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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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October 2002

Tree trivia and tree myths

Let your tree knowledge branch out.

Kim Sebastian

Urban forestry
Unusual facts
Parts of a tree
Managing and care

When someone mentions the word forest, we often think of huge tracts of land covered with trees, like a national forest. However, most of the nation's forests are not in remote areas and most Americans (over 80%) live in that forest, the Urban Forest.

Urban forestry goes beyond trees. The urban forest is a living animal and plant community that has been disturbed, modified or otherwise changed. As much as we try, there is no separation between our cities and nature. We live in nature and urban forestry is the management, and perpetuation, of the forest ecosystem, in which we live.

Urban forestry

The average life of a street tree growing in a typical downtown area is only seven years. Due to a lack of root space and poor, compacted soils, most downtown trees are essentially "potted plants."

We need trees to: save energy by blocking winds and shading; intercept rainfall and reduce urban runoff; filter air pollution particles from the air; muffle traffic noise; reduce glare and reflection; define space; screen undesirable views and provide privacy; shelter wildlife; and add color, texture and beauty to the urban environment. (from "What Trees Do For Your Community," a University of Wisconsin Extension slideshow).

And trees need us to: plant a diversity of species; water, fertilize, prune and care for them; guard against disease, insects and physical damage; and make a community effort to cultivate a thriving urban forest. ("What Trees Do For Your Community").

Unusual facts

The ginkgo tree is a "living fossil." Unlike most other kinds of trees living today, the ginkgo was around during the days of the dinosaurs.

Trees make up an estimated 80% by weight of the 49 trillion tons of green plants on the planet.

What kind of tree gets struck by lightning more than any other? Oaks, because they tend to grow taller than most other trees.

Trees inspire a sense of wonder and awe. They have long been viewed as symbols of life, strength and continuity. © Dick Rideout
Trees inspire a sense of wonder and awe. They have long been viewed as symbols of life, strength and continuity.

© Dick Rideout

Trees were used to help fortunetellers divine the meaning of dreams. In medieval Europe, dreaming of a green oak tree indicated a long life; a cypress was the harbinger of problems in business. Dreaming of a palm tree was the best of omens, while the vision of a pine was a dark hint of looming problems. (from "Growing Greener Cities: A Tree-Planting Handbook" by Gary Moll and Stanley Young).

Germans and Slavs often planted a tree in front of a newlywed couple's house. Many families in Europe would plant a tree upon the birth of a baby, especially an heir, whose fate was then tied up with that of the tree's. ("Growing Greener Cities: A Tree-Planting Handbook").

Why do we "knock on wood? It comes from a superstition. People knocked on wood to thank the tree's spirit for granting them a favor.

According to research done by the USDA Forest Service, the value of trees goes beyond cleaning the air and beautifying our cities. Trees reduce stress and improve health, help us reflect on change and act as symbols of human character, continuity and religion.

The research also cites reasons why people do not feel a kinship with trees: trees can hide criminals who may attack, trees harbor animals and insects that may invade the home, and branches or entire trees may fall, causing damage, injury or death.

Do you know that:

  • Coal is formed from trees that lived during the prehistoric times?

  • Less than 1% of a tree is made up of living cells?

  • It takes 30 leaves to grow a Jonathan apple and 50 leaves to grow a big Delicious apple?

  • There are over 20,000 different kinds of trees in the world?

  • When tree leaves turn upside down in a fresh breeze you can expect rain?

  • Wisconsin celebrates Arbor Day on the last Friday in April?

  • There are 98 Tree City, USA communities in Wisconsin?

  • The pull of gravity or the force of the wind can cause a tree to grow more on one side than on the other?

Parts of a tree

About 90% of a tree's roots are in the top 18 inches of the soil. This is why it's important not to compact the soil or disturb the ground beneath the tree.

Roots can extend up to three times the height of the tree. The notion that the root of a tree mirror its crown is more artistic than accurate. The shape of a tree actually resembles a wineglass set on a plate.

Root growth can occur any time the soil temperature is above 32° F.

A large leafy tree may take up as much as a ton of water form the soil every day.

Did you know that the cambium is the only part of a tree trunk that is alive. The cambium is a thin layer of growing cells, just under the bark.

Bark can be very thin or very thick. The bark of a birch tree may be only 1/4 inch thick, while the bark of a giant sequoia can be as much as 2 feet thick.

Managing and care

Nature can't take care of the urban forest as she does the rural forest. The science of managing the urban ecosystem consists of many factors, often with success dependent on citizen interest and involvement.

Did you know that you can kill a tree by:

  • Overfertilizing it

  • Not watering it

  • Planting it too deep

  • Banging a lawnmower into it

  • Changing the soil grade as little as two inches

  • Trenching near it

  • Never removing stakes and strapping

  • Planting the wrong tree in the wrong site

  • Compacting the soil around it

  • Over-watering it

When planting a tree with the roots balled and burlappped (B&B), it is necessary to remove to the burlap and locate the root collar. The root collar (where the trunk and roots meet) should be even with the final grade. Roots collars are frequently 4-6" below the top of the soil ball in a B&B tree.

To test for proper soil drainage before planting, dig a hole the depth of the root ball that you envision planting. Fill the hole with water, let it drain, and then fill it again. Come back in 24 hours and if no water is present in the hole, then drainage is good. If water exists, move to another site.

A two to three inch layer of organic mulch (wood chips) placed around a tree can reduce soil compaction, protect the trunk from lawnmowers, improve soil moisture retention, control weeds and grass, improve plant growth and recycle waste.

It is not necessary to paint a tree wound after you remove a branch. In fact, research shows that painting wounds actually may do more harm than good to a tree. The only exception is if an oak tree is pruned or otherwise wounded from bud break up to two or three weeks past full leaf development (generally April 15 to July 1). Oak trees are most vulnerable to oak wilt during this time.

Eight good reasons not to top: starvation, shock, insects and disease, weak limbs, rapid new growth, tree death, ugliness and cost (according to the National Arbor Day Foundation – Tree City USA Bulletin 8).

A shade tree positioned on the West Side of a home can keep it 20% cooler that a home without a tree. Trees are nature's air conditioners. The cooling effect of one tree is equal to that of five room air conditioners running 20 hours a day. ("What Trees Do For Your Community").

In one year, a single city tree provides $73 in air conditioning, $75 in controlling erosion and storm water, $75 in wildlife shelter and $50 in controlling air pollution. Trees are an extremely valuable part of a community's infrastructure.

On the average, cities are five to nine degrees warmer than the rural areas that surround them, a phenomenon known as the "urban heat island effect." In the summer, the urban heat island is more than just uncomfortable. Nationally, it amounts to $1 million per hour in additional cooling costs while producing millions of tons of carbon dioxide, the major greenhouse gas, and increases the likelihood of unhealthy smog levels.

"Growing Greener Cities" calls tree planting and care the least expensive ways to slow build-up of carbon dioxide and reduce the threat of global warming.