Modeling the Life Cycle of the Land

Procedures

1. Explain to students that just as an individual plant or animal has a life cycle, entire ecosystems have life cycles too.
2. Distribute one plant card to a small group of students. The cards include the name of the plant along with a list of the adaptations of that plant (pine tree, oak tree, shrubs, grasses, flowers, herbs).
3. Read the following to students, pausing at each blank for the small groups to determine if it is their time in the life cycle of the land.Many years ago this place was bare rock. Then erosion by wind and water broke off little bits that became mineral soil, and lichen grew on the rocks. Animals ate the lichen and contributed “scat” on the ground. Lichens died and decomposed on the ground. This organic or once-living matter combined with weathered bits of rock to form a shallow layer of very poor soils.

   Seeds blew or were dropped into the area. The abundant sunshine and poor soils provided a good place for __________ (annual plants, herbs, wildflowers and weeds)  to grow. As they grew, some plants died and contributed organic matter to the soil. Animals lived among and ate the plants, and those animals contributed “scat” to the soil and eventually died, contributing their decomposing selves to the soil.

__________ (shrubs) started growing in the sunny meadow, offering habitat and food for different types of animals. As the shrubs died and decomposed, and the animals died and decomposed, the soils gained more nutrients and were able to support larger plants and trees.

__________ (pine trees) started growing on the site and stayed in the sunlight by growing faster than any other trees. They reached their full height while other trees of the same age were still short. When pine trees grew tall, they shaded out the wildflowers, grasses, and shrubs that used to live there, when the place was a meadow. Different birds and animals moved in, to live and eat in the pine forest. As trees and animals died, the soil was further enriched.

Eventually the __________ (oak trees) finally caught up with the pine trees and were as tall as the tallest trees. But these tall trees caused the forest floor to be completely shaded and pine trees seedlings could no longer grow below the tall trees, because they cannot tolerate shade. Soon the only seedlings in the forest were little hardwood trees, which are suited to grow slowly in the shade.

Just when it seemed the forest had reached the climax stage of succession, where it would stay for many years, something happened to disturb the forest. Change came to this area and all the mighty oaks were gone.

4.  Brainstorm with students what could bring change to the forest (fire, farming, gardening, building of cities, tornado, grazing, logging, building of cities). Discuss with students what they predict will happen next in the life cycle of the land.