8
Plants
1.C4T1 2.C4T2 3.C4T3
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C14M3
4. The so-called Brush lily, with its characteristic form that
corresponds to its reproduction cycle, is highly toxic,
particularly for cattle. Its scientific name, Boophane haemanthoides,
comes from boos, which means beef and phonos meaning to kill.
The cricket Dictyophorus spumans absorbs the plant toxins that help
protect it from predators. Its black carapace, trimmed with
red and orange, warns predators of its toxic qualities.
© Jean-Michel Battin

Plant adaptations to drought

It is known that living organisms have evolved throughout the course of Earth's history. The processes of evolution enable animals and plants to adapt progressively to their environment. In this way, animals from cold regions possess fur or thick plumage while animals from hot regions possess close-cropped fur and long legs, to distance their body from ground surface heat. Moreover, vegetation in drylands present characteristics acquired over time that allows them to survive high temperatures and water shortages. To prevent dessication and therefore save water, the vegetation has reduced the number and surface area of leaves, which develop into scales or thorns. The loss of leaves during the hot and dry season also helps to save water.

They orient their leaves towards the shade, develop rounded or padded forms and stock water in specific organs such as thickened stems (fleshy, succulent plants, cacti) and oversized trunks (baobabs).
Such plants optimize water absorbtion by spreading out their roots horizontally over a large area below the plant or by driving their roots deep into groundwater reserves (See diagram).

C4M1

Only halophytes (salt-tolerant plants) develop in certain soils of the drylands where they contain a high salt content (salinity).

Plants protect themselves from herbivores in two ways:

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5. Bolivia: halophytes growing on salt-rich soils,
they are particularly tolerant to high salt concentrations.
© Yazid Tizi

Types of plant formations and ecosystems

Depending on the climate and soil type, various groups of plants develop concurrently to form living communities that are the basis of terrestrial ecosystems.
The phenomenon of desertification limits vegetation cover to a single level.
In drylands, six major types of plant formations are observed:

1. lichen forms that develop in coastal drylands.
2. the formation of fleshy or succulent plants (cacti, euphorbias, senecios).
3. shrubland steppes with discontinuous cover.
4. herbaceous savannah with open spaces where grasses predominate.
5. the shrub bushland (shrub, mallee, catinga) where plants often possess thorns.
6. dry forests with tall trees that shed leaves during the dry season.

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6. Succulent plants such as Cacti and euphorbias contain
water reserves in their thick stalks, leaves and trunks.
© Jean-Michel Battin

Cacti
Cacti are plants that are characteristic of the arid environment. Originating from drylands in the Americas, they are found from the United States of America through Central America to Chile. Cacti, whose thorns replace leaves to limit evaporation, help combat desertification by providing structure to the soil with their roots. The fruits and branches of certain cacti (prickly pear) are fit for human and domestic animal consumption (See the case study from Ecuador). In Africa, euphorbias have developed similar adaptation strategies to drought. When animal or plant species, which are geographically distant and/or belong to different families, evolve in a similar way due to comparable environmental pressures, evolutionary convergence is said to occur. Euphorbias and cacti are a good example of this type of evolutionary convergence.

activities

pencil

Which plants characterize the arid environment in your region?

Which plants characterize other arid regions?

Are there any similarities in plant type?

Paste photos or pictures of these plants on the wall chart.

pencil

Place several of these plants in plastic pots (Only select plants that are abundant in your area). Calculate the quantity of water needed for watering. Do certain plants need more water than others to grow?

Why do you think this is so?

smile

Which tree plays an important economic role in your region?

Describe the tree and all its possible uses.

Identify a tree that you recognize well. Visit it regularly and keep a check on it. If needs be, water it occasionally, add some compost, etc.

Do you see any improvement in the condition of the tree over days, weeks?

smile

Which of the following plants have adapted to aridity over
the course of evolution:

• cacti
• hyancinths
• orchids
• euphorbias
• palms
• baobabs
• water lilies
• ferns
• bamboo
• eucalyptus


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