Desert and Tundra Biomes Chapter Seven

Most of the year the desert looks lifeless. But when rainy season comes, the land explodes with life. Plants and animals hurry to feed, grow and reproduce. When the rain is done life seems to disappear again, until the next rainy season. This occurs in the desert and in the tundra, but in the tundra, it occurs in the short summer.

I Can… Describe the characteristics of a desert. Explain how desert organisms are adapted to live in their environment.

Deserts The one thing in common that all deserts have is the lack of water.

Desert Soil Desert soils are usually poor in organic materials. Rainwater moving through the soil carries minerals deeper into the soil in a process called leaching. However, because there is not much rain, there is not much leaching.

Desert Soil The lack of rainfall tends to prevent plants from growing. The decay of organic material is also slowed by the small amounts of precipitation. With the very little decaying material and little rain, there is not much topsoil.

Desert Soil Loose, dry desert soil is easily blown away by the wind. If the loose soil is removed, a lower layer of soil called pavement is exposed. Pavement is the desert floor, made mostly of hard-baked sand and/or bare rock.

Deserts in the US There are 2 types of deserts in the US. Cool deserts and hot deserts There is a variation because of the elevation and latitude.

Deserts in the us Cool deserts are located on the Eastern side of the Sierra Nevada and Rocky Mountains. Hot deserts are located in the southwest, specifically, Arizona, New Mexico, and western Texas. Cool deserts have sagebrush, while hot deserts have cacti.

Desert Climate Deserts rarely get more than 25 cm (10 inches) of precipitation. The amount of precipitation determines the types of plants that live there, and the plants determine what types of animals live in the area. The lack of rainfall is therefore the limiting factor in the desert biome. Most of the rain in the desert falls in short thunderstorms.

Desert climate Desert pavement is very dry and compacted, so when it does rain, the rain usually runs off rather than being absorbed into the ground. The lack of moisture also affects temperatures. Moisture tends to help act like a blanket to hold in heat. Since there is little moisture, temperatures can rise and fall dramatically, swinging from hot days to very cold nights.

Desert organisms Organisms that live in the desert are adapted to live with little water and extreme temperatures. Some adaptations involve physical structures, while others involve behaviors.

Desert plants Plants that live in the desert must be able to absorb water from the ground and prevent the loss of water from their tissues. Spines of cacti are one adaptation to reduce the loss of water from the plant. The spines are the leaves of the plant, and with little surface area they reduce the amount of water that can evaporate from them.

Desert plants Cacti can also store water in their tissues. Plants that have thick, water filled tissues are called succulents. This stored water allows plants to live for a long time during dry periods. The stored water also makes these plants attractive to desert animals.

Desert plants Cacti are only native to the American continents, but other succulents are found in other deserts. Aloe vera is one example of a succulent found in Africa Adaptations are also apparent when looking at the roots of desert plants. Plant roots tend to be very shallow, yet wide, or extremely deep (20m)

Desert animals Most desert animals get the water they need from their food. All insects and reptiles in the desert have outer coatings that reduce water loss. The shells of insects and the scales of retiles evolved to survive the life in the desert. Another desert adaptation that several mammals have is to be nocturnal, or be active at night.

I can Illustrate the processes that cause deserts to form.

Formation of deserts Deserts are found on every continent except Antarctica. Most deserts lie within two belts on the Earth known as the desert belts. They are at approximately 30 degrees north and south of the equator.

Natural desert formation Near the equator the air is warmest, and rises. As it rises it cools, and sinks back down to the Earth at about 30 degrees N and S of the Equator. It warms as it sinks, and thus creates the deserts.

Natural desert formation In the US, deserts are rain shadow deserts. The air is forced up mountains, forced to cool, water vapor condenses, it rains, and then the air is dry moving back down the other side of the mountain.

Natural desert formation Some deserts are semiarid deserts, meaning that they are dry, but not as dry as a textbook desert.

desertification Deserts are often bordered by semiarid regions. Human activities have cause many semiarid regions to become deserts. The transformation of semiarid land to desert is called desertification. It can be caused by too much grazing, which leads to topsoil erosion. This has occurred on every continent but Antarctica. An area the size of Maine turns into desert each year.

I can Describe why the characteristics of the tundra make it a fragile ecosystem. Compare the characteristics of tundra organisms with those of their relatives in warmer climates.

Tundra The tundra is a cold, windy, dry region. It is just south of the polar ice caps in Alaska, Canada, Greenland, Iceland, Scandinavia, and Russia. In the S. hemisphere this area is covered by oceans. The tundra is one of the largest biomes, covering 10% of Earth’s surface. However it has the fewest organisms, making it extremely fragile.

Tundra Climate Like the desert, the tundra receives little precipitation. The main difference between deserts and tundra is the temperature. Most precipitation falls as ice or snow, and temps are below freezing almost all year. Temperature is the limiting factor here.

Tundra climate Summer days are long and cool, and only the top layer of soil will thaw in the summer months. The soil beneath the active (thawed) zone is called permafrost because it is permanently frozen. Mats of grasses, mosses, and other plant life covers the ground in the summer. The growing season is extremely short.

Tundra climate Vegetation does not recover quickly from distruption. When it does rain, the water forms bogs and marshes at the surface, which attracts mosquitos and black flies. These insects are an important link in the food chain in the tundra. If the permafrost melts, the water will drain, and affect the first stages of the food webs.

Tundra plants The growing season is about 60 days in the tundra. The tundra plants tend to be small and grow close to the ground. Root systems are shallow because they cannot penetrate the permafrost. Trees are smaller and look more like shrubs. Plants are dwarfed by the short growing season and strong polar winds.

Tundra animals Many of the animals in the tundra are seasonal, that is, they migrate there only for breeding or raising of young. There are few predators in the tundra. Migratory birds come to feed on the insects, and serve as prey for foxes and other migratory predators. There are no reptiles or amphibians.

Tundra animals Caribou are a large migratory mammal that also lives in the tundra part of the year. Like many tundra animals, caribou have thick coats with hairs that are filled with air to act like insulation. Caribou fill the tundra each year to eat the lichens. Many are disappearing due to loss of lichens and interference with their migratory routes.

Tundra animals Some of the mammals in the tundra are year around residents. The arctic fox, musk oxen, polar bears (on the coasts), and wolverines are all year around dwellers. The fox hunts birds and buries them in the permafrost to eat during the winter.