Microstegium Vimineum Research Articles

Emerging fungal pathogen of an invasive grass: Implications for competition with native plant species.

Infectious diseases and invasive species can be strong drivers of biological systems that may interact to shift plant community composition. For example, disease can modify resource competition between invasive and native species. Invasive species tend to interact with a diversity of native species, and it is unclear how native species differ in response to disease-mediated competition with invasive species. Here, we quantified the biomass responses of three native North American grass species (Dichanthelium clandestinum, Elymus virginicus, and Eragrostis spectabilis) to disease-mediated competition with the non-native invasive grass Microstegium vimineum. The foliar fungal pathogen Bipolaris gigantea has recently emerged in Microstegium populations, causing a leaf spot disease that reduces Microstegium biomass and seed production. In a greenhouse experiment, we examined the effects of B. gigantea inoculation on two components of competitive ability for each native species: growth in the absence of competition and biomass responses to increasing densities of Microstegium. Bipolaris gigantea inoculation affected each of the three native species in unique ways, by increasing (Dichanthelium), decreasing (Elymus), or not changing (Eragrostis) their growth in the absence of competition relative to mock inoculation. Bipolaris gigantea inoculation did not, however, affect Microstegium biomass or mediate the effect of Microstegium density on native plant biomass. Thus, B. gigantea had species-specific effects on native plant competition with Microstegium through species-specific biomass responses to B. gigantea inoculation, but not through modified responses to Microstegium density. Our results suggest that disease may uniquely modify competitive interactions between invasive and native plants for different native plant species.

Frequent Fire Reduces the Magnitude of Positive Interactions Between an Invasive Grass and Soil Microbes in Temperate Forests

Fire activity is increasing in many regions. Although increased fire activity is expected to promote plant invasion, over longer time periods, frequent fire can shift the nutrient status of ecosystems, which may alter interactions between invasive plants and soil microbial decomposers. Here, we applied a fire treatment to plots embedded in deciduous forests under regimes of either fire exclusion or frequent fire and invaded by the most widespread invasive grass in the eastern USA (Microstegium vimineum) to determine how frequent fire affects plant–soil interactions while controlling for time after fire. We predicted that frequent fire would increase microbial nitrogen (N) limitation, leading to lower Microstegium productivity and reduced soil carbon (C) and N loss. We found that Microstegium leaf, root, and microbial biomass C/N ratios were significantly wider under frequent fire than fire exclusion. Consistent with these patterns, dissolved organic N concentration was 22% lower and the activity of an exoenzyme targeting N acquisition was 59% higher under frequent fire, indicating that frequent fire increased microbial N limitation. Higher surface soil C and N and fire-induced increases in particulate soil organic matter N suggest that frequent fire in these grass-invaded forests enhanced microbial N limitation through the accumulation of microbially resistant pyrogenic N. A structural equation model confirmed that these changes were interrelated and associated with 87% lower Microstegium aboveground biomass and 85% higher fine root biomass. These findings provide new insights into how frequent fire impacts plant–soil microbial interactions and thus may feedback to plant invasion over longer time periods.

Long‐term trends indicate that invasive plants are pervasive and increasing in eastern national parks

