Focus
My research centers on invasive species and disturbance ecology within terrestrial ecosystems, focusing on plant interactions with insects and other plants in regards to establishment and growth, as well as shifts and losses within communities as a result of human-induced disturbances and exotic species introductions. In addition, I am interested in how physical disturbance and microsite characteristics facilitate invasion and intensify impacts of exotic species in natural communities.Opportunities
Opportunities for student research exist in a wide range of ecosystems, from forests to sand dunes, focusing on numerous different plant species. If you are an undergraduate or graduate student interested in joining my lab, please email me (marshalj {at} ipfw.edu ) with research interests and ideas.Current Research
Competitive interactions between Centaurea biebersteinii and Tanacetum bipinnatum ssp. huronense
In the Great Lakes region, Lake Huron tansy (Tanacetum bipinnatum ssp. huronense) is limited in distribution to dune ecosystems, which are sensitive to anthropogenic disturbances and exotic species invasions. Spotted knapweed (Centaurea biebersteinii) is a common invader of these dune systems and can change dune plant community composition and structure. Marshall et al. (2008) found that areas without spotted knapweed had over 3 times greater percent cover of Lake Huron tansy than areas with spotted knapweed. By understanding the impacts on Lake Huron tansy growth (i.e. above and below ground biomass, seed production, leaf area, etc.) in competition with spotted knapweed, we can better understand the ecological impacts of invasive plants and the sensitivity levels of threatened species. The objectives of this study are to 1) investigate the competitive interactions between spotted knapweed and Lake Huron tansy, 2) quantify the above and below ground impacts on growth of Lake Huron tansy by spotted knapweed, and 3) test the hypothesis that specialized dunes species, like Lake Huron tansy, have limited competitive abilities when grown with aggressive invasive species.Allelopathic potential of Centaurea biebersteinii on
Tanacetum bipinnatum spp. huronense seed germination and seedling growth
Similarly to the abstract above, by understanding the potential impacts on Lake Huron tansy seed germination in the presence of spotted knapweed (foliage, roots, stems, and flowers), we can better understand the ecological impacts of invasive plants and the sensitivity levels of threatened species. The objectives of this study are to 1) investigate the impacts of spotted knapweed litter on Lake Huron tansy seed germination and individual growth, 2) quantify the success rates of subsequent individuals in biomass accumulation, and 3) test the hypothesis that seeds and seedlings of specialized dunes species, like Lake Huron tansy, are hindered in germinating in the presence of aggressive invasive species.Predicting ash survival based on bark characteristics in
the core emerald ash borer mortality zone
Collaborator Institution: Michigan Technological University
Attacking all North American ash species (Fraxinus spp.), emerald ash borer (Agrilus planipennis Fairmaire [EAB]) has caused significant mortality within it's introduced range. Mortality in ash trees occurs as a result of EAB larvae feeding on phloem within the trees during development following ovipositioning in bark crevices. The timeline for death ranges from a single year in smaller trees to 3-4 years in large trees. For other forest pests, host bark plays an important role in infestation density and egg ovipositioning. The objectives of this study are to 1) locate live ash trees in the core EAB induced mortality zone in SE Michigan, 2) examine differences in live and neighboring dead trees in terms of DBH and bark roughness, and 3) develop a potentially deployable and simple ash mortality probability system.Past Research
Competitive interaction between Microstegium vimineum and
first-year seedlings of three central hardwoods
We established an experiment designed to compare effects of Microstegium vimineum (Japanese stiltgrass) on seedlings of three native hardwood species to investigate the hypothesis that competitive effects of M. vimineum on juvenile trees will vary across different tree species. Growth and survival of Acer rubrum, Liriodendron tulipifera, and Quercus rubra first-year seedlings were compared in plots with and without M. vimineum in three planting beds under 50 percent shade. The tree species studied are abundant and of particular interest in the Central Hardwood Region. A. rubrum and L. tulipifera seedlings experienced reduced growth in several foliar characteristics in the presence of M. vimineum. Q. rubra did not exhibit any differences in foliar characteristics between plots with and without M. vimineum, however there was a reduction in Q. rubra stem weight as a result of the presence of M. vimineum. The differential responses of A. rubrum, L. tulipifera, and Q. rubra to the presence of M. vimineum observed in this study support the hypothesis that effects of this exotic species will vary across tree species. As a result of reductions in the growth of A. rubrum and L. tulipifera, the presence of M. vimineum in forest understories may reduce the rate at which seedlings of these species are recruited into larger size classes. (2009) Journal of the Torrey Botanical Society 136:342-349Influence of Microstegium vimineum presence on insect abundance in hardwood forests
