Temperate deciduous forests tend to comprise a mixture of species of varying ages, with mature trees forming a canopy with layers of overlapping branches that all receive a share of light as the sun moves across the sky.
What is crown shyness?
But in some other forests, particularly those with lodgepole pines, eucalyptus, mangroves and certain tropical dipterocarp trees, ‘crown shyness’ prevents neighbouring branches from overlapping and shading one another.
From below, the treetops appear to lock together like the pieces of a jigsaw puzzle, separated by channels of blue sky.
What causes crown shyness?
Botanists are still debating the mechanism behind the mutual shade-avoidance. Some think that the physical abrasion between branches colliding on a windy day inhibits growth, thus maintaining personal space between trees. Others claim that buds at the end of twigs sense the far-red (one down from infra-red) light reflected from neighbouring foliage, which prevents growth towards each other.
Phil Gates taught biology at Durham University and writes for The Guardian’s Country Diary column.