University of Sulaimani
College of Science
Department of Biology
• The common name "Oak" may also appear in the
names of species in related genera.
• The oak tree is about 600 species of this tree exist
• These belong to the genus Quercus. This genus,
which includes deciduous and evergreen species.
• This genus is native to the northern hemisphere.
• extending from cool temperate to tropical latitudes
in Asia and the Americas.
• These trees bear flowers in spring, and the acorn is
• Most acorns contain only one seed, and take
between 6 to 18 months to mature, depending
on the species.
• oak trees can live up to 200 years or more, and
mature trees have the capacity of absorbing
more than 50 gallons of water in one day.
• Leaf arrangement in some species of oak trees
is spiral with lobed margins, whereas in some it is
• The tree blossoms in spring producing cylindrical
clusters of flowers known as catkins.
• After about 20 years, these trees start producing
acorns. Some trees may even take up to 50
years to produce the first lot. Yearly production
of acorns for a mature tree may touch around
2,200 acorns per year.
• Out of all the acorns produced, only a few of
them are able to germinate and develop into a
tree. In fact, only one out of 10,000 acorns gets
the appropriate conditions to germinate and
• The 1 - 6 cm long and 0.8 - 4 cm wide acorns
constitute the diet of squirrels, mice, pigeons,
ducks, deer, beers and pigs.
• They have one characteristic in common, which is
the fact that their seeds are carried in little caps.
• Acorns vary considerably with the different kinds of
Oak trees. Some have stalked or stalkless caps
• Male and female flowers appear on the same tree
• Individual trees of Q. robur, Q. macrocarpa,
Q. rubra, and Q. velutina may attain heights
of 55 m and more and age of 700–900 years,
having thick trunks that are several meters in
• A few specialized species are shrubs and
even low shrubs to 30–40 cm high and even
in the most favorable conditions rarely attain
heights of 2–3 m
• The branching of oaks clearly expressed in
deciduous species in the winter period
appears to be very sharp and angular.
• This happens because of the high light
requirement of the tree and its attempt to
develop leaves only in the illuminated part
of the crown, which causes a change in the
direction of shoot growth.
• The oaks as a group are quite tolerant of drought,
primarily because they have large root systems,
leaf morphological characteristics that reduce
transpiration, and the ability to maintain gas
exchange and net photosynthesis to comparatively
low levels of leaf water.
• The development of a strong taproot system in
oaks provides them access to moisture from deep
soil layers, a source less available to their more
• The oaks are better adapted to xeric environments
than many of their common mesophytic
• Despite their adaptations to drought, oaks are
still subject to injury from water stress. Drought
can cause declines in leaf gas exchange,
dysfunction of their xylem water transport
system, decreases in shoot and root growth of
seedlings, and increases in the risk of mortality.
• Under water stress, oak seedlings exhibit lower
leaf area and new root production, delayed
bud break, reduced shoot elongation, and
increased shoot dieback, and they produce
less xylem tissue and fewer and smaller vessels
• Oaks are generally less susceptible to injury
or mortality from repeated burnings than
most of their competitors, because of
relatively thicker bark.
• Although young and small oak stems « 10.16
cm dbh) are just as likely as their competitors
to suffer shoot topkill from asingle fire, they
are better adapted to frequent burning
because of their ability to repeatedly
produce sprouts long after their competitors
• In addition to ecological and aesthetic landscape
value, another important role of oaks is in
maintaining watershed integrity.
• The sometimes deep, always extensive root system of
oaks stabilizes slopes, limits erosion, and
allows groundwater recharge.
• The wide canopies dissipate the rainfall and prevent
surface erosion,while allowing slow saturation into soil.
• The ability of oaks and other trees to reduce air
pollution and trap airborne particulates is well
• Noise abatement and temperature modulation in urban
areas is also provided by the large, dense oaks. These
important contributions of oaks to the sustainability and
livability of our landscapes are vital.