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林业害鼠（兔）是我国4大类林业有害生物之一,对林业生产和生态建设造成严重危害,探讨其分布范围、发生现状及防治措施对保护我国森林资源具有重要的理论和实践意义。文中论述了我国林业害鼠（兔）的主要种类、发生现状、分布范围、危害程度,并简要回顾了不同防治措施的发展历程,总结归纳了取得的防治效果及近年来涌现出的新技术、新药剂,指出了当前在我国林业鼠（兔）防治工作中存在的主要问题,并提出了将来林业鼠（兔）害防治研究设想,以期为我国林业鼠（兔）害防治技术的后续研究和科学治理提供参考。 相似文献
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调查结果表明森林鼠兔害在绥阳县主要危害10年生以下树木。在鼠(兔)害发生严重地区,被害株率达到55%以上,平均被害枯死株率在12%左右,林区鼠口密度35只/hm2、兔口密度60~90只/hm2。用血腥驱避法、无毒仿生剂(溴敌隆杀鼠剂)、捕鼠(兔)夹、鼠(兔)笼、钢丝绳套和索套等物理器械捕杀鼠(兔),能有效防治森林鼠(兔)的危害。 相似文献
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对兰州市3县5区的荒山造林地及退耕还林地的林业鼠(兔)害危害现状进行了调查,系统分析了其发生的原因,并针对鼠(兔)害现状提出了防治对策及建议。 相似文献
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近年来,我国中西部退耕还林工程区内,鼠、兔害频频发生。据统计,陕西省今春鼠害发生面积达14.2万公顷,兔害发生面积达12.4万公顷,林木被害株率普遍在30%以上,严重的可达70%。今年内蒙古全区共发生突发性森林鼠、兔害面积达94万公顷。森林鼠(兔)害已成为制约造林绿化成果和退耕还林工程顺利实施的一个重要因素。森林鼠(兔)害在我国发生范围广泛,涉及北京、河北、山西、内蒙古、辽宁、吉林、黑龙江、福建、河南、湖北、湖南、海南、四川、重庆、贵州、云南、陕西、甘肃、宁夏、青海、新疆等21个省、自治区、直辖市以及龙江森工集团、内蒙古森… 相似文献
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陇南地区退耕还林地鼠(兔)害现状及预防对策 总被引：1，自引：0，他引：1
论述了陇南地区退耕还林工程区森林鼠(兔)害发生危害现状，系统分析了发生原因，并提出了加强退耕还林区森林鼠(兔)害防治工作对策。 相似文献
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通过在不同海拔高度设置样地调查分析,祁连山区分布的36种啮齿动物形成4大类群7个亚群落.中华鼢鼠是林业生产的主要害鼠,因掘洞取食树木根系对幼林造成危害,年被害株率在10%～40%,平均18%.依据森林有害生物可持续控制原理,提出了祁连山自然保护区森林害鼠、兔的可持续控制策略,总结了区内主要森林害鼠中华鼢鼠的综合治理措施,进行了大面积推广防治. 相似文献
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随着天保工程的逐步推进,鼠、兔危害亦日趋加重,已严重影响到当前植被恢复的成活率和保存率。究其原因,分析其特点,对鼠兔害综合治理的对策和防治技术措施提出了一些初浅意见。 相似文献
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Free vibration testing was conducted to generate the first two mode shapes for damage detection in timbers. A wavelet transform
was proposed to postprocess the mode shapes for damage pattern recognition. The wavelet used here was “db3.” The different
damage severities, damage locations, and number of damaged areas were simulated by removing mass from intact beams. The results
showed that the chosen wavelet db3 is suitable and that the wavelet coefficients are sufficiently sensitive to identify the
existence of damage and its location in cases of different damage location, severity, and number. An edge distortion effect
was apparent at the two computing edges where the wavelet coefficients were abnormally high. The wavelet coefficients showed
dominant spikes around the damage locations and were zero everywhere else except the two computing edges. The dominant spikes
coincided well with the damage location. 相似文献
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Vegetation and weather explain variation in crown damage within a large mixed-severity wildfire 总被引：1，自引：0，他引：1
The 2002 Biscuit Fire burned through more than 200,000 ha of mixed-conifer/evergreen hardwood forests in southwestern Oregon and northwestern California. The size of the fire and the diversity of conditions through which it burned provided an opportunity to analyze relationships between crown damage and vegetation type, recent fire history, geology, topography, and regional weather conditions on the day of burning. We measured pre- and post-fire vegetation cover and crown damage on 761 digital aerial photo-plots (6.25 ha) within the unmanaged portion of the burn and used random forest and regression tree models to relate patterns of damage to a suite of 20 predictor variables. Ninety-eight percent of plots experienced some level of crown damage, but only 10% experienced complete crown damage. The median level of total crown damage was 74%; median damage to conifer crowns was 52%. The most important predictors of total crown damage were the percentage of pre-fire shrub-stratum vegetation cover and average daily temperature. The most important predictors of conifer damage were average daily temperature and “burn period,” an index of fire weather and fire suppression effort. The median level of damage was 32% within large conifer cover and 62% within small conifer cover. Open tree canopies with high levels of shrub-stratum cover were associated with the highest levels of tree crown damage, while closed canopy forests with high levels of large conifer cover were associated with the lowest levels of tree crown damage. Patterns of damage were similar within the area that burned previously in the 1987 Silver Fire and edaphically similar areas without a recent history of fire. Low-productivity sites on ultramafic soils had 92% median crown damage compared to 59% on non-ultramafic sites; the proportion of conifer cover damaged was also higher on ultramafic sites. We conclude that weather and vegetation conditions — not topography — were the primary determinants of Biscuit Fire crown damage. 相似文献
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A statistical algorithm for comparing mode shapes of vibration testing before and after damage in timbers 总被引：3，自引：0，他引：3
