Japanese climbing fern is an aggressive, non-native fern invading the groundcover of longleaf pine savannas along the Southeastern Gulf Coast. Lygodium japonicum has persisted in longleaf pine savannas, despite reinstitution of lightning-season prescribed fire regimes designed to benefit native herbaceous biodiversity. We asked if L. japonicum re-emergence is influenced by variation in maximum temperatures and duration of heating during prescribed fires. We hypothesized that increasing/decreasing fire temperature and duration through fuel load manipulation would decrease/increase L. japonicum frond re-emergence post-fire via belowground rhizome damage. Individual fern genets were randomly selected in different fire blocks in a frequently burned, second-growth longleaf pine savanna (Camp Whispering Pines, Tangipahoa Parish, LA) prior to 2008 prescribed fires. One of three fuel treatments (increased, reduced, or unaltered fine-fuels) was randomly applied to each plot. Fire data loggers were placed at the soil surface and 2 cm belowground within the rhizosphere to measure maximum temperature and duration of heating. Fuel biomass was measured pre- and post-fire to estimate effects of treatments on fuel consumption. Fronds were counted and percent cover estimated before prescribed fires and one, six, and twelve months after fire. Data were analyzed using pre-fire frond number as a covariate.
Results/Conclusions
Differences in fuel loads affected fire temperature and duration of heating. Fine-fuel increase plots, with and without a tree stump present, had higher fuel consumption, longer heating duration, and higher maximum temperatures at the surface than either fine-fuel reduction or unaltered plots. Increase plots also heated soil at 2 cm belowground significantly longer, with heating >50o C occurring for approximately 30 minutes in non-stump areas. Differences in fire characteristics were not reflected in post-fire frond re-emergence, expect in fine-fuel increase treatments where immediate recovery was suppressed. Mean frond number increased in all fine-fuel treatments one-month post-fire, with greatest increases in fuel reduction plots. Frond numbers increased after fire even in plots were soil was heated above 50oC. All frond increases were transient; frond numbers in all treatments decreased to pre-fire numbers within a year post-fire. Results suggest that rhizomes of L. japonicum can withstand typical fire intensities in pine savannas. Moreover, removal of above-ground fronds during fires appears to stimulate frond production, although such increases are transient. Because belowground structures are likely to survive fires typical of fire-frequented ecosystems, additional management measures will be needed to address the slow, but steady invasion of Japanese climbing fern of southeastern pine savannas.