Geoscience Reference
In-Depth Information
2.2 Study Area
Our study was conducted within the Washington Department of Fish and Wildlife
Game Management Unit (GMU) 524 and included approximately 22,300 ha to the
north and northwest of Mount St. Helens (Fig.
2.1
). It was bounded on the North
by the Green River and on the south by portions of the North Fork Toutle River,
Hoffstadt Creek, and Coldwater Lake. Physiographically, most of the area belongs
in the southern Western Cascade Province (Franklin and Dyrness
1988
), is located
in the western Cascade Mountains, and consists of steep mountainous terrain to the
east and rolling foothills to the west. Elevation ranges from 240 to 1200 m and the
climate is Pacific maritime wet. Mean annual precipitation ranges from 162 cm in
the Cowlitz River valley north of the study area to over 350 cm on the slopes of
Mount St. Helens to the south. Approximately 45% of the annual precipitation falls
as snow between November and January and summers are typically dry and cool.
Prior to the 1980 eruption, much of the study area was dominated by mature
coniferous forests, with occasional scattered openings and riparian corridors. Based
on elevation and moisture gradients, Franklin and Dyrness (
1988
) described two
major forest zones in the area; the Western Hemlock (
Tsuga heterophylla
) zone
at lower elevations and the Pacific Silver Fir (
Abies amabilis
) zone at middle
elevations.
Approximately 3/4 of the study area was affected by the 1980 eruption with dam-
age consisting mostly of forest blow down from the lateral blast, though some areas
of forest were scorched and left standing. The western 1/4 of the study area was
largely undamaged by the blast as was a small pocket of forest protected by topog-
raphy directly north of Mount St. Helens (Fig.
2.1
). The formation of the Mount
St. Helens National Volcanic Monument (hereafter Monument) in 1982 (Fig.
2.1
)
allowed much of the devastated area to recover naturally. Following the eruption,
lands outside the monument, mostly private industrial forest, were salvage logged
and quickly replanted, accelerating forest succession in many areas (Harrington
et al.
1998
).
According to the Washington Department of Fish and Wildlife (WDFW), deer
populations in this study area were largely wiped out in 1980, but by 1988 had
reached levels similar to pre-eruption numbers of just over 5000 deer estimated in
1974. By the year 2000 estimated numbers declined to less than 500 animals.
2.2.1 Habitat Requirements for Deer
Habitat evaluations for ungulates center on estimates of available forage and, in
forested environments, overstory attributes such as canopy cover are dominant fac-
tors affecting understory plant dynamics (Alaback
1982
; Pieper
1990
; Canham et al.
1994
; Nabuurs
1996
; Robinson and McCarthy
1999
; Jules et al.
2008
). In the west-
ern Cascades, forage habitats occur in natural and manmade openings typically less
than 10 years of age and canopy closure less than 60% (Brown
1961
; Crouch
1981
;
Witmer et al.
1985
).
