Wolves, elk, willows, and trophic cascades in the upper Gallatin Range of Southwestern Montana, USA

We summarized the status of wolves (Canis lupus), elk (Cervis elaphus), and woody browse conditions during the 20th century for the upper Gallatin elk winter range in southwestern Montana, USA. During this period, wolves were present until about the mid-1920s, absent for seven decades, and then returned to the basin in 1996. A chronosequence of photographs, historical reports, and studies indicated willows (Salix spp.) along streams became heavily browsed and eventually suppressed following the removal of wolves, apparently due to unimpeded browsing by elk. However, after wolf establishment in 1996, browsing intensity on willows lessened in some areas and we hypothesized that, at both a landscape and fine scale, browsing pressure reflects terrain configurations influencing predation risk (nonlethal effects), in conjunction with lower elk densities (lethal effects). We measured browsing intensity and heights of Booth willow (S. boothii) along 3000 m reaches of the Gallatin River and a tributary to examine the potential influence of wolf/elk interactions upon willow growth. Where the Gallatin Valley is relatively narrow (high predation risk), willows began releasing in 1999 and by 2002 were relatively tall (150–250 cm). In contrast, willow heights along a wider portion of the Gallatin Valley, along the open landscape of the tributary, and an upland site (all low predation risk) generally remained low (<80 cm). We identified terrain and other features that may contribute to the perceived risk of wolf predation, by elk for a given site. Although alternative mechanisms are discussed, changes in willow communities over time following wolf removal and their subsequent reintroduction were consistent with a top-down trophic cascade model involving nonlethal and possibly lethal effects. If similar top-down effects upon vegetation hold true in other regions of North America and other parts of the world where wolves have been extirpated, wolf recovery may represent a management option for helping to restore riparian plant communities and conserve biodiversity.     

蒙特卡罗在项目融资风险评估中的应用

项目融资具有强大的筹资能力，在我国的应用具有广阔的前景。但项目融资也存在巨大的风险，需要对风险加以管理．风险评估是风险管理的重要步骤。本文通过介绍蒙特卡罗的基木概念、基本原理和工作程序，采用蒙特卡罗模拟与Matlab程序相结合的方法进行了项目融资风险定量评估，并结合实例对此方法予以说明。     

浅论生态补偿制度建立及原理

生态补偿是为防止生态资源配置扭曲，通过制度设计来修正发展平衡的问题。本文简要介绍了生态补偿的由来，分析了生态补偿的公共产品、外部效应和生态资本三大理论基础，回顾了中国生态补偿工作开展的情况，对建立生态补偿机制进出了一些建议。     

贵州省退耕还林工程生态效益监测与评价初探

通过对贵州省退耕还林10个生态效益监测网络县设置的100个坡面固定样地,以及5个典型县16个坡面径流场各生态指标2年观测数据的分析,得出退耕还林后监测区各生态指标的改善情况如下:退耕还林后2年内土壤侵蚀模数和流失量减少78%,监测区植被覆盖率由12.4%增加到38.7%,平均综合生态效益指数已由0.18上升到0.53。     

第二代杉木林养分动态研究

根据连续定位观测所取得的数据,对4个小集水区第二代10年生杉木人工林生态系统中的养分循环进行了研究.结果表明.集水区由降水输入的N、P、K、Ca、Mg等营养元素总计为59.285kg/hm2a,径流输出为38.938kg/hm2a,净积累量为20.347kg/hm2a.与该林分7年生时相比,净积累量提高了7.2%,说明集水区第二代杉木林生态恢复处于进展的变化过程.     

目前我国森林环境价值评价的难点及对策

概述了目前我国森林环境价值评价的理论基础和评价方法，并对其难点进行了分析，阐述了构建我国特色的评价理论框架及评价体系的必要性，指出只有建立森林生态环境定位观测站及其动态监测体系，才能科学计量、评估森林生态环境价值.     

半干旱地区生态建设方略初探

以神华集团神府东胜矿区生态建设为例 ,探讨了半干旱地区生态建设的必要性、指导思想、原则、生态建设的内容及对策、措施等有关问题     

福建省自然保护区生态旅游现状分析与发展对策

本文阐述了福建省自然保护区所蕴藏的丰富的生态旅游资源，分析了其生态旅游的现状及存在的问题，在此基础上探讨了发展保护区生态旅游的对策。     

梨麦间作系统水分效应与土地利用效应的研究

对黄淮海平原农区宽带距多行带梨麦间作系统水分效应、产量效应与土地利用效应进行了研究。结果表明：小麦拔节一乳熟期间，间作系统内小麦日蒸腾耗水比单作麦田低21．6％；距梨树0．0～7．0m，为土壤水分的降低区，7．0～25．0m为土壤水分提高区，间作系统总体上使麦田0～200cm土壤贮水量提高11．81％；间作系统内小麦水分利用率比单作麦田约高8．7％；间作系统小麦单产量比单作麦田高6．6％，土地当量值可达1．19。就水分效应和土地利用效应而言，在黄淮海平原农区发展这种宽带距多行带梨麦间作模式具有一定的可行性。     

对森林生态旅游的认识

回顾了生态旅游与森林旅游的概念与实践内涵，通过比较分析，提出了森林生态旅游的概念及对森林生态旅游的基本认识，分析了森林旅游、 生态旅游及森林生态旅游三者的差别及相互关系，总结了现阶段我国森林生态旅游中存在的在实践和认识上的问题。