Geoscience Reference
In-Depth Information
of BTD. Gilbert et al. (
2007
) used forest harvest records to estimate forage biomass
in western Washington and found forage to be a critical determinant of the popula-
tion dynamics of female deer. This was likely the first study to connect landscape
forage conditions and population dynamics specifically for this species, although
general applicability would depend upon the availability of forest harvest records.
Remote sensing evaluations of forest conditions are common (e.g. Cohen et al.
1995
) yet to our knowledge no study has used such data to relate forest condi-
tions to population dynamics for BTD. Because it allows efficient mapping of large
land areas (Skovlin et al.
2002
;O'Neiletal.
2005
) geospatial data is often the most
practical means of quantifying habitat features for large ranging animals (Glenn and
Ripple
2004
) and could greatly facilitate evaluations of the potential links between
habitat quality and BTD population declines.
For deer and other ungulates, population success is a direct function of the
quantity and quality of available forage (Cook
2002
; Cook et al.
2004
), which is
mostly obtained from early successional habitats on the landscape (Heffelfinger
et al.
2003
). In the PNW, such habitat is becoming increasingly rare due to man-
agement for later successional habitats on state and federal lands (Lutz et al.
2003
).
Despite this management focus, deer populations remain an economically important
resource to many communities and state agencies are facing an increasing demand
from constituents to restore deer populations. Given decreased logging on state
and federal lands, successful habitat management for deer will increasingly depend
upon cooperation between private industry and wildlife managers to develop forest
management practices which produce conditions capable of supporting larger deer
populations.
In relating habitat to population dynamics, wildlife managers require detailed
knowledge of habitat carrying capacity (Beck et al.
2006
). Generally, this is quanti-
fied from some measure of critical habitat resources such as forage. However, even
given such measures, relating the quantity and distribution of habitat components to
population dynamics is often difficult because the underlying mechanisms are either
unknown or not incorporated into models (Morrison
2001
). Such mechanistic links
are critical if habitat quality is to be meaningfully evaluated (Hobbs and Hanley
1990
; Eberhardt
2002
), particularly in areas where habitat conditions are changing
rapidly.
2.1.1 Purpose and Objectives
Our purpose was to evaluate post-eruption changes in habitat composition and struc-
ture within a portion of the MSH blast zone and to compare these trends with
changes in the size of the BTD population. Specific objectives included: (1) use
Landsat TM imagery to develop landcover classifications depicting forest succes-
sional stages from 1984-2002; (2) estimate the available biomass of winter forage
as an indicator of habitat carrying capacity; (3) incorporate the potential mitigat-
ing effects of roads and cover; and (4) compare model estimates to estimates of
population size of BTD in the study area.
