BIOMES OF THE EARTH - GRASSLANDS Part 1 doc

As far as we can currently tell, our planet is unique.Isolated in the barren emptiness of space, here on Earth weare surrounded by a remarkable range of living things, fromthe bacteria t

Michael Allaby

Illustrations byRichard Garratt

BIOMES OF THE EARTH

GRASSLANDS

Copyright © 2006 by Michael Allaby

All rights reserved No part of this book may be reproduced or utilized in any form or by anymeans, electronic or mechanical, including photocopying, recording, or by any informationstorage or retrieval systems, without permission in writing from the publisher For informationcontact:

Grasslands / author, Michael Allaby ; illustrations by Richard Garratt

p cm.—(Biomes of the Earth)

Includes bibliographical references and index

You can find Chelsea House on the World Wide Web at http://www.chelseahouse.com

Text design by David Strelecky

Cover design by Cathy Rincon

Illustrations by Richard Garratt

Photo research by Elizabeth H Oakes

Printed in Hong Kong

CP FOF 10 9 8 7 6 5 4 3 2

This book is printed on acid-free paper

From Richard Garratt:

To Chantal, who has lightened my darkness.

Temperate grasslands and tropical grasslands 3

CONTENTS

Dry seasons and rainy seasons 51

CHAPTER 4

Mongooses, prairie dogs, marmots, ground

CHAPTER 6

How herding provides safety in numbers 153

CHAPTER 7

Homesteaders and the way the prairie was

Indians and gauchos: The peoples of the pampa 165

Traditional life on the steppe of Central Asia 171Genghis Khan, the Golden Horde, and

Sheep farms of Australia and New Zealand 186

Why it matters 199

CHAPTER 11

Grassland restoration and conservation 225

Soil classification: Orders of the soil taxonomy 235

Earth is a remarkable planet There is nowhere else in oursolar system where life can survive in such a great diversity offorms As far as we can currently tell, our planet is unique.Isolated in the barren emptiness of space, here on Earth weare surrounded by a remarkable range of living things, fromthe bacteria that inhabit the soil to the great whales thatmigrate through the oceans, from the giant redwood trees ofthe Pacific forests to the mosses that grow on urban side-walks In a desolate universe, Earth teems with life in a bewil-dering variety of forms

One of the most exciting things about the Earth is the richpattern of plant and animal communities that exists over itssurface The hot, wet conditions of the equatorial regionssupport dense rain forests with tall canopies occupied by awealth of animals, some of which may never touch theground The cold, bleak conditions of the polar regions, onthe other hand, sustain a much lower variety of species ofplants and animals, but those that do survive under suchharsh conditions have remarkable adaptations to their test-ing environment Between these two extremes lie manyother types of complex communities, each well suited to theparticular conditions of climate prevailing in its region

Scientists call these communities biomes.

The different biomes of the world have much in commonwith one another Each has a plant component, which isresponsible for trapping the energy of the Sun and making itavailable to the other members of the community Each hasgrazing animals, both large and small, that take advantage ofthe store of energy found within the bodies of plants Thencome the predators, ranging from tiny spiders that feed uponeven smaller insects to tigers, eagles, and polar bears that sur-vive by preying upon large animals All of these living things

PREFACE

form a complicated network of feeding interactions, and, atthe base of the system, microbes in the soil are ready to con-sume the energy-rich plant litter or dead animal flesh thatremains The biome, then, is an integrated unit within whicheach species plays its particular role.

This set of books aims to outline the main features of each

of the Earth’s major biomes The biomes covered include thetundra habitats of polar regions and high mountains, thetaiga (boreal forest) and temperate forests of somewhatwarmer lands, the grasslands of the prairies and the tropicalsavanna, the deserts of the world’s most arid locations, andthe tropical forests of the equatorial regions The wetlands ofthe world, together with river and lake habitats, do not lieneatly in climatic zones over the surface of the Earth but arescattered over the land And the oceans are an exception toevery rule Massive in their extent, they form an intercon-necting body of water extending down into unexploreddepths, gently moved by global currents

Humans have had an immense impact on the ment of the Earth over the past 10,000 years since the last IceAge There is no biome that remains unaffected by the pres-ence of the human species Indeed, we have created our ownbiome in the form of agricultural and urban lands, wherepeople dwell in greatest densities The farms and cities of theEarth have their own distinctive climates and natural history,

environ-so they can be regarded as a kind of artificial biome that ple have created, and they are considered as a separate biome

peo-in this set

Each biome is the subject of a separate volume Each richlyillustrated book describes the global distribution, the climate,the rocks and soils, the plants and animals, the history, andthe environmental problems found within each biome.Together, the set provides students with a sound basis forunderstanding the wealth of the Earth’s biodiversity, the fac-tors that influence it, and the future dangers that face theplanet and our species

