Non-native Plant Invasions Research Articles

Testing the Australian Post-Border Weed Risk Management (WRM) system for invasive plants in Iran

Given the global threat from invasive plant species, management systems are needed to determine the risk posed. Whilst pre-border weed risk assessment systems have been tested and applied broadly, risk assessment systems for species post-border (or weed risk management) are yet to be subjected to such levels of scrutiny. Here we adapted the Australian Weed Risk Management (AWRM) approach to the geographic, climatic and weed management context of Iran. Then we evaluated and tested the performance of the adapted WRM system using 38 candidate species, comprising both native and non-native invasive plant species present in Iran. Additionally we modified the post-border WRM approach by specifically focusing on the feasibility of containment, rather than control per se, given that eradication of native species is not appropriate; even when considered to be invasive. We also subsequently modified the management emphasis associated with each cell of the WRM matrix of weed risk and feasibility of containment levels, to account for the changes outlined above. We examined the effectiveness of the system using receiver operating characteristic (ROC) curves for the 38 candidate species, which showed that our results were similar to those observed during testing and evaluations of the WRM systems developed in Australia. Examination of the outcomes revealed that the current management and research for five of the highest priority species did not match or align with the level of risk derived from the WRM assessment. Additionally at least seven invasive plants species currently not on the lists examined should be included on the Noxious Weed lists of Iran based on our assessment of the risk posed. The two highest priority species (Ambrosia psilostachya and Imperata cylindrica) are both alien species and should be priorities for containment. Despite successfully modifying the AWRM for Iran, additional studies are required to further examine and test the best cut-off values for each risk level in the WRM matrix using larger numbers of plant species. Our results show that the AWRM can be modified for use in other countries, which could see broader adoption of post-border WRM systems for managing established alien plant species.

Stage-dependent effects of a non-native invasive saltmarsh plant on the seedling establishment of a native seagrass

Concerns on the environmental disruption and ecosystem degradation due to the biological invasions are growing, with far-reaching consequences for the resilience of recipient ecosystems. While numerous studies mostly emphasized the negative impacts of invasive species on native species at a single time point, there is a lack of knowledge whether and how the invasion impacts vary with time. Here, we provide an empirical study on stage-dependent invasive impacts in an intertidal seagrass habitat (Zostera japonica), which is undergoing invasion of an invasive cordgrass (Spartina. alterniflora). Combining results from field surveys and experiments suggested that, impacts of cordgrass on seedling establishment of native seagrass species shift from facilitation at the initial stage of invasion to inhibition at the later stage when the invasive cordgrass become densely vegetated, causing density-dependent effects. In addition, at the later stage, patch expansion of cordgrass triggered degradation of seagrass-dominant habitats, showing the remnant patches of seagrass-dominant habitat have a strong patch-size dependent effect, with an optimal patch size of ~8 m2 and ~1.5 cm detritus to the establishment of seagrass seedlings. These stage-dependent effects strongly linked to water movement and sedimentation rate. Both of them are modified by the abundance of the invasive cordgrass and patch formation through transforming native seagrass habitat with invasion. Our findings highlight the importance of unraveling stage-dependent impacts for assessing the consequences of biological invasion on native ecosystems degradation.

Ecological restoration of an urban demolition site through introduction of native forb species

Urban brownfields can provide habitats for endangered native plant species but may also support invasive non-native species. The aim of our study was to develop and test different measures for the ecological restoration of an urban brownfield. We aimed to enhance native plant species richness by seeding two native forb seed mixtures containing 25 (HD-mixture) and 13 species (LD-mixture), respectively, without affecting spontaneously colonizing plant species of nature conservation value. Additionally, we tested the effects of species introduction and mowing on the establishment of invasive non-native plant species, woody species development, and perennial grass dominance.With establishment rates of 84% (HD) and 92% (LD) in the first study year and about 60% for both seed mixtures in the fourth year, species introduction was successful and led to rapid re-vegetation of the formerly bare brownfield. Although seeding did not result in increased species richness using either seed mixture, the dominance of perennial grasses was significantly reduced by the establishment of forb species from the HD-mixture. Overall, we observed the spontaneous establishment of ten plant species of conservation value; seeding affected these species only temporarily, in the second year. Seeding (with either seed mixture) and mowing both resulted in reduced cover of woody species and a lower frequency of the invasive non-native Robinia pseudoacacia.Our study demonstrated the high nature conservation value of dry and nutrient-poor urban brownfields for spontaneously occurring threatened plant species. Further studies have to evaluate if the reduced cover of grasses and woody species through introduction of site-specific native forb species might increase these sites’ aesthetic value and broader acceptance of brownfields by urban residents.

