I recently encountered the term "crown shyness."
Crown shyness is a phenomenon observed in some tree species, in which the crowns of fully stocked trees do not touch each other, forming a canopy with channel-like gaps. It is also known as canopy disengagement, canopy shyness, or intercrown spacing.The term was new to me, but the concept was not; it's quite readily observable by anyone who spends a significant amount of time in the woods. What did surprise me was the notion that the cause of this phenomenon is unknown; I had always assumed it was a manifestation of contact inhibition of growth. Apparently it's not so simple.