Every biome on Earth has distinct conditions and challenges for the life forms that occur within it. Biomes are large-scale environment types such as deserts, tundra, and rainforests. Scientists recognise two divisions within the designation "rain forest." There are temperate rainforests, like those on North America's West Coast, and there are tropical rainforests like those in Central and South America. Tropical rainforest environments pose unusual challenges to plants, and they have adapted accordingly.
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Epiphytes are plants that grow on other plants and derive moisture and nutrients from air and rain. In the tropical rainforest, plants such as orchids and bromeliads (plants related to the pineapple) live and grow in the branches of large trees, sometimes very high up. In doing so they are not relegated to the lowlight conditions of the forest floor. This elevated status gives them access to the brighter light conditions in the forest canopy and to flower pollinators that might not visit them if they were growing on the ground.
Trees of the tropical rainforest benefit from the warmth and heavy rainfall, but these conditions also present problems. One is that the soils are wet and spongy and don't always provide adequate support for big trees. The other is that soil nutrient levels are fairly low. Many rainforest trees have adapted by developing what biologists call buttressed roots and trunks. The trees' trunks are flared at the bottom where they meets the roots. Often this flare can begin on the trunk considerably higher than the head of a person standing next to the tree. The buttress root system is also shallow, giving roots access to nutrients where they are most available, in the top layers of soil.
Some plants in the tropical rainforest are adapted to starting their growth as epiphytes, like the orchids and bromeliads, on trees' trunks or branches. But they take this adaptation a step further by sending down roots to the ground. The plants continue to grow, twining themselves around the supporting tree's trunk. Eventually they more or less strangle the tree. By the time the tree dies, the strangler has grown its own supporting structure, hollow where the tree trunk used to be.
Tree leaves everywhere are exposed to water, but in the tropics this exposure is extreme. Water is, of course, beneficial to the tree but too much can cause problems. Too much water on a tree's leaves can promote the growth of lichens and fungi. Left unchecked, this growth might block sunlight from the leaf, which would be detrimental to the tree. Scientist think that the more exaggerated tips on many tropical tree leaves are an adaptation for shedding water more efficiently. The enhanced water-shedding effect might help offset lichen and fungi growth.
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