“CROWN SHYNESS”—THE SHYNESS OF TREES. Tyler Cowen on the Marginal Revolution site linked to this twitter post by Jason Kottke entitled “The Shyness of Trees”. The term “”crown shyness” is used for “a phenomenon where the leaves and branches of individual trees don’t touch those of other trees, forming gaps in the canopy.” The wikipedia entry for “crown shyness” gives several possible explanations, including that it is an evolutionary adaption that inhibits the spread of leaf-eating insect larvae, that “trees in windy areas suffer physical damage as they collide with each other during winds”, and that “growing tips [are] sensitive to light levels and [stop] growing when nearing the adjacent foliage due to the induced shade.”
Thee is another explanation that I posted on here (“TREES WHO ARE TRUE FRIENDS”). Peter Wohlleben argues in THE HIDDEN LIFE OF TREES that “…a pair of true friends is careful right from the start not to grow overly thick branches in each other’s direction.”