Why Might There Be a Lot of Spacing Between the Desert

Why might there be a lot of spacing between the desert plants shown growing in this photo?

A) The plants need room to grow and expand as they mature.
B) The plants exploit the nitrogen produced in the atmosphere causing only stronger plants to survive the harsh desert- like environment.
C) The other plants around them have died because there is not enough space in the desert area where they grow.
D) The plants exploit water and nutrients preventing other shrubs from establishing in their area.
E) The roots of strong plants are established and force other plants out because they are more mature.