共查询到20条相似文献,搜索用时 15 毫秒
1.
Annika Kangas Mikko Nurmi Jussi Rasinmäki 《Scandinavian Journal of Forest Research》2014,29(7):154-165
The Finnish state forest enterprise, Metsähallitus, defines the regional harvest levels for a 10-year period in a strategic-level natural resources plan. Although this plan defines stand-level harvest schedules for all stands, in practice, it cannot be used, as the harvests need to be clustered in time and in space. It is applied by giving each subregion goals they need to fulfill in a tactical level planning process, and the harvests are manually clustered into predefined groups of adjacent stands (departments). In this study, we developed a hierarchical optimization process making use of departments for clustering the harvests. For each of the departments, 91 different stand-level harvest schedules (plans) were determined using incomes from one period and the forest value at the end as objectives. The department-level plans were then used as alternatives in a region-level goal optimization problem. The resulting hierarchic plan was compared to the stand-level solution of the strategic-level plan which served as a benchmark plan. The hierarchical plan clustered the harvests and achieved the goals set better than the benchmark plan, but the net present income was 3.3% lower. The approach turned out usable, but further developing of the approach is needed to reduce the costs of clustering. 相似文献
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Soil changes after traffic with a tracked and a wheeled forest machine: a case study on a silt loam in Sweden 总被引:2,自引:0,他引:2
Alterations to some soil physical parameters were evaluatedafter passes by a tracked forest machine and a wheeled one ofequal mass (about 20 000 kg). Measurements were made after arange of machine passes, with a maximum of eight. The measuredsoil physical parameters were dry bulk density, penetrationresistance, intrinsic air permeability, saturated hydraulicconductivity, porosity and pore-size distribution. Rut depthwas also measured. Although the wheeled machine caused deeper ruts than the trackedone, alterations caused by the two machines to the measuredsoil parameters were similar, except in the uppermost 510cm. The wheeled machine caused a decrease in bulk density at5 cm depth, whereas the tracked machine caused an increase,despite its lower ground pressure. 相似文献
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Kebin Zhang Rui Li Yunfang Liu Baitian Wang Xiaohui Yang Ruiping Hou 《Frontiers of Forestry in China》2008,3(3):326-333
The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid and semi-arid regions
in northwestern China and the main factors affecting the distribution pattern were studied. The Siertan wetland in the Haba
Lake Nature Reserve was the study area. Four transect lines, each about 1 km long, were set up in the growing season along
the biotope gradient in four directions: east, northeast, west and northwest. Attributes measured include frequency of occurrence,
height, density, coverage, biomass and environmental soil factors. The data were analyzed using a two-way indicative species
analysis (TWINSPAN), detrended correspondence analysis (DCA) and Spearman correlation coefficients. On this basis, the vegetation
in the Siertan wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh
vegetation, mainly distributed in the wetland zone. This type largely contains halophyte and hygric plants and its representative
association is Phragmites communis + Kalidium foliatum. The second type was meadow vegetation, distributed in the ecotone. The meadow vegetation species are mainly mesophytic and
their representative association is Nitraria tangutorum + Pennisetum flaccidum. The third vegetation type is grassland vegetation, which mainly consists of mesophytic and xerophytes, distributed in the
arid grassland zone. The representative association of the third vegetation type is the association of Anaeurolepidium secalium + Saussurea runcinata. Correlation analysis between the axes of DCA and environmental soil factors shows that soil moisture content, organic matter,
soil salt content and total nitrogen are the main environmental factors affecting the pattern of vegetation distribution along
the biotope gradients from wetland to arid grassland. Other factors affecting the vegetation are microtopography and grazing
pressure. Additionally, we have reported modifications and improvements to the importance value methodology.
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Translated from Journal of Beijing Forestry University, 2008, 30(1): 6–13 [译自: 北京林业大学学报] 相似文献
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利用RSM模型模拟计算三维水力旋流器模型,分析了计算结果,并且与相关文献比较后认为:三维模型模拟水力旋流器具有一定的可行性,而二维轴对称模型与实际有一定的差距。 相似文献
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The Silvopastoral Project is being implemented by CATIE in the Atlantic humid lowland of Costa Rica, in order to develop alternatives
to the current destructive mode of livestock production. The overall approach is briefly described and two superimposed on-farm
experiments are discussed in more detail. The main constraints for on-farm research within the project are analysed: the limited
previous knowledge of the area and of the local species, the difficulty of achieving a common understanding about research
with collaborating farmers, the need for additional staff supervision and the complexity of the statistical analyses. An attempt
is made to draw lessons from the ongoing project regarding how to resolve the apparent contradiction between rigorous scientific
requirements and questions of immediate value to extension, the compromises to be achieved between different types of evaluation
(statistical, risk, etc.) and the potentials and limitations of farmers' participation in research. 相似文献
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英犁 《绿色中国(A版)》2011,(6)
今天,你秒杀了吗?时下,许多网购爱好者都在津津乐道于秒杀话题:马尔代夫度假秒杀价1999元;iPhone手机秒杀价399元……果真有这样的好事?秒杀,就是以压倒性优势一招致命;在极短时 相似文献
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英犁 《绿色中国(综合版)》2011,(6):71-73
今天,你"秒杀"了吗?
