Efficacy of treatments against garlic mustard (Alliaria petiolata) and effects on forest understory plant diversity

Garlic mustard, an invasive exotic biennial herb, has been identified in the Upper Peninsula of Michigan, but is not yet widely distributed. We tested the effectiveness and impact of management tools for garlic mustard in northern hardwood forests. Six treatment types (no treatment control, hand-pull, herbicide, hand-pull/herbicide, scorch, and hand-pull/scorch) were applied within a northern hardwood forest invaded by garlic mustard. We sampled understory vegetation within plots to compare garlic mustard abundance (distinguishing first and second year plants) and native plant diversity before and after treatment. Results immediately following treatment indicated that garlic mustard seedling abundance was significantly reduced by herbicide, hand-pull/herbicide, scorch, and hand-pull/scorch treatments, and that adult abundance was reduced by all treatments. However, sampling of treatment sites one year later showed an increase in seedling abundance in herbicide and hand-pull/herbicide plots. Adult garlic mustard abundance after one year was lower than the control with the exception of the hand-pull plots where adult abundance did not differ. After one year, understory species richness and Shannon’s Diversity were lower in the herbicide and pull/herbicide treatments. Based on these results, we conclude that single-year treatment of garlic mustard with hand-pulling, herbicide, and/or scorching is ineffective in reducing garlic mustard abundance and may inadvertently increase the success of garlic mustard, while negatively impacting native understory species

Geographical patterns in openland cover and hayfield mowing in the Upper Great Lakes region: implications for grassland bird conservation

Abstract Populations of many grassland bird species such as Grasshopper Sparrow (Ammodramus savannarum), Henslow's Sparrow (A. henslowii), and Bobolink (Dolichonyx oryzivorus) have experienced considerable declines over the last century. To foster multi-species grassland bird conservation in the Upper Great Lakes (UGL) states of Michigan, Minnesota, and Wisconsin, we quantified geographic patterns within three sub-regional zones (e.g., North, Central, and South) of the UGL. Patterns of interest included the distribution and abundance of openland cover type (including managed pasture-hayland), the distribution, phenology, habitat affinity, and longterm population trends of ten grassland bird species, and (in particular) the geographic patterns in hayfield mowing and the temporal changes in hayfield cover. Approximately 10, 38, and 53% of the UGL openland was proportioned in the North, Central, and South zones, respectively. The distribution of hayland also varied by zone: North, 17%; Central, 46%; and South, 37%. In the central portion of the UGL where the greatest area is devoted to hay production, alfalfa-more intensively managed than mixed-grass hay-predominates. Although we found significance differences (P \ 0.05) in hayfield mowing intensity between zones (with the majority of land under relatively low-intensity mowing found in the North Zone, particularly the Upper Peninsula of Michigan) no strong relationships were found between hayfield mowing patterns, other land cover-land use variables, and bird population trends at finer scales of study. Nonetheless, we suggest that the geographic patterns illustrated here provide useful information for grassland bird conservation planning across the UGL

Invasion patterns of emerald ash borer and European earthworms in forested ecosystems

Invasive and exotic species present a serious threat to the health and sustainability of natural ecosystems. These species often benefit from anthropogenic activities that aid their introduction and dispersal. This dissertation focuses on invasion dynamics of the emerald ash borer, native to Asia, and European earthworms. These species have shown detrimental impacts in invaded forest ecosystems across the Great Lakes region, and continue to spread via human-assisted long distance dispersal and by natural modes of dispersal into interior forests from areas of introduction. Successful forest management requires that the impact and effect of invasive species be considered and incorporated into management plans. Understanding patterns and constraints of introduction, establishment, and spread will aid in this effort. To assist in efforts to locate introduction points of emerald ash borer, a multicriteria risk model was developed to predict the highest risk areas. Important parameters in the model were road proximity, land cover type, and campground proximity. The model correctly predicted 85% of known emerald ash borer invasion sites to be at high risk. The model’s predictions across northern Michigan can be used to focus and guide future monitoring efforts. Similar modeling efforts were applied to the prediction of European earthworm invasion in northern Michigan forests. Field sampling provided a means to improve upon modeling efforts for earthworms to create current and future predictions of earthworm invasion. Those sites with high soil pH and high basal area of earthworm preferred overstory species (such as basswood and maples) had the highest likelihood of European earthworm invasion. Expanding beyond Michigan into the Upper Great Lakes region, earthworm populations were sampled across six National Wildlife Refuges to identify potential correlates and deduce specific drivers and constraints of earthworm invasion. Earthworm communities across all refuges were influenced by patterns of anthropogenic activity both within refuges and in surrounding ecoregions of study. Forest composition, soil pH, soil organic matter, anthropogenic cover, and agriculture proximity also proved to be important drivers of earthworm abundance and community composition. While there are few management options to remove either emerald ash borer or European earthworms from forests after they have become well established, prevention and early detection are important and can be beneficial. An improved understanding the factors controlling the distribution and invasion patterns of exotic species across the landscape will aid efforts to determine their consequences and generate appropriate forest management solutions to sustain ecosystem health in the presence of these invaders

