Geoscience Reference
In-Depth Information
correlated (
r
0.72) with estimated deer numbers. Confidence intervals around
NCC estimates indicated a considerable amount of variability in all years although
a statistically significant decline in forage biomass was predicted between 1991 and
2002 (
P
< 0.03). Even given high variation, estimated declines in habitat quality
were similar to actual population declines indicating a predictable link between
habitat changes and population dynamics. Our models did detect relevant changes
in habitat quality similar to population changes observed and indicate that manage-
ment interspersion of early successional forests will be required for successful deer
management in this region.
=
Keywords
Mount St. Helens
·
Deer
·
Habitat quality
·
Remote sensing
·
GIS
·
Uncertainty
·
Forest Succession
·
Forrage
·
Carrying Capacity
2.1 Introduction
In evaluating habitat quality for wildlife, ecologists must often rely on geospatial
modeling, adaptive management, or natural disturbances to simulate experimental
conditions (Turner et al.
2001
). The 1980 eruption of Mount St. Helens (MSH) pro-
vided a dramatic natural disturbance and the opportunity to study vegetation changes
and wildlife recovery over time. The eruption devastated over 500 km
2
of forested
landscape (Franklin et al.
1985
; Frenzen and Crisafulli
1990
) leaving a seemingly
sterile landscape in its wake. Despite fears that recovery would take years, it began
soon after the eruption (Dale et al.
2005
) and included not only early successional
plants and small animals, but also predators and grazing mammals including elk
(
Cervus elaphus
) and BTD.
By the time of the 1980 eruption, ungulate populations in the Mount St. Helens
area were considered stable. The Washington Department of Game (
1983
) estimated
that 1600 elk and up to 5000 BTD were killed in the eruption, although natural
vegetation recovery and seeding in selected areas provided high quality forage and
ungulate populations recovered quickly in the years following the blast (Merrill et al.
1986
). By the early 1990's ungulate populations at MSH were declining, a trend
seen throughout much of the Pacific Northwest (PNW) as far back as the 1960's
(Carpenter
1998
).
Regional population declines for deer and elk have been attributed to an increase
in even-aged regenerating forests and the subsequent decrease in forage production
(Brown
1961
; Taylor and Johnson
1976
; Scharpf
1985
;Davis
1999
). Management
in the industrial forests of the PNW consists of patch clear-cutting followed by a
combination of herbicide treatments, slash burning (Taylor and Johnson
1976
), and
replanting to a single species. In productive areas, closed canopy conditions can be
reached in as little as 12 years and understory biomass levels drop dramatically by
this time (Taylor and Johnson
1976
).
Despite the impact of even-aged forest management on deer populations,
few studies exist relating landscape-scale forest changes to population dynamics
