Trees will adapt themselves to the light and moisture conditions to which they are exposed.

A tree that has access to plenty of moisture and sunlight grows evenly from the ground to its top with a bushy, wide-spreading crown.
The same tree, if it grows in the shade, will reach a greater height but will have a small compact crown.

Trees run a race in their rapidity of growth.

The winners get the desirable places in the sunlight and prosper.

The losers develop into stunted trees that often die, due to lack of light exposure.