Trees silhouetted against the clear January sky, or reaching out of the shadowy forest during a snow squall, tell the story of that place – the plant community – and the light that reaches it.
A tree with large, low, sprawling branches, the kind from which one might hang a child’s swing, grew in an open space like a field or forest clearing. With no neighbors to restrict its spread, it could stretch its arms outward to maximize the exposure of its leaves to the sun.
Trees that grow up tightly crowded with other trees, on the other hand, tend to reach their branches up high as quickly as possible, and have fewer lateral branches. They are in a bit of a race, it seems, to out-compete the other trees around them for available light. But is this really true? We now know that trees share resources through the mycorrhizae network of fungi in the forest soils, so perhaps it is more of a community benefit that we might have once thought. Trees of different sizes and shapes can aide each other by stabilizing soil, decreasing wind damage during storms and communicating about attacks by insects, to name just a few benefits. The forest is a community of trees, and all the associated plants, fungi and animals, that can support each other.
Certainly, different species of trees have different shapes stemming from the fact that they utilize different growth strategies. And forest communities benefit from this diversity, which makes them more resilient in the face of insect defoliation or disease.
Conifers, like pines and spruces, regardless of the light they receive as saplings, grow straight upwards. Their trunks are rarely curved and their branches tend to reach horizontally, regardless of the light. If there is less light, the tree simply stops producing branches and needles along the lower reaches and focuses on producing needles in the canopy, above the other trees.
Hardwoods such as maples and oaks grow more slowly and are more ‘thoughtful’ about how their branches grow – directing the branches, twigs, and leaves into the light-filled gaps within the forest. In Japanese, the term komorebi (木漏れ日 pronounced kō-mō-leh-bē), literally, “sunlight leaking through trees,” describes the rays of light dappling through overhead leaves and filling the air. I cannot find a similar word in English, or in ecological text books. But it is into these spaces that the hardwoods reach their branches, to fill them with their leaves.
“Crown shyness,” is a poorly understood phenomena where some tree species reach into the canopy in such a way as to seemingly avoid each other and create visible gaps between their branches. Not all tree species do this, and certainly those adapted to the understory do not, but oaks and maples can. There are many theories on how and why crown shyness happens: as a result of wind damage from branches hitting each other; through the detection of far-red light (light that falls on the far end of the visible spectrum, just before infrared) reflected from neighboring trees, causing the plant to adjust its leaf position and growth pattern to avoid being shaded by nearby vegetation; or a protective strategy to limit the spread of disease or defoliating insects.
Looking at the shapes that trees take can help us learn to see the “forest for the trees” – literally. Nature is much more complex than a story of one organism competing with others for survival. Even the form of a tree might be less about how that individual tree is competing with other trees to survive, and more about how the shape of that tree aides in its capacity to cooperate within the forest community.
