page_title: Tropical desert
section_title: Biological adaption to aridity
hierarchical_section_title: Tropical desert / Biogeography / Biological adaption to aridity
caption_attribution_description: The United States Congress designated the Juniper Dunes Wilderness in 1984 and it now has a total of 6,869 acres. All of this wilderness is located in Washington and is managed by the Bureau of Land Management. The Juniper Dunes Wilderness preserves the northernmost growth of western juniper, some of which have been around for 150 years, along with windswept sand dunes measuring 130 feet in height and 1,000 feet in width. Other than junipers, no trees grow in significant numbers here, but many bushes and flowers bloom wondrously come spring, although the mountains that separate western and eastern Washington generally wring the moisture from the air. The landscape here takes quite a battering, in fact, with strong southwest winds to build the dunes, seven to eight inches of precipitation to moisten them, a foot or so of snow that drifts down in winter, and summer temperatures that occasionally rise above 100 degrees Fahrenheit. Elevations range from 750 feet to 1,130 feet above sea level. But plenty of animals thrive despite the extremes: mule deer, bobcats, coyotes, badgers, skunks, weasels, porcupines, pocket gophers, kangaroo rats, several species of mice, hawks, owls, ravens, quail, partridge, pheasants, doves, numerous songbirds, and rattlesnakes. Currently no legal access to Juniper Dunes exists, as the entire surrounding land is privately owned. With permission, you can travel via old jeep trails that end near the boundary. Getting all the way to the Wilderness gate can be risky business, even with a high clearance 4-wheel drive (highly recommended), and there is a significant risk of getting stuck in the loose sand of the last jeep trail, Wilderness Road, especially in warm months when there is little moisture in the sand. One option is to park at the Off-Highway Vehicle staging area on Juniper Road (also a jeep trail) and walk an additional +1 mile to the Wilderness Gate. This is absolutely necessary if you are pulling a trailer. You'll find no maintained trails and no water in the Wilderness, and backpackers and horseback riders should also be aware of the likelihood of large temperature variation for overnight stays. Additional information about the Juniper Dunes Wilderness, and all the other BLM Wilderness areas in Oregon/Washington, is available online at: www.blm.gov/or/resources/recreation/wilderness2.php
context_page_description: Tropical deserts are located in regions between 5 and 30 degrees latitude. Environment is very extreme. They have the highest average monthly temperature on Earth. Rainfall is sporadic; precipitation may not be observed at all in a few years. In addition to these extreme environmental and climate conditions, most tropical deserts are covered with sand and rocks, and thus too flat and lacking in vegetation to block out the wind. Wind may erode and transport sand, rocks and other materials; these are known as eolian processes. Landforms caused by wind erosion vary greatly in characteristics and size. Representative landforms include depressions and pans, Yardangs, inverted topography and ventifacts. No significant populations can survive in tropical deserts due to extreme aridity, heat and the paucity of vegetation; only specific flora and fauna with special behavioral and physical mechanisms are supported. Although tropical deserts are considered to be harsh and barren, they are in fact important sources of natural resources and plays a significant role in economic development.
context_section_description: For flora, general adaptations including transforming leaves into spines to protect themselves. With the reduction in leaf area, the stem develops as a major photosynthetic structure, which is also responsible for storing water. A common example is the cactus, which has a specific means of storing and conserving water, along with few or no leaves to minimize transpiration.
  In addition to the protection provided by spines, chemical defences are also very common. Desert plants grow slowly as less photosynthesis takes place, allowing them to invest more in defence. 
  Another adaption is the development of extremely long roots that allow the flora to acquire moisture at the water table. Furthermore, some desert plants exhibit behavioural adaption; for instance, some flora live for only one season or one year, and desert perennials can survive by staying dormant during extremely dry periods; when the environment receives more moisture, they become active again.
  For fauna, the easiest way is to stay away from the surface of the tropical deserts as much as possible to avoid the heat and aridity. As a result of the scarcity of water, most animals in these regions get their water from eating succulent plants and seeds, or from the tissues and blood of their prey. They also have specific ways to store water and prevent water from leaving their bodies. Some animals live in burrows under the ground which are not too hot and relatively humid; they stay in their burrows during the heat of the day, and only come out to seek food at night. Examples of these animals include kangaroo rats and lizards. Other animals, such as wolf spiders and scorpions, have a thick outer covering that minimizes moisture loss. Animals in tropical deserts have also been found to concentrate their urine in their kidneys to excrete less water.
caption: Cactus
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