Nature Bulletin No. 130 November 8, 1947
Forest Preserve District of Cook County
William N. Erickson, President
Roberts Mann, Supt. of Conservation
When the glaciers covered and then uncovered this Chicago region, as
they did at least four times in the past million years, they left behind
them raw ground-up rock. In places it was only a few feet thick; in
others it was heaped up hundreds of feet deep. Some of this rock was
in the form of rounded boulders, many of them huge; some was gravel;
some was sand; but most of it was finely-ground rock "flour" which we
call silt or clay.
Such an area of the earth's surface uncovered near an ice sheet
becomes Trunda. The word is of Finnish origin, meaning a bare
treeless stretch of country. Only primitive plants can grow on such raw
earth -- lichens and mosses, with perhaps a little grass and small
willows -- and the only common animals are the insects that live in the
ponds, and the reindeer and lemmings that feed on the lichens and
Lemmings are small rodents that multiply in unbelievable numbers on
the tundras that spread over vast areas of the arctic regions in Europe,
Asia and North America.
A few predators -- foxes, wolves, hawks, owls and other birds that feed
on these animals -- are found, but that is all.
The tundra is frozen year in and year out except for a thin surface
layer that thaws during the brief arctic summer. Then the lichens and
mosses grow rapidly.
In some places the ground is covered by frozen Sphagnum moss to a
depth of twenty feet. Reindeer moss, which is not a moss but a lichen,
grows in thick beds covering large areas. In this short summer, hordes
of mosquitoes and other insects hatch, mate, lay their eggs, and
prepare for the long arctic winter.
Miniature tundras are found occasionally in the Chicago region where
the top soil has been removed artificially or by water erosion. In such
places there may be found dozens of kinds of lichens, mosses, and
other primitive plants crusting the otherwise barren earth. Trees and
other plants, and the animal life that goes with them, must wait for the
lichens and mosses to slowly convert the surface of the rock "flour"
into top soil.
A lichen is the curious marriage of two plants: a fungus and an alga.
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Update: June 2012