Invasive earthworms in a Northern Great Plains prairie fragment

Although ample research exists on the ecological impacts of earthworm invasion in the Great Lakes region and northern hardwood forests, little data is available on the presence, distribution, and impact of earthworms in the prairies of the Northern Tallgrass Prairie. Sampling in a Northern Tallgrass Prairie fragment yielded three species of invasive earthworms occupying three different functional groups: surface and litter dwellers (epigeic), subsurface horizontal burrowers (endogeic), and deep vertical bore inhabitants (anecic). This research note illustrates the presence of non-native and potentially invasive earthworms in Northern Tallgrass Prairie.     

Evidence of damage from exotic invasive earthworm activity was highly correlated to sugar maple dieback in the Upper Great Lakes region

Sugar maple (Acer sacharrum Marsh.) in the western Upper Great Lakes region has recently been reported with increased crown dieback symptoms, prompting investigation of the dieback etiology across the region. Evaluation of sugar maple dieback from 2009 to 2012 across a 120 plot network in Upper Michigan, northern Wisconsin, and eastern Minnesota has indicated that forest floor disturbance impacts from exotic invasive earthworms was significantly related to maple dieback. Other plot level variables tested showed significant relationships among dieback and increased soil carbon, decreased soil manganese, and reduced herbaceous cover, each of which was also be correlated to earthworm activity. Relationships between possible causal factors and recent growth trends and seedling counts were also examined. Maple regeneration counts were not correlated with the amount of dieback. The recent mean radial increment was significantly correlated with various soil features and nutrients. This study presents significant evidence correlating sugar maple dieback in the western Upper Great Lakes region with earthworm activity, and highlights the need for considering the impacts of non-native earthworm on soil properties when assessing sugar maple health and productivity.     

Local distribution of native and invasive earthworms and effects on a native salamander

North America is home to both native and invasive earthworms acting as ecosystem engineers as they build burrows that can serve as habitat for other species or otherwise alter soil structure, affecting nutrient cycling and other ecosystem processes. Here I determine where and what earthworm species commonly occur in my study area, and compare effects of native and invasive earthworms on the common woodland salamander, Plethodon cinereus, in field surveys and laboratory experiments. The native earthworm Eisenoides carolinensis was the most common earthworm, followed by two invasive species Dendrobaena octaedra and Octolasion tyrtaeum. The presence of O. tyrtaeum was associated with a narrower O-horizon (i.e., organic layer in the soil). Using structural equation modeling to explore direct and indirect pathways of these three most common earthworm species on salamanders, I found O. tyrtaeum occurrence was negatively correlated with nighttime salamander counts, a proxy for total salamander numbers, mediated by negative effects on O-horizon depth and microinvertebrate numbers. In the laboratory, O. tyrtaeum and D. octaedra consumed more leaf litter per gram of earthworm per day than the native E. carolinensis. However, salamanders consumed earthworms and used burrows of all native and invasive species of earthworms similarly. The potential for negative indirect effects of the invasive earthworm O. tyrtaeum on P. cinereus was demonstrated both in the field and laboratory, highlighting that seemingly small differences between native and invasive ecosystem engineers have the potential to significantly alter the effects of these closely related native and invasive organisms.     

Effects of non-native Asian earthworm invasion on temperate forest and prairie soils in the Midwestern US

Effects of invasive European earthworms in North America have been well documented, but less is known about ecological consequences of exotic Asian earthworm invasion, in particular Asian jumping worms (Amynthas) that are increasingly reported. Most earthworm invasion research has focused on forests; some Amynthas spp. are native to Asian grasslands and may thrive in prairies with unknown effects. We conducted an earthworm-addition mesocosm experiment with before–after control-impact (BACI) design and a complementary field study in southern Wisconsin, USA, in 2014 to investigate effects of a newly discovered invasion of two Asian jumping worms (Amynthas agrestis and Amynthas tokioensis) on forest and prairie litter and soil nutrient pools. In both studies, A. agrestis and A. tokioensis substantially reduced surface litter (84–95 % decline in foliage litter mass) and increased total carbon, total nitrogen, and available phosphorus in the upper 0–5 cm of soils over the 4-month period from July through October. Soil inorganic nitrogen (ammonium– and nitrate–N) concentration increased across soil depths of 0–25 cm, with greater effects on nitrate–N. Dissolved organic carbon concentration also increased, e.g., 71–108 % increase in the mesocosm experiment. Effects were observed in both forest and prairie soils, with stronger effects in forests. Effects were most pronounced late in the growing season when earthworm biomass likely peaked. Depletion of the litter layer and rapid mineralization of nutrients by non-native Asian jumping worms may make ecosystems more susceptible to nutrient losses, and effects may cascade to understory herbs and other soil biota.     

