Vegetation is sparse in hot desert regions due to a shortage of water, high levels of evaporation, lack of humus and shallow, stony soils. Despite these unfavourable conditions, some plant species have adapted to the extreme heat and drought. Vegetation is spread out to avoid competition for very limited resources.
Adaptations These adaptations include: • Root systems • Ephemerals
Root Systems
) Fig. 28.7 Root systems of desert flora
0 1 2 3 4
1 2 3 4 5 6
Cactus
0 1 2 3 4
Succulent Dry
Shallow roots gather rainwater close to the surface
Water table
1 2 3 4 5 6 7 8 9
Acacia tree Wide roots
spread out near the surface to absorb water close to the surface
Branches where water encountered
Capillary Fringe Taproots reach groundwater
• Succulents • Fruit growth
• Defence systems
Deep taproot
As water is scarce, plants must develop an efficient root system. Hot desert vegetation has one of two types of roots:
1. Some plants have developed shallow roots which spread outwards over a large area to collect moisture during times of rainfall. Shallow roots are also effective at collecting dew that forms on the surface at night. Most cacti have shallow roots, as does the creosote bush. By drawing water and any organic matter from close to the surface, the roots avoid having to penetrate calcium hardpans where calcification has occurred.
GEO DICTIONARY
Ephemerals: plants which have short life cycles; desert ephemerals have adapted to take advantage of short wet periods
556 EARTH
2. Some plants have developed deep taproots to allow them to reach groundwater deep in the soil. For example, the acacia tree’s taproots can reach water 6–7 metres beneath the surface.
Ephemerals
Some plants have adapted their life cycle to take advantage of the unpredictable desert rains. These plants are known as ephemerals. The seeds of ephemerals have waxy coats which allows them to retain their
