Without water, a tree’s life begins to ebb away. Trees die
from quiet exhaustion and starvation, not from a sudden,
dramatic
event. And the prime cause of death for trees is the lack of
water.

Yet trees are actually surrounded by water. It’s in the soil,
the air and even throughout their own wood. Water is everywhere,
but much of it is unusable or unreachable.

Water is where you find it, and you’ll find about 97 percent
of all water on our planet in the oceans. Ocean water contains
around 35,000 parts per million (ppm) dissolved materials,
comprising
at least 70 elements.

Fresh Water,
Please

Because of the dissolved elements, most trees can’t extract
a drop from the ocean. Trees need fresh water.

Fresh water, which has less than 1,000 ppm dissolved
materials,
makes up the remaining 3 percent of all the water on Earth. Of
the 3 percent that’s considered fresh, two-thirds of it is snow
and ice in glaciers and the polar ice caps.

The final 1 percent of the fresh water can be found in the
atmosphere, as ground water and as surface water in lakes and
streams.

Earth is a wet planet. Liquid and solid water covers roughly
three-quarters its surface. But for all the expanse of water on
or near the Earth’s surface, trees can use little.

Across the landscape above sea level is a patchwork quilt of
rain forests and deserts, bottomlands and mountaintops. Limited
water resources, in some form, are everywhere.

The air abounds with water. Water vapor in the air is the
humidity
everyone complains about. Large amounts of water vapor in the
air slows water loss from trees and soils.

In fog (100 percent relative humidity), trees lose no water
to the environment. Unfortunately, few of us live in a fog
forest.
Wind heated by pavements and dry ground surfaces reduce the
humidity
and increase landscape water loss. Water vapor is available to
the tree only when it’s condensed and absorbed.

Feed Roots

The soil is filled with water. Water in the soil coats every
particle and root tip. As the soil dries, more water evaporates.
At some point, the soil becomes dry enough to prevent tree roots
from extracting any more water.

The soil still has water held close around mineral and
organic
soil units and in tiny pores between clay particles. But it
holds
remaining water tighter than the trees can exert force to
extract
it.

Water is found in greater abundance deeper in the soil. But
this water is beyond trees’ reach. Tree roots can reach soil
depths
of hundreds of feet if plenty of oxygen is available. But they
have to have a lot of oxygen from the air to grow and survive.
Tree roots stay shallow because they can’t get enough oxygen to
live in the deep, water-soaked soils.

Like most things in life, it’s not how much you have, but how
much is accessible, that allows survival. Under drought
conditions,
trees must deal with low soil moisture levels and still
effectively
extract water.

Nature provides trees only a few tools to collect water. The
thirst a tree develops can be immense. Do your tree a favor,
when
you can, by watering. Water is a gift to trees beyond any silver
and gold, pruning or fertilization.

Water is life to a tree.

(For more information on water, what it is and how it works
in trees, visit the University of Georgia School of Forest
Resources
Web site at www.forestry.uga.edu/warnell/servic
e
/library.
Click on “Service & Outreach,” then
“Information
Library,” then “Drought Information.”)