April 20, 2007

Know Your Biomes VI: Temperate Grassland


Not a breath of air stirred over the free and open prairie; the clouds were like light piles of cotton; and where the blue sky was visible, it wore a hazy and languid aspect.

-Francis Parkman (Photo: Mongolian grassland)

Perhaps nowhere else on the planet can you find a better example of the rise and fall of ecosystems and the rise and fall of human cultures than on the North American prairie. So much of American history has taken place on the Great Plains: the emigration of nomadic peoples from Asia, their domination of the Plains and probable partial responsibility for the loss of most of the large vertebrates (the American lion, American cheetah, woolly mammoth, etc.) the eventual beginnings of agriculture, followed by the arrival of the Europeans, who removed and replaced the Native Americans with greater influence over the land.

Though the temperate grasslands in North America are the most familiar to westerners, they are minuscule compared with the vast expanse of flat land stretching from Eastern Europe to the foothills of the Himalayas. Areas in the southern hemisphere are also representative, like Patagonian steppes in South America and the grasslands in New Zealand.

Like the tropical savanna, the temperate grasslands are mostly treeless due to the influences of drought, fire and large, pounding herds of grazing animals, though small copses can be found near streams and lakes. Precipitation is relatively low; the grasslands typically receive about 25 to 100 cm of rainfall per year, mostly during the summer, the height of the growing season. The tangled roots of grasses, some reaching over two meters in length, form a thick sod, keeping the fertile, slightly alkaline "black soil" (black because of the high organic content) from washing or blowing away.

The untouched prairies are beautiful in the growing season, exhibiting the notable diversity of life of these areas. In North America, 300 different plant species and three million species of individual insects may live on three acres; up to 70 species of those plants may be seen flowering at the same time.

Mammals have evolved to fill niches seemingly based on their size: Wild horses and Saiga antelope roam the plains of Eurasia in large herds, just as the bison do in North America. Though most of the large predators are gone, packs of wolves still prey on the herbivores. On a smaller scale, many prey animals have gone underground. The pika of the Tibetan Plateaus live in burrows not unlike those of North American prairie dogs, trying to stay out of the jaws of fleet predators like the Tibetan fox.

Tibetan fox (Vulpes ferrilata)

It is impossible to describe temperate grasslands in the modern age without mentioning human influences. These areas are being reduced exponentially all over the world, valued by agriculture for the rich organic content of the soil. Unfortunately, much of the nutrients of the soil has become greatly reduced, as much as 35 to 40 percent in some areas, leading industry to rely more heavily on artificial fertilizers, which hamper growth in the world's waterways. Flying over the midwestern United States is enlightening; we have geometrically rewritten the future of one of the Earth's most unique and most beautiful areas.