Burned Area Emergency Rehabiltation Final Accomplishment Report
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Broomsedge Burn Hawai`i Volcanoes National Park Burned Area Emergency Rehabiltation Final Accomplishment Report National Park Service December 15, 2004 Prepared by: Rhonda Loh, Botanist, Hawaii Volcanoes National Park Alison Ainsworth, David Benitez, Sierra Mcdaniel, Matthew Schultz, Kimberly Smith, Tim Tunison, Maya Vaidya
Executive Summary The Broomedge Fire, 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 `ohi`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 `ohi`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 revegetation, 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, including four tree, three shrub, a lily, Hawaiian poppy, and two grass species. Monitoring will 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 `ohi`a woodlands in the Park. Table of Contents Page Executive Summary ii Introduction 1 Methods 2 Native Plant Restoration 2 `ohi`a woodlands 2 Mesic koa forest 3 Koa stands 3 Seed collection, storage, propagation 3 Alien Plant Control 4 Monitoring Plant Community Response 4 Data analysis 4 Results 5 Native Plant Restoration 5 Alien Plant Control 6 Plant Community Response to Fire 6 Discussion 7 Native Plant Establishment from Outplanting and Seeding 7 Prevention of Alien Woody Plant Establishment 8 Natural Recovery of the Preburn Community 8 Conclusion 8 Literature Cited 11
Table 1. Native species for introduction into burned communities. 13
by species. 14 Table 3. Outplant survivorship in the `ohi`a woodland site 15 Table of Figure Figure1. Map of plant communities affected by the Broomsedge Burn. 16
Figure 2. Seedling recruitment from seed additioninto the burned `ohi`a woodland site (indiv/plot). 17 Figure 3. Native and exotic plant abundance three years after the Broomsedge Burn. 18 Introduction The Broomedge Fire, started June 30, 2000, burned 1008 acres of native plant communities (3,800-4,000 ft elevation) in Hawai`i Volcanoes National Park (HAVO) (Figure 1). Communities affected were seasonally dry `ohi`a woodland (923 ac) and mesic koa forest (85 ac). Fire was expected to dramatically reduce native vegetation and stimulate fire-adapted alien grasses, thereby increasing fire potential in the burn area (D`Antonio and Vitousek1992 al, Tunison et al. 1995, D`Antonio et al. 2000). Two strategies were used to re-vegetate the burned communities with native plants. A third strategy to prevent the establishment of ecologically disruptive alien woody species was also included in the rehabilitation plan. The strategy in burned `ohi`a (Metrosideros polymorpha) woodlands (~900 acres) was to establish fire-tolerant native plants that could persist in competition with exotic grasses and recurrent wild fires. Since the invasion of fire-adapted invasive broomsedge (Andropogon virginicus) and bushy beardgrass (Schizachyrium condensatum) in the mid-1960's and molasses grass (Melinis minutiflora) in the 1970's, fire frequency has increased three-fold, and fire size 60-fold. Nearly two-thirds of the dry `ohi`a woodland system has been affected by wildfire and the remaining portions are at high risk for wildfire at HAVO. Re-introduction of formerly dominant but fire-sensitive native plants such as `ohi`a, and pukeawe was considered counterproductive given the widespread abundance of alien grasses that increased fuel loads and thereby the inevitability of future fires (D`Antonio and Vitousek 1992). Instead, the intent was to create modified native communities that were able to self-perpetuate, accepting that alien grasses and wild fire remained important ecosystem components. Between 1993-2001, seven research burns and laboratory experiments were conducted to test native species capacity to survive and colonize after fire. Fourteen native plant species, among them mamane (Sophora chrysophylla),a tree, `a`ali`i (Dodonaea viscosa), a shrub, and` ili`ahi (Santalum ellipticum var. paniculatum), a tree, were identified as fire-tolerant (Loh et al. unpubl.). Additional species were identified based on their ability to survive or colonize after natural fire. Many of these species were formerly abundant in the seasonally dry `ohi`a lowland ecosystem, but were depleted by historic browsing by feral goats. Park boundaries were fenced from sea level to 6,600 ft elevation and goats removed in the 1970`s. However, natural recovery of species was poor because the native seed bank has been depleted, and seedlings that did establish had a difficult