Riparian ecosystems are known for their high diversity, yet they represent one of the
most threatened habitats globally. I studied riparian and upland bird communities in
undisturbed old-growth forest on western Vancouver Island, B.C. and in riparian buffer
strips retained after harvesting. In undisturbed forest, species richness and diversity did
not differ over the riparian-upland gradient. Except for riparian specialists and species
associated with deciduous vegetation, there was broad overlap of species and abundances
between riparian and upland habitats. To test if fragmentation of riparian habitats alters
bird communities, I surveyed birds in buffers of varying widths 5-7 years post-harvest.
Effects of fragmentation on species richness and overall abundance were weak to absent
in these communities, which are dominated by several forest generalists. The few forestinterior
species were less abundant in all but the widest buffers and were replaced by
open-edge species in narrower buffers. Species assemblages in narrow buffers were also
least similar to controls. Species richness and abundance increased in both buffers and
adjacent clearcuts during the study period. Because populations able to use the forest
matrix may persist better in buffers, I studied movements of birds across river and forestclearcut
edges. Forest generalists, open-edge and ubiquitous species crossed riparian and
clearcut edges most often. Movements were more frequent across clearcut edges than
river edges and were positively related to densities in buffers rather than to buffer width.
Movements were highest in narrow buffers, however, suggesting that birds move in and
out of narrow buffers because they do not provide suitable habitat to support forestdwelling
species. I suggest that narrow buffers function as foraging sites or travel
corridors. Finally, I examined patterns of vegetation across varying buffer widths to test
if habitat diversity better explains patterns of bird species richness and abundance than
buffer width. Densities of faster-growing deciduous trees, and richness and cover of
shrubs and forbs differed over the range of buffer widths. While species richness and
abundances of several bird guilds and species were explained better by buffer width,
three habitat specialist guilds: riparian specialists, forest interior and open-edge species
and 4 of 8 individual species were best predicted by density and cover of deciduous
vegetation. Deciduous vegetation was more common in wider buffers providing further
evidence that retaining wide buffers enhances bird habitat.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/13563 |
| Date | 11 1900 |
| Creators | Shirley, Susan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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