| Summary: | 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. === Forestry, Faculty of === Graduate
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