The Red Squirrel: Spruce-Fir Forest
Bird song and the gray light of dawn wake the red
squirrel, curled in his grass-lined, leafy nest in an old woodpecker
hole. He climbs out, sits on a branch of the dead birch that is his
current home, and surveys his domain.
The acre he claims lies on top of a low ridge along
the Moose Trail, about one-half mile east of Rock Harbor Lodge. An open,
parklike forest of spruce, fir, birch, and a few aspens covers the
ridge. Underneath, sapling firs outnumber the young spruces, but nearly
all of the firs have been heavily browsed by moose, leaving the upper
stems bare of foliage. Large-leaved aster, thimbleberrywith its
big, maplelike leaveswild sarsaparilla, white-flowered Canada
dogwood, scattered bluebead lilies, and clumps of low juniper bushes
cover most of the ground, but not thickly. Moss grows on rotting logs
and stumps. On the north side of the ridge, where the underlying rock
tilts steeply down to the shore of Tobin Harbor, moss, other ground
plants, and young conifers are thicker, encouraged by the greater
moisture. Here old stumps of aspen, cut by beavers years ago, are
beginning to rot. On the south side, where the rock slopes gently but
faces the sun, the ground cover is scarcer, and includes some reindeer
lichens on the rock and patches of bracken fern. At the foot of the
slope lies a swamp, draining slowly between this little rise and the
next. Here tall spruces cast shade on the grasses, ferns, horsetails,
and broad-leaved skunk cabbage that cover the wet ground.
![](images/nh8ae.jpg)
The red squirrel, which feeds on the seeds of conifers, is found in
coniferous forests across North America from Nova Scotia to Alaska. (Photo by Robt. G. Johnsson)
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It is the third week in June. All the summer birds are
back and are insistently proclaiming their territories. To the squirrel's
ears come the ringing song of an oven-bird, the sweet loud whistle of a
white-throated sparrow, the flutelike rising swirl of a Swainson's
thrush. Nashville, magnolia, myrtle, blackburnian, and
black-throated green warblers add their small but distinctive songs to
the early-morning chorus. Down in the swamp, a winter wren unwinds its
tinkling medley, and a little yellow-bellied flycatcher quietly
whistles, "pun-wee." Intermittently, spring peepers peep.
None of these sounds is important to the squirrel,
though they indicate the general locations of nests he might rob. But
then a long, chattering "tcher-r-r-r" from down in the swamp
electrifies his nerves. "Tcher-r-r-r!" he answers, vibrating with
excitement and twitching his tail. It is another squirrel, one of two
that occasionally wander up the slope into his territory. He calls
again, angrily. Hearing no answer, he starts down the tree to begin the
morning's foraging.
![](images/nh8af.jpg)
The garter snake (shown here) and the red-bellied snake (not shown) are
the only two species of snakes that have become established on Isle
Royale. Garter snakes are found in many habitats, including wetlands;
the secretive red-bellied snake frequents open woods and sphagnum bogs. (Top photo by Greg Beaumont;
bottom photo by Robt. G. Johnsson))
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Many plants in the forest have something to offer him
at one time or another, but now in early summer he is concentrating on
the tender buds at the tips of spruce twigs. Stopping briefly on a log
to nibble a bracket fungus, he then leaps up onto the trunk of a large
spruce and scampers to its top, hardly pausing. For a half hour he
carefully examines each branch, crawling out each one until it threatens to
drop him. Then, surfeited with buds, he races down the trunk and out a
limb, and winds through a succession of tree tops until he is above the
top of the north slope. A crunching sound has roused his curiosity, and
investigate he must. Below, half hidden in the foliage, a cow moose is
stripping the leaves from young birches and noisily chewing them. Behind
her, two small, light-brown calves nibble tentatively at ground plants.
With the moose population high, most cows have borne only one calf, but
these two seem to be thriving. For a week now the calves have followed
their mother up and down Scoville Point, sometimes swimming across short
stretches of water but seldom leaving the peninsula. Chances are that
they will escape wolves this summer, because the pack on the island's
northeast end seldom comes near the lodge area during the busy season.
