Recreational Portage Trails as Corridors Facilitating Non-Native Plant Invasions of the Boundary Waters Canoe Area Wilderness (U.S.A.)

Abstract:  Wilderness areas are protected and valued in part for recreation; recreational use, however, can negatively impact these areas. In particular, recreational use can facilitate transport of non-native propagules and create open sites for establishment of non-native species. We examined the role of recreational portage trails in the introduction and establishment of non-native plants into the Boundary Waters Canoe Area Wilderness of northern Minnesota (U.S.A.). On 20 portages, we sampled non-native plant richness and cover at four distances (0, 10, 25, and 50 m) from trails. Non-native richness and cover were not related to distance from wilderness entry point. Non-native richness and cover were, however, negatively related to distance from trails. All six non-native species we observed were either directly on or within 1 m of trails. These results suggest that recreational trails act as corridors facilitating invasions of non-native plants into wilderness areas. It remains unclear, however, whether these effects are caused by dispersal of propagules, creation of bare ground, or changes in the native plant community.     

生态破坏诱发中国水旱灾害程度及计量——以90年代为例

生态破坏表现为植被破坏、水土流失、水系统淤塞，利用自然致灾因子和生态破坏因子可以构建水旱灾害的致灾函数。本文利用灾函数计算了生态破坏对中国９０ 年代水旱灾害的致灾影响度     

Indoor air quality and academic performance

I examine the effect of school indoor air quality (IAQ) on academic outcomes. I utilize a quasi-natural experiment, in which IAQ-renovations were completed at virtually every school in a single Texas school district at different points in time, combined with a panel of student-level data to control for many confounding factors and thereby uncover the causal effect of IAQ-renovations on academic outcomes. Results indicate that performance on standardized tests significantly improves while attendance is unresponsive to improvements in IAQ. Rough calculations suggest that IAQ-renovations may be a more cost-effective way to improve standardized test scores than class size reductions.     

Patterns of Citations of Open Access and Non‐Open Access Conservation Biology Journal Papers and Book Chapters

Abstract: Open access (OA) publishing, whereby authors, their institutions, or their granting bodies pay or provide a repository through which peer‐reviewed work is available online for free, is championed as a model to increase the number of citations per paper and disseminate results widely, especially to researchers in developing countries. We compared the number of citations of OA and non‐OA papers in six journals and four books published since 2000 to test whether OA increases number of citations overall and increases citations made by authors in developing countries. After controlling for type of paper (e.g., review or research paper), length of paper, authors’ citation profiles, number of authors per paper, and whether the author or the publisher released the paper in OA, OA had no statistically significant influence on the overall number of citations per journal paper. Journal papers were cited more frequently if the authors had published highly cited papers previously, were members of large teams of authors, or published relatively long papers, but papers were not cited more frequently if they were published in an OA source. Nevertheless, author‐archived OA book chapters accrued up to eight times more citations than chapters in the same book that were not available through OA, perhaps because there is no online abstracting service for book chapters. There was also little evidence that journal papers or book chapters published in OA received more citations from authors in developing countries relative to those journal papers or book chapters not published in OA. For scholarly publications in conservation biology, only book chapters had an OA citation advantage, and OA did not increase the number of citations papers or chapters received from authors in developing countries.     

Can Sustainable Agriculture Feed Africa? New Evidence on Progress, Processes and Impacts

Africa faces enormous food security challenges. Most commentators agree that, despite the complexities of food insecurity, there will have to be increases in food production from existing agricultural land. Most, too, are pessimistic about the future, judging likelihood of success on the basis of past performance of modern agricultural development. Sustainable agriculture, though, offers new opportunities, by emphasising the productive values of natural, social and human capital, all assets that Africa either has in abundance or that can be regenerated at low financial cost.This paper sets out an assets-based model of agricultural systems, together with a typology of eight improvements that are currently in use in sustainable agriculture projects. In the 45 projects/initiatives spread across 17 countries that are investigated, some 730,000 households have substantially improved food production and household food security. In 95% of the projects where yield increases were the aim, cereal yields have improved by 50–100%. Total farm food production has increased in all. The additional positive impacts on natural, social and human capital are also helping to build the assets base so as to sustain these improvements in the future.This analysis indicates that sustainable agriculture can deliver large increases in food production in Africa. But spreading these to much larger numbers of farm households will not be easy. It will require substantial policy, institutional and professional reform.     

THE NEED FOR A COMPREHENSIVE APPROACH IN THE MANAGEMENT OF ENVIRONMENTAL RESOURCES1

ABSTRACT Environmental resources can be managed properly only by adopting a comprehensive approach. The whole environment must be considered as a single system, and prior to any action, all types of environmental impacts caused by it should be studied in detail. This paper underlines the close relationship between different environmental problems, analyzes existing management patterns, and proposes new alternatives whenever applicable. The different constraints, which have to be considered in the decision-making process while developing a plan, are also discussed. It is concluded that efforts neglecting the interaction among different aspects of the environment do not upgrade the quality of water, air, and land to any appreciable degree.     

AN APPLICATION OF OPERATIONS RESEARCH METHODS TO BEACH RENOURISHMENT PROJECTS1

ABSTRACT: Mathematical models have been widely used in business to minimize cost and maximize profit. In this paper such models are used to help determine the optimum strategy for a beach renourishment project including the initial and subsequent fill quantities and the length of a complete renourishment cycle. The importance of considering economic factors is emphasized, and the sensitivity of the optimal values to changes in the basic parameters of the models are discussed. The possible extensions and limitations of the models are considered.     

室内空气污染对人体健康的影响与保护对策

本文首先介绍了室内空气污染的定义、室内空气中常见的污染物及其主要来源,分析 了室内空气中主要污染物对人体健康的影响,从而提出了保护室内环境的对策。