Fraxinus nigra (black ash) dieback in Minnesota: Regional variation and potential contributing factors

Extensive tree dieback is a recurrent issue in many regions. Crown dieback of Fraxinus nigra Marsh. (black ash; brown ash) in the northeastern and north central United States is an example. F. nigra is a widely distributed hardwood that is often the dominant species in wetland forests from Manitoba to Newfoundland and West Virginia to Indiana. Widespread crown dieback of F. nigra has been noted in many regions, but there are few quantitative assessments of dieback extent or relationship to potential causes. Most F. nigra dieback episodes are not associated with specific disease or pest agents. Drought, excessive soil moisture, cohort senescense, and road influences, have all been suggested as potential contributing factors. Our objectives were to (1) quantify variable dieback across northern Minnesota, a region described as having extensive dieback, (2) determine the relationship between dieback and site moisture, (3) relate dieback to tree age/size distributions, and (4) assess whether dieback was related to road proximity. Given the increasing threat of Agrilus planipennis (emerald ash borer) in the region, it is important to know the current health status of F. nigra populations before widespread infestation occurs. Many stands in our study exhibited high incidences of crown dieback. However, the incidence of dieback was variable across the region. Spatial variability in dieback was associated with site wetland characteristics; more dieback occurred on jurisdictional wetlands and on sites with a higher wetness index and a deeper depth to a perching layer. Dieback was also positively correlated with mean stand diameter, and tree diameters were generally correlated with age, suggesting that stands with larger and older individuals experienced more dieback. Cohort senescence is a possible explanation for this trend. Finally, dieback occurred with higher frequency nearer to roads. The road influence could be related to hydrological alterations or perhaps toxicity from road deicing salt. The fact that dieback is more severe close to roads may contribute to a general perception that black ash dieback is more severe throughout the region than our study suggests. Collectively, our results indicate that the healthiest F. nigra stands in our study region are likely to be younger and located on relatively drier sites and farther from roads, compared to stands with significant crown dieback.     

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树木叶片叶绿素含量的消长规律是反映叶片生理活性变化的重要指标之一。以健康白桦和受虫害加拿大杨为实验材料,利用SPAD-502叶绿素仪对其进行叶绿素相对含量测定,并结合相应的生长光照条件和病虫害程度进行分析,探索SPAD值在响应叶片光环境和健康水平方面的能力。研究结果表明,利用SPAD-502叶绿素仪对阔叶树种的光环境及叶片健康水平进行评价是可行的,如能同时结合其它检测手段和方法,则更能保证评价的准确度。     

河北省2001-2008年医学论文产出的文献计量分析

为了解和评估近8年来河北省二级以上医疗卫生机构的科研能力和学术水平,运用文献计量学方法,对其2001-2008年的论文产出量进行了分析,旨在为各级卫生行政部门领导提供参考。     

基于Big6模型的卫生政策研究信息资源采集策略

首先介绍了Big6模型的概念、特点及其流程,然后基于Big模型将卫生政策知识服务平台资源采集过程分成任务定义、确定采集策略、采集信息、运用信息、整合信息和过程评价6个阶段,并对各阶段的具体内容进行了分析,以提高采集流程的规范性和完整性。     

利用VPN网络平台服务社区医疗卫生单位

从分析我国社区医疗卫生服务的现状、特点入手,确定了地方医学情报机构对社区医疗卫生单位信息服务的定位,提出了利用VPN网络平台服务社区医疗卫生单位的设想。     

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对医药卫生科技查新工作中常用的中国生物医学文献数据库、中国期刊全文数据库、重庆维普中文科技期刊数据库和万方数据知识服务平台收录的期刊资源进行了对比分析,客观地描述了各数据库的收录特征以及数据库收录高质量期刊、医药卫生核心期刊比例和重复情况,并对数据库的未来发展做了SWOT分析,以期能为从事医药卫生科技查新人员和文献数据库研发人员提供指导和借鉴。