Oak

Hama NabazAso Akrem

University of Sulaimani College of ScienceDepartment of Biology4th stage

Introduction Introduction • 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 worldwide. • 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 its fruit.

• 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 serrated.

• 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 grow.

• 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 diameter.

• 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.

MOISTURE RELATIONSMOISTURE RELATIONS• 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 shallow-rooted competitors.

• The oaks are better adapted to xeric environments than many of their common mesophytic competitors

MOISTURE MOISTURE RELATIONSRELATIONS

• 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

Fire Fire • 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 have perished

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Ecological significance Ecological significance • 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 documented.

• 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.

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