What are canopy soils?

Soils are part of our daily life: from the food we eat to the home we live in. We are most familiar with the soils under our feet. But, did you know that researchers have also found soils in the trees above our heads? Such soils are called “canopy soils.”

Branch, moss and soil on Chilean tree
Branch of Alerce (Fitzroya cupressoides) at 15m of height covered with epiphytic mosses and vines in a temperate rainforest in southern Chile. Photo credit: Camila Tejo

In several forests around the world, treetop scientists have discovered a myriad of organisms living aboveground such as plants, insects, lichens and bacteria. The plants that grow on other trees are called epiphytes. Epiphytes are not parasitic and can be found from the base of a tree all the way up to the top of it. Examples of some epiphytes are mosses, ferns, vines and orchids. These plants are part of the forest’s diversity.

But how is it possible to have soil up in a tree?

To understand that, we have to imagine ourselves very high in a tree: right there we can notice the branches, leaves and the bark of our tree…don’t forget the epiphytes! While trees grow, the epiphytes also grow and accumulate within the canopy of our host tree, forming a carpet-like coverage on the tree.

Just like leaves in your yard might accumulate in the fall, dead leaves and needles from the treetops get caught in the epiphytes. The epiphytes themselves have a limited life span. All of this “organic matter” begins to decay. The naturally-occurring microbial life in the trees helps to decompose the organic matter, and eventually, the result is soil!

Canopy soils have been found trees from Costa Rica, USA, Chile, Taiwan, Colombia, New Zealand and other forests in the world. These soils have an important role in the forest. For instance, canopy soils provide habitat for several soil organisms as mites, springtails, earthworms, spiders, bacteria, and fungi. Some birds use the canopy for nesting, while other birds prefer the canopies for foraging. Besides providing habitat for organisms, canopy soils also regulate the climate within the canopy.

The accumulated canopy soil acts as a temperature and moisture buffer in the forest. This creates a favorable environment for microbial activity and plant growth. Epiphytic plants and vines absorb water and nutrients from canopy soils through their roots system. Their developing network of roots penetrate canopy soils and forms a tight pack of roots and soils up in the trees. The host tree can also obtain water and nutrients from canopy soils by growing – from a branch several feet aboveground – canopy roots that goes directly to the canopy soil.

Canopy soils are found high in the treetops – often around 15 meters (a little over 49 feet up…or 5 stories tall). This distance suggests they might be disconnected from the forest floor. But rainfalls are heavy in these areas, and wash nutrients and small particles down to the soils of the forest floor. Wind, and even animals, can also disturb fragments of canopy soils and epiphytes, again connecting them with the forest floor. These small fragments eventually decompose, transferring material to the plants rooted on the ground.

The canopy soils environment is a marvelous world to explore and discover. It’s a new area of research with much to be discovered. And, studying canopy soils makes soil scientists learn a new skill – we have to climb up instead of digging in!

Answered by Camila Tejo Haristoy, Universidad Austral de Chile

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