Students

I am an active member of the Environmental Science & Policy Graduate Program at the University of Wisconsin - Green Bay. We offer M.S. degrees with emphases in Ecosystem Studies, Resource Management, and Environmental Policy & Administration. If you are interested in pursuing a M.S. degree under my direction, please contact me directly.

Mandy K. Peterson:

Status: M.S. May 2012

Thesis: Interactive Effects of Native Plants and the Exotic Alliaria petiolata (Garlic mustard) on Emergent Insects and Root Production in a Northeastern Wisconsin Forest

Thesis Summary: Invasive plants significantly impact the ecosystems in which they invade by altering plant production and elemental cycling, native plant abundance and diversity, and ecosystem food web structure. All of these changes have direct or indirect implications for the ecosystem services benefiting human society. The objective of my research was to study the effect of A. petiolata on fine root production and soil emergent insect populations. Soil ingrowth cores were inserted to measure fine root production. Emergence traps were used to catch insects that emerged from the soil environment. A. petiolata had no significant effect on fine root production or emergent insect captures. Fine root production was positively related to non-A. petiolata plant cover and to native plant cover. Total insect and Dipteran captures, and order richness and Dipteran richness also had a positive relationship with native plant cover. Chironomidae abundance was positively related to fine root production. Dipteran diversity was positively related to native plant cover and A. petiolata cover, while Order diversity was negatively related to A. petiolata cover. These results suggest that native plant cover was more important to fine root production and emergent insects abundance and diversity than the direct effects of A. petiolata cover.

Adam C. von Haden:

Status: M.S. May 2012

Thesis: Interactive Effects of Soil Moisture, Temperature, and Depth on Fine Root Dynamics in a Restored Tallgrass Prairie in Northeastern Wisconsin: Implications for Carbon Sequestration.

Thesis Summary: Biofuels are likely to play a significant role in the impending shift from fossil fuel to renewable energy sources. Conversion of marginal agricultural lands to biofuel grasslands may provide additional ecological services such as erosion control, nutrient retention, and carbon sequestration. My first research objective was to quantify and predict fine root dynamics within the soil profile in relation to environmental variables. Surprisingly little is known about how root production and decomposition change within the soil profile, yet these processes are intrinsic to carbon sequestration. I found that root production mimicked the patterns of root biomass within the soil profile, but that root decomposition declined more dramatically with depth than had previously been reported. Soil temperature was the best predictor of all root dynamics, but soil moisture improved predictions of root production and decomposition. My results suggest that soil temperature and moisture can be utilized to predict carbon sequestration deep into the soil profile. My second research objective was to assess the effects of soil moisture on root dynamics and their relative distributions within the soil profile. I found that root biomass and production were unresponsive to changes in soil moisture, but that root decomposition declined in wet conditions. I also found that all root distributions tended to be more shallowly distributed in wet soils. I suggest that concurrent changes in plant species and soil moisture may have reduced the impact of water on root production. My results indicate that wet landscapes are ideal for carbon sequestration. My research highlights the increased potential for carbon sequestration in water-saturated perennial grasslands in northeast Wisconsin.

Publications:

von Haden, A.C., and M.E. Dornbush. Fine root dynamics throughout soil profiles of restored tallgrass prairie in Northeastern Wisconsin: evaluating the effects of soil moisture and temperature. Submitted.

Joshua A. Martinez:

Status: M.S. December 2011

Thesis: Facilitation as a Potential Tool for Understory Restoration in an Overgrazed, Invaded Woodland in Northeastern Wisconsin.

Thesis Summary: The interactive effects of herbivory, exotic species and other human mediated changes to the biosphere are reducing species diversity and altering ecosystem services globally. In this study, I tested if facilitation could be used as a management technique to restore a degraded NE Wisconsin, USA forest understory facing high white-tailed deer (Odocoileus virginianus) browse pressure and high abundance of the exotic herb Alliaria petiolata (garlic mustard). Specifically, I attempted to facilitate native understory restoration by planting or seeding native herbs into three different matrix densities of the native, browse-tolerant grass Elymus virginicus (Virginia wild rye), that were either protected from (fenced), or accessible to, deer grazing. Deer had minimal impacts on E. virginicus, but significantly reduced the cover, survival, and flower production of Ageratina altissima (white snakeroot) transplants, largely independent of the density of E. virginicus plantings in open-access plots. In contrast, native seeded species richness and abundance were not affected by deer access, but were reduced by increasing E. virginicus densities. Alliaria petiolata cover was significantly higher in plots accessible to deer, but declined significantly with increasing E. virginicus planting density in both open-access and fenced plots. These results were largely corroborated by results from an associated observational study, with the exception that natural E. virginicus stands supported slightly higher native species richness than adjacent areas lacking E. virginicus. Thus, while I found little support that establishing E. virginicus facilitated browse-susceptible native understory herbs during the short-term experimental study, the restoration of E. virginicus successfully increased total native species cover and significantly reduced the cover of the exotic A. petiolata. I suggest the planting of browse-tolerant native species, such as E. virginicus, as a viable restoration technique in heavily browsed, A. petiolata invaded woodlands.

Publications:

Martinez, J.A., and M.E. Dornbush. Use of a Native Matrix Species to Facilitate Understory Restoration in an Overgrazed, Invaded Woodland. In Press.

Andrew LaPlant:

Status: B.S. Environmental Science

Project Title: Exotic slug abundance in five contrasting NE Wisconsin forests.

Project Summary: Slugs occur globally, from the tropics through the temperate and boreal ecosystems, occupying a variety of habitats from grasslands to wetlands and forests. Slugs are global agricultural pests, with recent evidence that introduced slugs are also affecting plant community composition in natural areas as well. The effect of exotic herbivorous slugs in North American forested ecosystems has been overlooked, yet recent work suggests that they are having a significant effect on herbaceous community composition . Unfortunately, little information exists concerning their abundance and habitat distribution within Midwestern forests. Andrew’s research will determine the abundance of exotic slugs in five contrasting forest habitats in Northeast Wisconsin, then correlating slug abundance to plant cover, soil moisture, and soil pH. Andrew’s research will help to identify the factors shaping local slug abundance, and thus their potential influence on forest herbaceous composition among NE Wisconsin forest types.

Cody J. Sandahl:

Status: B.S. Environmental Science

Project Title: The effects of root growth on soil microbial biomass and enzyme activity.

Project Summary: The depletion of Midwestern soil carbon coupled with the large potential for carbon storage in those soils, suggests that biological sequestration of carbon can serve as an effective tool for stabilizing atmospheric CO₂ and, in addition, restoring soil fertility. Despite its importance, we insufficiently understand how soil carbon accumulates, since root inputs themselves do not directly form soil organic matter, rather, it is a byproduct of microbial activity acting upon root inputs. This study seeks to evaluate the effects of root inputs on soil microbial biomass and enzymatic activity. Cody is comparing the microbial biomass and enzyme activity along a gradient of belowground net primary production in soil samples (0-10 cm depth) from upland and lowland areas within a restored tallgrass prairie. The results of this study will enhance our understanding of soil organic matter formation, and in practice, our ability to restore soil fertility and stabilize atmospheric CO₂.

Philip G. Hahn:

Status: M.S. May 2010

Thesis: Drivers of native forest herbaceous layer decline: exotic slugs more limiting to native plants than competition for an exotic plant. - Awarded the
2010-2011 UW-Green Bay Outstanding Thesis Award

Thesis Summary: Recently, the effects of overabundant consumers have gained attention as a potential mechanism facilitating the dominance of invasive plants. The introduced slug Deroceras reticulatum is found in high abundances in Wisconsin woodlands invaded by Alliaria petiolata (garlic mustard) and appears to be selectively grazing on native plants. This provided a unique opportunity to study how competition and herbivory from introduced species interact to affect native plant diversity. Feeding experiments showed that the introduced slug Deroceras reticulatum exhibited a preference for many native plants, but avoided the invasive plant A. petiolata. Plant preference was negatively related to leaf thickness, and rosette plants were damaged significantly more than erect plants. In the field, herbivory significantly reduced both the growth and survival of seedlings from two species of native palatable rosette plants, whereas competition from A. petiolata had negligible affects on the growth and survival of any native seedlings tested. In contrast, A. petiolata was not affected by slug grazing, suggesting that consumer avoidance, not direct competitive exclusion, is most promoting A. petiolata dominance in our NE Wisconsin forest site.

Publications:

Hahn, P.G., and M.E. Dornbush. 2012. Exotic consumers interact with exotic plants to mediate native plant survival in a Midwestern forest herb layer. Biological Invasions 14: 449-460.

Hahn, P., M. Draney, and M. Dornbush. 2011. Exotic slugs pose a previously unrecognized threat to the herbaceous layer in a Midwestern woodland. Restoration Ecology 19: 786-794.

Simone E. Kolb:

Status: M.S. December 2007

Thesis: Understanding the mechanisms by which a manure-based charcoal product interacts with soil to affect microbial biomass and activity.

Thesis Summary: Phosphorous loading of freshwater systems is a serious, long-lasting, and unintentional environmental impact than can result from livestock production. At the same time, the offsite transport of manure needed to reduce potential environmental impacts is often hindered by the high cost of transporting the largely liquid waste. Recent advances in pyrolysis technology may provide the dual benefit of converting livestock manure into a local, renewable energy source, and an easily transportable and agriculturally beneficial soil amendment in the form of charcoal. To examine the potential effects of charcoal additions to temperate soils, Simone’s thesis examines the effect of varying charcoal application quantity on soil microbial biomass and activity among four distinct soil series from Wisconsin, USA.

Publications:

Kolb, S.E., K.J. Fermanich, M.E. Dornbush. 2009. Effect of charcoal quantity on microbial biomass and activity in temperate soils. Soil Science Society of America Journal 73: 1173-1181.