Document: ROB-3-64-37

Restoration of Hawaiian dry forests.

CABIN, R.J* ¹, S.GWELLER ², D.HLORENCE ³, S.CORDELL ¹ and L.JHADWAY ³

USDA Forest Service, Hilo, HI 96720, USA ¹
UC Irvine, Irvine, CA, USA ²
National Tropical Botanical Garden, Lawai, HI, USA ³

Abstract:
Like many other tropical dry forest ecosystems, Hawaiian dry forests are severely endangered and degraded. On the Island of Hawaii, remnant dry forests are dominated by fountain grass (Pennisetum setaceum), a highly invasive exotic bunchgrass that suppresses native vegetation and greatly increases the risk of fire. To investigate plausible cost-effective methods for controlling fountain grass and re-establishing native plant populations, we established 8 experimental blocks in a highly degraded, treeless area dominated by fountain grass. Each block consisted of 4, 6 by 6m plots randomly assigned to 1 of 4 fountain grass control treatments: Control, weed whack/herbicide, weed whack/black plastic mulch (to suppress and "cook" the remaining fountain grass), and bulldoze (to completely remove fountain grass from the plot). We also erected 50% shade cloth structures over 4 randomly selected blocks to simulate shade conditions found under intact native dry forests. We divided each plot into 4 quadrats: 1 outplant quadrat, 1 direct-seed quadrat, and 2 control quadrats, and watered all quadrats twice weekly. Six months after outplanting or seeding with a mixture of 12 native species, we found that the number of individuals and percent cover of native plants was significantly greater in the shaded vs. full sun plots, and found no significant difference between the % cover of fountain grass within these 2 treatments. The number of individuals and % cover of native species was greatest in the bulldozed plots, intermediate in the weed whack/herbicide and weed whack/plastic treatments, and least in the control plots. Percent cover of fountain grass did not differ among the 3 fountain grass removal treatments, which were all less than 1/5 that of the untreated control plots. We also found that the % cover of native species was greatest in the outplanted quadrats, intermediate in the seeded quadrats, and lowest in the control quadrats, while the % cover of fountain grass was greatest in the control quadrats and did not differ between the outplanted and seeded quadrats. These results suggest that relatively cheap and efficient techniques such as bulldozing and direct-seeding of native species can be employed to control fountain grass and restore Hawaii's native dry forest communities.

Keywords: restoration, tropical dry forest, Hawaii, alien species control

This abstract is being presented at: 9:00 AM in session:
Oral Session #60: Forest Restoration.