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Migrating Trees
Tue Aug 31, 2004
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook. Every fall and every spring, migrating
birds fill the forests and fields of North America. In one of the more readily observable
cycles in nature, birds follow summer weather from north to south, year after year,
generation after generation. But the birds aren't the only things migrating: the very trees
in which they roost are migrating, as well.
Tree migration is really forest migration, an expanding or shrinking of whole forest
zones over a huge area, and a long, long time. The forests are responding to changes
in the atmosphere -- just like the birds -- changes that take place over thousands of
years, too long for us to notice unless we look really close. In our present interglacial
period, the oak and hickory forests over much of the East are slowly creeping
northward from where they were 15,000 years ago, after the last Ice Age. But don't look
for an oak tree to go tip-toeing past your window; this forest movement is only a matter
of inches a year. And it takes place as each successive generation of trees grows from
seeds spread to the north and are able to grow in an ever so slightly warmer climate
zone.
Interestingly, it's a non-migrating bird -- the blue jay -- that helps oak tree migration by
gathering acorns, flying to the north and burying them. The jays don’t always remember
where they put the acorns, and this allows a new oak tree to grow, expanding the range
of the forest. Forest migration is also determined by climate, and, a warming planet
may speed up the migration process, affecting both logging and agricultural interests.
The Weather Notebook is produced by the Mount Washington Observatory, and funded
by the National Science Foundation and Subaru of America.
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