- Possible Questions
- Why Is There Always Enough?
- Students will learn what helps and prevents grasses from growing.
Grasses are adapted to the environment. While most plants grow from the top, grasses grow from the bottom and will not die off due to grazing because they replace lost parts by “pushing up” the surviving parts that have not been eaten by animals. Burning actually mimics a natural process and places rich nutrients in the soil allowing grasses to grow back. Grasses not receiving light will wither and die over time.
- Piece of string or ruler (for measuring)
- Four similar patches of grass close together
- Bucket (or other items to cover a patch of grass)
- Water (also for fire)
Gather above materials.
Take students to the four patches of grass. In their notebooks, have students either describe or sketch what they see. Tell the students that you are going to do different things to each patch, and they’ll need to hypothesize (predict) what will happen in their notebooks.
Measure the grasses with a ruler or length of string. (Tie a knot at the spot in the string where the grass is the highest for comparison purposes later.)
Clip the first patch close to the ground (or have a student do this). Burn the second patch. (Use caution and be sure there is water on hand. Do not allow the fire to go beyond the patch.) Cover the third patch with a bucket. Water the fourth patch regularly. Which will grow the fastest? The slowest? Which will look the healthiest? The weakest?
Check the progress of the patches frequently over the next few weeks. Use the ruler or string to see how long it takes for plants to return to their original height. Have students record the changes in each in the form of sketches or descriptions.
The precipitation is so erratic that drought and fire prevent large forests from growing. Grasses can survive fires because they grow from the bottom instead of the top. Their stems can grow again after being burned off. The soil of most grasslands is also too thin and dry for trees to survive.
- Did any of the results surprise you? Why?
- How are grasses different than other plants?
- If you needed to grow grasses quickly, what would you do to them?
Why Is There Always Enough?
Have you ever wondered why there is always enough grass for all those big grassland mammals to eat? Do the following experiment with your students:
Choose two patches of grass that are similar. Use wire to make a protective covering over each patch to keep animals out. Water the grass every other day until it is about 5 centimeters (2 in) tall. Using scissors, cut off the tops of the grass in one patch. Don’t do anything to the second patch of grass. Continue watering every other day and observe each patch for changes for one week. Have students record their observations. After three weeks, evaluate your data and observations and have students write a conclusion. Guide your students in concluding that grassland mammals are merely giving the grass a “haircut.” Help students understand that as long as the roots are left undisturbed, the grass will continue to grow, providing a constant source of food for mammals to eat.
Soil Erosion Project
Students will understand what causes soil erosion and what we can do to prevent it.
- 3 cardboard boxes of the same size
- plastic bags
- grass (with roots and good soil)
- dry soil
- 2 cups
- graduated cylinder
- three bowls
- Line the cardboard boxes with the plastic bags
- Fill one box with the healthy soil and grass
- Fill one box with the dry, unhealthy soil and grass
- Fill the last box with a mixture of the good and bad soil and grass
- Cut the plastic cups in half
- Cut a semi-circle hole in one side of the box
- Tape the half of the cup into the semi-circle cut in the box
- Place stones under one side of each box so that the boxes are on a slant
- Place a bowl under each of the spouts formed by the plastic cups
- Fill the graduated cylinder to the 50-ml mark and pour on the well-conserved grass
- Repeat for the other two boxes
- Do three rounds of pouring water on the boxes
- Analyze the results
- Did you see a difference in the amount of runoff in each of the bowls?
- Which box produced the most runoff and why?
- What are some of the problems caused by soil erosion?
- What can we do to prevent soil erosion?