On this page teachers and parents will find background information and activities that correspond to the subject on the 'What's New' page. Currently the topic is 'Fall Colors'. The data compiled here was provided by Elsie Sellars. If you have any questions or would like help with other activities please contact us.

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Trees are plants and that’s where the generalizations stop. Trees share many similar characteristics, but they don’t all fall into neat categories. Trees are essentially large plants, but there are exceptions there also. Trees are different sizes and shapes. There are over 20,000 different species of trees in the world with about 800 types in North America.

Some botanists use size to differentiate trees from other types of plants. They say trees have a main stem (trunk) that is at least three inches thick and grow to at least fifteen feet tall. The exceptions to this generalization are trees that grow in harsh climates such as deserts or extremely cold and windy environments.

Trees can be deciduous or evergreen. Evergreen trees, such as pines, gradually lose their leaves (needles) throughout the year. The leaves are always being replaced so the tree is never bare. Deciduous trees lose all of their leaves every year, generally in the fall. The leaves "change" color before dropping or "falling" off.

 

Let’s take a look at the parts of a tree by starting with the trunk and then working towards the center.

The trunk acts as a support rod for the tree. It gives it its shape and strength. The trunk also holds the plumbing system for the tree. It supports the network of tubes that carry food from the leaves down to the roots and water and minerals up to the leaves.

The outermost layer of the trunk is the outer bark or bark. It can be a variety of textures such as smooth, rough, scaly, or more. No matter how it feels, bark serves to protect the tree from injury and disease.

Next in is the inner bark or phloem. This thin layer acts as the food supply for the tree. Water containing dissolved sugars and nutrients called sap, travel down the phloem in the leaves, branches, and trunk to nourish the tree. Stored sugars in the roots also travel up the phloem to the rest of the tree.

The cambium is a very thin layer (only one or two cells thick) next to the phloem. This is the growing layer of the tree. It’s what makes the trunk, branches, and roots grow thicker.

The next layer is the sapwood. It is made up of the youngest layers of wood. This is the layer that forms the pipeline that carries water and minerals up the tree from the roots to the leaves.

The last layer makes up most of the trunk. That layer is called the heartwood or just wood. The heartwood is dead wood and is old xylem that no longer functions and is now filled with a resin-like material. The heartwood is often darker than the sapwood.

A tree has branches underground. These are called roots. They spread out to help anchor the tree and absorb water and minerals from the soil. Some trees have large taproots, which grow straight down to "tap" into water below. Other trees have lateral roots, which spread along just under the surface of the soil.

 

Here’s a quick review of the phenomenon that is so striking and regular that it gives its name to the entire fall season.

In autumn, the leaves of the aspen become sealed off the rest of the tree. Deprived of nutrients and moisture, the leaves cannot form new chlorophyll. The old chlorophyll breaks down, and the green color disappears. The yellow pigment, present all along but masked by the green chlorophyll, is revealed as it begins to dominate.

The main reason for this annual shedding of leaves is to conserve moisture. Broad leaves, with their large surface area, lose approximately 99% of the water the roots absorb from the soil through the leaves in a process called transpiration. The freezing of the soil in winter cuts off the supply of moisture to the roots, and water conservation becomes very important. If broad-leaved trees retained their leaves, they might become fatally dried out.

Conifers have a much smaller surface area with their needle-like leaves and can survive without dropping their leaves. They actually survive by keeping their leaves because they use their leaves in photosynthesis on mild winter days.

The seasonal shedding of leaves is directed by a combination of shortening hours of daylight and cooling temperatures that reach a critical point. A deciduous tree responds by creating a barrier of special corky cells where the leaf stem joins the twig. The leaf slowly dies as it is sealed from the tree’s circulatory system. Its attachment weakens and it drops from the tree. Another layer of specialized cells seals the tiny wound left when the leaf drops. This new layer protects the tree against loss of moisture and the entry of fungi.

 

bark: The outermost layer of the tree trunk.

cambium: The thin layer of cells next to the phloem that makes the trunk, branches, and roots of a tree grow thicker.

chlorophyll: The green plant pigment that absorbs the sunlight needed for photosynthesis.

conifers: Those trees whose seeds develop inside cones. Conifers are evergreen trees.

deciduous trees: Those trees that lose all of their leaves each year, such as aspen trees.

evergreen trees: Those trees that do not lose all of their leaves each year, such as pine trees.

heartwood: Sapwood that has become filled with resin-like material and no longer transports water and minerals. It may also be called old xylem.

phloem: The pipeline of cells that transports sugar and nutrients to all parts of a tree. It may also be called the inner bark.

photosynthesis: The process which plants use the sun’s energy to convert carbon dioxide and water into sugar (food).

sapwood: The most newly formed layer of wood. It is made of thick-walled cells that transport water and minerals. It may also be called new xylem.

Roots are underground branches that soak up water and dissolved minerals that the tree needs for nourishment.

stomata: The small pores in a tree’s leaves and stems that open to absorb carbon dioxide and release oxygen.

transpiration: The process by which a tree loses water through stomata on its leaves and stems.

trunk: The main stem of the tree that provides support and contains the pipeline for the transport of water, food, and minerals.

xylem: The conducting cells in a tree that carry water and minerals to the trunk, branches, and leaves.

 

1. Have students select a tree on the school grounds that they can observe throughout the year. Visit the adopted tree periodically to observe seasonal changes and record those changes in a journal. Use drawings and words to describe what is seen.

 2. Bring in a selection of leaves and have the students describe the similarities and differences observed in the leaves. Have them sort, count, and graph what they observe.

3. Using construction paper or felt, cut out pieces of tree parts and have the students name each piece, name its purpose, and assemble a tree.

4. Assign each student to be a component of a tree and have them collectively create a tree using their bodies.

5. Have a "Treats from Trees" party with such treats as nuts, fruits, spices (cinnamon, cloves, and nutmeg), and candy (maple sugar candy and chocolate).

6. Make leaf rubbings using crayons.

7. Make leaf prints: Place a leaf on a sheet of paper; paint the leaf; place a clean sheet of paper over it; use the side of a bottle to roll over the paper; and carefully lift off the top sheet.

8. Make leaf splatter prints: Pin a leaf to a clean piece of paper; dip a hairbrush or other stiff, broad brush in paint and using a Popsicle stick, scrape the paint from the brush so that it splatters covering the paper; and carefully remove the leaf.

9. Review the terms evergreen (coniferous) tree and deciduous tree. Which ones are more common in your area. Make a display from both kinds from fallen leaves and branches.

10. Using photographs or fallen leaves, identify native trees in your area.

11. Visit a demonstration garden or nursery or review catalogs from nurseries or garden book. Decide which trees would be best to plant at your school yard. Consider the needs of the trees. Raise money to purchase a tree to plant at the school yard and make it a class project to care for it by monitoring its water needs and growth rate.

12. Measure the temperature in the shade of the tree and in direct sunlight. How do they differ. Do this at different times of the day for a school week. Chart or graph your results. Do this again in a different season and compare your results.

 

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