共查询到20条相似文献，搜索用时 187 毫秒
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选择西山区生长云南松、华山松、油杉、早冬瓜、栎类、圆柏六个树种的四种立地类型,以林分产量、产值、主伐年龄作为效果,应用灰包局势采用效果测度计算和目标加权值化方法,使不同目标在同一量纲尺度及多目标转化为单一目标下进行决策。结果证实此法是立地类型树种优化选择的一种好方法。本文还着重介绍了灰色局势决策的方法和计算过程。 相似文献
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针对三都县林业发展存在的问题，用层次分析法将林业发展的目标，制约因素，对策措施等按目标层，制约层，对策层三个层次建立层次分析结构图，然后进行计算，排序和分析。制约层的分析结果表明，目前制约三都县林业发展的主要因素是消耗量过大，政策性影响，林政管理跟不上，投资不足等。对策层的分析结果表明，大力植树造林，扩大森林资源，是三都县当前林业发展的首要对策；要使三都林业健康持续发展，必须建立，健全和完善林业政 相似文献
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通过３年时间空前规模的大面积调查和１５种抽样方法的比较，筛选出了松毛虫卵（块）、越冬幼虫、５龄幼虫和蛹种群密度估计适宜的和较为适宜的抽样方法，即按平行于等高线方向抽取样方的平行线抽样法和分层抽样法效果较好．但对分层抽样要注意层内抽样方法的选择问题．３０～４５株的抽样量是生产中能够接受的，且只要方法适宜，估计的准确度是很高的．此外，文中还就有关问题进行了必要的讨论． 相似文献
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通过对下挖地面加大底层净高后钢梁铰接于框架柱增设夹层、框架屋面采用轻质钢结构加层、单层砖房外套排架大空间加层这三个加层改造实例的介绍，分析如何选择加层的结构方案，以及这三项工程中节点的处理方法。 相似文献
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段维华 《林业机械与木工设备》1999,27(7):19-19,24
1前言汽车钢板弹簧卷耳、包耳、打弯等成型弯曲加工时，弯曲部分的中性层向内移，中性层曲率半径r的通常计算方法是根据弯曲半径R和簧片厚度h的比值，按钮金工下料计算中推荐的参数来选择中性层内移系数。但这种计算方法没有考虑复杂断面板簧两侧圆弧、双槽槽形以及槽形朝... 相似文献
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【目的】以崇礼冬奥核心区华北落叶松人工近熟林为研究对象，探讨目标树抚育间伐采伐木选择方法及其对林分空间结构的影响，为更加合理开展森林经营活动、促进人工林质量提升提供科学依据。【方法】设置并调查6块面积0.09 hm2(30 m×30 m)标准地，按125株·hm-2目标树密度，采用定性与定量指标相结合的方法标记目标树。基于树冠重叠和树冠光竞争高度构建采伐木选择指标，设置不同光竞争截止系数(c)模拟选择采伐木，分析采伐强度变化，运用角尺度、混交度、密集度、交角竞争指数、林层指数和综合空间结构指数分析不同c值下目标树和林分空间结构指标的变化。【结果】c取值在0～1之间时，株数采伐强度和断面积采伐强度在10%～35%范围内变化，且呈随c值增大而降低的相同变化趋势。经模拟采伐后目标树空间结构得到优化，改善幅度随采伐强度增大而增大。综合空间结构指数在c值0.6时达到最大提升幅度45.50%，角尺度和密集度在c值0.7时变化幅度最大，分别为17.93%和46.83%，其他空间结构参数在c值0.6时达到最大变化幅度。抚育间伐可同时优化林分空间结构，对林分树... 相似文献
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丘陵红壤防护林树种优化模式选择 总被引：5，自引：0，他引：5
通过丘陵红壤上营造防护林的各树种生长调查、解析木分析和对８种林带配置模式进行技术效果评价，用多目标灰色局势决策的方法做出优化模式选择。这类地区造防护的优良树种为杉木、泡桐、香椿、擦树等；配置方法以混交为好； 优化模式以Ｇ和Ｅ综合效果为最佳。 相似文献
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J. Ram V. K. Garg O. P. Toky P. S. Minhas O. S. Tomar J. C. Dagar S. K. Kamra 《Agroforestry Systems》2007,69(2):147-165
Ground water table (g.w.t.) levels were measured twice a month for 2 years in 50 observation wells installed inside and outside
the two 18-year-old and 350 m apart plantations of Eucalyptus tereticornis (Mysure gum) at Dhob-Bhali research plot located in Rohtak district of Haryana state (north-west India). Throughout the study,
the g.w.t. underneath the plantations remained lower than the g.w.t. in the adjacent fields. The average g.w.t. in the plantations
was 4.95 m and the average g.w.t. in the control located in adjacent fields was 4.04 m. Interestingly, the spatial extent
of lowering of g.w.t. in the adjacent fields was up to a distance of more than 730 m from the edge of a plantation. Drawdown
in the g.w.t. developed due to the effect of a plantation was similar to the cone of depression of a pumping well and the
drawdown in the g.w.t. developed due to the joint effect of both the plantations was similar to the combined cone of depression
of two pumping wells. There was no correlation between soil salinity and the g.w.t. The fluctuations in g.w.t. caused fluctuations
in g.w.t. salinity in the plantation as well as in the adjacent fields, but there was no net increase in g.w.t. salinity underneath
the plantation. Sinker roots of Eucalyptus tree reached the zone of capillary fringe up to a depth of 4.40 m, indicating that
the Eucalyptus trees were absorbing capillary water of the g.w.t. Thus, in shallow g.w.t. areas of semi-arid regions with
alluvial sandy loam soils, the plantations of E. tereticornis act as bio-pumps and therefore, we recommend closely spaced parallel strip plantations of this species for the reclamation
of waterlogged areas. 相似文献
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《Forest Ecology and Management》1999,114(1):137-150
