Current Research

The role of burn seasonality, fire temperature, and residence time in controlling woody invasive plants

Tim Kuhman, Department of Biological Sciences, Edgewood College
Jed Meunier, Science Services, Wisconsin Department of Natural Resources
Nathan Holoubek, Science Services, Wisconsin Department of Natural Resources
Yari Johnson, School of Agriculture, University of Wisconsin–Platteville
Brad Strobel, Necedah Wildlife Refuge, U.S. Fish and Wildlife Service

The control of invasive woody species presents one of the greatest challenges for restoration and management of fire-dependent ecosystems. While the vast majority of prescribed burning occurs in the early spring, there is evidence that burning during other times of the year can offer more effective control of undesirable species. In this project, we asked how seasonality, fire temperature, and fire residence time interact to influence stem damage and resprouting of woody shrub and tree species that are often targeted by prescribed fire treatments in Wisconsin. Common buckthorn (Rhamnus cathartica) and honeysuckle (Loniceraspp.) are exotic invasive species that frequently degrade forest understories, edges, and grasslands in the Upper Midwest. Black oak (Quercus velutina) and red oak (Q. rubra) are natives that can be invasive in prairie and barrens restoration projects. Managing these species with prescribed fire can be challenging given the inability to inflict damage to larger stems under low-intensity fires and their tendency to resprout after being top-killed by fire. We targeted individual stems of red oak, black oak, exotic honeysuckle, and common buckthorn using controlled fire intensity and residence time treatments during spring, early growing season, late growing season, and fall to assess subsequent top-kill and resprouting for individual stems of each species.

The presence and disappearance of Cypripedium candidum in the southeast glacial plains of Wisconsin

Andrea Weissgerber, Department of Planning and Landscape Architecture
Advisor: John Harrington

This project will examine the presence and disappearance of the white lady’s-slipper orchid (Cypripedium candidum) in the glaciated region of southern Wisconsin. It will aim to determine species status, and the major environmental factors associated with distribution, abundance, and the presence/absence of white lady’s slipper. The goal is to determine why populations are no longer found where they were once prevalent. This project will provide insight into species status within the Arboretum and a glimpse into habitat quality of the study sites.

Effects of invasive jumping earthworms on sugar maple hydraulics at the UW–Madison Arboretum

Kim O’Keefe, postdoctoral researcher, Department of Botany
Advisor: Kate McCulloh

Invasive earthworms can have significant consequences for ecosystem structure and function, as they alter soil texture, soil nutrient cycling, soil microbial communities, and the diversity and cover of understory vegetation. However, whether invasive earthworms impact overstory tree functioning, either directly or indirectly through other ecological changes, is unknown. Because earthworms degrade soil organic matter and consequently reduce the capacity of the soil to retain water, invasive earthworms may indirectly induce water stress in trees and reduce their ability to move water. Here, we assessed the impacts of Asian jumping earthworms (Amynthas agrestis and A. tokiensis) on sugar maple (Acer saccharum) water use. Specifically, we asked: do jumping earthworms induce water stress and reduce the ability of sugar maples to move water? We addressed this question by sampling sugar maple trees at the University of Wisconsin–Madison Arboretum during the 2017 growing season. We measured the rate of water movement through stems (stem hydraulic conductivity), stem anatomy, and leaf water stress on sugar maple trees growing in areas with and without the jumping earthworms present. We found that the presence of jumping worms reduced the rate of water movement through sugar maple stems. Furthermore, lower water movement was associated with smaller and fewer water-conducting vessels in the stem tissue, but not with leaf water stress. These results suggest that jumping earthworms may induce long-lasting changes in the structure of sugar maple tissue, altering their ability to move water and having unknown consequences for sugar maple–dominated forests in a changing climate.

