Abstract Wingleaf primrose-willow ( Ludwigia decurrens Walter) is a pervasive rice ( Oryza sativa L.) weed native or naturalized to South America, the Caribbean, and the southeastern United States. While it was first noted in California in 2011 and provided with the highest pest rating “A” by the California Department of Food and Agriculture, enforcing eradication or quarantine was relatively disregarded, and it did not appear to spread significantly past its initial infestation area. Here, we report the spread within four counties (Butte, Placer, Shasta, and Tehama) of California, for which it has been found up to 184 km away from the initial infestation, and the expansion of the initial infestation within Butte County. As L. decurrens is already a problematic rice weed in parts of Asia, Africa, India, and the United States, monitoring new infestations is pivotal to prevent negative economic and environmental consequences to California and the United States.
Abstract Herbicides are a critical tool for controlling aggressive invasive species, especially during large-scale restoration efforts, but their persistence in soils can hinder the establishment and success of desirable vegetation. Soil residence times differ among herbicides, and plant species exhibit variable tolerance to residues, causing difficulty in determining appropriate timelines for revegetation activities following herbicide application. Imazapyr is a herbicide commonly used to control highly aggressive species such as giant reed ( Arundo donax L.), with reported soil residence time ranging from 3 to 12 mo. However, we observed herbicide damage on foundational tree species installed more than 2 yr after imazapyr was applied to control expansive A. donax monocultures as part of a large-scale riparian forest restoration project. We monitored signs of herbicide damage and growth for willow ( Salix ) and cottonwood ( Populus spp.) individuals installed from cuttings to evaluate the relative susceptibility to and differential impacts of imazapyr residues on trees established using this standard propagation technique. Individuals from all species exhibited signs of herbicide damage, and the height of damaged individuals was significantly lower than that of healthy individuals across species. Red willow ( Salix laevigata Bebb) had the greatest percentage of damaged individuals (27%), but the smallest reduction in height due to herbicide damage (−13%). The frequency of herbicide damage was similar among Populus species (≤13%), but the fastest-growing species, black cottonwood ( Populus trichocarpa Torr. & A. Gray), experienced a much greater decline in growth (−67%) compared with Fremont cottonwood ( Populus fremontii S. Watson) (−32%) and Fremont × black cottonwood ( P. × parryi Sarg.) (−31%). The study found that imazapyr, when used to control invasive monocultural species, can have lingering, previously undocumented effects on non-target riparian vegetation. Despite these negative impacts, imazapyr is still one of the most effective treatment options for some aggressive invaders. Thus, practitioners should be aware of the potential long-term effects of imazapyr and carefully consider species selection and planting schedule during revegetation.
Abstract Bracken fern [ Pteridium aquilinum (L.) Kuhn] is an invasive species with significant ecological and economic impacts, making its detection and mapping critical for effective management. This study reviews remote sensing techniques for mapping P. aquilinum from 1996 to 2023. A total of 32 peer-reviewed articles were selected from Web of Science (WOS) and Scopus following the screening of 1,612 retrieved records. Bibliometric analysis, using VOSviewer software and social network analysis (SNA), explored keyword relationships, author collaborations, and institutional contributions. The research output shows fluctuations, publication gaps, and a resurgence in interest post-2021. Most studies (28%) were conducted in North America and Europe, with 26% originating from Africa. Key sensors identified include Landsat, Worldview-2, SPOT-5, and unmanned aerial vehicles (UAVs). Recent advancements demonstrated the effectiveness of high-resolution optical sensors and machine learning (ML) models in improving detection accuracy. However, challenges remain, including data limitations, methodological inconsistencies, and classification accuracy issues. This review emphasizes the need for higher-resolution imagery, advanced ML approaches, and standardized methodologies for improved P. aquilinum monitoring. Enhanced detection methods are crucial for effective ecological management, early intervention, and mitigation of the spread of P. aquilinum .
