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1.
Maurice Keith R. Welch Joan M. Brown Christopher P. Latham Roger Earl 《Landscape Ecology》2004,19(6):603-620
The Pocono mesic till barrens (PMTB) are a unique assemblage of fire-maintained shrub communities that support numerous rare species. Historically these barrens covered a large area in the vicinity of Long Pond, Pennsylvania, USA. However, due largely to regional fire suppression instituted in the early 1960s, over 70% of the area covered by barrens succeeded to fire-intolerant forest that does not support the rare species. We investigated the influence of forest proximity on barrens succession across three geomorphic types during periods of high fire frequency and fire suppression, testing the hypothesis that forest processes such as seed rain, shading, and detrital enrichment of soils enhances barrens succession through a contagion effect. Evidence of a forest contagion effect should be shown by increased rates of barrens succession with increasing proximity to the nearest forest edge. In order to detect a forest contagion effect, barrens persistence and barrens succession were modeled in proximity zones of 0-50 m, 50-100 m, 100-200 m, and greater than 200 m from the nearest forest edge. We used existing GIS data layers for fire, geomorphology, and vegetation distribution in 1938, 1963, and 1992. The layers were modified and overlain using ArcView software to determine persistence and succession rates for each unique combination of layers in each proximity zone from 1938 to 1963 (pre-fire suppression) and 1963 to 1992 (post-fire suppression). ANCOVA results indicate that proximity to the nearest forest edge significantly affected barrens persistence rates in both time periods, but succession rates were significantly affected in 1938 to 1963 only. Twenty-eight percent of the 1938 barrens succeeded to forest by 1963; 56% of the 1963 barrens became forest by 1992. Results support previous findings that barrens persistence is enhanced by increased fire frequency, and that barrens persist longer where they overlie flat glacial till than on other geomorphology types. 相似文献
2.
严宁珍 《四川畜牧兽医学院学报》2008,(4):151-154
为了适应21世纪社会发展的需求和高等教育人才培养模式的转变,课程的教学改革势在必行。笔者就《地质与地貌学》课程在教学内容、教学条件、教学方法、考查考核等诸方面的改革进行了探讨。该课程的教改极大地激发了学生的求知欲,提高了学生的认知水平和创新能力,培养了学生的实践能力,收到了良好的效果。 相似文献
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The cross-referencing of sedimentological, stratigraphic, geoarchaeological and radiocarbon data enables us to establish the geomorphologic evolution of the Late Holocene coastal flood plain of the Turia River. The Holocene marine transgression formed a coastal barrier lagoon environment in the coastal plain. During the Late Holocene, increased sediments supplied to the low reach of the river promoted: (a): the progradation of deltaic coastal sandy ridges on the coastline and (b): the aggradation of the floodplain on top of the sedimentary sequence. Four phases are clearly recognised in the geoarchaeological record of the flood plain. (1): High magnitude flooding events (2800 BP to 3rd century BC). (2): Slow riverbed aggradation and progressive levee formation (low energy flood regime) in Roman times (2nd century BC to 5th century AD). (3): Swampy environmental processes (6th to 9th centuries). (4): Second high-magnitude flooding phase (11th century). The navigable channel of the Roman and early Islamic periods became a wide and shallow braided channel in Medieval times. These phases are correlated with others detected by researchers in many areas of the Mediterranean region and with global Holocene climate events. 相似文献
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J.?Mergani?Email author H.-D.?Quednau ?.??melko 《European Journal of Forest Research》2004,123(1):75-85
The presented paper analyses the relations between four features of geomorphology, i.e. aspect, slope, elevation and type of terrain, and tree layer diversity of forest ecosystems. The forest stand diversity is quantified by nine species diversity indices (N0, R1, R2, H, N1, N2, E1, E3, E5). The data used in this study come from the regional forest inventory of the Forest School Enterprise, Technical University Zvolen, Slovakia. Within this inventory, 26 permanent tracts were established in the systematic grid of 2×2 km, whereby a total of 120 sample plots were created on which 1,728 trees were measured. Analyses showed that species diversity is closely related only to elevation. However, the relationships of the individual species diversity indices to elevation are loose since the correlation coefficients do not exceed values of 0.30–0.40. The second part of this work presents spatial interpolation of species diversity degrees on a regional level using geostatistical methods. For this regionalisation, we used an indicator kriging. The final kriging map was found to be a suitable tool for the interpretation of tree species diversity over the investigated area. 相似文献
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There are only a few studies of land cover-land use changes which provide an integrated assessment of the biophysical and
societal causes and consequences of environmental degradation in Ethiopia. Our objectives were to determine the status of
the environmental degradation, analyse and evaluate the relationships among vegetation, geomorphological and socio-economic
factors contributing to environmental degradation, and propose opportunities for rehabilitation of these natural resources.
