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Oak Tree Profile
Two oak trees are native to the UK, the sessile oak (quercus
petraea) and the English oak (quercus robur). But around the
world there are approximately 500 species of oak tree. Most are
deciduous but some like the Holm (or Holly) Oak (quercus ilex)
are evergreen. Click here for our
oak tree identification page with lots of pictures and descriptions to
assist in identifying specific species. For more information on the Major Oak (pictured top
left), one of the most famous oak trees in the world,
click here.
The leaf shape of the various oak species also differs
considerably from the traditional lobe shape to those with a
long and narrow shape.
On the right is a picture of the leaf from the Common Oak. One identifier of an oak tree that does remain constant is
that they all produce acorns. But even then acorns differ considerably between
varieties, both in shape and size. The life span of an oak tree is variable but some
examples can live as long as a thousand years. They provide food and
shelter for a wide variety of other plants and wildlife. In part this is
because the canopy of most oak tress allow lots of light to reach the
ground below. The leaves decompose quickly and the acorns provide for
the common rabbits, wood-pigeon, grey squirrels and mice. Plants such as
hollies, brambles, ferns and primroses are very suited to growing near
oak trees. LIFECYCLE OF AN OAK TREE
PICTURE OF ACORN
Oak trees start to produce acorns when they are around 30
years old. An average mature oak tree will produce roughly 2,000
acorns a year.
When an acorn falls to the ground it has a one in 10,000
chance of growing into a mature oak tree. Around early May time the oak tree will produce male and
female flowers. Pollination is achieved by a mixture of wind and
insects. The pollinated female flowers develop into acorns which fall to
the ground in September. Their chances of surviving are minimal. Many
acorns are covered by leaves and rot, others are eaten by animals. If an acorn does survive, the seed within the acorn
feeds on the bulk of the acorn and roots into the ground. The whole
process then starts again. CONDITIONS FOR GROWTH
The oak trees we see today are what is termed 'climax
vegetation'. In other words they are, in relative terms, new
comers in the evolution of vegetation. When the ice age in
Northern Europe started to end 15,000 years ago, willows and
junipers evolved. As the ice retreated further birches and pines
evolved. Last in the cycle came tree such as the oak, hazel and
alder. GROWING OAKS FROM ACORNS PEST AND DISEASES
Oak Processionary Moth (Thaumetopoea
processionea)
Sudden Oak Death (Phytophthora ramorum)
This is caused by the fungus Phytophthora ramorum.
First identified in California in 2000, it spread to other parts of the
USA and has now reached many countries in Europe.
The principal symptom of Sudden Oak Death is the presence of
splits in the bark at low levels often with black sap coming
from them. The leaves can also be affected with dark marks on
them. The disease as spread by wind and rain splash back.
Although oaks suffer from this disease it is more common in
other plants such as rhododendrons and horse chestnut trees.
Oak Decline
The causes of Oak Decline disease are not fully understood
but it is thought to be caused by a combination of fungus, pest and
general condition of the trees.
The tree will first show the symptoms of yellowing and
unhealthy looking leaves. It will then literally die from the
top down. Branches may grow at the top but they will have no
foliage. This gives the tree an appearance of a stag's antlers
at the top. The disease can kill an oak in as little as 3 years. Oak Decline affects oak tree worldwide and has been know to
exist as far back as 1900. It affects trees in waves with 10 or
20 years separating the occurrences.
Major Oak, click to enlarge
Oak trees are icons of the British countryside. These pages will help
you to identify the different types of oak trees which grow around the
world.
Oak trees need a fertile and moisture retentive soil to
thrive. The average mature oak tree will absorb around 40 gallons of
water from the surrounding soil every day. More in summer, less in
winter.
Acorns will readily sprout into sapling oak trees with minimal care.
Click here for our page on how to grow oak trees from
acorns with step by step instructions and advice.
Photo by Haruta Ovidiu. www.forestryimages.org.
The Oak Processionary Moth is moving northwards through
Europe and has now reached London. The larvae (caterpillars)
become active in mid April through to early June. They feed on
the foliage of oak trees causing damage but they are not known
to kill trees.
The moth's name comes from their behaviour of exiting the nest to the
feeding area in a procession. The hairs on the larvae can
irritate human skin, in some cases badly.
Photo by Joseph O'Brien, USDA Forest Service. www.forestryimages.org.