The Ecology Book

208 BIOMES

botanist Arthur Tansley introduced

the term “ecosystem” in 1935.

When Clements and Shelford

published the results of their

collaboration in 1939, they were not

making a sudden breakthrough—

rather it was a consolidation of

ideas that had been taking shape

over a long time.

The collaboration between

botany and zoology was crucial.

Only by looking at the totality of

the natural world with its dynamic

interactions could scientists hope

to get a full picture, and Clements

defined a biome as “an organic unit

comprising all the species of plants

and animals at home in a particular

habitat.” Even so, biomes have

come to be defined principally

by vegetation type.

The most important feature of

biomes is that they link vegetation

and plant communities across the

world. There are tropical forests, for

example, in every continent, but

most tree species appear only in

one continent. So, the range of trees

within the Amazonian forests is

completely different from the range

of trees in the forests of Indonesia.

Yet both areas are identifiable as

tropical forest, because the trees

have features in common.

Since Bioecology first appeared,

there have been countless attempts

to define what a biome is, and many

different ways of classifying them.

Biomes provide a simple way

of understanding global vegetation

patterns, but when looked at closely

they present a crude way of grouping

ecosystems. There is no single

accepted classification system, and

the only division everyone seems to

agree on is that between terrestrial

(land-based) and aquatic (water-

based) biomes. Many of the same

biomes crop up in most systems,

such as the polar biome, tundra,

rainforest, grasslands, and deserts,

but there is no agreed definition

and there are marked variations.

The climate factor

The one common factor in all biome

classifications has been climate,

although other “abiotic” factors can

also play a part. Climate determines

the form of plant growth best suited

to a region, and plants that grow

in a certain way are restricted

to particular climates. The leaves

of deciduous trees are broad, with

a large surface for light absorption,

but little resistance to drying out

or frost. Conifer tree needles, on the

other hand, are narrow and can

survive the harshest frosts. Desert

shrubs often have very thin leaves,

or no leaves at all, to resist drying

out. Biogeographers acknowledge

climate’s key role when they talk

about “tropical” rainforests and

“temperate” grasslands.

Terrestrial biomes of the world

This map shows six biomes across the globe. Each area

has distinct flora, as major plant types vary from one climatic

region to another. Ocean and freshwater biomes are not

displayed here, but are equally important to the biosphere.

Mountains

Tropical forest

Grasslands

Temperate forest

Polar regions

Desert

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