Invasion by a non‐native ecosystem engineer alters distribution of a native predator

Aim

Shifts in diet composition, abundance or distribution of native predators can occur as a result of exotic prey introductions. We examined effects of non‐native earthworms and anthropogenic landscape disturbance on habitat selection by the American robin (Turdus migratorius), a generalist predator, at landscape and local levels. We also investigated whether robins could act as vectors of spread for earthworm cocoons (egg cases).

Location

Boreal forest of Alberta, Canada.

Methods

We conducted robin and earthworm surveys at campgrounds, well pads, roads, pipelines, seismic lines and forest interiors across northern Alberta. At a subset of paired locations that had similar habitats and anthropogenic disturbance levels, we sampled both robins and earthworms.

Results

Both groups were most likely to occur at campgrounds, well pads and roads. Furthermore, robins were more likely to occur at locations where earthworms were present in our paired local‐level surveys. This correlation between robin and earthworm distributions could be due to robins acting as a vector for earthworm spread, rather than robins’ use of earthworms as prey. However, in tests using captive robins, earthworm cocoons did not survive digestion.

Main conclusions

Robin and earthworm distributions were correlated, likely due to robins’ use of earthworms as prey. These results suggest exotic prey can strongly influence native predators at both landscape and local levels, with shifts in native predator distributions occurring as a result of spatial variability in exotic prey distributions. Although the impacts of ecosystem engineering by earthworms have been previously demonstrated, our study provides evidence that effects of earthworms can also cascade upwards via trophic interactions.     

The effects of eastern red cedar (Juniperus virginiana) invasion and removal on a dry bluff prairie ecosystem

Eastern red cedar (Juniperus virginiana) establishment increased dramatically in the tallgrass prairie biome of North America during the last 30 years. Since many of the remaining remnant prairies occur on steep, dry, and nutrient poor sites, threatened by the invasion of native and non-native woody species, it is important to understand how an invasive species such as eastern red cedar influences key environmental factors that may determine the future trajectory of these systems and whether abiotic and biotic components of the system are resilient following cedar removal. To address these issues we: (1) investigated the influence of eastern red cedar on micro-environmental factors; (2) evaluated how these micro-environmental factors responded to eastern red cedar removal; and (3) assessed the effect of eastern red cedar on herbaceous species germination and distribution. The invasion of eastern red cedar was associated with lower surface light availability and soil temperature, as seen in prior studies, but otherwise had effects distinct from those observed in prior studies. There was no effect of cedar on soil pH, and unlike prior studies, cedar patches had higher soil moisture compared to native C₄ prairie grass plots. Moreover, these effects had strong spatial signatures, with impacts of invasion on micro-environment and native vegetation differing dramatically with slope position and aspect. Three years after eastern red cedar was removed, micro-environmental factors and species composition became similar to the tree-free grass-dominated plots, indicating a significant capacity for recovery following possible cedar control. In a broader context, this study sheds light on the pathways and mechanisms driving the impacts of this biological invasion on dry, steep, nutrient poor systems and illustrates the capability of these systems to recover once the invading species is removed.     

Invasion Patterns of Lumbricidae Into the Previously Earthworm-free Areas of Northeastern Europe and the Western Great Lakes Region of North America

We examine the patterns of expansion of exotic European earthworms in northeastern Europe and the western Great Lakes region of North America. These areas share many ecological, climatic and historical characteristics and are devoid of indigenous earthworm fauna due to Quaternary glaciations. These regions are being colonized by a similar suite of exotic lumbricid species and it is unlikely that this is the result of chance, but rather indicates that these species have particular characteristics making them successful invaders. The present macro-scale distributions of earthworm species in northern Russia show little connection to the pattern of the last glaciation. Rather, the primary factors that determine the current distributions of earthworm species include climatic conditions, the life history traits of different earthworm species, the suitability of habitat and intensity and patterns of human activity. In the western Great Lakes region of North America, there are three primary factors affecting current distributions of exotic earthworm species including the patterns of human activity and land use practices, the composition of particular source populations of earthworms associated with different vectors of transport and the soil and litter properties of habitats across the region. Disturbance of a habitat does not appear to be a prerequisite to the invasion and establishment of exotic earthworms. Analysis of the macro-scale distributions of Lumbricidae species in northeastern Europe may provide important insights into the potential of invasive European earthworm species to spread in North America, and identify potentially invasive species.     

