Patterns of lizard species richness within National Parks and Biosphere Reserves across North America's deserts     

《Journal of Arid Environments》2013

Warm deserts world-wide provide habitats for rich lizard species assemblages; North American deserts are no exception, however the desert regions of the US and Mexico are experiencing increasing habitat changes from multiple anthropogenic sources. Our objective here was to document current lizard species richness patterns across the North American deserts within the existing network of conservation areas. We identified 110 lizard species occurring across one or more of the 19 sites we analyzed. Three species richness hot spots were identified; a northern Baja California faunal extension into southern California in the US, and in Mexico, two sites within the state of Coahuila, as well as high endemism in the Cape Region of Baja California Sur. Species richness was associated with sites where desert ecoregions overlap and with insular isolation. Our uncertainty regarding how species will respond to the multifaceted aspects of global change is such that large protected natural areas with complex topography may be the most effective strategy for protecting desert lizards along with overall biodiversity. The 19 sites we analyzed represent the cores of a more robust conservation network that will be needed for the protection of biodiversity across North American Deserts.  相似文献   

Retail and wholesale enterprise among ethnic groups in core and peripheral urban centers: the late-nineteenth-century United States   总被引：1，自引：1，他引：0  

Robert L. Boyd 《Urban geography》2013,34(3):454-470

Ethnic entrepreneurs often benefit from reciprocal relationships, such as buyer–supplier linkages, among co-ethnic businesses. The present study extends this insight, analyzing census data on the relationship between ethnic enterprise in the retail trade and co-ethnic enterprise in the wholesale trade in urban centers of core and peripheral regions of the late-nineteenth-century United States. As expected, this relationship varied markedly by ethnicity and region. For some groups (e.g., Russians), co-ethnic retail and wholesale enterprises were positively related on the periphery but not in the core; conversely, for other groups (e.g., Irish), co-ethnic retail and wholesale enterprises were positively related in the core but not on the periphery. The results imply that reciprocal relationships among co-ethnic businesses are significantly affected by variation in the characteristics of local opportunity structures across urban-regional locations.  相似文献   

Evolving United States metropolitan land use patterns     

Andrea Sarzynski  Lisa Stack 《Urban geography》2013,34(1):25-47

We investigate spatial patterns of residential and nonresidential land use for 257 United States metropolitan areas in 1990 and 2000, measured with 14 empirical indices. We find that metropolitan areas became denser during the 1990s but developed in more sprawl-like patterns across all other dimensions, on average. By far, the largest changes in our land use metrics occurred in the realm of employment, which became more prevalent per unit of geographic area, but less spatially concentrated and farther from the historical urban core, on average. Our exploratory factor analyses reveal that four factors summarize land use patterns in both years, and remained relatively stable across the two years: intensity, compactness, mixing, and core-dominance. Mean factor scores vary by metropolitan population, water proximity, type, and Census region. Improved measurement of metropolitan land use patterns can facilitate policy and planning decisions intended to minimize the most egregious aspects of urban sprawl.  相似文献   

PHYSICAL GEOGRAPHY EXPANDS TO FOUR ISSUES A YEAR IN 1986     

《自然地理学》2013,34(1):3-4

The interannual variability in warm-season soil-moisture deficits were examined for the Southern United States from 1895-2005. Moisture deficit values are computed using the Thornthwaite/Mather water budget technique. Five soil-moisture deficit regions were identified, each has a distinct pattern and magnitude of deficit. No long-term trends were evident but considerable interannual variability is observed. Severe deficits across the South are associated with high potential evapotranspiration in addition to reduced rainfall. The reduced precipitation across the region is associated with a decrease in frequency rather than any change in intensity. The role of atmospheric indices on affecting deficits, precipitation, and potential evapotranspiration was explored. In particular, the Bermuda High and PNA indices show the strongest correlations with soil-moisture deficits during the warm season.  相似文献   