Abstract Many non-native invasive grass species increase wildfire activity and regenerate more quickly than native species. This invasive grass–fire cycle has severe negative consequences for ecosystems, creating a need to understand how different invasive grass species alter fuel characteristics and fire behavior, as well as effective treatments to control their abundance. To address these needs and increase fire and natural resource management preparedness, we performed a review and meta-analysis of recent (1985 to 2023) scientific literature. We focused on the Intermountain West, USA, where six dominant invasive grass species have already transformed ecosystems, including winter annuals—cheatgrass ( Bromus tectorum L.), medusahead [ Taeniatherum caput-medusae (L.) Nevski], red brome ( Bromus rubens L.), and Mediterranean grass [ Schismus arabicus Nees and Schismus barbatus (Loefl. ex L.) Thell]; and summer perennials—buffelgrass [ Pennisetum ciliare (L.) Link] and Lehmann’s lovegrass ( Eragrostis lehmanniana Nees). Within the 204 selected articles, B. tectorum was the most well-studied species, treatment effectiveness was the most common study type, and more studies addressed fuel accumulation than fire characteristics. While initial reductions in B. tectorum following wildfire were followed by large increases, P. ciliare initially increased and then steadily declined, and other invasive grass species had no significant post-fire changes over time. Chemical treatments were more effective than other treatments for B. tectorum , P. ciliare , and Schismus spp., although T. caput-medusae had a greater reduction with chemical treatments compared with the other species. In many cases, treatment effectiveness was enhanced when treatment types were combined or repeat treatments were conducted. Both B. tectorum and T. caput-medusae increased to pretreatment conditions within 3 and 5 yr, respectively, although there were no detectable trends for other species. Our results provide comprehensive comparisons of the effect of invasive grass species on fuel and fire characteristics and much needed insight on effective strategies for reducing invasive grass impacts to ecosystems.
Amur honeysuckle [Lonicera maackii (Rupr.) Herder] is an abundant invasive species throughout Kentucky and the surrounding region. It forms dense stands, outcompeting and displacing native species and adversely impacting the regeneration, succession, and biodiversity of deciduous forest communities. The objective of this study was to compare the efficacy of L. maackii removal alone relative to removal followed by restoration plantings to suppress reinvasion and facilitate forest understory native plant community recovery. In March 2019, a field experiment was conducted with the following treatments: (1) untreated control; (2) L. maackii removal with 0.023 kg ae L-1 glyphosate cut stump application (CH plots); and (3) same treatment as in (2), plus restoration plantings of wildrye grasses (Elymus spp.) and northern spicebush [Lindera benzoin (L.) Blume] (CHP plots). Lonicera maackii removal and cut stump glyphosate treatments effectively reduced L. maackii canopy cover, increased herbaceous cover, decreased bare ground, and increased species richness over time compared with untreated plots. However, we did not find any differences (P > 0.05) in L. maackii cover or other plant community variables between CH and CHP treatments over time. Thus, we found insufficient evidence that restoration plantings of Elymus spp. and L. benzoin suppressed L. maackii reinvasion compared with L. maackii removal alone. Spearman rank-correlation tests indicate L. maackii removal correlated with increased herbaceous cover (rho = -0.75, P < 0.0001), lower bare ground (rho = 0.714, P < 0.0001), and higher species richness (rho = -0.693, P < 0.0001). Further studies of L. maackii removal plus restoration plantings are needed that test different species combinations and/or season of planting (i.e., spring vs. autumn) to determine the most effective restoration planting strategy to simultaneously suppress L. maackii reinvasion after removal and facilitate native plant community recovery in forest understories.
Leafy spurge (Euphorbia esula L.) and yellow toadflax (Linaria vulgaris Mill.) are pervasive weeds of pasture and rangeland in the Northern Great Plains. There are few effective herbicides to manage these species. Saflufenacil is a contact herbicide that is labeled to suppress perennial weeds when applied alone; however, saflufenacil+imazapic is labeled to effectively manage E. esula. While there are no currently published data regarding the effectiveness of saflufenacil alone or in mixtures with various herbicides, mixing herbicides with different modes of action can increase management effectiveness. Therefore, mixtures containing saflufenacil and various herbicides may effectively manage E. esula and L. vulgaris. Experiments were conducted to determine the effectiveness of mixing commonly applied herbicides (E. esula: imazapic and picloram; L. vulgaris: aminocyclopyrachlor and picloram) with saflufenacil to manage these weed species. Saflufenacil alone was the least effective on both species, as expected, due to the contact activity of the herbicide. Herbicide mixtures provided equal or greater responses (control estimates, height and stem reductions) than the tested herbicides applied alone. Mixing saflufenacil with the tested herbicides resulted in additive control estimates, plant height, and stem density reductions for both species 1 yr after treatment (YAT). Stem density reductions for E. esula never exceeded 79%, while L. vulgaris stem reductions were as much as 90% with herbicides at 1 YAT when compared with the nontreated. The results of these experiments suggest that saflufenacil could be mixed with commonly applied herbicides to increase the effectiveness of managing E. esula and L. vulgaris. However, additional management tactics will likely be necessary after 1 yr to successfully further reduce the infestations of these weed species.
