GOAL:

To develop an understanding of the interdependence of all organisms and the need for conserving natural resources

Ecological succession is a series of sequential changes caused by populations of a community producing conditions that are unfavorable for their own survival.

Ecology J2.00 To understand secondary succession

2.01 identify those forces which initiate secondary succession.
2.02 trace the steps of secondary succession in a selected habitat in which a catastrophe has occurred.
2.03 illustrate the effects of humans on both primary and secondary succession.
2.04 observe the succession of micro-organisms that occur in a hay infusion.

I. Forces which initiate secondary succession.
II. Secondary Succession on selected habitats.
A. Volcanic Islands
1. Mt. St. Helens (1980)
2. Surtsey (1963)
3. Krakatoa (1883)
4. Galapagos
B. Abandoned Land
1. Salisbury, Connecticut
2. Abandoned farmland (Old Field Succession)
III. Humans' effect on succession
IV. Succession of Microrganisms
A. Hay infusion
B. Molasses solution
C. Other

COMPONENT OF SCIENCE: Unifying Concepts of Science

GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical and earth/space sciences.

2.4 INTERACTIONS - At all levels of living and non-living systems, matter and energy act and react to determine the nature of our environment.

2.4b - Interactions of matter and energy shape our world.

BENCHMARKS Changes that occur in an environment may affect both living or non-living things.

TIME REQUIRED:

Five to six 55 minute class periods (Depending on the number of activities) (Part IV should be prepared before you begin the lessons.)

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; others; microscope; data sheets; graph paper; Part IV activities - Hay infusion, or Molasses Solution, or Bean-Water Microcommunity

Mt. St. Helens, Galapagos, Surtsey, Krakatoa, shade-tolerant, vertical stratification, catastrophe, secondary succession

This lesson addresses Instructional Objective 2.01 and 2.02.

(Hold up pictures or use transparencies showing succession.) What is happening in these pictures? (response) We have just completed a study of primary succession. Today we will begin a study of secondary succession.

What is secondary succession? (response) Secondary succession occurs where communities used to exist, but were destroyed by natural or man-made causes. These could be in areas where forests are cut down or destroyed by fire, other natural disasters, and diseases. Abandoned farmlands also undergo secondary succession. A volcano or other catastrophe will also cause an area to undergo secondary succession. (Have pictures of Mt. St. Helens, Krakatoa, Galapagos, Surtsey, pond, abandoned farmland, etc.) Usually, secondary succession re-establishes the original community much faster than primary succession because soil already exists; nevertheless, it may take a hundred years or more for the climax stage to return, if it ever does. (Have pictures of Krakatoa - 1983-1989, and Mt. St.Helens 1980-1989) What are some other forces that might result in secondary succession taking place? (response) (Hurricanes, earthquakes, a tree falling in a forest, a house being built, a new road, timber harvesting, etc.)

Where do you think secondary succession is most common? (response) Secondary succession is most commonly encountered on abandoned farmland and non-cultivated sites such as landfills, spoil banks, railroad grades, and roadsides. All areas that have been disturbed and are frequently subject to erosion and settling movements.

Whether primary or secondary succession, succession starts with the colonization of the area by pioneer species. Pioneer species most likely to colonize such places are the so-called weeds, plants able to grow on a substrate low in nutrients and organic matter, in an environment that is excessively dry from strong solar radiation and in wide variations of surface temperature. The number of plants colonizing and surviving on the site are few at first, but as conditions improve, more of them occupy the area.

Through the deposition of organic matter and shading of the surface, they reduce the surface evaporation and modify the environment enough to permit more demanding plants to assume dominance. Better adapted to utilize the nutrients, herbs, grasses, and shrubs eventually take over and crowd out the pioneers by shading and by vigorous growth. Some new arrivals may take hold not because of changed environmental conditions, but in spite of them. Many plants of an advanced serel stage could well have been the pioneers had they chanced to colonize the area earlier. Some pioneer species such as crabgrass, sunflowers, and horseweed may produce chemicals that inhibit their own growth and the growth of other herbaceous species, paving the way for invasion by grasses that are not affected by toxins. Grasses in turn may inhibit nitrogen fixing bacteria, slowing succession to the next stage.

Eventually the stage is set for other plants, cedar, pine, spruce, to invade and colonize the area for a different community to develop. Within 5 to 10 years, these evergreens are tall enough to shade out the grasses and a layer of poorly decomposed needles that prevents most evergreen seeds from reaching mineral soil, dense shade and competition for moisture between successfully germinated seedlings and shallow-rooted parent trees inhibit evergreens from regenerating themselves on the site. In time, however, shade-tolerant oaks and sweetgums, which have long taproots, exploit a moisture supply unavailable to shallow-rooted evergreens.

