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Activity: Measuring the Height of a Tree

Trees are the elephants of the plant family. Their long, woody trunks transport water and nutrients from the soil high up to the branches and leaves, which make up the canopy or crown of the tree.

The tallest tree in the world is a **Giant Redwood ( Sequioia)** in Northern California in the United States. It is 115.61 metres tall.

#### Trees of Uganda

**The tallest tree in Uganda** is the ** Entandrophragma excelsum**. It is a deciduous tree which grows in the montane forests of the Rwenzori and Virunga and can reach heights of 60 metres. Below is a picture looking up from the base of the tree.

Other big trees that are found in Uganda include :

**The Baobab**

This can grow up to 30 metres high. The Baobab tree is also called the upside-down tree, because its branches look like roots, and it appears as if the roots are pointing up to the sky.

Baobabs can survive long, dry periods because they store water in their trunks. For this reason elephants and antelopes chew the bark of the baobab in the dry season when they are thirsty. Animals eat the seeds of the tree, which are very nutritious, and weaver bird like to build their nests in the trees. Baobab trees can live for over a thousand years!

**Sausage Tree ( Kigelia Africana)**

The sausage tree grows up to 20 metres. It is found in tropical and wet savannah regions and often grows close to rivers, because it needs a good supply of water. The tree produces large flowers, which bloom for up to 2 months and are pollinated by bats. The sausage-shaped fruits are one of the largest fruits in the plant kingdom. They can grow up to 1 metre in length and weight 10 kgs. The leaves are eaten by elephants and antelope. The wood of the tree has been used in the past for building canoes.

**Borassus Palm ( Palmyra)**

Produces a fine specimen trees of up to 30 metres in height.

The Borassus Palm is found in grassland, where the water table is high. The leaves of the Palm are used for thatching roofs, making mats, sweeping brooms, baskets and hats. The fruit can be eaten fresh or dried and cooked and fruit juice can be extracted. It is also made into palm oil and, after processing, the excess oils provide raw materials to make soap and the residue is used for manure.

In some places the sap is made into palm wine or vinegar.

Elephants like the fruit, especially after it has started to ferment!?

**Mutuba ( Ficus natalensis)**

This is an evergreen or partly deciduous tree with a wide, spreading crown, that can grow up to 30 metres tall. The Mutuba tree (pictured left below) is special because part of the bark can be removed each year and it will grow again. Once removed (pictured right below) the bark is turned into bark cloth, to make the ceremonial dress of the Baganda. It is also turned into a variety of craft products and sold in the tourist industry.

A single tree can be harvested for up to 40 years and yield up to 200 sq. m of cloth. Each year after harvesting the bark, the areas must be wrapped around in plantain leaves to prevent the tree from drying out.

**Activity: Measuring the height of a Tree**

**Task for students:**

Work out a method you could use to work out the height of a tall tree?

The topic of trigonometry in mathematics might give you some ideas.

Once you have worked out a method, go out and measure the height of some trees around the school.

*Teacher: If your students cannot come up with a method here are two to compare:*

**45 Degree Angle Method**

Fold a square piece of paper diagonally to form a right angle and two 45 degree angles.

Using the hypotenuse as a sight line, walk back from the tree until the sight line points to the top of the tree. Measure the distance from where you are standing to the base of the tree, then add your height from the floor to your eye. The results will be a pretty good estimate of the height of the tree.

**Pencil Method with Similar Triangles**

- Find a pencil or a short stick (measure its height, b in the diagram).
- Hold the pencil in your outstretched arm (measure the distance from your eye to the finger of your outstretched hand, this is distance a).
- Stand far enough back that the tree height fits the length of the pencil. The base of the pencil should be in line with the base of the tree and the top of the pencil should match the top of the tree.
- Measure the distance from your eye to the base of the tree (this gives distance c).
*NOTE – if you are measuring a very tall tree, the distance will be roughly the same as the distance from your feet to the base of the tree.* - Use the formula above to estimate the tree height.