Complex sentence: There are only 231 specimens of this critically endangered species, the largest about 20 m tall; the majority are very old, estimated to be over 2000 years old, with very little regeneration due to the increasing desertification of the Sahara.
Split into simpler sentences: There are only 231 specimens of this critically endangered species, the largest about 20 m tall. The majority are very old, estimated to be over 2000 years old, with very little regeneration due to the increasing desertification of the Sahara.