Etiology of “Shimagare” dieback and regeneration in subalpineAbies forests of Japan

The “Shimagare” phenomenon relates to a striped pattern of stand-level dieback in the subalpineAbies (fir) forest of central Japan. Dieback fronts move gradually into pure stands ofAbies. As the dieback zones move forward they become regenerated with even-aged cohorts ofAbies which come up in form of waves. The phenomenon occurs mostly on the south slopes near mountain tops, exposing dieback fronts to south (i.e. downwards). Several facts suggest that desiccation stress and mechanical damage accelerated by the prevailing wind trigger the directional dieback ofAbies stands. The dieback is, however, promoted by over-crowded and even-sized stand structure. When less shade-tolerantBetula (birch) trees invade in an early stage of regeneration, mixed stands develop. These hardwood-mixed stands, with less-crowded and various-sizedAbies populations, hardly decay simultaneously. Here, alsoAbies trees become larger and live longer. Thus, the tendency of mass dieback ofAbies is not a characteristic of the species as such, but rather one of dense pure stands of the species.     

Dieback of rural trees in Australia

Much of Australia's woody vegetation has been cleared since European settlement, allowing extensive agricultural and pastoral industries to develop. Although scattered stands of native trees were often left on farmland, many of these trees are now in decline, particularly in regions where farm management is intensive. Rural dieback is a dramatic manifestation of this decline, and is characterized by a widespread, relatively recent upsurge of premature dieback and death of trees on farms. Comparatively little is known of its aetiology. Possible causal agents include insects, pathogens, drought and changes in the properties of soils or groundwater. We review and assess the evidence implicating each of these factors, and outline a conceptual model that demonstrates how several of them may be undesirable side effects of an intensification of pastoral management. The model shows how several different factors may interact to contribute to tree stress, and how dieback may eventuate if any one of them intensifies. Negative feedbacks operate between insect damage and the epicormic foliage that eucalypts produce in response to it, and also between dieback-related tree deaths and a worsening of the environmental degradation that contributed to the onset of dieback. These negative feedbacks will have most impact in those rural areas in which trees have become predisposed to chronic defoliation because of management practices or other environmental factors.     

An investigation of salt marsh dieback in Georgia using field transplants

In 2001 and 2002, Georgia salt marshes experienced a dieback event that, affected more than 800 ha throughout the coastal zone. The dieback event was unprecedented in the state and affected bothSpartina alterniflora andJuncus roemerianus. A transplant study was conducted from May to October 2003 to determine if healthy plants could survive in dieback areas. Transplants were carried out at two locations on the Georgia coast in areas ofS. alterniflora dieback along the banks of tidal creeks, an area ofS. alterniflora dieback in the mid marsh, and aJ. roemerianus dieback, area in the mid marsh. Transplant survival was nearly 100% and growth (measured as increases in the height of the 5 tallest stems and the number of stems per experimental pot) was observed in both healthy (control) and dieback areas.J. roemerianus grew more slowly thanS. alterniflora, with no, observed increase in stem height and an average 38% increase in stem density as compared to an average 57% increase in stem height and 137% increase in stem density inS. alterniflora. Differences in growth were inconsistent but in most cases no significant differences were observed between healthy and dieback areas. Soil characteristics measured over the course of the experiment were generally comparable between healthy and dieback areas (redox potential averaged 69±123 [SD] across all observations at all sites, pH averaged 6.7 ± 0.3 and salinity averaged 24.9±4.4), but porewater ammonium (NH₄) concentration was often higher in dieback areas (overall mean NH₄ concentration, was 138±127 μM in dieback areas versus 33±40 μM in healthy areas). These results suggest that the cause of dieback was no, longer present at the time of this study and that transplants are a possibility for restoring affected areas.     

