Essentials of Ecology

CONCEPT 5-4 117

burned or cut forests, heavily polluted streams, and

land that has been flooded. In the soil that remains on

disturbed land systems, new vegetation can germinate,

usually within a few weeks, from seeds already in the

soil and from those imported by wind, birds, and other

animals.

In the central, or Piedmont, region of the U.S. state

of North Carolina, European settlers cleared many of

the mature native oak and hickory forests and planted

the land with crops. Later, they abandoned some of

this farmland because of erosion and loss of soil nutri-

ents. Figure 5-17 shows one way in which such aban-

doned farmland has undergone secondary succession

over 150–200 years.

Explore the difference between primary and

secondary succession at CengageNOW.

Descriptions of ecological succession usually focus

on changes in vegetation. But these changes in turn

affect food and shelter for various types of animals. As

a consequence, the numbers and types of animals and

Time

Shrubs and

small pine

seedlings

Annual

weeds

Perennial

weeds and

grasses

Young pine forest

with developing

understory of oak

and hickory trees

Mature oak and hickory forest

Active Figure 5-17 Natural ecological restoration of disturbed land. Secondary ecological succes-
sion of plant communities on an abandoned farm field in the U.S. state of North Carolina. It took 150–200 years
after the farmland was abandoned for the area to become covered with a mature oak and hickory forest. A new
disturbance, such as deforestation or fire, would create conditions favoring pioneer species such as annual weeds.
In the absence of new disturbances, secondary succession would recur over time, but not necessarily in the same
sequence shown here. Questions: Do you think the annual weeds (left) would continue to thrive in the mature
forest (right)? Why or why not? See an animation based on this figure at CengageNOW.

As these tree species grow and create shade, they

are replaced by late successional plant species (mostly
trees) that can tolerate shade. Unless fire, flooding,

severe erosion, tree cutting, climate change, or other
natural or human processes disturb the area, what was

once bare rock becomes a complex forest community
or ecosystem (Figure 5-16).

Primary succession can also take place in a newly

created small pond, starting with an influx of sediments
and nutrients in runoff from the surrounding land. This

sediment can support seeds or spores of plants carried
to the pond by winds, birds, or other animals. Over

time, this process can transform the pond first into a

marsh and eventually to dry land.

Some Ecosystems Do Not Have

to Start from Scratch: Secondary

Succession

Secondary succession begins in an area where an eco-
system has been disturbed, removed, or destroyed, but

some soil or bottom sediment remains. Candidates for
secondary succession include abandoned farmland,