44.3C: Subtropical Deserts and Chaparral
- Recognize the distinguishing characteristics of subtropical deserts and chaparrals
Subtropical Deserts
Subtropical deserts, which exist between 15° and 30° north and south latitude, are centered on the Tropics of Cancer and Capricorn. In some years, evaporation exceeds precipitation in this very dry biome. Subtropical hot deserts may have daytime soil surface temperatures above 60°C (140°F) and nighttime temperatures approaching 0°C (32°F). In cold deserts, temperatures may be as high as 25°C (77°F) and may drop below -30°C (-22°F). Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in), with little monthly variation and lack of predictability in rainfall. In some cases, the annual rainfall can be as low as 2 cm (0.8 in), such as in central Australia (“the Outback”) and northern Africa.
Types of Deserts
There are several types of deserts including high-pressure deserts, mid-continent deserts, rain-shadow deserts, and upwelling deserts. In high-pressure deserts, the high atmospheric pressure enables the air to retain more moisture and there is little rainfall. High-pressure deserts include the Sahara, Arabian, Thar, and Kalahari deserts, and the desert regions within the Arctic and Antarctic circles. Areas in the middle of a continent can receive little rainfall because moisture tends to condense before it reaches the middle of a large continent. Modern examples of mid-continent deserts are the Turkmenistan, Gobi, and Great Australian deserts. Third, rain-shadow deserts are created when moisture from the ocean condenses on one side of a mountain range. These mountain ranges usually have a rainforest on one side and a desert on the other. Examples of rain-shadow deserts include the Mojave desert in the rain-shadow of the Sierra Nevada, the Patagonian desert in the rain-shadow of the Andes, and the Iranian desert in the rain-shadow of the Zagros mountains. Finally, upwelling deserts exist adjacent to areas where cold currents rise to the ocean surface, reducing evaporation. Examples include the Atacama desert, the Western Sahara, and the Namib desert.
Adaptations for Deserts
The type of vegetation and limited animal diversity of this biome are closely related to the low and unpredictable precipitation. Very dry deserts lack perennial vegetation that lives from one year to the next. Instead, many plants are annuals that grow quickly, reproduce when rainfall does occur, and then die. Many other plants in these areas are characterized by having a number of adaptations that conserve water, such as deep roots, reduced foliage, and water-storing stems. Seed plants in the desert produce seeds that can remain in dormancy for extended periods between rains. To reduce water loss and conserve energy, many desert animals like the fennec fox are nocturnal and burrow during the day.
Chaparral
The chaparral, also called the scrub forest, is found in California, along the Mediterranean Sea, and along the southern coast of Australia. The annual rainfall in this biome ranges from 65 cm to 75 cm (25.6–29.5 in), with the majority of rain falling in the winter. Due to the very dry summers, many chaparral plants are dormant during that season. The chaparral vegetation is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that only germinate after a hot fire. The ashes left behind after a fire are rich in nutrients, such as nitrogen, that fertilize the soil and promote plant regrowth.
Key Points
- Subtropical deserts are centered on the Tropics of Cancer and Capricorn.
- Subtropical deserts can be hot or cold, but they are all very dry,having very low annual precipitation.
- Because precipitation is so low in subtropical deserts, most plants are annuals which utilize adaptations to conserve water.
- Chaparrals (scrub forests) are found in California, along the Mediterranean Sea, and along the southern coast of Australia.
- Chaparrals are very wet in the winter, but very dry in the summer months; most chaparral plants stay dormant during the summer.
- Most chaparral plants are shrubs adapted to fires; some seeds only germinate after a fire.
Key Terms
- chaparral : a region of shrubs, typically dry in the summer and rainy in the winter
- subtropical desert : dry region centered on the Tropics of Cancer and Capricorn where evaporation exceeds precipitation