In addition to interesting facts about oak trees, this page
includes a description of the differences between the assumptions
made in the population model applet and the real thing. At the
end of the page you'll find references to other sites to learn
more about trees and forests.
Names and definitions --
Oak trees are a type of deciduous tree. These are broad-leaved
trees that shed all their leaves during one season. Forests
which are primarily composed of deciduous trees are called deciduous
forests. The oak tree is a member of the Beech family and its
scientific name is Quercus or Lithocarpus. The best type of
soil for a healthy and nutritious growth of deciduous trees
is referred to as podzol (also spelled podsol).
How old do they live? --
Oak trees can live 200 or more years. The largest oak tree of
record is the Wye oak in the community of Wye Mills in Talbot
County on Maryland's eastern shore in the U.S.A. It is believed
to be more than 400 years old, and it measures 9 meters (~ 32
feet) in circumference, it is 31 meters (~ 105 feet) tall with
a crown spread of 48.1 meters (~ 158 feet).
Sizes -- A trunk's circumference
can be as big as 9 or more meters (32 feet), which corresponds
to a trunk's diameter of 2.8 m (~ 9.5 ft). The height can reach
up to 30 m (~ 100 ft). The spread of the canopy of a full grown
oak tree ranges from 25 to 40 meters (85 to 135 feet) or more
in diameter.
Nutrients -- It is common
to refer to the nutrients given to plants as plant food, although
that is not technically correct. Plants need basic inorganic
elements which they use to manufacture usable food and lock
in the sun's energy into it. Here is a list of the different
mineral nutrients needed by oak trees and their basic functions:
Mineral Nutrients ..............Function
Magnesium........................Produces green chlorophyll
Calcium ............................Gives rigidity to cell walls
Potassium .........................Regulatory functions
Nitrogen1 .........................Provides proteins
Phosphorus ......................Provides proteins
Sulfur ...............................Provides proteins
To manufacture food, plants need: The nutrients + soil moisture
from water + Carbon dioxide from the air + the sun's energy.
A mature oak tree can draw up to 50 or
more gallons of water per day. Trees take up water through
their root system. Some of the water evaporates from the leaves
in a process called transpiration.
In the population program if you don't select all the nutrients
and all the water required for proper growth, the tree leaves
will grow yellow (more yellow the less water and nutrients).
Under these conditions, the acorn production will only reach
a percentage of their full potential. At some point because
of lack of nutrients and/or water, the trees will not grow at
all and will not produce any acorns. After looking at the previous
table you now know that lacking a specific nutrient affects
a different aspect of the tree development. Also, when not enough
water or not all nutrients are available, the trees will grow
much slower and smaller but will not stop growing.
Acorn Production -- Oak
trees can start producing acorns when they are 20 years old,
but sometimes can go all the way to 50 years for the first production.
By the time the tree is 70 to 80 years old it will produce thousands
of acorns.
The oak trees produce acorns once a year during the fall. Acorn
production varies year to year and normally alternates. Not
even the healthiest and largest oak can accumulate enough food
and energy to produce strong crops two years in succession.
Real strong acorn productions might happen every four to ten
years. In addition, a late spring frost can blight the flowers
which prevents acorn development. Droughts and insect ravages
can decimate crops.
Acorn production will increase year after year; following a
similar pattern as the size of the tree's canopy. The following
graph shows what a typical production for an oak tree might
be -- assuming no drastic jumps, which happen from time to time.
The chart shows that production starts very slowly at around
the 25th year, the number of acorns produced then accelerates,
and when the tree reaches about 100 years of age, it starts
slowing down until it reaches a yearly production of about 2,200
acorns per year.
The mathematical formula that relates the acorn production
(A) to the age in years of the tree (Y) as depicted in the previous
graph is:
As you can see, it is not a simple formula. You probably recognize
the 25 and the 2200 representing the year when the production
starts and the maximum acorn production respectively. You may
be wondering why the curve in the graph does not look smooth,
as one would expect. The reason is that randomness was added
when producing the graph to make it more realistic. In reality
the variations from year to year are much larger. This equation
which produces a sigmoid or S-shaped curve is called the Logistic
equation. You can find more information about this in the Facts
about Population Growth Mathematical Models page.
The program does not use this exact mathematical model to
represent the acorn yearly production. It uses instead a simplified
version using only lines. This method of replacing nice but
complicated continuous functions with a collection of lines
is referred to as a piece-wise linear approximation.
In the population program if one doesn't select all the nutrients
and all the water required for proper growth, the acorn production
will decrease proportionally. At some point acorns would not
be produced at all. That is really not the case with real oak
trees. Lack of different nutrients has different impacts.
