Fill out the Venn Diagram above using information from the reading.
Transcribed Image Text: WHAT IS SUCCESSION?
In the spring of 1988, much of Yellowstone National Park was a forest. The
trees grew close together. Large areas were in shade, and few plants grew under
the trees.
2 That summer, fires burned much of the forest and left a blanket of gray ash on
the forest floor. Most of the trees were dead, though some of them were still
standing.
3 The following spring, the forest floor was green. Some of the dead trees had
fallen over, and many small, green plants, such as grasses, were growing
Why were grasses the first things to grow?
After the fire, the forest floor was sunny and empty. Nonliving parts of
ecosystems, such as water, light, and space, are called abiotic factors. When the
trees were dead, grasses had the abiotic factors they needed, and their populations
grew quickly.
5 In a few years, larger plants began growing in some areas, and the grasses
could not grow without sunlight. Within 10 years, the trees were starting to grow
back. The trees began to shade out those plants. When one type of community
replaces another type of community, this is called succession. The grasses and
other species that are the first to live or grow in an area are called pioneer species.
PRIMARY SUCCESSION
Sometimes, a small community starts to grow in an area where living things
have never grown before. The area is only bare rock and there is no soil. Over a
very long time, a community can develop. The change from bare rock to a
community of organisms is called primary succession.
Lichens are pioneer species on bare rock. A lichen's structure allows it to
function on bare rock. Lichens don't have roots, and they get their water from the air.
This means they do not need soil. Most other organisms, however, cannot move into
the area without soil.
8Lichens produce acid that breaks down the rock they are living on. The rock
particles, mixed with the remains of dead lichens, become the first soil.
9 After many years, there is enough soil for mosses to grow. The mosses
eventually replace the lichens. Tiny organisms and insects begin to live there. When
they die, their remains add to the soil.
10Over time, the soil gets deeper, and ferns replace mosses. The ferns may be
replaced later by grasses and wildflowers. If there is enough soil, shrubs and small
trees may grow. After hundreds of years, the soil may be deep enough and rich
enough to support a forest community
Transcribed Image Text: SECONDARY SUCCESSION
11
Sometimes, a community is destroyed by a natural
disaster, such as a flood or fire. Sometimes, humans or
animals alter an environment. For example, a farmer may
stop growing crops in a field. In either case, if there is soil and
the area is left alone, the natural community can grow back.
12 The plant species change in a series of stages called
secondary succession. Secondary succession happens in
areas where living things already exist.
The figure to the right shows secondary succession in a
|farm field that used to be a forest.