Stem Borer Frequency and Composition in Healthy <Emphasis Type="Italic">Spartina alterniflora</Emphasis> (smooth cordgrass) and Dieback Zones in a Southern Atlantic Coast Salt Marsh

Unprecedented Spartina alterniflora (smooth cordgrass) dieback has recently plagued Atlantic and Gulf coast US salt marshes. The hypothesized drivers of dieback vary geographically but include drought and herbivory. Stem-boring insect larvae may also contribute to dieback, but have thus far been overlooked. Here we describe stem borer frequency and composition among healthy S. alterniflora morphs (tall and short) and dieback zones in Dean Creek Marsh on Sapelo Island, GA. Overall stem borer frequency was highest in tall morph S. alterniflora and dieback zones (present in 46.7% and 39.5%, respectively). Healthy habitat types were characterized by six stem borer families with only two of those families observed in dieback zones. Taxa from these two families, previously reported by others to cause stem death, were found at their highest frequency in dieback zones. Although we cannot infer causation, our results raise the possibility of stem borers contributing to the formation of dieback zones, meriting further research.     

Genetic effects of a large-scaleSpartina alterniflora (smooth cordgrass) dieback and recovery in the northern Gulf of Mexico

A large-scale dieback event struck marshes along the northwestern Gulf of Mexico coast during summer 2000, in apparent response to a prolonged and severe drought. Along the Louisiana coast, large areas of the dominant marsh species,Spartina alterniflora, turned brown, followed by death of at least the aboveground structures of entire plant mortality. Key ecological and genetic measures were studied in a dieback-affected marsh in southwest Louisiana (C83 marsh, Sabine National Wildlife Refuge), for which existed predieback ecologic and genetic datasets. Effects on genetic diversity only were studied in a second set of sites in southeastern Louisiana (near Bay Junop), where the dieback was more widespread. We hypothesized that stem density, live aboveground biomass, and genetic diversity would be significantly reduced compared to predieback conditions and to nearby unaffected marshes. Stem densities and biomass levels approached predieback conditions 14 months after first observance of the dieback in the Sabine marsh and were similar to or exceeded the same measures for a nearby unaffected marsh. DNA extracted from leaf samples in the Sabine and Bay Junop sites was used to construct genotype profiles using AFLPs and analyzed using the complement of Simpson’s Index (1-D), the richness measure G/N, average heterozygosity <H>, and the estimated proportion of polymorphic genes <P>. Genetic diversity was relatively unaffected by the dieback at either the Sabine or Bay Junop sites. Evidence from field observations and the results of the genetic analyses suggest that seedling recruitment is an important factor in the recovery of both the Bay Junop and C83 sites, although re-growth from surviving below-ground rhizomes appeared to dominate recovery at the latter site. Survival of below-ground structures, leading to the rapid recovery observed, indicates a high level of resilience of the Sabine marsh to drought-induced stress. Still, the genetic diversity ofS. alterniflora-dominated marshes may be promoted by occasional disturbance events, which produce open areas in which seedling recruitment can occur.     

An explanation of natural forest dieback based on the “pipe model” analogy

A decade of investigation of stand-level dieback ofmetrosideros in the Hawaiian montane rain forests has led to the theory that one of the major underlying causes is cohort senescence. A literature review shows that while there is little evidence of a senescence mechanism in polycarpic trees, the low vigor associated with the senescent state is correlated with a declining balance of photosynthesis to respiration. Specific Leaf Burden (SLB, cm³ of sapwood per g of leaf mass) is here defined as an index of respiring to photosynthesizing tissue. Using the assumptions of the pipe model theory, it is shown that SLB increases with stem elongation and is independent of tree diameter. Thus, the trees of a cohort that are the same height although variable in diameter will have the same carbon balance, as indexed by the SLB, and could be expected to decline synchronously, as stands ofMetrosideros do. Changes in growth patterns, deviating from the pipe model, that minimize the SLB as trees grow larger are identified. Research undertaken to test the assumptions of the pipe model and the conclusion of uniform SLB in a cohort of agingMetrosideros is described.     