Human-mediated introduction of geoengineering earthworms in the Fennoscandian arctic

It is now well established that European earthworms are re-shaping formerly glaciated forests in North America with dramatic ecological consequences. However, few have considered the potential invasiveness of this species assemblage in the European arctic. Here we argue that some earthworm species (Lumbricus rubellus, Lumbricus terrestris and Aporrectodea sp.) with great geomorphological impact (geoengineering species) are non-native and invasive in the Fennoscandian arctic birch forests, where they have been introduced by agrarian settlers and most recently through recreational fishing and gardening. Our exploratory surveys indicate no obvious historical dispersal mechanism that can explain early arrival of these earthworms into the Fennoscandian arctic: that is, these species do not appear to establish naturally along coastlines mimicking conditions following deglaciation in Fennoscandia, nor were they spread by early native (Sami) cultures. The importance of anthropogenic sources and the invasive characteristics of L. rubellus and Aporrectodea sp. in the arctic is evident from their radiation outwards from abandoned farms and modern cabin lawns into adjacent arctic birch forests. They appear to outcompete previously established litter-dwelling earthworm species (i.e. Dendrobaena octaedra) that likely colonized the Fennoscandian landscape rapidly following deglaciation via hydrochory and/or dispersal by early Sami settlements. The high geoengineering earthworm biomasses, their recognized ecological impact in other formerly glaciated environments, and their persistence once established leads us to suggest that geoengineering earthworms may pose a potent threat to some of the most remote and protected arctic environments in northern Europe.     

Spatial variability of an invasive earthworm (<Emphasis Type="Italic">Amynthas agrestis</Emphasis>) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park,USA

European and Asian earthworm invasions are widespread in North America. European earthworms especially are well-known to cause dramatic changes in ecosystems in northern, formerly glaciated portions of the continent, but less is known about the impacts of earthworm invasions in unglaciated areas inhabited by indigenous earthworms. We monitored fluctuations in the spatial extent of an Amynthas agrestis (Megascolecidae) population in the Great Smoky Mountains National Park in eastern Tennessee, USA. Two years of monthly growing-season observations revealed that the distribution of the earthworm population was dynamic, but overall distribution was closely linked to temperature and moisture with dramatic reductions of earthworm numbers associated with very dry conditions. In plots where A. agrestis were more often detected, we measured increased A-horizon soil aggregation and decreased thickness of the Oe/Oa-horizon. However, A. agrestis was not related to A-horizon microbial biomass, A-horizon C:N, Oi-horizon (litter) thickness, or mass of forest floor (O-horizon). Reductions in millipede species richness and density were associated with frequency of A. agrestis presence, possibly due to direct competition for food resources (Oe/Oa material). This evidence for potentially negative interactions between millipedes and A. agrestis suggests that expansion of the non-native earthworm into new habitats in the Park may alter soil physical properties and could pose a threat to native millipede diversity.     

Policy and management responses to earthworm invasions in North America

The introduction, establishment and spread of non-native earthworm species in North America have been ongoing for centuries. These introductions have occurred across the continent and in some ecosystems have resulted in considerable modifications to ecosystem processes and functions associated with above- and belowground foodwebs. However, many areas of North America have either never been colonized by introduced earthworms, or have soils that are still inhabited exclusively by native earthworm fauna. Although several modes of transport and subsequent proliferation of non-native earthworms have been identified, little effort has been made to interrupt the flow of new species into new areas. Examples of major avenues for introduction of earthworms are the fish-bait, horticulture, and vermicomposting industries. In this paper we examine land management practices that influence the establishment of introduced species in several ecosystem types, and identify situations where land management may be useful in limiting the spread of introduced earthworm species. Finally, we discuss methods to regulate the importation of earthworms and earthworm-containing media so that introduction of new exotic species can be minimized or avoided. Although our focus in this paper is necessarily North American, many of the management and policy options presented here could be applicable to the problem of earthworm invasions in other parts of the world.     

