Experimental tests of fire resprouting in Hawaiian plants

Context Fire is increasing in intensity and frequency, leading to novel fire regimes in many regions. For oceanic islands of volcanic origin, endemic plants have evolved in the context of lava-ignited fires. Aims Responses to fire were investigated in four endemic (Nototrichium humile, Hibiscus brackenridgei subsp. mokuleianus, Gossypium tomentosum, and Erythrina sandwicensis) and one invasive (Leucaena leucocephala) plant species in Hawai‘i. Because conservation efforts commonly rely on juvenile stages, which are predicted to be particularly vulnerable to fire, we tested fire resprouting in saplings. Methods Sapling resprouting was tested using experimental methods. Saplings were burned using a fire torch, and resprouting was monitored for 30 days. Proportion of plants resprouting and the timing of resprouting were the metrics of fire tolerance. Key results Resprouting rates were high in four of the species (65–95%). The endemic E. sandwicensis was the only species that failed to resprout. The timing of resprouting varied among species, with the invasive species resprouting faster than the endemics. Conclusions Saplings demonstrated surprisingly high tolerance to the fire treatments, indicating potential for these early stages to withstand fire. The invasive species resprouted faster than the endemics, which could contribute to competitive displacement in burned sites. At least one native Hawaiian plant species potentially lacks fire tolerance completely at the sapling stage. Implications Sapling fire tolerance informs restoration actions that rely on out-plantings into fire-prone sites. Scaling up these results requires additional species testing and fire treatments to mimic contemporary fires.