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This week let's continue tree science by investigating water movement through trees, and learning how to measure the height of a tree.

1. Tree Transpiration

Transpiration is a fancy word for the movement of water out of trees and other plants. Did you know that almost twice as much water enters the atmosphere through plants as through the surface of the oceans? (Another benefit of trees!)

Gather:

  • a nearby tree (outside) with branches you can reach
  • clear plastic baggy for each child
  • chenille or twist tie to hold bag around branch (enough for each child)

You might want to gather enough of these materials to compare branches on different parts of the tree and/or branches on different types of trees. (You will see the best results on a hot, sunny day.)

Place the bag over the tip of a branch so that it contains at least one leaf. Use the chenille or twist tie to close the bag around the branch to hold it closed. Make a prediction about what will happen. Now wait for 15 or 20 minutes and check the bag. See anything? Try again after 1/2 hour.

The bag should fill with moisture and condensation. Each tree leaf has tiny holes called stomata. Moisture exits the holes not only to cool the tree (like our sweat does for us), but also to help plants move materials up from the roots.

Were there any differences between different parts of the tree or different kinds of trees? What do you think would happen if you did the same experiment at night?

You can also perform this experiment indoors if you place a cut tree branch in a water-filled vase. Be sure to place the tree branch in a sunny window or under a bright lamp to encourage water movement into the plastic bag.

Extension (for older students):

Make up and perform experiments to test the factors that influence transpiration:

  • temperature
  • sunlight intensity
  • water supply
  • tree growth rate

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Where does the water come from?

Most plants and animals need a lot of water every day. Trees absorb the water they need through their roots and then move it up to the leaves through the xylem.

2. How far does the water have to travel from roots to top of the tree? Let's learn how to measure the height of trees.

There are several different methods to measure the height of any tall object, including a tree.

Method 1 (requires math):

Gather:

  • a stick
  • a tree that is apart from other trees (so you can see its entire shadow at least one time of day)
  • tape measure (longer the better)
  • paper and pencil

For this activity, you will need a sunny day. Place the stick upright in the ground near the tree. Use the tape measure to measure the height of the stick from the ground, and the length of the resulting shadow from the base of stick. Also measure the longest length of the tree's shadow from the base of the tree. Assuming the two ratios are the same, solve for the height of the tree by multiplying the length of the tree's shadow x (the height of the stick/the length of the stick's shadow). See the illustration:

tree-height2

I found this video that discusses two other methods. You will need a second person to help you and a measuring tape.

Now, how far does the water need to move? If you take into consideration that a tree's root may be a large or larger than its crown, then a tree one hundred feet tall may have to move water two hundred feet or more. That one big straw!

Let me know if you have any questions or other methods for measuring trees.

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I'm "sprucing" things up here at Growing with Science in preparation for hosting the Festival of the Trees Carnival at the end of the month. For the next few weekend science fun posts, we'll be learning about trees and doing some fun tree science activities.

I. What is a tree?

Most of us recognize a big tree when we see one, but sometimes it may be hard to tell whether a plant is a large shrub or a small tree. What do you think? Brainstorm and write down all the words you use to describe a tree.

One definition might be "a tree is a perennial, woody plant that grows to at least 20 feet tall and has an erect (straight up) main stem." Talk about what that means and if all the trees you know will fit this definition. Can you think of something more? Let us know what you decide.

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II. Why study trees?

Trees are so important. Can you think of a list of benefits of trees? Here's just a few we thought of:

  • shade (really important in Arizona!)
  • food and shelter for wildlife
  • rubber
  • paper and paper products
  • source of wood products such as furniture, houses, pencils, musical instruments
  • food for us
  • fuel for heating
  • medicines such as aspirin and quinine
  • produce oxygen
  • conserve water
  • reduce pollution

Can you add to this list? Do some research to find more benefits of trees.

III. External parts of a Tree

Vocabulary:

  • bark
  • trunk
  • crown
  • leaf/needle
  • branches
  • roots
  • twigs
  • nuts
  • fruit
  • flowers
  • buds

Make index cards with each of these names (make sure you have at least one card for each child participating.) Punch holes in the cards with a hole punch.  Cut pieces of yarn of various lengths. Find a tree outside and have the children attach the cards to the correct parts with pieces of yarn - a fun way to decorate a tree. Take extra cards and draw any parts that are missing, such as flowers, nuts or fruit. Add those to the tree where they might be found. Older children can discuss the function of each of the parts, such as roots hold up the tree (support) and bring water into the tree. (Scissors speed up card removal when you are finished.)

tree-parts

Sketching trees is a good way to learn the shape of different kinds. Claire Walker Leslie has an excellent guide to sketching trees (click on the Guide to Tree Sketching resource to download a .pdf file). Sketch a tree and label the parts if you can't go outside.

IV. How Trees Grow - The Internal Parts of a Tree

See if you can find a "tree cookie," a cross-sectional piece of wood through a tree trunk. These are often available at craft stores. Those with the bark still on are the best.

Internal parts of a tree:

  • cambium - layer of active cells that divide to form inner bark and sapwood
  • sapwood
  • xylem - water carrying elements (in sapwood)
  • phloem-food carrying elements (inner bark)
  • heartwood

Look at the tree cookie and see how new rings are added each year. Explain how the tree only grows from the cambium and cutting it (for example by carving initials on a living tree), damages its ability to grow and live. A fun demonstration of how a tree grows might be to add layers of clothes to a doll or person, to show how the tree expands by adding layers. See if you can tell how old the tree that made the tree cookie was when it was cut down by counting the rings. (More information on internal parts).

We'll continue with more activities next week. Until then, here are two sources of more information about trees:

Illinois Department of Natural Resources has  lesson plans in .pdf format

Arbor Day Foundation has education links and online games.

Hope you enjoy our celebration of tees this month. If you have any suggestions for activities or websites, please let us know.

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