Fire and Rain: Stemming the Tide of Invasive Plants in Hawaiian Ecosystems

In the rainforests of Hawai’i, wildfi re is an uncommon occurrence, and repeated wildfires in the same area rare indeed. In 2002 and 2003, successive lava-ignited wildfi res in Hawai’i Volcanoes National Park burned from seasonally dry to mesic low elevation plant communities to higher elevation rainforests, causing 95-percent mortality of the canopy. The lower elevation communities consisted of native shrubs in the overstory and invasive, non-native grasses and ferns in the understory. In the mid-elevation forested communities, non-native sword fern dominated the understory, while the higher elevation communities consisted of native trees in the canopy and native ferns and tree ferns in the understory. In the aftermath of these fires, park managers and researchers were concerned about the effects of fire on native plants and the role fire plays in encouraging the spread of non-native vegetation. Researchers measured the effects of successive wildfires on native and alien vegetation in shrubland and forest communities along an elevation/rainfall gradient. They found that, while native plants can recover after fire, after successive fires, non-native species rebound more aggressively, threatening the recovery of native vegetation. Non-native ferns in particular are encroaching on the higher elevation rainforest where they had not previously been observed