The Life History Patterns of the Invasive Fern, Lygodium microphyllum, at the Wholeplant, Community and Landscape Scale.
John C. Volin , Michael J. Lott, Jordan D. Muss, Dianne Owen and Joy E. Stewart
Florida Atlantic University, Davie, FL
One of the greatest threats to the integrity of native ecosystems is their invasion by nonindigenous species. Nowhere else in the continental United States is this threat more conspicuous than in Florida. In South Florida, Lygodium microphyllum, which is a relatively recent invader, is currently spreading throughout native ecosystems. Once established in a community, L.
microphyllum displaces native species and alters local fire ecology, eventually leading to collapse of the natural community. We studied the life history of this highly invasive fern across different spatial scales. The results of our studies will be presented, including L.
microphyllum reproductive biology and its growth and physiology at the whole-plant, community and landscape scale.
Examination of it’s reproductive biology shows that L.
microphyllum is capable of using all three mating systems: intragametophytic selfing, intergametophytic selfing, and outcrossing. This complex reproductive biology is highly unusual for the vast majority of fern species studied to date. The ability of L. microphyllum to utilize all three mating systems lends support to our hypothesis that its reproductive strategy partially explains its invasive spread across the landscape. Since spores are dispersed readily by wind, the ability of a single spore to form a sporophyte facilitates the rapid spread of L.
microphyllum to new habitats. In addition, we found that its invasiveness is enhanced by the ability of a female gametophyte to determine the sex of nearby gametophytes, making them male and thus ensuring cross fertilization.
It appears likely that a higher growth rate confers a competitive advantage to L. microphyllum relative to many native species but to date this hypothesis has not been tested. To test this hypothesis, seedlings of L. microphyllum, L. japonicum and the native vines Vitis rotundifolia and Parthenocissus quinquefolia were grown under three different light levels for 180 days. Over this period, relative growth rate and its determinants were measured over two sequential harvests. Early results show that both
Lygodium species, but particularly L. microphyllum , have a significant growth advantage in low light conditions compared to the two native vines. The mechanisms for this advantage in low light are currently being examined, although it appears to be a result of a significantly greater photosynthetic rate in low light-grown L. microphyllum seedlings compared to the other species.
The pattern of distribution of L. microphyllum was also examined at the community level in forested wetland sites within the Big Cypress Swamp. Species richness, abundance and distribution of herbs, shrubs and trees were characterized along with several physiographic and abiotic parameters. These parameters included elevation, substrate depth, substrate water content, substrate organic content, substrate texture and understory photosynthetically active radiation. The patterns of distribution of L. microphyllum indicated that presence of the fern was dependent on moderately hydric conditions, since

relatively low elevation, deep substrate and high substrate water content were significantly related to L. microphyllum presence. This information was utilized in developing a landscape model of its spread throughout South Florida.
The L. microphyllum dispersal model utilizes a cellular automaton methodology. The model is calibrated using actual data from 1978 to 1993, then validated independently using actual data from 1993 through 1999. The projection to 2009 uses the actual 1999 flight survey data as a starting point and shows an alarming increase in L. microphyllum establishment across South Florida, in particular in the cypress-dominated wetlands of the
Big Cypress Swamp.
These studies have been designed to increase our understanding of the ecology and physiology of this highly invasive species and to assist land managers in developing strategies to prevent and control its rapid spread.
John, Volin, Florida Atlantic University Environmental Sciences, 2912 College Avenue,
Davie, FL, 33314, Phone: 954-236-1115, Fax: 954-236-1099, jvolin@fau.edu
, Invasive and Exotic Species