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91.
The potential of allye cropping systems to sustain a high productivity with low external inputs and the reduction of maize/weed competition through weed suppression in different alley cropping and sole-cropped mulched systems was studied in Costa Rica at CATIE. Data were recorded eight years after establishment of the experiment. Plant residues ofErythrina poeppigiana trees (10 t/ha dry matter) planted at 6 by 3 m reduced weed biomass by 52%, whileGliricidia sepium trees (12 t/ha dry matter) planted at 6 by 0.5 m reduced weed biomass by 28%, in comparison to controls.Erythrina had a considerable impact on grass weeds, whileGliricidia reduced the incidence of some dicot weeds. Weed competition significantly reduced maize yield in all systems. Nevertheless weed suppression contributed to the higher maize grain yield underErythrina andGliricidia alley cropping of 3.8 t per hectare as opposed to the unmulched control yield of 2.0 t per hectare. 相似文献
92.
93.
姚利辉 《绿色中国(A版)》2005,(24):54-55
如何运用价值量指标来计算森林资产的价值,一直引起人们的争议。森林资产价值理论基础呈多元性。但无论是传统马克思主义经济学还是西方主流经济学,都存在局限性。文章对此进行了具体分析,提出“影响因素价值论”,以期解决自然资源定价出现的困惑。 相似文献
94.
95.
南方森林经理与可持续发展的思考 总被引:1,自引:0,他引:1
王永安 《中南林业调查规划》2001,20(3):46-49
从森林可持续发展的概念着手,论述了森林经理与可持续发展的关系及在新形势下森林经理理论定位,并提出了南方森林经营的基本思路。 相似文献
96.
This paper demonstrates the utility of the real options approach to forestry investment analysis. The main objectives are to discuss the real option theory and show how it can be adopted to model uncertainty and managerial flexibility in forest management and investment. Secondly, we show how to calculate the option values of selected options that may be available to managers of forest industry firms. The paper provides an empirical application, which compares a forestry investment using the static Faustmann model and the real options approach. Four management options are used for the real options approach: an option to delay reforestation, an option to expand the size of the wood processing plant, an option to abandon the processing plant if timber prices fall below a certain level or due to corporate take-over, and multiple options that evaluated all three options together. All options were evaluated using the binomial option-pricing model, where timber values are assumed to follow a multiplicative binomial process. The results show that the Faustmann analysis rejected the investments as unprofitable, while the option analysis showed that all three options were highly valuable if exercised. When real options are considered, the traditional Faustmann model for assessing the profitability of a forestry investment may fail to provide an adequate decision-making framework because it does not properly value management's ability to adjust to shocks in the economy, as well as risks and uncertainty. 相似文献
97.
The Regional Forest Agreement process has dominated Australian forest policy for the past decade. The RFA process set in place a mechanism by which benchmark conservation values were established for forest ecosystems, whilst addressing the needs of the timber industry. The outcomes of a number of RFA's have been fraught with controversy. Key stakeholder groups have shown disagreement with processes and outcomes of methods employed by government both in establishing conservation reserves and areas allocated to timber harvesting. This research uses non-linear techniques to examine the dynamical behavior in stakeholder responses and to identify patterns of behavior that may lead to prediction of stakeholder responses. The method developed in this research provides a bridge between social sciences and Chaos theory.1 相似文献
98.
We made several buckling tests of wooden columns with intermediate slenderness ratios () and examined the empirical formulas. On the basis of the examination, we formulated an equation for predicting the buckling stress () of an intermediate wooden column. Sitka spruce (Picea sitchensis Carr.) and buna (Japanese beech, Fagus crenata BI.) were used for the studies. A compressive load was applied on the specimen supported with pin ends, and the buckling stress was predicted by the tangent modulus theory and two empirical equations: those of Tetmajer and Newlin-Gahagan. The predicted - relations were compared with the test results, and the applicability of these predictions were examined. Based on the comparisons, we formulated an equation that can predict the - relations of materials with various stress-strain characters in the plastic strain range. 相似文献
99.
Takeshi Katayama Jyoji Tsutsui Kazuo Tsueda Takao Miki Yasuhiro Yamada Murao Sogo 《Journal of Wood Science》2000,46(6):458-465
When (±)--oxo-guaiacylglycerol--(vanillic acid) ether (1) is degraded byFusarium solani M-13-1, the-ketone is initially reduced to giveerythro andthreo guaiacylglycerol--(vanillic acid) ethers (2), arylglycerol--aryl ethers, both of which are enantiomerically pure. The absolute configuration in each2 was determined by Mosher's method; the products were converted to,-di-(R)--methoxy--trifluoromethylphenylacetates (MTPA esters) (3) oferythro (-)- andthreo (+)-veratrylglycerol--(methyl vanillate) ethers (3), whose1H nuclear magnetic resonance (NMR) spectra were examined and compared with those of four di-(R)-MTPA ester (3) diastereomers from chemically synthesizederythro (±)-3 andthreo (±)-3. To assign the- and-MTPA-OCH3 peaks, the1H NMR scans of several compounds that have substructures of 3 and their 3,4,5-trimethoxyphenyl analogues were examined. When a racemic alcohol reacts with (R)-MTPA to give a pair of (R)-MTPA ester diastereomers, the value was defined as the absolute value of the difference in the1H chemical shifts of the peak between the diastereomers. It was found that the values of-MTPA-OCH3 were larger than those of-MTPA-OCH3 owing to a shielding effect of the veratryl ring located on the-MTPA-OCH3, and that the-MTPA-OCH3 peaks in the 3,4,5-trimethoxyphenyl compounds shifted downfield relative to those in the veratryl compounds. On the basis of the1h NMR data of (R)-MTPA esters, the absolute configuration of the four chemically prepared diastereomers (3) were determined. The catabolicerythro
3 [fromerythro (-)-3] andthreo
3 [fromthreo (+)-3] were identical to (R, S, R)-erythro
3 and (R, S, S)- threo
3, respectively. An hydrogen species in the fungal reduction would attack the-ketone fromre-face of both (R)-1 and (S)-1, givingerythro (S, R)-2 andthreo (S, S)-2, respectively.Part of this paper was presented at the 33rd Lignin Symposium, Tsukuba, November 1988 相似文献
100.
浅析完善中国森林生态效益补偿制度 总被引:7,自引:0,他引:7
随着地球人口的增加和人类活动的加剧,保护森林资源已经提上了各国的议事日程。而对于我国这样的一个贫林国家,森林资源的保护问题与森林生态效益的补偿就显得愈加迫切与重要。文章针对我国现有的森林生态效益补偿制度的沿革、存在的问题进行了分析,并提出我国森林生态效益补偿制度需进一步完善或创新。 相似文献