Is there any practical value in studying the biomes of theEarth? Perhaps the most compelling reason to understandthe way in which biomes function is to enable us to conservetheir rich biological resources The world’s productivity is the

basis of the human food supply The world’s biodiversity

holds a wealth of unknown treasures, sources of drugs and

medicines that will help to improve the quality of life Above

all, the world’s biomes are a constant source of wonder,

excitement, recreation, and inspiration that feed not only

our bodies but also our minds and spirits These books aim to

provide the information about biomes that readers need in

order to understand their function, draw upon their

resources, and, most of all, enjoy their diversity

I also wish to thank Elizabeth Oakes for her fine work as aphoto researcher.

I must thank Frank K Darmstadt, Executive Editor, atChelsea House Frank shaped this series of books and guidedthem through all the stages of their development Hisencouragement, patience, and good humor have beenimmensely valuable

I am especially grateful to Dorothy Cummings, project tor Her close attention to detail sharpened explanations thathad been vague, corrected my mistakes and inconsistencies,and identified places where I repeated myself And occasion-ally Dorothy was able to perform the most important service

edi-of all: She intervened in time to stop me making a fool edi-ofmyself No author could ask for more This is a much betterbook than it would have been without her hard work anddedication

Michael AllabyTighnabruaich

ArgyllScotlandwww.michaelallaby.com

ACKNOWLEDGMENTS

What are grasslands?

A wave moves over the landscape as the rustling grass bowsbefore the wind and then rises again Another wave followsthe first, and then another, and the eye follows the ripplingmotion across the plain until each wave disappears in thehaze that obscures the distant horizon Overhead the cloud-less sky is the palest blue, and immensely large On a moon-less night the sky blazes with the light from countless mil-lions of stars

Grass is the predominant vegetation, but it is mixed with abewildering variety of other herbs Scattered shrubs andsmall belts of trees lining the river courses relieve what mightotherwise be a monotonous scene Birds fly overhead, forag-ing for insects or seeds, and high above them the hawks circleslowly, alert to the tiniest flicker of movement that betraysthe presence of a small animal Mice and ground squirrelslive on and below the ground, feeding on the vegetation andever watchful for snakes as well as birds of prey Herds of big-ger animals graze the pasture and browse the leaves of shrubsand the lower branches of the trees

This is one of the world’s great grasslands, which liebetween the temperate forests and the semiarid lands border-ing the desert, where meager seasonal rains allow a sparse,coarse pasture to survive Grasslands once covered more than

1 million square miles (2.59 million km2) in North America,extending from Illinois to Colorado and from Alberta toTexas

It is a place of changing colors In winter the northerngrasslands are white, hidden beneath a covering of snow.Southern grasslands see little or no snow, and there the land remains brown through the winter In spring both aregreen, as the returning warmth and moisture from the rain

INTRODUCTION

XVI GRASSLANDS

or melting snow stimulate new plant growth As the hot, drysummer progresses, the plants wilt and then turn yellow andbrown

Grasslands occur in the deep interior of continents, farfrom the ocean, where rainfall is generally low Temperategrasslands receive an average 12–40 inches (305–1,016 mm)

of rain a year and tropical grasslands 25–60 inches(635–1,524 mm) Rainfall is not distributed evenly throughthe year, however In temperate regions there is a dry seasonthat begins in the late summer, fall, or winter and continuesuntil spring In the Tropics the dry season begins in earlysummer and most of the rain falls in the winter

Although grasses are the most abundant plants in all land, there are many types of grasses, and grasslands are notall the same Tropical grasslands lie between the edge of thesubtropical deserts and the tropical forests They are often

grass-called savanna (or savannah) grasslands, a name that seems to

have originated in the Caribbean region and to have entered

English from zavana, which was the Spanish form of the

orig-inal name Savanna grasslands extend across Africa as twobelts, one on each side of the equator Grasslands of this typealso occur in South America, southern Asia, and Australia.They are usually dominated by grasses five to six feet (1.5–1.8m) tall, interspersed with thorn trees that are mostly lessthan 33 feet (10 m) tall and have distinctive flat tops

Savanna grasslands have regional names They are called

llanos in Venezuela and Colombia, and campo cerrado and campo sujo are two different varieties of savanna found in

Brazil The Australian grasslands are identified not by theirgrasses, but by the species of acacia trees that grow among

the grasses: brigalow scrub and mulga scrub.

