Role of Decaying Logs and Other Organic Seedbeds in Natural Regeneration of Hawaiian Forest Species on Abandoned Montane Pasture1

Natural regeneration is one mechanism by which native rnixedspecies forests become reestablished on abandoned pasture. This study was done to determine patterns of and requirement for natural regeneration of native species in an open woodland after removal of cattle. Ten 50by 50-m quadrats were randomly selected within a 16-ha exclosure located at 1,700-m elevation inside the Hakalau Forest National Wildlife Refuge on the island of Hawaii. In 1989 and 1991, data were collected for all regeneration in the quadrats, including species, height, and seedbed type. More than 2,000 individuals were found in 1989, two years after the cattle were excluded. By 1991, the number had doubled to more than 4,000 individuals. Ohia was the most abundant species both years. Mineral soil accounted for about 97 percent of the potential seedbed area inside the exclosure, but less than 25 percent of all regeneration was rooted there in 1989 and less than 33 percent in 1991. In contrast, decaying logs made up less than 2 percent of the potential seedbed area, but they supported about 70 percent of all regeneration in 1989 and 53 percent in 1991. The data indicated that organic seedbeds are preferred sites for recruitment, establishment, and early growth of olapa, kawau, and ohelo. Ohia's preference for organic seedbed was less pronounced. Tree fern showed a strong preference for mineral soil. Koa was nondiscriminatory. During the past 10 years, interest has grown in developing technology for restoring native mixed-species forests to deforested and degraded forest lands of Hawaii. Concern for the recovery of endangered species has been a key motivating factor for this interest. Federal and State forest landowners are mandated by law to protect and restore endangered species. Much of the effort to accomplish those goals is focused on habitat protection and restoration. The Forest Service has no National Forest land in Hawaii, and hence it has no management responsibilities in the State. However, the Forest Service maintains an active forest research program in Hawaii to help other Federal, State, and private forest owners develop technology for better management. Part of that research program is focused on reforestation. A 16-ha exclosure, hereafter called the woodland exclosure, was built by the Hakalau Forest National Wildlife Refuge in 1987 to provide a cattle-free area for conducting reforestation experiments (Conrad and others 1988). Two years after the fence was erected, I observed that native woody species were regenerating naturally, but almost always in association with fallen, decaying logs or other organic seedbeds. This study was done to determine if organic seedbeds were as important to natural regeneration of native species as cursory observations suggested. Specifically I wanted to (1) determine the abundance of native regeneration, by species and seedbed type, and (2) determine the areal extent of each seedbed type. The findings, if confirmed by similar studies elsewhere, could have application 'An abbreviated version of this paper was presented at the Session on Tropical Forestry for People of the Pacific, XVII Pacific Science Congress, May 27-28, 1991, Honolulu, Hawaii. 'Research Forester, Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture, Honolulu, HI 96813. USDA Forest Service Gen. Tech. Rep. PSW-129. 1992. in evaluating the potential for natural regeneration of open pasture where organic seedbeds no longer exist.