Instances of local damage in timber such as knots, decay, and cracks can be translated into a reduction of service life due
to mechanical and environmental loadings. In wood construction, it is very important to evaluate the weakest location and
to detect damage at the earliest possible stage to avoid future catastrophic failure. In this study, modal testing was used
on wood beams to generate the first two mode shapes. A novel statistical algorithm was proposed to extract a damage indicator
by computing mode shapes of vibration testing before and after damage in timbers. The different damage severities, damage
locations, and damage counts were simulated by removing mass from intact beams to verify the algorithm. The results showed
that the proposed statistical algorithm is effective and suitable for the designed damage scenarios. It is reliable for the
detection and location of local damage of different severities, location, and number. The peak values of the damage indicators
computed from the first two mode shapes were sensitive to different damage severities and locations. They were also reliable
for the detection of multiple cases of damage. 相似文献
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Local damage such as knots, decay, and cracks can result in a reduction of service life due to mechanical and environmental
loadings. In wood construction, it is very important to evaluate the weakest location and to detect damage at the earliest
possible stage to avoid future catastrophic failure. In this study, modal testing was carried out on wood beams to generate
the first two mode shapes. A novel statistical algorithm was proposed to extract the damage indicator by computing the local
modal flexibility before and after damage in timbers. Different damage severities, damage locations, and damage counts were
simulated by removing mass from intact beams to verify the algorithm. The results indicated that the proposed statistical
algorithm is effective and suitable for the damage scenarios considered. The algorithm was reliable for detecting and locating
local damage under different damage scenarios. The peak values of the damage indicators computed from the first two mode shapes
were sensitive to different damage severities and locations. This approach was also reliable for detecting multiple defects. 相似文献
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Changes in susceptibility to wind and snow damage due to thinningand fertilization were examined in even aged Norway spruce (Piceaabies (L.) Karst.) stands in southern Sweden. The stands arepart of a nationwide experiment to investigate growth and yieldfollowing different thinning and fertilization regimes establishedbetween 1966 and 1983. The material used in this study included16 replications of seven treatments. The treatments were: threelevels of thinning from below (20–70 per cent); 20 percent thinning from above; thinning from below in combinationwith N and NP fertilization (thinning percentage 25–28per cent); and unthinned control. The stands have been censusedtwice for damage during an average period of 12 years. The degree of wind and snow induced damage varied between 9and 20 per cent of the basal area increment produced duringthe observation period. For treatments with high basal arearemoval, the highest relative number of trees damaged by windoccured during the first period after thinning. The denseststands (i.e. unthinned controls and stands thinned from above)showed a high proportion of snow damage throughout the observationperiod. The block effect was in general more significant thanthe effect of treatments on damage level. When analysing theinfluence of the block effect (i.e. of site and stand characteristics)on damage level, wind damage was best predicted by stand basalarea left after thinning and stand age, while snow damage wasbest predicted by latitude, altitude, site index, and standage. On average the tested site and stand characteristics explained17 per cent of the variation in wind damage and 36 per centin snow damage. 相似文献
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Several heavy wet snowfalls occurred during 2007-2009 across a broad-scale thinning and fertilization experiment to bring overstocked juvenile lodgepole pine (Pinus contorta var. latifolia) in the foothills of Alberta, Canada into an intensive management regime. We examined the bending and breakage of trees in relation to thinning and fertilization and used a multimodel information-theoretic approach to model stand and tree level predictors of snow damage. Fertilized stands suffered the greatest amount of snow damage, and this was most noteworthy when stands were also thinned; here 22% (17% broken stems) of trees were damaged compared to 8% (4% broken stems) in the thinned