排序方式： 共有25条查询结果，搜索用时 0 毫秒
21.
22.
Graciela Gil-Romera Henry F. Lamb David Turton Miguel Sevilla-Callejo Mohammed Umer 《Global Environmental Change》2010,20(4):612-626
Bush encroachment is a significant phenomenon in savanna environments as it affects wildlife and local livelihoods by preventing new pasture generation. In this article we present a 2000-year record of vegetation change in the Dara range of the Mago National Park, southwestern Ethiopia, an area inhabited by Mursi agro-pastoralists. We use an interdisciplinary approach to understand whether bush encroachment in this area is a recent event or a transitional state of the savanna and describe the local understanding of encroachment as a species-specific process. The vegetation record was obtained from a fossil hyrax midden, a type of sediment already used in Southern Africa but never before in East Africa. Six encroaching phases, led by Capparaceae and Grewia, were found over the last two millennia. The system proved to be resilient, with alternating open and encroached phases, and showed a non-linear response to environmental change, thereby fitting the control theory hypothesis for hysteresis loops. Determining the thresholds conditioning the system's resilience could help to improve savanna management for both local people and National Park authorities. 相似文献
23.
Geospatial tools for assessing land degradation in Budgam district,Kashmir Himalaya,India 总被引：1，自引：0，他引：1
MEHNAZ RASHID MAHJOOR AHMAD LONE SHAKIL AHMAD ROMSHOO 《Journal of Earth System Science》2011,120(3):423-433
Land degradation reduces the ability of the land to perform many biophysical and chemical functions. The main aim of this
study was to determine the status of land degradation in the Budgam area of Kashmir Himalaya using remote sensing and geographic
information system. The satellite data together with other geospatial datasets were used to quantify different categories
of land degradation. The results were validated in the field and an accuracy of 85% was observed. Land use/land cover of the
study area was determined in order to know the effect of land use on the rate of land degradation. Normalized differential
vegetation index (NDVI) and slope of the area were determined using LANDSAT-enhanced thematic mapper plus (ETM+) data, advanced
space borne thermal emission and reflection radiometer, and digital elevation model along with other secondary data were analysed
to create various thematic maps, viz., land use/land cover, geology, NDVI and slopes used in modelling land degradation in
the Kashmir Himalayan region. The vegetation condition, elevation and land use/land cover information of the area were integrated
to assess the land degradation scenario in the area using the ArcGIS ‘Spatial Analyst Module’. The results reveal that about
13.19% of the study area has undergone moderate to high degradation, whereas about 44.12% of the area has undergone slight
degradation. 相似文献
24.
Francesco Dramis Mohammed Umer Gilberto Calderoni Mitiku Haile 《Quaternary Research》2003,60(3):274-283
Stratigraphic analysis of alluvial/colluvial sequences and 14C dating have been used as proxies for Holocene climate changes in the highlands of Tigray (northern Ethiopia). The studied records show alternations of buried soils and peaty–clayey sediments, pointing to wet, stabilization phases, and organic-free colluvium layers resulting from the abrupt occurrence of dry-climate episodes. The 14C dates, mostly unpublished, cluster in the 11,090–9915, 9465–9135, 8450–7330, 6720–3635, 2710–2345, and 1265–790 cal yr B.P. time spans. Evidence of subsequent pedogenesis is lacking in the area, apart from a buried humified horizon dated at 300 ± 60 14C yr B.P. (460–295 cal yr B.P.). Both the timing and the pattern of Tigray paleoclimatic events fit the corresponding framework, based on lake level changes, previously implemented for the Main Rift Valley. These findings give further support for arguing that the forcing mechanisms of the wet/dry fluctuations during the Holocene were effective over a large scale. 相似文献
25.