LEAF PERSISTENCE
Identify annual increments of twig growth by locating the bud scale
scars that demark the boundary between successive years growth of the twig.
Determine how many years leaves are retained on the twigs.
Evergreen: A tree is evergreen if it retains leaves for at least two years, that is there are still leaves associated with the nodes of two year old twigs.
Deciduous: A tree is deciduous if it only retains leaves for one year, that is there are leaf scars but no leaves associated with the nodes of two year old twigs.