Factors predisposing rata-kamahi(Metrosideros umbellata-Weinmannia racemosa) forests to canopy dieback,Westland, New Zealand

In many areas of WestlandMetrosideros umbellata (southern rata) andWeinmannia racemosa (kamahi) have undergone apparently excessive canopy dieback over the las 30–40 years. Browsing by the introduced brushtail possum is the predominant trigger involved. However, the roles of predisposing factors have received little attention. Dieback patterns indicate that the susceptibility of Westland rata-kamahi forest depends on their composition and structure. Stands containing abundant seral shrub hardwoods and a high proportion of old canopy trees are highly predisposed to dieback. Less dieback occurs in mature stands lacking seral species or in young apparently vigorous stands. Forest composition and structure are largely determined by site stability, i.e., the frequency and magnitude of physical disturbances such as mass movements. The underlying stability of different parent materials and landforms therefore largely determines rata-kamahi dieback patterns.     

The End Ever Nigh: Contemporary population change on Pitcairn island

Approximately 50,000 ha of native ‘ōhi’a (Metrosideros polymorpha) rain forest on the windward side of the island of Hawaii experienced a pronounced dieback of the tree canopy during the 1960s and early 1970's. The forests affected were located between 600 and 1,500 m elevation where the median annual rainfall was greater than 25000mm. Dieback stands were found on a variety of different substrates ranging from 500–10,000 years in age. Most of the stands that experiencel dieback had canopy cover greater than 60% prior to 1960. In 1976 and 1977 we established 43 relevés in dieback and non-dieback forest stands to assess canopy tree vigor, composition and structure of the vegetation, and to describe substrate characteristics.Metrosideros population structure and tree vigor were resampled for 25 of these relevés in 1982 and 1985–1986. The results of air photo analysis and ground sampling showed that dieback has not expanded very much within the study area since 1977. However, 5 of the relevés sampled in 1977 continued to decline in tree canopy vigor between 1977 and 1982 while 2 others showed a slight recovery in vigor over this same period. Seedling and sapling regeneration has been extremely vigorous in most of the sites that experienced a breakdown of the canopy while, in stands with an intact, dense tree canopy no such regeneration occurred. It appears that most of the stands which experienced canopy dieback have the potential to become closed forest communities again, dominated byMetrosideros. The natural recovery process may be disrupted in some areas due to additional competition for light and nutrients from invading populations of both native and alien plant species that have become established following canopy dieback.     

Stand-level dieback etiology and its consequences in the forests of Papua New Guinea

Stand-level dieback inNothofagus, mangrove andEucalyptus deglupta forests is examined. InNothofagus and mangrove forests, groups of largely even-aged trees die simultaneously, possibly triggered by drought stress which may directly affect the trees inNothofagus forests or indirectly increase water salinity in mangroves. Lightning strikes may be an additional dieback trigger in mangroves. Crown decline only was observed inE. deglupta forests and this may be associated with water-logging during periods of exceptionally high rainfall. Examination of rainfall records shows that severe droughts occur periodically in association with El Nino Southern Oscillations in the Pacific Ocean.     

The acid rain/carbon dioxide threat — Control strategies

Many of the world's most troublesome problems are closely interrelated. A case in point is the acid rain/carbon dioxide threat. Acid rain is the commonly used synonym for the major ingredients in the ongoing regional forest dieback, and carbon dioxide is a major influencing factor in the man-induced global geophysical experiment which is feared to lead to unacceptable climatic changes. Both problems have a major common cause, namely the squanderous use of fossil fuels. For this the most effective short-term preventive control measure is the reduction of fossil fuel combustion through more efficient use which drastically reduces the pollution output by minimizing the need of having to burn fossil fuels in the first place. However, the large differences in the quantity of the emissions involved (some 20 000 million tons of CO₂/yr. and about 130 and 50 million tons of SO₂ and NO_x, respectively) ingredients of acid rain, can be stripped from the gas stream by technical means which are affordable, the sheer quantity of CO₂ involved renders its sequestering and disposal technically, logistically and economically unfeasible. Through short-term measures the necessary time is gained for a sensible introduction of pollution-free sustainable resources. The long market penetration times (typically 50–100 years) force us to act now, ifwe do not wish to have upon us in the near future a major CO₂/climate problem that is of similar severity as the acid rain/forest dieback problem of today. To my knowledge this is the first attempt to analyse the acid rain/CO₂ problems in their genetic and functional context and to present ways which lead to feasible solutions.     

