An ecoregion is a large area of land that has a distinct group of plants, animals, and other species.
The species in an ecoregion have adaptations for the weather, elevation, soil, and amount of water available for that region.
1. Key Concept Check What is an ecoregion?
Examples of ecoregions are shown in Figure 1. The Great Plains is an ecoregion of central North America. It usually receives little rain. Grasses can grow there because they can survive periods with little moisture. The Arctic tundra of Canada is frigid and has a thin layer of soil. Only adapted plant species can survive there.
In many areas, human activities have disturbed ecoregions. For example, in Texas’s Pineywoods ecoregion, only about 3 percent of the forests remain. Most of the original forests were cut down for timber and to make room for towns and cities.
(t) Jorma Jaemsen/Corbis, (c) Pete Ryan/Getty Images, (b) Geoffrey Clifford/Getty Images
Figure 1 Ecoregions are defined by the species that live in them.
Weather, Climate, and Ecoregions
Some areas of Earth are hot and dry. Other areas are cool and rainy. Some places are cold all year long. Although there can be short-term variations in the wind, rain, and temperature in an area, each area has a typical overall weather pattern. The long-term weather conditions in an area make up its climate. Climates determine the distribution of ecoregions on Earth. Different species of plants, animals, and other organisms thrive in different climates.
Have you noticed that some areas of Texas are different from other areas? That’s because different parts of the state have different weather patterns. That means the state has many different ecoregions. Figure 2 shows some of the varied ecoregions in Texas and their characteristics.
2. Key Concept Check How do weather and climate affect ecoregions?
Figure 2 Texas has many ecoregions. Each has its own climate.
Visual Check Where in Texas is rain most common?
The amount of water available to an area is an important feature of an ecoregion. How much precipitation falls and where it drains are factors that determine which organisms can live in an area. Precipitation that soaks into the cracks and pores beneath Earth’s surface is groundwater. Surface water is the water that fills lakes and rivers. Humans rely on groundwater and surface water to irrigate crops, provide drinking water, for recreation, and for other uses.
3. 
Reading Check How do surface water and groundwater differ?
Reading Check How do surface water and groundwater differ?
Watersheds
Water that falls on land flows in streams and rivers and drains into a larger body of water. A watershed is an area of the land where all runoff drains to the same body of water. High points, such as mountains, form boundaries between different watersheds, as shown in Figure 3. All organisms in a watershed are affected by the amount and the availability of water in the watershed.
4. Key Concept Check What is a watershed?
Figure 3 Water on the two sides of a boundary flows to different places. Water that flows to the same area is part of a particular watershed.
How Watersheds Can Change
Watersheds change naturally over time. Over millions of years, the shape of the land changes. This can change the direction water flows. In a shorter time, floods can carry nutrients and sediments to new parts of a watershed.
Human Impacts Humans also can change watersheds. As shown in Figure 4, people build dams that change the flow of rivers. Lakes called reservoirs form behind the dams. People use the water in reservoirs to irrigate farms and to provide water for towns and cities. Changing the flow of rivers can change the watershed—and the organisms that live there. Sometimes these changes can be permanent.
Changing the Flow of Rivers Built to make reservoirs or control flooding, dams on a river prevent water from flowing through the watershed. That means areas downstream do not have as much water as they once did. This can change ecoregions.
Irrigation To provide crops with needed water, some farmers irrigate land with groundwater pumped from wells. Others use water from trenches that carry water to crops.
Water Pollution Rivers and lakes can be affected by pollution. If the water in a watershed is polluted, it can harm organisms living in the watershed. Pollutants can come from factories that release harmful chemicals into a river. Or, water flowing through farms or towns can pick up pesticides or oil and carry it into lakes and rivers. These pollutants will pass through layers of soil and rocks, but some will still make it into the groundwater. This groundwater is what we depend on for our drinking water. If pollution is not controlled or stopped, then the groundwater and drinking supply will be polluted and will not be suitable for consumption.
5. Key Concept Check How can humans change watersheds?
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Figure 4 This dam allows the reservoir to fill with water. The water is essential for people living in this region.
6. Visual Check Where is the reservoir?
Visual Check Where is the reservoir?
Weathering, Erosion, and Deposition
As water, wind, and ice move across Earth, they can break down rock in a process called weathering. The rate of weathering depends on the temperature and humidity in an area. Typically, weathering occurs more quickly in hot, humid areas, such as a rain forest. Weathering occurs more slowly in cold, dry areas. Look back at the map of Texas ecoregions in Figure 2. Where do you think weathering occurs quickly? Where do you think weathering occurs slowly?
In Texas, weathering would likely occur rapidly along the southeastern coast, where temperatures and humidity are high. The coast is also subject to weathering from the Gulf of Mexico and severe weather events, such as hurricanes. The west Texas ecoregions contain mostly desert areas, where temperatures are high and humidity is low. Weathering would likely be slower there than in other areas of the state.
After rock is broken down into smaller pieces, or sediment, water, wind, ice, and gravity can move sediment from place to place. The process of moving weathered material from one location to another is called erosion. Erosion can change ecoregions because it can change the landscape, change a river’s course, or sweep beaches into the ocean.
As water slows, eroded material is laid down and settles in a process called deposition. The cycle of erosion and deposition can move fertile soil to new areas, build barrier islands, and build and move sand dunes. Erosion and deposition also can move pollutants or cover up areas where plants and animals once lived. Erosion and deposition are natural processes, but the way humans use land can increase or decrease the impact of these processes. For example, erosion increases when trees, grasses and other natural vegetation are cleared from the land. People can plant trees, shrubs, or grasses to help reduce erosion.
7. Reading Check How can erosion and deposition affect ecoregions?
Reading Check How can erosion and deposition affect ecoregions?
1
WORD ORIGIN
erosion
from Latin erosionem, means “gnaw away”
from Latin erosionem, means “gnaw away”
Lesson Review
Visual Summary
An area that has a distinct group of plants, animals, and other organisms is an ecoregion. Organisms in an ecoregion have adaptations for a particular climate.
All water that falls on land and drains to the same area is part of the same watershed. Natural events and humans can both affect a watershed.
Pollution from humans can get into surface water and groundwater.
Hutchings Photography/Digital Light Source
What do you think NOW?
You first read the statements below at the beginning of the lesson.
1. All Earth’s climates are part of one ecoregion.
2. Human activity can change a watershed.
Did you change your mind about whether you agree or disagree with the statements? Rewrite any false statements to make them true.
Use Vocabulary
1. Use the terms erosion and deposition in a sentence.
2. Water that fills lakes, rivers, and streams is called __________.
3. Define climate in your own words.
Understand Key Concepts
4. Which is NOT an ecoregion in Texas?
A.desert
B.plains
C.prairie
D.tundra
5. Compare the effects of human activity and natural processes on watersheds.
6. Relate How are groundwater and surface water related to a watershed?
7. The distribution of ecoregions on Earth depends on
A.air pressure.
B.climate.
C.convection.
D.tornadoes.
Interpret Graphics
8. Organize Copy the graphic organizer below. List three ways humans can impact watersheds.
9. Explain Describe how the feature pictured here changes the watershed.
ThinkStock/SuperStock
Critical Thinking
10. Infer What positive and negative effects could heavy rainfall have on a desert ecoregion?
11. Hypothesize Describe two ways water pollution released from a factory into a small stream could
travel through a watershed.
travel through a watershed.
12. Infer What might be some effects of soil erosion in a heavily populated area?
13. What are some of the differences between long-term and short-term severe weather effects?
14. What effect do weather patterns have on ecoregions?
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