HOW A TREE GROWS
As we walk through the forest and view the trees, we
remember they were once tiny seeds. Nearly all hardwood seeds are the
same. They have an outer cover for protection, food and water inside
to use for the first surge into growth, a part that has an affinity
for water that will seek out the soil and become roots and a part with
an affinity for light that will seek the sun and become leaves and
branches. Nature gives all seeds another characteristic. An acorn
will always grow into an oak tree and a pine seed will always grow
into a pine tree.
While nature provides a seed all it needs to
survive, she provides great opposition to survival. From the
beginning, each seed must compete with its neighbor for water, food,
sunlight and space in which to grow. Trees produce thousands of
seeds. Very few grow to maturity. In fact, from a start of 10,000
seedlings per acre at age one year, the final stand of mature trees
may number less than 50.
Seeds compete not only for food and sun with each
other but many are eaten by forest animals, others are destroyed by
insects and disease, and some simply do not find a suitable place to
Some trees produce flowers, from which the seeds
come, before the leaves come out in the spring. These flowers produce
seeds that ripen in the spring and fall to the ground and start to
grow that year. Other seeds ripen and drop off in the fall and lay
dormant over the winter and start to grow the following spring.
Temperature is the main factor in starting seed
growth. When warm weather comes in the spring and the sun's rays hit
the earth at a more direct angle, nature springs to life. Seeds have
various means by which they are scattered over the countryside. An
acorn falls down right under an oak tree but squirrels will often
carry it away and bury it. Some seeds have wings that allow the wind
to blow them over great distances. The outer covering of seeds can
pass through a bird's digestive tract without damage, and be dropped
far away. The maples, the yellow poplar and ash have winged seeds,
the wild cherry is a seed spread by birds.
In order for any seed to sprout and develop it must
have food, water, sunlight and warmth. Until it gets roots, a stem
above ground, and some leaves or needles, the seed uses the food
stored in its shell to develop growth. As roots go deeper into the
soil they absorb water and minerals form the soil and send these up
into the stem.
The leaves act as a chemical laboratory. In a
process called photosynthesis, which takes place in the green leaves
of a tree in the presence of chlorophyll and sunlight, the tree takes
carbon dioxide from the air and manufactures starches and sugars and
gives off oxygen as a waste product. The formula is simple but the
process has never been artificially duplicated.
For each ton of wood that is produced, a little more
than a ton of oxygen is released into the atmosphere. This takes
place only on growing forests. In our old overmature forests where
growth has become stagnate and decay has set in, more oxygen is used
than produced. Thus, from an air quality standpoint alone it is
essential to maintain healthy, viable forests in vigorous growing
In a process called transpiration, a tree gives off
large quantities of water through a section of a leaf called stomata.
All trees manufacture more food than they need for growing. The extra
food is stored in the tree cells for use in the spring when it puts
out leaves, flowers and seeds.
A tree grows upward from the tips of the branches,
downward from the roots, and outward from the trunk. The roots anchor
the tree to the ground, and the trunk gives support to the branches.
As the tree grows from the food it manufacturers, it adds new layers
of wood to its trunk. Because one is formed each year, these layers
are called annual rings, and may be used to tell the age of the tree.
This is a drawing of the cross section of the stem
of a tree. The outer bark is dead material, outside protection for
the growing part of the tree. Next is the inner bark, composed if
living cells through which water and food are conducted down into a
tree, giving life to its roots and other parts. Next is the cambium
layer, which you cannot see in a cross section without a magnifying
glass. The cambium layer is made up of cells, those toward the
outside make bark and those toward the inside make wood. Next is the
sapwood, also composed mostly of living cells through which food and
water are collected by the roots and sent up to the branches and
The center of the stem is the heartwood. This is
composed of dead cells that give the tree strength to stand. The
heartwood was once sapwood but when new sapwood formed, the older died
and formed the heartwood of the tree.
As you study the cross section of a tree, note that
some annual rings are wider apart than others. When you see a wide
space between the rings this means the tree grew faster at that time
because it got more sunlight, water, and food. Lack of sunlight,
food, water and competition with neighboring trees or being subjected
to destructive forces such as forest fires, insects and disease, slow
down the growth of the tree. The years marking slow growth show the
rings closer together and narrow in width.
In Appalachia, a tree's growing season is during
late spring, summer, and early fall.
Many wood-using industries today are doing an
excellent job of managing their forests and harvesting the trees so
that other trees will grow and replace those which were removed. This
practice, known as "sustainable forestry," assures that we will have
trees of a variety of species and sizes growing forever to make the
products we need in our daily lives.