Field and other environmental data in northern Ethiopia and those acquired by remote sensing techniques were used to accomplish
these objectives. These were integrated with socio-economic data obtained from official sources using a Geographic Information
System (GIS).Spatial information such as the percent of land cover-land use types and geomorphological categories, and the
percent of each land cover-land use type in the geomorphological categories were calculated using Geographic Information System
(GIS). The three most dominant features of the geomorphological categories (93.0%) are scarps and denuded rock slopes, erosion
surfaces and badlands, while the three most dominant features in the land cover-land use types (71.3%) are croplands, open
woodlands and bushlands. Badlands account for 38.7% of the geomorphological units and 41.8% of the croplands currently occur
on badlands. Simple and partial correlation analyses were applied to explore the extent of the interaction between the anthropogenic
and the natural system. The anthropogenic system is influenced by elevation, which is positively correlated with human population
and livestock densities and area of croplands. The natural system finds its place only on steep slopes as shown by the positive
correlation between woodland,slope, high potential erosion, scarps and denudational rock slopes. The study indicates that
agriculture in the study area is in a critical environmental situation. A change of paradigm in land-use and development is
needed to encourage participation of the landowners and users in the efforts to conserve the vegetation and the soil. This
study provides sound options that could be used to rehabilitate the vegetation directly and to alleviate the current pressure
on the land and improve human welfare indirectly. Matching the human and livestock densities with the carrying capacity of
the land through recruitment of the surplus labour force for a modern economy, resettlement,off-farm employment and intensification
of agriculture are t he long and short-term actions that may contribute to the rehabilitation of the degraded areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Excavations at four archaeological sites consisting of the material remains of A.D. 1050–1170 era farmers along the Colorado River in Grand Canyon National Park, yield geomorphic information used to address questions related to settlement patterns. Archaeological excavation units, test pits, feature fill, and natural exposures contain sediments used to interpret geomorphic history that can, in turn, shed light on archaeological site selection in a challenging environment. The Grand Canyon experiences dramatic geomorphic events such as catastrophic floods and destructive debris flows that are preserved in the stratigraphic record, and can be used to understand cultural/landscape interactions. By combining new geomorphic, stratigraphic, and archaeological data collected during recent excavations with results from previous geomorphic and sediment transport studies, observed trends can be interpreted regarding the possible influence of paleofloods on past settlement patterns. For example, at each of the four sites, reconstructed paleoflood elevations (from existing HEC-RAS virtual shorelines), flood recurrence intervals, site layout, and site stratigraphy/geomorphic setting suggests a temporal trend in site location. The two early sites (Early Pueblo II period: A.D. 1050–1080) contain habitation features located above the approximately 6–8 year high flood (3500 cubic meters per second [cms]) recurrence interval; larger floods (4800 to 5900 cms) of a longer recurrence interval between 40 and 80 years inundate these features. The two later sites in the sample (Late Pueblo II; A.D. 1080–1170) contain habitation features located well above the 40–80 year recurrence high flows. We suggest that early farmers (Early Pueblo II period: A.D. 1050–1080) may not have had adequate experience with flood magnitudes and frequencies and therefore their habitation structures were located in risk-prone areas relatively close to the river. Later habitations (Late Pueblo II; A.D. 1080–1170) were positioned in more protected areas further from the river, perhaps reflecting an acquired knowledge of river dynamics. These trends, although currently based on a limited data set, provide insights into site selection decisions and settlement patterns of early farmers along the Colorado River through Grand Canyon. 相似文献
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The Holocene landscape history and historical soil erosion were reconstructed at Albersdorf (Schleswig-Holstein, Germany) from soils and colluvial layers. In contrast to many landscapes in central Europe, agricultural land use and soil erosion were more frequent during pre-historical times, whereas it has almost ceased after the advent of history. Pre-historical soil erosion rates from about 0.1 to 6.9 t ha− 1 a− 1 were reconstructed with no significant differences between the prehistoric cultural phases. The study of buried soils within the soil/soil-sediment-sequences provided evidence for an acceleration of soil formation processes probably as a consequence of excessive prehistoric woodland pasture on poor sandy soils. 相似文献
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近代及现代黄河三角洲不同尺度地貌单元土壤盐渍化特征浅析 总被引：13，自引：3，他引：10
近、现代黄河三角洲近50%的土地为不同程度的盐渍化土。在土壤盐渍化过程中,地貌因素至观重要。地形的高低起伏,影响地面、地下径流的运动,土壤中的水分和盐分也就随之重新分配和积累。研究的目的是分析不同尺度下地貌单元之间土壤盐渍化特征差异及原因。为此,利用2002年5月23日到29日对近、现代黄河三角洲野外考察、GPS定点和土壤采样分析所得数据,对6个表征土壤盐渍化特征的参数（土壤的全盐量、pH值、有机质、Cl-/SO42-、HCO3-/(Cl-+SO42-)、(K++Na+)/(Ca2++Mg2+)）进行统计分析,并进行多个独立样本的非参数检验（Kruskal-Wallis Test和Median Test）,检验6个参数在同一尺度不同地貌单元之间是否有明显的差异,结果表明：（1）近、现代黄河三角洲土壤盐渍化程度严重,整体属于滨海氯化物型盐渍土类型,有机质相对缺乏,土壤偏碱性。随土层深度增加（0cm~10cm、10cm~30cm、30cm~60cm）,盐渍化程度逐渐减轻;（2）同一尺度下不同地貌单元之间土壤盐渍化特征存在差异。一般地,随尺度变小（从一级到四级地貌单元）,土壤盐渍化特征差异越来越明显,存在差异的参数也逐渐增加。一级地貌单元只有pH值明显不同,从二级地貌单元到四级地貌单元,3个土层土壤的全盐量随不同的地貌单元而有明显的差别,且随着土层深度的增加,HCO3-/(Cl-+SO42-)和(K++Na+)/(Ca2++Mg2+)也变得明显不同。这也说明不同地貌单元下盐分组成及离子比例、积盐、脱盐过程存在差异,且随土层深度增加差异越大。 相似文献
10.
太行山在造山运动过程中由于构造时间和强度的差异,在地貌上形成了高低、大小不一的山体。依据地貌形成规律和植被类型,将太行山中南部分为低山、中低山、中山、中高山4个立地类型亚区。在海拔的控制下,再根据坡向、地形部位划分出17种立地类型;结合乡土树种分布调查,为17种立地类型提出了可选用的乔灌木树种;根据立地类型和指示植物生物学与生态学特性进行宜林性质划分,提出了水土保持林、水源涵养林、经济林、用材林的适宜树种。 相似文献