While invasive plant distributions are relatively well known in the eastern United States, temporal changes in species distributions and interactions among species have received little attention. Managers are therefore left to make management decisions without knowing which species pose the greatest threats based on their ability to spread, persist and outcompete other invasive species. To fill this gap, we used the U.S. National Park Service's Inventory and Monitoring Program data collected from over 1,400 permanent forest plots spanning 12yr and covering 39 eastern national parks to analyze invasive plant trends. We analyzed trends in abundance at multiple scales, including plot frequency, quadrat frequency, and average quadrat cover. We examined trends overall, by functional group, and by species. We detected considerably more increasing than decreasing trends in invasive plant abundance. In fact, 80% of the parks in our study had at least one significant increasing trend in invasive abundance over time. Where detected, significant negative trends tended to be herbaceous or graminoid species. However, these declines were often countered by roughly equivalent increases in invasive shrubs over the same time period, and we only detected overall declines in invasive abundance in two parks in our study. Present in over 30% of plots and responsible for the steepest and greatest number of significant increases, Japanese stiltgrass (Microstegium vimineum) was the most aggressive invader in our study and is a high management priority. Invasive shrubs, especially Japanese barberry (Berberis thunbergii), Japanese honeysuckle (Lonicera japonica), multiflora rose (Rosa multiflora), and wineberry (Rubus phoenicolasius), also increased across multiple parks, and sometimes at the expense of Japanese stiltgrass. Given the added risks to human health from tick-borne diseases, invasive shrubs are a high management priority. While these findings provide critical information to managers for species prioritization, they also demonstrate the incredible management challenge that invasive plants pose in protected areas, particularly since we documented few overall declines in invasive abundance. As parks work to overcome deferred maintenance of infrastructure, our findings suggest that deferred management of natural resources, particularly invasive species, requires similar attention and long-term commitment to reverse these widespread increasing invasive trends.

Non-native Microstegium vimineum populations collapse with fungal leaf spot disease outbreak

Non-native plants may meet little resistance in the novel range if they leave their biological enemies at home. As a result, species invasion can be rapid and appear unlimited. However, with time, organisms may acquire novel enemies in the novel range, or home-range enemies also may colonize the novel range. For plants, several authors have suggested that enemy release may give way to enemy acquisition in which pathogens accumulate and suppresses non-native plants. The ‘naturalization’ that occurs with acquired enemies may take decades to develop, yet most species invasion research lasts less than 4 years, and data tracking plant invasion before and after the appearance of pathogens are rare. Microstegium vimineum is an Asian grass that has invaded deciduous forest habitats in the southern Midwestern and Southeastern USA and is currently expanding in the Northeastern USA. We recorded widespread expansions in M. populations in North Carolina and Georgia (USA) between 2009 and 2011 but noticed that a fungal pathogen (indicated by leaf lesions; Bipolaris sp.) appeared on several of the populations in 2011. In 2019, we re-sampled these populations to determine whether the appearance of the fungal pathogen corresponded with a suppression of M. vimineum expansion. We found the once-expanding M. vimineum populations in retreat in 2019, and the plant population contractions were greater (and seed production lesser) where the fungal leaf spot disease was most extensive. These results suggest that enemy acquisition suppressed an active non-native plant invasion. We also found that where M. vimineum populations declined (or disappeared) native plants appeared to fill in the gap. Hence, whereby exotic species may gain advantage in novel habitat with the loss of their native-range pathogens, with longer time spans, enemy release may give way to enemy acquisition and native populations may recover if they are immune to the pathogens.

Invasive grass (Microstegium vimineum) indirectly benefits spider community by subsidizing available prey.

Invasive plant species cause a suite of direct, negative ecological impacts, but subsequent, indirect effects are more complex and difficult to detect. Where identified, indirect effects to other taxa can be wide‐ranging and include ecological benefits in certain habitats or locations.Here, we simultaneously examine the direct and indirect effects of a common, invasive grass species (Microstegium vimineum) on the invertebrate communities of understory deciduous forests in the eastern United States. To do this, we use two complementary analytic approaches to compare invaded and reference plots: (a) community composition analysis of understory arthropod taxa and (b) analysis of isotopic carbon and nitrogen ratios of a representative predatory spider species.Invaded plots contained a significantly greater abundance of nearly all taxa, including predators, herbivores, and detritivores. Spider communities contained over seven times more individuals and exhibited greater species diversity and richness in invaded plots.Surprisingly, however, the abundant invertebrate community is not nutritionally supported by the invasive plant, despite 100% ground cover of M. vimineum. Instead, spider isotopic carbon ratios showed that the invertebrate prey community found within invaded plots was deriving energy from the plant tissue of C3 plants and not the prevalent, aboveground M. vimineum. Synthesis and applications. We demonstrate that invasive M. vimineum can create non‐nutritional ecological benefits for some invertebrate taxa, with potential impacts to the nutritional dynamics of invertebrate–vertebrate food webs. These positive impacts, however, may be restricted to habitats that experience high levels of ungulate herbivory or reduced vegetative structural complexity. Our results highlight the importance of fully understanding taxon‐ and habitat‐specific effects of invading plant species when prioritizing invasive species removal or management efforts.

