Invasion of a Southeastern Pine Savanna by Japanese Climbing Fern

Lygodium japonicum (Thunb. ex Murr.) Sw. is an invasive fern in the southeastern United States. This perennial fern, which produces twining fronds from underground rhizomes (Clarke 1936), is native to open forests and forest edges in temperate, subtropical and tropical regions of eastern and southeastern Asia, East Indies, and northern Australia (Singh and Panigrahi 1984, Munger 2005, Willis et al. 2006). Lygodium japonicum was introduced to North America as an ornamental; the first known wild populations were recorded in Georgia in 1903 (Pemberton and Ferriter 1998), but this fern is now widespread in the southeastern United States. Japanese climbing fern occurs in human-modified habitats, as well as forests and woodlands (Langeland and Burks 1998, Rosen et al. 2003), where it often forms dense mats that grow on and cover native species (Gagnon et al. 2005, Zeller and Leslie 2004). Some management plans have emphasized the dearth of scientific data on invasions by climbing ferns (e.g., Ferriter 2001). Lygodium japonicum has been noted as present in pine savannas. Nonetheless, there is minimal documentation of invasion of pine savannas by this fern in the literature, although it has been designated a threat to southeastern pine savannas (Munger 2005, Stocker and Hupp 2008) and invasion of pine savannas has been hypothesized to be facilitated by fires (e.g., Wade et al. 2000). Pine savannas (sensu Platt 1999) have been reduced to less than 3% of their original extent by fragmentation and fire suppression, and most that remain are degraded (Platt 1999, Varner et al. 2005, Means 2006). Invasion by L. japonicum thus could have major consequences for these fire-frequented ecosystems containing species rich and endemic groundcover vegetation (Sorrie and Weakley 2006). Mesic pine savannas may be particularly vulnerable to invasion by L. japonicum. Lygodium japonicum tends to be intolerant of extreme drought and/or flooded conditions (Bargeron et al. 2008), suggesting that oldgrowth mesic pine savannas with mixed sandy-clay soils ideal for fern growth may be susceptible to invasion (e.g., the Wade Tract; Platt et al. 1988). Such pine savannas also tend to have pronounced biodiversity at small scales (Peet 2006, Platt et al. 2006, Carr et al. 2009). Might invasion by a species capable of forming mats on top of existing groundcover plants compromise the high biodiversity of mesic pine savannas? Lygodium japonicum has been present at Girl Scout Camp Whispering Pines in eastern (Tangipahoa Parish) Louisiana for more than two decades. This upland, mesic site, described in Platt et al. (2006), historically contained pine savannas with a two-layered physiognomy resembling that described in Gilliam et al. (2006). The overstory contained predominantly longleaf pine, Pinus palustris Mill. (Noel et al. 1998). Groundcover vegetation was dominated by warm-season grasses, especially bluestems [Schizachyrium scoparium (Michx.) Nash, Schizachyrium tenerum Nees], but also contained high biodiversity of herbaceous plants mixed with shrubs and lianas (Platt et al. 2006). Pine savannas at Camp Whispering Pines have experienced different land uses during the past century: logging in *email address: eleich1@tigers.lsu. edu Received June 8, 2010; Accepted February 18, 2011. CASTANEA 76(3): 293–299. SEPTEMBER 2011