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A Little Known Layer: Piggyback in the Rainforest

A rainforest looks like a rainforest partly because of all the plants growing on other plants there. A great many of these are epiphytes, plants that use other plants as support…But that don’s use them as food (the way a parasite would).

In a rainforest, tiny epiphytes like algae, mosses, cacti, and lichens grow on the surface of leaves. Larger epiphytes like ferns, bromeliads, and other orchids often make their homes on tree branches or trunks.


Epiphytes’ point of view

One main reason that they do this is to get sunlight. How much easier it is to begin life in a tiny bit of soil where two branches meet in the sunshine of the upper canopy…than to have to struggle all the way up from the relative darkness at the bottom of the forest.

There are other advantages to living up here. Wind to disperse the epiphytes’ seeds, for example, and canopy animals like bats, birds, and bees to carry the epiphytes’ pollen.

But living at the top of the rainforest has drawbacks too. The main one is lack of water. Rain pours down and is gone. Epiphytes have no roots in the ground to suck up water lingering there.

Epiphytes have a variety of ways of dealing with this water problem. Some epiphytes have fat stems or thick leaves to store water in. Others have pores they can close to keep water from evaporating. Some are evenshaped to be living water storage tanks.

Tank bromeliads – The thick leaves of these epiphytes form a hollow that can hold water. One kind can store as much as 12 gallons!

These tanks increase the plants’ supply of nutrients as well as water. They do so by providing a place where water-loving creatures can live. These creatures in return supply the nutrients.

Dust, animal droppings, dead flowers, and leaves fall into the bromeliad pool and sink to the bottom. They are the basis of a whole miniature ecosystem. Bacteria and tiny one-celled animals feed on the decaying matter, and in turn are food for slightly larger animals. Mosquito larvae, dragonfly larvae, meat-eating beetles all feed in the pool and leave their wastes there.

These creatures are prey to vertebrates like birds, mouse opossums, salamanders, and frogs. They come to the pool to eat, and the salamanders and frogs also lay their eggs there.

The wastes produced by all these creatures are full of minerals that dissolve into the pool, where they are a rich source of nutrients for the bromeliad. Tank bromeliads are another example of the trade-offs between species that are so common in rainforests.