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1.
The purpose of our study was to compare the number, proportion, and species composition of introduced plant species in forest
patches situated within predominantly forested, agricultural, and urban landscapes. A previous study suggested that agricultural
landscape context does not have a large effect on the proportion of introduced species in forest patches. Therefore, our main
goal was to test the hypothesis that forest patches in an urban landscape context contain larger numbers and proportions of
non-native plant species. We surveyed the vegetation in 44 small remnant forest fragments (3–7.5 ha) in the Ottawa region;
15 were situated within forested landscapes, 18 within agricultural landscapes, and 11 within urban landscapes. Forest fragments
in urban landscapes had about 40% more introduced plant species and a 50% greater proportion of introduced plant species than
fragments found in the other two types of landscape. There was no significant difference in the number or proportion of introduced
species in forest fragments within forested vs. agricultural landscapes. However, the species composition of introduced species
differed among the forest patches in the three landscape types. Our results support the hypothesis that urban and suburban
areas are important foci for spread of introduced plant species. 相似文献
2.
We surveyed birds in patches of native eucalypt forest and in surrounding exotic matrix (Radiata pine forests) in south-eastern
Australia. Our objectives were: (1) to examine the influence of the width of native forest patches and the age of surrounding
pine forests on bird occurrence in patches of native forest; and (2) to verify the relationship between the use of the surrounding
pine matrix and bird species response to variation in width of patches of native forests. A total of 32 study sites (boundaries
between eucalypt and pine forests) were surveyed. Birds were counted by the area search method within 0.5-ha quadrats. Data
were analysed using generalised linear models. Wide patches of eucalypt forest supported higher species richness and greater
numbers of birds, such as foliage searchers and nectarivores, than narrow patches. Matrix age also influenced the occurrence
of some species in native patches. The abundance of species in wide and narrow patches of native forest was related to their
use of the matrix. This was true for native forests surrounded by old but not by young pine forests. We suggest that management
in wood production landscapes take into account both characteristics of native patches and the surrounding matrix. Negative
impacts of fragmentation in managed landscapes might be reduced by promoting matrix types that are suitable for bird species. 相似文献
3.
Landscapes resulting from human activity may be expected to present simpler shapes than more natural landscapes. In the case of forest landscapes, the boundaries of native forest patches may be more irregular than those of exotic forest plantations. There is however a lack of quantitative results to this respect, and it is not clear which shape indices are more adequate for such discrimination. In this study, we analysed the shape of a large number of forest classes in the region of Galicia (Spain) using the Spanish Forest Map at a scale 1:50000 as the spatial information source. We considered a set of fifteen shape irregularity indices including those that have been commonly used in landscape ecology studies. We found systematic differences in the shape of the analysed forest classes, with native forests presenting both more complex and elongated boundaries than exotic forests. We suggest that these differences are due to the combined effects of human action and other topographical and hydrological factors. The only index that perfectly discriminated both types of forest was the mean circumscribing circle index. Other six indices provided also a significantly good discrimination: density of shape characteristic points, area-weighted mean perimeter-area ratio, area-weighted mean contiguity index, mean shape index, perimeter-area fractal dimension and mean largest axis index. Comparisons of pure and mixed forests with the same dominant species indicated that an increase in tree species richness is in general associated with more irregular boundaries in the forest. Discarding indices on the basis of a high statistical correlation may not be an adequate procedure to retain the best-performing indices. Finally, we discussed several limitations of some frequently used indices that may be relevant to prevent an improper characterization of landscape shape. 相似文献