But one forest researcher, Dr. Roman Dial, studies the negative space of the forest by literally measuring the forest parts that are not occupied by solids.
Dr. Dial first shoots a horizontal line over two tree canopies with a crossbow, and ties vertical ropes at intervals along that line. Then, hanging from a harness on each of those ropes, he uses a laser range-finder to measure the distance between his eye and the nearest solid object, like a branch, a leaf or a trunk, at eight compass directions around him.
He then calculates the volume and shape of the airspace around him, and creates images that look like giant asymmetrical vases placed among the solid trees. Those images help us understand how a bird or grain of pollen or even a molecule of air would “see” and navigate its way through the forest interstices.
His work has also shed light on the evolution of forest-dwelling animals. Scientists have wondered why rainforests in South America support many species of canopy-dwelling mammals, like opossums and sloths, that can hang from branches with prehensile tails or claws. But very few mammals in those forests have evolved to glide from tree to tree.
In contrast, rainforests in Asia have almost no hanging animals. But those habitats support many species of gliding mammals, along with snakes, lizards and frogs. Being able to glide from one treetop to another lets an animal move more quickly in search of food or in flight. Dr. Dial's images document that there are far larger volumes of airspace between trees in Asian forests than in South American forests.
Measuring the air space between trees provides insights about many subtle aspects of forests, helping us think about how pollen grains, birds — and gliding lizards — navigate the complex three-dimensional spaces of forests.