How do shrubs adapt to the desert

It has tiny leaves that close their stomata pores during the day to avoid water loss and open them at night to absorb moisture. Creosote has an extensive double root system -- both radial and deep -- to accumulate water from both surface and ground water. Some perennials, such as the Ocotillo , survive by becoming dormant during dry periods, then springing to life when water becomes available.

After rain falls, the Ocotillo quickly grows a new suit of leaves to photosynthesize food. Flowers bloom within a few weeks, and when seeds become ripe and fall, the Ocotillo loses its leaves again and re-enters dormancy. This process may occur as many as five times a year.

The Ocotillo also has a waxy coating on stems which serves to seal in moisture during periods of dormancy. Another example of perennials that utilize dormancy as a means of evading drought are bulbs, members of the lily family. The tops of bulbs dry out completely and leave no trace of their existence above ground during dormant periods.

They are able to store enough nourishment to survive for long periods in rocky or alluvial soils. The Desert Lily, also known as the Ajo, is found at a depth of 18 inches or more. Adequate winter rains can rouse it to life after years of dormancy. The term "annuals" implies blooming yearly, but since this is not always the case, desert annuals are more accurately referred to as "ephemerals. Contrary to the usual idea that deserts are uniformly hot, dry and homogeneous in their lack of plant life, they are actually biologically diverse and comprise a multitude of micro-climates changing from year to year.

Each season's unique precipitation pattern falls on a huge variety of mini-environments. And each year in each of these tiny eco-niches, a different medley of plants bloom as different species thrive. Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are the sprinters of the plant world, sending flower stalks jetting out in a few days.

The peak of this bloom may last for just days or many weeks, depending on the weather and difference in elevation. The higher one goes, the later blooms come. Different varieties of plants will be in bloom from day to day, and even hour to hour, since some open early and others later in the day. Ephemerals such as the Desert Sand Verbena , Desert Paintbrush and Mojave Aster usually germinate in the spring following winter rains. They grow quickly, flower and produce seeds before dying and scattering their progeny to the desert floor.

Desert plants have developed three main adaptive strategies: succulence, drought tolerance and drought avoidance. Each of these is a different but effective suite of adaptations for prospering under conditions that would kill plants from other regions. Succulent plants store water in fleshy leaves, stems or roots.

All cacti are succulents, as are such non-cactus desert dwellers as agave, aloe, elephant trees, and many euphorbias. Several other adaptations are essential for the water storing habit to be effective.

A succulent must be able to absorb large quantities of water in short periods. Desert rains are often light and brief, and the soil dries rapidly under an intense sun. To cope with these conditions, nearly all succulents have extensive, shallow root systems. The roots of a saguaro extend horizontally about as far as the plant is tall but are rarely more than four inches 10 cm deep. The water-absorbing roots are mostly within the upper half inch 1.

Succulents must be able to maintain their water hoards in a desiccating environment and use it as efficiently as possible. The stems and leaves of most species have waxy cuticles that render them nearly waterproof when the stomates are closed. Water is further conserved by reduced surface areas; most succulents have few leaves agaves , no leaves most cacti , or leaves that are deciduous in dry seasons elephant trees, ocotillos, boojums.

Many succulents, as well as semisucculents such as most yuccas, epiphytic orchids, and xerophytic bromeliads, possess a water-efficient variant of photosynthesis called CAM, an acronym for Crassulacean Acid Metabolism. CAM plants open their stomates for gas exchange at night and store carbon dioxide. By day, while the stomates are closed, photosynthesis is conducted using the stored carbon dioxide. Because of the lower temperatures and higher humidity at night, CAM plants lose one-tenth as much water per unit of carbohydrate synthesized as standard C3 plants.

Another valuable attribute of CAM plants is their capability for idling metabolism during droughts. When CAM plants become water-stressed, the stomates remain closed both day and night; gas exchange and water loss nearly cease. The plant, however, maintains a low level of metabolism in the still-moist tissues. Just as an idling engine can rev up to full speed more quickly than a cold one, an idling CAM plant can resume full growth in 24 to 48 hours after a rain.

Therefore, succulents can take rapid advantage of ephemeral surface moisture. Stored water in an arid environment requires protection from thirsty animals. Most succulent plants are spiny or toxic, often both.

Some protect themselves by growing only in inaccessible locations. A variety of shrubs grow in the desert including tumbleweed, a symbol of the American western deserts, most commonly seen when wind pushes the round, dry balls across the landscape. Brittle bush grows in the Mojave and Sonoran deserts where it produces beautiful yellow flowers in the spring. Other bushes include turpentine bush, creosote and prickly pears. In the cold deserts, shrubs grow very close to the ground and include several types of willows.

Desert climates stay dry because the air coming down from high-pressure zones gets heated from the hot ground before it can turn into rain. A range of hot and cold temperatures also causes shrubs to adapt. In the hot and dry desert, shrubs must deal with warm days and soaring summer temperatures. In the semi-arid desert, the climate consists of hot, dry summers and mild winters. Coastal deserts feature hot summers and cool winters with temperatures dropping down to freezing.

Shrubs in the cold desert must deal with lots of snow in the winter and cool, short summers.