排序方式： 共有7条查询结果，搜索用时 846 毫秒
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北京郊区生态果园数量较多。对不使用除草剂,主要采取清耕措施为主的生态果园中非靶标植物进行调查、分类和分析,将果园中植物分为4类,即果园杂草、果园行间生草和种草、果园趋避植物、果园栅栏植物。其中果园杂草有34科95属115种,其中常见的83种。常见种中以一、二年生草本和具地下根状茎或以地面芽越冬的多年生草本为主,彻底清除比较困难。并和30年前果园杂草从物种多样性和分布情况方面进行了比较,发现物种多样性有所下降,少了10科31属59种植物,但也新增加了2科17属30种,净减少8科14属29种;杂草中有7种属于外来入侵物种。统计出行间种草10种,种植趋避植物20种,建议用作栅栏植物8种。 相似文献
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《Scandinavian Journal of Forest Research》2012,27(6):651-660
A set of hypotheses was formulated on the basis of available knowledge about non-industrial private forest (NIPF) owners' risk preferences. The empirical material used for testing the hypotheses was gathered in telephone interviews with 130 randomly selected NIPF owners. The results confirm that direct economic risks such as price and cost changes are seen by this group as much more important than indirect economic risks such as biological damage. The forest owners regarded forest holdings as a safer investment than stocks or bank savings. The results on risk attitudes were ambiguous. However, when larger amounts of money were at stake, the forest owners could be considered risk averters and a decrease in absolute and relative risk aversion could be confirmed. 相似文献
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以桂醛、邻苯二甲酸二辛酯、二甲基萘3种化学挥发物作为信息素,对吉林省白山市抚松县露水河镇红松育苗林昆虫的趋避与吸引作用进行了实验研究。结果表明,粘板诱集到的昆虫有双翅目、膜翅目、鞘翅目、同翅目、鳞翅目、直翅目、长翅目几类。通过实验组与对照组之间的对比得知,这3种试剂皆能诱到双翅目、膜翅目和同翅目的昆虫,且数量较多;桂醛和邻苯二甲酸二辛酯还能诱到少量鞘翅目的昆虫。3种试剂对昆虫引诱作用最强的是邻苯二甲酸二辛酯,诱到昆虫数量最少的是二甲基萘。邻苯二甲酸二辛酯对鞘翅目昆虫作用不明显,二甲基萘对鞘翅目昆虫具有趋避作用,桂醛对鞘翅目昆虫具有一定的诱导作用。 相似文献
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为什么中央银行在制定货币政策时往往是比较谨慎或保守的?从具体的货币政策规则的经验估计如泰勒规则看,这些货币政策比具体经济模型所要求的最优货币政策更为保守。本文从模型不确定性及决策者对不确定性态度变化的角度,运用美联储数据进行实证来解释这一现象。经过分析发现,若与降低利率的变动相比,央行更为关心产出缺口的稳定性,则央行对模型不确定呈厌恶或呈中性将会大大降低泰勒规则中的反应系数,随之产生较为保守的货币政策,若央行对不确定性呈偏好,则产生较为积极的货币政策。 相似文献
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Eigil Reimers Bjørn Dahle Jonathan E. Colman Eldar Gaare 《Biological conservation》2007,134(4):484-494
Linear infrastructures such as roads, pipelines and power lines can hinder Rangifer migration and reduce the total amount of area available for foraging. We studied the barrier and aversion effect of a 66 kV power line transecting the range of wild reindeer in North Ottadalen, south central Norway using aerial surveys of reindeer distribution (direct measurement of reindeer use) and lichen measurements (indirect measurement of reindeer use) at varying distances from both sides of the power line. We present a clear definition of the expected barrier and aversion effects, and present specific hypotheses and predictions based on these two terms that are often used unclearly in the literature. The aerial surveys and ground observations showed that reindeer crossed underneath and grazed under and on both sides of the power line during 14 out of the 22 years (63.6%) surveys were conducted over the last 31 years. This behaviour was confirmed by the lichen measurements, indicating a higher use of lichen pastures along ridges close to and under the power line compared to those at increasing distances and up to 3 km from both sides of the power line. This winter grazing pattern probably reflects the topographical channeling of reindeer to the ridges along an 8 km wide topographical corridor encompassing the power line and cannot be attributed to the power line itself. We found that direct measurement data (visual observations such as ours or GPS/telemetry tracking) provide less ambiguous information for testing barrier and aversion effects than indirect measurement data (pasture/lichen measurements) that are likely influenced by numerous uncontrollable environmental variables independent of reindeer grazing. Our results contrast with recent studies indicating strong barrier and aversion effects of similar power lines for Rangifer migration and grazing behaviour in alpine terrain. 相似文献
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根据吉林省蛟河市太平山林场目前的森林资源经营状况,对该林场今后的发展方向进行了分析,指出应投资速生丰产用材林建设项目,以恢复和发展森林资源,保护生态环境。同时还预测分析了建设项目的投入产出情况和存在的风险。 相似文献
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