Friday, February 29, 2008

Quercus suber L.

by: Cristina Goncalves, Portugal

The cork oak is an evergreen tree belonging to the family Fagaceae and the genera Quercus.
Its origin is placed without a doubt in the Mediterranean and can be traced back to the Tertiary period.

Quercus suber is not a very widely spread species, presenting similar characteristics throughout its range. It can be found forming stands in Algeria, France, Italy, Morocco, Portugal, Spain and Tunisia, though it can be found isolated as an ornamental tree in some other countries.
The distributio of this species is located between 44o N and 33o N and about 16o E and 2o W.

As the ecological and cultural characteristics of this species, it can be said that it requires a mean annual temperature between 22o and 24o C in the summer and 8o and 10o C in the winter and the annual precipitation between 400 and 800 mm, but stands well precipitations up to 200 mm. The cork tree can not live at temperatures below -5o C.
The culture of the cork tree is well suited to regions above 200 m altitude but it can reach 2400 m without any loss of vigor. It prefers coastal areas, though it grows well inland.

It does better in silical and xist soils, but does not grow well in compact and calcium-rich soils. It is not a demanding species in terms of soil nutrients, growing in soils of low fertility where other species can not go.
The cork oak is slow-growing and can reach 20 m in height. It is a tree of great longevity, easily reaching 200 years of age and capable of living much longer.
The crown is characterized by an irregularly globose to an umbrella with thick, almost horizontal branches with age and pruning.

Its stern is short and thick, with big branches that have an open angle of insertion, if it grows isolated. When in stand, the stem is longer and the branches have smaller insertion angles. Its bark is very characteristic: thick and corky and forming sinuous interconnecting ridges. Its colour is grayish-brown.
The root system of this tree is constituted by the main, vertical and well developed root and numerous lateral roots capable of great expansion. This last characteristic is common to the xerophytes.

The leaves are persistent, remaining on the tree for 2 or 3 years. This oak has an accentuated heterophylly with sizes between 3 – 7 X 2 – 3 cm. The most common shapes are ovate or ovate-oblong with a long and desenly pubescent petiole. The leaf has a main vein and 5 – 8 pairs of lateral veins that emerge from a somewhat sinuous midrib. Its margins are wavy with spine-tipped teeth. The lower face is grey and covered with the dense tomentous layer of star-shapped hairs. The upper face is dark green and smooth, with less dense tomentum than on the lower face.

The flowers form catkins situated in the leaf axils. The male inflorecences are placed at the extremity of the annual shoot and form thin, pendulous catkins. The female flowers are disposed in a short ear or spike in the middle part of the annual shoot. The flowering period lasts from April to June.

The fruits are acorns. The cup which encloses half of the nut, is 1.2 – 1.8 cm wide and is composed of long scales that project at right development of one year. They mature from the middle of October until the end of December.

The cork tree starts to fruit when it is about 15 – 20 years old and usually alternates years of very good productions with others of very bad ones.
The most important product is the cork. It can be used for many things, but its most noble product is without a doubt the stops for wine and champagne. One can not forget the other uses of cork that are: parquet for floors, insulation from heat and noise, floats, shoes (this use dates back to the Roman Empire), and cork paper used for folders, purses or dresses.

The fruits were used to fatten pigs in the Iberian Peninsula. Nowadays they provides feed for sheep, cattle and even ostriches.
The last two products are the cambium and felogene, and wood. The first one was used for the easy to work and not having very good quality, is used mainly for coal or firewood.

Nowadays, the main problems with the culture of Quercus suber are the diseases caused by:
Totrix viridana L.
Coeliodes rubber Marsh.
Orchestres irroratus Kiews.
Orchestres crythopus Germar.
Periclista Andrei Konow.
Lymantria dyspar L.

The major problem that affects the cork stands (montados de sobro) is the existence of large areas of dying stands. This is caused by the advanced age of the trees, or by the premature death caused by plowing and deep grading for agricultural purposes that impede the natural regeneration of the cork trees and improvish the soils. In these conditions the trees are attacked by:
Hypoxylon mediterraneum De Not.
Coraebus undatus Fab.
Coraebus florentinus L.

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