Warm Desserts Of North America

5 Pages 1233 Words

North America contains three “warm” deserts. They are known as the Chihuahuan, the Sonoran, and the Mojave deserts. Warm deserts have relatively high temperatures during the long summer months and low amounts of rainfall; as a result, the evolutionary affinities of their plant life are largely with the subtropical plant communities to the south. Desert soils tend to be poorly developed, with a high content of mineral particles but little organic matter. The poor soil is caused by low plant productivity, which restricts the soil-building properties of microorganisms that convert organic matter into the humus components of soils. Soils with low organic matter content have a low water-holding capacity, adding to the aridity of the land (Smith et al 1997).
Unlike other types of North American biomes, warm desert plants are competing for water, not light. The availability of water is the major factor determining the types of organisms that can live in the deserts. Warm deserts typically receive less than 25 cm of precipitation per year. The amount of evaporation is often greater than the amount of rainfall that occurs. Evaporation is an important factor contributing to aridity. Rising air cools and can hold less moisture, producing clouds and precipitation; falling air warms, absorbing moisture. Areas with few clouds, bodies of water, and little vegetation absorb most of the sun's radiation, thus heating the air at the soil surface. High wind in open country also contributes to aridity of the warm desert (Eddins, 2002).
Plants that have adapted to dry habitats by altering their physical structure are known as xerophytes. Xerophytes, such as cacti, are the largest type plants living in the deserts of the North America. To reduce transpiration, xerophytes usually have few or no leaves and have special means of storing and conserving water. Most annual desert plants germinate only after heavy seasonal rain, and then comple...