KEEPING WARM 
Plants in High Places 
From the high equatorial mountains to the arctic tundra, plants 
must grow rapidly and reproduce in the cold. Flow do they do it? 
by William Dwight Billings 
It is mid-July in the Medicine Bow 
Mountains of Wyoming, but the tem- 
perature is well below freezing and the 
wind-blasted snow rattles on the back of 
my parka. One doesn’t face into that 
summer blizzard. Underfoot, the moss 
campion flowers are pink; snow catches 
in the cushion of small leaves and is then 
blown over the 1 1 ,000-foot ridge, adding 
to the snowdrift on the lee side. 
It is mid-July at Cape Sparbo, Devon 
Island, in the High Arctic of Canada. 
The cold northeast wind is blowing a 
mixture of snow and cold rain off the sea 
ice of Jones Sound. The low arctic 
plants catch the wet snow, but the famil- 
iar pink flowers of moss campion at my 
feet are not yet covered. 
These two places are 2,500 miles 
apart, as the arctic tern flies. The alpine, 
or mountain, location is at latitude 
41°2T north; the arctic one is at sea 
level at latitude 75°33 / north, only 950 
miles from the North Pole. How can the 
moss campion ( Silene acaulis, in the 
pink family) grow and reproduce so well 
in two places so far apart in latitude and 
elevation? 
The moss campion, which also grows 
in Lapland, the Alps, and on Mount 
Washington, is not the only species that 
shows a widely disjunct distribution be- 
tween arctic and alpine places. Of the 
approximately 1,000 species of flower- 
ing plants that live and reproduce in the 
Arctic, more than half also live on high 
mountain crests to the south. Are such 
A summer thunderstorm forms over 
alpine tundra in Wyoming's 
Beartooth Mountains. Half of the 
alpine plant species that thrive there, 
watered by such storms and melting 
snowdrifts, also grow in the Arctic. 
widely separated places alike in their 
environments? Were their sites easy for 
certain kinds of plants to get to? Very 
few of these species, however, reach the 
high equatorial mountains and fewer 
still cross the Equator into the colder 
parts of the Southern Hemisphere. 
What are the barriers, in space and 
time, to the migration of plants? 
Estimating the amounts of glacial ice 
and open land available to plants beyond 
or above timberline is difficult. At times 
during the last 25,000 years of the Pleis- 
tocene Epoch, glacial ice covered as 
much as 30 percent of the earth’s land 
area, compared with the present 12 per- 
cent; there have also been times when 
glaciers occupied a much smaller area. 
At present, of the earth’s approximately 
57 million square miles of land and 
glacial ice surface above sea level, about 
1 3 million square miles are too cold for 
the growth of trees. Of these 13 million 
square miles, approximately 6.8 million 
are glacial ice: more than 5.3 million are 
in Antarctica; about 1.1 million are in 
Greenland and in smaller arctic icecaps; 
and alpine glaciers outside the Arctic 
and Antarctica may occupy 400,000 
square miles. The total ice-free land 
between the glaciers and timberline is 
about 6.2 million square miles: an esti- 
mated 2.3 million square miles are in the 
Arctic; the remainder consists of about 
3.8 million square miles of alpine coun- 
try in the middle latitudes and less than 
100,000 square miles in Antarctica. 
Only 0.4 percent of the earth’s known 
vascular plant species occur in the cold 
3.9 percent of the earth’s land surface 
that is ice-free in the Arctic. Compari- 
sons of the floristic richness (the number 
of species per unit of land area) in three 
areas of approximately the same size 
(about 24,000 square miles) in arctic, 
temperate, and tropical latitudes reveal 
a striking arctic-to-tropics gradient. 
Peary Land, in northern Greenland, has 
William Dwight Billings 
no more than 100 species of vascular 
plants; West Virginia has 2,126 species; 
Costa Rica has at least 9,000. Colder 
climates clearly support far fewer kinds 
of plants. In addition, arctic plants be- 
long mainly to families that are not 
common in Costa Rica, whereas except 
for such wide-ranging families as the 
grasses, sedges, and composites, the 
principal plant families of Costa Rica 
are absent, or almost so, from the Arc- 
tic. The ability to grow and reproduce 
under the stress of low temperatures is 
critical to survival in arctic and alpine 
environments, and in spite of the genetic 
diversity in large families, there seems 
to be a tendency for low-temperature 
metabolism to be either present 
throughout an entire family or almost 
completely absent. 
But apart from the cold, how similar 
is the environment in the Arctic to that 
on high mountains? Certain factors, 
such as cold nights during the growing 
season, are more influential in alpine 
areas than in the Arctic. Other factors 
important in the Arctic are lacking in 
alpine areas: continuous daylight for 
weeks or months, for example, and very 
cold soils due to permafrost. Further- 
more, alpine locations in the tropics 
have less snow, more ultraviolet irradia- 
tion, and a longer (year-round) growing 
season than those of temperate regions. 
The relative environmental impacts of 
many such physical factors vary along 
latitudinal and elevational arctic-alpine 
gradients. Only one factor does not 
change much: the daily mean tempera- 
ture during the growing season. No mat- 
ter how cold the winter, how deep the 
snow, or how brilliant the sun, arctic and 
alpine plants must metabolize, grow, 
and reproduce at a consistently cold 
growing-season air temperature. 
Ecologists working to decipher how 
arctic and alpine species evolve toler- 
ances to such extreme environments 
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