THE January meeting of the Leek Group of Staffordshire Wildlife Trust welcomed the return of Dr Peter Thomas of Keele University to tell us Can a tree live 5000 years?
Peter began his talk with a general indication of the average lifespan of our commoner trees: oak 800 years, birch 150 years, beech 250 years, ash 450 years.
But many individual trees can exceed these ages considerably; the Marton oak in Cheshire is over 1,000 years old and the Astbury yew is believed to be nearly 2,000 years old.
It has been found that trees grow at a pretty fixed rate – 2.5cm in circumference per year (in woodland about half that rate).
So circumference can be used to determine the age of a tree.
This can be complicated in some species like the yew which can stop growing for 300 years and then start again!
The Fortingall yew in Perthshire may be Britain's oldest tree and could be well over 3,000 years old.
A Bristlecone Pine named Prometheus which grew in Wheeler Peak, Nevada, was at least 4,862 years old when it was cut down in 1964.
Peter then went on to inform us of the defences trees can employ to enable longevity.
Some leaves and fruits can survive for long periods, on holly for seven years,
Monkey Puzzle tree for 15 years and Bristlecone Pines for 30 years.
This saves energy compared to producing new leaves every year.
External defences such as spines, thorns and prickles help prevent larger herbivores from attacking the tree.
The holly leaf has prickles which deter deer from eating them while the thickened edge of the leaf helps deter caterpillars feeding on them.
Above two metres and out of reach of deer, the holly saves energy by not producing prickly leaves.
Some trees have hairs on young leaves or they contain chemicals to deter predation, others can use animals such as ants as a deterrent. Chemicals including caffeine, morphine, tannins, curare, strychnine and taxol can all come to the defence of a tree.
Conservation of energy is another means to longer life.
The production of tannins can use as much as 15 per cent of energy taken up by a tree so such chemicals will only be produced when required.
When produced by one tree, amazingly, other adjacent trees can pick up the scent and begin production thus resisting attack.
Defence of the wood itself is by producing resins (on pines and firs), or gums (on cherries and plums), or latex (on rubber trees), all flow and seal any wounds.
For longer term defence trees grow callous tissue over wounds.
Tree heartwood generates chemicals to harden the wood and prevent rot. Cells develop internal walls within the wood which prevent rot spreading throughout. Commonly concern is expressed when a tree develops a hollow centre but in fact trees can lose the middle two thirds of the trunk without losing any of their strength. Hollow trees can bend in the wind and are therefore less likely to snap in strong winds.
This was an absolutely fascinating talk leaving the audience awestruck by the complexity of the defences trees have developed that allow them to maximise their lifespan, which can be 5,000 years.
Sponsor for the evening was Hugh Williams of Tree Heritage Ltd, North Street, Leek, (Arboricultural Contractors and Consultants) Tel; 01538 384019
The next event for the group will be an illustrated talk by Paul Hobson, author, tutor, tour leader & photographer, entitled The Importance of Gardens for Wildlife.
This takes place on Tuesday 11th February at St. Paul's Church Centre, Novi Lane, Leek, at 7.30pm and will be briefly preceded by the group's A.G.M. Admission £2.50. All welcome. Contact tel. no. 01538 300264