Estimating non-native plant richness with a species-accumulation model along roads.

Monitoring non-native plant richness is important for biodiversity conservation and scientific research. The species-area model (SA model) has been used frequently to estimate the total species richness within a region. However, the conventional SA model may not provide robust estimations of non-native plant richness because the ecological processes associated with the accumulation of exotic and native plants may differ. Because roads strongly dictate the distributions of exotic plants, we propose a species-accumulation model along roads (SR model), rather than an SA model, to estimate the non-native plant richness within a region. Using 270 simulated data sets, we compared the differences in performance between the SR and SA models. A decision tree based on prediction accuracy was created to guide model application, which was validated using field data from 3 national nature reserves in 3 different provinces in China. The SR model significantly outperformed the SA model when non-native species were restricted to the roadsides and the proportion of uncommon exotic species was small. More importantly, the SR model accurately estimated the non-native plant richness in all field sites with an error of <1 species per site. We believe our new model meets the practical need to efficiently and robustly estimate non-native plant richness, which may facilitate effective biodiversity conservations and promote research on non-native plant invasion and vegetation dynamics.

Comparative study on the floral spectral reflectance of invasive and non-invasive plants

This paper reports the dissimilar floral spectral reflection of invasive and non-invasive angiosperms. Hyper spectral floral reflectance of 22 non-invasive and 8 invasive, co-habiting and co-flowering angiosperm from Trivandrum, India were measured from 350 to 700 nm. using hand-held spectroradiometer. The ultraviolet, blue and green portions of the electromagnetic spectrum was converted to corresponding photoreceptor excitation values, and insect pollinator (bee) perceived colours respectively. The colour distance between invasive and non-invasive flowers was calculated. Spectral similarity and principal component analysis carried out on photoreceptor excitation values in the ultraviolet, blue and green region reveal the markedly different floral colour perception rendered by invasive species from that of their co-flowering, non-invasive counterparts. Floral spectral reflection in the ultraviolet and blue region was the least similar.

Potential Phytotoxic Effect of Essential Oil of Non-Native Species Impatiens parviflora DC.

Impatiens parviflora is non-native invasive plant species occupying large areas all over the Europe and threatens native communities by altering their species composition and reducing native biodiversity. The factor responsible for its spreading could be explained by releasing biochemical to the environment. On the other hands, high demand on secondary metabolites as potential source of new ecofriendly biocides could be beneficial. The analysis of I. parviflora essential oil (EO) led us to identify more than 60 volatiles. The main compound was hexahydrofarnesyl acetone, other dominant components were phytol, carvacrol, germacra-4(15),5,10(14)-trien-1-α-ol, and pentacosane. The potential phytotoxic effect of I. parviflora EO collected in two vegetation periods (summer and autumn) was evaluated on seed germination and root elongation of three dicot species (Raphanus sativus, Lepidum sativum, and Lactuca sativa) and on one monocot species (Triticum aestivum). The seed germination of only one dicot species, L. sativa, was affected by both EOs. In contrast, seed germination of monocot species T. aestivum was influenced only by the highest doses of EOs isolated from I. parviflora in autumn. The root elongation of tested plant species was less influenced by I. parviflora EOs. L. sativum showed sensitivity to one dose of EOs hydrodistilled in summer, while the monocot species was influenced by both EOs samples in highest doses. Our findings revealed that I. parviflora contained phenolics that were phytotoxic to the germination of some plant species, mainly at higher EOs doses, while root elongation of tested plants was not suppressed by essential oils.