Large-spored Drechslera gigantea is a Bipolaris species causing disease on the invasive grass Microstegium vimineum

ABSTRACT Environmentally damaging invasive plants can also serve as reservoir hosts for agricultural pathogens. Microstegium vimineum is an invasive C4 annual grass that is present throughout the midwestern and eastern United States. It can reach high densities in disturbed areas such as crop-forest interfaces, which creates the potential for pathogen spillover from M. vimineum to agricultural crops and native plants. A previous study that surveyed disease on M. vimineum found a large-spored Bipolaris species that was widespread on M. vimineum and also isolated from co-occurring native grasses. Here, we report that the large-spored fungus isolated from M. vimineum and the native grass Elymus virginicus is Drechslera gigantea, based on comparison with published descriptions of morphological traits, and establish that D. gigantea is a pathogen of M. vimineum and E. virginicus. We review the phylogenetic placement and taxonomic history of D. gigantea and propose that it be reassigned to the genus Bipolaris as Bipolaris gigantea.

The Weed Flora of Turkish Tea Plantations

This study was performed to find out the vascular weed taxa of tea ( Camellia sinensis (L.) Kuntze) plantations in Turkey and determine the critical control periods of the taxa which are negatively affect both of crop quality and yield. These taxa were determined with the studies and observations of authors both in tea plantations and local herbarium (KATO). A total of 114 native and naturalized/cultivated vascular plant taxa were found out as weeds in tea plantations. The most noxious weed, which were unintentionaly added to harvested shoots and negatively affected the tea quality, were underlined. The most commonly growing taxa in tea plantations in the region were: Pteridium aqulinum (L.) Kuhn., Smilax excelsa L., Alnus glutinosa (L.) Gaertn. subsp. barbata (C.A. Mey.) Yalt., Crassocephalum crepidioides (Bentham) S. Moore, Calystegia silvatica (Kit.) Griseb, Commelina communis L. , Microstegium vimineum (Trin.) A. Camus. , Oplismenus undulatifolius (Ard.) P. Beauw. and Rubus spp. A high number of the observed weed species are ecologically tolerated taxa which are naturalized in the region. Furthermore, of these taxa 9 are climbers and 14 are woody plants. The critical periods of weed control in tea plantations were derived from both literature and our ecological/phenological observatins in tea plantations.

Soil pH influences patterns of plant community composition after restoration with native‐based seed mixes

Reclamation of highly disturbed lands typically includes establishing fast‐growing, non‐native plants to achieve rapid ground cover for erosion control. Establishing native plant communities could achieve ecosystem functions beyond soil erosion, such as providing wildlife habitat. Pipelines, or other disturbed corridors through a landscape, present unique challenges for establishing native plant communities given the heterogeneity of soil environments and invasive plant propagule pressure. We created two structural equation models to address multiple related hypotheses about the influence of soil pH on plant community composition (current diversity and vegetative cover of the original restoration seed mix and background flora, and invasive plant density during mix establishment and current density) of a highly disturbed landscape corridor restored with native species. To test our hypotheses we conducted a plant survey on a gas pipeline crossing two state forests in the north‐central Appalachians that had been seeded with a native‐based mixture 8 years prior. Low soil pH was a strong predictor of density of the invasive annual plant, Microstegium vimineum, and had resulted in lower species diversity and cover of the seeded mix. Overall, our data provide evidence that native‐based grass and forb mixtures can establish and persist on a wide range of soil environments and thrive in competition with invasive plants in moderately acidic to neutral soils. Advancing knowledge on restoration methods using native species is essential to improving restoration practice norms to incorporate multifunctional ecological goals.