VASCULAR PLANTS OF MOUNTAIN TALUS SLOPES,MT. RAE AREA,ALBERTA, CANADA     

Linda J. Kershaw  James S. Gardner 《自然地理学》2013,34(3):218-230

The vascular flora of talus slopes in the Mt. Rae area, Canadian Rocky Mountain Front Ranges, is discussed in the context of edaphic and geomorphic conditions. Thirteen talus slopes were sampled systematically for the presence of vegetation, and vascular plants were identified to the species level. Such talus slopes are generally considered relatively sterile and too unstable for the development of distinctive flora. The presence of vegetation is usually taken as an indicator of slope stability. A total of 77 species with boreal and arctic affinities was identified. Most plants display growth forms suitable to the unstable and xeric talus substrate with Schroeter's Schuttstrecker and Schuttdecker forms being most common. Although areal coverage by plants is sparse, a large number of species with morphological characteristics suitable for the talus environment suggests that the presence of plants should not be regarded as an absolute indicator of slope stability. Rather, these plants may represent a long-term equilibrium assemblage characteristic of active talus slopes in a mountain environment.  相似文献   

MEASURED ALTITUDINAL PROFILES OF UV-B IRRADIANCE IN HAWAI'I     

Dennis Nullet  James O. Juvik 《自然地理学》2013,34(4):335-345

Erythemally weighted UV-B irradiance was measured between sea level and 4,205 m in several midday altitudinal transects and continuously for several months at sea level and 3,400 m on the Island of Hawai'i. Between sea level and 4,205 m, standardized UV-B increased 25% and 29% for solar zenith angles of 10° and 45°, respectively, under clear-sky conditions. The standardized diffuse component constituted 28% to 58% of the total as a function of optical path length. Under all sky conditions, the monthly average UV-B irradiance increased 50% in summer and 103% in winter from a cloudy, windward, sea-level location to a site at 3,400 m in generally clear skies above the trade-wind inversion. [Key words: solar radiation, ultraviolet-B irradiance, Hawai'i.]  相似文献   

Historical and Projected Climate Trends Along the Appalachian Trail,USA, and the Implications for Trail Usage     

《自然地理学》2013,34(1):22-51

Recent climate analyses indicate that average global temperature is rising and both global drought occurrence and precipitation intensity are increasing. The nature of climate change is unique to each location, and its impact, both positive and negative, is predicted to be widespread. One area to be potentially affected includes management and use of outdoor natural resources such as the Appalachian Trail (AT), a 3500 km continuous hiking trail in the eastern United States. Observed historical (1895-2008) and projected future (to 2099) seasonal temperature and precipitation trends were examined along the AT. The AT has generally warmed since 1895, with greater warming occurring more recently. The warming has been greatest in the northern part of the AT and during winter. Precipitation trends show wide spatial variation depending upon the season, but generally precipitation has increased more in the northern than southern AT. Temperature and precipitation are projected to increase for all regions during all seasons in the future. Implications of these changes are discussed with respect to hiker experience and trail management.  相似文献   

再工业化背景下美国制造业发展变化及影响研究     

刘毅  周春山 《世界地理研究》2013,(4):13-24

文章基于金融危机后美国实施再工业化战略的背景,根据美国从2005年到2011年的经济数据,运用空间分析法、技术密度法和投入产出法综合剖析了再工业化战略实施后美国制造业的发展变化及影响。文章认为,再工业化战略实施后美国制造业的发展水平开始提升;制造业发展的变化增强了产业间的互动,促使了都会区职能的演变,改变了美国经济的发展路径。  相似文献   

Fieldwork Unbound: Spaces of Association in Postconflict Vietnam     

Jamie Gillen 《The Professional geographer》2013,65(4):599-609

This article traces the ways in which the field emerges and becomes emplaced among three groups of people by presenting an inclusive reading of fieldwork in postconflict Vietnam. It employs a heuristic device called spaces of association to illustrate the different yet interrelated socio-spatial fields that surface when conducting fieldwork in an environment known for violence. In shedding light on the field's ability to extend beyond the territorially defined “field site,” this article speaks to debates surrounding the socio-spatial production of multiple and overlapping fields, describes the audiences engaged with and implicated in research, and contributes to understandings of ethical research engagement with postconflict field sites.  相似文献   

SOIL QUALITY IN ILLINOIS—AN EXAMPLE OF A SOILS GEOGRAPHY RESOURCE ANALYSIS∗     

《The Professional geographer》2013,65(2):127-136

Although acts of creation, scientific or artistic, result from metaphorical and mythological speculations, the role of metaphor and myth has largely been neglected in attempts to develop a geographical epistemology. The significance of these concepts is illustrated by the use of the frontier symbol as a means of understanding both the social structure of the contemporary black inner city and the temporal dimension of the recent expansion of human activities into nighttime.  相似文献