Herbivory may promote a non-native plant invasion at low but not high latitudes.

The strengths of biotic interactions such as herbivory are expected to decrease with increasing latitude for native species. To what extent this applies to invasive species and what the consequences of this variation are for competition among native and invasive species remain unexplored. Here, herbivore impacts on the invasive plant Alternanthera philoxeroides and its competition with the native congener A. sessilis were estimated across latitudes in China. An common garden experiment spanning ten latitudinal degrees was conducted to test how herbivore impacts on A. philoxeroides and A. sessilis, and competition between them change with latitude. In addition, a field survey was conducted from 21°N to 36.8°N to test whether A. philoxeroides invasiveness changes with latitude in nature as a result of variations in herbivory. In the experiment, A. sessilis cover was significantly higher than A. philoxeroides cover when they competed in the absence of herbivores, but otherwise their cover was comparable at low latitude. However, A. philoxeroides cover was always higher on average than A. sessilis cover at middle latitude. At high latitude, only A. sessilis emerged in the second year. Herbivore abundance decreased with latitude and A. philoxeroides emerged earlier than A. sessilis at middle latitude. In the field survey, the ratio of A. philoxeroides to A. sessilis cover was hump shaped with latitude. These results indicate that herbivory may promote A. philoxeroides invasion only at low latitude by altering the outcome of competition in favour of the invader and point to the importance of other factors, such as earlier emergence, in A. philoxeroides invasion at higher latitudes. These results suggest that the key factors promoting plant invasions might change with latitude, highlighting the importance of teasing apart the roles of multiple factors in plant invasions within a biogeographic framework.

Characterisation of invasive plant proliferation within remnant riparian green corridors in Lusaka District of Zambia using Sentinel-2 imagery

Natural riparian corridors can serve as biodiversity reservoirs in urban environments. Despite the many opportunities that riparian corridors present for biodiversity conservation within urban environments, they may present conservation challenges by providing a thriving hub for local and alien invasive plants. The aim of the study was to map and characterise the occurrence of local and alien invasive plants along the natural green riparian corridors in Lusaka district of Zambia. A combination of field surveys and remote sensing approaches using Sentinel-2 imagery were employed to conduct the vegetation mapping and characterise the invasive plant proliferation. Five local and nine alien invasive plant species were identified within the natural green riparian corridors at 23 field survey sites. A total of 108 plant species were recorded in the study area out of which 57 were grasses of the Poacea family, five were local invasive and nine were alien invasive plant species. Six of the invasive plant species were mapped using Sentinel-2 data. The study showed that 47.35% of areal extent of the natural green riparian corridors in Lusaka had invasive and alien plant presence. Invasive and alien plant richness was determined to affect non-invasive plant richness and diversity. There was no linear association between poverty and percentage cover of invasive plant species but percentage cover of invasive plants seemed to be concentrated around wards with a poverty headcount around 0.15. The outcomes of this research are relevant for the management of invasive species within natural green corridors in urban areas.

Do roads or streams explain plant invasions in forested protected areas?

Giving land managers the ability to predict invasion patterns can provide planning tools for acquisition and management of protected areas. We compared the effects of roads and streams, two substantial pathways for delivery of invasive plant propagules and sources of disturbance that may facilitate invasions, on the abundance of non-native invasive plants in 27 protected areas in the Appalachian Mountains of the eastern United States. As an extension of our road analysis, we also evaluated specific road type as a predictor of protected area invadedness. We found that road and stream predictors did not improve on a model that included only other covariates (e.g., distance to an urban area, average canopy cover, average slope, edge-to-interior ratio, percent agricultural land, and percent developed land). In this model, only percent agricultural land was marginally significant in predicting parcel invadedness. However, we found that four-wheel drive (4WD) roads did predict protected area invadedness well relative to other road types (primary, secondary, and local) and better than a covariates-only model. The role of 4WD road density in predicting protected area invadedness may be explained by their relation to recreation, the unmaintained nature of 4WD roads, or the accumulation of mud and plant materials on 4WD vehicles. Although we found overall streams and roads in general to be poor predictors of invadedness of protected areas by invasive plants, we do propose that our finding of a relationship between plant invasions and density of 4WD roads merits further investigation in the future.

