The How's and Why's of Trees

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Both trees and people living in the city endure exposure to similar adversities on a daily basis: pollution, limited space, disease, vandalism, injury. But, by learning the basics of the natural physiology of trees, you’ll discover how to help care for them, resulting in direct benefits for you, your family, and your community.

Basic Tree Physiology

0347623TreeRingsPhotosynthesis is the process by which trees develop their food. Energy from the sun mixes with carbon dioxide in the air, chlorophyll in the leaves (the pigment which makes them green), and water and nutrients from the soil to create the sugars necessary to feed the tree. In addition to making food from non-food substances, this system of nourishment is responsible for one other necessity of life: oxygen. Oxygen is "burned off" as a natural by-product of photosynthesis.

The tough exterior of the tree is called the bark. It is the "skin" which protects the delicate cell-producing layer beneath it called the cambium. The cambium produces the living tissue of the tree, called the sapwood. The sapwood forms the "highways" by which water and nutrients travel from the ground up to the leaves, and where the food—produced in the leaves—returns back down to the trunk and roots. Each year, the cambium creates a new layer of sapwood to replace the old one, which then becomes the wood of the tree and makes up its structure. This external layering creates an internal record of the tree's age. Look at a cross section of a tree (see illustration) and you'll see that each year's layer of cells creates a ring inside the tree. Each ring is equal to one year's growth.

Roots are a tree's foundation. Large roots not only anchor the tree to the ground, but they store sugars—the tree's source of energy. The fine root hairs and feeder roots growing from larger lateral roots collect water and nutrients from the soil. A mature root system can expand 1.5 - 3 times the width of the tree's aboveground canopy, though. Only about 40% of the tree's roots are underneath that canopy; the rest grow outside the canopy where they can access rainwater.

When the cambium or sapwood of the tree becomes damaged or is removed, the circulation of water and nutrients from the roots to the leaves, and that of sugars from the leaves to the roots, is interrupted. Photosynthesis becomes impaired and the health of the tree suffers. The same is true when foliage is damaged or more than half of it removed through inappropriate pruning. Even soil that is too wet, too dry, overly compacted or lacking nutrients can adversely affect the growth and health of the tree.

Only a healthy, well-maintained community forest can provide maximum benefits. Please make an effort to support the care and planting of trees in Claremont.

The Benefits of Trees

0127476TreeHouseFamilyReduction of Air Pollution: Leaves filter out particulate matter from smog-laden air, as well as odors, dust and other forms of pollution. Leaves also help clean the air by producing oxygen through photosynthesis.

Sound Barriers: An abundance of trees can muffle street and traffic noises.

Prevention of Global Warming: Heat from the earth is trapped in the atmosphere due to high levels of carbon dioxide in the air. Trees absorb and utilize the carbon from carbon dioxide, and store it as cellulose in their trunks and roots.

Increased Property Values: Studies show that property values increase as much as 20% when the land includes healthy, well-maintained trees.

UV Protection and Shade: Trees help to cool the high temperatures of urban settings. Cities create "heat islands" which are a result of thermal energy being stored in steel, concrete and asphalt. A dense urban forest can help to cool temperatures by as much as 15 degrees.

Control of Soil Erosion and Conserving Water: Roots of trees hold the soil in place and help to decrease the surface runoff of water. Erosion problems become critical in areas like Claremont that are subject to infrequent but heavy rains.

Wildlife Habitats: Birds, squirrels, and other creatures make their homes in the branches and hollows of trees. Trees are a valuable part of our ecosystem.

Aesthetic Value: Some trees produce brightly colored flowers, some trees' leaves change colors with the seasons; whatever the method, trees add beauty to our daily life. Many studies have shown that hospital patients with a view of trees outside their windows will recover more quickly than those faced with only walls and cement.

Energy Conservation: Strategically planting deciduous trees on the southern side of your home will also reduce your monthly energy bills. By providing shade to your house on summer days and allowing sunlight in during the winter, deciduous trees can help you save money on your heating and cooling costs year-round.

Making Mulch: Leaves, twigs, branches, bark and other debris falling from trees can become a natural fertilizer that helps to keep moisture in the ground and replenish nutrients.