Two young bulls, and occasionally a yearling cow, wander through the
squirrel's territory from time to time. He chatters at the trio below
him, but they pay no attention.
Getting no response here, he works his way through
trees and along the ground to a little grove where an aspen stands.
Climbing the trunk he reaches a hole just as a downy woodpecker pops
into it to feed four noisy young. The squirrel scurries around the hole
excitedly, then loses interest and descends to investigate the
ground.
Restlessly he bounds along the forest floor, through
plants, along logs, then pauses, investigates under an old stump,
emerges and continues. He knows every foot of his acre what food it
offers, what hiding places for himself and his seed stores, what
possible nesting places. He also knows its dangers. A few woodpecker
feathers lie scattered near the trail where some hawk or owl has
feasted; it might as well have been squirrel fur. An old thigh bone of a
hare under a juniper bush wakes an image of a red fox kill he witnessed
here the past winter. The fox is a frequent visitor, forcing the
squirrel to be ready always to dash for a tree or tunnel. Mink and
weasel are occasional threats, but the marten, scourge of red squirrels
through much of the north woods, no longer lives on the island. The deer
mouse whose territory overlaps the squirrel's is a night animal, subject
to attack by weasel, mink, fox, and especially owl. With alertness and
luck, the squirrel may live two or three years. The mouse will do well
to see another spring.
![](images/nh8ag.jpg)
Canada dogwood, a tiny plant related to dogwood trees, grows on the
floor of the coniferous forest.
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The squirrel pauses on a log to rest. Near him a
bumblebee sprawls on the white bloom of a Canada dogwood. The late
morning sun sparkles on the transparent wings of a hovering dragonfly,
before it dives at a mosquito dancing in the air. There is an endless
supply of mosquitoes; but there are also many birds that catch
dragonflies. The dragonfly's chances for lasting the season are much
less than those of squirrel or even mouse.
Feeling a certain lassitude in the warm sun, the
squirrel climbs up a favorite spruce tree and stretches out on a limb
where he can soak up the sun's rays. On the trail beneath him a little
red-bellied snake also lies stretched, taking the sun. Like regular
second hands of some giant clock, herring gulls fly over on their patrols
of Tobin and Rock Harbor, drawing shadows through the dappled forest.
Less often, ravens in ones and twos skim the tree tops, croaking as
they pass. So familiar are these birds, the squirrel pays no attention.
Suddenly a shape comes gliding under the tree tops. The squirrel
tenses for flight, but the broad-winged hawk sails past him and lands on
a branch over a small grassy pool. For several minutes it sits hunched
and still. Then suddenly it drops toward a green frog at the edge of the
pool. But at the last moment the frog dives; it will not today feed
hatchling hawks a mile or two away on Tallman Island.
Some time later, after the hawk has left, the
squirrel resumes his rounds. It is an uneventful afternoon, except for a
short chase when he surprises one of the swamp squirrels raiding a food
cache. The sun drops toward the ridge behind Tobin Harbor. Sitting
beside the Moose Trail, the squirrel feels vibrations. A human family
comes by. He runs up a small tree and chatters at them. They stop to look,
then walk on. As the sun touches the top of the ridge behind Tobin Harbor,
the squirrel starts toward his nest in the dead birch. He has successfully
completed another day.
This particular squirrel's patch of forest, though
unique like every other patch, has many elements found throughout Isle
Royale's spruce-fir stands. The variations in these stands consist
mostly in the proportions of the plants and animals common to all of them.
The abundance of the constituent plants and animals in turn is determined
by the moisture, soil, and sunlight, and by the history of the immediate
arearecentness of fire, wind damage, intensity of moose browsing, and
other things. All of these factors are strongly influenced by the
stand's topography and its location with respect to the Lake Superior
shoreline.
![](images/nh8ah.jpg)
The spruce-fir forest grows to the water's edge on
Inner Hill Island. (Photo by Robt. G. Johnsson)
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Forests near the shore are the moistest and also most
subject to wind damage and moose browsing. The cold waters of Lake
Superior cool the adjacent layer of air and contribute moisture to it.
