The Growth and Physiological Ecology of Two Invasive Non-indigenous Fern Species,
Lygodium microphyllum and Lygodium japonicum
Michael S. Lott and John C. Volin
Florida Atlantic University, Davie, FL
Throughout the world, invasions by non-indigenous plant species threaten the survival of
many natural plant communities. This is particularly true in Florida where 125 plant
species are listed as invasive by the Florida Exotic Pest Plant Council. Two of these
species are Lygodium microphyllum (Cav.) R. Br. (Schizaeaceae) and L. japonicum
(Thunb.) Swartz. Both species have a climbing habit and are capable of smothering
native vegetation, resulting in the displacement of native understory vegetation, and in
extreme infestations, shrub and canopy vegetation as well. This is especially notable in L.
microphyllum, which can form rachis mats up to a meter thick, effectively eliminating
most understory vegetation.
This study examines the growth and physiological ecology of both Lygodium species, as
well as two native vines, Vitis rotundifolia and Parthenocissus quinquefolia. The four
species were grown in shade houses under three different light treatments (70, 50 and 20
percent full sunlight). Two harvests were performed, the first at 90 days and the second at
180. At each harvest photosynthetic light response curves were completed on a subsample of each species. Harvested plants were divided into roots, stems, and leaves and
all tissues were dried and weighed. Relative growth rate (RGR) and its allocational and
morphological determinants, i.e. leaf area ratio, specific leaf area, root weight ratio, stem
weight ratio, and leaf weight ratio were calculated. The RGR of L. microphyllum was
significantly greater in both the low- and medium- light treatments as compared to the
other three species. For example, under low light conditions the RGR of L. microphyllum
was 22.6 mg g-1 day-1 as compared to 18.8 mg g-1 day-1 for L. japonicum, 17.0 mg g-1 day1
for V. rotundifolia, and 9.7 mg g-1 day-1 for P. quinquefolia. Large differences in
biomass allocation were observed between the two non-native vines versus the two native
vines. Under all three light treatments the non-native ferns allocated significantly less
resources to their climbing frames (5-20%) as compared with the native vines (40-60%).
This allows both Lygodium species to allocate greater resources to either their leaves or
roots. For example, under low light conditions L. microphyllum averaged 5,000 cm2 of
leaf area per plant as compared to 3,000 cm2 for V. rotundifolia. A similar pattern was
also observed in roots under low-light conditions, where L. microphyllum averaged 17.5
g belowground per plant as compared to 6.4 g belowground in V. rotundifolia. Despite
these large differences in allocation, leaf physiology appears to play an even greater role
in explaining the differences in growth among the four species. In both the low- and
medium-light treatments, leaf photosynthesis was significantly greater in the two nonnative vines, particularly so in L. microphyllum, compared to the two native vines.
Michael, Lott, Florida Atlantic University Environmental Sciences, 2912 College
Avenue, Davie, FL, 33314, Phone: 954-236-1157, Fax: 954-236-1099, mlott@fau.edu,
Invasive and Exotic Species