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Relationships between shrews (sorex spp.) and downed wood in the Vancouver watersheds, B.C.

University of British Columbia

I studied relationships between shrew populations, downed wood, and vegetation in 1991 and 1992 on study areas in the Vancouver watersheds, B.C. I conducted a mark-recapture study on grids with varying amounts of downed wood ('low', 'medium', and 'high'). Three species of shrews, Sorex monticolus, S. vagrans, and S. cinereus were captured during the study. Shrew populations were small, and appeared to increase between 1991 and 1992, but trends were influenced by a change in trapping regime between years. Size of shrew populations did not vary directly with amount of downed wood but showed a more complex relationship with habitat. In general, larger shrew populations were associated with abundant, moderate-sized pieces of wood, and increased vegetative and litter cover. Larger populations also had a disproportionately greater number of reproductively active females, suggesting that the areas they lived in were better shrew habitat. Relation of shrew captures to the microhabitat surrounding trap sites indicated that shrews associated with larger pieces of downed wood and potential foraging sites. Shrews inhabiting areas with diversity in characteristics of downed wood, both in size and in abundance (on 'high' grids), were caught more frequently on sites with larger pieces of wood and on sites where downed wood was closer together. The three species of shrew captured were similar in terms of life history and microhabitat use, and appeared to be dispersed in the environment through territoriality/dominance relationships. Tracking individual shrews confirmed that downed wood was an important habitat component. Shrew travel routes had greater continuity of cover than did areas farther away from their trails. Shrew trails were negatively associated with downed wood <6 cm in diameter. On areas with low diversity in characteristics and abundance of downed wood, shrews were associated strongly with abundance, but not diameter of downed wood. On areas with high diversity in characteristics and abundance of downed wood, shrew trails were associated with greater abundance and cover by logs >12 cm in diameter. To encourage larger, reproductively active shrew populations in managed forest stands, I recommend that a range of tree species and lengths of wood pieces be left on a cutblock. Emphasis should be placed on providing pieces >6 cm in diameter. Pieces should be dispersed to provide a continuous log network. Patches of trees should be left standing to provide a future source of downed wood on the site. Areas should not be burned, because it destroys litter, moss, associated insect communities, and hardens logs.

Thesis/Dissertation

application/pdf

2009-01-31

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http://hdl.handle.net/2429/4025

Forestry

University of British Columbia

UBCV

DSpace