Browsing by Subject "Earthworm invasion"

Now showing 1 - 5 of 5
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    Arctic worming: Human-facilitated earthworm invasion transforms soil organic matter budgets and pools in Fennoscandian forests
    (2018-12) Wackett, Adrian
    Earth’s high latitude ecosystems are already under dire threat from climate warming, permafrost thaw, and intensifying natural resource exploitation. In addition to these ongoing concerns, accelerating urbanization, agricultural expansion, and greater opportunities for recreation in high-latitude regions are likely to introduce a less conspicuous but potentially potent threat: non-native geoengineeing earthworms. Earthworms were eradicated from northern N. America (including Minnesota) during the last glaciation, and it is now established that humans are (re-) introducing exotic earthworm species into these forests with dramatic consequences on soil and ecosystem functioning. However, their invasiveness and capacity to modify high-latitude boreal and arctic forests like those in Fennoscandia remains largely unknown. Here I explore two inter-related hypotheses concerning earthworms and soils in Fennoscandian forests: H1) despite their different human history and proximity to the native range of Lumbricidae earthworms (Southern and Central Europe), I predicted that Pleistocene glaciations also extirpated earthworms from Fennoscandia, suggesting that European earthworms (if present) are also non-native and invasive in these landscapes; and H2) if introduced by humans, the invasive earthworms transform Fennoscandian forest soil morphologies and soil organic matter (SOM) dynamics by removing thick organic layers at the forest floor and forming A-horizon (mineral topsoil) in their wake. To address H1, I tested a series of sub-hypotheses stating that: 1) earthworms did not colonize the Fennoscandian landscape via dispersal by brackish seawater, nor were they introduced by early indigenous peoples (Sami) who followed the retreating glaciers into northern Fennoscandia; and 2) earthworms are spreading into Fennoscandian forests from ‘worm point sources’ created by modern human-mediated dispersal vectors such as farming, fishing, gardening, and logging (among others). Although I could not dispel the possibility that small epigeic-type earthworms may have entered the Fennoscandian landscape considerably earlier via water-mediated dispersal and/or by ‘hitch-hiking’ along with Sami settlers, I found that more impactful ‘geoengineering’ species are only present in arctic landscapes associated with more modern (i.e. last two centuries) human disturbance (supporting H1) and are radiating outward from these anthropogenic point sources into virgin arctic and boreal forests. Furthermore, in line with H2, expansion of these geoengineers into adjacent forests consistently induced changes to forest soil morphologies and nutrient cycling regimes, including rapid reduction of the SOM pool in organic horizons and re-allocation of this SOM into mineral horizons: wherein it is sorbed onto mineral surfaces and/or occluded within aggregates. This belowground transformation likely has significant aboveground consequences as well as implications for the long-term carbon balance of boreal and arctic ecosystems, which store more than half (~ 53%) of earth’s soil carbon. Furthermore, based on results from N. America, this ‘unseen’ invasion may also have cascading effects on fungal and microbial associations, plant communities, and overall ecosystem functioning. Considering that the arctic is already being disproportionately affected by climate change and that human activities in these regions are likely to accelerate as these regions warm, additional research assessing the ecological impacts of arctic worming is urgently needed.
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    Carbon-mineral interactions and bioturbation: an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota
    (2013-05) Lyttle, Amy Marie
    European earthworm species have been introduced into previously glaciated hardwood forests in North America over the past centuries. The invasive earthworms reorganize soil structure, losses of carbon and nitrogen, and the reduction in abundance and diversity of understory communities. One of the direct impacts of earthworms on soils is increased bioturbation, which has domino effects on soil properties that include decrease in litter layer and thickening and increasing bulk density of the A horizons. Such enhanced interactions between organic matter and minerals due to invasive earthworms and earthworms in general have been studied in the context of soil carbon cycle. In this study we attempt to better understand exotic earthworms' impacts on the sorption of organic matter on mineral surfaces and how this fundamental process determining the soil carbon storage and turnover is affected by bioturbation and different earthworm functional groups. Despite the reduction of total C inventory with the arrival of endogeic species, such reduction is largely derived by the loss of light density fraction C. In contrast, the C inventory in heavy density fraction - which we associate with mineral-sorbed - shows little change, which is consistent with likewise stable inventories of mineral surface areas and C-covered mineral surface areas. Mineral-sorbed C pool appears to be in dynamic equilibrium across the diverse ecological stages of earthworm invasion. Our study suggests that the direction and size of changes in soil C inventory in response to bioturbators in general and invasive earthworms specifically will be strongly dependent upon the soil depth profiles of mineralogy and texture.
