Page 695 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 20 Terrestrial Biomes 659
this biome is known as the mattoral, and in southwest- ern Australia, it is mallee scrub. In Australia, the bulk of the eucalyptus species are sclerophyllous in form and structure in whichever area they occur.
As described in Chapter 10, commercial agricul- ture of the Mediterranean climates includes subtropi- cal fruits, vegetables, and nuts, with many food types (e.g., artichokes, olives, almonds) produced only in these climates. Animals include several types of deer, coyote, wolf, bobcat, a variety of rodents, other small animals, and various birds. In Australia, this biome is home to Malleefowl (Leipoa ocellata), a ground-dwelling bird, and numerous marsupials.
Midlatitude Grassland
Of all the natural biomes, the midlatitude grassland is the most modified by human activity. This biome includes the world’s “breadbaskets”—regions that produce bountiful grain (wheat and corn), soybeans, and livestock (hogs and cattle). In these regions, the only naturally occurring trees were deciduous broadleaf trees along streams and other limited sites. These regions are called grasslands because of the predominance of grasslike plants before human in- tervention (Figure 20.17).
In North America, tallgrass prairies once rose to heights of 2 m and extended westward to about the 98th meridian, with shortgrass prairies in the drier lands far- ther west. The 98th meridian is roughly the location of the 51-cm isohyet, with wetter conditions to the east and drier conditions to the west (see Figure 18.15).
The deep, tough sod of these grasslands posed prob- lems for the first European settlers, as did the climate. The self-scouring steel plough, introduced in 1837 by John Deere, allowed the interlaced grass sod to be broken apart, freeing the soils for agriculture. Other inventions were critical to opening this region and solving its unique
spatial problems: barbed wire (the fencing material for a treeless prairie); well-drilling techniques developed by Pennsylvania oil drillers, but used for water wells; wind- mills for pumping; and railroads to transport materials.
Few patches of the original prairies (tall grassland) or steppes (short grassland) remain within this biome. In the prairies alone, the natural vegetation was reduced from 100 million hectares down to a few areas of several hundred hectares each. The Nature Conservancy of Can- ada is working in conjunction with the Nature Conser- vancy in the United States to develop a natural corridor that will extend from Canada to the American Midwest. The northern extent of this corridor, the Manitoba Tall- grass Prairie Preserve, strives to preserve the last signif- icant remnants of tallgrass prairie in Canada. More than 5000 hectares have been preserved, but another 4000 hectares are needed to make this preserve ecologically viable. The map in Figure 20.7 shows the natural loca- tion of this former prairie and steppe grassland.
Characteristic midlatitude grasslands outside North America are the Pampas of Argentina and Uruguay and the grassland of Ukraine. In most regions where these grasslands were the natural vegetation, human develop- ment of them was critical to territorial expansion.
This biome is the home of large grazing animals, in- cluding deer, pronghorn, and bison (the almost complete annihilation of the latter is part of American history, see Figure 20.18). Gophers, prairie dogs, ground squirrels, turkey vultures, grouse, and prairie chickens are com- mon, as well as grasshoppers and other insects. Preda- tors include the coyote, nearly extinct black-footed ferret, badger, and birds of prey—hawks, eagles, and owls.
Deserts
Earth’s desert biomes cover more than one-third of its land area (Figure 20.7). We subdivide the desert biomes into warm desert and semidesert, caused by the dry air and low precipitation of subtropical high-pressure cells, and cold desert and semidesert, which tend toward higher latitudes, where subtropical high pressure affects climate for less than 6 months of the year. A third sub- division, Earth’s polar deserts, occur in high-latitude re- gions, including most of Antarctica and Greenland, with very cold, dry climates. Vegetation, sparse in these pre- dominantly ice- and rock-covered regions, is mainly li- chens and mosses.
Desert vegetation includes numerous xerophytes, plants that are adapted to dry conditions with mecha- nisms that prevent water loss, such as cacti and other succulents (plants that store water in their thick and fleshy tissues). Xerophytic plants have a range of ad- aptations, including long taproots to access groundwa- ter (mesquite trees); shallow, spreading root systems to maximize water uptake (palo verde trees); small leaves to minimize surface area for water loss (acacia); waxy leaf coatings to retard water loss (creosote bush); leaf drop during dry periods (ocotillo); and as previ- ously mentioned, the succulent tissue to store water. A
▲Figure 20.17 Farming in the grasslands of North America. Midlatitude grasslands of Alberta, Canada, under cultivation. [Comstock/Thinkstock/getty Images.]