Many plant species reach the top of the forest by climbing the tall trees. It is much easier to ascend this way, because the plant doesnt have to form its own supporting structure.
Some plant species, called epiphytes, grow directly on the surface of the giant trees. These plants, which include a variety of orchids and ferns, make up much of the under story, the layer of the rainforest right below the canopy. Epiphytes are close enough to the top to receive adequate light, and the runoff from the canopy layer provides all the water and nutrientsthey need, which is important since they dont have access to the nutrients in the ground.
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 plants 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.
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 dont 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.
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