This garden is named after Puna, the deity of the kumara. Kumara was introduced from Polynesia by the early Maori settlers, becoming their most important crop and essential to the survival of many communities. Kumara tubers rot if they were grown in wet soil so they were planted into mounds.
Interesting shot, the mounds give texture and lines. In NW Spain storage barns - called 'horreos' - are built on pillars to safeguard the crops from animals. Is that the same reason here?