Exotic earthworm communities within upland deciduous forests of national wildlife refuges in the upper Midwest

The invasion of exotic earthworms into forests of the Upper Midwest region of the United States is a considerable management issue due to the ability of earthworms to act as ecosystem engineers and modify existing ecosystems. Earthworm taxa differ in their biology and behavior, such that earthworm abundance and community composition can be related to the type and degree of alteration expected to occur. Many National Wildlife Refuges of the Upper Midwest have enabling legislation that identifies migratory birds as a specific management priority, and past studies have indicated that earthworm-modified forests provide lower quality habitat for migratory, ground-nesting birds. We quantified exotic earthworm community composition, abundance, and variability within and among upland deciduous forest stands at six of these refuges (Horicon, Ottawa, Rice Lake, Seney, Shiawassee, and Tamarac), providing a baseline for estimating the status of earthworm invasion. Analyses revealed a significant difference in mean earthworm biomass among upland deciduous forest stands sampled (ANOVA, F5,52 = 2.81, P = 0.03) and indicated significant differences in earthworm community composition (multiresponse permutation procedure, T = 212.57, A = 0.24, P \u3c 0.001) at each refuge. Based upon existing theories regarding earthworm invasion, we suggest that the stage, and impact, of earthworm invasion is varied across the region. Continued research and monitoring of earthworm communities should test this theory and seek to elucidate drivers of earthworm invasion patterns and impacts to forest ecosystems

Multi-criteria risk model for garlic mustard (Alliaria petiolata) in Michigan\u27s Upper Peninsula

Throughout Midwestern forests, invasion by the exotic plant garlic mustard Alliaria petiolata M. Bieb. (Cavara & Grande) has become increasingly problematic. A multi-criteria risk model was developed to predict invasion in the Upper Peninsula of Michigan where garlic mustard is present but not yet widely distributed. The model uses geographic information system (GIS) data to predict the risk of invasion at three phases: introduction, establishment and spread. Known occurrence data for garlic mustard were used to validate the model predictions, with 89 of points correctly identified at moderate to high risk for invasion. The risk model predicted 13 of the Upper Peninsula to be at high risk and 33 at moderate risk for establishment of garlic mustard. Field sampling of randomly generated points across the Upper Peninsula provided only two additional observations of garlic mustard presence. The low encounter rate during field sampling may indicate that garlic mustard has not yet reached its full invasion potential in the Upper Peninsula. This presents an opportunity to use the model predictions and associated risk maps for monitoring and management in a relatively uninvaded region. © 2011, American Midland Naturalist

Predicting exotic earthworm distribution in the northern Great Lakes region

Identifying influences of earthworm invasion and distribution in the northern Great Lakes is an important step in predicting the potential extent and impact of earthworms across the region. The occurrence of earthworm signs, indicating presence in general, and middens, indicating presence of Lumbricus terrestris exclusively, in the Huron Mountains located in the Upper Peninsula of Michigan were modeled using generalized linear models and stepwise regression to identify important environmental variables. Models were then applied to earthworm occurrence data from Seney National Wildlife Refuge, also located in the Upper Peninsula of Michigan to validate results. Occurrence of earthworm signs was associated with high soil pH, high basal area of earthworm preferred overstory species, and north facing aspects. Middens of L. terrestris were associated with high soil pH, high basal area of preferred species, and close proximity to roads. The resulting model for L. terrestris was incorporated into a geographic information system (GIS) to map the expected distribution, both current and potential, across the study area. Results indicate that L. terrestris has not yet fully saturated its potential habitat, as it is currently found close to roads and has yet to establish in most interior forests sampled. Comparing field measured data to GIS layers revealed limitations in the precision of publicly available spatial data layers that should be addressed in future attempts to predict the extent of earthworm invasion across the larger Great Lakes region. However, within the Huron Mountains, it is predicted that the distribution of L. terrestris will cover, at minimum, 41 % of the area. © 2013 Springer Science+Business Media Dordrecht

Geographical patterns in openland cover and hayfield mowing in the Upper Great Lakes region: Implications for grassland bird conservation

