Roots and soil · Rainforest ValleyScience for kids

How do tree roots protect soil and rivers?

In short: Tree roots form an underground net that holds soil together, so riverbanks and hillsides are less likely to wash away. But to make a river clear again, planting its banks isn't enough: slopes upstream must be protected so less mud washes in.

Roots and soil: a nature card illustration

How it works

Roots come in all sizes. Thick roots anchor deep into the ground, while fine roots wrap around soil crumbs like thousands of threads. Just as steel rods make concrete stronger, roots make soil much harder for rain and rivers to wash away.

Plants along a riverbank are especially important. Their roots stop the current from eating away the bank, their leaves shade the water so it doesn't get too warm, and the leaves and insects that drop in become food for fish and tiny water creatures.

But if hillsides upstream are bare, every storm washes lots of mud into the river, and planting downstream can't stop it. Mud makes the water murky and smothers the stones on the riverbed where insects live and fish lay eggs. So repairing a river means caring for its whole catchment.

Where to see it in New Zealand

On many New Zealand farms, streams are fenced off so cattle can't trample the banks, and the banks are planted with native plants such as harakeke (flax), tī kōuka (cabbage trees) and sedges. Many schools and community groups help with this kind of riverbank planting.

Try it together

Fill two paper cups with soil. Sprinkle grass seed in one and leave the other bare. Keep both on a windowsill and water them regularly. After two or three weeks, gently tip both out. Does the soil with grass roots hold together while the bare soil crumbles?

Kids also ask

Why is muddy water bad for fish?

Mud blocks sunlight so water plants struggle, fills the gaps between riverbed stones where insects and fish eggs shelter, and can clog fish gills, making it harder for them to breathe.

Are more trees always better?

Choosing the right plants for the right place matters more. Along riverbanks, native plants with strong roots work well, because they suit local conditions and feed local birds and insects.

In the game, “Roots and soil” is a nature card on Rainforest Valley.

Your child finds this card by reaching the right place or meeting the right weather on the island, and lights it up by answering the question on the back. Tap the button below and the game shows your child which island it is on and how to find it. Mochi Isle is a browser learning game for ages 5 to 18; the main island and the daily lesson are free.

Find “Roots and soil” on the island ↗ All cards from Rainforest Valley