Plant Community Composition in Two Human-Modified Landscapes, a Powerline Corridor and an Old Field

Human landscape modification elicits changes in plant community composition due to altered microclimate conditions. We asked the question whether floristic composition, abundance, species richness, and diversity differ between habitat types in two human-modified landscapes, with contrasting management regimes. We measured species richness and cover of all vascular plants in forest, edge, and corridor habitats of a powerline easement, as well as in a nearby old field. Powerline corridor habitat had 21% more species than adjoining forest habitat and was dominated by shrub and herbaceous species. We also found that soil pH and litter depth are significant predictors of species richness along powerline corridor edges and in open old-field habitat. Particularly, we observed maximum species richness in plots with moderately high soil pH of between 5 and 5.5 along powerline corridor edges and in open old-field habitat. Powerline corridor plots with less surface litter also had higher species richness. Invasive species such as Microstegium vimineum and Rosa multiflora were more abundant in the open old-field habitat maintained annually by mowing than in powerline corridor habitat maintained usually every five years by herbicide spraying and selective removal of trees. Our findings indicate that the diverse floristic composition of powerline corridors support organisms at higher trophic levels and hence provide opportunity for conserving biodiversity within human-modified landscapes.

Comparison of decay rates between native and non-native wood species in invaded forests of the southeastern U.S.: a rapid assessment

Invasive plants have the potential to affect decomposition both directly, by introducing novel substrates that may differ from native species in key structural or chemical properties, and indirectly through changes to soil properties and microbial communities. The relative importance of these two mechanisms is unclear, especially with regard to wood decomposition. To explore these questions, we used a novel method to rapidly assess the wood decay rates of 11 native and 11 invasive non-native angiosperm species. The study was repeated at three pairs of sites, each consisting of an invaded and a relatively uninvaded forest. The invaded sites had either been colonized by a non-native grass (Microstegium vimineum (Trin.) A. Camus), a non-native woody shrub (Ligustrum sinense Lour.) or by multiple invasive species. After one year in the field, mass loss varied more than two-fold among the 22 wood species (24.2–52.3%). Wood origin (i.e., native or non-native) was only important at the Microstegium sites, with non-native species decomposing marginally faster than native species. Wood decomposed faster at both the Ligustrum-invaded and multiply-invaded sites than in their respective uninvaded sites but there were no differences between sites invaded or not by Microstegium. We detected positive relationships overall between mass loss and pH, K, P and NO3−, but invasion had no consistent effects on these soil properties. The results from this study show that the differences in wood decay rates between native and non-native species and the effects of invasion are highly idiosyncratic, with effects depending greatly on species and ecological context.

Control of Japanese stiltgrass (Microstegium vimineum) in golf course natural areas

AbstractJapanese stiltgrass is regarded as one of the most troublesome invasive species in the United States. It is commonly found invading forested areas; however, more recently it has been noted to be invading golf course roughs and out-of-play areas. The purpose of this study was to evaluate POST herbicide control of Japanese stiltgrass in golf course and highly maintained turfgrass facilities. None of the treatments provided >80% Japanese stiltgrass control 2 wk after treatment (WAT). At 4 WAT >80% Japanese stiltgrass control was observed with MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim, whereas metsulfuron, pinoxaden, and imazapic provided minimum control. By 8 WAT, MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim provided >98% control, whereas quinclorac, metsulfuron, pinoxaden, and imazapic provided no visible control. Thiencarbazone-methyl + foramsulfuron + halosulfuron-methyl, and sulfentrazone provided limited (≤60%) control. This study indicates that POST control of Japanese stiltgrass can be achieved with MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim. Future research should include long-term control over multiple growing seasons, repeat applications of herbicides, and evaluation of herbicides in combination for increased and longer-term Japanese stiltgrass control.