Lesser celandine (Ranunculus ficaria L.) is an ephemeral perennial invasive species on which limited research has been conducted. In a field experiment, we studied methods of R. ficaria control and the effects of different control methods on the response of the native understory. In a full-factorial study, we used two different types of herbicides (glyphosate or imazapyr), two different concentrations of herbicide (low or high), and three different dates of herbicide application (pre-flowering in mid-March, flowering in early April, or post-flowering in early May). Treatments were applied in 2 by 2 m plots in heavily infested riparian areas (100% cover of R. ficaria in each plot) at three different sites in southwestern Ohio. Treatment combinations were replicated three times per site. One year later, plots were measured for percent cover of R. ficaria and percent cover of native species. Imazapyr was most effective in reducing R. ficaria regardless of application date, while the effectiveness of glyphosate application decreased over the season. The presence of native species 1 yr later was affected by date of application. Application in mid-April led to greater native species cover than application in early May, with applications in mid-March intermediate between the two. We found that there were differences among sites in efficacy of control and in the cover of native species, which are likely related to differences in conditions at each site.
The broad-leaved Zornia, Zornia latifolia Sm. (Fabaceae), is a perennial herb, known for reported psychoactive and medicinal properties, with a native range from Argentina to South Texas and some West Indian islands. There is disagreement on the status of Z. latifolia in Florida concerning whether it is a native species, an established non-native species, or a waif (i.e., a non-native species growing outside cultivation, but not maintaining a viable population). In Florida, there is only one published record of Z. latifolia growing outside cultivation, in Hillsborough County, but multiple records of this species cultivated for research. I observed extensive populations of Z. latifolia in St Lucie, Martin, Palm Beach, and Orange counties, and confirmed observations posted online from Hillsborough County. Based on the recentness of its first record of growing outside cultivation in Florida (2015), its substantial persistent populations at multiple locations in peninsular Florida, and its occurrence primarily in and adjacent to mowed areas, Z. latifolia appears to be an established non-native species in the state. Whether it becomes a major invasive species in Florida remains to be seen.
Post-seeding vegetation management is critical for restoring grasslands dominated by invasive species, yet few studies have evaluated these strategies in the Aspen Parkland ecoregion. We tested the effects of no treatment (Control), mowing-only (Mow), herbicide-only (Herbicide; aminopyralid 52.5% + metsulfuron-methyl 9.45% at 230 g ai ha(-1)), and mowing and herbicide application (Combination) on plant community composition, diversity, and biomass over two growing seasons following seeding of seven cool-season native grass species. The study was conducted on a disturbed site in Edmonton, AB, Canada, where non-native Canada thistle [Cirsium arvense (L.) Scop.], field sowthistle (Sonchus arvensis L.), and smooth brome (Bromus inermis Leyss.) dominated before treatment. Treatments with aminopyralid + metsulfuron-methyl (aminopyralid + metsulfuron-methyl alone and Combination) significantly reduced noxious and introduced species richness and cover (P < 0.001), eliminated forbs, and shifted plant composition toward greater dominance by seeded and native grasses. However, these treatments also eliminated native shrubs [Woods' rose (Rosa woodsii Lindl.) and western snowberry (Symphoricarpos occidentalis Hook.)], reduced litter biomass, and increased bare ground. The Mow treatment maintained high species richness and forb biomass, with noxious and introduced species remaining dominant and seeded species establishment improving slightly relative to the control. Despite differential species responses, overall seeded species richness, diversity, and cover did not differ significantly among treatments. Needle and thread grass [Hesperostipa comata (Trin. & Rupr.) Barkworth], Western wheatgrass [Pascopyrum smithii (Rydb.) & Aacute;. L & ouml;ve], and green needle grass [Nassella viridula (Trin.) Barkworth] showed moderate establishment under treatments with aminopyralid + metsulfuron-methyl, while Plains rough fescue [Festuca hallii (Vasey) Piper], Idaho fescue (Festuca idahoensis Elmer), Rocky Mountain fescue (Festuca saximontana Rydb.), and June grass [Koeleria macrantha (Ledeb.) Schult.] established less in any treatment. Community composition diverged most between treatments with aminopyralid + metsulfuron-methyl and the Control treatment. These results highlight trade-offs between invasive species control and impacts on non-target natives and ecosystem function. Among the treatments, aminopyralid + metsulfuron-methyl alone provided the most balanced outcome, suppressing invasive species while minimizing soil disturbance and improving seeded grass recruitment. This study highlights the importance of integrating vegetation treatments with species-specific seeding when restoring heavily invaded grasslands in the Aspen Parkland.