This cool, moisture-laden air inhibits evaporation in the shoreline
forests, thus allowing most of the moisture in the soil to remain there
to be used by plants. A plus factor for tree growth, this is
counterbalanced by the effect of wind, which can sweep across the wide
expanses of the lake and hit the shore full force, toppling many trees.
Shoreline forests also receive the heaviest winter browsing by moose,
because these animals find here the greatest quantity of fir, a favorite
winter food, and, because of the roof effect of close-packed conifers,
somewhat lessened snow depths.
The result near shorelines is a damp forest of small
trees with a high proportion of birch, which often springs up in
wind-created openings; a high proportion of fir, which would be more
numerous without moose; scattered white spruce trees, usually, because
of greater resistance to windthrow, taller than the firs; a sprinkling
of mountain-ash and white-cedar; and a generally thick, diverse cover of
ground plants and shrubs. Old man's beard, a lichen resembling Spanish
moss and dependent on high moisture, festoons the trees. Mott and
Raspberry Islands have good examples of shoreline forest, though they
do not suffer much moose browsing.
Inland and higher up, as the lake influence
diminishes, temperatures become higher, thus increasing evaporation.
Wind is reduced by the buffering effect of ridges and by the intervening
expanse of the forest itself. Oldman's beard disappears. In sheltered
valleys, trees can grow fairly tall.
![](images/nh8ai.jpg)
The spruce on the left is unbrowsed; the firs on the right have been
heavily browsed.
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One of the most noticeable changes inland is the
increase of spruce and decrease of fir. This happens, apparently,
because of differences at the surface of the soil. Near the shores
decomposition of organic matter is slow on the cool ground. The litter
of twigs, needles, and dead plants may become several inches thick. This
layer of litter, filled with air spaces, tends to dry out fast after a
rain, thus making a poor bed for tree seeds to germinate and grow on.
But the roots of fir seedlings grow faster than do those of spruce, and
thus are able to reach soil moisture sooner. In the shore zone, more
firs survive to become trees. And fir is also more tolerant of shade.
Inland, warmer temperatures speed up decomposition, reducing the depth
of the litter layer. Also, the drier soil supports fewer trees, which
shed less material onto the forest floor. The relative dryness also
makes for more frequent and intense fire, which often produces open
areas with mineral soil. Spruce is better able than fir to germinate
and grow under these conditions and thus is more abundant inland.
The spruce-fir situation illustrates one aspect of
the intense competition between plants on the forest floor. In many
places, the growth is so thick that tree seedlings of all species can
get started only on rotten logs, stumps, or mossy rocks.
The ground cover in spruce-fir forests varies
greatly, depending mainly on the amount of moisture and sunlight
present. Where conifers stand close to gether, shutting out the sun, the
forest floor is nearly bare of plants. Where
the canopy is more open, the ground is likely to be
covered with mosses, club-mosses, ferns, and a
wide variety of herbaceous plants, such as Canada dogwood, wild
sarsaparilla, large-leaved aster, star flower, twin flower, wild
lily-of-the-valley, blue-bead lily, and fringed polygala. Orchids,
though less common, are frequently found; calypso orchid, one-leaf rein
orchid, and spotted coralroot are among those forest species seen most
often. In northern coniferous forests such as those on Isle Royale, many
of the ground plants are evergreenan adaptation to the short
growing season. The wildflowers bloom abundantly through July, unlike
those in the deciduous forest farther south, where the majority of
flowers blossom in spring before unfurling tree leaves shut off most of
the sunlight.