Microstegium vimineum (Japanese Stiltgrass) is an exotic, annual grass that has invaded hardwood forests throughout the Southeastern United States. Four forests, in four Tennessee counties, were selected, and insects and plant communities were sampled along transects with and without M. vimineum. Insects were sampled using a terrestrial vacuum sampler. Percent plant cover was measured using a point-intercept technique, and plant species richness and diversity were calculated. Of the 60 families collected, significantly more individuals in the families Acrididae, Cicadellidae, and Gryllidae, were collected in areas with M. vimineum, whereas areas without M. vimineum resulted in significantly more individuals in the families Blattellidae and Chrysomelidae. Herbaceous plant richness and diversity did not significantly differ between areas with and without M. vimineum. Areas without M. vimineum had significantly lower percent vegetation cover (30.41%) than areas with M. vimineum (91.48%). The overall herbaceous plant community diversity and structure may be more influential factors in the abundances of insect families in central hardwood forests than the invasion of M. vimineum. (2009) Southeastern Naturalist 8:515-526Comparative Analysis of Plant and Ground Dwelling Arthropod Communities in
Lacustrine Dune Areas with and without Centaurea biebersteinii (Asteraceae)
Open dune systems are being degraded through human development and exotic species invasions. The Grand Sable Dunes, Pictured Rocks National Lakeshore, Michigan, are protected from development but not from the spread of exotic species. The invasive exotic spotted knapweed, Centaurea biebersteinii, has invaded significant portions of this dune system. Areas without spotted knapweed had higher native plant diversity than areas with spotted knapweed, as well as lower exotic plant diversity. Of native plant species occurring in the highest frequencies along transects in both spotted knapweed infested and non-spotted knapweed infested areas, four out of the five species were more likely to be encountered along transects in non-spotted knapweed areas than along transects in spotted knapweed areas. Insect families Curculionidae and Formicidae were captured more often in areas with spotted knapweed. Increased dune stabilization increased the ability of exotic plant species not adapted to the actively shifting sand dunes to invade and alter the plant communities. Differences in Curculionidae and Formicidae abundance were due to the changes in plant communities. Also, increased stabilization of sand dunes as a result of spotted knapweed invasion increased the abundance of Formicidae by increasing the stability of nest sites. Limiting the range of spotted knapweed in dune systems could maintain naturalinsect distribution and native plant diversity. (2008) American Midland Naturalist 159:261-274Influence of litter removal and mineral soil disturbance on
the spread of an invasive grass in a Central Hardwood forest
Soil and litter disturbances within Central Hardwood forests may facilitate exotic plant species invasion of interior forest areas. Microstegium vimineum is an annual exotic grass that has become common throughout the Southeastern United States. Three replicates of three different mineral soil and litter disturbance treatments, plus a control with no disturbance, were established on the leading edge of M. vimineum patches prior to seed fall. All patches were located in areas with similar forest canopy structure and slope in three Central Hardwood forest stands prior to seed fall. At the beginning of the following growing season, each individual M. vimineum seedling was mapped within the treatment plots. The mean number of M. vimineum individuals that established within each treatment did not differ significantly from the control. The distance at which 90% of the individuals had spread, and the overall mean distance spread were significantly farther for the litter removal treatment than the control. The farthest individual seedling from the boundary of existing patches in both the litter removal and the mineral soil disturbance and litter removal treatments were significantly farther than the control. The individuals that spread the farthest are of most concern due to the large number of viable seed that a single M. vimineum plant can produce. These results suggest that disturbance of the litter layer may increase the spread rate of M. vimineum and facilitate its invasion of new habitats, and that leaving litter layers intact may slow the spread of M. vimineum. (2008) Biological Invasions 10:531-538Effects of Microsites Created by Selective Harvesting on
Growth of Microstegium vimineum in a Central Hardwood Forest
Disturbances related to silvicultural activities are inevitable and may facilitate the spread of established populations of exotic species. Microstegium vimineum is an annual exotic grass that has spread throughout the eastern United States. Different categories of understory microsites resulting from cutting and the operation of logging machines within three selective harvest units were identified and characterized by measuring several environmental variables. M. vimineum was sown within the microsites categorized. Differences in growth of M. vimineum across different microsites were quantified. As percent canopy cover increased, M. vimineum percent cover, mean length, and mean number of nodes decreased. Also, as litter depth increased, M. vimineum percent cover and stem length decreased. In undisturbed microsites in which M. vimineum was not sown, the exotic grass was not a dominant species, whereas in all other microsites created by logging machine operation M. vimineum was a dominant species whether those areas were sown or colonized by wild populations. These results suggest that unique microsites created by logging may facilitate M. vimineum invasion of central hardwood forests. The apparent connection between soil and canopy disturbance and invasion by M. vimineum provides further impetus for careful planning and use of haul roads and skid trails. (2008) Forest Science 54:534-542
Indiana University-Purdue University Fort Wayne - Department of Biology
valid XHTML CSS 508