Did you know trees can be shy too? Crown shyness (also known as canopy disengagement, canopy shyness, or intercrown spacing) 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 like the photo above.
According to Wikipedia, the phenomenon is most prevalent among trees of the same species, but also occurs between trees of different species. There are several hypotheses as to why crown shyness is an adaptive behavior, and research suggests that it might inhibit the spread of leaf-eating insect larvae.
The phenomenon has been discussed in scientific literature since the 1920s and the variety of hypotheses and experimental results suggest that there may be multiple mechanisms across different species, an example of convergent evolution.
You can read several of the leading hypotheses on crown shyness on Wikipedia.