The Understory

THE FOREST FLOOR

The forest floor of primary tropical rainforest is rarely the thick, tangled jungle of movies and adventure stories. It is actually rather the opposite: the floor is relatively clear of vegetation due to the deep darkness created by perhaps 100 feet (30 m) of canopy vegetation above. The canopy not only blocks out sunlight, but dampens wind and rain, so much so that a visitor to the rainforest may not immediately know it is raining because raindrops are deflected and collected by various canopy plants. Wind is also cut by overhead vegetation.

In undisturbed primary forests, a flashlight may be more useful than a machete since the subdued lighting limits ground growth. Instead of choking vegetation, a visitor will find large tree trunks, interspersed hanging vines and lianas, and countless seedlings and saplings and a relatively small number of ground plants.

The term "jungle" is frequently applied to forest areas having dense ground growth. Such "jungle" is characteristic of disturbed forest, usually near the forest edges, in recently opened light gaps, river banks, and areas where the forest is reclaiming previously cleared land. Vigorous ground growth is only possible where plenty of light is available—where there is a break or thinning in the light-absorbing canopy which screens out all but the 0.5-5 percent of light that reaches the floor in the primary forest.

Despite its constant shade, the ground floor of the rainforest is the site for important interactions and complex relationships. The forest floor is one of the principal sites of decomposition, a process paramount for the continuance of the forest as a whole. It is also home to thousands of plants and animals, and provides support for trees responsible for the formation of the canopy. The ground level is the region of the forest which was first explored and has been the most intensively studied.

Review questions:

• What is the difference between jungle and rainforest?
• Why is there generally little light on the forest floor?

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Continued / Next: Soils and Nutrient Cycling