Populations of many grassland bird species such as Grasshopper Sparrow (Ammodramus savannarum), Henslow\u27s Sparrow (A. henslowii), and Bobolink (Dolichonyx oryzivorus) have experienced considerable declines over the last century. To foster multi-species grassland bird conservation in the Upper Great Lakes (UGL) states of Michigan, Minnesota, and Wisconsin, we quantified geographic patterns within three sub-regional zones (e.g., North, Central, and South) of the UGL. Patterns of interest included the distribution and abundance of openland cover type (including managed pasture-hayland), the distribution, phenology, habitat affinity, and long-term population trends of ten grassland bird species, and (in particular) the geographic patterns in hayfield mowing and the temporal changes in hayfield cover. Approximately 10, 38, and 53% of the UGL openland was proportioned in the North, Central, and South zones, respectively. The distribution of hayland also varied by zone: North, 17%; Central, 46%; and South, 37%. In the central portion of the UGL where the greatest area is devoted to hay production, alfalfa-more intensively managed than mixed-grass hay-predominates. Although we found significance differences (P \u3c 0.05) in hayfield mowing intensity between zones (with the majority of land under relatively low-intensity mowing found in the North Zone, particularly the Upper Peninsula of Michigan) no strong relationships were found between hayfield mowing patterns, other land cover-land use variables, and bird population trends at finer scales of study. Nonetheless, we suggest that the geographic patterns illustrated here provide useful information for grassland bird conservation planning across the UGL

Broad and local-scale patterns of exotic earthworm functional groups in forests of National Wildlife Refuges of the Upper Midwest, USA

The National Wildlife Refuge System is the world’s largest network of lands set aside specifically for wildlife conservation. For refuge planners and managers tasked with maintaining ecological integrity and wildlife habitat, many uncertainties exist. In forests in the Upper Midwest, for instance, exotic earthworms are impacting ecosystem structure and function, but their community composition and effects on refuges is unknown. We examined the association of earthworm functional group abundance and community composition within upland forests of refuges with broad scale patterns of anthropogenic land use and local scale differences in forest characteristics. Patterns of anthropogenic land cover, including proportion of the land, mean patch area, and largest patch index, were strongly correlated with the biomass of epi-endogeic earthworms. Earthworm community diversity, however, was inversely related to patterns of dominating anthropogenic land cover, and increased under high ratios of natural to anthropogenic lands in the surrounding ecoregion. Within forests, earthworm community composition could be partially explained by variables representing both dispersal opportunities and habitat suitability. In general, heavily-invaded forests had low conifer dominance, high silt content, high basal area, greater amounts of anthropogenic cover within 500 m, and were closer to roads and farther from agriculture. However, the relationship between local forest characteristics and biomass differed greatly among earthworm functional groups and between refuges dominated by natural lands and those dominated by anthropogenic lands. For refuges with high earthworm loads and well developed earthworm communities, managers may be confounded in restoring historic conditions and may need to look at multiple tools, including artificial regeneration, to mitigate for current earthworm effects. In refuges seemingly in earlier stages of earthworm invasion, future planning and management should be tempered by potential effects observed in those refuges in more anthropogenic landscapes

Variability and persistence of post-fire biological legacies in jack pine-dominated ecosystems of northern Lower Michigan

On the dry, flat, jack pine (Pinus banksiana Lamb.)-dominated ecosystems of the northern Lake States and eastern Canada, wildfire behavior often produces narrow, remnant strips of unburned trees that provide heterogeneity on a landscape historically shaped by stand-replacing wildfires. We used landscape metrics to analyze a chronosequence of aerial imagery to examine these stringers of mature trees within historical wildfires in northern Lower Michigan. Our major objective was to describe the natural range of variability of stringer patterns and their persistence and change during the fire-free interval. Field studies were then used to examine stringer composition and structural variability. Stringers were found to occur in all fires \u3e 1000. ha, in about one-third of wildfires \u3e 80. ha, but never in fires \u3c 80. ha, likely because of the lack of fire intensity on smaller fires that is necessary for stringers to be formed. Stringers were typically composed of many small, well-aggregated patches that represented 3-14% of the area within the burn perimeter, and stringer formation was relatively independent of pre-fire forest structure or composition. Stringer patterns changed mostly in the first decade after the fire that created them and then stabilized. Major changes that occurred in stringer patterns after this period were most often due to human activities, highlighting their natural persistence through the fire-free interval. The historical persistence and importance of these features also highlights their importance on modern fire-prone landscapes, particularly in northern Lower Michigan where a high proportion of land management is focused on jack pine plantations for breeding habitat for Kirtland\u27s warbler (Dendroica kirtlandii Baird), an endangered species. © 2011 Elsevier B.V