Natural History

Natural History of Pu’u ‘Ohia (Mt. Tantalus)

Our story begins with one of the series of post rejuvenation eruptions of the Ko’olau Volcano that included everyday O’ahu landmarks like Punchbowl and Diamondhead. Somewhere around 60,000+ years ago the cinder cones of Tantalus and Pu’u Kakea became active. This is much later than the main eruptions of the Ko’olau Volcano, which for all intents and purposes went dormant roughly 1.8-2.6 million years ago. Because of this, the soils on Pu’u ‘Ohia are much younger than the surrounding area. Some other quick facts:

  • Soil – Tantalus silt loam series (40-70% slope) with cinder substratum, pH of approximately 5.5-7
  • Topography – Max elevation 2000 ft., slope from 10% to more than 70%
  • Rainfall – Approximately 150 inches (400 cm) annually
  • Vegatation – Mesic to Wet Forest

From these initial conditions, a lush lowland mesic forests developed. This forest would have been dominated by various ‘Ohia lehua species (Metrosideros spp.) and Koa (Acacia koa). Other common trees would have included Kopiko (Psychotria mariniana), Kalia (Elaeocarpus bifidus), Kokio ke’o ke’o (Hibiscus arnottianus) and Hame (Antidesma platyphyllum). The understorey would have been densely covered with plants such as Hawaiian lobeliads (Cyanea & Clermontia ssp.), tree ferns (Cibotium & Sadleria ssp.) and ‘Ie’ie (Frycinetia arborea).

This forest would have had denizens found nowhere else in the world. Visitors to this forest would have been greeted by many birds that had lost the ability to fly. The largest herbivores would have been giant, flightless ducks (Thambetochen xanion). Other flightless birds that would have been found poking about the understorey were several species of flightless rails (Porzana ssp.)

Oahu extinct birds

Courtesy of Julian Hume

The volant birds found in the trees would have been unique too. Unknown today but probably common in the not too distant past would have been a couple species of corvids. ‘Alala (Corvus hawaiiensis) used to be found here as well as the strange Deep-billed Crow (Corvus implexus). One species of the new world solitaires, the Amaui (Mydestes wahuensis), would have been seen foraging for fruits. ‘Elepaio, luckily still extant, were a common fly-catching bird in the forest.

Endemic Hawaiian Honeycreepers, which radiated spectacularly in the chain, are still found in the forests today. ‘Amakihi (Hemignathus flavus) and ‘Apapane (Himatone sanguinea) can be seen with ease whenever the ‘ohia trees are in bloom. They are a small sample of the diversity of the group once found here. Icterid-like gapers (Aidemedia chascax), ‘Akialoa (Hemignathus ellisiana), Nukupu’u (Hemignathus lucidus subsp. lucidus), and ‘Alauahio (Paroreomyza maculata) were insectivores that would have been seen probing moss covered trees and the leaf litter. Brightly colored ‘Akepa (Loxops coccineus subsp. wolstemholmei) were most commonly seen high in the treetops.

The uniquely Hawaiian mohoidae would have been found in the forests of Pu’u ‘Ohia. Kioea (Chaetoptila angustipluma) and the spectacularly plumed O’ahu ‘o’o (Moho apicalis) would have been seen chasing away other nectivorous birds from favored trees.

2011 Hawai’i Conservation Conference – Glenn Metzler / The Dynamic Forest at Pu’u ‘Ohi’a (Mount Tantalus), O’ahu