How Rainforests Work

Many tropical trees have stilt roots as a mechanism to counter the shallow, loose soil of the tropics. Instead of the roots splitting off the trunk underground, stilt roots split several feet above ground, making the tree more stable, and allowing it to utilize the soil more efficiently.

Photo courtesy Todd Fearer

Stranglers and Buttresses

Some epiphytes eventually develop into stranglers. They grow long, thick roots that extend down the tree trunk into the ground. As they continue to grow, the roots form a sort of web structure all around the tree. At the same time, the strangler plant's branches extend upward, spreading out into the canopy. Eventually, the strangler may block so much light from above, and absorb such a high percentage of nutrients from the ground below, that the host tree dies. When the host decomposes, the strangler's lattice of roots remains, giving the plant the structure it needs to reach from the forest floor to the canopy.

Competition over nutrients is almost as intense as competition for light. The excessive rainfall rapidly dissolves nutrients in the soil, making it relatively infertile except at the top layers. For this reason, rainforest tree roots grow outward to cover a wider area, rather than downward to lower levels. This makes rainforest trees somewhat unstable, since they don't have very strong anchors in the ground. Some trees compensate for this by growing natural buttresses. These buttresses are basically tree trunks that extend out from the side of the tree and down to the ground, giving the tree additional support.

Rainforest trees are dependent on bacteria that are continually producing nutrients in the ground. Rainforest bacteria and trees have a very close, symbiotic relationship. The trees provide the bacteria with food, in the form of fallen leaves and other material, and the bacteria break this material down into the nutrients that the trees need to survive. Even with this amazing symbiotic cycle, nutrients are scarce. Some plant species gather additional nutrients by capturing bugs or catching plant material that falls from the canopy above.

One of the most remarkable things about rainforest plant life is its diversity. The temperate rainforests of the Pacific Northwest are mainly composed of a dozen or so tree species. A tropical rainforest, on the other hand, might have 300 distinct tree species. This plant life is spread out over wide areas -- in a square acre, an entire species might be represented by only a few individual plants. As we'll see in the next section, rainforest animal life is similarly diverse.