Describe the characteristics of semi-desert vegetation.

Candidates are expected to describe the characteristics of semi-desert vegetation as follows ;

• The vegetation has bush thorny trees with scrubs growing in between.
• Many plant have deep /tap penetrating roots that enables them to draw water from underground
• Many plants have tiny thorny leaves that help them to reduce the rate of water loss e.g. cacti, acacia etc. and to deter animals which may wish to eat them
• Some trees have swollen trunks in which they store water for use during the long dry seasons e.g. Baobab.

• Some desert plants particularly those in the cactus family have stems that swell up with water only to  contract later as moisture is slowly lost through transpiration.
• In some desert plants e.g. the cacti transpiration takes place through the stems but is reduced by the stomata closing during the day and opening it at night to control loss of water.
• Stems of some desert plants e.g. Australian eucalyptus have a thick, waxy cuticle / bark to control loss of water through transpiration.
• Plants such as creosote bush, desert holly, sage and saltbush have roots that spread out over wide areas near to the surface to take advantage of any rain or dew to support their growth due to limited rainfall.
• Some desert / semi-desert plants for example the cactus in the Sahara, Namib desert have very long roots that may exceed 15metres deep to tap underground water supplies.
• Desert plants such as cactus, desert holly and creosote are widely spaced  to avoid congestion and competition for water.
• Some desert plants e.g. the cactus have bulbous roots for storing water for  use during the long periods  of drought which may be more than 10 metres.
• Seeds of deserts plants have a thick case that protects the inner centre. This enables them lie dormant for months or even several years until the next rainfall. The thick case provides protection against pests and animals.
• Some desert plants e.g. salt bush in the Sahara and Namib Desert are halophytic and can survive in salty depressions while others like date palm survive where water table is near enough to the surface to form Oases.
• Many of them can complete their life cycles in two or three weeks during periods of short lived rains. These are termed as ephemerals. An occasional downpour produces a short lived burst of plants grown where shrubs and herbaceous plants like sunflower primroses, poppies, lupines exotically for a brief season and a carpet of grass springs up, soon to be scorched by the heat.