Buttresses are tension elements, being larger on the side away from the stress of asymmetrical canopies.
When the roots spread horizontally, they are able to cover a wider area for collecting nutrients.
They stay near the upper soil layer because all the main nutrients are found there.
The largest for which there is photographic evidence is a Moreton Bay Fig (Ficus macrophylla) at Fig Tree Pocket (an outlying district of Brisbane, Queensland) which was photographed in 1866 with an adult man.
[4] The most extensive buttresses are those of the Kapok, or Silk Cotton Tree (Ceiba pentandra), of the Neotropics and tropical Africa.