TEKS 7.12D
TAKS Objective 2 – The student will demonstrate an understanding of
living systems and the environment.
TEKS Science Concepts 7.12D
The student knows that there is a relationship between organisms and the
environment. The student is expected to:
(D) observe and describe the role of ecological succession in
ecosystems.
Overview
Ecosystems are constantly changed. Different organisms are adapted to certain
conditions. After an event that can change the ecology of an area, the flora and
fauna also changes. Students will look at what happens after several such
changing events such as a fire or glacier movement.
Instructional Strategies
Students will investigate what happened in Yellowstone National Park after a
major fire through a virtual field trip.
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Lesson Objectives
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The learner will
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The learner will
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The learner will
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 For Teacher’s Eyes Only
Teacher Background:
From http://www.jimswan.com/111/succession/succession.htm and needs to be
revised.
Succession is the process by which the communities we see in nature
were established. It consists of a series of stages which result in the
establishment of a climax community. These stages involve changes in
both the biological and physical components of the habitat. The climax
community represents the combination of plants and animals which make
the most efficient use of available resources and conditions. In other
words, the community established by nature is the one which works best
given the climate, topography and other characteristics of the area. Climax
communities are designated according to the dominant plant type, but
many other plants as well as animals make up the community. Examples
of types of climax communities are: spruce-fir forest, ponderosa pine
forest, beech-maple forest, creosote bush desert, etc. However, even
these can vary from one place to another with regard to the specific
organisms found and their relative abundance.
Succession on barren terrain, i.e. rock or other inorganic material, is
called primary succession. Primary succession initially formed all climax
communities, but we can only see it at work on recently deposited volcanic
land, rock exposed by retreating glaciers, and inorganic sand, silt., or
cinder which has little or no organic material present. The chart below
shows primary succession that results in a forest community. In grassland,
desert, or tundra the process would lead to a grass or shrub stage,
stopping short of the establishment of trees. The types of organisms are
shown in bold with some examples shown in plain type.
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The process must begin with organisms that form organic soil, the
pioneers or soil builders. This soil will be necessary to provide for the next
group of plants to succeed. Lichens are found in most every habitat, wet &
dry, hot & cold, and come in a wide variety of shapes and colors. They are
a symbiont composed of fungus, algae and , sometimes, bacteria. If
cyanobacteria are involved the lichens are nitrogen fixers. In wet climes
mosses and liverworts are important pioneers. In dry sand or clay soils
cryptogamic organisms are critical to the buildup of organic materials and
the ability of the soil to hold water. Cryptogamic soil consists of a
combination (not a symbiont) of lichens, fungi, and mosses which form a
crust on the surface which is very susceptible to physical damage.
Cryptogamic soil is critical to the sustainability of desert soils in the
Southwest and the damage resulting from off road travel and overgrazing
is a major factor in soil loss.
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Once the soil is produced the
quick-growing grasses and
weeds come in. Some of these
are significant, like fireweed
which supports a wide variety of
wildlife with its nectar, foliage and
seeds, and lupine which harbors
nitrogen-fixing bacteria. The next group to arrive is the shrubs which often
includes food-rich blueberry, salmonberry, raspberry, blackberry etc.
Eventually the early trees gain a foothold. They are called early trees
because they are the first to arrive and are species which generally grow
quickly and well in new and disturbed soils. They are NOT simply young or
small members of the climax trees. Early trees include types such as
willow and alder which thrive in wet habitats, and aspen and birch which
are important species in the habitats recovering from fire and other
disturbance. Both are capable of growing back quickly from their roots
after the standing trees are cut or burned. The early tree stage will be
firmly established by about 20 years after the start of succession.
The late trees produce the climax forest. (See Figure 2) They
require the most soil support and are the slowest to grow, but once
established they will dominate the forest, usually in about 65 to 75 years.
Old growth is a climax forest with a preponderance of trees 200 years old
or greater. Most of the earlier stages are still represented in the climax and
old growth forests to some degree. This results in increased diversity
which is often enhanced by the natural disturbances which return a portion
of the forest to an earlier stage (secondary succession). A natural fire for
instance will burn a small section of forest returning it to a stage containing
grasses, weeds, and shrubs. This will increase habitat value for the
herbivores which depend on these foods, while the unburned portions of
forest will continue to support the species which live in and on the old
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trees, and the species which eat them. A natural forest is heterogeneous
with earlier and later stages of succession forming a mosaic of diversity.
One problem with fire suppression by man is that it allows lots of fuel to
build up so that when a fire eventually does occur (and in the dryer forests
it always does) it will be very destructive and burn a much greater portion
of the forest than the small cyclical fires which would occur naturally. Even
so, the forest will grow back if left to itself.
