Plant growth is essential in the tundra environment, as plants are the primary food source for the rest of the consumers in the food chain. Plant growth and decomposition are constrained by the comparatively small amount of light and heat and by the very short but intense growing season. These limiting factors affect the ability of wildlife and plants to reproduce successfully and to maintain their populations over time.
The following activities demonstrate the effects of temperature and freezing on decomposition and the effect of permafrost on plant growth.
|The honeycomb polygonal shape is the result of the seasonal churning of the ground above the underlying layer of permafrost.|
Temperature and Decomposition
Decomposers are a crucial link in food chains and food webs because they return to the soil organic compounds that enhance plant growth. Decomposition is slower in the far North than in the rest of North America. Because decomposing matter takes longer to become integrated into the soil, plant growth may be limited by the lack of organic compounds in the soil. The slow process of soil formation in cool climates means that existing soil is slow to recover from disturbance by humans, animals, or the forces of erosion.
Have students try the following activity to help them understand the effect of cool temperatures on decomposition. Prior to the investigation, record students' hypotheses about how temperature relates to decomposition.
Materials: You will need four fresh apple slices, four sealable plastic containers, and a thermometer.
Procedure: Have students put an apple slice in each of the sealed containers, and place each container in a different environment: a cold place, a cool place, a warm place, and a hot place. Keep the light conditions reasonably similar in each environment. Then let a child lay the thermometer alongside each apple slice, and measure and record the temperature in each place. Have students examine the containers once each week and record the changes. What did they observe? How did cold affect the process of decay? (Cooler temperatures keep the microorganisms that decompose matter from multiplying quickly, which slows the rate of decomposition.)
Freezing and Decomposition
Although decomposition is limited by the arctic climate, freezing and thawing actually speed access for bacteria and fungi to the insides of the cells of dead plants and animals. This is because water in tissue cells expands when it freezes, thus breaking cell walls and opening the inner cells to invasion once the tissue thaws. Nevertheless, the net effect of the arctic climate is to slow the rate of decomposition.
Materials: You will need four potatoes about the same size, two shallow dishes, a set of scales, and access to a freezer.
Procedure: Ask students to predict which potato will decay first: one that has been frozen and then thawed, or one that has never been frozen. Students should record their predictions and reasoning in their journals. Then have the children measure the mass of two potatoes and freeze them. The next day, thaw the potatoes in the open air and again measure their mass. Measure the mass of two potatoes that have not been frozen. How do they all compare? Have students squeeze a once-frozen and a never-frozen potato. Does water come out of both? Where did the water come from? (A living cell contains 85-90 percent water. When water inside the cell freezes and expands, the cell walls break. Thus the once-frozen potato releases more water than the never-frozen potato.) Next, have the class place in two labeled dishes the once-frozen potato and the never-frozen potato that were not squeezed. Keep both containers in the same location. Students should then observe and keep a daily record of changes in the potatoes for two weeks. (The once-frozen potato should decompose at a faster rate because when the water in its tissue cells froze and expanded, breaking the cell walls, the inner cells were opened to invasion once the tissue thawed.)
Heaving and Thawing
Permafrost, or permanently frozen ground, underlies all lowland tundra areas (except large lakes and rivers) in the Arctic. When present, permafrost and seasonal frost play an important part in shaping tundra lands and ecosystems. Permafrost prevents plant roots from penetrating deeply into the soil and leads to unstable growth--without a strong anchorage, even large plants could be ripped out of the ground by the wind.
|Large blocks of tundra-covered sediment, bounded by ice-wedge polygons, collapse into the Beaufort Sea as a result of mechanical and thermal erosion of the ice-rich sediment by wave action.|
L. David Carter, U.S. Geological Survey
Photograph originally printed in Alaska Geographic
Permafrost also retards the percolation and infiltration of ground water into the soil, and in some low-lying areas, can lead to shallow, water-covered formations known as peat bogs. Water-saturated soils and peat bogs restrict the variety of supportable life-forms in the tundra. The following investigation gives students an opportunity to observe the effects of permafrost on soil.
Materials: You will need two shallow baking pans, a sealable plastic container, soil, tap water, a fork, a tablespoon, and access to a freezer.
Procedure: Day 1--Have students completely fill a plastic container with tap water and seal it securely with a lid. Ask students to predict what will happen after the water-filled container has been in the freezer for several hours. Then, have the children put moist soil to a depth of about 5 cm into each of the two pans. Ask students what they think will happen when a soil-filled pan has been in the freezer for several hours. Place both the water-filled container and one of the soil-filled pans in a freezer overnight. Put the other soil-filled pan aside.
Day 2--Explain to students that permafrost is a word used to describe soil that is frozen year-round. Ask the class how they think permafrost might differ from unfrozen soil. Ask them to think about the following questions:
- Would permafrost be warmer or colder than regular soil?
- Would it be harder or softer?
- Would it soak up more or less water?
- Would it take up more or less space?
Next, retrieve the pan of soil from the freezer and have students test their predictions by comparing the frozen soil with the unfrozen soil set aside the previous day. Ask a student to find out which soil is harder by using a fork. Next, have students pour a spoonful of water first on the frozen soil and then on the unfrozen soil. What happens to the water? Does one type of soil soak it up more readily? Remove the water-filled container from the freezer. Ask students what made the container's sides push out or break. Explain that water expands when it freezes. There was not enough space in the plastic container to hold the water once it had frozen and expanded. Using the information gathered from this lesson, ask the children to answer the following question: "Why does a road break, buckle, and form potholes in the spring?" (When water seeps into cracks in rocks and then freezes with falling temperatures, it expands and forces the rock to break into smaller parts. Thus, ice wedging occurs. Rocks are no different from city streets in this regard.)
Few people would identify this verdant
vista as a part of arctic Alaska.
This activity was adapted with permission from Alaska's Tundra and Wildlife: Alaska Wildlife Curriculum Teacher's Guide, published in 1995 by the Alaska Department of Fish and Game.
Drilling for oil in ANWR would help the United States become less dependent on oil from other countries. Oil companies say they have developed special building techniques, used in other arctic regions, to reduce the effects of construction on the environment and avoid harming the region's wildlife. However, many people think that drilling for oil will damage the arctic ecosystem beyond repair, pointing out that in other arctic regions where oil wells have been drilled, toxic wastes have been released into the environment. Shipping the oil also can cause environmental problems, as was painfully evident after the 1989 Exxon Valdez spill.
In a wolf pack, only one pair has young but the
entire pack works to feed and protect the pups.
After researching this issue, have students consider the pros and cons of drilling for oil along the arctic coast of ANWR. With such an activity, you might ask them to assume the role of a member of Congress and to argue either in favor of or against drilling in the refuge, or you might have each student write a speech presenting his or her reasoning.
Back to the Alaska's Cold Desert page