Effects of spatial distribution and abiotic conditions on regeneration success in Southern Wisconsin forests

Jared Beck, Department of Botany, UW–Madison
Christy Lowney, UW Arboretum
Advisor: Don Waller, Department of Botany, UW–Madison

This project will describe the spatial distribution of trees, saplings, and seedlings in Abraham’s Woods to better understand how the distribution depends on abiotic conditions (light availability and soil moisture) and proximity to neighboring trees. Findings from Abraham’s Woods will be compared to sites in the Baraboo Hills. Over the long-term, the data we gather will serve as an important baseline for monitoring forest dynamics using detailed information about environmental conditions, as well as individual tree-level growth and mortality information.

Forest succession in a southern-mesic hardwood forest: Abraham’s Woods

Christy Lowney, Brad Herrick, UW Arboretum

Abraham’s Woods is a 40-acre southern mesic forest, dominated by sugar maple, basswood, and red oak. Tree, shrub, and herbaceous plant data for this stand date back to 1948, when Dr. John Curtis and the Plant Ecology Laboratory at the UW–Madison Botany Department surveyed this forest using plotless sampling methods. In 2008, long-term monitoring plots were established at this site. These plots were resampled in 2018. This data will be analyzed to track changes in forest composition and plant diversity over the last 70 years, with an in-depth look at changes over the last decade. During the 2018 sampling, individual trees were tagged to study overstory mortality and recruitment. Diversity of both spring ephemerals and understory herbaceous species is also being monitored.

Effect of Climate Change on Subnivium Habitat

Larry Werner, Department of Forest and Wildlife Ecology
Advisors: Jonathan Pauli and Benjamin Zuckerberg, Department of Forest and Wildlife Ecology

Many organisms in the Great Lakes Region survive extreme winter conditions by taking refuge in the subnivium, which maintains temperatures around 0 degrees C throughout the winter. The snow pack forms an insulative layer that traps warm air escaping from the soil. However, as the snow pack decreases in depth and becomes denser, it becomes less insulative, and as a result the subnivium becomes colder and less thermally stable. Warming winter conditions are likely to cause a decrease in snow depth and snow duration across North America, and we predict that the result will be a subnivium that is colder and less thermally stable.

To test this hypothesis researchers have built 27 micro-greenhouses which are distributed throughout the Great Lakes Region and across different habitat types. Three of these greenhouses are at the Arboretum. The greenhouses have automated roofs that open during precipitation events, allowing the same amount of snow to accumulate both inside and outside of the greenhouse. Once it has stopped snowing, the greenhouse heats to a set temperature above ambient, allowing researchers to simulate the effects of future warming winters on snow pack characteristics and subnivium temperature.

Long- and Short-term Vegetation Dynamics at Greene Prairie

Brad Herrick, Arboretum

Prairie plants at Greene Prairie have been monitored since the 1950s, resulting in a dataset of plant species richness over 60+ years. This data will be analyzed to investigate trends in native and invasive plant diversity. More recently, we have collected plant species richness and cover data in areas of the prairie before and after invasive woody shrubs and trees were removed to determine how this common restoration technique affects plant diversity.

Intervention Strategies for Deer Ticks and Tick-borne Pathogens in Wisconsin and the Arboretum

Jordan Mandli, School of Medicine and Public Health
Advisor: Susan Paskewitz, UW Medical Entomology Lab

Spurred by the discovery of a single larval deer tick in 2010, UW–Madison researchers have worked diligently with Arboretum staff to assess the growing threat of a newly established deer tick population. Since 2010, surveys have not only indicated an increasing number of ticks throughout the Arboretum property, but have also shown growing incidences of tick-borne pathogens such as Lyme disease that threaten community health. To quell these growing trends, members of the UW–Madison Medical Entomology Laboratory have begun exploring host-targeted interventions designed to reduce the tick population and reduce the infection rate of reservoir hosts that perpetuate the pathogen’s life cycle. Researchers continue to monitor the status of tick infestation in the Arboretum and possible tools to protect neighbors and outdoor enthusiasts alike.

