Current Research Projects

• Introduction
• Impacts of Invasions
• Community Invasibility
• Periodical Cicadas
• Restoration of Invaded Communities

Introduction

Anthropogenic dispersal of plants to non-native ranges and human disturbances such as forest fragmentation has resulted in widespread invasions of exotic plants. Exotic plants have been introduced intentionally for use in horticulture, landscaping, wildlife management, and habitat restoration and accidentally in contaminated seed sources, boat ballast, and packing material. When exotic plants invade, they can reduce native plant and animal diversity and alter fundamental ecosystem processes such as nutrient cycling, hydrology, and fire regimes. My work is motivated by the need to understand the dynamics and mechanisms of plant invasions in order to preserve intact systems and restore invaded communities.

Back to topImpacts of Invasions

Effects of the exotic annual grass Microstegium vimineum (Japanese stiltgrass) on native communities.

Observational studies of exotic species commonly suggest that invasions have negative effects on native communities, but in fact we have surprisingly little experimental evidence regarding the impacts of invasions on native systems. Quantitative studies of the consequences of exotic plant invasions are needed to understand the ecological implications of plant invasions, prioritize management efforts, and leverage resources for invasive plant control.

Microstegium vimineum (Japanese stiltgrass) is a highly shade tolerant C4 annual grass that is rapidly invading deciduous forests in the eastern U.S. I am conducting a large-scale, long-term experiment to quantify the effects of Microstegium invasion on forest communities. I established 32 replicated early-successional forest communities containing nine species of tree seeds or seedlings plus twelve herbaceous species. I then added Microstegium seed to half of the plots to experimentally manipulate invasion.

Within this experimental setup we are determining the effects of invasion on:

1. Native trees at the seed and seedling life-history stages
2. The native herbaceous community
Arthropod abundance and diversity (with undergraduate Ben Eddy, Dr. Jennifer Rudgers at Rice University, and Dr. Al Cady at Miami of Ohio)
3. Plant resource availability including light, water, and nutrients (with fellow graduate student Brett Mattingly)
4. Survival of two species of ticks (with fellow graduate student Dave Civitello)

Thus far, I have found that Microstegium invasion reduces the survival and alters the growth of some, but not all tree species and dramatically decreases the productivity and diversity of herbaceous communities. Microstegium also indirectly impacts tree regeneration by encouraging vole activity and may decrease the diversity and abundance of ground and canopy-dwelling arthropods. Finally, Microstegium invasion may reduce human disease risk by decreasing the survival of two tick species that are important disease vectors.

These results suggest that Microstegium invasions will significantly alter forest communities in the eastern U.S. by changing tree species composition and herbaceous community structure. Furthermore, these changes in plant community composition and structure may result in cascading effects on other trophic levels. Studies of other plant invaders should adopt this experimental approach for quantifying the impacts of exotic plant invasions.

Previously I conducted an experimental study of how light conditions affect the impact of Microstegium on native graminoid species. The paper on that project can be found here:: Flory et al. 2007, Natural Areas Journal

Back to topCommunity Invasibility

Effects of distance to road and forest successional age on invasions of exotic shrubs

Identifying the landscape and community features that promote invasions of exotic plants can aid in the prediction of areas that are vulnerable to invasions and help to prioritize management efforts. Throughout the eastern U.S., agriculture, urban sprawl, and industrial development have resulted in highly fragmented forests that are dissected by roadways. Roads are known to facilitate the spread of exotic plants by providing corridors for invasion and habitat suitable for exotic plants. Independent of the presence of roads, the successional age of communities is important in determining their susceptibility to plant invasions, with younger systems often more vulnerable to invasions than mature communities.

As part of my Ph.D. work, I investigated the role of roads and forest successional age in invasions of exotic shrubs in southern Indiana forests. I found that more exotic shrubs had invaded near roads than in interior forest and in young and mid-successional forests than in mature forests. This work was published in 2006 :: Flory and Clay, Plant Ecology

I then conducted a three-year experimental study using seedlings of three invasive exotic shrub species and three native understory species to examine the mechanisms underlying the invasion process along roads. I found that there was no effect of distance to road on exotic shrub survival but that native species were more likely to survive near roads than in interior forest. Further, both native and exotic species grew larger near roads than in interior forest. Levels of herbivory were greater for native than exotic species and there was more herbivory with increasing distance to roads for both native and exotic species in mature but not young forests.

Together these results indicate that roads are providing corridors for exotic shrub invasions, that young forests are particularly susceptible to invasions, and that interior forests may be prone to invasion if propagules are dispersed to interior sites. These results also suggest that forest fragmentation from roads, power line right-of-ways, and trails can promote plant invasions by providing forest edge habitat and that plant invasions may be slowed by conserving intact forests.

Back to topPeriodical Cicadas

Oviposition preference, host plant response, and cicada offspring performance

Fellow graduate student Brett Mattingly and I conducted a field experiment during the periodical cicada emergence of 2004 to examine cicada oviposition preference and offspring performance and the response of host plants to cicada oviposition. We established a plantation using three native and three exotic host plants and experimentally excluded cicadas from half of the plants. Our goal was to answer the following specific questions:

1. Are native plant species more susceptible to cicada oviposition than exotic species?
2. Does cicada oviposition increase the amount of dead branches and reduce the growth and reproduction of host plants?
3. Do cicadas oviposit based on species identity or plant architectural traits?
4. Does cicada hatching success depend on host plant species identity, egg nest density, or structural attributes of the plant?

S.L. Flory and W.B. Mattingly. 2008. Response of host plants to periodical cicada oviposition damage. In Press, Oecologia.

W.B. Mattingly and S.L. Flory. Host plant architecture affects oviposition site selection of periodical cicadas. In review, Journal of Animal Ecology.

Back to topRestoration of Invaded Communities

Management of Microstegiumm vimineum invasions and recovery of resident plant communities

Restoration of plant communities invaded by exotic species requires effective eradication of the invader and re-establishment of the resident plant community. Despite the commonly cited need for techniques to accomplish such goals, studies that test strategies for removing invasive plants, monitor effects on resident communities, and incorporate replicate sites are generally lacking. For example, poorly-tested biocontrol agents have resulted in damage to native thistle species and routinely implemented invasive plant removal methods such as prescribed burns have later been found to actually increase rates of invasion.

I conducted a field experiment at eight sites over two growing seasons to evaluate three techniques for removing Microstegium:

1. Hand weeding (HW)
2. Grass-specific postemergent herbicide (POST)
3. Postemergent herbicide plus a preemergent herbicide the following spring (POST+PRE)

Compared to reference plots (REF), the three treatments each reduced Microstegium biomass at the end of the growing seasons to relatively low levels. However, after the second year of the experiment, POST and POST+PRE resulted in very low levels of Microstegium spring cover, while HW plots were substantially re-invaded by Microstegium. HW and POST, but not POST+PRE, increased resident plant community productivity and spring resident community cover compared to reference plots. In addition, plant community composition, recovery of functional groups, and tree regeneration all differed based on removal methodology.

These results indicate that Microstegium invasions can be eradicated using hand-weeding or a grass-specific post-emergent herbicide but that the removal technique will determine the amount of tree regeneration and the composition of the native plant community following Microstegium removal. Given these results, removal and restoration experiments should consider the efficacy of removal techniques and their effects on native plant community recovery.

S.L. Flory. 2008. Management of Microstegium vimineum invasions and recovery of resident plant communities. In press, Restoration Ecology.