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白雪皑皑的白山黑水,椰林高耸的南海琼崖,西北边疆的天出雪峰,锦秀江南的鱼米之乡,林海起伏的大兴安岭,水波粼粼的五百里滇池,一望无际的内蒙古大草原,四季鲜花的西双版纳;雄伟的泰山,奇险的华山,铁骨冰肌的黄山,秀逸飘然的武夷 相似文献
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绘画水平的提高离不开良好的常规的建立,良好常规的建立能引发幼儿与周围环境相互作用,进一步促进孩子们的动手能力的发展。在良好常规的建立中孩子们的倾听习惯的养成起着很重要的作用。在孩子们作画习惯和整理工具等方面的培养同样的是需要良好常规的支撑。 相似文献
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指出了随着气候的异常变化,使得全球变暖的情况加剧,世界提前进入了暖季,基于此,在全人类可能遭遇气候危机的情况下有众多国家领导人联合签署了关于"可持续发展"的理念的倡议书,建议全面发展以可持续理念为核心的环保的能源建设和资源开发。面对"可持续发展"的时代大潮,在我国,一些旧有的、效能低下的、产能落后的事物也即将经历改革发展的大潮进而焕发新面貌,其中就包括我国的一些国有林场。以广东省境内的国有林场的改革为例,探讨了可持续发展的理念对于我国的国有林场改革的意义,以及其能为我国的国有林场的未来发展带来怎样的质的飞跃,并根据广东省的地理特点,结合可持续发展理念的理论要求,提出了国有林场全面改革的相关建议。 相似文献
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A major problem for small farmers in the semi-arid tropics is the chronic shortage of fodder for draft animals. Leucaena leucocephala has improved productivity in many places in India and in various cropping systems, usually as either a pure crop or in a
hedgerow alley-cropping configuration. Mixed cropping with arboreal forms is seldom seen. For off-season fodder production,
hedgerows have the disadvantage of being open to unmanaged browsing when unfenced (as is usual). Arboreal forms are generally
far less vulnerable.
In this paper, the components of production of sorghum and arboreal Leucaena are measured under different intensities of canopy lopping. The most productive management system of those examined was pollarding
of the Leucaena at the time of under-sowing with sorghum. In a year with less than 50% of average seasonal rainfall, this system gave a yield
of 4.6 tonnes/ha/yr fresh wt fodder and 3.8 tonnes/ha/yr dry wt. of fuel harvests, while increasing the standing crop of wood
by 1.8 t/ha/yr and retaining a yield of sorghum grain equivalent to 46% of pure sorghum cropping; the LER of this system was
1.35.
Cash values of the alternative management systems were estimated, including the discounted Net Present Value of the standing
crop of timber. Maximum value was attained with unlopped pure crop Leucaena followed by pollarded Leucaena with sorghum; pure crop sorghum achieved a lower value.
These results demonstrate both the high productivity of Leucaena/sorghum based systems, and the stability of production even in poor rainfall conditions. Pollarding transferred the high
future value of Leucaena timber to the present value of sorghum grain and fuelwood. 相似文献
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Srisuda Thippayarugs Banyong Toomsan Patma Vityakon Viriya Limpinuntana Aran Patanothai Georg Cadisch 《Agroforestry Systems》2008,72(2):137-148
In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic
or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts
(stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea
(Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content
as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest
N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized
to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea,
largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for
N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant
components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N
released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures
were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality
components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in
the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols.
Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest
age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its
components are mixed. 相似文献
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The olive psyllid, Euphyllura phillyreae Foerster is one of the most destructive pests on buds and flowers of olive tree (Olea europaea L.) in May when the olive growers cannot apply any insecticides against the pest. Temperature-dependent development of the
psyllid was studied at constant temperatures ranged 16–26°C. A degree-day (DD) model was developed to predict the larval emergence
using the weekly cumulative larval counts and daily mean temperatures. Linear regression analysis estimated a lower developmental
threshold of 4.1 and 4.3°C and a thermal constant of 164.17 and 466.13 DD for development of egg and larva, respectively.
The cumulative larval counts of E. phillyreae approximated by probit transformation were plotted against time, expressed as the sum of DD above 4.3°C, the starting date
when the olive tree phenology was the period of flower cluster initiation. A linear model was used to describe the relationship
of DDs and probit values of larval emergence patterns of E. phillyreae and predicted that 10, 50 and 95% emergence of the larvae required 235.81, 360.22 and 519.93 DD, respectively, with errors
of 1–3 days compared to observed values. Based on biofix depends the development of olive tree phenology; the DD model can
be used as a forecasting method for proper timing of insecticide applications against E. phillyreae larvae in olive groves. 相似文献
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竹类是一类具特殊生长习性与生长型的植物,其分布范围广泛、有性生殖脆弱而无性繁殖发达,易于受到人为和自然因素的影响而沦为小种群或濒危物种。本文从小种群近交危害与集合种群上分析了竹类种质保护的适度思想,即适宜的局域种群与集合种群结构度是优化竹类野生种质保护的重要依据;并从区域相对封闭生态系统结构度与竹类种质稳定性上分析了野生种质适度保护的策略;最后从加强竹类种质种群生态学特征的编目清查、自然野生栖息地就地保护、竹类种质保存圃建立与完善,以及竹类原料林的定向培育4方面阐述了竹类种质的适度保护体系。 相似文献
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Eugenol and thymol, alone or in combination, induce morphological alterations in the envelope of Candida albicans 总被引：1，自引：0，他引：1
The envelope of Candida albicans, with its outermost array of macromolecules protruding towards the environment, is pivotal to the expression of major virulence factors such as adhesiveness, and the morphological transition to hyphal form. We tested the anticandidal activity of eugenol, main component of clove oil, and thymol, main component of thyme oil, alone or in combination, by investigating their ability to interfere with the architecture of the envelope of C. albicans. Both molecules alterated the morphogenesis of the envelope, but the effects of thymol were more pronounced than those of eugenol. Certain combinations of the two molecules led to a synergistic effect, which is interesting in the view of potentiating their inhibition of C. albicans colonisation and infectiousness. 相似文献
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《Journal of Sustainable Forestry》2013,32(2-3):133-146
Abstract A sustainable use of forests may be conceived of differently by different scientific disciplines. An underlying definition of sustainability is therefore central to the understanding of any analysis on the subject. This paper approaches the idea of sustainability from an economic perspective. The interpretation of sustainability in terms of concepts such as efficiency, equity and welfare are initially described. Empirical research aiming at obtaining basic elements of economic sustainability analyses is subsequently outlined. Finally, the implications for applied welfare and sustainability analysis at different economic and geographical levels of aggregation are discussed 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):53-61
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. 相似文献