Question

Why the tree of the thorn forest has long roots and thin and small leaves

Answer 1

Thorn forests are mostly found in dry regions like cold or hot deserts.In such regions water is scarce and heat is scorching.Thorn forests of these areas have adapted themselves to these surroundings like long roots and small leaves or thorns.
1)Long roots- they have long roots to collect water from even several meters beneath the earth(underground water) so that they are never out of water.
2)Thorns or short leaves- they have leaves that are very small and some leaves have turned themselves into thorns to prevent loss of water by the process of transpiration.

Answer 2

to prevent transpiration and to collect water from underground.

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