Bristlecone pine forest affected by Mountain Pine Beetle |
By Jim Robbins, The New York Times, April 11, 2012
Trees are on the front lines of our changing climate. And when the
oldest trees in the world suddenly start dying, it’s time to pay attention.
North America’s ancient alpine bristlecone forests are falling victim
to a voracious beetle and an Asian fungus. In Texas, a prolonged drought killed more than five
million urban shade trees last year and an additional half-billion trees in
parks and forests. In the Amazon, two severe droughts have killed billions
more.
The common factor has been hotter, drier weather.
We have underestimated the importance of trees. They are not merely
pleasant sources of shade but a potentially major answer to some of our most
pressing environmental problems. We take them for granted, but they are a near
miracle. In a bit of natural alchemy called photosynthesis, for example, trees
turn one of the seemingly most insubstantial things of all — sunlight — into
food for insects, wildlife and people, and use it to create shade, beauty and
wood for fuel, furniture and homes.
For all of that, the unbroken forest that once covered much of the
continent is now shot through with holes.
Humans have cut down the biggest and best trees and left the runts
behind. What does that mean for the genetic fitness of our forests? No one
knows for sure, for trees and forests are poorly understood on almost all
levels. “It’s embarrassing how little we know,” one eminent redwood researcher
told me.
What we do know, however, suggests that what trees do is essential
though often not obvious. Decades ago, Katsuhiko Matsunaga, a marine chemist at
Hokkaido University in Japan, discovered that when tree leaves decompose, they
leach acids into the ocean that help fertilize plankton. When plankton thrive,
so does the rest of the food chain. In a campaign called Forests Are Lovers of the Sea, fishermen have
replanted forests along coasts and rivers to bring back fish and oyster stocks.
And they have returned.
Trees are nature’s water filters, capable of cleaning up the most
toxic wastes, including explosives, solvents and organic wastes, largely
through a dense community of microbes around the tree’s roots that clean water
in exchange for nutrients, a process known as phytoremediation. Tree leaves
also filter air pollution. A 2008 study by researchers at Columbia University
found that more trees in urban neighborhoods correlate with a lower incidence
of asthma.
In Japan, researchers have long studied what they call “forest
bathing.” A walk in the woods, they say, reduces the level of stress
chemicals in the body and increases natural killer cells in the immune system,
which fight tumors and viruses. Studies in inner cities show that anxiety,
depression and even crime are lower in a landscaped environment.
Trees also release vast clouds of beneficial chemicals. On a large
scale, some of these aerosols appear to help regulate the climate; others are
anti-bacterial, anti-fungal and anti-viral. We need to learn much more about
the role these chemicals play in nature. One of these substances, taxane, from
the Pacific yew tree, has become a powerful treatment for breast and other
cancers. Aspirin’s active ingredient comes from willows.
Trees are greatly underutilized as an eco-technology. “Working trees”
could absorb some of the excess phosphorus and nitrogen that run off farm
fields and help heal the dead zone in the Gulf of Mexico. In Africa, millions
of acres of parched land have been reclaimed through strategic tree growth.
Trees are also the planet’s heat shield. They keep the concrete and
asphalt of cities and suburbs 10 or more degrees cooler and protect our skin
from the sun’s harsh UV rays. The Texas Department of Forestry has estimated
that the die-off of shade trees will cost Texans hundreds of millions of
dollars more for air-conditioning. Trees, of course, sequester carbon, a
greenhouse gas that makes the planet warmer. A study by the Carnegie
Institution for Science also found that water vapor from forests lowers ambient
temperatures.
A big question is, which trees should we be planting? Ten years ago, I
met a shade tree farmer named David Milarch, a co-founder of the Champion Tree
Project who has been cloning some of the world’s oldest and largest trees to
protect their genetics, from California redwoods to the oaks of Ireland. “These
are the supertrees, and they have stood the test of time,” he says.
Science doesn’t know if these genes will be important on a warmer
planet, but an old proverb seems apt. “When is the best time to plant a tree?”
The answer: “Twenty years ago. The second-best time? Today.”
Jim Robbins is
the author of the forthcoming book “The Man Who Planted Trees.”
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