Rehabilitation of seasonally dry ‘ōhi‘a woodlands and mesic koa forest following the Broomsedge Fire, Hawaii Volcanoes National Park

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Loh, Rhonda; McDaniel, Sierra; Schultz, Matthew; Ainsworth, Alison; Benitez, David; Palumbo, David; Smith, Kimberley; Tunison, Tim; Vaidya, Maya
Broomsedge Fire; Metrosideros polymorpha; Acacia koa
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The Broomsedge Fire, accidentally started June 30, 2000, burned 1008 acres of native plant communities (3,800-4,100 ft elevation) in Hawaii Volcanoes National Park. The communities affected were seasonally dry ‘ōhi‘a woodland (923 ac) and mesic koa forest (85 ac). Fire is expected to dramatically reduce fire-sensitive native vegetation and stimulate fire-adapted alien grasses, thereby increasing fire potential in the burn area. Two strategies were used to revegetate burned communities. The strategy in former seasonally dry ‘ōhi‘a (Metrosideros polymorpha) woodlands (923 ac) was to establish a community of fire-tolerant native species that could co-exist with alien grasses and wildfire. The strategy in fire damaged mesic koa (Acacia koa) forest (85 ac) was to increase fire resistance in specific sites by rebuilding the structure of the native understory thereby reducing the risk of wildfire spreading into high priority areas. This same strategy, to increase fire resistance by establishing a thick understory beneath a strip of koa forest, was used to reduce the likelihood of fire carrying between the Park and private landowners in the nearby Volcano Golf Course Subdivision. Restoration efforts began one week after the fire and continued to 07/08/03. Approximately three thousand worker days, including 1,239 volunteer days, were spent completing the project. Thirty native plant species were established in the burn by a combination of seeding >2.7 million seeds and outplanting 18,798 individuals that were propagated in park temporary greenhouses. Along with re-vegetation, workers searched and removed aggressive alien woody species (e.g. Myrica faya, Psidium cattleianum, Rubus argutus) in order to prevent their establishment in the burn. Over 7,400 individuals were discovered and chemically or manually eradicated. Permanent monitoring plots were established and the vegetation measured to evaluate the success of the project. Average survivorship of outplants in the plots was >80% (all species). There was significant recruitment of four species (Acacia koa, Bidens hawaiiensis, Dodonaea viscosa, Sophora chrysophylla) from seed additions into the burn. By 2004, eleven re-introduced native species had reached reproductive maturity in the burn area, Including four tree, three shrub, a lily, Hawaiian poppy, and two grass species. Monitoring should continue over the next few decades to evaluate long term successional outcomes as a result of the restoration project. The successful establishment of species by outplanting and artificial seeding in the Broomsedge Burn serves as a model for restoration in other fire-affected dry ‘ōhi‘a woodlands in the Park.