and unfertilized stands. At the stand level, needle weight and crown cover were reliable predictors of snow damage. At the tree level, separate models were developed for each combination of thinning and fertilization. All models used total tree volume; usually the smaller trees in the stands were more susceptible to damage but in the thinned and fertilized stands larger but slender trees with large asymmetrical crowns tended to be damaged. Also, trees with lower total stem volume were more susceptible to damage. Only in the thinned and fertilized stands were variables related to crown shape and asymmetry important predictors of snow damage. We conclude that snow damage is an important agent for self-thinning in unthinned stands and fertilization tends to exacerbate damage because of increase in foliage size. In areas with regular occurrence of heavy snow, we do not recommend fertilization at the same time as thinning, as the larger and more economically important trees in the stand are at risk. 相似文献
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In deciduous forests, tree seeds and seedlings are frequently exposed to high predation by small rodents, and this predation
can have an important effect on forest regeneration. However, damage to large trees by small rodents has not been studied,
except for damage observed during timber production. To determine factors affecting damage to large trees by the grey red-backed
vole (Myodes rufocanus bedfordiae), the characteristics and spatial patterns of tree damage by voles at vole wintering sites were examined over 3 years in
a deciduous forest in Hokkaido. This study found that the location of damaged trees was related to vole wintering sites. Vole
damage was affected by tree species. Damaged trees were heavily concentrated in small areas. Leaning trees and trees that
had suffered previous damage were more likely to be damaged. However, the diameter at breast height was not significantly
related to vole damage. These differences in susceptibility to vole damage may result in different tree mortality. 相似文献
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Farzam Tavankar Angela Lo Monaco Mehrdad Nikooy Rachele Venanzi Amireslam Bonyad Rodolfo Picchio 《林业研究》2019,(4):1383-1394
Snow damage on natural stands is an important problem concerning mountainous forest management.In the present research,the frequency and intensity of heavy snow damage on natural stands and the relationship of damages with characteristics of trees,stand and topography were studied in mountainous forests of northern Iran.A systematic sampling design was applied to the study area(140 ha),with 122 circular plots.The grid dimension was100 m and each plot area was 1000 m^2.The four types of snow damage to trees include:crown damage(8.6%),stem breakage(5.4%),uprooting(3.2%),and bending(1.4%).The frequency of crown damage grew with an increase inthe diameter at breast height(DBH),while the frequency of stem breakage,uprooting and bending decreased with an increase the DBH.The frequency of crown damage,stem breakage,and total damages was related to tree species(p<0.01).Not all tree species were equally susceptible to snow damage.The amount of damage grew with increasing elevation and slope angle and decreased with increasing soil depth.Young trees(DBH<25 cm)were more susceptible to snow damage than other trees.Snow damage decreased by as the trees in the stand became more mixed in age.The susceptibility of trees to snow damage increased by height and slenderness coefficient.With adequate silvicultural operation,snow damage can be reduced to a minimum level in these natural forests. 相似文献
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Modal-based damage-detection algorithms were used to identify the location of defects commonly found in timber and to estimate
their severities. In this study, the authors propose modifications to an existing damage-detection algorithm for locating
and evaluating damage by comparing the modal strain energy before and after damage using the first two flexural modes of vibration.
Experimental verification was performed on pin-pin supported timber beams by employing the algorithms with extracted modal
parameters using experimental modal analysis. Single and multiple cases of damage used to simulate pocket(s) of rot with various
severities were inflicted by removing sections of timber beam specimens. The proposed damage indicator, computed from the
first two flexural modes, was capable of detecting all damage locations. It was also able to estimate, with reasonable accuracy,
the severity of damage in term of loss of sectional moment of inertia. The modified damage index method is generally reliable
in detecting the location and estimating the severity of simulated defects in timber beams. 相似文献