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Effects of forest loss and fragmentation with urbanization on bird communities in Vancouver Er, Kenneth Boon Hwee

Abstract

Habitat modification with urbanization encompasses the processes of habitat loss and fragmentation. In line with the urban wildlife management goal of maximizing species diversity at the landscape and within-patch scales, it is important to understand the effects of these two processes on wildlife communities. Using Vancouver in British Columbia as the study area, I tested the hypotheses that (1) loss in forest area in the landscape with urbanization results in bird extirpations as expressed by the species-area function; and (2) fragmentation of the remaining forest into fragments with urbanization results in large fragments having greater bird species richness and densities than small fragments because large fragments contain a greater diversity and/or abundance of habitat resources. Prior to European settlement in 1859, Vancouver was covered completely by coastal western hemlock forest. By estimating the area of forest loss in Vancouver since 1859 and reviewing the conservation status of birds in Vancouver, I show that the observed number of bird extirpations due to forest loss matches that predicted by the species-area function for bird species closely associated with lowland coastal temperate forests and restricted in their geographic distribution in British Columbia. Using bird and habitat data collected in 14 forest fragments in Vancouver and lower West Vancouver, I show that large fragments support higher bird species richness and density than small fragments in spring, summer and fall. This could be attributed to large fragments containing a greater diversity and/or abundance of habitat resources, especially tree species diversity and abundance of decaying standing material. However, this mechanism is unable to satisfactorily explain all the patterns across seasons. I also found that bird species richness and density were responding to habitat resources that remained constant with area. Hence, there is a possibility that birds may not even select for large fragments despite the greater diversity and/or abundance of habitat resources, if resources that are independent of area are changed dramatically.

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