Stand Structure of a Montane Rain Forest on Mauna Loa, Hawaii

Cooray, Ranjit G.
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Island Ecosystems IRP, U.S. International Biological Program
It has been suggested that the native tree species Acacia koa var. hawaiiensis Rock is not adequately reproducing and may be gradually disappearing from the montane rain forest in Hawaii. A structural analysis was carried out in an Acacia-Metrosideros-Cibotium montane rain forest on the east slope of Mauna Loa on the island of Hawaii, to determine the status of all woody plant species and especially the status of the tall dominant tree species Acacia koa. Profile diagrams were also made for systematically chosen segments in the stand. The profile diagrams showed three important structural variations within the homogenous vegetation stand. Woody plant distribution by size-classes, regardless of species, showed an inverse J-shaped distribution characteristic of a stable, self maintaining forest. Structural analysis of individual species populations showed good stability trends for most low-stature and intermediate-stature tree species, but some species were less abundant than others. Acacia koa was present in all size-classes. The stand contained four times as many seedlings and suckers as tall emergent trees. Thus, this species is regenerating and maintaining itself. Low numbers of koa saplings, small trees and intermediate-sized trees may reflect rapid height growth, rather than a gradual decline of this species in the forest. Larger numbers of koa seedlings may also get established in pulses when large canopy gaps are formed. Rooting activity of feral pigs destroys Acacia koa seedlings rooted in mineral soil. Most of the healthy koa saplings were observed on root collars of scattered wind-thrown koa trees. This type of “gap-phase replacement” can be related to the protection seedlings receive from pig activity. Pig populations, if allowed to increase, may cause a change in the stability trends of species populations, and an overall deterioration of this native rain forest ecosystem.
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Kilauea Forest Reserve, Acacia koa, Metrosideros, Cibotium, stand structure
Cooray RG. 1974. Stand structure of a montane rain forest on Mauna Loa, Hawaii. Honolulu (HI): Island Ecosystems IRP, U.S. International Biological Program. International Biological Program Technical Report, 44.
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