Recruitment and Growth of Old World Climbing Fern in Hurricane-Caused Canopy Gaps

Abstract

Abstract Following 2 y of severe hurricanes in 2004 and 2005, we examined the role of canopy gaps in promoting recruitment and growth of the exotic fern, Old World climbing fern Lygodium microphyllum (hereafter Lygodium), on tree islands of the Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida. We selected 12 sample tree islands, on which we placed three 1-m2 plots in a hurricane-caused canopy gap and three plots in an adjacent closed canopy area. Spore traps were placed in canopy gaps and closed canopy areas to quantify the number of spores reaching the forest floor on each island. In addition, in each plot occurrence and growth of Lygodium was measured across four height classes (recruitment class, understory, midstory, and canopy). We predicted that recruitment and growth of Lygodium would be higher in canopy gaps than in closed canopy areas. After 3 y of biannual monitoring, a significantly greater number of spores were foundin canopy gaps (4,804 spores·m2·d) than in closed canopy areas (4,288 spores·m2·d). Furthermore, we observed significantly greater recruitment and growth in canopy gaps compared with closed canopy areas in the recruitment class only. Presence of recruitment-class Lygodium in canopy gaps increased from four to five treatment areas and decreased from 1 to 0 treatment areas in closed canopy areas. These results suggest differences in recruitment and growth of Lygodium between canopy gaps and closed canopy areas on tree islands after severe hurricanes. However, despite the large number of spores in both canopy gaps and closed canopy areas, recruitment and growth were much lower than expected, with only two treatment areas having an average percent cover greater than 10% in any height class. If conducted within several years after a hurricane, focused monitoring efforts on hurricane-impacted tree islands may allow managers to detect and treat new infestations before they are able to overrun tree islands.