Trees will last for a long time even though it may appear that they are on their last legs. Their survival depends on a complex mix of fungi, water and nutrients in their local environment.
What often kills veteran trees is cultivation (ie ploughing) too close to the tree.
Compaction of roots by machinery and damage to roots (that are often shallow) by ploughing are the cause. No tree will survive when ploughing for crops is carried out a couple of metres from the tree trunk
Farmers should be aware of this.
Ideally, no work should be done closer to the tree than 5 m outside the extent of the canopy, or a distance from the centre of the tree of 15 times the diameter of the trunk at breast height, whichever is the greater. This establishes a ‘separation distance’ or exclusion zone round the tree and gives it the best chance of long-term survival. It can be quite surprising how far away the roots of some of these trees extend, eg up to 50 m.
This old tree did creak alarmingly in strong winds but the land was cultivated very close to the tree. I suspect that this hastened its demise.