time growing in competition with alien grasses (Hughes and Vitousek 1993, D`Antonio et al.1998). Restoration in the Broomsedge Fire focused on establishing 14 of these fire-tolerant native species by a combination of seeding and outplanting of nursery-propagated individuals in the burn (Table 1). The intent was to establish species rapidly before exotic grasses fully recover (estimate ~ 3 yrs). Koa (Acacia koa), a species uncommon in dry `ohi`a woodlands, was included as a restoration species because of its prolific ability to regenerate from root suckers in response to disturbance, and its natural occurrence in the area prior to the burn. The strategy in mesic koa forest was to create a vegetated fuel barrier that would reduce the likelihood of fire penetrating Kipuka Puaulu Special Ecological Area (Figure 1). Kipuka Puaulu is a rare mesic soapberry-koa-`ohi`a community that contains a number of endangered and rare plant species. Surrounding the Kipuka is degraded koa forest that is vulnerable to wild fire. These are koa forests that have regenerated in abandoned pastures following the removal of cattle in the 1950`s. Koa came up vigorously and reformed a forest canopy, but very little regeneration of the subcanopy and understory vegetation occurred. The result was an over-simplified koa community composed of koa and alien grasses (Ehrharta stipoides, Pennisetum clandestinum) that was more vulnerable to wild fire. In the Broomsedge Burn, fire carried by meadow ricegrass (Ehrharta stipoides) burned 85 ac of koa forest and came within 50 m of Kipuka Puaulu Special Ecological Area before changing weather conditions and control lines constructed by fire fighters stopped the fire. Restoration efforts were focused on restoring the native understory that existed prior to ungulates in degraded koa forest that lie immediately adjacent to Kipuka Puaulu. Re-establishing native understory plants would create a shadier, moister environment that would suppress alien grasses and possibly reduce the risk of fire being carried in this environment and penetrating Kipuka Puaulu. The koa canopy that was damaged by fire is expected to recovery naturally through vigorous production of root suckers (Parman 1976, Hauss unpubl.). Seeds and cutting of nineteen native plant species were collected and individuals propagated in park greenhouses and subsequently outplanted beneath the koa (Table 1). The 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. This is an area where young koa stands were beginning to naturally establish in `ohi`a woodlands (Figure 1). Eleven native species were propagated and subsequently outplanted beneath a 400 m strip of naturally recovering koa (Table 1). A subset of species was also established by artificial seeding of the area. Koa was outplanted in sections of the strip where the density of trees was sparse in order to establish a continous strip of koa forest. In addition to native plant introductions, ecologically disruptive alien plant species were prevented from establishing in the burn. Faya tree (Myrica faya), Himalayan blackberry (Rubus argutus), Himalayan raspberry (Rubus ellipticus) and strawberry guava (Psidium cattleianum) are invasive weeds that have the potential to form dense stands or thickets that displace native plant communities and disrupt ecosystem processes (Smith 1985). Faya tree is a nitrogen-fixing tree that forms dense monotypic stands that excludes all native vegetation, and increases nitrogen inputs upto four-fold in invaded areas (Vitousek and Walker 1989). Strawberry guava is considered among the worst weeds in lowland Hawaiian forest (Smith 1985, Huenneke and Vitousek 1990). Individuals establish across a broad range of light environments (Loh 2004), and form dense monospecific stands that preclude all other vegetation. Himalayan raspberry and blackberry are major pests that form large persistent thickets or mats in seasonally dry and mesic forest (Smith 1985). These species are present in low numbers in unmanaged areas near the burn (Benitez unpubl.), and may severely limit native plant restoration if allowed to establish in the burn. Between 2001 to 2003, work crews searched and chemically or manually removed these species in the burn. Vegetation monitoring to evaluate recovery of the vegetation and the efficacy of the restoration efforts was conducted between 8/01 and 4/04. Included were measurements of native outplant survivorship, recruitment from seed additions, and natural recovery of the vegetation community following wildfire. |