The decline of native plant species associated with alien plant invasion is often assumed to be driven by competitive exclusion. However, invasive alien plant species could also directly or indirectly impact native plants by limiting reproductive success. Here, we tested whether invasive alien plants influence seed production, viability, and germination using the Benjoin [Terminalia bentzoe (L.) L.f. subsp. bentzoe], a critically endangered tree endemic to the Mascarene Islands (southwest Indian Ocean), as a model species. Seed production was estimated from seed densities under the canopy of adult individuals from one of the largest remaining subpopulations of the species (in Cirque de Mafate, Reunion Island). Seed viability was determined using a tetrazolium test on the different sets of seeds collected in the field. Densities of seeds and viable seeds were then tested for correlation with the percentage cover of invasive alien plant species in the liana, tree, shrub, and herbaceous forest layers. Seed germination was studied by sowing seeds in soils where three alien invasive plants, three endemics, and T. bentzoe subsp. bentzoe had previously been grown. Seed production and viability decreased with increasing abundance in invasive alien plants in the liana and tree strata but not in the lower vegetation strata. Mechanisms specific to tall-statured invasive alien plants could include competition for resources, interference with pollinator behavior and mechanical constraints. Seed germination was inhibited by the invasive alien succulent Mauritius hemp [Furcraea foetida (L.) Haw.] and T. bentzoe subsp. bentzoe itself, but enhanced by the endemic tree species Poupartia borbonica J.F.Gmel. These species may differ in their resource use intensity, associated microbial communities, and allelopathic effects. Our findings therefore suggest that plant invasions can significantly contribute to the decline of native plants through reduced reproductive ability and induce an extinction debt due to a lack of regeneration.
To effectively prioritize the management of invasive plants, it is necessary to reduce the risks posed by trade. This is particularly critical for the ornamental plant sector, which acts as a primary pathway for the introduction and distribution of non-native plant species. In this context, it is necessary to understand the perceptions of ornamental plant producers, who are the primary actors in the ornamental plant trade, about non-native plants and their impacts and risks. Using the Alt & imath;nova District of Yalova Province, T & uuml;rkiye, we conducted a survey to explore the perceptions of 20 ornamental plant producers regarding non-native and invasive ornamental plant taxa. We also generated a list of ornamental plant taxa produced in the study area by using local sources referencing ornamental plants (such as producers' catalogs). We found that of the 121 plants produced, 92 taxa were non-native, 23 were native, and 6 were non-native hybrids, of which 31 taxa (11 taxa native and 20 taxa non-native to T & uuml;rkiye) were found to be invasive elsewhere. Most of the plants produced were perennials (103 taxa). The vast majority of producers (70%) had heard the term "invasive plant" before. However, the concept of invasive plants is considered in the context of "plants other than for production purposes, i.e., weeds." There is a lack of awareness among producers about the possible impacts caused by non-native taxa and their management status. We conclude that appropriate regulations should be made for the sale and use of non-native plants, and awareness activities should be organized for all stakeholders and the public. Further research is required to identify, prioritize, and manage non-native ornamental plants and their potential impacts across all countries engaged in the ornamental plant trade to prevent future ornamental plant invasions.
Invasive, non-native plants frequently restructure ecosystems by homogenizing vegetation and altering trophic interactions, but the ecological consequences of invader removal are less predictable. Removal can redistribute light, nutrients, and detrital resources, initiating community reassembly that extends beyond vegetation recovery and may facilitate secondary invasions. We used a single-site invasive-removal field study to examine how management of European buckthorn (Rhamnus cathartica L.) reshaped vegetation structure, litter accumulation, and faunal communities in a postindustrial forest preserve in western New York State, USA. Across 18 plots representing managed, not-treated, and regrown R. cathartica conditions, we quantified herbaceous vegetation, leaf litter biomass, and the abundance of arthropods, pollinators and small mammals. Rhamnus cathartica removal was associated with a 10-fold increase in herbaceous plant cover and species richness, producing structurally complex understories and higher arthropod and pollinator abundance. However, managed plots also supported 3- to 5-fold higher densities of the invasive European fire ant (Myrmica rubra)-corresponding with increased leaf litter in managed plots. Ant abundance was positively associated with thicker, more persistent litter layers rather than canopy openness, and increasing M. rubra density, in turn, corresponded with reduced pollinator abundance. Detritivore and rodent responses were more closely linked to vegetation structure and litter conditions than to ant abundance.