Effects of culling white-tailed deer on tree regeneration and Microstegium vimineum, an invasive grass

Reduction of forest regeneration due to overbrowsing by white-tailed deer is a growing concern for land managers. Abundant deer can impede forest regeneration through direct predation on tree seedlings. Additionally high deer density can facilitate the establishment of a dense understory of browse tolerant plant species that shades seedlings and persists even in the absence of deer. In response to these challenges, land managers have sought to reduce deer herds to restore tree regeneration, but few studies have evaluated the effectiveness of this management. Our study took place in Catoctin Mountain Park, a US National Park Service unit with a history of high deer density. The park has been heavily invaded by Microstegium vimineum, an invasive grass that can completely cover the forest floor. Using permanent plots established prior to the start of deer management, we were able to assess the joint effects of deer culling and M. vimineum on tree seedling density. We found that tree seedling density increased in response to deer reductions. M. vimineum cover initially increased, but then decreased. Seedling densities were higher in plots with more M. vimineum cover, indicating that it did not form a recalcitrant understory that would suppress regeneration. However, eight years after deer management began, few tree seedlings were >30 cm tall, implying that it will be many years before they grow into the sapling stage. Our results indicate that deer culling can be an effective tool in restoring tree regeneration despite the presence of M. vimineum, but that success will require a long-term commitment.

Comparing the impacts of an invasive grass on nitrogen cycling and ammonia-oxidizing prokaryotes in high-nitrogen forests, open fields, and wetlands

Numerous invasive plant species can increase soil nitrate (NO3−) by altering the nitrification process through plant-soil microbe interactions with ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). We evaluated how the invasive species Microstegium vimineum influenced physico-chemical soil properties, inorganic nitrogen (N) cycling, and AOA and AOB abundances under various environmental conditions. We paired 75 M. vimineum-invaded plots with 75 neighboring reference plots across forests, open fields, and forested wetlands within a state park in the Mid-Atlantic United States that has received high levels of N deposition. Soils were sampled for physico-chemical properties, NO3− and ammonium (NH4+) pools and availability, and AOA and AOB abundances. There were multiple soil impacts associated with M. vimineum across all ecosystems, most consistent were increased soil pH and increased NO3− pools. For other impacts, the directionality and effect sizes varied among ecosystems (e.g. NH4+ pools were 34% lower in forests, 35% lower in open fields, and 90% higher in wetlands relative to reference plots). Finally, forests had nearly all of impacts predicted by a pH-mediated nitrification plant-soil feedback. This study highlights the ability of an invasive grass to alter N cycling and soil properties in forests, open fields, and wetlands that have received high N deposition. We also show how invader-mediated impacts to N cycling may be dependent on the context of the ecosystem being invaded, including its hydrology, ambient soil conditions, and substrate-availability.

Plant community and phylogenetic shifts in acid seep springs over 49 years following Microstegium vimineum invasion

Community composition and diversity can change following exotic invasion. We tested the extent to which acid seep spring communities in southern Illinois had changed in composition and community heterogeneity based on three species surveys over 49 years. We also investigated the extent of changes in taxonomic and phylogenetic diversity since the invasion of Microstegium vimineum, an exotic grass. Floristic surveys of ten acid seep springs in southern Illinois were conducted in summer 2017 and compared to two previous surveys from 1968 and 2008. We investigated changes among acid seep springs and between surveys in species composition and community heterogeneity with multivariate ordination based on site dissimilarity, and univariate analyses comparing changes in taxonomic diversity (species richness and exotic species richness) and phylogenetic diversity [net relatedness (NRI) and nearest taxon indices (NTI)] determined from a species phylogeny based upon two plastid sequences (rbcL and matK). Acid seep spring communities became more compositionally similar to each other following woody plant encroachment and M. vimineum invasion. Total species richness declines were observed between surveys while exotic species richness increased. While NRI did not exhibit any temporal patterns, NTI significantly increased over time indicating that a decrease in phylogenetic diversity accompanied exotic invasion over almost half a century within these plant communities.