In a typical forest the diversity increases as shown in Figure 2 as
succession proceeds to climax. In a moist coniferous forest like the forests
of the Pacific northwest, diversity is maintained and even increases as the
forest proceeds to old growth and the organisms of rot and decay foster a
new community of species. This biological turnover of old trees helps to
keep the entire system rejuvenated. In drier forests such as pine,
however, the pines tend to suppress other species on the forest floor. The
pine needles and cones are very acidic and inhibit the organisms which
produce organic soil (humus) and therefore the weeds and shrubs are
also inhibited. An old growth pine forest tends to be a less diverse uniform
stand of old trees. Fire and other physical disturbances are the important
agents in these forests in maintaining an overall heterogeneous forest.
The production of wood from a forest (the productivity line on the graph)
depends upon the climax trees reaching what is called the young, mature
status. This means that they are mature enough to have harvestable
wood, but they are not yet beginning to succumb to disease and rot. This
peak of productivity occurs well before the forest has reached its
maximum diversity. These days hybrid varieties of douglas fir and other
trees are being developed which reach maturity at ever younger ages. In
the near future we will have plantation forests which mature at less than
60 years.
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And therein lies the conflict of "modern forestry" with forest ecology.
Younger maturing forests are more productive and more profitable for
timber companies and help to satisfy our society's increasing demand for
wood. But they reduce the diversity and other ecological values of the
natural forest by never allowing it to return to the original diverse climax,
let alone old growth. Add to this the fact that "type conversion" changes
the natural forest over to a plantation monoculture as uniform rows of
even-aged hybrid trees replace the random diversity of the original forest.
The push in recent years by the timber industry to cut the last remaining
old growth forests is as much due to its desire to replace them with these
quick maturing monocultures as for the wood they contain. It is these
techniques, together with the use of herbicides and other chemicals,
removal of competing vegetation and decaying wood, erosion and other
edge effects, that threaten the integrity of our forest resources.
Edge effects occur when forests are chopped up and criss-crossed with
roads, exposing much of the forest to edges along roads and cutover
lands. Some edges are good. Natural forests benefit from the edges
created between meadow and forested land. But edges also allow the
freer movement of insects and plant diseases and manmade edges along
roads are prime areas of erosion and exposure to pollution such as solid
waste, air pollution, oil and gas residues etc. The straight edges created
along clearcuts and roads allow insects and fires, otherwise natural
phenomena when in limited amounts, to spread great distances and
become more destructive than they otherwise would.
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Misconceptions
 Misconception
As plants grow back after a disturbance, the same plants that were there
previously grow back. They are just shorter because they are growing
back.
 Science Concept
Certain types of plants and animals are better adapted to grow in certain
environments. There is a natural succession of life that grows back after a
disaster.
Rebuild Concept
Allow students to explore the online field trip about the natural succession
in a national park.
 Misconception
Fires are bad.
 Science Concept
Fires are natural occurrences and are necessary for maintaining a balance
and clearing out plant debris. When fires can become bad is when humans
prevent fires for long periods of time, allowing debris to build up. The
debris acts as fuel to intensify the fire. If the fire gets to big, then we see
the major fires that we have become accustomed to hearing about in the
news.
Rebuild Concept
Allow students to explore some of the positive impacts fires have.
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Student Prior Knowledge
While the idea of succession is a new one to students, the following TEKS should
be covered in the 7th grade prior to lessons on ecological succession. Background
on ecosystems is imperative to understanding succession.
7.12) Scientific Concepts. The student knows that there is a relationship between
organisms and the environment. The student is expected to:
(A) identify components of an ecosystem;
(B) observe and describe how organisms including producers, consumers,
and decomposers live together in an environment and use existing
resources;
(C) describe how different environments support different varieties of
organisms; and
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5 E’s
ENGAGE
Show a video clip of a forest fire such as the one found at
http://video.google.com/videoplay?docid=9039257627990588050&q=forest+fire
&hl=en
Have student make a T-chart in their notebook or journal. On one side have them
list possible causes of the forest fire. On the other side have students brainstorm
effects of a forest fire.
EXPLORE
Virtual Field Trip: If you have access to a computer lab, students can go through
the field trip at their own speed. If not, the field trip can be taken as a class with a
projector.
The field trip is located through the Yellowstone National Park website.
http://www.windowsintowonderland.org/fire/index.html
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EXPLAIN
Pictures and/or transparencies: all types of succession; Mt. St. Helens
(Then and now); Krakatoa; Surtsey; Galapagos; overgrazings' effect on
land; fires effect on land; clear-cuttings' effect on land
Go through the pictures with students and have them explain what the
cause of starting succession was and the processes the different landscapes
went through/are going through to reach a climax community.
http://www.countrysideinfo.co.uk/successn/second.htm
The Heathland Project site at the Woodland Education Centre
In 1993 the land here was cleared purposefully and then treated
with Roundup to clear the site of all plants. The purpose was to
observe the natural succession.
1993
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1998
2002
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2004
ELABORATE
Elaboration 1
Students will make a film strip of what might happen to an area after an
ecological changing event. Each frame will show the changes that are made over
time. Students will note pioneer species and a climax community. See Blake-Line
masters.
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EVALUATE
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