Fungal communities do not recover after removing invasive Alliaria petiolata (garlic mustard)

The negative impacts of non-native invasive plants on native plants has prompted intensive eradication efforts, but whether eradication can restore soil microbial communities that are also sensitive to invasion is generally not considered. Some invasive plants, like Alliaria petiolata (garlic mustard), specifically alter soils in ways that promote the invasion process. Garlic mustard disrupts mycorrhizas, increases fungal pathogen loads, and elevates soil nutrient availability and soil pH; thus, the fungal community and soil property responses to garlic mustard eradication may be key to restoring ecosystem function in invaded forests. We conducted a garlic mustard eradication experiment at eight temperate, deciduous forests. 1 and 3 years after initiating annual garlic mustard removal (hand pulling), we collected soil samples and characterized fungal community structure using DNA metabarcoding alongside a suite of edaphic properties. We found that fungal richness, the number of shared fungal species, fungal biomass, and the relative abundance of fungal guilds became less similar to invaded plots by year three of eradication and more similar to uninvaded reference plots. However, fungal community composition did not resemble uninvaded communities by the third year of eradication and remained comparable to invaded communities. Soil chemical and physical properties also remained similar to invaded conditions. Overall soil abiotic–biotic restoration was not observed after 3 years of garlic mustard removal. Garlic mustard eradications may therefore not achieve management goals until soil physical, chemical, and biological properties become more similar to uninvaded forested areas or at least more dissimilar to invaded conditions that can promote invasion.

Springs ecosystems: vulnerable ecological islands where environmental conditions, life history traits, and human disturbance facilitate non-native plant invasions

Ecosystem invasion by non-native plants depends on plant life history characteristics that influence the species’ invasiveness, as well as environmental factors that determine site invasibility. Small, insular ecosystems are thought be especially vulnerable to invasion but evidence for this pattern has been mixed. Freshwater springs form island-like ecosystems, allowing for a test of this proposal. Here, we investigated the effects of physical environmental factors, human disturbance, and plant life history traits on the occurrence of native and non-native plant species at 55 springs across different biomes in Alberta, Canada. A total of 526 plants were identified, 12.5% of which were non-native. Among these, species richness and abundance were greater at springs within biomes subject to increased land use intensity, especially livestock grazing, as compared to springs in parks and protected areas with limited land use. Subsequently, springs with higher human impact supported greater richness (r2 = 0.13) and abundance (r2 = 0.31) of non-native species, while native species abundance declined with increasing human impact (r2 = 0.14). Common native and non-native plant taxa exhibited life history traits that confer greater tolerance to human disturbance, such as that arising from livestock production that can disperse propagules, including clonal capacity and physical and chemical herbivory defenses. Our results indicated that springs ecosystems with greater human disturbance were more vulnerable to invasion by non-native plants, and this can reduce plant biodiversity and the ecological services provided by these distinctive, insular ecosystems.

Eco-physiological performance may contribute to differential success of two forms of an invasive vine, Dolichandra unguis-cati, in Australia

Invasive plant species are hypothesized as being more efficient at resource acquisition and use, resulting in faster growth than co-occurring non-invasive plant species. Nonetheless, some findings suggest that trait differences between invasive and non-invasive species are context dependent. In this study, two forms of an invasive vine species,Dolichandraunguis-cati, were used to test the context-dependent hypothesis.Dolichandraunguis-catiis a weed of national significance in Australia with two different forms: the ‘long pod’ (LP) and ‘short pod’ (SP). The two forms have different levels of distribution on the eastern Seaboard of the continent, with the SP form occurring extensively in both States of Queensland and New South Wales while the LP form is found only in isolated sites in South-East Queensland. This study examines whether differences in eco-physiological performance could be responsible for differential success of the two forms. A partially factorial experiment was set up in controlled conditions where potted plants of both forms were grown under two levels of light, water and nutrient resources (high and low) for 15 months. We measured several traits that are known to correlate with plant performance and resource use efficiency (RUE). The SP form exhibited higher values of carbon assimilation, RUE, number of subterranean tubers and leaf nitrogen than the LP form. However, the LP form produced greater biomass than the SP form, with the difference driven mainly by high resource conditions. The LP form displayed significantly higher phenotypic integration (number of traits significantly correlated) than the SP form in response to all treatments while the SP form exhibited higher phenotypic integration than the LP form in response to high resource conditions only. The SP form displayed traits that are well suited for successful colonization, possibly explaining its increased success in Australia, while the LP form possessed traits of opportunistic plants. Overall, we find that the two forms of the weedy vine deploy different carbon economies in response to resource conditions, which is evidence of the context-dependent trait hypothesis.

