Forest leaf litter quantity and seedling occurrence along an urban-rural gradient

Leaf litter, by modifying microenvironmental conditions, can alter plant population distributions and is considered to be a major force in structuring many plant communities. Comparative studies of urban, suburban, and rural forests in the New York City (NYC) metropolitan area have identified numerous biotic and abiotic differences among these forests, including several involved in leaf litter decomposition. These differences in decomposition among the forests could result in differences in litter quantity on the forest floor and hence microenvironmental conditions and safe sites for germination of different plant species. We conducted a survey of forest floor leaf litter quantity in forests located along an urban-to-rural land-use gradient originating in urban NYC and extending to rural Connecticut. Mean litter depth, mass, and density increased significantly with increased distance of the forest from NYC.We also surveyed woody seedlings and compared the litter depth in which they naturally occurred to the mean litter depth of the surrounding forest. Seedlings of small-seeded species were much more likely to be located in litter shallower than mean forest litter depth than were seedlings of large-seeded species. Taken together, these results suggest that environmental changes associated with urbanization may have profound effects on long-term patterns of forest regeneration.     

Urban tree cover: an ecological perspective

Analysis of urban tree cover is generally limited to inventories of tree structure and composition on public lands. This approach provided valuable information for resource management. However, it does not account for all tree cover within an urban landscape, thus providing insufficient information on ecological patterns and processes. We propose evaluating tree cover for an entire urban area that is based on patch dynamics. Treed patches are classified by their origin, structure, and management intensity. A patch approach enables ecologists to evaluate ecological patterns and processes for the entire urban landscape and to examine how social patterns influence these ecological patterns and processes.     

Methods for spatial and temporal land use and land cover assessment for urban ecosystems and application in the greater Baltimore-Chesapeake region

Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods: (1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A geographic information system (GIS) integrates core analyses with historic data on land use change to yield a comprehensive land use and land cover framework and rates of change. These data resources establish the regional foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological and social patterns and processes for varying degrees of urbanization.     

Effects of parasitoid community structure upon the population dynamics of the honeysuckle leafminer,Chromatomyia suikazurae (Diptera: Agromyzidae)

Population dynamics of a leafminer,Chromatomyia suikazurae (Agromyzidae, Diptera) and its parasitoid community were studied for ten years at seven natural populations along an altitudinal gradient in Japan. This species which mines leaves of a forest shrub,Lonicera gracilipes (Caprifoliaceae), was attacked by 25 hymenopterous parasitoid species. Annually, the parasitoid community structure varied less within a population than among populations. The seven parasitoid communities were clustered into three groups corresponding to the altitudinal gradient: (a) lowland communities dominated by late-attacking, generalist pupal idiobiont eulophids and with highest species diversity, (b) hillside communities dominated by an early-attacking, specialist larval-pupal koinobiont braconid and (c) highland communities dominated by an early-attacking, generalist larval idiobiont eulophid. Annual changes of the host larval densities among the local populations were largely synchronous rather than cyclic. Among these populations, host density levels and mortality patterns greatly varied. By analyzing these inter-populational differences of host mortality patterns, the following conclusions were drawn: (1) The host mortality patterns were determined by the host utilization patterns of the locally dominant species. (2) The host pupal mortality but not larval mortality was related to species diversity but not to species richness itself of each parasitoid community. (3) Density dependence was detected only in pupal mortality at a lowland population dominated by late-attacking pupal parasitoids. These results suggest that interspecific interactions of parasitoids add additive effects to host population dynamics dissimilarly among local populations with different parasitoid communities.     

一类新的自适应非单调谱投影梯度法

给出了求解凸约束优化的一类新的自适应非单调谱投影梯度法.通过引入具有自适应性的权重参数,使算法在迭代过程中能自动调节非单调策略. 在适当条件下证明了算法的收敛性.数值试验结果表明,该算法在一定程度上能减少在线搜索过程中对非单调参数M的依赖.     

颜色渐变的算法研究

科学计算可视化中数据场可视化的一个关键问题,是如何运用不同的颜色来表达和区分不同的数据源．在分析彩色系统的基础上,研究了10种用于伪彩色表达的颜色渐变算法,在与MATLAB软件算法比较的基础上,将这些算法运用在科学技术研究的实际应用中,并给出了实例．试验结果和实际使用结果都表明,本文的算法是有效的方法,具有良好的科学和工程应用价值。     

新吉坪隧道斜井进正洞挑顶施工技术研究

沪昆铁路客运专线新吉坪隧道所处地质条件复杂,区域地质作用剧烈,碳酸岩分布广泛,不良地质特别发育。针对斜井进正洞施工,提出了纵向爬坡导坑法。并以2#斜井为例,介绍了纵向爬坡导坑法施工工艺和斜井进正洞挑顶施工的控制要点,以及在施工过程中的控制量测方法,为新吉坪隧道斜井进正洞挑顶施工提供了技术指导,为类似工程施工提供参考。