Next time you visit one of our parks or parkland estates, keep your eyes peeled for some of these interesting features, as described by our ancient tree advisor, Brian Muelaner.
Pollarding is an ancient form of tree management where trees are grown within grazed pastures and the tree’s crown was regularly cut at around eight feet high, well above the browsing height of the stock below. This allowed the land to be used for both grazing animals and to provide useful material from the trees. The uses varied between species and location which in turn determined the pollarding cycle.
In the uplands, ash and holly were often cut every five to ten years in the summer months while in leaf and gathered for winter fodder, the woody branches of the ash could also be used to provide handles for rakes and other farm tools.
Oak was cut on a longer cycle of 20 to 25 years to provide firewood. Around London, hornbeam was cut on a short cycle to provide fuel for the bread ovens of London.
The practice of pollarding died off over a hundred years ago leaving the lapsed pollards that we can now see in some of our parklands.
Stag headed trees
Oak and sweet chestnut can be very long lived trees. There is an old saying that ‘oaks grow for 300 years, rest for another 300 years and then slowly decline for a further 300 years’.
When these trees get to be around 600 years of age their massive crowns start to die back because the root and vascular system is no longer able to maintain the large crown. This allows light to reach the lower inner crown, which in turn stimulates dormant buds to grow, eventually creating a new smaller lower crown.
The old branches which formed the original high crown die off, but on species such as oak and sweet chestnut, both of which have very durable wood, these dead branches remain for decades, even centuries. This is what gives the tree its stag headed appearance.
Walking or layering trees
Did you know that trees can walk across the countryside? They can, but in tree time, which is very slow.
Many species of trees are able to do this but lime trees are particularly good at it. Limes have very weak wood which is very susceptible to decay, but if one of its lower limbs gets big and heavy enough it will be slowly pulled down by gravity until it rests on the ground.
Once the branch has made contact it will begin to grow roots where it touches the ground and will eventually form a new tree. Over time the young tree’s roots will be able to supply all the water and nutrients necessary for it to survive, the umbilical cord connecting it to the mother tree is no longer necessary and may die and decay, removing all signs that they were once connected.
This is how a tree slowly walks across a parkland.
Air and bird trees
Air and bird trees refer to trees growing on or in other trees.
When birds eat holly or rowan berries and then roost on a mature oak limb the seeds inside the berries will eventually pass through the bird and can land on an area of branch or hollow of the trunk where soil has accumulated. The seed can then germinate and a small seedling can grow forming a bird tree.
Air trees are very similar but not produced by birds but by the wind blowing tiny seeds from birch or other small seeded trees onto suitable locations in mature trees.
In both cases these trees do no harm to their host. If they are lucky, and the host tree has an exposed decaying trunk, they will send roots into this decaying wood which can eventually reach the ground.
Like the mythical bird a phoenix tree rises up after death, but in this case not from fire but from falling over or snapping off near to the ground. Both of these occurrences would normally kill a tree, but sometimes the tree lives on.
In the case of trees which fall over, usually from a strong wind, if there are sufficient live roots still attached the tree can continue to live. What were once side branches become new trees growing along the fallen trunk. Over time roots are created beneath each branch where the trunk is in contact with the soil and eventually the original trunk can decay and disappear leaving a row of trees arising from the one fallen tree.
Very large trees that snap off at their base can sometimes have many new limbs growing around the edge of the broken trunk which can develop into a circle of new trees.
All trees rely on a symbiotic relationship with micorrhizal fungi living beneath the soil. Trees are able to take base elements from the soil and convert them into complex sugars and starches through photosynthesis which fungi are unable to do.
Trees have limited numbers of rootlets in which to make contact with the soil to absorb water and nutrients, but through a symbiotic relationship with micorrhizal fungi trees are able to absorb additional water and nutrients obtained by the micorrhizal fungi’s vast network of mycelia which it converts to sugars and starches and shares with the fungi.
These essential fungi, which sheath the rootlets, also acts as a defence against pathogenic fungal trying to attack the trees. So both organisms greatly benefit from this symbiotic relationship.
The heartwood of trees is made up of dysfunctional wood whose only purpose is to provide rigidity for the tree. It is no longer able to transport nutrients and water from the roots to the leaves for photosynthesis and then sugars and starches back to the trunk and roots for growth.
As the tree becomes very mature the need for this volume of rigidity diminishes and heartwood decay begins to takes place. This is a natural process that all old trees go through.
The decay fungi breaks down the structure of the wood, which then enables the tree to reabsorb the nutrients locked away in the heartwood for centuries. This is done by producing internal aerial roots which grow inside the decaying wood. These can become visible if the decay process extends all the way to the outside in fragmented sections of the trunk.
The decaying wood acts like a slow release fertiliser for the tree.