Characteristics of the soil seed bank of invasive and non-invasive plants in their native and alien distribution range

The ability to form persistent seed banks might contribute substantially to determine the invasion potential of alien plants in their new distribution ranges, given the role of seed banks as sources of propagules, genetic diversity, and in spreading the risk of germination failure over time. Using the largest seed bank dataset collated to date, comprising 14,293 records for 2566 species, we examined whether the type (transient vs persistent) and density of the seed banks of invasive species differ in their native (home) and alien (abroad) range, and whether these attributes differ among invasive and non-invasive congeners, at home and abroad. A lower probability of forming a persistent seed bank in the alien range was identified when analyzing data for 140 invasive species, although phylogenetic analyses run for 104 of those species did not confirm such differences. However, invasive woody species formed denser seed banks in the alien range, suggesting greater seed production and/or lower seed predation or mortality in the alien than native range. Interestingly, invasive species consistently showed a higher probability of forming persistent seed banks as well as denser seed banks than their non-invasive congeners in their native range, but not in their alien range. These findings provide the first quantitative evidence, based on a large number of species globally, of preadaptation with respect to species life-history traits resulting in the formation of a persistent seed bank in invasive species compared to their non-invasive congeners. The fact that both invasive and non-invasive congeners have similar probabilities of forming persistent seed banks abroad suggests that this might be an important attribute for the establishment of alien species in new ranges (naturalization phase), but not for their spread (invasion phase). Our findings also indicate that the characteristics of native seed banks should be an important component of risk assessments aimed at identifying species that are more likely to become invasive if introduced in new ranges.

Discrimination between regional biotypes of Impatiens glandulifera using a simple MALDI-TOF MS-based method for use with seeds

BackgroundWe have recently developed a simple, rapid, and relatively-cheap method for matrix-assisted laser-desorption and ionisation time-of-flight mass spectroscopy (MALDI-TOF MS) sample preparation that is applicable to plant material (in addition to microbial and insect material), and have used this to discriminate between closely-related Impatiens species and between regional biotypes of the invasive weed Impatiens glandulifera (commonly known as Himalayan balsam) using leaf samples. In the current paper, we have developed a complementary MALDI-TOF MS-based method for use with seeds. We have employed a combination of principal-component analysis and blind-tested comparison between reference-sample MALDI-TOF MS spectra and test-sample spectra to discriminate, on the basis of the acid-soluble seed-protein spectra generated by our method, between four regional biotypes of I. glandulifera from within the UK that differ in their susceptibility to the biological control agent Himalayan balsam rust (Puccinia komarovii var. glanduliferae).ResultsPeak-rich and highly-reproducible spectra were obtained and, in blind testing with test seeds collected in 2017 against reference seeds collected in 2017, we observed 100% identification accuracy in 12 blind tests. In blind testing with test seeds collected in 2016 against reference seeds collected in 2017, we observed 92% identification accuracy in 12 blind tests.ConclusionsMALDI-TOF MS analysis of seed material is able to discriminate between regional biotypes of I. glandulifera. MALDI-TOF MS therefore has the potential to improve the efficiency and efficacy of weed biological control using co-evolved natural enemies of invasive non-native plant species, through the matching of biological control agents with susceptible regional biotypes.

Seed predation does not explain pine invasion success.