Acorn tales -- We now have
a few interesting tales about acorns.
Acorn tale 1: Chances of making it -- In a good year the oak
tree will have many flowers -- up to several thousand. With
the right humidity, the right temperature, no late frost in
the spring, and sufficient rainfall in the summer, tiny scale-covered
acorns (called nubbins at that point) begin to grow. They will
mature to become full grown and ripe acorns by late summer.
The chances of one acorn making it to become an oak tree are
very slim -- less than 1/10,000. That means that for every 10,000
acorns, only one will become a tree!
Acorn tale 2: Beetles destroying Acorns -- Little insects called
weevils like to plant their seeds inside acorns before they
mature -- during the late summer months. Up to 90% of the acorns
in a region can be destroyed by the larvae of the weevils. On
the other hand, if there are not enough acorns, that can impact
the weevils' population.
Acorn Tale 3: About hiding those Acorns -- It is well known
that squirrels hide acorns to last them through the winter season,
when food is scarce. They might hide them in their homes, but
they also bury them in the ground. In addition to squirrels,
bluejays and woodpeckers also hide acorns underground. The number
of acorns hidden by animals is pretty small; however, most of
the acorns get hidden by the oak trees. When the oak trees shed
their leaves during the autumn, they end up covering (and thus
hiding) most of the acorns. It is interesting to know that many
of the hidden acorns get rotten by mold and can not serve as
food for the animals that hid them. In addition, many acorns
are found by other animals, such as deer and wild turkeys, who
benefit from them.
What can destroy oak trees? --
One common element that destroys oak trees is fire. When fire,
caused by lightning or by a careless human being, hits a tree,
the fire can spread and burn several trees. Another common destruction
is caused by developments and the use of trees for wood.
Another common cause of oak tree deaths is beetles, fungi,
and bad weather. As I am finishing developing this lesson (Jun
2000) I heard on the radio the following amazing story. Oak
trees in Marin County (which is north of San Francisco) are
dying at a rate that has reached epidemic proportions, and scientists
still don't know the cause of this2,3. Oaks, which typically
take a year or so to die from infections, have been reported
to die in just two to three weeks. Such massive die back of
live oaks has never been reported in California, and a severe
environmental crisis is expected in the months and years to
come.
Balancing Tales -- For a forest to grow and develop into such
nice habitats, there needs to be an almost perfect balance between
the different species that live in the forest. Here are a few
examples where the intricate forest balance can be upset:
Balancing tale 1: Can insects destroy trees? -- Leaf-eating
insects, such as walking sticks, can damage a tree. However,
these insects are eaten many times by birds; thus balancing
things.
Balancing tale 2: Can fungi destroy trees? -- Fungi can invade
the trunks and limbs of old trees with wounds. They soften and
prepare the wood so that beetles, wasp larvae, and carpenter
ants build tunnels, which further weakens the tree.
Balancing tale 3: Can caterpillars destroy trees? -- Caterpillars,
when they grow in big numbers, can defoliate an oak tree. However,
there is a type of parasitic wasp that destroys the caterpillar
moth's eggs. If there are enough wasps that eat a good number
of the eggs, there will be less caterpillars, and the trees
will be happy. Three or four defoliates can destroy a tree!
Balancing tale 4: Can worms help trees? -- A crucial and unsung
hero is the earthworm. During warm rainy periods it stays above
ground, but during the cold winter, it wriggles downward as
far as it can to avoid freezing. It spends most of the winter
one to four inches below the surface. In doing so it conditions
the soil for shallow probing oak roots by literally eating his
way around. This is very helpful, and many times necessary,
for the tree growth.
--------------------------------------------------------------------------------
References --
[Note 1] -- Nitrogen is not really a nutrient. It is an inert
gas that is required by all living things to live. Nitrogen
helps plants grow large and healthy! You can visit this site
to find out more interesting information about Nitrogen: http://www.webelements.com/webelements/elements/text/key/N.html.
[Note 2] -- http://himalaya.cnr.berkeley.edu/oaks/
- This site monitors the sudden oak death in coastal California
and has a great description, pictures, and information about
this major problem.
[Note 3] -- http://phytosphere.com/tanoak.html
- Very good description of the oak tree mortality in Marin County.
[Reference 1] -- http://www.nationalgeographic.com/features/96/forest/
- An interactive site by National Geographic that allows students
to explore what's in a forest.
[Reference 2] -- http://www.californiaoaks.org
- The California oak Foundation's site is a very interesting
site with lots of good information about oaks in California,
how to preserve them, how to take care of them, etc.
--------------------------------------------------------------------------------
Information taken from an article by Java Educational
Programs
