Fire effects on growth of the invasive exotic fern Lygodium microphyllum and implications for management.
The extremely invasive Old World Climbing Fern, Lygodium microphyllum, has invaded New World tropical and subtropical habitats. Lygodium microphyllum has indeterminate twining leaves that grow up on and shade out host shrubs and trees, their epiphytes, and the understory. This invasive plant threatens numerous native habitats in Florida USA and the Caribbean, including internationally valued conservation lands such as Everglades National Park. Fire, which can reduce or stimulate growth and/or reproduction in different plant species, is one intervention used to manage L. microphyllum, but the effects of burning on this species' growth are unknown. We experimentally burned greenhouse-grown plants, then monitored their growth in response to burning for 18 months. We also clipped a subset of the greenhouse plants to determine whether fire effects were explained by aboveground biomass removal. In our experiment, fire either killed or reduced the regrowth of L. microphyllum plants. Burning killed 25% of the burned plants and slowed growth of the remaining burned plants for up to 18 months post-burn. Size had a significant effect on plant mortality: smaller burned plants had greater mortality than larger plants. Mechanically removing the aboveground biomass (leaves) by clipping did not kill any plants but reduced their growth as compared to controls in the first six months after treatment. Clipped plants, however, had substantially recovered after 12 months. Burned plants were more sensitive to drought than clipped or control plants. The results show that burning does more than remove biomass, compromising the root system and perhaps damaging the hydraulic support system, similar to the latent mortality effects of fire on forest trees. We discuss how fire could affect invasion by this species, incorporating fire effects on spore viability and dispersal, as well as on subsequent plant regrowth. These results show that fire is a useful management tool for L. microphyllum invasions that both kills plants and reduces plant regrowth for up to 18 months.