Heathland has existed for more than 3000 years in one field area, and the oak wood has probably not been deforested since the last glaciation about 14 000 years ago in the other field area. This vegetation history provides a unique opportunity for considering the effect of vegetation-type on the weathering processes of the percolation zones of fluvio-glacial sediments. The role of atmospheric deposition and organic internally produced acidity in controlling the weathering processes of the percolation zones is examined. Soil texture, carbonate content, CEC, and the soil water chemistry of the percolation zones under heathland and oak wood were studied from 6 and 7 m deep wells in which suction cells were installed at different depths. The carbonate dissolution front of the sandy Weichselian (14 000 BC) sediments under the oak wood was found at a depth of 3.5 m below ground level, whereas under heathland the percolation zone down to 6.3 m depth was decalcified. An important finding from this investigation is that alkalinity matches the sum of Ca+2+Mg+2 in equivalents in the percolation zone of the oak wood. This means that carbonic acid and/or other organic acids, and not acid deposition causes the dissolution of carbonate in the percolation zone under the oak. The oak wood ecosystem is able to neutralize the percolating soil solution better than the heather vegetation at the expense of a high degree of acidification of the solid phase of the percolation zone. Simulation with the hydro-geochemical model PHREEQM showed that vegetation-type, via the chemical composition of infiltration water, controlled the dissolution of carbonates as are present. Additionally, preferential flow in the percolation zone also seems to influence the dissolution process. 相似文献
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2006年四川发生了百年一遇的特大干旱。按照自然地理条件相近、森林覆盖率有较大差异的原则,采用对比分析方法,于干旱末期,调查了四川盆地丘陵区13对乡镇(森林覆盖率高的乡镇森林覆盖率为28.26%～56.23%,平均为38.22%,相对应的低的乡镇森林覆盖率为5.65%～27.10%,平均为16.41%)内的溪河流量、堰塘和水井干枯情况以及人畜饮水现状。结果表明,在干旱季节,森林覆盖率低的乡镇溪河断流率平均为69.1%,断流天数平均为52 d;而覆盖率高的乡镇溪河断流率平均为25.5%,比前者少43.6%,断流天数平均为35.3 d,比前者少16.7 d,溪河平均断流起始时间比前者推迟17.3 d。森林覆盖率低的乡镇堰塘、水井平均干枯率分别为62.5%、70.0%,新打水井中,出水井率为48.2%;而覆盖率高的乡镇堰塘、水井平均干枯率分别为40.9%、43.7%,比前者分别低21.6%、26.4%,新打水井中,出水井率为57.7%,比前者高出9.5%。人畜饮水困难数占总人畜比例,覆盖率高的乡镇比覆盖率低的乡镇分别少24.0%、23.2%。 相似文献
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Wild forest fires are one of the greatest environmental disasters affecting forest resources. Along the coastal zone of the Mediterranean region in Turkey,forested areas are classified as first-degree, fire-sensitive areas. Every year, thousands of hectares of forests have been destroyed in Turkey. In this study, fire-access zones were determined in the Mediterranean forests of Turkey, by utilizing geographic information systems(GIS) technology. The effective reach distance of fire hoses from both sides of roads was considered in order to delineate fireaccess zones. The effective reach distance can vary based on the technical capabilities and hydraulic capacity of fire trucks(minimum and maximum pressures on water pump);terrain structures(uphill, downhill and flat); and ground slope. These factors and their influences were studied in fire sensitive forest areas located in the eastern Mediterranean city of Kahramanmaras? in Turkey. First, terrain structures on both sides of the road network and groundslope classes were determined based on GIS data layers.Then, fire access zones were delineated according to water pressure data, terrain structures, and ground-slope classes.The results indicated that 69.30 % of the forested areas were within the fire-access zones, while the rest of the forest was out of reach the fire hoses. The accessible areas were also calculated for forested areas with different firesensitivity degrees. The accessible areas were 69.59, 69.96,and 67.16 % for the forested areas that are sensitive to fires at the first, second, and third degrees, respectively. This finding has implications for the monitoring and management of fire threats in areas outside of the reach distance.The outside areas should receive extra attention and monitoring during the fire season so that fires are detected ahead of time and management has sufficient time to react.Besides, new roads should be considered for these areas in order to access more lands in a shorter amount of time. 相似文献
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在加格达奇城区给水系统改造工程中,关于水源技术改造项目,笔者首先时原有水源工作区可开采水量进行了科学的论证,然后对现有水源设备进行系统的分析,找到了虽然有水但采不出来的问题所在。通过调整水源井设备,并对个别水源井加以改造,使其在枯水期增加产水量,达到了挖潜的目的,满足了城市用水量的需求。 相似文献
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Vladimír Račko František Kačík Oľga Mišíková Pavol Hlaváč Igor Čunderlík Jaroslav Ďurkovič 《Annals of Forest Science》2018,75(3):82
Key message
Fungal infection was outlined as a potential reason for the onset of indented annual growth ring formation during the juvenile phase of hazel wood growth. Annual growth ring indentations resulted from the formation of disturbed zones which originated solely in close proximity to leaf traces.Context
