Interactive influences of repeated fires and non-native species on plant community succession at Hawaii Volcanoes National Park

Fires are a relatively rare event in tropical wet forests and fires in rapid succession represent an uncommon disturbance with significant influences on forest structure and function.  Few studies have examined influences of wildland fire in tropical lowland wet forests and even fewer have examined repeated fires in these ecosystems.  We had the opportunity to study the effects of this extreme event following the Kupukupu fire in 2002 and the Luhi fire in 2003 at Hawaii Volcanoes National Park.  To examine the effects of repeated wildfires (2002-2003) on forest composition and structure, we established replicate plots (n=5) in two native communities which were mesic Metrosideros polymorpha/ Dicranopteris linearis and wet Metrosideros/ Cibotium glaucum forests.  The first fire was stand replacing where over 95% of the dominant Metrosideros polymorpha trees were top-killed.  The occurrence of a second fire dramatically increased mortality of Metrosideros.  In the Dicranopteris community, 71% of Metrosideros trees survived a single fire, but only 22% survived repeated fires.  Similarly in the Cibotium community, Metrosideros survival was reduced from 48% to 6% following repeated fires.  Vegetative survival of the native tree fern Cibotium glaucum was also significantly reduced from 93% following a single fire to 56% following a second fire.  Metrosideros seedling recruitment did not differ between forests that burned once and forests that burned twice.  The composition of the understory in both of the sampled communities following repeated fires differed from that of forests that burned once and unburned control forests.  Repeated fires resulted in lower Metrosideros survival, no significant increase in seedling establishment, and rapid occupation by aggressive herbaceous species, all of which may delay, or even prevent, recovery to native forest dominance.