What it shows
A census records every tree in an area with its species, girth and canopy, the same way city forest departments do. The data show which species dominate, which trees are oldest, how much ground is shaded, and where new trees would help most.
The science
Girth at breast height, 1.3 metres above the ground, is the standard measure of a tree's size; it grows a little every year, so bigger girth usually means an older tree. The canopy diameter, measured from the shadow at noon or by pacing under the branches, gives the shade area as pi times the radius squared. Adding canopy areas shows what fraction of the ground is shaded, which cools the campus and cuts dust. A species list shows whether native trees that feed birds and insects are present.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A measuring tape
- A notebook or a printed census sheet
- A tree identification guide or a plant app
- Chalk or ribbon to mark counted trees
- A sketch map of the ground
- Graph paper
Safety
For this project: Do not climb trees or pull branches. Watch for ants and bees on trunks.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Draw a sketch map of the ground and divide it into four zones.
Walk each zone, mark every tree with chalk as you count it, and number it on the map.
For each tree write its species, using the guide or an app, and mark it native or exotic.
Measure the girth with the tape at 1.3 metres from the ground.
Pace or measure the canopy from one edge to the other in two directions and average them.
Calculate each canopy area and add them up for the whole ground.
Make a species bar chart and a table of the five largest trees.
Mark on the map three sunny spots where new native trees could be planted.
What you should see
A map and table listing every tree, a species chart, a total shaded area as a percentage of the ground, and a planting proposal.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why measure girth at 1.3 metres?
It is the standard height, above root flare and buttresses, so trees can be compared.
2How do you estimate shade area?
Measure the canopy diameter and use the area of a circle.
3What is a native tree?
One that naturally grows in the region, such as neem, peepal or jamun.
4Why do native trees matter for birds and insects?
Local wildlife evolved to feed on them; many exotic trees give little food.
Take it further
Repeat the girth measurements a year later and see which trees grew most.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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