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Bruno Vila Franck Torre Frdric Guibal Jean-Louis Martin 《Forest Ecology and Management》2003,180(1-3):413-424
Taking advantage of the introduction of the black-tailed deer to the Queen Charlotte Islands (British Columbia, Canada), we used dendrochronological analyses to understand the consequences of deer browsing on Sitka spruce growth. We compared shape, radial growth, height growth and age of young spruce in three sites. We identified two types of trees growing side by side: (1) stunted and heavily browsed spruce, smaller than the browsing limit and (2) escaped spruce that were taller than the browsing limit but still browsed in their lower part. The compact and heavily ramified shape in stunted spruce was the result of repeated and intense browsing. In escaped spruce this was also the case below the browsing limit (1.16 m±0.07 m), in sharp contrast with the normal shape that escaped spruce resumed above the browsing limit. We show that the release of browsing pressure, once the tree reaches the browsing limit, is characterised by an abrupt increase in radial growth. Before release, trees show a growth stagnation characterized by narrow rings (0.5 mm per year) and small annual height increments (<5 cm per year). After release, trees show a growth stabilisation characterised by wider rings (3 mm per year) and larger annual height increments (20 cm per year). We use this pattern to estimate frequency and age at release and their possible variation over time. Age differences between stunted and escaped spruce are highly significant and indicate that, despite of browsing, most if not all trees will ultimately reach the browsing limit and escape. Heavy deer pressure (30 deer per km2) delays spruce sapling recruitment by about 8 years. This delay varies in relation to site quality and seems to have increased over time, suggesting an increase in browsing pressure. 相似文献
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研究了中小比例尺航片在森林蓄积量判读上的应用,结果表明：可以根据航片上影像灰度的平均值来进行树种的判别;利用灰度标准偏差进行林分蓄积量的估测,其拟合误差不足5%,满足林业生产实践的精度要求。填补了中小比例尺森林蓄积量判读的空白,是建立森林蓄积量判读的不同比例尺、不同遥感来源立体判读体系的重要补充,具有十分重要的现实意义。 相似文献
4.
Masoud Parsinejad Mohammad Reza Yazdani Hamed Ebrahimian 《Irrigation and Drainage》2009,58(2):147-156
Limitations on available water have caused increased attention toward research on techniques to use water more efficiently. In this study, the actual water application efficiency of rice paddy fields for 13 different sites throughout the province of Guilan, Iran, was investigated. Based on field measurements of water inflow and outflow, deep percolation and calculation of evapotranspiration, water application efficiency was determined for cases where the outflow was considered as a loss, i.e. at field scale, and for cases where a percentage of the outflow was considered as recoverable water, i.e. regional scale. The results show that, at field scale, the application water efficiency for the western, central and eastern section of the Sefidrood Irrigation Network was 38, 41 and 34%, respectively. On the other hand, at regional scale, if 80% of the outflow were considered as recoverable water, the above values were found to be 52, 51 and 46%, respectively. More recent proposed definitions on water management, such as consumed fraction (CF) and recoverable fraction (RF = 1 − CF) are also evaluated. Calculation of CF and RF values indicate that water potentially available for reuse is about 60% for the entire network. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
利润最大化是市场经济条件下,渔业企业追求的目标,那么,渔业企业在什么条件下才能获得最大利润以及在长短期中,随着市场价格的变化,渔业企业的盈亏状况怎样和如何调整生产规模,才能获得最大利润。本文就这些问题进行了分析。 相似文献
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对照“金牌住区”七大特色目标,对哈尔滨市近年开发的规模住区人居环境进行深入调研,分析总结现状存在的共性特征和发展的优劣势,指出今后规模住区人居环境改进方向。 相似文献
7.
S. BUSILACCHI A. J. WILLIAMS G. R. RUSS G. A. BEGG 《Fisheries Management and Ecology》2012,19(3):233-244
Abstract Retaining coral reef fish for subsistence during commercial fishing is a common practice for indigenous fishers in the Torres Strait, Australia, despite being inconsistent with legislation. Fisher access point surveys were completed between 2004 and 2006 on three islands in Torres Strait to characterise this subsistence practice and assess the level to which it undermines current minimum legal fish sizes. Approximately 15% of the annual total catch was retained for subsistence during commercial fishing. Notably, subsistence catch of the most commercially valuable species almost entirely comprised individuals smaller than the minimum legal sizes. The higher proportions of undersized individuals of valuable species retained during commercial fishing on some of the islands were most likely associated with an increase in professionalism of the fishers. These results demonstrate how the intended outcomes from a management strategy can be undermined when the specific operational conditions of the fishery are not considered. Successful implementation of management arrangements in indigenous communities ultimately depends on the sociocultural conditions of the communities and their understanding and adherence to the rules. A productive way forward for the management of this fishery is greater engagement of indigenous communities and managers in co‐management arrangements. 相似文献
8.
重新构建乡村林场产权制度的研究 总被引：1，自引：1，他引：1
浙江省乡村林场近几年有了迅速发展,但同时其产权制度建设是严重滞后和欠缺的。文章认为重新构建乡村场产权制度是适应社会主义市场经济发展,建立现代林业企业制度的客观要求的。是深化南方集体林区林业改革,推行林业股份合作制的前提条件,是发展规模经济的需要。根据不同类型乡村林场产权制度建设的调查研究。文章提出理顺产权关系,明晰产权主体,改革现行产权结构和切实保护产权主体利益等具体措施,以促进乡村林场的健康发展 相似文献
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近年来．江苏省新沂市围绕农业增效、农民增收,把市场手段与高效服务相结合,以项目农业为突破口,按照“东部花木、南部水产、西部设施瓜菜、中部规模畜禽养殖”的发展思路．积极推进高效农业规模化．不仅有效地提升了农业农村经济发展水平。而且显著提高了农民收入,有力地加快了社会主义新农村建设的步伐。 相似文献