Hazel wood is an abnormal type of woody tissue that is formed as a result of exogenous stimuli that may trigger long-term responses in the cambium. Cambial responses produce anatomical alterations in the surrounding xylem tissue that can be observed as an indentation of annual growth rings. The chemical profiles of lignan hydroxymatairesinol may provide an indication of its possible role in the protection of a living tree against the spread of a fungal or microbial infection at the onset of indentation.Aims
The objectives of this study were to reveal the anatomical differences in the altered woody tissue of Picea abies hazel wood at both the onset and the later stages of annual growth ring indentation and to determine the chemical profiles for hydroxymatairesinol upon elicitation by a fungal infection in the disturbed zones.Methods
Light and scanning electron microscopy observations were carried out on radial, tangential, and cross sections of hazel wood zones separated from P. abies stems. Concentrations of hydroxymatairesinol were determined for both the disturbed zones and the non-indented zones using a gradient high-performance liquid chromatography.Results
The formation of disturbed zones was accompanied by significant changes in both the direction and width of the tracheids which produced an abnormal formation of intertwined and twisted tracheids. Fungal hyphae, radial cell wall cracks, and unusually large cross-field pitting were all found in the tracheids of the disturbed zones.Conclusion
The content of hydroxymatairesinol in the acetone extract determined from the disturbed zones was 3.4 times greater than that present in the non-disturbed tissues. By means of vascular dysfunction in the leaf traces, host trees responded to the fungal infection by plugging the lumens of conductive leaf trace tissue and filling the vascular pathway with polyphenolic compound deposits.18.
Alfred J. Stamm 《Wood Science and Technology》1977,11(1):39-49
Calculations of the monomolecular water vapor adsorption by three different celluloses (cotton, wood pulp and cellophane) from structural considerations are in agreement with the BET determined values for crystallite diameters of 16 to 200 on the basis of adsorption being confined to the fraction f of the three hydroxyl groups per anhydroglucose unit that are available on the surface of the crystallites and within the amorphous zones, when f ranges from 0.16 to 0.29. These low values of f are compatible with the fact that the void volume of the amorphous zones does not exceed about 6%. More exact values for f are needed before more definite values for the crystallite diameters can be estimated. A modified fringe micelle diagram containing a considerable amount of chain association in the amorphous zones is given that meets the requirement dictated by the calculations. Another approach, involving direct estimation of the adsorbing surface areas of crystallites and amorphous zones, on the basis of adjacent surfaces being shared by water molecules adsorbed between them, gives surface areas somewhat larger than the BET values using the same f values. Agreement with values from the former approach is obtained if only 75% of the surface per anhydroglucose unit is considered effective for adsorption. 相似文献
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Johanna Lundström Karin Öhman Hjalmar Laudon 《Scandinavian Journal of Forest Research》2018,33(5):493-501
Increased awareness of the connection between forest management activities and negative effects on water quality means that forestry needs to consider its potential impact on the aquatic environment when planning operations. Protective buffer zones are effective, but their design can vary. To be able to incorporate up-to-date scientific theory into practical applications easy-to-use planning tools are needed. In this study, we evaluate different buffer zone alternatives by using the freely available decision support system Heureka. The consequences on both economic and ecological values over a time period of 100 years were evaluated for two buffer zone approaches and three management alternatives within the buffer zones. Results indicated that there is a trade-off between economic and ecological values when managing the buffer zones. To be able to perform the analyses within Heureka, a new tool was developed. This software development provides access to a forest planning tool that can help improve nature conservation. 相似文献