Ecological Zones: A Hike Up Mount Washington
Ascending 1000 vertical feet in the mountains of the northeast can be likened to driving
hundreds of miles north. On average temperatures decreases 3 to 5oF and precipitation increases
by 8 inches a year with each 1000 foot elevation gain. As a result, the plant and animal
communities change drastically as you hike up a mountain.
I. The Northern Hardwood Forest and Transition Zones (less than 2500 ft)
Primarily deciduous forest, dominated by sugar maple, American beech, and yellow birch.
Other trees include red maple, red oak, black cherry, paper birch, hemlock, and white pine.
A variety of shrubs, ferns, and wildflowers are also found in this zone.
At or above 2000 ft the northern hardwood forest gives way to a transition zone in which
spruce and fir trees intermix with sugar maple and other deciduous trees. As elevation
increases, hemlocks and pines and most deciduous trees are unable to grow. Of the primary
hardwood forest trees, yellow birch is able to grow at the highest elevation.
II. The Spruce-Fir Forest Zone (2700-4000 ft)
Temperatures are colder, leading to a shorter growing season. The combination of cold
temperatures and higher precipitation leads to wetter, more acidic, and less fertile soils because
decomposition of organic matter is slower at lower temperatures and large amounts of
precipitation leeches nutrients. In these conditions, evergreen conifers, especially red spruce
and balsam fir, have an advantage over most deciduous trees, although paper birch, striped
maple, and mountain maple are still found in the lower elevations of this zone.
III. The Balsam-Fir Forest Zone
Around 4000 feet red spruce drops out and as you continue climbing the forest is almost entirely
balsam firs. As elevation increases, the balsam fir forests become stunted. As forests
approach the upper elevation limit for their upright growth, they form a nearly impenetrable
thicket or “tuckamore”.
Krummholz, “Crooked Wood” Zone (up to 5400 ft)
The Krummholz or “crooked wood” zone consists of dwafted trees, primarily balsam fir and
black spruce. This zone is not contiguous, rather Krummholz is found in the dwarfed balsam
forest ringing the alpine zone and in small patches within the alpine zone itself. Trees are
dwarfed due to harsh growing conditions and extreme wind and ice abrasion leads to the gnarled
shapes. In the Krummholz, balsam fir and black spruce form prostrate mats, hugging the
ground to escape the wind. When trees grow upright, the windward branches often die, leaving
green branches on only one side of the tree: a “flag tree”, signaling the prevailing wind
direction.
Prostrate balsam fir
Flagged krummholz trees
What determines treeline?
Interestingly, it is not the winter cold, but
the lack of summertime heat that correlates
best with treeline.
The length of the growing season determines
whether a tree has enough time to produce
and harden new growth before the first frost
The limit of tree growth in both the alpine
zone and the arctic is close to the 54oF
isotherm for the warmest month of the year.
IV. Alpine Zone
Life is harsh in the alpine zone, with a short growing season, extremely cold temperature, and
strong winds. To survive in the alpine environment, plants capitalize on a number of
adaptations, including small size, compact shapes to conserve heat, creeping mats to anchor the
plant to the ground, protective hair, and narrow leaves that bend in the wind.
Despite the harsh environment a large
number of species are found in the alpine
zone. Wind pollinated sedges, grasses, and
rushes are a major component of alpine
flora. Spore bearing plants, such as ferns
and clubmosses, have well-developed food
and water conducting systems and thus are
well adapted to alpine environments.
Mosses, liverworts, and lichens adorn even
available surface, from windblown ground,
to rocks, to branches and even small trigs.
A variety of dwarfed shrubs are also found
in alpine regions, including Lapland
rosebay, several species of blueberries,
mountain cranberry, and Labrador tea.
Finally, a good number of perennial
herbaceous plants are able to survive in
alpine areas; dazzling displays of flowers
mark the coming of spring in alpine areas.
Harebell and other flowers in Alpine Garden
on Mt. Washington in spring
Alpine Communities
Due to the extreme habitats in the alpine zone, many plants exist only in very specific niches.
Therefore, alpine flora and fauna are often divided into “communities”. The most common
communities on Mt. Washington include:
Bigelow Sedge Meadow Communities
Most common community on the upper
slopes of Mt. Washington:
The Sedge community looks like a grassy
field but it is actually a Bigelow Sedge
meadow, kept moist by fog and frequent
rain. Little else grows except mountain
sandwort.
Dwarf shrub/heath/rush communities
Species rich community found on peaks
within a few hundred feet of treeline:
Covers much of the alpine garden on Mt.
Washington. Sedges, highland rushes,
dwarf shrubs are the prominent vegetation,
but 17 species of vascular plants are also
found as are a variety of mosses and lichens.
QuickTime™ and a
TIFF (Uncompressed) decompressor
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Dwarf Shrub/Heath Communities
Primarily dwarf shrubs, such as bilberry,
mountain cranberry, Labrador tea,
bunchberry, and low-sweet blueberry are
dominant. A number of rare flowering
plants are also found in this community.
The dwarf shrub/heath communities form
dense mats with brown Icelandic lichen
covering the ground underneath the shrubs.
Diapensia Communities
Inhabit the windiest, most exposed sites.
Hummock shaped diapensia surrounded by
patches of bare ground. Dwaft shrubs alpine
azalea, Lapland rosebay, and bog bilberry as
well as highland rush are found in this
community.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Info from: Slack, Nancy and A.W. Bell. AMC Field Guide to Alpine Summits, 2006.