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Giant Trees
South of the taiga are other forests, of course. But they are impressive for entirely different reasons. The coast redwoods are the tallest trees in the world — towering 300 feet above the ground along the foggy coasts from southern Oregon down to Monterey County, Calif.
These 20-million-year-old forests were extensively logged in the 1800s and early 1900s. Luckily, and unbeknownst to the loggers, these trees can sprout like weeds from their own roots. Today you can tell when you're in a second-growth redwood forest because there are always younger trees growing in a ring around a decayed giant stump. They make an eerie circle of columns, like some sort of strange sylvan temple.
Towering as the coast redwoods are, they're matchsticks compared to their Sierra Nevada cousins, the giant sequoias. These are the largest trees on Earth. They can get as tall as coast redwoods, but are far wider, some reaching 29 feet in diameter. The oldest giant sequoia is about 3,200 years old, based on a coring of its annual growth rings.
When it comes to age, the giants have to concede to the far smaller, infinitely more twisted and humble bristlecone pines of the eastern Sierra Nevada and other mountains of the Great Basin. By growing very slowly at the highest reaches of the mountains, some of these trees have survived for more than 5,000 years. That's halfway back to the last ice age.
Falling Leaves
Of course, not all forests are evergreen. There are large broadleaf, deciduous forests all over the world — for example, in Russia, the eastern United States and the Rocky Mountains. All these forests have one thing in common: They experience hotter, wetter summers than the taiga.
That extra water and summer heat makes broad, water-wasting leaves possible and speeds up decay of older leaves on the ground, which feed the soil and recycle many nutrients to the trees.
But dropping leaves is not only about cold. It's also about dryness. Winter in some places can be arid. That's why the leaf-dropping tactic is used by tropical trees in India and even some desert plants.
Future Forests
What all these forests have in common is that global warming is pushing their habitats poleward, or shrinking what little habitat they have. Since trees can't uproot themselves and walk to the right climate, they have to depend on their seeds dispersing farther toward the poles, germinating along the way to grow new forests. Needless to say, this is not something that happens overnight.
A more immediate threat is the demand for lumber, which has pushed loggers into even the virgin taiga of Siberia. The battle for preserving these forests has just begun, and the people trying to save them cleave to the words of the 19th-century American writer Henry David Thoreau: "... the pine is no more lumber than man is, and to be made into boards and houses is no more its true and highest use than the truest use of a man is to be cut down and made into manure."
