ZICM are typically very dense, and the high canopy
closure associated with competitive stems tends to
inhibit understory growth. Additionally, there is little
subcanopy structure in the form of CWD and shrubs
to serve as protective cover for voles within these
stands (Thompson and Curran, 1995; Sturtevant et
al., 1996b). Thus, while meadow vole abundance
may increase after tree harvest (Kirkland, 1977;
Monthey and Soutiere, 1985; Yahner, 19921, data
from Sturtevant and Bissonette (19%) indicate that
Newfoundland meadow voles become scarce at the
time of canopy closure, and may not increase significantly
in abundance until the stand enters the senescent
stage. This observation is supported by the
trapping results of Thompson and Curran (1995).
By using the SDMD to trace the conceptual trajectory
of a typical unmanaged stand as it progresses
from regeneration to overmaturity, one can predict
when various habitat resources become available
(Fig. 2). Immediately after a clear-cutting there is
typically abundant herbaceous growth (Meades and
Moores, 19941, as well as some residual coarse
woody debris. While voles should be present, there
is no vertical structure available for marten. In the
absence of subsequent disturbance, this stand should
enter and remain within the ZICM as it develops.
Though vertical structure becomes available as trees
increase in size, the subcanopy structure is sparse,
with little CWD and very few voles. Vertical stem
structure is still available as the stand senesces, but
the canopy becomes more open, allowing for herbaceous
growth and the potential for increased vole
abundance. Furthermore, the subcanopy debris structure
also is available to provide access to the small
mammal prey resource in winter. Thus, the elements
necessary for marten winter foraging habitat are only
present simultaneously within senescent stands, suggesting
that marten within this system should be
highly dependent on the overmature stage of forest
development.