新疆北疆地区季节性冻土结冻过程与日积温的关系

传统的度日因子模型很难分辨在结冻期土壤每日结冻和解冻的过程,而日小时积温可以区分正积温和负积温对土壤冻结过程的影响.利用北疆地区1951-2010年气象站数据和决策树算法,分析计算日小时积温及表层5cm和10cm土壤冻结状态数据及日小时积温对季节性冻土冻结现象的影响.结果表明:在北疆范围年小时正积温以每年平均160℃增长,而年小时负积温以每年平均153℃减少.季节性冻土发生冻结现象所需的临界值分布与北疆地区气候和土壤分布基本一致,但仍存在空间差异性.北疆地区5cm土壤结冻所需的日小时负积温为-50℃以下,而5cm到10cm土壤结冻所需日小时负积温的平均值差值为-15℃左右.与日最低气温和日平均气温作为土壤结冻判据相比,日小时积温临界值作为判据可获得较高的精确度.在昌吉地区和阿勒泰地区冻土的平均深度随着日小时负积温临界值的增加而减少.     

Degraded forest,degraded land and the development of industrial tree plantations in Laos

The concepts of degraded forest (pa mai xout xom) and degraded land (din seuam xom) have been variously applied in official Lao government policy narratives and law over the last couple of decades. In this article I focus on the concepts of degraded forest and land, and the relationship with industrial tree plantations, using two examples from southern Laos. I argue that the concepts have been significant in both facilitating and obstructing the development of large‐scale industrial tree plantations in different times and spaces, thus significantly influencing access and exclusion, as well as the spatialization of tree plantations. I provide a tentative genealogy regarding the emergence of these concepts in land and forestry policy in Laos, and briefly explain the links between degradation and ‘the land rush’ presently affecting Laos.     

A dynamic riparian forest structure model for predicting large wood inputs to meandering rivers

Fluvial processes strongly influence riparian forests through rapid and predictable shifts in dominant species, tree density and size that occur in the decades following large floods. Modelling riparian forest characteristics based on the age and evolution of floodplains is useful in predicting ecosystem functions that depend on the size and density of trees, including large wood delivered to river channels, forest biomass and habitat quality. We developed a dynamic model of riparian forest structure that predicts changes in tree size and density using floodplain age derived from air photos and historical maps. Using field data and a riparian forest chronosequence for the 160-km middle reach of the Sacramento River (California, USA), we fit Weibull diameter distributions with time-varying parameters to the empirical data. Species were stratified into early and late successional groups, each with time-varying functions of tree density and diameter distributions. From these, we modelled how the number and size of trees in a stand changed throughout forest succession, and evaluated the goodness-of-fit of model predictions. Model outputs for the early successional group, composed primarily of cottonwoods and willows, accounted for most of the stand basal area and large trees >10 cm DBH for the first 50 years. Post-pioneer species with slower growth had initially low densities that increased slowly from the time of floodplain creation. Within the first 100 years, early successional trees contributed the most large wood that could influence fluvial processes, carbon storage, and instream habitat. We applied the model to evaluate the potential large wood inputs to the middle Sacramento River under a range of historical bank migration rates. Going forward, this modelling approach can be used to predict how riparian forest structure and other ecosystem benefits such as carbon sequestration and habitat quality respond to different river management and restoration actions.     

树轮氢氧同位素方法在环境变迁研究中的应用

树轮氢氧同位素方法是过去环境气候变化研究领域内的主要技术手段之一，因其时间分辨率高，反映环境参数多，准确定量的优点，近年日益受到重视。     

丝绸之路青海道吐蕃时期墓葬出土木材记载的森林干扰史

森林动态与气候变化及人类活动有着紧密的联系,了解森林干扰的发生历史对准确预测全球变暖背景下的森林动态具有重要意义,也可为理解历史时期的气候变化和人地关系演变提供线索.文章利用丝绸之路青海道沿线吐蕃时期3个墓葬中出土的78棵祁连圆柏(Juniperus przewalskii Komarov)原木作为研究对象,利用树木年...     

Climatic significance of<Emphasis Type="Italic">δD</Emphasis> time series in tree rings from Tianmu Mountain

Based on cross-dating tree ring age from Tianmu Mountain, Zhejiang Province, theδD      

环境污染对成都市古树名木的危害及防治对策研究

对成都市的主要古树名木被环境污染物质危害的现状进行实地调查，从受害症状入手，对受害机理作分析。并提出保护古树名木的具体措施。此工作对本市治理污染及合理绿化将有意义。     

Niveo-aeolian sand deposition in subarctic dunes,eastern coast of Hudson Bay,Québec,Canada

Aeolian sand transport during winter and the snow-free season was assessed quantitatively by direct year-round field measurements along transects on the lee side of parabolic dunes in subarctic Québec. In 1987–1988, niveo-aeolian deposition was more important than aeolian sedimentation in three of the four study sites, and contributed > 75% of the total annual accumulation in exposed sites and < 25% in protected forest sites. The maximum depth of interstratified snow and sand deposits (3.5 m) was recorded in March. Semi-permanent snow lenses may persist longer than 2 years in the aeolian sediments. After dissipation of snow, 22 cm of sand (as a maximum) accumulated on the slipface of the most active dunes, whereas only minor sand accumulation occurred in distant areas from active sand erosion. Wind-driven sand was dispersed over 7.4 km² in the Whapmagoostui-Kuujjuarapik area. The acumulation of snow and sand during the snow season, together with spring thaw and collapse of the niveo-aeolian deposit, caused different types of injuries to trees, especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period.     

Relative Response of Biological and Non-Biological Monitors in a Coastal Environment

A field study was carried out in the spring and summer of 2003 (2 months each), to assess the efficiency of alternative exposure modes of biological monitors – lichen biomass and tree-bark biomass – together with prospective, non-biological monitors – cellulose acetate and Chelex-100 resin – versus conventional transplants of the same species. After exposure to the marine atmosphere of Sines (SW Portugal), saline elements (Cl, Na, K, Mg) contents were determined in all samples by instrumental neutron activation analysis (INAA). Manganese was used as the crustal reference for data normalisation. As a whole, the results pointed to a consistent elemental accumulation regardless of the season (spring, summer), and to some fair reproducibility of data. There were good correlations between Cl and Na in terms of both raw and normalised data, for either the biomonitors or the cellulose acetate. Elemental ratios generally agreed with the average relative composition of bulk seawater. The degree of association between Cl and Na appeared rather unaffected by the normalisation procedure, which suggests that (i) both elements most likely had an almost exclusive marine origin; and (ii) accounting for crustal inputs via Mn did not bias the results. Other sources than the sea-spray might contribute to the Mg levels, though, as only Mn-normalised data showed intrinsic (correlation) and extrinsic (ratio) consistency. The performance of the Chelex-100 resin was rather disappointing when compared to the other monitors.     

关于线状地理特征空间关系的自然语言描述的形式化表达

目前的地理信息系统都使用定量的方法存储和查询空间信息,不能反映人们的定性思维方式,因此它表达地理空间信息的能力受到限制。在关于空间关系的自然语言描述的调查的基础上,本文定义了一组能反映线状物体空间关系的度量指标,结合反映拓扑关系的定量指标,使用决策树的数据挖掘算法,对调查结果进行分析,形式化了描述空间关系的自然语言词汇,建立了模糊的自然语言表达和图形的几何特征之间的联系。自然语言形式化后得到的规则可用于空间关系的自然语言查询系统。