Browsing by Subject "Earthworms"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Allometric Equations for Estimation of Ash-free Dry Mass from Length Measurements for Selected European Earthworm Species (Lumbricidae) in the Western Great Lakes Region
    (University of Notre Dame, 2004) Hale, Cindy M; Reich, Peter B; Frelich, Lee E
    In the last decade the invasion of European earthworms into previously worm-free glaciated areas of North America has stimulated research into their impacts on native forest ecosystems in the region. As a first approximation, the impacts of invading earthworms are related to their biomass. However, direct measurements of biomass can be significantly affected by the moisture conditions under which the earthworms are collected and their relative gut contents. Ash-free dry mass is the best standardized measure of earthworm biomass, but requires the destruction of specimens. This paper presents five allometric equations that allow for estimation of ash-free dry biomass based on length (mm) measurements for European earthworm species (Lumbricidae) commonly seen in the United States.
  • Thumbnail Image
    Item
    Climate Change and Future Forests of the Boundary Waters Canoe Area Wilderness: An assessment of Temperate Tree Abundance, Earthworm Invasion and Understory Regeneration Trends
    (2019-07) Chaffin, David
    The forests of the Boundary Waters Canoe Area Wilderness (BWCAW) are dominated by boreal tree species at their southern range limit, making them particularly sensitive to climate change. Numerous studies have modeled potential climate change induced tree species range shifts across northern Minnesota and the BWCAW, projecting declines for boreal tree species and increases for northern temperate tree species currently at low abundances in the wilderness. The coarse resolution of these models, their lack of some biological interactions and the unprecedented velocity of projected future climate change could lead to over and/or under estimates of tree species range shifts at the scale of the BWCAW. To better understand potential forest successional shifts within this ecologically important wilderness we assessed 1) the abundance and spatial distribution of northern temperate tree species, 2) the stage, pattern, and extent of earthworm invasion in the wilderness, and 3) the impact of seasonal temperature, overstory composition, earthworm invasion and soil moisture potential on the understory relative density of ten boreal and northern temperate tree species. We found that red maple (Acer rubrum) is the most abundant temperate tree species in the BWCAW by orders of magnitude across all size classes, with its spatial distribution strongly correlated with an existing west to east summer temperature gradient. Conversely, our results raise questions about whether adequate seed sources of other temperate species are currently present in the wilderness to support a successful boreal to temperate transition. Earthworm invasion in the BWCAW is widespread, yet incomplete. Modeling results indicate the spatial pattern of earthworm invasion in the wilderness is driven by anglers dumping unused earthworm fishing bait at campsites. We predict that 33% of total land area in the BWCAW is currently invaded by earthworms. Lastly, our results indicate that summer temperature is a key driver of differences in understory relative density of boreal and northern temperate tree species across the mixed-boreal forests of the BWCAW, but that earthworm invasion and areas with increased soil moisture availability may support the short-term resistance of boreal tree species under future warmer and drier conditions.
  • Thumbnail Image
    Item
    Impacts of earthworm bioturbation on elemental cycles in soils: An application of a geochemical mass balance to an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota.
    (2013-06) Resner, Kathryn "Kit" Elizabeth
    Earthworms are arguably the best known soil bioturbator, yet their impacts on soil biogeochemistry are difficult to quantify as a function of their roles in physically mixing soils. In glaciated regions of North America, northern hardwood forests have evolved without native earthworms since the last glacial retreat. However, earthworms have invaded northern hardwood forests owing to agricultural expansion, fishing, recreational, and logging activities. Earthworm consumption of the organic horizon in Minnesota hardwood forests has resulted in dramatically changing forest floor ecology and soil morphology, yet their impacts on soil biogeochemistry remain largely unknown. An earthworm invasion chronosequence near Leech Lake in Northern Minnesota provides an ideal outdoor laboratory to quantify the interactions between biogeochemical and physical processes associated with different earthworm species and biomasses. Across the earthworm invasion transect, the A horizon elemental chemistry profiles show that earthworms have vertically relocated minerals, which is consistent with 210-Pb activity profiles. While soil elemental depth profiles confirm increased mixing with earthworm invasion, the depth profiles cannot be solely explained by mixing. I used a geochemical mass balance model to examine soils' biogeochemical responses to invasive earthworms. Fractional and absolute mass losses/gains of biologically important elements such as Ca, P, K, Fe, and Si, relative to the parent material, are substantially altered by invasive earthworm species. The arrival of A-horizon-mixing, endogeic earthworms most dramatically reduces the level of the elemental enrichments in the A horizons. The declined elemental enrichments are likely derived from the consumption of particulate organic matter by endogeic species, which leads to the mineralization and leaching of Ca, P, K. The dramatic losses of the enrichments also suggest that the newly mineralized nutrients are in excess of the nutrient demand from understory plants. Our results indicate the significant and potentially negative impacts of invasive earthworms on the soil nutrient cycling and consequently the sustainability of the hardwood forests in the Great Lakes Region.
