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991.
我国的森林资源中人工林已逐渐成为主导林分,科学合理的生态集材方式对人工林的可持续发展具有重要的意义.本文就如何实现人工林的生态集材问题,分别从选择集材方式和确定采育模式两个方面进行探讨. 相似文献
992.
热带雨林濒危树种望天树的致危原因及保护策略 总被引:2,自引:0,他引:2
望天树自身的开花结实特点、种子顽拗性和低成苗率、幼苗生长缓慢、过度砍伐和生境破碎化等导致其更新困难,以致陷入濒危的境地。加强自然保护区管理与法制建设、在天然林保护和次生林恢复工作中辅以人工抚育、防治病虫害和人工接种菌根菌以及实施迁地保护等措施可有效地保护望天树种质资源。 相似文献
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994.
中国水稻科技发展战略 总被引:31,自引:0,他引:31
分析了现代水稻科技与产业发展的国际趋势与特点、我国国民经济和社会发展对水稻的需求,回顾了我国水稻科技创新体系的建设历史与成效,着眼于现代水稻科技发展方向和水稻行业的需求,提出了我国水稻科技发展战略和重点课题。关键词: 相似文献
995.
主/从机器人系统设计与双向伺服控制 总被引:1,自引:1,他引:0
建立了主/从异构式机器人力反馈遥操作控制系统。主操作系统采用2个2-DOF操作手,分别采用伺服阀控制液压马达获得2个解耦的旋转自由度。用力信息对伺服阀进行控制以驱动主操作手运动,解决主手操纵力不能直接驱动主操作手液压马达的问题。从机器人为4-DOF串联关节型四自由度机器人,采用比例方向阀控制。分别采用力反射伺服型和力对称型双向伺服控制策略,对主/从机器人系统进行遥操作力反馈双向伺服控制实验研究。验证了本设计的主操作手结构的合理性,力对称型双向伺服控制策略具有较好的控制性能。 相似文献
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998.
Responses of the endemic leguminous shrub Bauhinia faberi var. microphylla, to various soil water supply regimes were studied in order to assess water stress tolerance of seedlings. Two-month-old
seedlings were grown under water supply regimes of 100, 80, 60, 40, and 20% water field capacity (FC), respectively, in a
temperature and light-controlled greenhouse. Plant height and leaf number were measured monthly over a 4-month period, while
water use (WU), water-use efficiency (WUE), leaf relative water content (RWC), biomass production and its partitioning were
recorded at the end of the experiment. Seedlings exhibited the greatest biomass production, height, basal diameter, branch
number, leaf number, and leaf area when soil content was at 100% FC, and slightly declined at 80% FC. These parameters declined
significantly under 60% FC water supply, and severely reduced under 40 and 20% FC. RWC, WU and WUE decreased, while the ratio
of root mass to stem mass (R:S) increased in response to decreasing water supply. Water stress caused leaf shedding, but not
plant death. The results demonstrated that B. faberi var. microphylla seedlings could tolerate drought by reducing branching and leaf area while maintaining a high R:S ratio. However, low dry
mass and WUE at 40 and 20% FC suggested that the seedlings did not produce significant biomass under prolonged severe water
deficit. Therefore, before introducing B. faberi var. microphylla in vegetation restoration efforts, water supply above 40% FC is recommended for seedlings to maintain growth. 相似文献
999.
Selection harvesting, by mimicking natural disturbance regimes of eastern deciduous hardwood forests, has been applied as a sustainable management practice that combines wood production with biodiversity conservation. However, the effects of this technique on understory herbs are unclear, particularly for spring ephemerals which have been suggested as sensitive to disturbance. Here, we experimentally assess the immediate effects of single-tree and group selection harvesting on spring ephemeral richness, diversity and abundance in deciduous forests of southwestern Ontario, Canada. Spring herbs were quantified in 4 m2 plots before and one growing season after harvesting and compared to similar uncut, reference stands. The percent of species lost was significantly higher in reference than harvested plots. Mean species richness significantly increased after harvesting, predominately due to an increase in spring–summer species. Increases in the diversity of early spring flowering species were significantly greater in the group selection plots than reference plots. At the community level, no species appeared to be vulnerable to harvesting, and ordination analysis indicated that post-harvest communities were primarily determined by pre-harvest community composition. Furthermore, no species declined in abundance in response to harvesting, and overall percent cover increased proportionately more in single-tree selection plots than in group selection or reference plots. While harvesting appears to have negligible effects on spring ephemerals immediately following harvest, we recommend additional studies over longer time frames to assess possible successional effects and to discriminate treatment induced changes from naturally high yearly variation in species composition. 相似文献
1000.
基于虚拟经营的木材企业运作策略初探 总被引:1,自引:1,他引:0
随着信息技术及物流技术的发展,虚拟经营模式已经成功地应用于很多企业,但是却没有在国内木材行业成功应用的先例。本文以广东鱼珠国际木材市场为例,采用定性的分析方法,结合虚拟经营运作理论,提出基于虚拟经营的木材企业运作策略,并对广东鱼珠国际木材市场虚拟经营的具体实施过程进行初步探讨。 相似文献