tree climbing

Posted by Ellen

One variety of redwood tree, the dawn redwood, is deciduous, dropping its needles in the fall. This same variety happens to be the only kind of redwood that will grow in the eastern United States; this example of a dawn redwood appears to be thriving in the Fairmount Park arboretum in Philadelphia.

Dawn redwoods may be the midgets of the redwood family; coast redwoods and giant sequoias in California reach heights greater than 300 feet, while dawn redwoods, though very fast-growing, may not get much taller than 200 feet. Their potential height is not known for certain, however, because the oldest dawn redwoods in America are only about 70 years old now, descended from a single specimen found in China in 1944. In California, coastal redwoods and giant sequoias live for hundreds or even thousands of years.

Dawn redwoods were known to scientists from the fossil record long before the live specimen was found in China; they were assumed to be extinct. Fossilized dawn redwoods dating back to the Eocene, 50 or more million years ago, have been found in many parts of the world, including Greenland and islands in the Arctic Ocean, which had a tropical climate at the time. It is believed that the trees became deciduous in response to the extreme light-dark cycle of their high-latitude habitat; even though winters were not cold, they were very dark, rendering leaves or needles useless.

The young man in the tree, of course, is Hank, who is a college student studying ecology and climate change.