Why some non-native plant species invade, and others fail remains an elusive question. Plant invasion success has been associated with specific species traits. Yet, we have limited knowledge of the mechanisms relating these traits to invasion potential. General patterns of biotic resistance by seed predation may provide a mechanism that helps separate invasive from non-invasive plants. Seed predation is an important barrier against plant establishment for many plant species. It may, therefore, create a selective filter against non-native plant establishment based on plant traits related to seed predation rate. In two cafeteria-style seed predation experiments in a steppe ecosystem in Patagonia (Argentina) we provided seeds of 16 non-native Pinaceae covering a 300-fold variation in seed mass, a 200-fold variation in seed volume and 75-fold variation in seed toughness. Seed removal decreased with seed mass and seed volume. Seed toughness was not a significant predictor while seed volume was the best predictor of predators' preference. However, for species of this family small seed size is the most important predictor of species invasiveness. Our results show that seed predation does not explain Pinaceae invasive success. In our system, species that have smaller seeds (i.e., more invasive) are preferentially consumed by seed predators. Seed mass was not the best predictor of granivory rates, despite being the seed trait on which most studies have been focused. Our ability to predict future invasion and understand invasion success could benefit from other studies that focus on the mechanisms behind invasive traits.

All change at the water\u2019s edge: invasion by non-native riparian plants negatively impacts terrestrial invertebrates

Riparian zones are complex, dynamic habitats that play a critical role in river ecosystem functioning. Terrestrial invertebrates comprise much of the diversity found in riparian habitats and facilitate the transfer of energy between aquatic and terrestrial systems. However, the consequences for terrestrial invertebrates of invasion of riparian zones by invasive non-native plants (INNP) remain poorly understood. Responses of terrestrial macroinvertebrate morphospecies to invasion by two common INNP, Fallopia japonica (Japanese knotweed) and Impatiens glandulifera (Himalayan balsam) were assessed, relative to local environmental factors. Terrestrial invertebrates were collected from 20 sites on low order streams in June and August alongside data on physical attributes and land use. Greater cover of F. japonica and I. glandulifera cover reduced total invertebrate abundance and morphospecies diversity at the individual sample scale, whilst increasing spatial heterogeneity of invertebrates at the site scale. Impatiens glandulifera reduced morphospecies diversity at the site scale with increasing cover, but this was not observed for F. japonica. INNP affected terrestrial invertebrate morphospecies abundance and diversity, to a greater extent than prevailing environmental conditions. Our findings therefore offer support for managing riparian plant invasions to improve habitat heterogeneity, restore terrestrial invertebrate diversity and repair aquatic-terrestrial linkages.

Aquatic invasive species rapid response planning partnerships in the Lake Champlain basin: Bridging international, political, social, and economic gaps

The Lake Champlain Basin is threatened by several non-native invasive plant and animal species. The U.S. states of Vermont and New York, and the province of Quebec, Canada share the Lake Champlain watershed. The three jurisdictions work together to protect their water resources and implement Opportunities for Action, a long-term watershed management plan for the Basin. Together they recognise the need to control the introduction, spread, and impact of non-native invasive species in order to preserve the biological and ecological integrity of the Lake Champlain ecosystem independent of political borders. The Lake Champlain Basin Program Aquatic Nuisance Species Subcommittee is developing an invasive species rapid response action plan that addresses invasive species control and spread prevention in the Basin. A rapid response is an effort to contain and control non-native invasive species introductions while they are localised in a short amount of time, such as weeks or months, before they become established and more expensive to manage. Lake managers, policy makers, scientists, academics, and representa- tives of local watershed organisations from the three jurisdictions have shared information and data to foster the development of a comprehensive plan. Gaps in interstate and inter-jurisdictional laws and policy have been identified by reviewing all necessary permits for aquatic invasive species control methods. Examining the interface of law, policy, and permits aids in identifying regulatory and policy inadequacies, and opportunities for corrective legislation. Partnering among diverse organisations has allowed strategic invasive species rapid response planning that builds on managers' and policy makers' concerns, provides options, fosters inter-jurisdictional cooperation, and considers social, economic, and political impacts of invasive species man- agement. The rapid response planning process identifies lead agencies from each of the three jurisdictions, recommends the formation of one governing body, and includes detailed steps of a rapid response process. The goal of the rapid response plan is to foster dialogue among permit applicants, scientists, and regulatory agencies, to ensure the fastest action possible. The Lake Champlain Basin invasive species rapid response planning process provides an applicable model for the United Nations Educa- tional Scientific Organisation Hydrology for the Environment, Life, and Policy (HELP) basins around the world.

