The Ecology Book

175

Diseases such as American chestnut

blight challenge the idea of a fully

integrated climax community, as the

loss of the dominant tree species should

cause the entire ecosystem to collapse.

See also: The ecosystem 134–137 ■ The distribution of species over space and time 162–163 ■ Ecological succession

170 –171 ■ Climax community theory 172–173 ■ The ecological guild 176–177 ■ Biomes 206–209

ORGANISMS IN A CHANGING ENVIRONMENT

denied that there is any endpoint or

climax community; he believed that

communities are always changing.

Changing opinions

Gleason’s argument with Clements

caused quite a stir at the time.

Clements seemed to be creating an

overview in which natural patterns

of vegetation were determined by

clear rules, just as in Newtonian

science the movement of the planets

is dictated by incontrovertible laws.

Clements and his supporters were

able to look at the bigger picture,

while Gleason was viewed as a

reductionist, myopically intent on

the details and challenging the

entire idea of ecology as a science

controlled by laws.

Gleason appeared to be saying

that there are no patterns in nature:

it is all random. Worse still, he was

accused by some of justifying

exploitative farming, since his

ideas seemed to imply that man

need not worry too much about

disturbing the balance of the

natural environment—because

there is no balance. Gleason’s ideas

were therefore forgotten in the

enthusiasm for developing ecology

as a science. He became so

frustrated that he gave up ecology

during the 1930s as holism became

progressively supported by the idea

of the interactive “ecosystem.”

Nonetheless, as ecologists

continued to study the world, they

found more and more flaws in

Clements’s theory. In the 1950s, the

work of American plant ecologists

Robert H. Whittaker and John Curtis

showed how impossible it was to

identify communities as neat units

of holistic theory, and that the real

world was more nuanced and

complex. When it comes to studying

ecosystems in the field, Gleason’s

ideas seem to provide a better fit.

In the ensuing decades, while

environmentalists continue to

champion holistic ideas, ecologists

have also increasingly incorporated

Gleason’s concepts into their work.

He is now considered to be one

of the most significant figures in

20th-century ecology. ■

Henry Allan Gleason

Born in 1882, Henry Gleason

studied biology at the University

of Illinois. He held faculty posts

and conducted acclaimed early

ecological research in Sand

Ridge State Forest, Illinois. In

the 1920s, Gleason’s theory of

individualistic—rather than

holistic—plant communities was

not accepted by ecologists. This

rejection led Gleason to abandon

ecology in the 1930s. He had

long held posts at the New York

Botanical Garden and became

famed for his work on plant

classification. With botanist

Arthur Cronquist, he co-wrote a

definitive guide to the plants of

the northeastern US. He retired

in 1950 but continued to write

and study. He died in 1975.

Key works

1922 “On the Relation between

Species and Area”

1926 “The Individualistic

Concept of the Plant

Association”

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