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Focus

My research centers on species of concern, invasive species, and disturbance ecology. Within terrestrial ecosystems, I focus 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.

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Opportunities

Opportunities for both undergraduate and graduate student research exist in a wide range of terrestrial ecosystems, from forests to sand dunes, focusing on numerous different plant species. If you are interested in conducting plant ecology and invasion biology research in my lab, please email me (marshalj {at} ipfw.edu ) with research interests and ideas.

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Current Research

Lake Huron tansy (Tanacetum bipinnatum ssp. huronense)
In the Great Lakes region, Lake Huron tansy is limited in distribution to dune ecosystems, which are sensitive to anthropogenic disturbances and exotic species invasions. I am conducting several studies to identify competitive interactions between Lake Huron tansy and spotted knapweed (Centaurea stoebe), allelopathic influence of spotted knapweed on Lake Huron tansy seed germination and seedling growth, and the distribution of Lake Huron tansy within dune ecosystems in relation to spotted knapweed presence. This is related to my previous research (Marshall et al. 2008), where we found that areas without spotted knapweed had over 3 times greater percent cover of Lake Huron tansy than areas with spotted knapweed.

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Other dune species of concern
I'm also working on looking at the distribution and related plant communities for Pitcher's thistle (Cirsium pitcheri) and longstalk starwort (Stellaria longipes) in Grand Sable Dunes, Pictured Rocks National Lakeshore, with the intent to expand this into other Great Lakes dune systems (i.e. Indiana Dunes and Sleeping Bear Dunes National Lakeshores).

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Spotted knapweed (Centaurea stoebe)
In addition to the research above related to distributions of spotted knapweed and Lake Huron tansy, I am also working on a study of the reproductive timing of spotted knapweed. Typically, spotted knapweed is described as a biennial or short lived perennial species. By this description, there is a period of time where flowers and, by extension, seeds are not produced. For spotted knapweed, after germination, the plant establishes a rosette of leaves for the first year, and then produces flowers in the subsiquent year(s). However, some spotted knapweed plants can produce flowers in the first year. I am attempting to identify if this is an inheritable trait or a response of the plant to certain environmental conditions. Either way, the rate at which this species flowers in the first year is important in understanding population growth and dynamics.

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Ash (Fraxinus spp.)
Emerald ash borer (Agrilus planipennis) attacks all species of North American ash. I am involved with several studies with the objectives of identifying potential physical characteristics that assist in predicting the survival of individual mature ash trees within a forest infested with emerald ash borer (in collaboration with Michigan Technological University), and modeling seedlings of ash within pine and hardwood dominated forest stands in order to understand the distribution of ash regeneration and identify utilization rates of these regenerating trees by emerald ash borer after they are recruited into suitable size classes.

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Garlic mustard (Alliaria petiolata)
Garlic mustard is a common invader of hardwood forests. Currently, I am investigating the influence of drought intensity and timing on garlic mustard growth and reproduction. This has implications in the population dynamics and management of garlic mustard in regards to weather related pressures.