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1.
A method of determining the Young’s modulus of timber using the stress wave propagation velocity without knowing the timber density was developed in our previous study. This method enables the estimation of Young’s modulus by Monte Carlo simulation using an existing database of the Young’s modulus versus density relationship as reference. Here, in Part II, we consider the effect of the reference distribution database on the accuracy of the estimated Young’s modulus by the developed method. Twelve different reference distribution databases were used in this study, containing Young’s modulus versus density data for more than 13 000 real-size timber specimens of ten different species. We obtained the following results: (1) the distribution of Young’s modulus estimated using an arbitrary stress wave propagation velocity depends on the reference distribution database employed, (2) the most important factor is not that the reference database has data on the same species as the timber in the test, but rather that the reference distribution database covers the foreseeable range of timber densities within the test, and (3) the estimation accuracy is higher than about 80% when the database covers many species and has wide ranges of densities and Young’s moduli. This estimation method was developed in order to measure the Young’s modulus of timber whose density cannot be measured. Considering that the quality of lumber has a large variation, such estimation accuracy will be useful for practical applications.  相似文献   

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Marquis  Benjamin  Bergeron  Yves  Simard  Martin  Tremblay  Francine 《New Forests》2021,52(6):1079-1098
New Forests - Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in...  相似文献   

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The role of agroforestry systems in biodiversity conservation was investigated in the semiarid Tehuacán Valley, Central México. Richness and diversity of native plant species were compared between agroforestry systems (6 sampling sites) and the following forests (6 sampling sites) dominated by columnar cacti: (i) “chichipera” dominated by Polaskia chichipe; (ii) “jiotillal” dominated by Escontria chiotilla; and (iii) “garambullal” dominated by Myrtillocactus schenckii. Our information on genetic variation of dominant arboreal species in the study sites was reviewed and included in the analysis. Factors influencing household’s decisions to maintain vegetation cover were compiled through a survey and interviews and analyzed. All the samples of the agroforestry systems studied maintained on average nearly 59% plant species and 94% genetic variation of dominant cacti occurring in the forests, although their ability to preserve endemic rare species is limited. Social factors favoring maintenance of perennial species in agricultural plots include collective rules, households traditions, use of the plants maintained in the systems, and the environmental information gathered from NGOs, the local Biosphere Reserve, and researchers. However, agroforestry systems are losing their capability to maintain vegetation cover, mainly because of (i) decreasing amount of land managed by households, determined by a progressive fragmentation of the land area given to new families, (ii) adoption of technologies to intensify agriculture, and (iii) governmental programs penalizing the presence of vegetation patches within agricultural lands since they are considered “useless” areas. Necessary policies to stop degradation of the agroforestry systems and to improve their conservation capacity are discussed.  相似文献   

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By the Royal Decree issued on the 21 of September 1900 the forests in the Los Vélez region were divided between the Ducal House of Medina Sidonia and, jointly, to the villages of María, Vélez Blanco and Vélez Rubio.The said forests are the result of evolution of the history of Spain itself, in which, during almost three centuries, there has been coexistence between the communal uses inherited from their Muslim forbears and the feudal rights that the House of Fajardo, the present Ducal House of Medina Sidonia, received from the Catholic Monarchs.The beginning of the nineteenth century saw the end of the Old Spanish Regime and, with it, the complete transformation of society and customs in force up to that time. Many of these changes were produced by the laws established by the Cortes de Cadiz (a parliament which established a new Spanish constitution), one of which abolished feudal estates. The political instability the country was going through and the controversies that arose as regards how to execute these rulings postponed their effective implementation and created a legal vacuum regarding what, until then, had been the exclusive right of the nobles, rights that included the ownership and exploitation of the forests.This vacuum caused a rapid deforestation in the district, in which the Administration could not intervene until the enactment of the Royal Order of 31 of January 1879. From this date and until the publication of the Royal Decree dated 21 of September 1900 several Forest Engineers carried out and in depth study of the said forests and the causes of their ruin, which finally lead them to be shared between the Ducal House of Medina Sidonia and the villages of María, Vélez Blanco and Vélez Rubio. This established the bases for the forest management which would be carried out during the twentieth century, some aspects of which have continued up to the present moment.In order to gain knowledge of the evolution of the forests of María and Vélez Blanco during this period, as well as the influence the Forestry Administration had on the same, a study has been carried out on the events that occurred during the last quarter of the nineteen century. These commence with the first years of public intervention and end with the drafting of the Forestry Engineer Domingo Olazábal's Report regarding the specification of territories, approved by Royal Decree dated 21 September 1900 which, by sharing the forests between the Ducal House and the villages, confirmed the public nature of those assigned to the latter, thus establishing the bases for the public forestry management carried out during the twentieth century.  相似文献   

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Academic scholarship and development paradigms promote non-timber forest products (NTFPs) as potential options to link environmental conservation with sustainable economic development objectives for rural communities worldwide. The açaí berry (Euterpe oleracea) is a native palm found in forest ecosystems of northern Brazil and historically extracted and sold in regional markets. Recent increases in national and international açaí demand have resulted in dramatic price increases. Management decisions on a local producer level reflect trends not typically associated with traditional NTFPs as future production and income expectations increase. This case study draws on research conducted in peri-urban communities in close proximity to Belém, Brazil. The work draws links between recent açaí intensification trends in upland areas and information pathways that are contributing to this pattern. This paper argues that external information sources regarding land use choices are prioritized over local knowledge and market indicators which previously have been described as drivers for intensification processes of NTFPs. This qualitative analysis highlights the power structures that influence information sharing and in turn, land use choices on a community level. The results of this analysis are important for NTFP intervention initiatives focused on risk management for smallholders. Finally, this study is a useful complement for ecological studies currently being conducted on intensification processes of non-timber forest products.  相似文献   