Temperate grasslands occur between the subtropical serts and the temperate forests or the coniferous forest

de-known as taiga Where rainfall is relatively high, the grasses

are about five feet (1.5 m) tall These are the typical grasses

of North American prairie and they occur on the eastern side

of the continent Shorter grasses—less than 18 inches (45

cm) tall—grow on the drier western side, in the plains,

although nowadays the two types of grassland are usually

called tallgrass and short-grass prairie Palouse prairie, also

called bunchgrass prairie, grows in Washington State and

British Columbia

In South America the temperate grassland is called pampa.

The Eurasian grasslands stretch from Hungary in the west,

across Russia, and as far as Mongolia and China They are

called puszta in Hungary and steppe in Russia There are two

main types of steppe Meadow steppe occurs in the north,

where the climate is relatively moist, allowing many

flower-ing herbs to flourish Dry steppe occurs in the south and

sup-ports fewer herbs Southern African grasslands are called veld

or grassveld.

Climate determines the growing season for plants

any-where in the world, and grasslands are no exception In

tem-perate regions plants are able to grow when the temperature

is above freezing The growing season in the prairie lasts from

about 150 days in the palouse prairie to 270 days in Texas In

the Tropics, where the temperature is warm enough for plant

growth throughout the year, rainfall is the crucial factor

A type of vegetation that covers a very large area in

conti-nents around the world is called a biome, and geographers

divide the entire world into a series of biomes The species of

plants vary from one part of a biome to another; what

mat-ters is that the predominant plants are all similar They might

be temperate trees, for example, or tropical trees, or grasses,

but regardless of the species, North American grassland is

much more similar to South American, Eurasian, African, or

Australian grassland than any of these is to forest

All biomes are important to us, but the grassland biome is

especially important Most of our staple foods, including

wheat, rice, barley, rye, corn (maize), and sugarcane, are

grasses, and wheat, barley, and rye were first cultivated on

the grasslands of what are now Turkey and Iraq Our cereal

and livestock farms are like artificial grassland and in many

places the lands they occupy were natural grasslands until

farmers cleared away the wild grasses to grow cultivated

grasses

Some areas of natural grassland are not suitable for

farm-ing, usually because they experience severe and prolonged

drought from time to time, but many make good farmland

This means they are valuable, and over the centuries most of

the natural grassland has been converted into farmland.When the grassland is plowed, the plants that grow amongthe grasses are destroyed along with the grasses themselves,and many of the animals that find food and shelter amongthe plants die or move away If we wish the members of thenatural grassland community to survive, we must preserveareas of the grassland itself.

XVIII GRASSLANDS

Where grasslands occur

Grasslands once covered more than 40 percent of the Earth’s

land surface Grasses are geographically more widespread

than any other group of plants, and grasslands compose one

of the most extensive types of vegetation on the planet As

the map shows, they are found on every continent except

Antarctica

Although the map shows the areas where grassland is the

natural vegetation, in fact large areas of grassland have been

converted to farmland Where the rainfall is sufficient to

sup-port farming, the abundant sunshine, level plains, and fertile

soils are ideal for growing wheat and corn These crops are

also grasses, so the conversion is from one type of grassland

to another Agricultural grassland may also consist of pasture

grasses that have been sown to feed livestock

Grasses thrive in climates that are too dry for most trees

They tolerate grazing by animals (see “How grasses work” on

pages 85–90), but they cannot survive in deep shade

Consequently natural grasslands occupy those parts of the

world that are neither desert, which is too dry, nor forest,

which is too shady

The map divides grasslands into two types—temperate

grassland and tropical savanna grassland Temperate

grass-land occurs in regions with a temperate climate and is most

widespread in North America, eastern Europe, Turkey and

northern Iran, central Asia, and part of southern China

There is much less land in the Southern Hemisphere to the

south of the tropic of Capricorn, and that is why southern

temperate grasslands are confined to part of Argentina and a

small area of Peru and South Africa

Savanna grassland covers a large part of Africa, extending

from the southern edge of the Sahara to the southeastern tip

GEOGRAPHY

OF GRASSLANDS

CHAPTER 1

1