Interspecific competitive potential of wavyleaf basketgrass (Oplismenus undulatifolius), a recent introduction to the mid-Atlantic United States

AbstractUnderstanding the mechanisms by which an invasive plant species is able to colonize and successfully expand into native plant communities can help in estimating the potential threat posed by a new invader and predict impacts on community diversity, structure, and function. Wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) P. Beauv.] is a perennial, shade-tolerant grass species that has been recently introduced to the mid-Atlantic United States. Areas invaded by O. undulatifolius typically have low species richness, but it is unknown whether O. undulatifoius actively outcompetes other species or simply thrives primarily in species-poor habitats. This study used a greenhouse experiment to quantify interspecific competition in shade and sun among seedlings of O. undulatifolius; Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], an invasive annual grass common in the region; and a mix of three native perennial grass species commonly used in restoring areas invaded by M. vimineum. In this experiment, shade did not significantly affect growth or competitive ability. Interspecific competition irrespective of shade had a negative effect on growth of all species, but O. undulatifolius was affected to a much greater degree than either M. vimineum or the native grass mix. These results suggest that, at least under these conditions, O. undulatifolius is a weak interspecific competitor and may be capable of forming dense monotypic stands only in areas that already have low species diversity. In the mid-Atlantic region, postagricultural legacies and overabundant deer populations, which lead to depauperate understories, may be a major facilitator of O. undulatifolius invasion in forests.

Organic matter priming by invasive plants depends on dominant mycorrhizal association

While it has long been held that invasive plants alter ecosystem processes, the magnitude and direction of these effects have rarely been quantified in situ. We measured the effects of an invasive C4 grass (Microstegium vimineum) on soil organic matter (SOM) decomposition in a deciduous forest in south-central Indiana, USA. The unique 13C signature of the C4 grass relative to the C3 trees allowed us to partition soil CO2 fluxes and estimate M. vimineum effects on decomposition. The magnitude and direction of priming effects hinged on the soil characteristics, which related to the mycorrhizal association of dominant trees. In forest plots dominated by ectomycorrhizal trees, with low nitrogen availability and most SOM in particulate (i.e., unprotected) forms, M. vimineum increased SOM decomposition by 58%. In contrast, in plots dominated by arbuscular mycorrhizal trees, characterized by high nitrogen availability and most SOM in mineral-associated (i.e., protected) forms, M. vimineum decreased decomposition by 14%. Collectively, our results demonstrate that invasive species can play a large role in altering ecosystem processes and suggest that the magnitude and direction of such effects depend on the dominant trees and edaphic characteristics of the stand.

Nonnative vegetation dynamics in the understory of a fragmented temperate forest1

Although the conditions that render forests likely to support nonnative plants are well documented, there are surprisingly few data on the long-term dynamics of nonnative invasive species in eastern temperate forests. We examined 11 years of compositional and structural change in a small (60 ha) forest preserve in Connecticut with abundant invasive plants, a diverse land use history, and varied edaphic characteristics. We quantified the extent to which vegetation composition changed at the species, life form, and community scales and then assessed the possible factors driving these changes. Fifty-four plots were sampled in 2004, 2009, and 2015; these plots spanned two major forest types, (a) Acer rubrum L.-Fraxinus americana L and (b) Quercus montana Willd.-Quercus coccinea Muenchh. Significant changes in composition occurred over time with a greater magnitude of change in the Acer-Fraxinus forest than in the Quercus forest at all scales of analysis. Large increases in the abundance of the invasive Microstegium vimineum (Trin.) A. Camus (+1760%), Berberis thunbergii DC. (+180%), and Rosa multiflora Thunb. ex Murr (+1790%), along with a surprisingly large decline in the dominant Alliaria petiolata (Bieb.) Cavara & Grande (–86%) occurred in the Acer-Fraxinus forest. Native shrub and herb life forms growing alongside these invasive species remained unchanged or increased in abundance. Soil moisture predicted change in abundance of R. multiflora and B. thunbergii. Our results suggest that A. petiolata may be less persistent over time than previously believed and underscore the difficulties of generalizing about invasive species dynamics and relationships with native plants.