Biogeography of <Emphasis Type="Italic">Phragmites</Emphasis><Emphasis Type="Italic">australis</Emphasis> lineages in the southwestern United States

The environmental and social impacts of Phragmites australis invasion have been extensively studied in the eastern United States. In the West where the invasion is relatively recent, a lack of information on distributions and spread has limited our ability to manage invasive populations or assess whether native populations will experience a decline similar to that in the East. Between 2006 and 2015, we evaluated the genetic status, distribution, and soil properties (pH, electrical conductivity, and soil texture) of Phragmites stands in wetlands and riparian systems throughout the Southwest. Native (subspecies americanus), Introduced (haplotype M), and Gulf Coast (subspecies berlandieri) Phragmites lineages were identified in the survey region, as well as watershed-scale hybridization between the Native and Introduced lineages in southern Nevada. Two Asian haplotypes (P and Q) that were previously not known to occur in North America were found in California. The Native lineage was the most frequent and widespread across the region, with four cpDNA haplotypes (A, B, H, and AR) occurring at low densities in all wetland types. Most Introduced Phragmites stands were in or near major urban centers and associated with anthropogenic disturbance in wetlands and rivers, and we document their spread in the region, which is likely facilitated by transportation and urban development. Soil pH of Native and hybrid stands was higher (averaging 8.3 and 8.6, respectively) than Introduced stands (pH of 7.5) and was the only soil property that differed among lineages. Continued monitoring of all Phragmites lineages in the Southwest will aid in assessing the conservation status of Native populations and developing management priorities for non-native stands.     

Geographic independence and phylogenetic diversity of red shiner introductions

Identifying areas at risk of invasion can be difficult when the distribution of a non-native species encompasses geographically disjunct regions. Understanding genealogical relationships among native and non-native populations can clarify the origins of fragmented distributions, which in turn can clarify how fast and far a non-native species may spread. We evaluated genetic variation across the native and invasive ranges of red shiner (Cyprinella lutrensis), a minnow known to displace and hybridize with native species, to reconstruct invasion pathways across the United States (USA). Examination of mitochondrial cytochrome-b variation found that native range populations of red shiner fall into four highly divergent lineages that likely warrant species recognition. Introduced red shiner populations in the eastern and western USA are derived from only two of these lineages. Western USA populations originate from the mid-western and western genetic lineages, whereas eastern introductions derive only from the mid-western lineage. Western USA invasive populations exhibit fewer, but more diverse haplotypes compared to eastern USA invasive populations. We also recovered an undescribed, divergent lineage of Cyprinella that has been cryptically introduced into the western USA, which raises the possibility that hybridization has proceeded following secondary contact between previously allopatric lineages. Approximate Bayesian Computation modeling suggests that the disjunct distribution of red shiner across North America is an agglomeration of independent regional invasions with distinct origins, rather than stepwise advance of an invasion front or secondary introductions across regions. Thus localized control may be effective in managing non-native red shiner, including further spread to areas of conservation concern.     

Ecosystem effects of non-native earthworms in Mid-Atlantic deciduous forests

In many mid-Atlantic forests where both native and non-native earthworms exist, it is the non-native species that are the dominant component of the soil macrofauna. Few earthworm ecology studies, however, focus attention on these forest systems in order to determine the relative ecological roles and potential interactions of the native and non-native earthworms. In a series of field samplings and experimental manipulations we collected data on the effects of earthworms on below-and aboveground ecosystem processes. Earthworm abundance and the ecological processes measured were dynamic in space and time across the range of study sites. Leaf litter decay rates doubled at sites that had abundant non-native earthworms. Earthworms also altered the abundance of soil fungi, the activity of extracellular enzymes, soil respiration, and the growth of tree seedlings but the effects varied among sites depending on differences in land-use history and forest age. Red oak seedling growth was less at sites that had abundant earthworms but tulip poplar and red maple seedlings grew equally well with and without abundant earthworms. These preliminary results suggest that non-native earthworms have significant ecosystem effects, even in forests where native earthworms still occur. Land use history, however, plays an important role in determining what those effects will be, and these effects are likely to be dynamic, depending on the abundance of non-native earthworms.     

