What is a Veteran Tree, why not call them Ancient trees?

The following general descriptions come from the Ancient Tree Forum The Ancient Tree Forum

There is no precise definition of either an Ancient or Veteran tree, however it is generally accepted that an Ancient Trees are:

• Trees that are of interest biologically, aesthetically or culturally because of their age 
• Trees in the ancient stage of their lives (based on the limits of knowledge we might have for both any tree's age and the expected life span of that particular species)
• Trees that are old relative to others of the same species

A Veteran tree has a slightly broader definition, but the distinction is really quite subjective and the terms are often interchangeable.

A veteran tree can be defined as "a tree that is of interest biologically, culturally and aesthetically because of its age, size or condition"

A veteran tree is a survivor that has developed some of the features found on an ancient tree, not necessarily as a consequence of time, but of its life or environment.

Some trees are instantly recognisable as veterans but others are less obvious.

Some trees experience events around them that in effect 'veteranise' them, fire and storms in Australia are often just such events.

Veteran trees do not have to be the biggest trees in the area, indeed it is often the case that as trees move further into the last third of their life span that they begin the process of canopy retrenchment...again something that can be accelerated by external factors.

Ancient veterans are ancient trees, not all veterans are old enough to be ancient. A veteran may be a young tree with a relatively small girth in contrast to an ancient tree, but bearing the ‘scars’ of age such as decay in the trunk, branches or roots, fungal fruiting bodies, or dead wood.