Japanese Stiltgrass (Microstegium vimineum) Germination Pattern and its Impact on Control Strategies1

Abstract Field trials were conducted by Virginia Master Naturalists to determine the germination period for Japanese stiltgrass and its impact on timing of postemergence herbicide applications. Germination rates declined from April to June, with no germination seen after mid-June. Glyphosate applications in early May significantly reduced Japanese stiltgrass cover that month, but post-treatment germination resulted in approximately 25% cover by October, with 78% cover seen in untreated plots. However, no Japanese stiltgrass was observed in October when glyphosate was applied in either the third week of June or the third week of July. A single application of glyphosate was effective for Japanese stiltgrass control if applications are made in June after new germination had ceased, verified by multi-year herbicide field trials. Field trials conducted by Virginia Tech showed preemergence applications of prodiamine reduced Japanese stiltgrass stand from 30 to 94%, depending on rate and timing, but even in the most effective treatment there was still at least 19% cover by August. Prodiamine treatments that utilized May applications were more effective for crabgrass (Digitaria spp.) control than for Japanese stiltgrass, supporting the earlier germination pattern for Japanese stiltgrass. Inclusion of this work in this paper provides a more complete picture of the treatment options for Japanese stiltgrass. A timed postemergence herbicide application may be a better control option for this weed than use of a preemergence herbicide application. Index words: herbicide application, invasive plants, weed control. Chemicals used in this study: Glyphosate [N-(phosphonomethyl)glycine)], prodiamine (2,6-Dinitro-N,N-dipropyl-4-(trifluoromethyl)-1,3-benzenediamine). Species used in this study: Japanese stiltgrass (Microstegium vimineum (Trin.) A Camus.).

Impacts of an invasive grass on soil organic matter pools vary across a tree-mycorrhizal gradient

Increases in carbon (C) inputs can augment soil organic matter (SOM), or reduce SOM by accelerating decomposition. Thus, there is a need to understand how and why ecosystems differ in their sensitivity to C inputs. Invasive plants that invade wide-ranging habitats, accumulate biomass rapidly, and contribute copious amounts of C to soil can be ideal for addressing this gap. We quantified the effects of the invasive C4 grass, Microstegium vimineum, on SOM in three temperate forests across plots varying in their relative abundance of arbuscular mycorrhizal (AM) versus ectomycorrhizal (ECM) trees. We hypothesized that invasion would differentially affect SOM along the mycorrhizal gradient owing to recognized patterns in nitrogen availability (AM > ECM) and the proportion of unprotected SOM (ECM > AM). Across all sites, M. vimineum was associated with lower particulate organic matter (POM) in ECM-dominated plots, consistent with our hypothesis that invader-derived C inputs should stimulate decomposers to acquire nitrogen from unprotected SOM in soils with low nitrogen availability. However, the pattern of lower POM in the ECM-dominated soils was offset by greater mineral-associated organic matter (MAOM)—and isotopic data suggest this was largely driven by native- rather than invader-derived SOM—implying an invasion-associated transfer of native-derived POM into MAOM. Our results demonstrate a context-dependent shift in the form of SOM in a system with presumably enhanced C inputs. This finding suggests a need to look beyond changes in total SOM stocks, as intrinsic SOM changes could lead to important long-term feedbacks on invasion or priming effects.

Alteration to Woodland Structure through Midstory Mastication Increased Fuel Loading and Cover of Understory Species in Two Upland Hardwood Stands

AbstractThe contemporary decline of open woodlands in the eastern United States has prompted land managers to implement management prescriptions that encourage landscape and habitat diversity, often using mechanical thinning and prescribed fire as tools to alter stand structure. To increase habitat diversity and restore natural processes, a long-term oak woodland restoration project was planned for two upland hardwood stands in the Daniel Boone National Forest, Kentucky, United States. As an initial phase of restoration, we examined the effects of midstory mastication on stand structure, understory vegetation response, and fuels. The mastication treatment reduced stem density and basal area of trees ≤7.9 in. (20.1 cm) dbh by 69 percent and 47 percent, respectively, encouraged vigorous stump/root sprouting, and increased ground cover of forbs (204 percent) and native graminoids (253 percent) the first year on treated plots. Additionally, mastication created a variable cover of woody mulch on the forest floor and increased 1-h and 100-h time-lag fuels compared with controls. In year 2, Microstegium vimineum (invasive grass) cover increased by 700 percent on treated plots. This study imparts novel information on the mastication of upland hardwoods to benefit land managers in directing future treatments to shape desired stand structures and compositions, and increase landscape heterogeneity.