| Of the Oak and the Ivy |
Seven of the eight photos above show the same ancient oak viewed from different angles and at
different times (both before and after it was pollarded). Old ivy (Hedera helix) covers this tree and the
smaller oak shown. The tree has suffered fire damage and its great trunk is hollow. I doubt that the fire
hollowed it out, though it might have done by burning away the dead wood, but rather I suspect it had
been hollow for some time before tinder that collected inside it caught alight, perhaps by a lightning
stroke. The heartwood of a tree is non-conducting and often described as 'dead' wood and once a
wound in the tree (such as from a fallen or felled branch) creates an opening to this heart wood, fungi
enter and break it down. The material rots down inside the trunk and the released nutrients are
reabsorbed by the tree's roots. Indeed, some trees, yews for example, grow roots down the inside of
the trunk and into this source of nutrients, in order to recycle the goodness into the tree. Thus, the
hollowing of an old trunk is a useful strategy for prolonging the tree's life by recycling nutrients. I would
estimate that this tree is about 450 years old.
This tree was pollarded, perhaps because it was feared that the hollow burnt trunk would collapse. This
can happen in old pollards, such as this, since when cut back these trees put out many shoots, and if
pollarding stops for a long time, then these numerous shoots grow too big and this can make the crown
too heavy. However, often such precautions are not necessary, since these hollow stems are often
stronger than the solid stems of youthful trees. They are wide and so hard to bend, they are lighter
and so less likely to collapse under their own weight when bent by winds, and most of the strains from
these bending forces occur on the outside of the trunk, where the wood is still solid and strong. I once
saw an oak of about 400 years of age pollarded by tree surgeons, though I never understood why, its
trunk was solid and the branches were sound too.
different times (both before and after it was pollarded). Old ivy (Hedera helix) covers this tree and the
smaller oak shown. The tree has suffered fire damage and its great trunk is hollow. I doubt that the fire
hollowed it out, though it might have done by burning away the dead wood, but rather I suspect it had
been hollow for some time before tinder that collected inside it caught alight, perhaps by a lightning
stroke. The heartwood of a tree is non-conducting and often described as 'dead' wood and once a
wound in the tree (such as from a fallen or felled branch) creates an opening to this heart wood, fungi
enter and break it down. The material rots down inside the trunk and the released nutrients are
reabsorbed by the tree's roots. Indeed, some trees, yews for example, grow roots down the inside of
the trunk and into this source of nutrients, in order to recycle the goodness into the tree. Thus, the
hollowing of an old trunk is a useful strategy for prolonging the tree's life by recycling nutrients. I would
estimate that this tree is about 450 years old.
This tree was pollarded, perhaps because it was feared that the hollow burnt trunk would collapse. This
can happen in old pollards, such as this, since when cut back these trees put out many shoots, and if
pollarding stops for a long time, then these numerous shoots grow too big and this can make the crown
too heavy. However, often such precautions are not necessary, since these hollow stems are often
stronger than the solid stems of youthful trees. They are wide and so hard to bend, they are lighter
and so less likely to collapse under their own weight when bent by winds, and most of the strains from
these bending forces occur on the outside of the trunk, where the wood is still solid and strong. I once
saw an oak of about 400 years of age pollarded by tree surgeons, though I never understood why, its
trunk was solid and the branches were sound too.
The oak above is heavily smothered by ivy. The oak's foliage is golden-brown (usual for this time of year)
and the ivy's foliage is the deep green. The ivy is not feeding on the tree, since it does not penetrate the
bark and manufactures its own food and obtains nutrients from the soil through its own roots, but it is
simply clinging to the tree, using it for support and it will drape over walls in similar fashion. The ivy is
Britain's only native evergreen liana or climber, and will also creep across the floor in the absence of
support and can stand on its own, unsupported, when mature. The stems of the ivy can grow very thick
and woody. I have seen ivy trunks as thick or thicker than a man's thigh (though typically somewhat
flattened) attached to old oak trees. Eventually, the ivy's foliage may smother the oak and prevent it from
getting enough light and carbon dioxide and cause it to slowly whither and die. The ivy also adds to the
weight that the tree must support, making it more prone to damage in high winds. Presumably, the ivy
also competes for water and nutrients from the soil around the tree. However, in a natural ecosystem,
climbers and trees coexist side-by-side, so the tendency to cut down ivy at first sight is probably not
entirely necessary.
The ivy clings on by putting out numerous adhesive roots. Climbing plants have touch sensors that direct
growth around nearby obstacles. In many climbers these sensors are born on tendrils, as in the passion
flower (Pasiflora), and when the tendril touches a solid object it will slowly wrap around the object and
contract, pulling the climber in.
See also sensitive plants to see how climbers find their way by touch!
and the ivy's foliage is the deep green. The ivy is not feeding on the tree, since it does not penetrate the
bark and manufactures its own food and obtains nutrients from the soil through its own roots, but it is
simply clinging to the tree, using it for support and it will drape over walls in similar fashion. The ivy is
Britain's only native evergreen liana or climber, and will also creep across the floor in the absence of
support and can stand on its own, unsupported, when mature. The stems of the ivy can grow very thick
and woody. I have seen ivy trunks as thick or thicker than a man's thigh (though typically somewhat
flattened) attached to old oak trees. Eventually, the ivy's foliage may smother the oak and prevent it from
getting enough light and carbon dioxide and cause it to slowly whither and die. The ivy also adds to the
weight that the tree must support, making it more prone to damage in high winds. Presumably, the ivy
also competes for water and nutrients from the soil around the tree. However, in a natural ecosystem,
climbers and trees coexist side-by-side, so the tendency to cut down ivy at first sight is probably not
entirely necessary.
The ivy clings on by putting out numerous adhesive roots. Climbing plants have touch sensors that direct
growth around nearby obstacles. In many climbers these sensors are born on tendrils, as in the passion
flower (Pasiflora), and when the tendril touches a solid object it will slowly wrap around the object and
contract, pulling the climber in.
See also sensitive plants to see how climbers find their way by touch!
 | |  | |  | |  | |  | |  | |  | |  | |  |
 |  |  |  |  |  |  |  |