时下,许多网购爱好者都在津津乐道于"秒杀"话题:马尔代夫度假"秒杀"价1999元;iPhone手机"秒杀"价399元……果真有这样的好事? 相似文献
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Wind Measurements in a Pine Forest During a Destructive Gale 总被引:3,自引:0,他引:3
Anemometer readings were recorded during a gale which blew downsome of the trees in an even-aged 16 m stand of Pinus sylvestrison sandy soil at Thetford forest. Gusts at the top of the canopyattained 175 m/sec. Wind profiles agreed well with thetheoretical logarithmic profile above the canopy and the exponentialprofile below. During the gale the zero plane displacement androughness length values were similar to those at lower windspeeds. It is therefore possible to estimate wind profiles andthe forces to which a tree in the crop is subjected from measurementsof wind speed at a single point within or above the forest.The wind speeds which blew trees down were much lower than thosepredicted as necessary from tree pulling studiesin the same forest. This discrepancy suggests that any considerationof windthrow must take into account the effects of tree vibrationon the deterioration in the strength of the root-soil complex. 相似文献
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为适应我国山地丘陵多、坡度陡和绞盘机作业强度大、维护不便等特点,提升绞盘机的操作性和转运能力,设计了一种无卷筒离合器的轻型绞盘机,阐述了绞盘机总体布置方案和工作原理,设计了采用齿轮传动的新型选筒机构,取代传统绞盘机的卷筒离合器,传动可靠,制造工艺简单,对选筒机构的花键轴和齿轮进行了强度校核,并对绞盘机传动系统的主要零部件进行了选型与设计,利用Matlab对绞盘机卷筒进行了轻量化优化设计,利用Solidworks进行了卷筒三维建模和有限元分析。结果表明,优化后的卷筒强度满足要求。该绞盘机采用新型的选筒机构,结构紧凑,安全可靠,整机轻量化程度高,便于运输,操作简便,可以有效提升绞盘机的工作效率。 相似文献
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Tomohito Sano Takashi Hirano Naishen Liang Ryuichi Hirata Yasumi Fujinuma 《Forest Ecology and Management》2010
A typhoon event catastrophically destroyed a 45-year-old Japanese larch plantation in southern Hokkaido, northern Japan in September 2004, and about 90% of trees were blown down. Vegetation was measured to investigate its regeneration process and CO2 flux, or net ecosystem production (NEP), was measured in 2006–2008 using an automated chamber system to investigate the effects of typhoon disturbance on the ecosystem carbon balance. Annual maximum aboveground biomass (AGB) increased from 2.7 Mg ha−1 in 2006 to 4.0 Mg ha−1 in 2007, whereas no change occurred in annual maximum leaf area index (LAI), which was 3.7 m2 m−2 in 2006 and 3.9 m2 m−2 in 2007. Red raspberry (Rubus idaeus) had become dominant within 2 years after the typhoon disturbance, and came to account for about 60% and 50% of AGB and LAI, respectively. In comparison with CO2 fluxes measured by the eddy covariance technique in 2001–2003, for 4.5 months during the growing season, the sum of gross primary production (GPP) decreased on average by 739 gC m−2 (64%) after the disturbance, whereas ecosystem respiration (RE) decreased by 501 gC m−2 (51%). As a result, NEP decreased from 159 ± 57 gC m−2 to −80 ± 30 gC m−2, which shows that the ecosystem shifted from a carbon sink to a source. Seasonal variation in RE was strongly correlated to soil temperature. The interannual variation in the seasonal trend of RE was small. Light-saturated GPP (Pmax) decreased from 30–45 μmol m−2 s−1 to 8–12 μmol m−2 s−1 during the summer season through the disturbance because of large reduction in LAI. 相似文献
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介绍一种以TI公司TMS320LF2407a为核心处理器的无线爬壁机器人嵌入式控制系统硬件电路.该系统实现了对爬壁机器人的运动控制、真空吸盘内的负压控制、对锂电池的电压检测和与上位机的无线通信. 相似文献
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基于DSP2407a的爬壁饥器人控制系统硬件电路设计 总被引:1,自引:0,他引:1
介绍一种以TI公司TMS320Ⅱ2407a为核一心处理器的无线爬壁机器人嵌入式控制系统硬件电路,该系统实现了对爬壁机器人的运动控制、真空吸盘内的负压控制、对锂电池的电压检测和与上位机的无线通信。 相似文献
19.
Shinji Kaneko Noriko Akieda Fumiya Naito Koji Tamai Yasuhiro Hirano 《Journal of Forest Research》2007,12(1):38-44
Rehabilitated forests established about 100 years ago on denuded lands in a hilly granitic area are widespread in the Kyoto–Osaka
area, the second largest megalopolis in Japan. From 2001 to 2003, we monitored the annual nitrogen (N) budget of a rehabilitated
forest watershed dominated by Quercus serrata and Ilex pedunculosa. The ion concentrations of bulk rain in the watershed were similar to those of other watersheds in Japan. The annual bulk
rain input of N ranged from 5.1 to 6.3 kg N ha−1 year−1, and the N deposition from throughfall and stem-flow ranged from 7.5 to 8.2 kg N ha−1 year−1. Estimated annual outputs of N from the stream ranged from 3.3 to 10.6 kg N ha−1 year−1. These results indicate that the amount of N deposition in this area is less than that in urban Tokyo (>10 kg N ha−1 year−1), but the N output of the watershed is comparable with that of the Tokyo area. We discuss the characteristics of N dynamics
in rehabilitated forests, focusing on the biogeochemical processes of this watershed. 相似文献
20.
北方某电厂现有电厂设备已经老化,而且供热出力不足,环保设施也不达标。同时,现有部分低温直供供热管网严重老化,热损失较大,现已超负荷运行,对其改造势在必行。 相似文献