Persistence of Native Species Planted in a Stormwater Retention Pond

Brad Herrick, Elizabeth Buschert, Arboretum
James Doherty, Stanford Online High School
Erik Olson, Northland College

Native wetland species are often planted in and around stormwater treatment facilities to create or restore habitat in these artificial systems. However, few plantings are monitored thereafter. In 2009, a 1.6 ha. (4 ac.) retention pond was constructed at the Arboretum to treat an average of forty-four million gallons of stormwater annually. After pond construction, eight native emergent macrophyte species were planted in the shallow water zone. Shortly after planting, invasive cattails move in and competed with the planted natives. Species richness in plots was documented one year after planting in 2010, and again in 2016 to determine what impact, if any, the cattails have had on the native species.

Predicting Dragonfly Occupancy at Stormwater Retention Ponds in Southern Wisconsin

Andy Cassini, Department of Zoology
Robert Bohanan, North Temperate Lakes Long-term Ecological Research, WISCIENCE
Brad Herrick, Arboretum

Stormwater retention ponds are common best management practices (BMPs) for improving the quality of runoff and protecting downstream lakes and wetlands. However, few studies have looked at these ponds for their value as wildlife habitat. In 2016, more than 50 stormwater retention ponds in southern Wisconsin, including ten at the Arboretum, were surveyed for dragonfly species. In addition, numerous habitat variables such as vegetation cover type(s), amount of buffer, water clarity, pond size, etc., were collected. Occupancy models will be used to predict which habitat variables are most important for certain species of dragonflies and their overall diversity in and around these artificial ponds.

Recent Findings

Interaction Between the Jumping Worm (Amynthas spp.) and European Buckthorn (Rhamnus cathartica)

Carly Ziter, Ecosystem and Landscape Ecology Lab
Advisor: Monica Turner, Ecosystem and Landscape Ecology Lab

This project asks how a recently discovered invasive species, the Asian jumping worm, might interact with European buckthorn. European earthworms – on which much of the current understanding of invasive earthworm impacts is based – aid buckthorn spread via alterations to the forest floor that enhance buckthorn germination. European earthworms also prefer nutrient-rich buckthorn litter to that of native species, facilitating earthworm invasion in buckthorn-dominated areas. Recent studies suggest jumping worms may outcompete their European counterparts and have greater impacts on litter reduction. Yet no research exists on Amynthas spp. litter preferences or potential impacts of the recent invader on buckthorn germination and establishment. Interactions between these species could have substantial consequences for ecosystem services in areas where they co-occur. The presence of both species and available facilities at the UW–Madison Arboretum provide a unique opportunity to study this species interaction and its potential consequences within the Madison area, with implications for other Midwestern landscapes.

Ziter, C. 2018. Ecosystem service supply in an urban landscape: roles of landscape structure, historical land-use, and biodiversity. Dissertation. University of Wisconsin–Madison, Madison, Wisconsin, USA.

The Effect of Jumping Worm (Amynthas spp.) on Above-ground Woodland Vegetation

Katie Laushman, Nelson Institute, Environment and Resources
Advisor: Sara Hotchkiss, Department of Botany

Laushman and Hotchkiss are researching the effect of the newly discovered Asian jumping worm on the overall health of vegetation in Wingra Woods and Gallistel Woods. Laushman has set up plots to survey the diversity of herbaceous and woody plants in areas invaded by the worm and uninvaded areas to assess the differences in the plant communities. Her work will add to our knowledge of how jumping worms affect native Wisconsin ecosystems and will help us better understand restoration challenges at the Arboretum in light of this new invasion.

Laushman, K. M., S. C. Hotchkiss, and B. M. Herrick. 2018. Tracking an invasion: community changes in hardwood forests following the arrival of Amynthas agrestis and Amynthas tokioensisin Wisconsin. Biological invasions 20(7): 1671–1685.

Laushman, K. M. 2017. Investigating a novel invasion: jumping worms in Wisconsin. Thesis. University of Wisconsin–Madison, Madison, Wisconsin, USA.

