The Ecology Book

169

Like other epiphytes, Spanish moss

lives on other species but draws water

and nutrients from the air rather than

from its host. It thrives in tropical and

subtropical environments.

See also: Evolution by natural selection 24–31 ■ Ecophysiology 72–73 ■ The ecosystem 134–137 ■ The foundations of plant

ecology 167 ■ Biogeography 200–201 ■ Biomes 206–209

ORGANISMS IN A CHANGING ENVIRONMENT

the prevailing climate. For example,

tropical vegetation was divided into

savanna, thorn-forest, woodland,

tropical rain forest, or woodland

with a pronounced dry season,

according to whether the climate

was wet all year round, seasonally

wet, or mostly dry.

Adaptations for extremes

Schimper made a close study of

plant physiology—the structures of

plants and how they had adapted to

varying temperature and moisture

conditions. He was particularly

interested in plants growing in

extreme climatic conditions. Salty

environments, for example, require

plants to survive high levels of

soil and water salinity. Schimper

found that vegetation growing on

the coastal mangroves of Brazil, on

Caribbean and Sri Lankan beaches,

and in sulfur-emitting volcanic

craters in Java, were similarly

tolerant to salt.

Schimper also studied how

plants coped in the challenging

conditions of arid environments.

He found that plants growing in

hot, dry places had evolved “varied

contrivances for regulating the

passage of water.” To illustrate this,

he chose a type of vegetation with

tough leaves, short internodes (the

distances between the leaves along

a stem), and leaf orientation parallel

or oblique to direct sunlight. This

type grew in various parts of the

world, where arid conditions meant

that water was scarce. The name

Schimper gave to these plants—

sclerophyll, from the Greek words

skleros (“hard”) and phullon (“leaf”)—

is still used today.

Epiphytes, plants that grow on

the surface of other plants and

derive their moisture and nutrients

from the air or rain, also fascinated

Schimper. He observed epiphytes

such as Spanish moss growing in

the southern US and the Caribbean

islands and similar species in

South America, South Asia, and

southeast Asia. He found that they

were linked by warm temperatures

and year-round moisture—traits of

what he called a tropical rain forest.

Although the broad geographic

divisions devised by Schimper still

hold true, there is now a better

understanding of how vegetation

develops in response to many

different stimuli beyond simple

climatic differences. For example,

measures of potential water

evaporation into the atmosphere,

water surplus, and water deficit,

which can be combined in a

moisture index, are more useful

determinants of plant distribution

than simple temperature and

rainfall figures. ■

... the time is not far

distant when all species

of plants and their

geographical distribution

will be well known.

Andreas Schimper

US_168-169_Climate_Vegetation.indd 169 12/11/18 6:25 PM