  • Thumbnail Image
    Item
    Multiple Disturbances and the Turbulent Forest
    (2023-08) Reed, Samuel
    I have always been drawn to change, whether I liked it or not. As a kid, I was obsessed with dinosaurs and their extinction, all while having to move constantly as a Navy brat. As an adult, I am devoted to understanding how and why systems change, likely inspired by the unending change of my childhood. However, as I matured, I realized that change is almost never spurred by a single event, but rather a multitude of shocks to the system. This dissertation focuses on the complexity of multiple ecological disturbances and highlights their importance in the world. Using several multi-disturbance experiments, I explore a wide variety of disturbance interactions in the temperate deciduous forest. The first chapter of this dissertation focuses on how deer and canopy gaps influence invasive earthworms, shedding new light on how aboveground events can change belowground communities. The second chapter builds upon the first and tests how combined deer and canopy gaps influence understory regeneration over 15 years, with some reference to invasive earthworms. Lastly, the third chapter explores how combined fire, deer, and canopy gaps change the seed bank over 13 years. Each of the aforementioned disturbances are common and influential in eastern forests, although they are not often studied together. In each chapter we find that community responses vary depending on the disturbances in question. This dissertation is meant to highlight how little we know about the many ways in which multiple disturbances change ecosystems and how critical it is that we start to study these complex drivers of change, particularly as the climate warms and disturbances become more frequent on the landscape.
  • Thumbnail Image
    Item
    A study of herbaceous vegetation in Chequamegon - Nicolet National Forest: relationship of earthworms, white-tailed deer browsing and Carex pensylvanica Lam
    (2014-12) Ojanen, Paul Thomas
    Invasive earthworms alter multiple forest components. By accelerating litter decomposition, they alter nutrient flows, soil composition and vegetative communities. White -tailed Deer (Odocoileus virginianus) are known to alter vegetative communities by selective browsing; severity varies with population density and affects plant community population and composition. Both factors are associated with reduced vegetative community richness and dominance by graminoids. In this study, 101 randomly selected Northern Mesic Hardwood Sugar Maple sites in the Chequamegon - Nicolet National Forest were sampled for vegetation, earthworm occurrence and browsing intensity. Over three years, eighty-two percent of sites were positive for earthworms; in two non-drought years, ninety percent of sites were positive. Non-metric Multi-dimensional Scaling (NMDS) and Multiple Response Permutation Procedure (MRPP) found divergent communities; a Carex pensylvanica Lam dominated community associated with earthworm invasion and strongly linked to Lumbricus rubellus presence, and remaining Acer saccharum seedling stands associated with reduced earthworm impacts. Additionally Carex pensylvanica was strongly linked to Lumbricus rubellus presence by Indicator Species Analysis. Lumbricus rubellus invaded sites had both reduced species richness and vegetative cover. White-tailed deer (Odocoileus virginianus) browsing was found to be heavy and extensive throughout both forests, impacting Acer saccharum regeneration and further driving graminoid dominance. The results indicate earthworm invasion is geographically extensive and a principal driver of Carex pensylvanica understory dominance and reduced Acer saccharum regeneration.