Influence of Sediment on Dissolved Phosphorus Levels in Stormwater Runoff though Curtis Prairie

Elizabeth Buschert, Biological Systems Engineering, Arboretum

Soil and sediments can be a source or sink for phosphorus in aquatic systems, depending on present levels of phosphorus and phosphorus-absorbing constituents. This project will analyze sediments in Curtis Pond and at 5 to 6 downstream points of the outlet along the effluent path, to try to determine the influence of sediment on dissolved phosphorus levels in stormwater runoff. Buschert will also analyze soil cored from the bottom of Curtis Pond to determine if there is a significant change in these characteristics below the accumulated sand and sediment. Finally, Buschert will monitor phosphorus levels in Curtis Pond and effluent to see how they relate to sediment levels. This project has the potential to benefit the Arboretum by shedding light on the potential for sediments to be a source or sink for phosphorus in stormwater, which may inform future management decisions for Curtis Pond.

Buschert, E. 2018. Phosphorus and stormwater in a pond-prairie system. Thesis. University of Wisconsin–Madison, Madison, Wisconsin, USA.

Effects of European Buckthorn (Rhamnus cathartica) on Small Mammal Post-dispersal Seed Predation

Peter Guiden, Nelson Institute, Department of Zoology
Advisor: Dr. John Orrock, Department of Zoology

Spatial patterns of animal foraging have important consequences for understanding the dynamics of animal movement, the strength of plant-animal interactions, and the ecology of disease. Although invasive plants, such as buckthorn (Rhamnus cathartica), can modify the abundance and activity level of small mammals by providing a low-risk environment for them to forage, it is unknown whether this produces significant changes in space use by small mammals. Guiden and Orrock are testing the influence of invasive R. cathartica on spatial patterns of small mammal foraging by investigating the spatial distribution of small mammal seed predation on red oak (Quercus rubra).

Guiden, P. W. and J. L. Orrock. 2017. Invasive exotic shrub modifies a classic animal-habitat relationship and alters patterns of vertebrate seed predation. Ecology 98(2): 321–327.

How do invasive Asian earthworms affect soil and litter properties?

Jiangxiao Qiu and Monica Turner investigated the effects of a newly arrived exotic, invasive Asian earthworm on soil and litter properties at the Arboretum. Commonly referred to as “jumping worms” these earthworms were first documented in Wisconsin in 2013 at the Arboretum. Qiu and Turner found that jumping worms significantly reduced leaf litter and increased total carbon, total nitrogen and total phosphorus in the upper 5 cm of soil. Soil inorganic nitrogen and dissolved organic carbon both increased. This rapid mineralization of soil nutrients may make ecosystems susceptible to nutrient losses which may affect plants and soil biota.

Qiu, J., and M.G. Turner. 2016. Effects of non-native Asian earthworm invasion on temperate forest and prairie soils in the Midwestern US. Biological Invasions. 16 pp. doi:10.1007/s10530-016-1264-5

Effects of Common Buckthorn (Rhamnus cathartica) on small mammal post-dispersal seed predation

Invasive plant species can drastically affect ecosystem functions as well as plant and animal communities. These changes in habitat structure might generate novel indirect effects in ecological communities, such as affecting activities of foraging animals. Bartowitz is studying whether exotic shrubs might alter rates of seed predation by providing a structural refuge for small mammals or altering the litter layer. She completed three seed removal studies in July, September, and November 2014, in an Arboretum forest invaded by common buckthorn (R. cathartica). Half the research plots were cleared of R. cathartica. Seed depots were used to track predation by small mammals. The depots has R. cathartica seeds as well as native maple, cherry, and oak seeds (Acer rubrumAcer saccharumPrunus serotina, and Quercus rubra).

Bartowitz found that total seed removal was significantly higher in buckthorn plots than in cleared plots, and leaf litter depth was significantly higher in cleared plots. Removal rates differences suggest that buckthorn invasion affects seed removal rates. These differences could influence the survival of native seeds and the way plant communities are established. Understanding these changes can assist with restoration efforts through management and seed additions.

Bartowitz, K.J., and J.L. Orrock. 2016. Invasive exotic shrub (Rhamnus cathartica) alters the timing and magnitude of post-dispersal seed predation of native and exotic species. Journal of Vegetation Science 27(4): 789–799. doi: 10.1111/jvs.12397