Comparison between the lower Nansi Lake and its inflow rivers in sedimentary phosphorus fractions and phosphorus adsorption characteristics

There were many differences between rivers and lakes such as flow velocity, hydraulic retention time, water vegetation community and other chemical-physical factors that may lead to different characteristics of sedimentary phosphorus. In our research, sedimentary phosphorus fractions and its phosphorus adsorption differences between the lower Nansi Lake and its main inflow rivers were compared. The results showed that the contents of NaOH-P, Org-P, IP-P, and TP in lake sediments were obviously higher than those in its inflow river sediments while HCl-P had no obvious difference between them. Based on analysis, the unstable NaOH-P would accumulate in lake sediments, while it is difficult for it to retain in sediments of rivers because of a high frequency of flood flows and unstable bed sediments. In addition, water vegetation communities were helpful in the accumulation of Org-P in lake sediments. From phosphorus adsorption experiments results, the Ceqc (equilibrium concentration of phosphorus release/adsorption) of lake sediments was higher than that of river sediments. It was indicated that sedimentary phosphorus would be more easily released from lake sediments than river sediments. So in future more work should be focused on internal P loading from lake sediments release.     

What makes territory important: tangible and intangible dimensions

Conflicts over territory have resulted in innumerable wars and other violent incidents, but the reasons that some territory is more highly valued or volatile than other areas may not be obvious. This paper demonstrates a taxonomy for analyzing international territorial disputes that seeks to capture their tangible and symbolic dimensions and to weigh them as the international community might. Twenty-six territorial disputes, including offshore areas and separatist issues, were examined and scored according to 15 criteria for objective prominence and 7 criteria related to how a country might view the dispute in terms of its national interest. The taxonomy used Saaty’s Analytic Hierarchy Process to identify tangible and intangible properties, measure their interrelations, and produce intermediate and overall ranks. Each dispute was evaluated for prominence by examining intensifying (symbolic) factors, measures of magnitude, and characteristics that retard resolution. The magnitude of a dispute was judged to contribute the most to overall prominence, having twice the weight of the other two factors. The top five disputes in terms of prominence were the Kurdish issue, Kashmir, Tibet, Nagorno-Karabakh, and Xinjiang. The second hierarchy evaluated the disputes from the perspective of an international actor, in this case the United States. When judged by U.S. national interest, the most important factors were the deployment of U.S. forces in the claimant countries and if one of the claimants were a U.S. ally. Finally, the results from the two hierarchies were compared.     

树轮气候学中树木年轮密度分析方法的研究进展

树木年轮密度（树轮密度）分析作为树轮气候学的一种研究方法,能够提取更准确的环境信息,应用范围更广,在过去环境变化研究中受到越来越广泛的重视。讨论了树轮密度测量技术与树轮密度分析方法在过去气候变化研究中的发展历程及最新研究成果,认为X射线分析法仍然是目前被广泛采用的树轮密度分析手段,基于树轮密度数据的过去温度变化重建仍是树轮密度研究的主要方向。相关研究表明：森林上限和高纬度地区树木年轮的最大晚材密度对夏季温度变化非常敏感,可以用来重建过去几百年、乃至千年的不同空间尺度的温度变化;树轮早材密度或最小早材密度对降水量的响应比较显著,但目前主要集中于重建区域小尺度的降水量变化方面。另外,树轮密度分析结果还可以用来研究某些气候要素分量的变化（季节变化、气候事件爆发的早晚和持续时间等）、区域气候变化的影响因子以及海气动力机制、气压异常等。     

