Ice Age Vegetation

Lakes are for fishing and boating, but now they are taking on increasing importance as windows into the past. The thicknesses and compositions of deposits on the lake floors record volcanic eruptions, seasonal variations, climatic changes and sometimes even the occurrence of earthquakes. An example of what can be learned is a new conclusion about past vegetation that comes from sampling the pollen content in two lakes in Yukon Territory.

During the ice ages when Siberia and North America were joined by the Bering Sea Land Bridge (Beringia), central Alaska and Yukon Territory supported a rich variety of herbivores. The horses, bison, mammoths, camels and antelopes of the region were prevented from travel southeasterly into the rest of North America by extensive glaciation.

For many years it has been thought that the herbivores and the animals that fed upon them, including humans, lived on steppe tundra or grasslands that provided more extensive foods than the present-day vegetation cover.

This idea now is rejected by two scientists, L. C. Cwynar and J. C. Ritchie of the University of Toronto (20 June 1980 issue of Science). Based upon their counts of pollens from lakes in the Porcupine River watershed of northern Yukon Territory, they conclude that the vegetation 14,000-30,000 years ago was much as it is now in the tundra country, only sparser.

Thus when the ice retreated, it did not eliminate the feeding grounds of the many herbivores that became extinct. Consequently, the finding of Cwynar and Ritchie seems to lend support to the view that man rather than lack of food may be to blame for causing extinction of many of the herbivores.