Geoscience Reference
In-Depth Information
Tabl
e 2.4
Probability values associated with comparisons of habitat models among selected y
ears
Comparison
NCC
NCC_Rd
NCC_FC
Combined
1984-1988
0.16
0.26
0.36
0.41
1984-1991
0.12
0.11
0.12
0.11
1988-1991
0.53
0.31
0.29
0.86
1988-1999
0.09
0.21
0.31
0.33
1988-2002
0.01
0.17
0.11
< 0.001
1991-1996
0.36
0.37
0.33
0.17
1991-1999
0.03
0.03
0.02
< 0.001
1991-2002
0.01
0.01
0.05
< 0.001
2.5 Discussion
The general pattern of forest succession and subsequent increases and declines in
NCC in these models were consistent with the pattern suggested by BTD population
trends as well as general ungulate population declines in this region (Brown
1961
;
Taylor and Johnson
1976
;Davis
1999
; Peek et al.
2002
). Forage has previously
been associated with population trends of BTD in western Washington (Gilbert et al.
2007
), our study provides a widely applicable tool for managers allowing them to
predict both the direction and magnitude of BTD population changes in response
to management actions and ultimately the proportion of the management area that
needs to be in various successional classes to achieve a desired relative density of
BTD. Further, remote sensing and GIS allow the opportunity to assess habitats over
multiple spatial and temporal scales particularly where detailed timber management
data are lacking.
In addition to forage estimates, GIS modeling allowed for incorporation of effects
of multiple factors that could affect BTD use of habitat (i.e., roads, forage-cover
ratios) and evaluation of landscape variation at a scale potentially more ecologi-
cally relevant to BTD than previous stand-level studies. Specifically, it allowed for
characterization of the uncertainty around model estimates, which can be critical
in habitat studies (Bender et al.
1996
). While high variation and overlapping con-
fidence intervals meant that some model comparisons among some years did not
differ statistically, all modeled estimates of NCC did demonstrate significant for-
age declines between 1991 and 2002, which coincided with the general population
decline in deer.
To what extent the high degree of variation in annual estimates of NCC reflect
actual habitat quality available to deer is unknown, although some of the variation
was likely due to the random placement of home range polygons in our analyses.
Foraging animals are unlikely to distribute themselves randomly over a landscape;
rather, they tend to match the distribution of forage resources (see Fretwell and
Lucas
1970
; Stephens and Krebs
1986
; Senft et al.
1987
). Distribution of forage
was highly variable across the landscape (Fig.
2.2
), and consequently some random
