Interactions of Fire and Nonnative Species Across an Elevation/Plant Community Gradient in Hawaii Volcanoes National Park

Abstract

ABSTRACTInvasive species interacting with fires pose a relatively unknown, but potentially serious, threat to the tropical forests of Hawaii. Fires may create conditions that facilitate species invasions, but the degree to which this occurs in different tropical plant communities has not been quantified. We documented the survival and establishment of plant species for 2 yr following 2003 wildfires in tropical moist and wet forest life zones in Hawaii Volcanoes National Park, Hawaii. Fires were ignited by lava flows and burned across a steep environmental gradient encompassing two previously burned shrub‐dominated communities and three Metrosideros polymorpha forest communities. Fires in all community types were stand replacing, where >95 percent of overstory trees were top killed. Over half (>57%) of the trees survived via basal sprouting, but sprout growth differed among forest communities. Sprout growth (>250,000 cm3) was greatest in the forest community where postfire understory cover was lowest presumably due to thick native Dicranopteris linearis fern litter that remained postfire. In contrast, M. polymorpha sprout growth was much slower (<100,000 cm3) in the two forest communities where there was rapid understory recovery of nonnative ferns Nephrolepis multiflora and invasive grasses Paspalum conjugatum. These results suggest that the rapid establishment of an invasive‐dominated understory limited recovery of the overstory dominant M. polymorpha. In contrast to the three forest communities, there were few changes in vegetation composition in the shrubland communities. Nonnative species invasions coupled with repeated fires selectively eliminated fire‐sensitive species thereby maintaining these communities in dominance of primarily nonnative, fire‐resilient, species.