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Tropical Rainforest Trees: Buttress Roots

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Author: Tricia Edgar

How do roots help a tree stay upright? In the tropical rainforest, some trees have roots that stick out at the base and on top of the ground called buttress roots.  Do these aboveground roots help trees stand tall?

Problem: Do buttress roots provide more support to trees than underground roots?

Materials

  • 10-inch long, thin dowel
  • 12 pipe cleaners
  • Scissors
  • 3 small squares of floral foam
  • Hair dryer
  • Plastic ruler

Procedure

  1. First, place your dowel on the top of one of the pieces of foam. Balance it there.
  2. Turn on the hairdryer and point it at the dowel from about 2 inches away. What happens?
  3. Next, take the plastic ruler in your hand and pull it backwards about half an inch, releasing it so it hits the dowel. What happens to the dowel?
  4. Now, you’ll create some roots for your dowel tree. Cut a pipe cleaner into two-inch-long sections and wrap them around the bottom of the dowel. Place the “roots” into the floral foam as pictured in the diagram. Turn on the hairdryer and point it at the dowel from about 2 inches away. Next, take the plastic ruler in your hand and pull it backwards about half an inch, releasing it so it hits the dowel. What happens to your tree?
  5. Finally, design some buttress roots for your tree. Cut several pipe cleaners in half and wrap them around the middle of the dowel tree. Sink the ends into the floral foam so that they’re just barely extending into the foam. Turn on the hairdryer and point it at the dowel from about 2 inches away. Next, take the plastic ruler in your hand and pull it backwards about half an inch, releasing it so it hits the dowel. What happens to the dowel?

Buttress Roots Diagram

Results

Buttress roots provide more stability than the underground roots.

Why?

In different ecosystems around the earth, the soil is very different. In Arctic areas, the soil is often frozen, and when it thaws, you’ll find squishy, boggy conditions in the summer months. In temperate zones, debris rains down onto the forest floor, forming a thick layer of soil. In these zones, some trees have webbed networks of roots, while others have a large, deep taproot that sticks down into the ground.

Because the soil is different, the trees in these forests are different too. Trees are woody plants, which means that they not only use the wood inside them to move water and nutrients around but also use it for structural purposes. Inside the tree, xylem tissues act like straws to move water inside the tree. When the working xylem cells die, new cells take their place. The old cells become heartwood inside the tree. Heartwood is the dry, hard wood that helps the tree stand up.

Some places have few or no trees because they are too cold. Other places have a variety of hardwood (deciduous or broadleaf) trees and softwood (coniferous) trees. In the tropical rainforest, most of the nutrients are housed in the plant and animal life. The soil is actually fairly thin and poor. 

When you built a model tree without roots, it easily fell down. Roots help take nutrients from the soil, but they also help hold a tree up. What can trees do in areas where the soil is thin?

Since roots in the tropical rainforest don’t necessarily extend very far into the ground, trees need a strategy to stay upright, especially if they are very tall. These tall trees poke out through the forest canopy and form the emergent layer. The tall trees in the rainforest often have buttress roots on their sides. Buttress roots allow a tree growing on thin soil to grow high into the air. They provide support for that tree, preventing it from falling down. Some trees grow in areas that are particularly challenging, like swamps. These trees may also have roots that look like stilts and extend down from the branches into the soil below.

Going Further

Try the experiment again, this time with stilt roots that come down from branches on your tree. Experiment with different aboveground and underground roots. Can you create a combination that is very sturdy? 

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