Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 307

thresholds are passed. A quick change then occurs, perhaps leading to a new succession of
a different type of ecosystem.
I am not a botanist, but I wonder if what we are seeing is simply the slow way in
which a new climax community will be established on the southern tundra. Here on the
west coast of Canada, the climax community is dominated by cedar and Douglas fir. When
logging strips the forest, it is initially replaced by a mixed bag of shrubs, including alder.
After about several decades, the alder gives way to a community dominated by tall coni-
ferous species, such as hemlock. Finally, after the passage of more decades, the cedar and
Douglas fir reassert their dominance.
Arctic vegetation is an obviously vital element for the habitat of Arctic terrestrial an-
imals. How are they impacted by change? Lemmings exist as several species in North
America and Eurasia. To a large degree, they shape the tundra through their grazing of ve-
getation and by being the main food for predators, such as the snowy owl and Arctic fox.
Typically, their populations undergo cycles. At the cycle peak (which usually lasts for only
one year), they are most numerous. The population then crashes and reaches another peak
after about three to five years. Recently, a number of studies suggest a trend towards lower
peaks and a slower frequency of the cycle. Both trends may be caused by winter snow con-
ditions being less than ideal for reproduction (which occurs in winter). In the sub-Arctic of
Norway, recurrent snow-thaw cycles and winter rain in a warming climate create icy layers
that make it difficult for lemmings to reach their food plants. We will see the same problem
with caribou and reindeer.
Caribou and reindeer also undergo population cycles that in this case are quite slow.
Although it varies between herds, a cycle may take 30-40 years to complete. This makes
it difficult to detect population trends that may be associated with climate change over the
last few decades. For example, since 1970, the number of caribou and wild reindeer in 23
surveyed circumpolar herds has declined from about 5.5 million to 2.7 million. There are
now some indications that in just the last two years, the declining phase may have ended
and that at least for the herds occupying the western and central parts of the coastal regions
of North America, an increasing trend may be setting in.