PARENT SESSION
Contributed Oral Session 106: Restoration and Adaptive Management: Forests; Grasslands
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal

Effects of shade, water and grass removal on Hawaiian dry forest restoration.

Thaxton, Jarrod^*,1, Cabin, Robert², Cordell, Susan¹, Sandquist, Darren³, ¹ USDA Forest Service, Hilo, HI² SUNY Plattsburgh, Plattsburgh, NY³ California State University Fullerton, Fullerton, CA

ABSTRACT- Tropical dry forests are one of the most endangered forest types worldwide. In the Hawaiian islands, native dry forests presently cover less than 10% of their original area. Many sites that historically supported dry forest now contain open grasslands dominated by alien species. In an effort to develop restoration strategies for these degraded sites, we are exploring how non-native grasses may limit establishment and growth of native dry forest species at a site dominated by African fountain grass (Pennisetum setaceum) on the leeward side of the island of Hawaii. In a factorial field experiment, we examined the effects of shade (60% shade vs. full sun), water (supplemental vs. ambient ) and fountain grass removal (bulldozing vs. weed-whack + herbicide vs. control) on growth and survival of native seedlings. In April 2004, we outplanted 1800 seedlings of 10 native species of trees (Caesalpinia kavaiensis, Diospyros sandwicensis, Kokia drynarioides, Pleomele hawaiiensis, Reynoldsia sandwicensis),shrubs (Chenopodium oahuense, Senna gaudichaudii, Sida fallax) and vines (Canavalia hawaiiensis, Cocculus orbicularis). After one year, our results indicated significant effects of shade, water and fountain grass removal on seedling growth and survival. Seedling survival and growth tended to be highest in plots that were shaded and received supplemental water. These effects were particularly pronounced where fountain grass had been removed by bulldozing. In contrast, seedlings tended to perform poorly in plots where fountain grass was left intact, particularly when coupled with a lack of supplemental water. These results indicate that fountain grass may limit native seedlings primarily through competition for water. Furthermore, any positive effects of fountain grass shade appear to be outweighed by negative effects on water availability. Restoration on these sites appears to be contingent on removal of fountain grass, coupled with at least an initial period of supplemental water and shade.

Key words: tropical dry forest, invasive species, Hawaii, restoration