136 CHAPTER 6 Ecosystems and EvolutionAverage monthly temperature in°CAverage monthly precipitation in cm
JMMJJASONDF A14
12
10
8
6
4
2
028
24
20
16
12
8
4
0
–4Months© DLILLC/Corbis
Based on data from http://www.worldclimate.compredators (foxes, black-footed ferrets, and
various birds of prey), grouse, reptiles such
as snakes and lizards, and great numbers of
insects.
Shortgrass prairies are temperate grass-
lands that receive less precipitation than
moist temperate grasslands but more pre-
cipitation than deserts. In the United States,
shortgrass prairies occur in parts of Montana, Wyoming,
South Dakota, and other midwestern states. Grasses that
grow knee high or lower dominate shortgrass prairies.
Plants grow less abundantly than in the moister grass-
lands, and bare soil is occasionally exposed. Native
grasses of shortgrass prairies are drought-resistant.
The North American grassland, particularly the
tallgrass prairie, was well suited to agriculture. More than
90 percent has vanished under the plow, and the remain-
ing prairie is so fragmented that almost nowhere can you
see what Native Americans experienced prior to the ar-
rival of European settlers in the Midwest. Today, the tall-
grass prairie is considered North America’s rarest biome.
It is not surprising that the North American Midwest,
Ukraine, and other moist temperate grasslands became
the breadbaskets of the world, because they provide ideal
growing conditions for crops such as corn and wheat,
which are also grasses.Temperate Grassland
Summers are hot, winters are cold, and
rainfall is often uncertain in temperate grass-
land. Average annual precipitation ranges
from 25 to 75 cm (10 to 30 in). Grassland soil
has considerable organic material because
the aboveground portions of many grasses
die off each winter and contribute to the or-
ganic content of the soil, while the roots and rhizomes
( underground stems) survive underground. Many grasses
are sod formers—that is, their roots and rhizomes form
a thick, continuous underground mat. Although few
trees grow except near rivers and streams, grasses grow
in great profusion in the deep, rich soil (Figure 6.8).
Periodic wildfires help maintain grasses as the dominant
vegetation in grasslands.
Moist temperate grasslands, also known as tallgrass
prairies, occur in the United States in parts of Illinois,
Iowa, Minnesota, Nebraska, Kansas, and other midwest-
ern states. Several species of grasses that, under favor-
able conditions, grow as tall as a person on horseback,
dominate tallgrass prairies. The land was originally cov-
ered with large herds of grazing animals, such as bison,
pronghorn, and elk. The principal predators were
wolves, although in sparser, drier areas coyotes took their
place. Smaller animals included prairie dogs and their/i«iÀ>ÌiÊ}À>ÃÃ>`ÊUÊ}ÕÀiÊÈ°nÊ
Bison graze on mixed-grass prairie in Custer State Park, South Dakota. Climate graph shows monthly
temperatures and precipitation for Lawrence, Kansas.Interpreting Data
When is the rainy
season in temperate
grasslands? the dry
season?temperate
grassland A grassland
with hot summers,
cold winters, and less
rainfall than is found
in the temperate
deciduous forest
biome.