2There Are Three Major Types of Forests Forests are lands where the main form of plant is the tree.Many forests have been destroyed by logging or burning.
3Tropical RainforestsTropical rainforests are found near the equator where hot, moist air rises and dumps its moisture.The temperature year-round is very warm with high humidity and daily heavy rainfall.Many plants can grow here because of all the water.The main type of tree in the tropical rainforest is the broadleaf evergreen tree.These trees keep their leaves all year.The tops of the trees form a thick canopy that blocks most sunlight from reaching the forest floor.There are very few plants on the rainforest floor.
5Some trees in the rainforest are draped with vines called lianas. The vines reach up into the canopy and stretch from tree to tree.This creates pathways for many rainforest animals.If a large tree is cut down, its lianas can pull down other trees.
7There is a very large amount of biodiversity in the rainforest. Tropical rainforests have a very high net primary productivity (they produce a lot of plants, which do a lot of photosynthesis).There is a very large amount of biodiversity in the rainforest.50% of all the species of land plants and animals live in the tropical rainforest.Rainforest plants have been found to contain chemicals that can be used to make prescription medication.
8This allows all these species to avoid or minimize competition. Rainforest species occupy specialized niches in distinct layers of the forest.We say that the rainforest is stratified because it has these layers.This allows all these species to avoid or minimize competition.
10The ground layer is the forest floor. There is very little sunlight here, so there are very few plants.Dead organisms and waste decompose very quickly because there are a lot of decomposers living here.Many insects live here, so there are also many animals that eat insects like the giant anteater and the black- crowned antpitta.
14The shrub layer is just above the ground layer. Small plants that do not need a lot of sunlight can live here.Saplings that will eventually become tall trees are in the shrub layer.Many house plants come from this layer.The rainforest’s large predators live here, like the jaguar.Apes, like gorillas and chimpanzees, live in this layer.
17The understory is the part of the rainforest just below the canopy. It is still dark, so the trees grow large leaves to capture all the sunlight they can.The trees in this layer grow to about 12 feet tall.The animals that live here often live in the short trees and are good climbers.Some animals that live here are spider monkeys, boa constrictors, and kinkajous.
20The canopy layer is the tops of the tall trees, that can reach 100 feet tall. The canopy blocks the sun from reaching the layers beneath it.The large leaves in the canopy prevent the heavy rain from pounding on the soil and washing it away.Many of the trees in the canopy have air plants living on them.Air plants grown on the branches of trees and absorb nutrients and water from the air, so they do not need soil.The canopy is the busiest layer of the rainforest because most species live in the layer.Animals that live here include cockatoos, sloths, toucans, and the golden lion tamarin.
24The emergent layer is the very tops of the tallest trees that break through the canopy. These trees can be over 200 feet tall.This layer receives the most sunlight.The emergent layer is home to a third of the world’s bird species, like the harpy eagle and the macaw.Primates like the gibbon live in the trees.Other animals include the vampire bat and many species of butterflies.
27The soil in the rainforest is not very fertile. Even though decomposition is fast, all the nutrients are immediately absorbed by the plants.This leaves no nutrients in the soil.People think that the large trees mean good soil, so they cut down the forests to build farms.These farms fail.At least half of the tropical rainforests on Earth have been destroyed or disturbed by humans.There are only four areas with tropical rainforests left on Earth.The Amazon rainforest in South America is the largest.
29Temperate Deciduous Forest The temperate deciduous forest is cooler than the tropical rainforest.These forests have warm summers and cold winters.Deciduous trees lose their leaves in the winter.This helps the tree save water during the cold winter when there may not be liquid water available.Temperate forests have fewer decomposers than the tropical rainforest, so the falling leaves build up on the forest floor.The leaves will decay slowly and release their nutrients slowly.
34If given time, the temperate forest can grow back. Many of the world’s temperate forests have been degraded, mostly through logging and urban expansion.The temperate forest has been degraded more than any other biome.If given time, the temperate forest can grow back.It takes about years.
35The Taiga Evergreen coniferous forests are also called the taiga. The taiga is found just south of the arctic tundra.It can also be found high on mountain slopes.The taiga’s winter is very long and cold.The Sun is only out for 6-8 hours a day.The summers are short with cool to warm temperatures.Summer can have 19 hours of sunlight.
36The main type of tree in the taiga is the coniferous tree. These are trees with cones, or evergreen trees like fir and pine.Coniferous trees have small, needle-shaped, wax- coated leaves that they keep all year long.The needles allow the tree to survive heavy snowfall.Broad leaves would hold too much slow and make the tree branches break.
38Decomposition in the taiga is slow because of the cold. Also, the needles from the trees are difficult to decompose because of their waxy covering.Few small plants grow in the taiga because the soil is acidic.The needles release an acid into the soil as they decompose, preventing other plants from growing.Some animals like bears, wolves, moose, and lynx live year-round in the taiga.During the summer, insect-eating birds like warblers migrate to the taiga.
41Temperate Rainforests Temperate rainforests are found scattered along coastal areas that have a lot of rainfall.These forests are often covered by a dense fog.These forests have huge trees like redwoods and Douglas firs.These forests used to be very common along the western coast of North America.
45Mountains Play Important Ecological Roles Mountains are steep or high-elevated lands.They cover about one-fourth of the Earth’s land surface.On a mountain, large changes in altitude, slope, climate, soil, and plant life can happen over a very short distance.
46About 1.2 billion people live in mountain ranges, and another 4 billion depend on mountain systems for their water.Because of their steep slopes, mountain soils are easily eroded when their plants are removed.The roots of the plants would normally hold the soil in place.This could cause an avalanche or a landslide.
48Most of the world’s forests are found on mountains. This means that most of the planet’s land species live on mountains.Mountains are often homes to endemic species.These are species that are found nowhere else on Earth.Mountains play an important role in the water cycle by storing water as snow and ice.During the summer, some of this snow and ice melt and enter rivers and lakes.
49How Have Human Activities Affected the World’s Terrestrial Ecosystems? Concept 1: In many areas, human activities are impairing ecological and economic services provided by the earth’s deserts, grasslands, forests, and mountains.
50Humans Have Disturbed Most of the Earth’s Land About 62% of the world’s terrestrial (land) ecosystems have been degraded or are being used unsustainably.Many environmental scientists are calling for a global effort to save the Earth’s remaining wild biomes.Many people do not want to do this because the biomes have valuable resources like lumber, fossil fuels, and minerals.
51Humans Degrade the Desert Humans build large cities in the desert.These cities use the groundwater that is found under the desert.The soil and underground habitats of the desert are destroyed by off-road vehicles.There are many minerals under the desert and mining these minerals leads to pollution.
52Humans Degrade the Grasslands Many of the world’s grasslands have already been turned into farms.In order to clear the grass to make the farm, people burn the grass and release carbon dioxide into the air.Some grasslands are used as fields and are overgrazed by livestock.
53Humans Degrade the Forests Many forests have already been cut down to make room for farms, cities, and suburbs.Some forests are used as tree farms where only one type of tree is grown.This results in less biodiversity.Forest streams can be polluted by nearby urban areas.
54Humans Degrade the Mountains The slopes and bottoms of mountains are cleared for farmland.Mountains are mined for their minerals.Air pollution can blow in from urban areas near mountains.