黄河上游康杨滑坡堆积体特征及形成机理分析

滑坡堆积体特征及其成因机理是进一步研究滑坡防治及开发利用的基础与前提。位于青藏高原东北缘的黄河上游群科—尖扎盆地内的康杨滑坡属于典型的巨型古滑坡,其堆积体特征及形成机制在该地区具有典型性和代表性,具有较高的学术研究价值。结合工程地质钻孔资料,通过详细的野外调查、粒度分析等方法对康杨滑坡形态特征、形成年代、滑坡体粒度特征及其成因机理进行了研究,主要认识如下:（1）康杨滑坡为晚更新世晚期发生的泥岩滑坡,体积约为12.59×108?m3,为一典型巨型古滑坡,后壁高耸直立;（2）滑坡前缘曾滑移至黄河北岸,堆积体可能堵塞黄河,后被黄河从中部侵蚀切穿,目前在黄河北岸仍存留有古滑坡堆积体;（3）高原抬升和黄河下蚀等作用可能是滑坡发生的背景条件,降水入渗形成软弱滑带和黄河侧蚀作用可能是触发康杨滑坡的主要因素。     

Successful Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) Restoration in a Formerly Eutrophic Estuary (Boston Harbor) Supports the Use of a Multifaceted Watershed Approach to Mitigating Eelgrass Loss

From a watershed perspective, Boston Harbor, MA, USA is an ideal site for eelgrass restoration due to major wastewater improvements. Therefore, by focusing on site selection and transplant methods, high survival and expansion rates were recorded at four large eelgrass-restoration sites planted in Boston Harbor as partial mitigation for a pipeline construction project. Transplanted sites met and exceeded reference and donor bed habitat function after 2 years. Hand planting and seeding in checkerboard-patterned transplant plots were efficient and effective methods for jump-starting eelgrass growth over large areas. Although restoration through planting can be successful, it is highly site specific. Even using a published site-selection model, intensive fieldwork was required to identify sites at fine enough scale to ensure successful planting. Given the effort required to identify scarce potential sites, we recommend that future focus includes alternative mitigation strategies that can more adequately prevent eelgrass loss and address water quality degradation which is the leading cause of dieback, site unsuitability for planting, and lack of natural re-colonization.     

检波器数量对组合压噪能力的影响

根据组合压噪的有关理论,在其他因素不变的情况下,采用数量越多的检波器,组合压制干扰波的效果越好。这使得人们认为在施工中应该采用尽量多的检波器以提高资料的信噪比。但是通过分析组合中检波器数量对规则干扰波,随机干扰波以及耦合高频微震衰减的影响证明:在其他因素不变的情况下,线性等灵敏度组合增加到"γ_max+3"个检波器以后(其中γ_max=组合基距/最小干扰波视波长), 组合对于规则干扰波的衰减能力不再随着检波器数量的增加而显著提高。在组合基距确定的情况下,检波器数量越多,对随机干扰的衰减越明显(包括在组内距小于随机干扰相关半径的情况下);但是增加到一定数量后,衰减效果不再出现明显变化。检波器数量的多少对衰减耦合高频微震没有明显作用。同时指出,确定组合中合理的检波器数量要与组合的摆放形式相结合;组合图形不合理的情况下,增加检波器数量不会显著提高组合的压噪能力;灵敏度分布不合理,是导致组合压噪能力降低的重要原因。在线性等灵敏度组合的基础上,利用玫瑰图进行分析,可以确定工区面积组合(包括道间混波后)中使用的合理的检波器数量。     

