Trees Please, Pt. 2: Above Ground

(Judy Herman)

Along the Path: A Young Person’s Guide to Exploring Nature

By Susan Rothrock Deo

“I don’t know if you know this, but trees are like us. They talk like us. This is why I’m very careful about cutting them down. People hurt them a lot. If I cut down a tree, the kin will ask, ‘Why did you kill my brother?'”

–Ntoni, leader of the Kīsêdjê people, an indigenous tribe of the Amazon rainforest, 2008 (Quoted in Environmental Defense Fund Special Report, Spring 2021)

Last time, we looked at trees from below the surface; now let’s look at the parts we know best, above ground. First is the long, tall trunk with branches. There may be one straight trunk or multiple ones. Branches may be symmetrical and high up, or low and spreading and, occasionally, haphazard and “creative.” Some of this is determined by genetics and some by the environment.

Some trees, like figs, have multiple trunks. (Susan Deo)

As a tree grows, it builds the structure of its trunk and branches, adding more material year after year. This is wood, one of the strongest, most resilient, and flexible materials on the planet. It’s so versatile that we humans use it for many things such as building houses, boats and musical instruments or carving into art. Have you ever studied the shape of a tree, the texture and color of its bark? In wintertime when there are no flowers or leaves, you can look at the bark and the general shape of a tree to determine its species. Is the bark smooth? Bumpy? Peeling? Is it white? Brown? Mottled?

Bark protects trees from pests. The silk floss tree goes even farther, producing thorns, not just on the trunk, but also on branches like these. (Judy Herman)

The outer layers, just under the bark, are alive. As the tree grows a new outer sheath is added and the inner, no longer alive rings become the woody skeleton that holds the tree upright. This living sheath grows new branches and repairs gaping holes from damaged ones.

(Susan Deo)

As a general rule, a tree has about as many leaves as there are hairs on your head. The green leaf (or needle on the conifers) is the tree’s food factory.

 “A leaf is filled with chambers illuminated by gathered light. In these glowing rooms photons bump around, and the leaf captures their energy, turning it into the sugar from which plants, animals, and civilizations are built.”

“The Glory of Leaves,” National Geographic Magazine, October 2012

Leaves harness the sun’s energy to make sugar from carbon dioxide and water. Some of this energy the trees use themselves to grow more wood and leaves, to produce flowers and fruit. But it’s not only the tree that uses this sugar manufactured in its leaves. Leaves are food to almost every living thing on Earth. 

In a dense forest, a tree will most often grow tall and straight, reaching toward the canopy so its leaves can gather as much of the sun’s energy as possible. A single tree on its own in your yard or a park, without the competition of other trees, will grow broad and bushy. If you stand beneath a tree and look up, you will see a mosaic of leaves aligned so each has the most exposure to the sun, with little overlap. Upper leaves are smaller as they have more direct sunlight; lower leaves are larger.

Magnolia leaves orient for maximum sunlight. (Susan Deo)

Have you noticed how much cooler it is if you stand beneath a tree? The canopy intercepts about 90% of the sunlight streaming down, but there’s more. The tree is cooling the air as well. On the underside of the leaves are tiny openings called stomata. The leaf can close or open these stomata, depending on its needs. The leaves make sugar with water pulled up from the soil through its roots and carbon dioxide pulled from the air through its stomata. They release the leftover oxygen into the air through the stomata as well. (Thank you, trees. We animals need this oxygen to survive!) And at night, when there is no sun, trees take in oxygen to “burn” some of the sugar they’ve stored for energy. The leaves lose more than oxygen and carbon dioxide through their stomata, though.

Trees provide shade and beauty.

Up to 99% of the water that reaches the leaves from the roots is lost through the stomata also. As this water evaporates into the air, it cools the air. This is called transpiration. Since most of the stomata are on the underside of the leaves, it is the air BELOW the canopy that cools. Evaporation of water from the soil beneath the tree also contributes to cooling. Trees create their own natural air conditioning! 

(Susan Deo)

So, let’s plant a tree! Or two! Here’s another reason: a typical hardwood tree, like a maple or oak, can absorb as much as 48 pounds of carbon dioxide in a year. This means it will sequester approximately ONE TON of carbon dioxide by the time it reaches 40 years of age. Forest ecosystems are the largest terrestrial carbon sink on planet Earth. Trees and forests are very important for combating climate change.

So many reasons to love a tree! No wonder I never met a tree I didn’t like—and maybe you won’t either.

Further Resources

More on how transpiration works:,sunlight%20and%202)%20transpiration%20cooling.

Forests and Carbon Sequestration

Watch a BBC film hosted by Judi Dench, “My Passion for Trees,” that illustrates some of the wonder of trees.

For the young person in your life, or for the adult who wants to learn more, explore “gardens in the sky” in the California Redwoods in this counting picture book. The back notes are chock full of great information to study redwoods and the animals that live in their gardens in the sky, including reference to the video below. 
Tall Tall Tree by Anthony D Fredericks, illustrated by Chad WallaceDawn Publications, 2017

Visit the sights and sounds of California’s redwood forests in this 7 minute 41 second YouTube video, Redwood Forest Relaxation HD Video-Nature Sounds 1080p HD

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