Introduced Species and Management of a <Emphasis Type="Italic">Nothofagus/Austrocedrus</Emphasis> Forest

Isla Victoria (Nahuel Huapi National Park, Argentina), a large island dominated by native Nothofagus and Austrocedrus forest, has old plantations of many introduced tree species, some of which are famed invaders of native ecosystems elsewhere. There are also large populations of introduced deer and shrubs that may interact in a complex way with the introduced trees, as well as a recently arrived population of wild boar. Long-standing concern that the introduced trees will invade and transform native forest may be unwarranted, as there is little evidence of progressive invasion, even close to the plantations, despite over 50 years of opportunity. Introduced and native shrubs allow scattered introduced trees to achieve substantial size in abandoned pastures, but in almost all areas neither the trees nor the shrubs appear to be spreading beyond these sites. These shrub communities may be stable rather than successional, but the technology for restoring them to native forest is uncertain and probably currently impractical. Any attempt to remove the exotic tree seedlings and saplings from native forest would probably create the very conditions that would favor colonization by exotic plants rather than native trees, while simply clear-cutting the plantations would be unlikely to lead to regeneration of Nothofagus or Austrocedrus. The key to maintaining native forest is preventing catastrophic fire, as several introduced trees and shrubs would be favored over native dominant trees in recolonization. Deer undoubtedly interact with both native and introduced trees and shrubs, but their net effect on native forest is not yet clear, and specific management of deer beyond the current hunting by staff is unwarranted, at least if preventing tree invasion is the goal. The steep terrain and shallow soil make the recently arrived boar a grave threat to the native forest. Eradication is probably feasible and should be attempted quickly.     

COLUMBIA RIVER FLOW AND DROUGHT SINCE 17501

ABSTRACT: A network of 32 drought sensitive tree‐ring chronologies is used to reconstruct mean water year flow on the Columbia River at The Dalles, Oregon, since 1750. The reconstruction explains 30 percent of the variability in mean water year (October to September) flow, with a large portion of unexplained variance caused by underestimates of the most severe low flow events. Residual statistics from the tree‐ring reconstruction, as well as an identically specified instrumental reconstruction, exhibit positive trends over time. This finding suggests that the relationship between drought and streamflow has changed over time, supporting results from hydrologic models, which suggest that changes in land cover over the 20th Century have had measurable impacts on runoff production. Low pass filtering the flow record suggests that persistent low flows during the 1840s were probably the most severe of the past 250 years, but that flows during the 1930s were nearly as extreme. The period from 1950 to 1987 is anomalous in the context of this record for having no notable multiyear drought events. A comparison of the flow reconstruction to paleorecords of the Pacific Decadal Oscillation (PDO) and El Nino/Southern Oscillation (ENSO) support a strong 20th Century link between large scale circulation and streamflow, but suggests that this link is very weak prior to 1900.     

Determination of the effect of operating cost uncertainty on mining project evaluation

Mining projects are complex businesses that demand constant risk assessment. This is because several kinds of uncertainties influence the value of a mine project, typically. These uncertainties may be classified as exploration uncertainties, economic uncertainties and engineering uncertainties. The evaluation of a mine project under these uncertainties is a complicated job, which may lead to making a wrong decision by managers and stockholders. Therefore, at first, the engineers must recognize the mining uncertainties before carrying out the project evaluation. The economic uncertainties are the most important factors, which may affect the project evaluation. Among the mentioned uncertainties, the operating cost uncertainty is an important and effective factor, which is ignored to a certain extent.     

形率法测算单株立木材积公式选用

单株立木求积,是林业科研和生产的重要内容.本文通过对临武县杉木人工林分590株标准木进行测算研究,发现不同的立木求积式其求积精度有明显差异,由此优选出精度高简便实用的测算公式.     

山东省高速公路主要绿化树木叶片硫、铅含量分析

汽车尾气会给高速公路路域环境带来一定程度的硫(S)、铅(Pb)污染,而绿化树木可通过吸收作用从而有效降低这些污染物在空气中的含量,目前这方面的研究较少。对山东省高速公路路侧主要绿化树木叶片S、P质量分数的研究表明,I107杨树(Populus Linn.)叶片S、Pb质量分数与高速公路车流量呈显著正相关。I107杨树叶片S、Pb质量分数对高速公路路域环境污染具有一定指示作用,不同路段杨树叶片的S、Pb质量分数存在明显差异,济青高速公路路侧杨树叶片的S、Pb质量分数最高,其次是京沪高速,最低的是日东高速。I107杨和龙柏对S污染物的吸收能力较强,其次是垂柳(Salix babylonica L.),较差的是紫叶李(Prunus cerasifera cv.Pissardii.)、大叶女贞(Ligustrum lucidumAit)和雪松(Cedrus deodara(Roxb.)Loud);而I107杨和紫叶李对Pb的吸收能力较强。     

Relation Between Individual Tree Mortality and Tree Characteristics in a Polluted and Non-Polluted Environmentx

