KBS K12 Partnership

July 28-Aug 1, 2003

T. Parshall

Human disturbance and succession:

investigating land use around your school

I. Disturbance, succession and landscapes

On October 25th, 2001 a thunderstorm with winds up to 100 mph swept through Kalamazoo County, uprooting thousands of trees, blowing roofs from buildings, and leaving approximately 15,000 people without power. This kind of natural disturbance is not uncommon and affects not only towns and personal property but also the way that ecosystems work and the kinds of plants and animals that grow there.

Disturbances affect ecosystems by killing plants and animals and changing environmental conditions such as light and nutrient availability. As a result, different kinds of species are able to survive than were there before the disturbance. Over time the kinds of plants and animals living in an ecosystem will change, and this change is called succession. Succession happens because plants and animals alter the environment around them and influence which species are capable of growing in an area next.

Before the arrival of Europeans, natural disturbances like windstorms and fire played an important part in the dynamics of ecosystems in southwestern Michigan. Natural disturbances usually do not affect an ecosystem the same way everywhere. For example, a fire might burn very hot in some places and not at all in others, leaving a patchwork of burned and unburned areas. Over a long period of time, landscapes become a mosaic of ecological communities, each differing in age depending on how long it has been since the last disturbance took place. This kind of mosaic increases the kinds of habitats that are available for plants and animals, which increases the diversity of species across the landscape.

1900 1950 2000

Figure 1. Patches of forest may have been burned by fire (or disturbed by wind) at different times in the past. The result is a mosaic of forest patches on a landscape with different ages of trees.

II. Human disturbance

The landscape that we live in today is also a mosaic of ecological communities, but the patchwork is created almost completely by human land use and very little by natural disturbances. Many European settlements in southwestern Michigan about 150 years ago (AD 1850) and dramatically altered the ecosystems that were here. There are four main ways that human land use affects ecological communities:

1)  Prevent plants and animals from growing at the site completely. [Greatest impact]

Examples: paved roads, houses and buildings

2)  Restrict ecological communities to only a small number of selected species.

Examples: agricultural crops, golf courses and lawns, forest plantations

3)  Allow plants and animals to return to areas that were previously managed.

Examples: abandoned farmland and woodlots

4)  Maintain areas that have never been disturbed by humans. [Least impact]

Examples: wilderness areas

III. Questions for study of land use and succession around your school

When studying succession around your school, you can focus on the effects of human impacts on ecosystems across the entire landscape. Some important questions to think about might be:

·  Which kinds of human impacts are most common around your school? Why are they so common?

·  Where are the areas that have been disturbed the least? How old are they and why haven’t they been disturbed?

·  How has land use affected the forests in your community? Are the sizes and types of trees the same in all forests?

·  Are agricultural areas all in the same place in your community or are they spread out over the landscape? Why might this be?

·  Where are ecological communities that are similar to each other? What plants and animals grow there? Can those plants and animals make it to other, similar habitats?

·  How does the pattern of land uses around your school impact the quality of water that you drink? How does it impact the quality of water in a stream or pond or groundwater?

Historical air photo interpretation -- Student Activity

One way to determine the impact of human activity across landscapes is to study photographs taken on the same place over a period of time. Air photographs were taken for the entire state of Michigan at various times over the past 70 years and are a great source of information on how the landscape and its ecosystems have changed. The photographs for this activity come from the Imagery Archive from the Center for Remote Sensing at Michigan State University. **Update: there is a fee for aerial photos through MSU, contact or 517-355-3771 to see if this fee can be waived.

I. Preliminary observations

Take a look at a series of air photographs for one location.

1)  Identify a significant feature that has not changed over the years. This will give you a frame of reference for looking at the change.

2)  Determine your “study area” and draw its boundaries on each air photograph.

3)  Study the photographs and become familiar with the different kinds of land use categories that could be found in each of the photographs. Which are most common?

  1. Residential

smaller buildings arranged along streets

  1. Commercial/Industrial

buildings, factories, parking lots

  1. Agricultural

rectangular fields, fences

  1. Open spaces

parks, golf courses, etc.

  1. Forested

continuous tree cover

  1. Water

lakes and streams

  1. Other? Describe here:


II. Record your observations

In the tables below, record the most common land uses that you found in your photographs. Include under comments any information that you think might be important when interpreting the changes that took place over time.

Date:

Land-use category / Comments

Date:

Land-use category / Comments

Date:

Land-use category / Comments

III. Questions

1)  What were the major changes that you observed in your photographs?

2)  Compare your observations with those of other groups. Did all of you see the same changes?

  1. What was the same?
  1. What was different?

3)  How do you think the changes of the past 70 years affected populations of plants and animals? Choose two examples and explain.

4)  How do you think the changes of the past 70 years affected water quality in the lakes and streams around your school?

5)  What do you think will happen in the next 50 years?