Distribution and impacts of invasive earthworms in Canadian forest ecosystems

In Canada it is generally accepted that most indigenous earthworms did not survive glaciation, and that the majority of the earthworms now inhabiting Canadian soils are relatively recent introductions of European origin. Although these exotic earthworms are generally considered to be beneficial in agricultural soils, their effects can be less benign in forested ecosystems. Studies have shown that invading earthworms can significantly alter the forest floor, affecting the distribution of carbon, nitrogen and other chemicals, roots, microbes and other elements of the soil fauna, and even understory vegetation. This paper summarizes the current distribution of exotic and native earthworm species in Canadian forests and draws on the results of studies of invasion patterns and environmental impacts in northern forests in North America and Europe to discuss potential outcomes for forests in Canada. The potential for variables such as temperature, pH, litter palatability and dispersal, to limit or promote the invasion of exotic earthworms in Canadian forests is discussed, and areas for future research are proposed. The same earthworm species that are invading forests in northern Europe and the US are also invading Canadian forests. Several species of exotic earthworms are already established in a wide range of deciduous and coniferous forest types, including the boreal. Evidence is presented to suggest that further expansion into Canadian forests is likely.     

Soil-borne seed pathogens: contributors to the naturalization gauntlet in Pacific Northwest (USA) forest and steppe communities?

Soil-borne seed pathogens are omnipresent but are often overlooked components of a community’s biotic resistance to plant naturalization and invasion. Using multi-year greenhouse experiments, we compared the seed mortality of single invasive, naturalized, and native grass species in sterilized and unsterilized soils collected from Pacific Northwest (USA) steppe and forest communities. Native Pseudoroegneria spicata displayed the greatest seed mortality, naturalized Secale cereale displayed intermediate seed mortality, and invasive Bromus tectorum was least affected by soil pathogens. Seed mortality across all three species was consistently greater in soils collected from steppe than soils collected from forest; seeds sown into sterilized steppe soil experienced half the overall seed mortality compared to seeds sown into unsterilized steppe soil. Soil sterilization did not affect grass seed mortality in forest soils. We conclude that (1) removing soil-borne pathogens with sterilization does increase native and non-native grass seed survival, and (2) soil-borne pathogens may influence whether an introduced species becomes invasive or naturalized within these Pacific Northwest communities as a result of differential seed survival. Soil-borne pathogens in these communities, however, have the greatest negative effect on the survival of native grass seeds, suggesting that the native microbial soil flora more effectively attack seeds of native plants than seeds of non-native species.     

Introduced earthworms in agricultural and reclaimed land: their ecology and influences on soil properties, plant production and other soil biota

Accidental and deliberate introductions of earthworms into agricultural and reclaimed land are natural experiments that provide opportunities to understand the attributes of successful invaders and their impacts on local biota and ecosystem processes. We consider various case studies (e.g., earthworm invasions in agricultural soils in Australia and Brazil) and deliberate introductions of earthworms into reclaimed mine sites, landfills and cutaway peat in the U.K. and Ireland. Invasions of exotic earthworms, such as European Lumbricidae in Australia, have been geographically extensive, but remain very patchy at regional and field scales. Their impacts on soil properties, plant production and other biota are therefore also likely to be patchy. Various methods have been developed to deliberately inoculate exotic earthworms into disturbed lands, with varying degrees of success. The factors controlling success are, in general, poorly understood. A broad range of impacts of invasive earthworms on soil properties (e.g., soil structure, nutrient availability, burial of surface materials, incidence of root diseases) and plant yield and quality have been reported. Less is known of the impacts of invasive earthworms on other soil fauna, but they are likely to occur due to alterations in food availability and habitat structure. Influences on other biota are likely to extend to aboveground communities as well as those belowground. Introductions of earthworms to disturbed lands can yield substantial benefits in agricultural productivity and amelioration of soil degradation. However, the potential impact of the promotion or control of such introductions on non-target biota and ecosystem processes in pristine ecosystems nearby should be considered.     

Evidence for human-mediated dispersal of exotic earthworms: support for exploring strategies to limit further spread

As potent ecosystem engineers, non-native earthworms are altering the fundamental structure and function of previously earthworm-free cold-temperate hardwood forests in North America. Discarded earthworms used for fishing bait has been presumed to be an important vector for the continued spread of non-native earthworms because epicentres of invasion often include boat landings, lakeshores and roads. However, controversy has remained about the overall importance of human-mediated spread vs. natural expansion of established earthworm populations. In this issue of Molecular Ecology , Cameron et al . explore the continued role of humans in dispersing non-native earthworms.     