The hardwoods grow up through the evergreens, and as the evergreens die out (If they are not cut), take over the field. Further development of the hardwood forest continues as shade-tolerant trees and shrubs fill in the understory, dogwoods, redbuds, sourwood, hydrangla, and others, the sere (Sequence of communities) has arrived at a mature or tolerant stage; maple, black walnut, oak, hickory, tulip popular,(The state tree of Tennessee) and chestnut, in which only the dominant species of the crown can reproduce themselves in their own shade. As the seral stages change, the animal life they support changes with them until the climax community is established.

Early terrestrial successional stages support animals of the open field; field sparrows, meadow vales, meadow larks and grasshoppers to name a few. As woody plants appear, stratification increases (make a list of animals on the board or overhead) and habitat conditions change animals of annual plants and grass stages give way to animals of mixed herbaceous and shrubby habitats. Woodland mice replace meadow vales, and birds of thickets and shrubland appear, rabbits, towhees, song sparrows and purple finch. As the area passes into forest, vertical stratification increases. Animals of the forest edge and forest appear along with species that occupy the upper strata; robins, white-tail deer, short-tail shrew, ruffed grouse, and Junco. As the forest matures shrub and edge species decline and are replaced by the tree squirrels, black-throated green warblers, Nashville warbler, red fox, white-footed mice and veery. Each stage supports its own more or less distinctive forms of animal life and when those stages pass, their animal life also passes.

A climax community is more stable than the communities that come before it, but the climax communities can also change over time. Before a fungus killed most of them, the American chestnut trees were a major part of the climax community forest of the eastern North America. Now oak and hickory have replaced the chestnut trees.

Today we discussed several forces which could initiate secondary succession. Tell your neighbor at least two of those forces. (pause, summarize)

This lesson addresses Instructional Objective 2.02.

Succession is going on all around us. Today we will discuss secondary succession in a habitat where a catastrophe has occurred. Can someone tell me of such a place? (response) (You may want to study several, but Mt. St. Helen will be one the students will remember.)

Mt. St. Helens: On May 18, 1980, the volcanic core of Mt. St. Helens in western Washington erupted, spewing millions of tons of ash into the air and destroying many square kilometers of once-lush vegetation. In the most highly devastated regions, the ash completely blanketed the existing soil, and the heat vaporized soil particles and nutrients. Four months after the eruption, biologist Roger del Moral found an active ant nest high on the mountain and far from any visible vegetation. Presumably, these ants were at the top of a subterranean food chain. The lower levels of this micro food chain probably survived on decomposing organic matter buried by the ash. The following spring, a mushroom was found in the original blast zone, growing in the ash and the slowly decomposing organic matter present. Within a year after the eruption, many different types of pioneer plants were colonizing the less severely disturbed areas. Migrating deer and elk passed over the ash, and their footprints formed small indentations that provided shelter and pockets of moisture favorable for the germination of seeds blown in the wind or transported by birds. In border areas between the devastated zone and places where vegetation had survived, pocket gophers are burrowing into the ash and breaking up the impermeable layers. Full succession to a stable climax system will take many years, but the process has already begun.

Surtsey: On November 14, 1963, 12 miles off the southern coast of Iceland, volcanic activity on the ocean floor began to form a new island. By the next day, a narrow black ridge broke the surface of the ocean, and the island began to grow. By March of 1965, a mass of lava, ash, cinders, and pumice, 2.8 kilometers square, had formed. The people of Iceland named this newly formed island Surtsey.

This newest land on earth has been declared a sanctuary. This emergence of Surtsey from the ocean floor has provided scientists with a unique opportunity. They can study the natural succession of life on a new land. Many questions about succession have resisted answers in laboratories around the world. Some of the answers now may be found on this small piece of land that formed just a few short years ago in the North Atlantic.

Two graduate students in biology from the University of Iceland watch over Surtsey each summer. They live in a simple wooden house on the island. The house and the biologists' footprints are the only signs of human occupation on this new land.

Each day that the weather permits, the biologists walk around the entire island. They observe the seaside sandworts, the hardy succulents that have replaced Surtsey's first flowering plants, the sea rackets. They also check their insect traps. Tiny flies, called midges, are the only insects that reproduce on the island. However, many other insects, including butterflies, are carried to Surtsey by winds from surrounding islands.

The only birds now nesting on Surtsey are the fulmars. They have built nests high in the cliffs on the west side of the island. Each nest contains a single egg. Occasionally, some of the nests are robbed by blackbacked gulls.

