In a study on the world's tallest trees, researchers
from Northern Arizona University have revealed the factors controlling
tree growth. (1,2)
There is evident creation in the tree. The cells that comprise the tree
are organised in such a way as to constitute the roots, trunk, bark, water
columns, branches and leaves. The cells constitute components that permit
the tree to survive by performing their necessary functions, and there
is a systematic division of labour among these components.
In addition, a tree resembles a giant chemical factory. Exceedingly complex
chemical processes are carried out, in the light of a flawless order.
There is evidence that the organs that carry out these processes perform
calculations like a computer.
One of the most striking facts about trees is that the information about
this organisation and system is loaded into their DNA, when they are still
tiny, round seeds. The seed follows the instructions loaded in its DNA
and turns into a giant structure with which nothing can compare in terms
of appearance and dimensions. The way that a seed puts out roots and turns
into a tree after it has fallen to earth and been moistened a little,
is a clear sign of God's impeccable creation.
The way that growth in this miraculous living thing comes to a halt after
a particular point is part of the equilibrium created on Earth by God.
If the cells that comprise a tree were to keep growing in an uncontrolled
manner, then consequences might arise that would spell the end of life
The scientists researching the factors that determine how much trees
can grow carried out a most fascinating study on the world's tallest trees.
Climbing up to the top of trees more than 100 metres high, the researchers
sought clues regarding these factors by taking measurements.
They studied the world's five tallest trees, including the 112.7 metre
tall giant redwood (Sequia sempervirens), which holds the title
of the world's tallest tree. A tree that high is the same as a 30-storey
Previously, scientists thought that the main factor determining the height
of a tree lay in the mechanical stresses of height. However, it was realised
that trees possessed a rather sound structure of such a nature as to overcome
these tensions. This led to research focussing on water raising capacity.
In the study in question, performed by a team led by the Northern Arizona
University ecologist George Koch, findings along these lines were obtained.
The studies carried out by the researchers in a natural environment and
under laboratory conditions revealed that the main control of maximum
tree height is indeed the water supply to the tree top.
Water reaches to treetops by means of transpiration, in other words by
vaporising through the pores on the surface of the leaves. Transpiration
carries the water into the plant through the roots, and up to the top
through the water-conducting cells of the xylem tissue. This movement
of the water overcomes the forces of gravity and friction, and water continues
to rise upwards in the form of a column. Since the forces of gravity and
friction that oppose the movement of water are at their maximum at the
top of the tree, the force that propels the water upwards also reaches
its maximum level at the top. Water columns are capable of withstanding
this tension up to a fragmentation threshold. This expresses the point
at which bubbles appear in the water column and interrupt it. This situation
is known to botanists as "embolism."
Koch and his colleagues measured the maximum tension of the water column
at the tops of the tallest redwoods. This measurement revealed that maximum
tension was close to the embolism point. At the same time, this tension
level was a factor controlling how tall the tree would grow. Three other
factors determining tree height were also revealed in the study.
The water reaching the leaves at the top of the tree would normally have
a propulsive effect on cellular growth. However, the increased effect
of gravity and friction at the tree top reducing the water flow capacity,
thus leading to the cells at the top being small and possessing thick
walls. As a result, the leaves at the top are also small and dense. Leaf
density reaches its highest level at the top of redwoods. This indicates
that tree development is to a large extent prevented. Thus the increasing
leaf density at the tree top represents a second factor controlling height.
The small, thick leaves at the top of trees also reduce the photosynthesis
carried out in these regions. This effect, which lowers photosynthesis
productivity, was identified as the third factor determining tree height.
Koch and his team also determined that the CO2 level in leaves 100 metres
high was at the lowest level observed at ambient atmospheric CO2 concentrations.
This constituted the fourth factor: the limitation on CO2 diffusion taking
place by means of leaf pores.
Based on these four physiological factors, the scientists sought to calculate
the maximum height to which tree could grow. As a result, they revealed
that trees could achieve a maximum height of between 122 and 130 metres.
Observations that trees grow an average of 0.25 metres a year further
support this idea.
The restricting factors revealed in this study are of great importance
for ecological equilibrium. To summarise in brief, the facts that
" Water that rises in opposition to the forces of gravity and friction
cannot progress past a particular level,
" The leaves grower smaller and denser
" There is a reduction in photosynthesis productivity, and,
" The necessary CO2 diffusion in photosynthesis falls to a minimum,
mean that the tree is prevented from growing past a particular point.
In this way, the natural equilibrium brought about by the mutual influence
of several living and non-living factors is not endangered by uncontrolled
tree growth. Looked at from this point of view, this study comprises the
latest example of how biological processes in living things support the
wide-ranging balance of nature, and of how perfectly these have all been
arranged. There can be no doubt that each one of these factors is a cause
that has come into being by the will of God. Every phase, from the sprouting
of the seed, to the seed becoming a shrub, and the shrub a tree, and the
tree growing until it comes to a halt, takes place under the control of
Almighty God. Every stage in the life of the tree, every activity concerning
its biology, is a manifestation of the infinite might of Allah.
In one verse of the Qur'an God states,
He erected heaven and established the balance. (Qur'an
1 Ian Woodward, "Plant science: Tall storeys" Nature 428, 22
April 2004, pp. 807 - 808
2 George W. Koch, Stephen C. Sillett, Gregory M. Jennings & Stephen
D. Davis, "The limits to tree height", Nature 428, 22 April
2004, pp. 851 - 854