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The potential of alley cropping systems supplied with a limited amount of fertilizer to restore crop productivity on a degraded site and to maintain crop productivity on a recently cleared, non-degraded site on ‘terre de barre‘ soils in Southern Bénin was investigated from 1994 to 1996. Leucaena leucocephala, Senna siamea and Gliricidia sepium were used as hedgerow species. Maize yields of the no-tree control plots dropped from the initial (1990) 401 kg ha−1 and 2181 kg ha−1 on the degraded and non-degraded sites, respectively, to 109 kg ha−1 and 1346 kg ha−1 in 1996, even with application of a minimal amount of mineral fertilizer. The alley cropping systems produced on average (mean of three treatments and three years) 107% more grain than the initial 1990 values on the degraded site and 11% less grain than the initial 1990 values on the non-degraded site. Especially the Senna and to a lesser degree the Leucaena treatment yielded consistently more grain than the control. The Senna trees contained a larger amount of N and produced more wood during the first pruning on the degraded site (155 kg N ha−1 and 14.0 ton fresh wood ha−1) than on the non-degraded site (49 kg N ha−1 and 6.6 ton fresh wood ha−1) most likely because of differences in subsoil fertility, as indicated by the higher clay, exchangeable bases, and N content between 60 and 125 cm cm. N accumulation and wood production by the Leucaena and Gliricidia trees was similar in both sites (82 and 36 kg N ha−1 and 4.6 and 9.3 ton fresh wood ha−1, respectively). When a limited amount of fertilizer is available, Senna appears to be the best choice as hedgerow species on sites with a relatively fertile subsoil. For other soils, a N2-fixing species may be a better choice. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

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Please refer to Br Med J, September 8, 1962, pp 621–627 for a copy of this article.  相似文献   

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In this study we analysed: (1) the biodiversity conservation capacity of Agroforestry Systems (AFS) in temperate highlands of the Tehuacán–Cuicatlán Valley, Central Mexico, (2) human cultural motives and actions for conserving such diversity and (3) problems endangering that capacity. We evaluated the richness and diversity of perennial plant species maintained in AFS through vegetation sampling of 14 agricultural plots and compared their composition with that of natural forests (14 plots of 500 m2 each). We examined the situations among communities of Náhuatl, Ixcatec and Cuicatec people, documenting through interviews the management practices of plant species and the whole system, reasons why people maintain vegetation cover within AFS, and factors influencing changes in decisions favouring agriculture intensification. In the AFS studied we recorded a total of 79 species of trees and shrubs, 86 % of them being native species and representing 43 % of all species of trees and shrubs recorded in the sampling of the natural forests the AFS derive from. People leave standing on average a total of 40 individual trees and shrubs per agricultural plot. Reasons for leave plant species standing were more frequently associated with their use as fruit trees, firewood, shade, beauty, respect to nature and other environmental benefits. Water availability for irrigation, land tenure, and dependence on agriculture and forest for peasant's subsistence were main decision factors influencing AFS variation in their composition. AFS in temperate zones are important reservoirs of biodiversity and biocultural heritage and should be keystones for conservation policies in the Tehuacán–Cuicatlán Valley.  相似文献   

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Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.  相似文献   

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Community forestry, promoted as a “win–win” forest management strategy yielded a variety of results that includes both failure and relative success. The willingness of government to hold control over forest resources while transferring only part of property rights to local communities is one of the major constraints. Therefore, there is a need to explore alternative approaches, which enhance the position and accountability of local communities in community forest management. This study evaluated socio-economic and ecological outcomes of community forestry in a context of important property rights conceded to local communities. The study was conducted using focus groups discussions, forest income evaluation and assessment of forest resources and their dynamics. Findings showed that institutional design with important property rights conceded to local communities partially empowered local communities and reduced threats while improving the condition of forest resources. The approach also yielded positive economic outcomes that enabled bordering populations to make up to 25% of their global annual income from the forest. However, the sustainability of this scheme of forest management was mostly limited by the financial dependency on local non-governmental organization, by local institutions and discrepancy in forest benefits sharing among local forest users.  相似文献   

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Psyttalia concolor is a parasitoid of fruit flies (Tephritidae) which is used to control the olive fruit fly (Bactrocera oleae). Detailed knowledge of its reproductive biology is required to optimise mass rearing conditions and use in biological control. In this study, the mating behaviour of P. concolor was investigated in order to understand the factors that can influence the success of male mating, using both high-speed video and biological assays. P. concolor males were more likely to be successful in mating during the early morning as opposed to the afternoon, and their courtship behaviour was not affected by the female mating status (i.e. virgin or mated). Wing fanning and copulation attempts were also frequently displayed among males, but male mating status did not influence male–male courtship behaviour. Video data revealed that during wing fanning, male wings were kept raised and moved rhythmically in a dorsoventral fashion. Frequency, pulse duration and interpulse interval of the fanning males during female courtship differed significantly in successful mating attempts compared to unsuccessful ones. Wingless males had significantly lower mating success compared to winged males, suggesting that wing fanning increases the likelihood of attracting a mate. Overall, the study increases the knowledge of the reproductive biology of P. concolor and suggests the importance of fanning behaviour among the range of sensory modalities used by this parasitoid in intra-specific communication.  相似文献   

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