The biologists do not interfere with any of the natural events that occur on the island. To do so would be to destroy the succession they are studying. They must even resist the temptation to cover the exposed roots of a dying plant.

On Surtsey, scientists have a rare opportunity to study succession at its beginning--to see what comes first, what is destroyed, and what survives. They will be able to chart the entire history of animal and plant life on a fresh, new land.

Krakatoa: In 1883 much of the island of Krakatoa, which is located off the coast of Java, was blown apart by several volcanic explosions. Scientists began to study the area almost immediately. This island soon became one of the largest examples of primary succession ever studied.

The scientists studied the island over a number of years. After 3 years, they found a few tiny algae, mosses, and ferns on the island. It took about 10 years before flowering plants were growing again on the island. Very few animals had returned after 10 years, and the animals that were there were animals that could fly, such as insects and birds. Almost 25 years passed before the island had abundant vegetation again. Young trees occupied only about half of the island 40 years after the explosions. (Several books have been written on this island. You might like to see if they are in your library.)

Salisbury, Connecticut: In northwestern Connecticut lies the old colonial town of Salisbury. Here Revolutionary War furnaces cast cannon for the American army and anchors for the U. S. S. Constitution. On the fifty-square-mile Mount Riga plateau, Salisbury ironmasters (Ethan Allen was one) cut great numbers of trees for charcoal to use in the ironworks.

The furnaces have been cold since 1860. The woods have grown back haphazardly. First goldenrod and blackberry filled the clearings. Chestnut, low gray birch, and white pine trees next appeared. These were replaced later by maple, yellow birch, beech, oak, and ash. After about three hundred years, hemlock and oak trees will dominate the forest once again.

Communities change because each biological stage modifies the environment and adapts it to a later somewhat different grouping. Thus on Mount Riga, the pioneering gray birch and white pine prepared the shade and the seedbed for maples and succeeding trees. Much later, when the forest is more mature, shade-loving hemlocks will take over.

Galapagos: The Galapagos Islands have been of interest to biologists because they are new islands, in geological terms. These tiny islands are located on the equator in the Pacific Ocean, 600 miles off the coast of Ecuador, and belong to Ecuador. They were formed 2.5 million years ago by volcanic eruptions. Very gradually, a succession of organisms reached their shores and began to form communities on the islands. The gradual replacement of populations on bare rock is called primary succession.

Biologists have examined and identified the species now living on the islands. These have been compared to populations that inhabit the nearest land on South America. How did organisms reach the islands? Why are some of the organisms living there similar to other living thousands of kilometers away? Why are others different? These are some of the same questions that have puzzled scientists for years.

This could be the way succession has gone on these islands; first, seabirds probably nested on the barren rock formed from cooled lava. Their droppings would furnish nutrients for bacteria. Meanwhile, erosion caused by rain and surf would very gradually form the small mineral particles that become the basis for soil formation.

Tropical storms probably carried other organisms to the islands. These may have included seeds, spores, small arthropods, eggs, and an occasional small mammal floating on an uprooted tree or debris. Many organisms reaching these islands would die because of lack of food, but some would live and produce offspring. At the very beginning, there would have been no producers on the volcanic island, so no land animal could flourish there until the arrival of plants.

Plants that reached the island and lived were the pioneers that began the events of succession. Their remains were added to the developing soil. These plants or their seeds could have reached the island by means already mentioned. They could also have been carried by the wind or on the feathers or feet of birds.

The mangrove plant is a good pioneer that begins populating newly formed islands. It produces seeds that float. These seeds can travel long distances and germinate in salt water. When they lodge in a rock, they send a primary root down into a crevice. As the plant grows, many more roots, called aerial roots, are produced. These roots are partially exposed at low tides. They trap sand, dirt, and fallen leaves. Eventually, soil forms among the roots. Crabs and worms can burrow in this new soil. The mangroves provide important food and shelter for many island communities throughout the world.

Newly arriving organisms would find resources very different from those that were available in their original habitats. All the small land birds on the islands are believed to have descended from one type of small finch. Today there are several distinct species. They eat different types of food and use different nesting spaces.

Galapago has many strange birds and animals. They include a rare cormorant that cannot fly; the penguin (Widely believed to live only in the Antarctic); and mocking birds of a type unknown elsewhere. There are great turtles that weigh more than 500 pounds. The Spanish word for the turtles, Galapagos, gave the islands their name. Most fantastic of all are the thousands of lizards called iguanas. Many are four feet long. More familiar creatures include herons, sea birds known as boobies, and scarlet crabs, which are the same as an Atlantic species from which they have been separated for possibly 35,000,000 years.

