In what type of forest is the terrain rough and the floor sparsely vegetated?

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.

trachea, alveoli, lung capillaries, arteries