Data on individual tree mortality in relatively healthy (Berezinskiy biosphere reserve) and damaged (surroundings of the mineral fertilizer plant ‘Achema’) even-aged Scots pine (Pinus sylvestris L.) stands are presented. Tree size and competition intensity were found to be the most significant predictors of individual tree mortality in all age groups of the relatively healthy Scots pine stands, however, an essential reduction in the closeness of relations between the tree mortality rate and these variables was determined with the aging of stands. An exponential decrease in tree mortality probability with an increase of tree size is characteristic for trees suffering different competition intensity, however, this decrease becomes much more pronounced as the competition pressure increases. The relations of different tree and stand variables with tree mortality probability have been found to become much weaker in the polluted environment. An exponential increase in tree mortality probability with an increase of crown defoliation was characteristic of damaged Scots pine stands, however, the rate of the increase was different in different age and diameter classes. The impact of crown defoliation on tree mortality rate increased with the aging of stands. At the same defoliation level, individual tree mortality probability was much higher for smaller suppressed trees, however, a relative increase in tree mortality probability along with an increase of crown defoliation was more pronounced for dominant trees. Conclusion: a higher mortality of damaged (defoliated) trees should be considered while assessing losses in forest productivity in a polluted environment.     

Physics of failure analysis of power section assembly for positive displacement motor

Power section assembly is the core part of positive displacement motor (PDM), and its mechanical behavior and service life determine the drilling efficiency and cycle. In this paper, fault tree of power section assembly was established, failure reasons were analyzed and improvement measures were put forward. Finite element models of conventional lining and uniform wall thickness lining of 5/6 PDM were established, and the mechanical behaviors were investigated. Working parameters such as drilling fluid pressure, rubber hardness, downhole temperature and pressure difference were discussed. The results show that wear and rust are the main failure modes of the rotor. Failure modes of rubber lining are wear, tear, rupture, peeling off, thermal failure and fatigue failure. Under the action of drilling fluid pressure, the maximum effective stress of rubber lining appears in the bottom of arc, and the minimum stress appears at the top of arc. But deformation distribution is opposite to the effective stress. Deformation of uniform wall thickness lining is more uniform. Effective stress of the lining increases with the increasing of drilling fluid pressure and rubber hardness, but it decreases with the downhole temperature increases. Deformation of the lining increases with the drilling fluid pressure increases, but it decreases with the increasing of rubber hardness and downhole temperature. Effective stress and deformation distribution of rubber lining are more uneven with the pressure difference increases. High stress area lies between the two smallest chambers.     

高峰水库下采空区重大安全风险评估及治理对策

湖南柿竹园多金属矿老蛇形坪矿区闭坑后被高峰水库淹没,周边民采矿点超深越界偷采井下保水矿柱,形成了高峰水库下积水采空区透水隐患。为了保证临近矿区安全开采,消除采空区透水隐患,在三维流固耦合有限差分数值模拟的基础上,对53#关键采空区和18m隔水矿柱的稳定性进行了分析,采用事故树法排查了可能发生出突水事故的104种基本事件,分析了高峰水库重大安全隐患的风险等级,并提出了隐患治理对策,可为水下开采的矿山突水安全评估及治理提供参考。     

Forecasting the Risk of Brown Tree Snake Dispersal from Guam: a Mixed Transport-Establishment Model

Abstract:  The brown tree snake ( Boiga irregularis ) is a devastating invader that has ecologically and economically affected Guam and is poised to disperse further. Interdiction efforts are being conducted on Guam and some of the potential receiving sites, but no tools exist for evaluating the potential for snake incursion; thus, the amount of effort that should be invested in protecting particular sites is unknown. We devised a model that predicts the relative risk of establishment of the brown tree snake (BTS) at a given site. To calculate overall risk, we incorporated in the model information on the likelihood of an organism entering the transportation system, avoiding detection, surviving to arrive at another location, and establishing at the receiving end. On the basis of documented rates of snake arrival at receiving sites, the model produced realistic predictions of invasion risk. Model outputs can thus be used to prioritize interdiction efforts to focus on especially vulnerable receiving locations. We provide examples of the utility of the model in evaluating the impacts of changes in transportation parameters. Finally, the model can be used to evaluate the impacts that BTS establishment at an additional site and that creation of a new source of snakes would have. The use of qualitative inputs allows the model to be adapted by substituting data on other invasive species or transportation systems.     

A SYSTEMATIC ANALYSIS OF THE CONSTRAINTS TO URBAN STREAM ENHANCEMENTS1

ABSTRACT: The environment surrounding urban streams imposes constraints upon stream enhancement projects. Constraints include bridges, culverts, highways, sewer and water lines, lack of easements, and other floodplain structures. The consequences of failure of these infrastructure constraints can be significant and should be considered in the design process. Fault tree analysis provides a systematic technique for analyzing the interactions of events that could lead to infrastructure failure. A case study of a stream in Pittsburgh, Pennsylvania, shows that fault tree analysis can effectively model the interactions between the stream system and the infrastructure constraints and predict the most likely modes of failure. In addition, the relative success of alternative designs and failure mitigation techniques can be assessed using this analysis tool, lending insight into the urban stream enhancement design process. The method could also provide justification in the design permitting process and input for risk assessment.