Effects of fire and treefalls on Japanese climbing fern and native species groundcover in a restored longleaf pine savanna

Abstract

Recurrent disturbances play an important role in maintaining longleaf pine savannas. Windstorms and fires contribute to the heterogeneity of pine savanna understory through generation of canopy gaps and fuel accumulation, distribution and consumption. The combination of windstorms and fires promotes native herbaceous species, but also promotes invasion of Japanese climbing fern (Lygodium japonicum). Lygodium japonicum is an invasive fern with subterranean rhizomes and copious spore production invading pine savannas along the southeastern Gulf Coast Region. This dissertation examines how fire, previous windstorm disturbances, and animal disruptions influence L. japonicum and native species abundance in a restored longleaf pine savanna. Studies were conducted at Girl Scout Camp Whispering Pines, an upland mesic site containing longleaf pine in Tangipahoa Parish, Louisiana. I experimentally examined L. japonicum response to various fire severities during prescribed fire by manipulating fine fuels in the understory. Three fine-fuel treatments (increased, reduction, unaltered) were applied to plots containing fern genets. The effect of fire severity through duration of heating was transient on frond emergence, suggesting that established fern genets survive subsequent fires. Native groundcover species abundance and composition was also transiently influenced by fire severity, as examined in a post hoc fuel manipulation study. Abundance and composition of native species within localized areas differed based on heterogeneity of fire severity, indicating sensitivity to prolonged heating. Heat released, a product of fuel accumulation, may stunt recovery of native groundcover in localized areas and contribute to understory patches susceptible to invasion by non-native species. Animal biopedturbations were strongly associated with stump locations, which provided refuge and foraging opportunities in the understory. Biopedturbations did not, however, promote or suppress L. japonicum frequency or density. Windstorms and fire disturbances contributed to heterogeneity of groundcover and, thus influenced L. japonicum spread. Particular growth characteristics of L. japonicum enabled persistence in certain locations. Areas with open canopy, where fire severity was low, were at higher risk of invasion than areas under pine trees. Fire is essential for restoration, yet promotes invasion by L. japonicum. Careful consideration of disturbance regime and characteristics of invasive species are required for successful maintenance of longleaf pine savannas.