Trees Growing in the Greenhouse Effect
People who study the Greenhouse Effect know that there is more at stake than just global
warming. Caused primarily by the smoke
of burning fossil fuels, the Greenhouse Effect is a direct result of higher
levels of
carbon dioxide in our atmosphere. Carbon dioxide in the air is used by all land plants for
photosynthesis to make food. What happens when plants
get overfed?
For many a tree, the first response to the
increase of carbon dioxide levels in the air is an increase in
photosynthesis. More carbon dioxide, CO2,
in the air means more sugar can be made by photosynthesis. Making more sugar pushes the tree into a
growth spurt. Trunks and branches grow
taller, longer, and thicker; new branches and leaves form; and roots send out
more long, thin root strands covered with root hairs. One way to refer to such growth is to say
that there was “an increase in biomass.”
Research shows that when trees are grown in an area of greater than
normal amounts of CO2, the trees show an increase in
photosynthesis followed by an increase in biomass (Luo, et al, 2004).
When a tree grows it needs new roots to take up more
minerals from
the soil. After all, plant growth requires more minerals
to make the new cells. But fast-growing trees can use up the important
nutrients needed for making the new plant cells
of the new plant parts. Will the
ecosystem be able to replace these minerals quickly enough to keep
up with the growing trees? Will the photosynthesis
slow down to keep pace with the mineral supply even if the CO2 level
in the air is higher than normal? What
if the CO2 levels begin to change from year to year, rising and
falling, rising slightly, rising greatly, rising slowly, rising
rapidly? Will the ecosystem be able to adjust? Will the
trees remain healthy? Will the trees become stressed, spindly,
disease-prone? Will ecosystem
equilibrium be reestablished, its balance restored? These are
questions that concern scientists today (Luo, et al, 2004).
Nitrogen is
probably the most important of the minerals that plants take from the soil to
live and grow. Will a fast-growing tree
use up the soil’s supply of nitrates?
Nitrates are the types of chemicals that contain nitrogen in a form that
a plant can use. The Nitrogen Cycle
shows that nitrogen is constantly being replaced in the soil as nitrates, but
can this recycling occur fast enough to keep up with the demands of faster
growing trees? (Luo, et al, 2004)
Think about the need for fertilizer in farming, flower gardening,
and even in lawn care. Fertilizer is used to replace the nitrogen,
phosphorus and other minerals that these quickly growing plants have
removed
from the soil. The assumption is that gardens, farms and lawns use
these minerals more rapidly than natural recycling
can replace them in the soil. The
natural nitrogen replacement processes just cannot keep up. So we
fertilize our gardens and lawns.
Some foresters worry about trees
growing too fast. Will a forest be able to recycle its nitrogen and other minerals quickly enough to keep up with the
increasing growth rate of trees? After
all, how can we fertilize an entire forest?
What will the new ecosystem equilibrium be like?
Researchers say that rapid growth
of trees in a healthy forest over a decade or so will not damage the ecosystem. Unfortunately, there is not
enough information to know what will happen when trees continue to grow faster
over many decades of increasing growth rate (Luo, et al, 2004).
Meanwhile, as more fossil fuels are burned than ever before, more CO2 is dumped into the air than ever before.
The trees will respond with more photosynthesis and fresh growth more
quickly than ever before--until some kind of balance in the forest
is reached. Will the new ecosystem equilibrium be a benefit for
he trees, or harmful? Will man’s
economy be affectedd? Will man’s culture
be forced to change somehow? Can man
guide the changes in a direction acceptable to the diverse political,
social
and economic groups of society? If there
will be damage, can man stop the damage in time?
People that are concerned about the
Greenhouse Effect have more questions than answers. It is just too early to tell what will really
happen. The good news is that by taking
more carbon dioxide out of the air, rapidly growing trees might slow Global
Warming just a bit, for awhile, anyway.
Reference
Luo, Y., et al. 2004. Progressive nitrogen limitation of
ecosystem responses to rising atmospheric carbon dioxide. BioScience 54: 731-739.
More abstracts about the Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide