Browsing by Subject "Invasive species"

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Beyond the message: Examining how engaging message mediums impact visitor displacement in emerald ash borer-treated woodlands
(2022-10) Rannow, Brett A.
A variety of factors, including aesthetics, can significantly influence a recreator’s decision to revisit or displace from a setting. Invasive species can significantly change an area’s appearance and, unless visitors are informed about and understand the change, discourage visitation (McFarlane & Watson, 2008; Müller and Job, 2009; Schneider et al., 2019). Moving beyond static signs, advanced communication technologies like augmented and virtual reality show promise to meaningfully engage visitors (Ahn et al., 2014; Petty & Cacioppo, 1986), increasing understanding of landscape changes and potentially retaining visitation. However, limited work addresses if and how such technologies significantly influence visitor behavior. To address this gap, four informational interventions about forest management treatments utilized in response to emerald ash borer (Agrilus planipennis) were tested. Informational interventions included photos with text, augmented reality (AR), virtual reality (VR), and a control group that received no treatment information. State park visitors were randomly assigned to interventions and indicated displacement intentions following intervention exposure. Displacement intentions in response to the treated landscapes ranged from 12-26%. A Chi-Square Test compared displacement intentions across informational interventions and found more engaging technologies changed displacement intentions in only one of the four management responses assessed. Future research with other outcomes and management topics will be useful to refine the utility of AR and VR in this realm.
Climate change, the invasion of Bythotrephes longimanus, and recent changes in the zooplankton community of Lake Superior
(2016-07) Pawlowski, Matthew
In recent decades, average summer surface temperatures in Lake Superior have increased and the invasive predatory zooplankton, Bythotrephes longimanus, became established. While climate warming and Bythotrephes have influenced zooplankton communities in other lakes, it is unclear how either have or will influence the zooplankton community in Lake Superior. A late spring ice out in 2014 provided an opportunity to observe the response of zooplankton in Lake Superior to inter-annual variation in temperature. To evaluate this response, I compared biomass estimates, phenologies, and community compositions of the zooplankton communities in western Lake Superior during the 2014 and 2015 growing seasons. I also compared the community compositions observed in these years to published literature to determine whether the community has changed in response to climate warming or planktivory by Bythotrephes. I evaluated the possible role of Bythotrephes in zooplankton community changes using a bioenergetic model to compare the consumptive demands of Bythotrephes to the production rates of their potential prey. Annual peaks in zooplankton biomass were correlated with peaks in surface temperature. Peak biomass in 2014 occurred approximately 20 days later than in 2015 suggesting that continued warming could have long-term effects on the timing of peak zooplankton biomass in Lake Superior. The amount of biomass at the peak did not differ between years nor did overall community structure suggesting that zooplankton biomass and species composition in Lake Superior may be more constrained by food availability than temperature. However, long-term comparisons of zooplankton community composition indicate that densities of Bosmina longirostris declined and the proportional contribution of Daphnia mendotae to cladoceran biomass increased since the 1970s. These community changes are more consistent with the expected outcome of planktivory by Bythotrephes than the expected outcomes of changes in temperature, primary production, or vertebrate planktivory. The results suggest that Bosmina is the cladoceran species most vulnerable to suppression by Bythotrephes in Lake Superior, which supports the hypothesis that Bythotrephes has altered the cladoceran community in Lake Superior. While consumption by Bythotrephes did not exceed total zooplankton production in Lake Superior during 2014 or 2015, future increases in Bythotrephes density and temperature could cause the top-down effects of Bythotrephes on the zooplankton community to increase. This work helps to clarify how climate warming and Bythotrephes could influence the zooplankton community and energy flow pathway in Lake Superior in the future.
Cold tolerance of drosophila suzukii (Diptera: Drosophilidae)
(2015-04) Stephens, Amanda Ruth
Drosophila suzukii Matsumura, or spotted wing drosophila (Diptera: Drosophilidae), is a fly that is believed to be native to Japan. Spotted wing drosophila females lay eggs into ripe and ripening soft skinned fruits, where larvae develop. The species was first found in the continental United States in 2008, where it was reported to cause extensive economic damage in many fruit crops, including raspberry, blackberry, blueberry and cherry. Spotted wing drosophila is believed to overwinter as a seasonally acclimated winter morph adult. While spotted wing drosophila is found in northern states with colder climates, the ability of it to establish and overwinter in these regions is unknown. Likelihood of spotted wing drosophila overwintering survival was hypothesized by reviewing literature on other Drosophila species cold tolerance. Cold tolerance of spotted wing drosophila was then measured by comparing the supercooling points and lower lethal temperatures of seasonally acclimated (winter-morphs) and non-acclimated adults (summer-morphs). The ability of winter-morphs and summer-morphs to rapidly cold-harden was also studied to determine if the fly can quickly acclimate to new cold temperatures.
Community assembly, invasion, and management of aquatic plant communities
(2022-12) Verhoeven, Michael
Determining what mechanisms drive native species declines and what governs their recovery is foundational to understanding community change, and successfully applying this knowledge to limit further losses or restore degraded ecosystems. Efforts to reduce invasive plant populations are often considered critical for halting degradation of native plant communities and fostering their subsequent recovery or restoration. To assess whether management of two invasive plants—Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus)—is likely to foster recovery of native aquatic plant communities, I integrate experimental and observational methods to study community assembly processes in aquatic plants. Chapter 1 builds the foundation for subsequent studies by constructing an observational monitoring database, compiled from more than 500,000 plant observations collected by disparate sources over a 19-year period. In Chapter 2, I use niche models to unpack how patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, predicting direct competition with native species is less likely for P. crispus than M. spicatum. The aquatic plants database is used in Chapter 3 to assess invader control for boosting native plant communities in real-world management projects, with a focus on comparing the two invaders to test predictions from niche models. I show that limitations of monitoring data constrain estimation of causal effects of management. This limits the generalizability of the findings, highlighting the need for more strategic allocation of aquatic plant monitoring efforts and improved tracking of management interventions. In Chapter 4 I synthesize results of a 4-year, in-lake field experiment and the 19-year, statewide observational data, using community assembly theory to ascribe changes in plant communities to three major mechanisms (invader competition, environmental conditions, and regional species pools) and assess the scales at which these mechanisms shape aquatic plant communities. The results highlight complexity and interactivity of community assembly in this system, with mixed evidence for each mechanism and strong differences across scales. This research demonstrates that contrary to common dogma in aquatic plant management, invaders’ relationships with recipient communities are nuanced, and that invader control alone is insufficient to achieve restoration.
Comparison Of Multi-Piscivore Foraging Success On Native And Invasive Prey Fish Under Variable Light Intensities
(2020-05) Michels, Noland
The majority of fish predator-prey studies have focused on interactions using a single predator. We explored the complexity of foraging at different times of the day by examining the interactions of paired native predators (Burbot Lota lota or Smallmouth Bass Micropterus dolomieu) with either native (Mottled Sculpin Cottus bairdii) or invasive (Round Goby Neogobius melanostomus) benthic prey (n=20). The study allowed the comparison of a pursuit (Smallmouth Bass) and ambush (Burbot) predator. Trials were performed under natural relevant lighting conditions with downwelling light intensity and emission spectrum matched to the irradiance at 10 m depth found in the St. Louis River estuary during summer at night, civil twilight, sunrise, and midmorning. Smallmouth Bass were more active than burbot and initiated 1,510 reactions that resulted in the successful capture of 61 Round Goby and 103 Mottled Sculpin (10.9% success rate overall) whereas Burbot initiated 475 reactions resulting in 24 successful retentions including 9 Round Goby and 15 Mottled Sculpin (5.0% success rate overall). The percentage of successful retentions was greater for Smallmouth Bass at 10.9% compared to only 5.0% for Burbot. Reaction probabilities to each prey differed significantly which resulted in a two-fold increase in attacks on Mottled Sculpin compared to Round Gobies within the same time period. Reaction distances for both predator species did not differ in regard to prey species, but Smallmouth Bass reacted farther than Burbot (max. reaction distances of 159 and 98 cm, respectively). Greater success of native predators on native prey likely cause predators to expend more energy capturing invasive prey and cause higher mortality on native prey populations due to greater predator success.
Data and R-code for "Aquatic Macrophyte and Water Quality Response to Aluminum Sulfate Treatments"
(2025-03-05) Hembre, Kaitlyn; Newman, Raymond M; Bajcz, Alex W; Berg, Matt; James, William; newma004@umn.edu; Newman, Raymond; Minnesota Aquatic Invasive Species Research Center (MAISRC); water
This study examines data from 6 lakes in Minnesota and 2 in Wisconsin to assess the response of aquatic plants and water quality to aluminum sulfate (alum) treatments. The dataset spans from 2011 to 2023 and includes measurements of total epilimnetic phosphorus, Secchi depths, and the frequency of native and invasive macrophyte species. Data were collected directly by project personnel but we also include data provided by project collaborators that were used in the formal analysis. Additional data collected by project personnel, including all point intercept aquatic plant data, temperature, light and dissolved oxygen profiles, and additional water chemistry data are included to facilitate further analysis in the future. Results indicate a marked reduction in total epilimnetic phosphorus levels and improved water clarity (Secchi) after alum treatment, with notable increases in native macrophyte occurrence. Invasive species such as curly-leaf pondweed decreased after alum treat, while Eurasian watermilfoil exhibited variable responses. This comprehensive dataset highlights the effectiveness of alum treatments in enhancing water quality and supporting macrophyte health, with considerations for ongoing invasive species management.
Development of Environmental Indicators for the U.S. Great Lakes Basin Using Remote Sensing Technology
(University of Minnesota Duluth, 2006) Niemi, Gerald J; Johnston, Carol A; Wolter, Peter T.
In 2001 we initiated a study of remote sensing technology to complement our development of environmental indicators for the U.S. Great Lakes coastal region. Our objectives were to: 1) quantify land use/land cover (LULC) and change for the U.S. portion of the Great Lakes basin between 1992 and 2001; 2) identify salient LULC change categories that are most likely to affect near-shore ecosystems; 3) recommend landscape indicators to guide managers toward long-term sustainable development; 4) develop methodologies to quantify SAV within near-shore areas of the Great Lakes; and 5) use historically low water levels in Lakes Michigan and Huron to produce a digital elevation model of recently exposed lake bed using radar interferometry to better model coastal wetland inundation events as lake water levels returns to normal. In addition, we completed four focused studies in the Great Lakes basin: 1) two studies to determine the degree of accuracy of Quiclcbird satellite imagery to identify specific vegetation types within a wetland; 2) an examination of 63 years (1940 to 2003) of land use change in a 100 km2 area in western Lake Erie; and 3) a study to test the use of Hyperion hyperspectral satellite imagery for mapping PhragmitesL an invasive plant species in the Great Lakes. All of the objectives were successfully completed, except objective 5 in which we had technical difficulties with the use of radar interferometry because of changes in ice and snow in the region. A total of six peer-reviewed publications have been completed and three additional publications are either in review or in preparation. The land use/land cover map produced for 1992 and 2001 will serve an extremely important baseline for future monitoring of change in the U.S. Great Lakes basin. A special issue of the Journal of Great Lakes Research is in preparation that summarizes additional work on this project. It is scheduled for publication in 2007.
Did Cryptic Invasion of North America by Common Reed Change Exposure to Pollen Allergens?
(2011-02-24) Schimpf, David J.; White, Natalie A.
Common reed, Phragmites australis (reed), is a very tall grass that spread greatly to occupy large areas near many eastern North American cities over the past century. Its aerially dispersed pollen is known to incite allergic reactions, and possibly asthma, in some persons, but is not distinguished from that of any other grass in routine pollen monitoring. We hypothesize that this regional expansion by reed has increased late-season exposure to grass-pollen allergens in parts of these metropolitan areas. The information available indicates that reed's geographic location, high abundance, small pollen size, release of pollen relatively far above ground, substantial pollen productivity, pollen allergen composition, and late season of pollen release all point to its potential importance for a large number of persons whose health may be degraded by grass pollen. If the other common late-flowering grasses in the same area have larger pollen grains, it may be possible to visually distinguish reed pollen captured by monitoring devices. If not, ratios of stable isotopes of carbon in the pollen may permit differentiation. Otherwise, analytical techniques based on molecular differences need further development in order to estimate local population exposure to allergens from reed. Some 90 million North Americans may live close enough to large tracts of reed to be exposed to substantial concentrations of its pollen, so much more attention to this situation seems warranted. If reed pollen were found to be a health hazard for a particular metropolitan area, removal of the pollen sources may be more feasible than is the case for many other species.
Ecological, Social, And Educational Dimensions Of Restoration: Insights From Berenty Reserve, Madagascar
(2024) Mondragon, Ariadna
Amidst a global biodiversity crisis, ecological restoration emerges as a critical solution to mitigate the devastating effects of biodiversity loss and climate change. Focusing on Madagascar, a biodiversity hotspot facing significant forest loss, this dissertation explores various aspects of ecological restoration in the Berenty Reserve. It integrates ecological, social, and educational perspectives to provide applied knowledge and practical insights, addressing the unique challenges of restoring the tropical dry forest. The study includes a comprehensive baseline inventory of the forests in Berenty to characterize a reference ecosystem to set restoration goals in the reserve. I found that the spiny and gallery forests were different structurally and compositionally, requiring tailored restoration interventions. Special attention was given to Tamarindus indica, the tamarind tree, a species critical for the forests of the reserve and its lemurs, but facing regeneration challenges. I conducted three experiments to understand the impacts of light and water availability on its early life history stages, showing that light is the most limiting resource for tamarind growth and that water availability impacts tamarind more than water frequency. I also addressed management alternatives of the invasive vine Cissus quadrangularis. Investigating its desiccation thresholds, I found that C. quadrangularis can remain viable after losing 80% of its mass, concluding that management strategies should ensure complete desiccation of Cissus fragments to prevent its regrowth. Leveraging on my experience in the Berenty Reserve, I developed a decision case study for use in undergraduate or graduate student classrooms, where students grapple with the complexities of choosing between native and non-native plant species for restoring a tropical dry forest. This educational tool enhances the understanding of restoration ecology and motivates broader engagement. Finally, I examined the integration of the social sciences and/or local ecological knowledge within restoration research, highlighting the gap between theoretical advocacy and practical application and indicating the need for more inclusive and interdisciplinary approaches. Collectively, this work contributes valuable practical and theoretical insights aimed at improving restoration strategies, not only for the dry forests in Madagascar but also for similar ecosystems globally.
Evaluation of DNR Aquatic Vegetation Surveys: Data Summaries and Comparative Analysis
(University of Minnesota Duluth, 2006) Reschke, Carol; Host, George E; Johnson, Lucinda B
Evaluation Plan for an Earthworm Rapid Assessment Tool Training Program for Land Managers in Northern Hardwood Forest Types in the Western Great Lakes Region
(2012) Hueffmeier, Ryan M
Invasive species are causing environmental and economic harm all across the globe. Stopping the introduction of non-native species is the most effective way to deal with them. Non-native earthworms are one particular invasive species affecting the Great Lakes region. There is a need for a rapid assessment method to understand current impacts and identifying areas still earthworm-free. Through research in Minnesota and Wisconsin an Invasive Earthworm Rapid Assessment Tool (IERAT) was developed. The IERAT is a tool for the identification of earthworm impacts using visual indicators. Once earthworms are established there is no known effective way to remove them from the landscape and it is proposed that outreach and education are an effective method to prevent new introductions and to slow the spread of earthworms in northern hardwood forests of the Great Lakes region. This project develops the evaluation framework of the IERAT training. Using the framework evaluators will be assessing the tools’ validity, reliability of land mangers to use the tool, ability of trainers to conduct workshops, best dissemination techniques, changes in participants’ knowledge, attitudes and behaviors from before and after the training, and effects on management decisions. The evaluation plan will be carried out during the second year of training season. The results of the evaluation will be used to make appropriate adjustments to the IERAT and trainings. With earthworm distribution data that the IERAT provides, land managers will be able to develop important areas of protection and work with other interested parties to protect these areas for future generations.
Flight capacity of emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) and its parasitoid Tetrastichus planipennisi (Hymenoptera: Eulophidae), in response to several experimental treatments
(2014-12) Fahrner, Samuel Joseph
Emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive beetle native to eastern Asia. Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) is one of three hymenopteran parasitoids currently being introduced into North America as part of a classical biological control program against emerald ash borer. Here, custom-built, computer-monitored flight mills were used to measure the effects of age, feeding status, mating status, sex, and size on flight metrics of T. planipennisi. The flight mill was then used to measure flight metrics of emerald ash borer and T. planipennisi across a range of temperatures and relative humidity. The relationship between flight energetics, specifically flight distance, with temperature was then integrated with landscape temperatures at ten locations throughout the continental United States to compare relative dispersal capacity for emerald ash borer and T. planipennisi. The goal of this research was to elucidate factors that mediate the flight capacity of both insects and, for T. planipennisi, to infer the pre- and post-release conditions that may optimize flight capacity.
Impacts of woody biomass harvest on small mammals and plants in Northern Minnesota Aspen Forests
(2014-05) Rentz, Michael S.
Over the last decade, interest has grown in expanding the sources of energy produced in Minnesota, including burning wood alongside or in place of fossil fuels in commercial power plants. One possible source of this wood is through the harvest of residual material (hereafter "woody biomass harvest") left behind following traditional timber harvest. Although voluntary site-level harvest guidelines endorsed by the State initially called for the retention of residual material in the forest, the rules were modified in 2007 to allow for such harvest. It remained unclear, however, what, if any, ecological impacts woody biomass harvest could have in the region. I examined the immediate impacts of woody biomass harvest on small mammals and vegetation in 3 aspen (Populus spp) forests in northeast Minnesota. The study used of a "Before-After, Control-Impact" (BACI) design, with baseline surveys prior to treatment, follow up surveys after treatment, and a paired control that was not treated. I had two treatment categories: clearcut with slash left in situ (hereafter "slash-retention"), and clearcut with whole tree skidding and no replacement of residue (slash-removal). Each research site received a full complement of two treatments plus a control, giving me three replicates at each site.Prior to harvest, the stands contained an average coarse woody debris (CWD) density of 465 cm2/m2 (SE=49 cm2/m2). After harvest, the density of CWD increased in the slash-retention plots by an average of 422 cm2/m2, while slash-removal plots lost on average 29 cm2/m2. Prior to harvest there were no statistically significant differences in CWD density between treatments, but after logging CWD was higher in the retention than in the control plots, and higher in the control plots than in the removal plots.. In addition to gross changes in CWD area, the nature of the CWD in the harvested plots also shifted from initial conditions, with slash-retention plots gaining a disproportionate share of wood in less decayed conditions, while the slash-removal treatments shifted to a CWD base dominated by more decayed wood.Overall shrub stem counts increased similarly in both harvest treatments though more so in the slash-removal plots. Hazel (Corylus cornuta) stem counts increased by more than 3 stems/m2 in the slash-retention treatment, but stem counts were steady in the slash-removal treatment. Both treatments show a strong, similar regeneration of aspen stems after harvest (3-5 stems/m2).Both harvest types exhibited a decline in native forb species cover and an increase in bare ground, cover of non-native plants, and cover of graminoids compared to pre-existing conditions and associated control stands. Changes in native forb cover, non-native forb cover, and bare ground were greater in the slash-removal compared to the slash-retention treatment, but there was not a statistically significant difference between the plots for the increase in graminoid cover. Native species richness of survey plots 2 years post-harvest was not different from pre-harvest values for either treatment.In just over 29,000 trap nights I recorded 4,838 captures of 1,794 individual animals. I captured 15 mammal, 6 amphibian, and 1 snake species. Overall amphibian captures were low, but trended downward post-harvest in treatment plots. Population estimates of deer and white-footed mice (Peromyscus spp.) were little affected by treatment type or harvest status, while red-backed voles (Myodes gapperi) showed a positive response to harvest. Shrews (Sorex sinereus and Blarina brevicauda) and chipmunks (Tamias striatus) responded negatively to harvest of both types. The abundance of the communities overall (all individuals of all species lumped) were generally higher after treatment on the harvest sites than either before conditions or the adjacent controls, with slash-retention plots showing slightly greater gains than slash-removal plots.In conclusion, although many metrics responded similarly to either harvest type, in all cases where there were differences between the two treatments, the slash-removal treatment yielded a less favorable outcome for wildlife and a further shift from pre-treatment conditions than did the slash-retention treatment. This is especially true for the loss of native species cover, the increase in bare ground and non-native species cover, the loss of CWD, and the lower levels of C. cornuta. Although overall small mammal population sizes increased across both harvest types, increases were slightly greater for slash-retention treatments. Overall the results here do not warrant an avoidance of woody biomass harvest, but do argue for some caution, careful monitoring, and thoughtful siting. Future work should revisit these stands to assess longer term impacts.
Integrated emerald ash borer management: Testing a novel approach to assess stakeholder perceptions
(2023-01-23) Schneider, Ingrid; Rannow, Brett; Russell, Matt; Gupta, Angela; Windmuller-Campione, Marcella; ingridss@umn.edu; Schneider, Ingrid
These data describe Minnesota state park visitors' perceptions, attitudes, preferences, and behaviors pertaining to landscapes managed in response to emerald ash borer (EAB, Agrilus planipennis) and EAB itself. Two primary datasets are included: 1) Onsite data captured from visitors at Fort Snelling, Lake Bemidji, and Wild River state parks and 2) Data obtained from online surveys. These data aim to inform researchers and managers of the public's understanding of EAB, their acceptance of common Minnesota forest management strategies, their intended visitation behaviors in response to management surrounding EAB, and preferences for landscapes managed in response to EAB. Coding manuals, data descriptions, and participant consent forms are included. Data were released to provide transparency and data to potential stakeholders and interested parties.
Minnesota’s Lake Superior Coastal Program: Evaluating Vital, Small Forested Wetlands
(University of Minnesota Duluth, 2015) Olker, Jennifer; Hueffmeier, Ryan; Johnson, Lucinda B
Phenology data for the invasive macroalga Nitellopsis obtusa (starry stonewort) in Minnesota, USA, 2017 - 2018
(2021-11-22) Glisson, Wesley J; Muthukrishnan, Ranjan; Wagner, Carli K; Larkin, Daniel J; wjglisson@gmail.com; Glisson, Wesley; Minnesota Aquatic Invasive Species Research Center (MAISRC)
Understanding the phenology of aquatic invasive plants is critical for evaluating and predicting their ecological impacts and timing control efforts. Despite its 45-year invasion history in North America, relatively little is known about the phenology of the invasive macroalga Nitellopsis obtusa (starry stonewort). We tracked N. obtusa phenology from 2017-2018 in two Minnesota (USA) lakes representing northern and southern clusters of N. obtusa invasion in Minnesota. We measured N. obtusa biomass and counted bulbils (asexual reproductive structures) throughout the growing season and in winter, under ice. These data are provided and documented here.
Prevention and Early Detection of Asian Earthworms and Reducing the Spread of European Earthworms
(University of Minnesota Duluth, 2013) Hale, Cindy
We used a multi-pronged approach to quantify of the relative importance of different vectors of spread for invasive earthworms, make management and regulatory recommendations and create mechanisms for public engagement and dissemination of our project results through the Great Lakes Worm Watch website and diverse stakeholders. Internet sales of earthworms and earthworm related products posed large risks for the introduction of new earthworm species and continued spread of those already in the state. Of 38 earthworm products sampled, 87% were either contaminated with other earthworm species or provided inaccurate identification.
Raw Data from Silver, Bighead, and Common Carp Acoustic Avoidance tests, December 2013 - February 2014
(2017-02-16) Sorensen, Peter W; Zielinski, Daniel P; dzielinski@usgs.gov; Zielinski, Daniel P
Raw data of fish position and sound measurements from acoustic avoidance tests with silver, bighead, and common carp. The data is made available to support a open access publication submitted to PLOSONE entitled "Silver, bighead, and common carp orient to acoustic particle motion when avoiding a complex sound."
The Response of Aquatic Macrophytes to Lake Management Practices and the Role of Light in the Germination of Macrophyte Propagules
(2017-09) Dunne, Melaney
Macrophytes are a vital component to functioning aquatic ecosystems. Specifically, macrophytes promote good water clarity by stabilizing sediments, sequestering nutrients, and reducing the abundance of phytoplankton in the water column. Also, macrophytes provide habitat for other aquatic organisms. Healthy, robust aquatic macrophyte communities are indicated by diverse, abundant stands in the littoral zones of lakes. Poor water clarity and invasive species are primary limiting factors that cause diminished aquatic plant communities. Poor water clarity reduces the light quantity, impeding the growth of macrophytes. Invasive fish, such as common carp (Cyprinus carpio), damage macrophyte communities by uprooting plants and suspending sediment and nutrients in the water column. Invasive plants, such as curlyleaf pondweed (Potamogeton crispus) and Eurasian watermilfoil (Myriophyllum spicatum), often outcompete native species creating dense monoculture stands. To improve the growing conditions for macrophyte communities, several management actions can be pursued to limit the damage by invasive species and improve the water clarity. Common management practices in Midwestern lakes include invasive species control and nutrient sequestration. These practices have been documented to enhance native macrophyte communities. Lake management often requires several years of consistent, adaptive management to effectively restore the ecosystem. Adaptive management is the systematic process of learning from past management outcomes and subsequently incorporating that knowledge into current management decisions. I evaluated the change in the macrophyte community in Lake Riley, Chanhassen, MN over the course of 6 years of lake management actions using aquatic plant point-intercept surveys from 2011 to 2016. The results of the surveys found that after a carp removal in 2010, curlyleaf pondweed dominated the littoral zone and water clarity did not greatly improve. Once invasive macrophytes were managed starting in 2013, incremental increases in the species richness of the macrophyte community occurred. However, native macrophyte expansion was limited because water clarity was still poor during the summer growing season. In 2016, after an alum treatment, water clarity improved and the macrophyte community abundance and richness further increased. Species richness increased from 9 observed species in 2011 to 15 in 2016. During peak growth in August, the native species frequency of occurrence was 50% through 2013 and then increased up to 80% of sites in 2016. The August native macrophyte biomass increased from 30g/m2 in 2011 to 600g/m2 in 2016 (p<0.05). Prior to 2016, the average maximum depth of rooted native plant growth was 3.1m and in 2016 it increased to 4.1m. Overall, the density, coverage, and richness of the macrophyte community increased throughout the study period demonstrating that the macrophyte community had a positive response to the multi-year management practices on Lake Riley. The specific mechanism of macrophyte recruitment following improved growing conditions, such as in Lake Riley, is an understudied area of macrophyte restoration. Macrophytes typically propagate through clonal growth and fragmentation. However, when macrophyte populations are reduced, the lake seed bank may contribute to the reestablishment of the population. In previous studies on temperate lake seed banks, seeds from vascular aquatic plants and spores from macroalgae have been found in varying densities and viability levels suggesting that recruitment from the seed bank is possible in some systems. I conducted a controlled laboratory experiment using sediment from Lakes Ann and Riley located in Chanhassen, MN, to 1) evaluate the response of the seed banks to different treatments and 2) compare the observed taxa sprouting from the seed banks to the taxa observed growing in the lakes. The treatments included a maximum germination treatment using a germination promoter to evaluate the full extent of the viable seed bank, a treatment representative of a lake with good water clarity, and a treatment representative of a lake with poor water clarity. The good and low clarity treatments were designed to evaluate the response of seeds to two different light levels that were observed in lakes with high turbidity (low-light intensity) and low turbidity (high light intensity). It was hypothesized that the maximum germination treatment would have the highest amount of germination, the high clarity treatment would have the second highest amount, and the low clarity treatment would have the lowest amount of germination due to the low-light quantity. The seed banks of both Lakes Riley and Ann were similar to the macrophyte community observed growing in the lake. In Lake Ann, 16 species were observed sprouting and every species observed in the experiment grew in the lake. In Lake Riley, 17 species were observed sprouting and all but two species were observed both in the lake and in the seed bank. The seed banks did not show any significant difference in response to the germination treatments. Chara, curlyleaf pondweed, and wild celery were the most frequent species observed. Under maximum germination conditions, Lake Riley had a viable vascular seed density of 2,916 ± 1,828 seeds/m2 and a viable chara spore density of 1,033 ± 698 spores/m2. Lake Ann had a viable vascular seed density of 1,100 ± 440 seeds/m2 and viable chara spore density of 13,833 ± 2,825 spores/m2. The study demonstrated that germinating propagules from a lake seed bank can be a valuable tool for managers to evaluate the viable macrophyte taxa present and better understand the potential for recruitment from the seed bank. Overall, to restore native macrophyte communities, it requires several multi-year management actions and will likely include multiple forms of propagule recruitment.
Role of leafing phenology in the invasion of forest ecosystems by Rhamnus cathartica
(2015-04) Pretorius, Andrew
Buckthorn breaks bud earlier in the spring and holds leaves later in the fall compared to co-occurring native understory species and the forest canopy. This phenology may allow buckthorn to take advantage of high light levels prior to canopy closure in spring and after leaf drop in fall. We hypothesized that this unique phenology is one mechanism that facilitates invasion of the forest interior by buckthorn. To test our hypothesis, we experimentally shaded buckthorn seedlings, reducing high light levels in the spring and fall to simulate intact canopy conditions. We measured spring and fall leafing phenology, light availability and seedling survival and growth. After a year and half of shading little mortality was observed but individuals receiving shading treatments had significantly decreased growth. Supporting our hypothesis that access to phenology-induced high light levels in the spring and autumn is one mechanism for buckthorn success in closed canopy forests.

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