Desert Plant Adaptations

Concepts:
Plant Anatomy
Desert Survival

Objectives: 
Students will be able to identify adaptations that plants have developed to deal with harsh desert conditions, as well as explain how these adaptations help to protect these plants. 

Background: 
information summarized from:
Phillips, Steven J. and Patricia Wentworth Comus. A Natural History of the Sonoran Desert. Arizona-Sonora Desert Museum Press: Tucson, 2000.

In order to survive in the desert, plants must develop adaptations to help them to tolerate the harsh conditions of the desert. The major desert condition that desert plants and animals must deal with is the lack of water.  There are three main ways to deal with this: succulence, drought avoidance, and drought evasion.  

Succulents are very unique to desert environments.  They store water in spongy, fleshy leaves, stems or roots.  The roots are very efficient at absorbing large amounts of water in a short amount of time.  Saguaro roots are shallow but expansive, reaching as far as the plant is tall.

Plants also must conserve this water which they store.  Because of the extreme summer heat, plants can lose water from evaporation.  This can be avoided by having a waterproof, waxy coating over the leaves and stems.

Water can also be conserved by having a reduced surface area through which to lose water by evaporation.  Surface area is reduced by having few, smaller, or no leaves.  Cacti and most succulents have no leaves, trees like the palo verde and mesquite, as well as shrubs like bursage and creosote have very small leaves. 

Plants must also conserve water by protecting it from animals in search of water.  Many desert animals get the water that they need from plants.  Succulents are often targeted because of their water storage systems.  Succulents protect themselves by having spines or by being bitter or toxic.  Plants without these defenses must defend and protect themselves in another way.  They either grow only in inaccessible places, or are camouflaged. 

Another method of survival for desert plants is drought tolerance.  Plants may look dead, but in order to avoid desiccation, they drop their leaves and become dormant.  These plants often have a more extensive root system than plants in wetter conditions, as well as more extensive roots than those of succulents. 

Desert plants can also survive the harsh conditions of desert summers and droughts by simply avoiding them.  Many wildflowers, as well as other plants are annuals; they survive one season, release seeds and die.  These seeds can survive dormant in seed banks until the conditions are right for them to grow. 

Activity:
Desert Ecology Scavenger Hunt
Plant Adaptation Scavenger Hunt
Creature Creation (this activity relates to animal rather than plant adaptations)
Plant Collection

Sources:

Phillips, Steven J. and Patricia Wentworth Comus. A Natural History of the Sonoran Desert. Arizona-Sonora Desert Museum Press: Tucson, 2000. 

For more information, see: Desert USA -- Desert adaptations