水土流失已成为威胁我们生存和发展的一个重要问题,该文用事实证明了山西省水土流失的现状,指出水土流失的危害,及森林在控制水土流失中的作用。 相似文献
20.
我国GIS的发展及其与测绘的关系 总被引:1,自引:0,他引:1
本文简要介绍了GIS在我国的发展概况和GIS与测绘的关系。并指出了面向未来测绘事业的GIS的发展前景。即向智能化、集成化、自动化和网络化发展。以便适合于不同测量工作者的需要。 相似文献