Emergent Layer – a few tree species grow very tall and emerge up through the canopy. These may be 150 feet tall. Canopy Layer – tall trees for this dense layer that absorbs most of the light energy. 80 to 100 feet tall. Understory or Subcanopy Layer – made of seedlings that will grow to canopy if light is available and a few shade specialists. Ground Layer – very limited diversity
Lianas – are vines that grow up trees to their crown then between the branches of neighboring trees. They “lace” the trees together adding support so they won’t fall over since their roots grow in very shallow soil.
The dominant vegetation in Tropical Rainforests is tall, broadleaf , evergreen trees. Broadleaf = leaves have flat, wide blades instead of needles. Evergreen = trees maintain foliage (leaves) all year. Deciduous trees, those that drop their leaves seasonally, do so as an adaptation to cold conditions. In the tropics, there is no cold season, therefore there is no need for trees to drop their leaves.
Buttress roots are common on Tropical Rainforest Trees. They grow across the surface of the thin rainforest soil. They work like kick stands to keep the tree from tipping over. Also, because the soil is so nutrient poor, deep roots have no need to grow deep. They’re more effective at the surface where they can absorb nutrients from fallen leaves as they decompose.
E:desktop photosMY PHOTOGRAPHSCosta Rica24 JuneDSC01415.JPG This Costa Rican Tropical Rainforest’s canopy goes on for miles. Tree species diversity in such a forest is extremely high. For example, at Triple Creek Park, we might be able to identify 10 or 15 tree species. In an Amazonian rainforest, one could walk for a mile through the forest before encountering a tree species more than once.
Warm, wet conditions are prefect for the growth of fungi and algae. Rainforest plants often have leaves with drip tips . You should remember from Physical Science, Biology, and Chemistry that water is a polar molecule. Water runs towards drip tips and drips off. Because it’s polar, it pulls more water with it. This helps dry the leaves. Consequently they don’t get growths of algae which would block light and they don’t get fungal infections on their main photosynthetic surfaces.
Of course trees aren’t the only plants that grow in Tropical Rainforests. As a matter of fact the plant species diversity is highest in this biome. Epiphytes – (epi = outer and phyte = plants) – are plants that grow on other plants. By growing up off the forest floor epiphytes have access to higher quality light (red and blue). A diversity of plants have adapted to an epiphytic life. There are epiphytic flowering plants, mosses, cacti, ferns, and liverworts.
Many of the trees are covered with epiphytes. The trunks are cloaked in mosses. The large epiphyte in the center is a bromeliad. Large bromeliads like this one are called “tank bromeliads” because their cup of leaves holds a lot of water. That water is the drinking source for arboreal animals. Several species of frogs lay their eggs in it and the tadpoles develop in the treetops.
Adder’s Tongue Fern is a tropical, epiphytic species.
This is one of my favorite photographs. More than 20 species of plants were identified on one 8 foot section of a branch. Rainforest canopy at Monta Verde in Costa Rica
Not all Tropical Rainforest fern species are epiphytes, nor are all of them particularly small. This is a tree fern.
Not all Tropical Rainforest fern species are epiphytes, nor are all of them particularly small. This is a tree fern. This tall “tree” is actually a fern. Some tree ferns grow 40 to 50 feet tall! Notice the person (circled in white) for size comparison.
The Tropical Rainforest floor is shady. Few plants grow on the ground.
Plants growing on the ground in Tropical Rainforests have leaves loaded with accessory pigments . Chlorophyll absorbs red and blue light, but most of that is absorbed in the canopy. Accessory pigments absorb other wavelengths of light to help promote photosynthetic productivity where little light exists.
When a canopy tree falls, it creates a light gap . Understory trees compete for the newly available light by growing straight and tall to fill in the gap.
North American Tropical Rainforest Climate 80+ inches of precipitation per year Temperatures are relatively stable. Rarely does the temperature (even at night) fall below 70 o F and highs seldom exceed 95 o F. This stability is the primary reason for the high biodiversity in Tropical Rainforests. Temperature fluctuation is stressful on organisms. The Tropical Rainforest’s stable conditions limit stress on them. As a result, as species evolve in the tropics, their chance for success is very high. It’s the opposite of a biome like the Tundra where conditions are so harsh, the few species are able to adapt.
Tropical Rainforest soil is deceiving. One would expect the soil to be very rich in order to support such dense, diverse plant growth. These photos show eroded stream banks. On the left is a soil profile of a tropical rainforest in Belize. Rich soil is brown. There are a only a couple of inches of brown soil just below the trees’ roots. The light tan soil is primarily clay and nutrient poor. This is typical Tropical Rainforest soil. On the right is a stream bank in Butler County, Ohio. The soil profile shows several feet of dark brown, very nutrient rich soil. In rainforests, all the nutrients are tied up in the trees. As soon as a leaf falls or a tree dies & decomposes, the nutrients are absorbed right back up into the trees.
Animal diversity in Tropical Rainforests is higher than in all other biomes as well. Because the climatic conditions are so stable, these forests are most suitable for ectothermic (“cold-blooded”) animals like amphibians and reptiles. Amphibians are particularly well suited to the warm wet conditions. For example, in Ohio there are 15 species of frogs & toads. In one patch of Rainforest in Panama, 72 species of frogs were found on only one acre!!! Because large trees dominate the landscape in Tropical Rainforests most of the frogs are treefrogs. Red-eye Treefrog
Another favorite example that illustrates the difference between Ohio and the Tropical Rainforest biodiversity….. If you are a birdwatcher in Ohio and you spot a hummingbird you might pull out your Field Guide to Birds of North America and what you would find is that there is only one species of Hummingbird, the Ruby-throated Hummingbird, in all of the eastern U.S. In Belize, you spot a hummingbird, take out your Guide to Birds of Mexico and the Yucatan Peninsula. You find that there are 16 pages of pictures illustrating 72 species of hummingbirds.
Violet Saberwing Rufus-tailed Hummingbird Longtail Hermit Least Hermit Purple-crowned Wood Nymph White-throated Jacobin Violet-headed Hummingbird About 10% of Belize’s Hummingbirds 100% of Ohio’s Hummingbirds
Tropical Rainforest Birds Keel-billed Toucan - Belize King Vulture - Nicaragua Three-wattled Bellbird Costa Rica Resplendent Quetzal Costa Rica Spectacled Owl Belize Crested Guan Belize
Arthropod Diversity in Tropical Rainforests is beyond belief.
Reptile species are diverse. Lizards are very abundant as are snakes and turtles.
<ul><li>If there is an obvious “theme” to the adaptations of Tropical Rainforest animals it is that the great majority are arboreal. </li></ul><ul><li>Arboreal organisms are those adapted to life in the trees. </li></ul><ul><li>There are a couple of explanations for this….. </li></ul><ul><li>The ground layer has little vegetation </li></ul><ul><li>and therefore few places to hide. </li></ul><ul><li>The most available and abundant </li></ul><ul><li>source of cover is up in the trees. </li></ul><ul><li>2. There are so many trees that it makes </li></ul><ul><li>sense that life would abound there. </li></ul>
Botanists were astounded by the number of plant species that were rooted in soil that accumulated on the branches of the trees. They analyzed the chemistry of that soil to determine its origin. They found that it matches the chemistry of African soils. It blows across the Atlantic from Africa! To better understand Tropical Rainforest ecology scientists recognized they had to get up in the trees.
In Tropical Rainforest countries, ecotourism has taken to the trees. This canopy walk in Costa Rica was anchored to emergent trees and allowed us to walk through and over the canopy for more than a half mile.