Staying upright in the rainforest
Requirements:
Students to work together in groups of 2-5.
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Two buckets or washing up bowls per group of students, one with a thin layer of sand or
gravel in the bottom, one with a thicker layer of sand or gravel.
Old newspapers or other large sheets of flimsy paper
Scissors
Sticky tape
Getting started:
Q: What are soils made of?
A: weathered bedrock, remains of plants and animals that have died, silt/materials brought
in by erosion or river floods
Q: In rainforest areas, where the climate is hot and wet and conditions are good for many
plants and animals, would you expect soils to be thick or thin? Why?
A: soils are often quite thin. This is because of a combination of factors. Some you might
have thought of include:
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The abundance of living things means high demand for food, so some of the
material that might otherwise rot into the soil gets eaten rapidly (e.g. fruit and dead
animals that fall to the floor)
Turning dead stuff into soil involves all sorts of living things, like worms and fungi.
There are lots of them in the tropical rainforest, and they are active all year round,
so decay processes happen really quickly.
And there’s lots of demand from the plants for the nutrients released by these
decay processes, so broken-down materials don’t remain in the soil for very long;
they’re used by plants and other sorts of life.
It rains a LOT in tropical rainforests. So that means that there is a lot of soil
erosion…
…and soil leaching, a process where nutrients and other soil chemicals produced by
the breakdown of rocks and dead matter dissolve into water and then flow away
into the rivers.
Briefing: In rainforest areas, the climate is very suitable for life. Plants grow quickly, and compete
intensely for light. Trees dominate the vegetation in the rain forest, because their stiff, woody
trunks allow them to grow taller than other plants. Because they are also competing with each
other, trees in rainforests tend to be really tall, without many side branches below the canopy.
Q Why is light important for plants?
A Photosynthesis – plants use light as an energy source to turn carbon dioxide from the
atmosphere into the building blocks for all the organic chemicals that make up a living thing,
such as sugars, proteins, enzymes, carbohydrates etc.
How do tall trees stay upright in thin soils?
Activity
Make two trees from newspaper.
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Take a few sheets of newspaper and, starting at the long side, roll them up fairly tightly into
a long tube.
Using the scissors, cut short slits along the length of the tube from one end (10-20 cm long,
about 1cm apart, all around the opening).
Now fan out the strips of paper at the top to make ‘leaves and branches’: you have a tree!
You can also pull upwards gently on the inside of the roll to make a longer tree. You’ll
probably need to trim the bottom.
Using small pieces of sticky tape, stick down the loose edge at several points to hold the
‘trunk’ together along its length.
o Making a tube for a trunk from brown paper then making a green tube and snipping
it deeply, then sliding it into the top of the brown tube, gives more attractive trees
o Or old kitchen roll or wrapping paper inner tubes can be used as the trunk, and
leaves added at the top with craft paper.
ROLL
CUT
FOLD &
TAPE
Try and stand one tree up in each bucket
You should find that, by burying the trunk in the sand, the tree stands up easily in the bucket with
deep sand, but is not very stable in the bucket with shallow sand. Blowing on the trees is a good test
of stability.
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You could also use an office fan as a challenge for all the different trees – can they stand up
to the ‘fan hurricane’?
Q: Evolution allows plants and animals to adapt to meet the challenges of their environment. Using
only one extra sheet of paper (which you can fold or cut), your scissors and sticky tape, can you
come up with some adaptations to help the tree in the shallow sand layer stand up?
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Students can cut slits into the base of the tube to make roots, fan them out and bury them
Students can also create various above-soil-level propping structures, like ‘rocket fins’.
Conclusion:
Images of rainforest trees showing aerial prop roots and buttress root development. Trees have
finite resources (remember, they are trying to grow as tall as possible and outcompete the others!),
so the best adapted trees are stable, but have propping systems which are made using the least
amount of resources possible, allowing them to still grow tall.