easily when it rains. In desert regions,
feathery leaflets with a small surface area
lose moisture slowly in the hot sun.
HOW TREES WORK
Leaves Large
and Small
This
is
what tree mouths look
like
under
a
microscope.
Just like other living things, trees need water. And because they are the elephants
of the plant
world,
they need a lot of it. On a hot summer day, a large beech
tree can easily drink up three or four bathtubs full of water.
OF COURSE,
THERE
ARE NO
BATHTUBS
in the forest,
which means that beech trees have to get every
drop of water from the ground. They do this
using their roots to feel for the spots where
it's nice and moist.
Once they've found a moist spot, they
quickly suck up all the water. And to make sure
they really do get every last drop, the roots
team up with fungi. Fungi grow fine threads
around the roots of these forest giants and, like
cotton balls, they soak up even more water for
the
trees.
Different salts from the ground are carried
into the tree trunks along with the water. The trees
need these salts to grow, and they like
them.
It's like
when you eat chips–once you start, you can't stop!
We still don't really know how trees get water
all the way up to their crowns. (Maybe you'll want
to research this yourself when you get older.) What
scientists do know is that it takes
a
lot of energy for
trees to do this–more energy than you would need
to blow up
a
balloon as big as a house.
*
In the winter, when the water in the ground freezes,
the trees take a break from drinking. After all, you
can't drink ice cubes. That's why, before they grow
leaves again in the spring, they suck a whole lot of
water up into their trunks in one big gulp. If
you
take
a stethoscope (that thing the doctor uses to listen to
your heart) and hold it up against the bark, you may
actually be able to hear the water rushing up inside
the tree. As soon as the tree leafs out, the water
pressure drops back down.
Trees that belong to the same species usually drink
about the same amount. But some learn to drink
a
little
less.
During a hot summer, the ground can dry out.
If
a
tree keeps trying to suck water from dry
soil,
its
wood may crack. That helps it learn to do
a
better job
of managing its water supply.
Come
the next spring,
instead of drinking up all the water in May and June,
it saves some for July and August.
Some
trees learn more quickly than others. There
are reckless trees that drink a lot, and careful trees
that prefer to conserve water, Fortunately, the careful
trees are very nice to the others. When they notice
that the ground is drying out, they warn their fellow
trees through the fungi that act
as
the forest internet.
(You can read all about this in Chapter 3.) When the
news gets out, even trees that like to guzzle water
begin to cut back.
*
The forest's water supply is constantly refilled by rain
and snow. To catch every possible drop of
rain,
decid-
uous
trees such
as
beech and oak angle their branches
up into the air to act
as
big funnels. The rain runs along
their branches to the trunk, where it shoots down to
the ground. Sometimes so much water runs down the
trunk that it froths up when it hits the ground.
Conifers are not as good at catching
rain.
Many
of them come from colder places, so they're better
prepared for snow
than
for dry weather, After
a
snowfall,
their flexible branches hang down close to their trunks
so the tree doesn't fall over under the heavy snow.
This doesn't work with deciduous trees. Their
branches reach up to the sky, and they would break
off under
a
heavy load of
snow.
That's why these trees
drop their leaves in the
fall.
Then the snow can simply
fall