Mature:   For the purpose of the Surviving Elm Project the definition of 'mature' is a tree that has a girth at breast height of two metres or more. A simple test of girth that avoids the need for a tape measure is to hug a tree. A person's height and arm span are roughly equivalent. Knowing this it is possible to estimate girth. For example, if you are two metres tall and your hands can touch when hugging a tree its girth is approximately two metres. If your span is less than two metres and your hands can't touch get a friend to estimate the gap between your hands. A two metre girth would indicate an age of around 80 years, so trees of this girth (or more) will have been mature when the Dutch elm disease epidemic was at its height during the 1970's and 80's.