Simplify the following text for a Grade 12 native English-speaking person.
Original: White ( 1998 ) proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree 's stem diameter , growth character and age .
Simplified: White proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree 's stem diameter , growth character and age .