![](images/nh8aj.jpg)
Twinflower grows in the spruce-fir forest along the Mount Franklin
Trail. (Photo by Robt. G. Johnsson)
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The common shrubs include squashberry, red-berried
elder, and bush honeysuckle. Where the forest is particularly open and
contains much birch and aspen, thimbleberry abounds. This big-leaved
plant with the red, raspberry-like fruits has an odd distribution. It
occurs around the northern Great Lakes and from the Rocky Mountains
northward and westward. Devil's-club, a spiny shrub restricted on Isle
Royale to Blake Point, a few islands at Rock Harbor, and Passage Island,
has an even more disjunct distribution. It occurs in a few places
around Lake Superior, but its principal range is in the Pacific
Northwest. The favored explanation for the split distribution of these
two species is that in early post-glacial times, when a cool, wet
climate stretched all the way across the continent, they had a
continuous distribution; when a warmer, drier climate expanded the
central grasslands, the area where these plants could grow was cut in
two. Climatic change is often a suspected factor when a plant or animal
has such an odd range.
![](images/nh8ak.jpg)
The spruce-fir climax forest on the Mount Franklin Trail looked like
this in 1964. (Photo by Wm. Dunmire)
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One's walks through these forests of spruce, fir,
aspen, and birch are enlivened by encounters with animals. We meet the
red squirrel most often; in fact, it seems to be everywhere. Squirrel
populations on Isle Royale are higher than on the mainland, although one
litter a year, averaging three young, is the rule (compared with two
litters averaging more young in other areas). The lack of an efficient
predator on squirrels, such as the marten, may be an important reason
why Isle Royale's populations are so high. Red squirrels prefer mature
forests where conifers abound, though their numbers are also high in
sugar maple forests. Conifer seeds and fungi are their staple foods, but
they also eat many other things, including seeds, flowers, fruits, and
roots of various plants, as well as insects and carrion. Amazingly fewer
young are born in poor cone years, though development of the cones
occurs after the breeding season. Apparently, the females can detect
early signs of cone production and in poor years avoid or inhibit
conception.
Early or late in the day you may surprise a snowshoe
hare nibbling some plant beside the trail. These animals occur where
there is thick cover, such as low-spreading conifer boughs, windfalls,
or dense shrubs. The population fluctuations of snowshoe hares are
famous, though not well understood. Farther north the cyclic swings are
enormous; on Isle Royale these are damped but still quite noticeable.
The cycles last about 10 years. Recent peaks on Isle Royale occurred in
1953 and 1963.
![](images/nh8al.jpg)
The deer mouse is found in almost every state and in all the provinces
of Canada. (Photo by Greg Beaumont)
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The deer mouse is the only small rodent on Isle
Royale. Of the half dozen or so species of small rodents occurring on
the nearby Canadian mainland, this is the only one that has bridged the
water gap. Why this and no others is a mystery. Deer mice live
throughout the island now but seem to be most abundant in coniferous
forests. Individual deer mice, like squirrels, maintain territories.
These range from about one-half to one acre in size. The resulting
density of deer mice is thus quite low in comparison with that of some
other small rodents that occur elsewhere.
The red fox preys on squirrel, hare, and mouse, but
hares are its mainstay. So closely is the fox tied to this food source
that its numbers fluctuate with those of the hare. Squirrels and mice
are relatively unimportant fox food here, since the energy gained from
them seldom justifies the energy required to catch them. Occasionally
muskrats are caught, but these are too scarce on Isle Royale to provide
much food. Birds, too, figure in the diet in a small way, as do frogs,
snakes, fish, and insects. Isle Royale's foxes turn their main
attention from hares only in late summer, when they gorge on fruits,
particularly the dark blue berries of wild sarsaparilla. In winter,
they supplement their hare diet with moose meat scavenged at wolf kills.
Your chances of seeing foxes are good, since many of them have become
accustomed to people at developed areas, and some have become
panhandlers and camp robbers.
Like fox, hare, squirrel, and mouse, moose are found
over virtually all of Isle Royale. Being dependent on moose, wolves,
too, course the whole island. You are quite likely to meet moose,
especially around lakes and ponds; but wolves are the island's needle in
a haystack. With luck you may hear them howling, and with greater luck
catch a glimpse, but for most people they are simply an unseen presence
in the forest, adding to it a special dimension of wildness.
In a later chapter we shall look more closely at the
lives of moose and wolves. Meanwhile, let's see what is happening in
other land and water environments of Isle Royale.
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