Plant Communities
Key Topics
Introduction
Learning to recognize plant communities
increases your ability to spot their resident plants and animals. Knowing that
grizzly bears seek out buffaloberry in the fall, you can avoid encountering this
burly resident by avoiding area’s with high concentrations of this plant, or
by making sure you make noise when traveling through stands of buffaloberry.
Communities are not random in their
organization. Nor are they merely a collection of plants and animals that have
learned to tolerate living in proximity to each other. A true community is
composed of plants and animals that depend upon one another for their survival.
For instance, without mice and voles, coyotes would have little to feed on, and
would have to leave the area. On the other hand, without the coyotes, the
population of mice and voles would increase to the point of overpopulation,
likely damaging their habitat.
Communities may have sharp boundaries, but
most show a gradual transition as one community ends and an adjacent one begins.
These zones of transition are called edges, or ecotones. They offer a mixture of
the two adjacent habitats, and may offer more diversity than either on their
own. The foothills are a classic ecotone, mixing a little of the plains with a
touch of the Rockies. Within the foothills, there are many smaller communities.
A lodgepole pine forest may have a pond located within its boundary. The pond
itself is a community within larger and larger communities. It is influenced by
the larger lodgepole pine forest, as needles blow in from the surrounding
forest, or a duck lands on the pond and defecates. For simplicity, these outside
influences are generally ignored and the community studied in isolation.
Communities may be dominated by a single
species. In the pine forest, the lodgepole pine has significantly more mass than
any other species. This dominant member provides the defining component of the
ecosystem, and most of the other members will have some connection with it. The
pine provides shelter for spruce growing beneath it, cones for the red squirrel,
and an ideal habitat for the tiny Calypso orchid (Calypso bulbosa).
Each member of the community plays a role.
Some are producers, and some consumers. Others help break down dead material.
Each role is critical, and all depend on the presence of the other.
The plants defiantly covering the landscape
of the Rockies are the producers. While the producers are usually easy to
conceptualize, the consumers occupy a diversity of roles or ‘niches’. This
group includes the carnivores, animals like bears, wolves and cougars, along
with aerial hunters like eagles and hawks. In addition to these consumers, there
are other less clearly defined groups of consumers. Parasites, like dwarf
mistletoe, take their nutrients from other plants. Other parasites, like tape
worms, rely on our large mammals for sustenance.
Coyotes and ravens fall into the category of
scavengers, taking on the role of cleanup crew. Before an animal carcass has
cooled off, these scavengers begin the job of cleaning the bones and making sure
that little goes to waste. Finally, the decomposers include those microscopic
residents that help break down waste from a miniature scale. Rapidly attacking
excreta and carcasses, they transform these materials into a form that is usable
for plants. This helps the process to begin anew.
Aspen Forests
Aspen forests are found on lower elevation
slopes within the Montane, Lower Foothills and Upper Foothills habitats.
Within the Lower Foothills, look for mixed
stands of aspen separated by open fields. Understory plants occur in very
specific groupings. For instance, look for an understory of bearberry mixed with
hairy wild rye in fairly dry soils with plenty of sunshine. As the soil gets
moister, numerous other understory collections begin to appear. Dominant
understory communities may include prickly rose mixed with low-bush cranberry
and wild sarsaparilla. In other locations, buffaloberry or green alder dominate.
Along wet western slope area’s, devil’s club may form a thorny understory.
Aspen trees have the amazing ability to clone
themselves in large numbers. As a single tree grows from a seed, it sends out a
series of roots, horizontally, just beneath the surface. These periodically
sprout as new shoots, or suckers, each a clone of the original tree. Scientists
have recently designated a single aspen grove in Colorado as the largest living
organism on the planet. In the autumn, all the shoots of one tree will betray
their common root system as they all turn golden on the same day. In spring,
they will all sprout leaves simultaneously as well.
Aspen have very specific conditions to ensure
its survival. If it doesn’t receive at least 100 mm of rainfall during July
and August, it cannot survive. If it receives too much, it may be replaced by a
spruce forest. In Chinook blasted locations, like the entrance to the Bow
Valley, these dry winter winds severely damage the aspen leaving them short,
bent, and twisted. As the bark swells with the heat of the Chinook, only to
contract as the night brings cooler temperatures, the tree may split. This
allows diseases like the Hypoxylon Canker access to the tree. Infected trees
usually die within 4 years.
Aspen forests are a favourite habitat for
large herbivores. Regular forest fires stimulate growth of new suckers, allowing
aspen to take advantage of such regular disturbances. Also, listen for the
warbling vireo, a regular avian resident.
Douglas-fir Forests
The Douglas-fir along with its 5-needled
neighbour, the limber pine, characterize the true montane. They do well in the
intense, dry winds of these Chinook blasted valleys. The harsh conditions
created by these winds partially accounts for the limited extent of the true
montane – at around 0.5% of the province, and only 2% of the Rockies. The
montane, and its associated trees, generally range between 1200 and 1650 metres
(3,900-5,400 ft).
Douglas-fir is one of the few trees to grow
to any significant size on the eastern slopes. Well adapted to forest fire, it
sports a thick cork layer which protects its delicate living tissues from all
but the hottest fires. This allows it to survive fires that kill off its
neighbours, and leaves it more of that precious sunshine. Douglas-fir is also
the single most important timber tree in North America, supporting extensive
forestry operations throughout British Columbia and Alberta.
This tree shows remarkable variability in its
habitat. While indeed it is indicative of dry habitats on the eastern slopes, it
does very well in wet, western slope forests as well. It is often found
intermixed in stands of western hemlock with which it competes for sunshine.