Herbaceous Vegetation Responses to Gap Size within Natural Disturbance-Based Silvicultural Systems in Northeastern Minnesota, USA

The use of silvicultural systems that emulate aspects of natural disturbance regimes, including natural disturbance severities and scales, has been advocated as a strategy for restoring and conserving forest biodiversity in forests managed for wood products. Nonetheless, key information gaps remain regarding the impacts of these approaches on a wide range of taxa, including understory plant species. We investigated the 6- or 7-year response of herbaceous vegetation to natural disturbance-based silvicultural harvest gaps in a northern hardwood forest in Northeastern Minnesota. These results indicate that harvest gaps are effective in conserving understory plant diversity by promoting conditions necessary for disturbance-dependent understory plant species. However, harvest gaps also contained non-native invasive plant species.

Sexual Reproduction of Kudzu (Pueraria montana [Lour.] Merr.) in Oklahoma

Non-native invasive plants pose major threats to biodiversity across the globe. In the southeastern United States, kudzu ( Pueraria montana [Lour.] Merr.) was introduced as a flowering, ornamental vine. In many areas, it quickly escaped cultivation and has caused major disruption to native ecosystems. Over the past two decades, kudzu has gradually spread north and west, being found as far north as Illinois and Indiana, and as far west as Kansas and Oklahoma. Only recently has the species distribution been thoroughly assessed in Oklahoma, and these studies have found its statewide range to be more extensive than previously thought. As a result of the species being understudied in the region, the reproductive ecology of kudzu in Oklahoma has gone largely unexamined. Our research provides evidence of sexual reproduction at two sites in southeastern Oklahoma. This is the first documentation of germination of kudzu in Oklahoma. While kudzu reproduces primarily through rhizomatous vegetative growth, the production of viable seeds is essential to the maintenance of genetic diversity and is often important at range limits. This research, coupled with further plant demographic research, could provide key details surrounding the potential further spread of kudzu in Oklahoma.

Stream invertebrate diversity reduces with invasion of river banks by non‐native plants

Abstract Invasion of riparian zones by non‐native plants is a global issue and commonly perceived as a challenge for river and fishery managers, but the type and extent of ecological changes induced by such invasions remain poorly understood. Established effects on sediment delivery, allochthonous inputs, and channel shading could potentially alter aquatic macroinvertebrate assemblages, with implications for in‐stream ecological quality. We assessed responses in the diversity, quality, and heterogeneity of stream macroinvertebrate communities to riparian invasion by non‐native plants. Macroinvertebrates were collected from 24 sites on low order streams in central and southern Scotland during spring and autumn. The effect of invasive non‐native plants (INNP) on macroinvertebrates was assessed relative to that of local physical and chemical factors. Invasive non‐native plants cover was associated with stronger effects than other factors on local diversity of macroinvertebrates (33% reduction at the highest INNP cover) but also increased macroinvertebrate abundance across sites. Invaded sites were also associated with lower macroinvertebrate biomonitoring scores. Community composition differed between invaded and uninvaded sites in autumn, but not in spring. However, INNP influence on macroinvertebrate composition was generally secondary to that of physicochemical variables (e.g. channel shade, substrate diversity). We demonstrate that the influence of INNP extends beyond well‐known impacts on plant communities to reductions mainly in stream macroinvertebrate diversity. Combined with the negative impact on pollution‐sensitive macroinvertebrate taxa this raises concerns over the ecological health of streams with heavily invaded riparian zones. Our findings suggest that efforts to improve low order streams by actively managing severe riparian invasions are merited, but the size and uncertainty of the likely ecological gains must also be evaluated against the effort involved.