Dominance of an invasive earthworm in native and non-native grassland ecosystems

More attention is currently being focused on earthworm invasions; however, in many ecosystems the relative abundance of native and invasive earthworm species is unknown. We characterized earthworm populations of two grassland types within the Palouse region: native prairie remnants and Conservation Reserve Program (CRP) set asides planted with exotic grasses. The earthworm community in both grassland types was completely dominated by the exotic-invasive Aporrectodea trapezoides. Only one individual of a native species, Driloleirus americanus (the giant Palouse earthworm), was found in a prairie remnant. No differences were found between prairie remnants and CRP sites for mean earthworm density (24–106 individuals m⁻²) or fresh weight (12–45 g m⁻²). Our results suggest that the combined effects of land-use change, habitat fragmentation and competitive interactions have resulted in the decimation of native earthworm populations and dominance of invasive earthworms in native and non-native grasslands of the Palouse region.     

Tracking an invasion: community changes in hardwood forests following the arrival of <Emphasis Type="Italic">Amynthas agrestis</Emphasis> and <Emphasis Type="Italic">Amynthas tokioensis</Emphasis> in Wisconsin

Because Upper Midwest temperate forests lack native earthworms, the invasions of European and Asian earthworms can significantly alter soils and understory vegetation. Earthworms’ ability to increase leaf litter decay, alter nutrient cycling by mixing the organic layer with mineral soil, and decrease plant species richness leads to concern about the Asian ‘jumping earthworm’ (Amynthas agrestis and A. tokioensis) species that were recorded in the University of Wisconsin—Madison Arboretum in 2013. In 2015, we found A. agrestis and A. tokioensis in a distinct 8-ha region of a 23-ha hardwood forest surveyed in the Arboretum; by 2016 A. agrestis and A. tokioensis had spread over an additional 7 ha. Plots also contained the European earthworm species Lumbricus terrestris, L. rubellus, and Apporectodea spp., whose distributions decreased from 2015 to 2016. While leaf litter, plant species richness, and tree and shrub seedling abundance were generally reduced in areas with European earthworms, they were typically slightly increased in areas with A. agrestis and A. tokioensis versus those without. Although our results do not show substantial impacts of A. agrestis and A. tokioensis on vegetation in the initial years of invasion, the rapid replacement of European earthworms by A. agrestis and A. tokioensis suggests continued monitoring of these new invasive species is important to better understand their potential to change the Upper Midwest’s forests.     

Effects of Grazing on Restoration of Southern Mixed Prairie Soils

A comparative analysis of soils and vegetation from cultivated areas reseeded to native grasses and native prairies that have not been cultivated was conducted to evaluate restoration of southern mixed prairie of the Great Plains over the past 30 to 50 years. Restored sites were within large tracts of native prairie and part of long‐term grazing intensity treatments (heavy, moderate, and ungrazed), allowing evaluation of the effects of grazing intensity on prairie restoration. Our objective was to evaluate restored and native sites subjected to heavy and moderate grazing regimes to determine if soil nutrients from reseeded cultivated land recovered after 30 years of management similar to the surrounding prairie and to identify the interactive influence of different levels of grazing and history of cultivation on plant functional group composition and soils in mixed prairies. For this mixed prairie, soil nitrogen and soil carbon on previously cultivated sites was 30 to 40% lower than in uncultivated native prairies, indicating that soils from restored sites have not recovered over the past 30 to 50 years. In addition, it appears that grazing alters the extent of recovery of these grassland soils as indicated by the significant interaction between grazing intensity and cultivation history for soil nitrogen and soil carbon. Management of livestock grazing is likely a critical factor in determining the potential restoration of mixed prairies. Heavy grazing on restored prairies reduces the rate of soil nutrient and organic matter accumulation. These effects are largely due to changes in composition (reduced tallgrasses), reduced litter accumulation, and high cover of bare ground in heavily grazed restored prairies. However, it is evident from this study that regardless of grazing intensity, restoration of native prairie soils requires many decades and possibly external inputs to adequately restore organic matter, soil carbon, and soil nitrogen.