Since Douglas-fir are intolerant of shade, they need some disturbance, either
fire or blowdown to clear space for them to regenerate. In old growth western
slope forests, they tend to be replaced by the more shade tolerant western
hemlock. Since the two trees are similar in appearance, they are often mistaken
for one another.
Many animals call Douglas-fir forests home.
Animals like red squirrels and yellow pine chipmunks eat large quantities of
seeds. Birds like crossbills, winter wrens and song sparrows are also fond of
the seeds. The shoots are also a favourite of deer, while bears will
occasionally strip the bark off of young trees.
Lodgepole Pine Forests
Typical of the Upper Foothills ecoregion, the
lodgepole pine is common on both sides of the Continental Divide. It is
difficult to mistake forests of lodgepole pine for any other species. It is a
tall slender pine with needles in groups of two, and very few branches along the
lower part of the trunk. What few branches remain on the bottom half of the tree
are usually dry and dead. This is a fire adapted species which uses the forest
fire to clear out the forest and reset the clock to zero. Since its cones only
open in the heat of a fire, it is one of the first trees to follow a
conflagration. It is also a tree with an incredible range of habitat tolerances
and is found from the coast to the foothills. In the Rockies, it is typical of
the Upper Foothills, the wettest of the eastern slope ecoregions. It is also
found on the western slopes in fire regenerated locations.
Because of the open character of lodgepole
pine forests, they offer a very diverse mixture of plants and animals. Since the
canopy is quite open during the early stages of growth, many other plants share
the limited amount of sunlight. The understory includes bearberry, buffaloberry,
twin-flower, and juniper. Plants like buffaloberry attract black bear and
grizzlies, while red squirrels crop the cone filled branches, letting them drop
to the ground for collection at a later time. Birds like the red-breasted
nuthatch and the brown creeper collect insects from behind the bark scales.
Beneath the shade of the lodgepole pines,
white spruce will often sprout. More tolerant of shade than the pines, they will
eventually take over if a forest fire doesn't interrupt the process. Since the
pines were all born on the same day, the entire stand will often appear to be
almost exactly the same height.
The arrow straight character of the lodgepole
pine led to its use as native Indian teepee poles. Non-natives followed their
lead by using them for building cabins and as telephone and fence poles.
Trembling aspen are another fire adapted species that intermixes with the
lodgepole pine.
Subalpine Forests
As one climbs above 1,675 m (5,494 ft), many
of the lower elevations species begin to falter and the subalpine fir and
Engelmann spruce take over. This heavy snowfall region begins with tall stands
which gradually diminish in size until they take on the rough growth form known
as kruppelholz. At this point, the trees hug the ground, growing only a metre or
so tall, and often showing little growth on the windward side. It almost appears
like they turn their back on the strong high elevation winds. With the reduced
competition from trees at the upper subalpine, shrubs and wildflowers thrive.
The subalpine fir grows with a perfect Christmas tree shape, and sports branches
all the way down the trunk. Sometimes, the branches nearest the ground will
sprout roots when they come in contact with the ground only to later send up a
new shoot. This vegetative reproduction is referred to as layering and is
typical of the subalpine fir.
South of Lake Louise, as one approaches the
subalpine, another tree may become common, the alpine larch spreads its soft
needles towards the sunshine. Very resistant to the harsh conditions of the
subalpine, the alpine larch forms defiant stands right at the margin of
subalpine and tundra. The soft branches, are very resilient and seem to move and
bend with the conditions as necessary. While other trees are reduced to low
growing kruppelholz, the alpine larch is able to bend and fold its branches to
withstand winter avalanches, only to spring erect again when the snow releases
its grip.
The understory within the subalpine is thick
with dwarf birch, thimbleberry, heather, false azalea and grouseberry.
Many animals take advantage of the subalpine.
With the reduced amount of forest coverage as the altitude increases, the
potential for smaller, nutritious plants increases. This attracts grizzly bears,
bighorn sheep and mountain goat, along with a diversity of small birds. Pikas
scurry about the talus and the whistling call of the hoary marmot is
occasionally carried long distances on the wind.
Alpine Tundra
There is never any doubt as to when the
subalpine ends and the alpine begins. Suddenly the last twisted trees disappear
and the landscape is left to the rocks, lichens and wildflowers. The alpine in
the Rockies is a diverse landscape of more than 400 species of wildflowers.
Anyone who has experienced the explosive colours of an alpine meadow rarely
forgets the experience. The western anemone quickly trades in its delicate
petals for a shaggy seed head earning it the nickname “hippie on a stick”.
The tiny blue of the alpine forget-me-not ensures its memorability. The eye is
attracted to the brilliant reds, purples and drabber yellows of the Indian
paintbrush. For the novice, the cacophony of colour that forms an alpine meadow
can be incredibly intimidating. An average meadow may have dozens of individual
species all waiting for identification. In moister habitats, globeflower and
valerian catch the eye.
This open landscape, like the upper subalpine, is a very productive habitat for wildlife. A favourite haunt of the grizzly, they may be seen munching on wildflowers like the avalanche lily or digging up colonies of ground squirrels. Mountain goats, still not satisfied, may climb even higher in search of wind-swept ledges. Often left free of snow in winter, these form the winter home for these agile climbers. Mountain goats, less talented climbers than the goats, prefer the lower meadows where there is more plentiful pickings. In the winter, they may even move further downhill for winter forage.
All Material © Ward Cameron 2005