What Good Is a Tree?

While revisiting my childhood elementary school, I encountered an old friend. We both had grown over the decades, but my buddy now stood more than 30 feet tall. We first met on Arbor Day when the school gathered to put my friend, a blue spruce, in the ground. The principal told us that planting trees was important. Scientists tell us the same today.

Trees are so common and quiet that we pay them little mind. But trees sustain our lives and our planet in a thousand practical ways. This morning at breakfast in your wood-framed house, on your wooden kitchen table—you might have enjoyed orange juice or a grapefruit. Both come to us from trees.

Trees do more than make life pleasant; they make life possible. Trees get water through their roots and, primarily through their leaves; they draw carbon Cartier Roadster Replica dioxide from the air. Then, with the action of sunlight on cells containing chlorophyll and other materials, chemical reactions occur, and oxygen is released. Through photosynthesis, an acre of trees produce enough oxygen to sustain three humans.

Trees have always been green machines, producing substances that humans learned to use. For years, the Chinese have derived medicines from the ginkgo tree. As scientists unlock the secrets of trees, they uncover surprising facts. In the early 1980s David Rhoades, a chemical ecologist at the University of Washington, Seattle, discovered that trees send unseen signals to each other. When willows are attacked by webworms and tent caterpillars, they give off a chemical that alerts nearby willows. The neighboring trees respond by pumping more tannin into their leaves, making them more difficult for the insects to digest.

Researchers have found similar responses in sugar maples, birches and other trees. To their surprise, the scientists found evidence that trees respond differently to different attackers—trees will not react if leaves are nipped with sterilized scissors.

It has long been known that trees enhance rainfall by cooling the land, slowing wind evaporation and erosion, and transpiring water into the sky from their leaves. An a-cre of large, healthy maples, for instance, puts 20,000 gallons of water into the air each day. Without trees our entire world would be a much drier place.

Now scientists have found that trees may cause rain in more peculiar ways, too. Many species are inhabited by the bacterium Pseudomonas syringes. When wafted into the air, the microscopic bugs are believed to act as ice nuclei, thus increasing the likelihood of rain or snow. In this symbiotic arrangement, trees provide a home for the bacteria and the bacteria help bring water from the sky for the trees.

Of course, humans live in symbiosis with trees too: trees take in the carbon dioxide; people and their machines make and turn it into needed oxygen. And we plant and care for trees in return for the benefits they confer on us. Unfortunately, it often takes the loss of trees to remind us just how much we depend on them.

A safely canopy shades about 30 percent of the average American city. But in many cities only one tree is replaced for every four that die.

As settlers came to Los Angeles, they found it hot and dry. They brought in water and planted groves of orange trees across the L. A. Basin. “That cooled the climate by several degrees,” says Art Rosenfeld, a physics professor at the University of California at Berkeley.

In recent decades the orange groves have been cleared for buildings and the climate is now six degrees hotter. Says Rosenfeld: “Residents each year use up to two gig watts of electricity to compensate for the extra heat, at an added cost of $2 billion”.

The need for trees is even greater elsewhere in the world. In some countries, researchers are now experimenting with agro forestry—the planting of crops between rows of special trees. Gliricidia sepium, for example, is a Central American tree that grows well even in poor, dry soil. It provides leaves that farmers can feed to cattle, and it has roots Audemar Piguet Replica that enrich the soil with nitrogen. The trees protect crops from wind and prevent soil erosion. When cut for firewood, they will sprout new growth from the stump.

Trees have great practical value, but they also partake of the eternal. They are a link to the past and a bridge to the future. Trees touch something deep in the soul that naturalist John Muir recognized when he wrote,” The clearest way to the universe is through a forest wilderness. “