Forests, water, and our world

Happy Earth Day!

In honor of Earth Day, Arbor Day, and Earth Week, iSchool students learned about the importance of forests.  The activity is a fun, dirty, outdoor, hands-on exploration of forests using a model of a hill.  It’s also great for family science time. Be careful – you will get dirty!


– Boxes or pans
– Shovel
– Spray bottles or watering cans
– Sticks, leaves, branches (and possibly clippers to cut them)
– Soil or dirt
– Food coloring (if desired)

To get started, find two boxes in which to make your hill.  I used a recycled cardboard box, which I cut diagonally into two pieces.  I have also done this activity using high baking dishes. I lined the bottom of each box with a white plastic bag.  This makes each box a bit more hardy, but the white bottom also allows students to see the water and dirt more clearly.  Put a couple of shovel-fulls of dirt – any kind – into the corner of each box and pat into the shape of a hill.

"Hills" ready for an experiment
“Hills” ready for an experiment

During class, ask students to discuss the importance of trees.  Depending on their age, students will discuss topics such the role of trees to oxygen production, animal and plant habitats, natural resource use by humans, providing shade, and others.  This lesson explores the role of trees and forests to water and land.  Then the fun begins!  I sent my older students out to clip small branches and leaves to make “trees”. (For my preschoolers I provided these). Then, they stuck those branches into one of the hills, leaving the other bare.

"Planting" trees on the hill
“Planting” trees on the hill

I asked the older students to predict what would happen when it rained on each hill. Then, the students let loose with the spray bottles and small watering cans, spraying water (which I colored blue using food coloring) onto both hills. We then compared the differences and discussed the implications.

Making it rain with spray bottles
Making it rain with spray bottles

After comparing the resulting wet hills we noticed several things:

1. Water quality – The water that drained off the forested model had noticeably clearer water – you could see through the blue water to the white plastic below. The bare hill produced a cloudy, light blue water. We discussed how trees leaves reduce the force by which water hit the ground, create less splash, and reduce erosion.
2. Water storage and amount – The amount of drained water at the bottom of the forested model was noticeably less than the amount of water in the bare hill model. We talked about how forests slow down water flow and “store water” through a variety of mechanisms, including storing it on leaves and slowly supplying water to the ground, channeling it to the ground via the trunk, and allowing more absorption into the soil.  Conversely, bare areas allow water to run off the surface rapidly and exit a watershed into a downstream river or ocean (where it cannot be used by humans) more quickly. We discussed how this might contribute to water shortages in some places.
3. Landslides – After the “rain” stopped the bare soil hard large cracks.  I used my hands to easily dislodge pieces of mud to demonstrate what a landslide looks like. The forested hill had no cracking. We also discussed current events, such as a landslide in Washington State, and used the model to illustrate the difference between selective logging (pulling out a few large sticks) and clear cutting (taking out all sticks from a small portion of the hill).
4. Flooding – Building on the findings of water storage, it was also clear to see on the bare model that areas without trees might be more prone to flooding. There was more water at the bottom of the bare hill, and it had accumulated there in a short time.
5. Quality of life – We discussed how everyone in class would find living in the forest nicer than living on a bare hill.

There is so much to learn from this one activity!

The forested hill after the rain
The forested hill after the rain
The bare hill after the rain (and after a human-induced landslide)
The bare hill after the rain (and after a human-induced landslide)