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Weiqi?ZhouEmail author Ganlin?Huang Steward?T.?A.?Pickett M.?L.?Cadenasso 《Landscape Ecology》2011,26(5):645-659
Landscape structure in the Eastern US experienced great changes in the last century with the expansion of forest cover into
abandoned agricultural land and the clearing of secondary forest cover for urban development. In this paper, the spatial and
temporal patterns of forest cover from 1914 to 2004 in the Gwynns Falls watershed in Baltimore, Maryland were quantified from
historic maps and aerial photographs. Using a database of forest patches from six times—1914, 1938, 1957, 1971, 1999, and
2004—we found that forest cover changed, both temporally and spatially. While total forest area remained essentially constant,
turnover in forest cover was very substantial. Less than 20% of initial forest cover remained unchanged. Forest cover became
increasingly fragmented as the number, size, shape, and spatial distribution of forest patches within the watershed changed
greatly. Forest patch change was also analyzed within 3-km distance bands extending from the urban core to the more suburban
end of the watershed. This analysis showed that, over time, the location of high rates of forest cover change shifted from
urban to suburban bands which coincides with the spatial shift of urbanization. Forest cover tended to be more stable in and
near the urban center, whereas forest cover changed more in areas where urbanization was still in process. These results may
have critical implications for the ecological functioning of forest patches and underscore the need to integrate multi-temporal
data layers to investigate the spatial pattern of forest cover and the temporal variations of that spatial pattern. 相似文献
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A high-resolution record of holocene climate change in speleothem calcite from cold water cave, northeast iowa 总被引:2,自引:0,他引:2
Dorale JA González LA Reagan MK Pickett DA Murrell MT Baker RG 《Science (New York, N.Y.)》1992,258(5088):1626-1630
High-precision uranium-thorium mass spectrometric chronology and (18)O-(13)C isotopic analysis of speleothem calcite from Cold Water Cave in northeast Iowa have been used to chart mid-Holocene climate change. Significant shifts in dagger(18)O and dagger(13)C isotopic values coincide with well-documented Holocene vegetation changes. Temperature estimates based on (18)O/(16)O ratios suggest that the climate warmed rapidly by about 3 degrees C at 5900 years before present and then cooled by 4 degrees C at 3600 years before present. Initiation of a gradual increase in dagger(13)C at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present. 相似文献
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The disposal of sewage wastes may cause severe environmental problems as was graphically demonstrated with pollution on Sydney's ocean beaches in recent years. Sewage sludges contain valuable plant nutrients and organic matter which can improve the fertility and structure of the soil. However, human parasites, pathogenic micro-organisms and chemicals capable of causing soil contamination, phytotoxicity and residues in animal products may also be present. Although sewage sludge is frequently spread on agricultural land overseas, it is not common in Australia and most states do not have specific regulations to minimise risk and promote good practice. A sludge-to-land program began in the Sydney region in 1990. It follows guidelines written by NSW Agriculture to encourage beneficial agricultural use of sludge by adoption of environmentally sustainable practices. This article describes the major risks to the food-chain and the environment, which may be associated with applying sewage sludge to agricultural land. It summarises how the risks are managed, and where further research data are required. 相似文献
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