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Scoured by Wind or Buried
by Snow: Alpine zones are places of intensity and drama, of fierce winds, harsh snows, and rough terrain. But they can be places of subtlety as well, where a slight shift in topography can lead to an array of differences in plant life. Groups of plant species that are commonly found together are known as “communities” and the structure of these communities is determined by environmental factors such as moisture, elevation, drainage, wind, soil type and quality, and snow cover. These factors vary in their significance depending on the location of the communities.
It seems logical that a plant community at 2,000 feet is different than one at 5,000 feet, or that a community on the north slope of Mt. Adams differs from one on its south slope; but what about different communities that appear side by side? I recently studied such a situation on the north slope of Mt. Adams as part of a course on Alpine Flora with Antioch New England Graduate School in Keene, New Hampshire. These two plant communities are just off Lowe’s Path, a few hundred feet from the Quay. The first community is covered in low sweet blueberry and also has significant amounts of bog bilberry and Labrador tea. The second site lies just 1.5 meters west of the first. Diapensia is the primary species here and is sometimes accompanied by alpine azalea, which has a similar growth pattern. Bog bilberry is still present but is less prevalent. What makes these communities different? The plants are responding to subtle environmental changes that humans may not even notice. Because these two sites are at the same elevation, we can eliminate elevation and its corresponding factors of temperature and moisture level as responsible for the difference. They are also both situated on the north slope of the mountain, so they are both receiving approximately the same amount of sun. Let’s consider the plants themselves. Low sweet blueberry, bog bilberry and Labrador tea are all members of the heath family. The blueberry and bilberry are usually less than 1 foot tall; Labrador tea is often taller than 1 foot. In the winter, their height would make them vulnerable to the high winds that make the Whites such an extreme environment. In order to survive, they need to spend winter beneath a blanket of snow for protection. Although these plants do not require very nutrient-rich soils, some soil development is necessary for their growth. Diapensia and alpine azalea, on the other hand, lie close to the ground in tight mats. This strategy allows them to withstand the high winds but they cannot survive the winter if buried beneath the snow. Diapensia prefers to grow on rocky areas with shallow soils, as deeper soils can actually limit root growth.
As we climb on and around the RMC paths that wend their way above treeline, we constantly adjust to changes in the local environment. We put on warm hats and windbreakers when temperatures drop, reach for sunglasses and extra water when the sun bears down in the summer. Plants are also responding to these cues, as well as many others that we don’t notice, by growing in specific locations that are best suited to their requirements. Those cues can be dramatic changes in temperatures or soil quality or smaller, subtler differences in how wind affects the area. On your next hike in the alpine zone of the Northern Presidentials, pay attention to the changes in plant communities that you observe and consider what the plants are experiencing that you may not even notice. Kelly Towle is currently working toward her Master's degree in Environmental Studies and science teacher certification at Antioch New England Graduate School in Keene, New Hampshire. She spent a week at Gray Knob in July as part of a course on Alpine Flora that provided the background for this article. Further Reading Bliss, L.C. “Alpine Plant Communities of the Presidential Range.” Ecology 44(4), Oct. 1963, pp. 678-697. Sperduto, D. and Cogbill, C.V.
“Alpine and Subalpine Vegetation of the White Mountains,
New Hampshire.” New Hampshire Natural Heritage Inventory,
Sept. 1999.
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Alpine plant
communities are largely governed by climate conditions. In our
Northern Presidentials, factors such as snow cover, temperature,
wind, and moisture level play important roles in determining
which plants grow in certain places. These factors change according
to elevation—the higher up Mount Adams or Mount Madison
you climb, the more temperatures drop and wind speeds increase.
They may also be different on different sides of the range, as
north-facing slopes will receive harsher winds and southerly
slopes will be exposed to more sunlight. Below the alpine zone,
drier sites are typically host to red spruce, sheep laurel, and
Lapland rosebay. Moist areas with limited drainage and late-melting
snowpacks are usually inhabited by mats of sphagnum moss as well
as bog bilberry, sheep laurel and black spruce. It is important
to remember that some species will be found in multiple different
communities and that gradients exist as one community transitions
to the next. Above the alpine zone, the larger trees and shrubs
eventually drop out and members of the sedge and rush families
become dominant. Plants that grow in dense mats, such as diapensia
and alpine azalea, also have many advantages at higher elevations
where climate conditions can be severe.
Site 1 (low
sweet blueberry and Labrador tea) and Site 2 (diapensia and alpine
azalea) have different needs for the survival during the harsh
mountain winters. But how are those different needs being met
when they are so close together? Let’s look at some of the
environmental factors that are affecting the two sites in different
ways. Wind is an important factor to plant communities in the
White Mountains. In the winter, these winds typically come from
the north-northwest. These two sites are located on the north
slope of Mt. Adams, which would seem to indicate that wind would
be affecting them both equally. There are clues at the sites,
however, that dispute that logic. Trees can be an excellent indication
of wind direction. As the winds barrel over them, the trees end
up being stripped of branches in the direction that the wind
is coming from. The wind also pushes them down so that they end
up leaning away from where the wind blows. Several small trees
near these sites show that the wind here is actually coming out
of the west instead of from the north. Now the question becomes,
why is the wind coming from the west instead of from the north?
The main reason that winds in the mountains are so strong is
the funnel effect that the mountains have on the wind. As the
winds come down from the north-northwest, they are being pushed
and squeezed through the mountains, which increases their speeds
and alters their directions. As the winter winds come from the
north, they are deflected by Mt. Jefferson and the Castellated
Ridge and some end up being pushed to the west, across Mt. Adams
and these two sites. Site 2, being slightly further to the west,
gets scoured by these winds. In the winter, these winds pick
snow off Site 2 and deposit it not too far away, on Site 1. This
snow buries the low sweet blueberry and Labrador tea on Site
1, ensuring its winter survival. If the winds did not scour Site
2 but instead left that site buried beneath the snow, the diapensia
and alpine azalea currently found there would not be able to
survive the winter months. Westerly winds may also play a role
in the spring and summer, as these winds may be picking up soil
from Site 2 and dropping that on Site 1. While diapensia and
alpine azalea may prefer rocky areas, heaths need some soil development
in order to grow.