Invasive nonnative grasses have altered the composition of seasonally dry shrublands and woodlands throughout the world. In many areas they coexist with native woody species until fire occurs, after which they become dominant. Yet it is not clear how long their impacts persist in the absence of further fire. We evaluated the long-term impacts of grass invasions and subsequent fire in seasonally dry submontane habitats on Hawai'i, USA. We recensused transects in invaded unburned woodland and woodland that had burned in exotic grass-fueled fires in 1970 and 1987 and had last been censused in 1991. In the unburned woodlands, we found that the dominant understory grass invader, Schizachyrium condensatum, had declined by 40%, while native understory species were abundant and largely unchanged from measurements 17 years ago. In burned woodland, exotic grass cover also declined, but overall values remained high and recruitment of native species was poor. Sites that had converted to exotic grassland after a 1970 fire remained dominated by exotic grasses with no increase in native cover despite 37 years without fire. Grass-dominated sites that had burned twice also showed limited recovery despite 20 years of fire suppression. We found limited evidence for "invasional meltdown": Exotic richness remained low across burned sites, and the dominant species in 1991, Melinis minutiflora, is still dominant today. Twice-burned sites are, however, being invaded by the nitrogen-fixing tree Morella faya, an introduced species with the potential to greatly alter the successional trajectory on young volcanic soils. In summary, despite decades of fire suppression, native species show little recovery in burned Hawaiian woodlands. Thus, burned sites appear to be beyond a threshold for "natural recovery" (e.g., passive restoration).

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The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non‐indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass‐fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there.

The endemic Hawaiian silversword and lobeliad lineages, which are two of the world’s premier examples of plant adaptive radiation, exemplify the severity of the threats confronting the Hawaiian flora, especially the threats posed by alien species. We have implemented collaborative reintroduction efforts with the endangered Kaʻū silversword (Argyroxiphium kauense) and Pele lobeliad (Clermontiapeleana) in Hawaiʻi Volcanoes National Park. The efforts with the Kaʻū silversword have involved rediscovery, helicopter assisted rescue of diminutive remnant founders, managed breeding, outplanting at two sites in the Park of more than 21,000 seedlings deriving from 169 founders, and facilitated achene dispersal following flowering. The efforts with the Pele lobeliad have involved rediscovery, air-layering of remnant founders while suspended on climbing ropes, managed breeding, and outplanting at two sites in the Park of more than 1,000 seedlings (to date) deriving from six of the seven known founders. We have linked the reintroduction efforts to landscape restoration at large scales in the Park and in adjacent State and private lands, thereby increasing the opportunities for substantial population growth and expansion of the Kaʻū silversword and Pele lobeliad in the future. Additionally, we have extended the reintroduction efforts, including the link to landscape restoration, to encompass all other endangered silversword and lobeliad taxa occurring historically on the eastern slopes of Mauna Loa or on Kīlauea. In so doing, we seek to restore the possibility of adaptive radiation of the silversword and lobeliad lineages going forward, especially on the youngest and most geologically active, and thus perhaps most evolutionarily dynamic, part of the Hawaiian archipelago.DedicationThis paper celebrates the centennial of Hawaiʻi Volcanoes National Park, which was founded in August 1916.

The endemic Hawaiian silversword and lobeliad lineages, which are two of the world's premier examples of plant adaptive radiation, exemplify the severity of the threats confronting the Hawaiian flora, especially the threats posed by alien species. We have implemented collaborative reintroduction efforts with the endangered Kaʻū silversword (Argyroxiphium kauense) and Pele lobeliad (Clermontia peleana) in Hawaiʻi Volcanoes National Park. The efforts with the Kaʻū silversword have involved rediscovery, helicopter assisted rescue of diminutive remnant founders, managed breeding, outplanting at two sites in the Park of more than 21,000 seedlings deriving from 169 founders, and facilitated achene dispersal following flowering. The efforts with the Pele lobeliad have involved rediscovery, air-layering of remnant founders while suspended on climbing ropes, managed breeding, and outplanting at two sites in the Park of more than 1,000 seedlings (to date) deriving from six of the seven known founders. We have linked the reintroduction efforts to landscape restoration at large scales in the Park and in adjacent State and private lands, thereby increasing the opportunities for substantial population growth and expansion of the Kaʻū silversword and Pele lobeliad in the future. Additionally, we have extended the reintroduction efforts, including the link to landscape restoration, to encompass all other endangered silversword and lobeliad taxa occurring historically on the eastern slopes of Mauna Loa or on Kīlauea. In so doing, we seek to restore the possibility of adaptive radiation of the silversword and lobeliad lineages going forward, especially on the youngest and most geologically active, and thus perhaps most evolutionarily dynamic, part of the Hawaiian archipelago..