Old Field Succession: A familiar example of secondary succession is "old field succession or old farmland succession", by which abandoned farms return to the climax deciduous forest. When a farmer stops cultivating land, grasses and weeds quickly move in and cover the earth with a carpet of green: wild carrot, black mustard, and dandelions. The "pioneers" of newly available habitats, these plants grow rapidly and produce seeds adapted to dispersal by wind or animals over a relatively wide area. Soon taller plants, such as goldenrod and perennial grasses, move in. Because these newcomers shade the ground and their long root systems monopolize the soil water, it is difficult for seedlings of the pioneer species to grow. But even as these tall weeds choke out the sun-loving pioneer species, they are in turn shaded and deprived of water by the seedlings of pioneer trees, which take longer to become established but command the lion's share of the resources once they reach a respectable size. Succession is still not complete, for the pioneer trees are not members of the species that make up the mature climax forest. Slower growing tree species will eventually move in and take over, shading out the saplings of the pioneer tree species. After several hundred years the land is once again covered with a mature climax forest. (In Tennessee this is the Oak-Hickory forest.)

(Any of the catastrophes I have written about can be used for this objective, but if you know of others, please feel free to use them in place of these or with them.)

(This will depend on the catastrophe you select to study.)

This lesson addresses Instructional Objective 2.03.

We have been discussing primary and secondary succession for several days. What are the two kinds of succession? (response) Today we will talk about some effects humans have on both kinds of succession.

Winds, fires, volcanic activity, and other natural events tend to disturb a community, but this also happens when humans clear land, build dams, and change the course of a river. If disturbed areas are left alone, succession begins. Putting rocks in a bay for a breakwater or sinking piles for a pier can also begin a succession.

One of the reasons that succession occurs is that many species, especially those characteristic of early successional systems, change the environment in which they live in ways that make it less favorable for themselves and more favorable for others. For example, a corn plant removes the nitrogen it needs from the soil, leaving soil which corn cannot grow on again (unless fertilizer is added), but in which alfalfa, which needs no nitrogen from the soil, can flourish.

In the Rocky Mountain region, when the leaves and branches of aspen trees decompose, the soil chemistry is changed, making land less fit for aspen, but quite fertile for pine, spruce, and fir.

Some of our agricultural pest problems stem from the fact that many crop plants originated as pioneer species. In nature, these plants depend on their sparse distribution and their nomadic habits (never in the same place for many seasons in a row) to protect them from their insect predators. By planting fields exclusively to one crop year after year, farmers create a paradise for animals that eat these species, such as cabbage worms and cucumber beetles, which no longer have to spend energy to find food and have nothing to do but eat and multiply.

Mismanagement of the forest--such as clear cutting excessively large areas, erosion initiated by poor layout of logging roads, and poor slash disposal--can limit the rate of succession and delay the return of the original vegetation.

Overgrazing of grasslands by domestic stock results in denudation and erosion of the land, and will also, limit the succession rate.

Fires, set by natural or human activities, occasionally sweep through large areas of forest, burning tree crowns and destroying entire communities of plants and animals. Burned areas undergo secondary succession.

In some communities, fire is sufficiently frequent to determine the nature of the climax vegetation. Such communities include chaparral, temperate grassland, and many southern and western pine forests in the United States. Seedlings and saplings of deciduous trees are especially susceptible to fire, whereas many pines are relatively resistant and so are favored in regions where fires occur often. Many pines are adapted to survive, and even to exploit, fires, and recurrent fires may prevent grasslands or savanna from ever turning into woodland.

If humans prevent fires in a fire-adapted pine forest, deciduous trees may become established. In addition, dead wood and litter build up on the ground, and so when a fire eventually does occur, it is more severe than usual, destroying not only any deciduous colonizers, but also the pines and other species. Odd though it may seem at first, frequent burning is essential for the preservation of many natural communities.

Succession is going on everywhere in the world. If an area has been disturbed by nature or by man, primary or secondary succession begins at once, and in some areas both kinds of succession could be going on at the same time.

Today we have discussed the effects humans have on succession. On a piece of paper list at least four of these effects. Have your neighbor check your answers. Put the paper in your science notebook.

(Take a field trip to an abandoned farm, area where a fire has destroyed the forest, etc. Have them find and list the pioneer species that are coming into the area to begin secondary succession. A graph could be made of what is taking place. A farmer in your area might have just dug a pond in the last few years. This would be a good place to go.)
To view the classroom connector which
addresses Instructional Objective 2.04,
please click Ecology J2a

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