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    Investigation of soil and plant characteristics across a continuum of non-native earthworm invasion in hardwood forests, Tettegouche State Park, MN USA
    (2013-06) Bennett, Zachary David
    Invasive earthworms cause profound changes in forest floor thickness, soil structure and chemistry, and plant community composition within cold temperate hardwood forests. However, few studies have examined these effects across a continuum of earthworm invasion and in conjunction with canopy disturbance. The research objectives of this thesis were to determine the changes of earthworm invasion on the upper soil horizon's thickness, gravimetric water content, potential horizon field capacity, and available nitrogen and phosphorus; and plant communities in hardwood forest sites within Tettegouche State Park, MN USA. All sites were uneven-aged, unmanaged northern hardwood forests of an approximate age of 225 years. The canopies were dominated by sugar maple and had experienced substantial canopy disturbance (9.7 - 20.5% opening) during an ice storm in spring 2009. Earthworms were sampled in the fall of 2010-2011. Each of the four sites were invaded by differing earthworm assemblages ranging from minimally invaded (1 species and average biomass of 0.1729 AFDgrams/m2) to heavily invaded (5 species and average biomass of 14.12 AFDgrams/m2). In the upper soil horizons O horizon thickness decreased and A horizon thickness increased with increasing earthworm richness and biomass. Mineral soil gravimetric water content was measured biweekly (May-August 2011) but did not differ among sites. Total potential horizon field capacity, including the O horizon, determined that 53-59% of the available water in a 12 cm deep core at field capacity is held in the O horizon. Availability of NO3 was significantly higher in the heavily invaded site compared to all other sites. Plant communities were assessed in the summer of 2009-2011, nonmetric multidimensional scaling was used to analyze the relationship of herbaceous plant species richness and percent cover to environmental variables and that species richness and diversity indices were positively correlated with O horizon thickness and negatively correlated with earthworm richness and biomass. The main conclusions of this study are that 1) moderate canopy disturbance had no affect on soil characteristics, or earthworms and plant communities; 2) earthworm assemblages (richness and biomass) were strongly correlated with changes in forest floor thickness, moisture holding capacity, nitrogen availability and plant community composition in these sugar maple forests, and 3) traditional exclusion of the O horizon when measuring water holding capacity in forest soils should be reconsidered given the large proportion of potential water holding capacity it provides, and is lost when a site is heavily invaded by earthworms. The implications of the loss of the O horizon and the associated loss of water holding capacity on ecosystem functions and biotic communities of hardwood forest systems need to be more fully explored.
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    Tree rings detect earthworm invasions and their effects in northern Hardwood forests
    (2010) Larson, Evan R; Kipfmueller, Kurt F; Hale, Cindy M; Frelich, Lee E; Reich, Peter B
    Invasions of European earthworms into the forests of northern North America are causing dramatic changes in forest floor structure, vegetation communities, biogeochemical cycling, and site hydrology. However, long-term studies on the effects of invasive earthworms are limited because little data exist on the timing and rate of earthworm invasion at specific sites. We successfully used tree rings to identify the timing of earthworm invasions and the effects of earthworm activity on the Acer saccharum overstory of two recently invaded sites in northern Minnesota, thereby establishing a method to date earthworm invasions at other sites. In addition to identifying a tree-ring signature related to earthworm invasion, we found trees growing in invaded conditions were more sensitive to drought than trees growing in earthworm-free conditions. Increased drought sensitivity by A. saccharum has important implications for possible range shifts under climate change scenarios that include increasing drought frequency and severity.
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    Understanding human activities and global w“o”rming and its impacts on soil properties and temperature in a Minnesota hardwood forest
    (2023-05) Baumann, Tyler
    Invasive earthworms create widespread ecological changes after they are introduced.Exotic earthworms are transported mainly through anthropogenically-mediated activities, including fishing, agriculture, horticulture, and development. Here, we use a conceptual framework to review the ways in which exotic earthworms are transported to new environments. This conceptual framework involves invasion filters (human activities filter and climate & edaphic filter) that constrain which exotic earthworm species can be transported within specific contexts. Differences in earthworms’ ecological behaviors, life cycle, and physiological tolerance of environmental conditions influence which species are transported and which regions can successfully be invaded. Within the human activities filter, we utilize the pathways of invasion laid out by Hulme et al. 2008, including release, escape, contaminant, stowaway, corridor, and unaided. These pathways follow a continuum of human intention; five of these pathways are associated with human activity: with release, escape, and contaminant pathways related to commodities, and stowaway plus corridor related to transport infrastructure. We find that the major human activities that transport exotic earthworms include discarding of fishing bait, agriculture, composting and horticulture, and development (e.g. the construction of roads, trails, houses, or campgrounds). Our review finds that although a diverse number of human activities transport exotic earthworms, the magnitude that specific activities transport earthworms is vastly understudied. We conclude that more research needs to be conducted to understand the methods that transport exotic earthworms in order to slow their spread. In the Upper Midwest, temperate hardwood forests have been heavily altered followingthe introduction of invasive earthworms of European, and more recently, Asian origin. Earthworms significantly modify the biological, chemical, and physical composition of soils in these ecosystems by mixing overlying organic horizons with underlying mineral soil layers. The recent invasion of these forests dominated by invasive European earthworms (Lumbricus terrestris, Lumbricus rubellus, Aporrectodea spp.) by ‘jumping worms’ (Amynthas agrestis and Amynthas tokioensis) has created profound and distinct changes to the soil that are not well understood. We surveyed forests at the University of Minnesota Landscape Arboretum in 2020 and 2021 and established transects with discrete areas of European or jumping worm dominance. We found that these discrete areas had distinct soil features and that jumping worm populations appear to replace Lumbricus spp. populations. Soils in areas dominated by jumping worms had a loose, granular casting layer near the surface, decreased bulk density, increased soil organic matter, increased pH, and higher leaf litter mass than soils in sites dominated by European earthworms. We also measured lower monthly average soil temperature, lower maximum soil temperature, and lower soil temperature variability in our jumping worm dominated sites. Our soil temperature results indicate that Amynthas spp. will not be limited by soil temperatures in advancing much further north than central Minnesota. It remains to be seen how invasive earthworm populations and soil properties will evolve with the continued invasion of jumping worms in the long-term.