油气成藏条件下低渗透砂岩石油运移的渗流特征实验研究

在室内低速渗流实验的基础上,采用恒压测试法,对成藏条件下石油在低渗透砂岩中的运移渗流规律及影响因素进行了研究。结果表明：(1)石油在低渗透砂岩中低速渗流时存在着启动压力梯度,非达西渗流特征明显。(2)低渗透砂岩中石油非达西渗流曲线主要有两种基本类型,视流度≤1时,非达西渗流曲线表现为上凹型曲线;视流度＞1时,表现为变性达西流曲线。(3)低渗透砂岩的物性、石油性质以及它们的相互作用对渗流曲线的位置、非线性段的曲率和变化范围以及直线段在压力梯度轴的截距具有重要影响。(4)随着低渗透砂岩渗透率的降低和石油粘度的增加或视流度的减小,石油在低渗透砂岩储层的非达西渗流特征更加明显。     

Quantitative Calculation of Groundwater Vulnerability Assessment Based on Quantification Theory III

There are a lot of key qualitative variables in factors affecting groundwater vulnerability. The processing of qualitative variables of the existing superimposed index method generally relies on experience, so the results are normally subjective. Quantitative theory can handle qualitative variables quantitatively, achieve the unity of quantitative and qualitative indicators, highlight the decisive role of the main factors and reflect the actual situation more objectively. We took Yulin City as the research area to verify the feasibility and applicability of quantitative theory III, which is used for the quantitative evaluation of groundwater vulnerability. The results show that it has obvious advantage in the screening of indicators and the groundwater vulnerability partition, so it can be used as a quantitative calculation method of groundwater vulnerability assessment     

Use of GIS mapping and modeling approaches to examine the spatial distribution of seagrasses in Barnegat Bay, New Jersey

Due to the ecological importance of seagrasses and recent indications of disease and dieback, we have synthesized existing mapped survey information concerning the spatial and temporal distribution of seagrass beds (primarily eelgrass,Zostera marina) in Barnegat Bay, New Jersey. Mapped surveys from the 1960s, 1970s, 1980s, and 1990s were digitized and compiled in a geographic information system to facilitate analysis. Comparison of the earlier maps with the 1990s survey shows an overall decrease of approximately 2,000 to 3,000 ha in the area of seagrass beds. While there are indications of seagrass decline, due to the great difference in mapping methods used for each of the surveys, we are cautious in directly attributing the decrease in mapped eelgrass acreage to a large-scale dieback. We examined the extent to which light could be used to predict the distribution of seagrass in Barnegat Bay. Data on Secchi depth throughout the bay were combined with a modification of an existing model (Duarte 1991) of the relationship betweenZ. marina compensation depths and light attenuation coefficients to predict the distribution of seagrasses in Barnegat Bay. When compared with mapped seagrass distribution in the bay, the model correctly predicts seagrass presence-absence over two-thirds of the time. The majority of the model error is due to errors of commission, i.e., the model predicts seagrass occurrence where it was not observed to occur. Most of this commission error is located in specific geographic areas (i.e., southern third of Little Egg Harbor and the western shoreline of the bay).     

红层泥岩及其改良填料路基动力响应试验研究

基床作为路基结构的重要组成部分,其填料的质量对路基、轨道、列车的动力响应影响显著。在实际工程中,基床填料通常可根据设计规范取为A、B组填料,但考虑到经济因素、力学性能等,也可采用既有填料或改良的既有填料。为了研究红层泥岩,A、B组填料,石灰改良红层泥岩分别作为基床填料时对路基动力响应的影响,进行了不同基床填料的现场激振试验。通过对动应力、加速度及沉降等数据的对比分析,得到以下结论：红层泥岩作为基床填料时,动应力与路基沉降在加载激振次数内可满足设计要求;与红层泥岩相比,当基床填料为A、B组填料与石灰改良红层泥岩时,路基表面的动应力与加速度分布更加均匀,因而此时路基的整体承载性能更优越。除此之外,后两种填料时路基内部动应力与加速度的衰减相对前者更显著,并且路基的沉降变形更小,特别是为石灰改良红层泥岩时。