Hawaiian Forest Restoration

We were incredibly lucky to see the endangered 'Akiapola'au in the wild!

During the summers of 2002 and 2003 I was incredibly fortunate to participate in restoration research with Dr. Steve Goldsmith at Austin College. We studied the distribution and abundance of the primary food item of a highly endangered forest bird, ‘Akiapola’au (Hemignathus munroi), in mature forest and two different ages of restored forest tracts.

Hakalau Forest National Wildlife Refuge contains some of the last great tracts of Hawaiian montane wet forest at an upper elevation boundary of 6,000 feet above sea leve.

The upper boundary of native montane wet forest at Hakalau Forest National Wildlife refuge sits at approximately 6,000 feet above sea level. Clearing of native vegetation for cattle ranching and plantations of non-native trees has endangered many species of endemic plant and bird species. Koa is also a commercially desirable hardwood that has been logged in all but the most inaccessible areas. ‘Akiapola’au fills a woodpecker-type niche, using its strong lower bill to bore into the dead branches of Koa (Acacia koa) trees, and then using its curved upper bill to dig out the larvae of native Hawaiian longhorned beetles (Plagathmysus clavager and P. varians). You can see a neat video of this behavior on ARKive.org here.

A Hawaiian longhorned beetle adult from Hakalau Forest National Wildlife Refuge. The larvae feed only on the dead branches of Koa trees.

This research is important in determining whether re-planting tracts of native Acacia koatrees – the host for the native Hawaiian Longhorned beetles  – is successful in providing suitable foraging habitat for the ‘Aki’s. Our results show that the age of koa plantation affects density of beetles; older plantations harbor more beetles than young plantations, and canopy trees harbor more beetles than older plantations.

Dr. Steve Goldsmith collects a dead Koa branch from mature canopy using the manual version of a chainsaw that was installed in the canopy of this Koa tree by slingshot.

Our results also indicate that a particular characteristic of koa trees, diameter of branch, plays an important role in determining density of beetles in a given branch. Diameter of branch increased significantly with age of tree, and had a significant positive effect on number of beetles per branch in all age categories. Our results suggest that Koa plantations are providing additional foraging habitat for ‘Akiapola’au, and as plantations age their longhorned beetle fauna will come to resemble that of intact forest. Another important benefit of koa plantations is that they facilitate recolonization of understory plants and foster reestablishment of other elements of forest biological diversity, and thus have great potential to result in long-term restoration of forest community processes. Our research findings were published in The Southwestern Naturalist in 2007. Click here to download a PDF.

Hakalau Forest National Wildlife Refuge, Hawai'i: Doing conservation research on the Big Island of Hawai'i. Behind me are the big Koa (Acacia koa) and Ohi'a lehua (Meterosideros polymorpha) trees of Hawa'i's native montane wet forest.