Hydrilla [Hydrilla verticillata (L.F.) Royle] is a known, persistent aquatic weed in many lakes and reservoirs across the United States. Recently, focus has been placed on the management of invasions of H. verticillata into flowing systems due to increased difficulty in achieving effective control. In flowing environments, increased flow and water exchange rates commonly result in shorter herbicide exposure times using traditional application techniques. This research evaluated the concept of intermittent herbicide exposure as a potential management strategy to overcome operational challenges in high water exchange environments. Monoecious H. verticillata response to intermittent exposure to florpyrauxifen-benzyl, endothall, and fluridone at multiple concentrations and nontreatment intervals was evaluated in greenhouse-scale mesocosm experiments. Decreased efficacy was not observed when nontreatment intervals between exposures were introduced in florpyrauxifen-benzyl treatments. Monoecious H. verticillata treated with 30 & micro;g ai L-1 florpyrauxifen-benzyl and a 6-d nontreatment interval resulted in 89% reduction in aboveground biomass. Nontreatment intervals did not influence endothall efficacy and biomass reduction increased with herbicide concentration (66% to 93%). Fluridone treatments at 5 & micro;g L-1 resulted in 82% biomass reduction, while treatments at 10 and 15 & micro;g L-1 resulted in 89% biomass reduction. Biomass reduction was slightly lower in fluridone applications with a 12-d nontreatment interval (83%) compared with other nontreatment intervals (85% to 91%). The high biomass reduction and similar response between treatments observed suggests the need for additional refinement and operational verification of intermittent herbicide exposures for monoecious H. verticillata control to increase cost-effectiveness and efficiency in public H. verticillata control programs.
Submerged aquatic vegetation (SAV) is often underdocumented at the species level in routine monitoring and regulatory assessments, where vegetation is commonly recorded without species-level identification. Here, we present a summary of existing records and field collections made in the Pennsylvania portion of Monongahela River system. Our findings suggest that the dominant SAV in this river is hydrilla [Hydrilla verticillata (L. f.) Royle], one of the most aggressive invasive macrophytes in North America. Further, our recent collections indicate the presence of other invasives: Eurasian watermilfoil (Myriophyllum spicatum L.) and curlyleaf pondweed (Potamogeton crispus L.). Native species such as coontail (Ceratophyllum demersum L.) and vallisneria (Vallisneria americana Michx.) were present but not prominent in sampled locations. The documentation of H. verticillata and other non-native invasive SAV species suggests that the Monongahela River is now hosting an invasive epidemic, one that may have widespread ecological implications.
Cogongrass [Imperata cylindrica (L.) P. Beauv.] is a recalcitrant invasive grass widespread in the southeastern United States. In non-crop systems, management relies on foliar applications of glyphosate and imazapyr; multiple applications over several years are often required, increasing labor, logistical, and chemical costs. Although numerous herbicide alternatives have been evaluated, few match the efficacy of glyphosate or imazapyr. Glufosinate is a broad-spectrum herbicide, and demand for glyphosate alternatives has generated interest in its potential for invasive grass management, but long-term evaluations of glufosinate and tank mixes for I. cylindrica are limited. This study evaluated single foliar spot applications of glufosinate (2.0 kg ae ha-1) alone and in tank mixtures with glyphosate (3.4 kg ae ha-1) or imazapyr (1.1 kg ae ha-1) at three Florida field sites heavily invaded (88% to 92% cover) by I. cylindrica using percent cover and belowground biomass. All treatments containing glufosinate produced rapid foliar necrosis, reducing cover to 15% to 21% within 14 days after treatment (DAT). By 270 DAT, cover increased in the glufosinate-alone (43%) and glufosinate + glyphosate (42%) treatments but remained approximately 25 to 30 percentage points lower than the control. At 540 DAT, cover in these treatments did not differ from that in the control. Across all sites, I. cylindrica cover at 540 DAT was reduced relative to the control by glyphosate (37%), imazapyr (9%), imazapyr + glufosinate (7%), and imazapyr + glyphosate (11%). Notably, the imazapyr + glufosinate mixture produced both rapid and sustained reductions in I. cylindrica cover. These results suggest glufosinate alone provides short-term suppression of aboveground tissue but can be enhanced through tank mixing with soil-active herbicides such as imazapyr to improve long-term suppression of belowground meristems.
Water hyacinth (Pontederia crassipes Mart.) is a free-floating aquatic plant native to South America that has spread to nearly 50 countries, becoming one of the world's most invasive aquatic weeds. In Florida, the biocontrol agents Neochetina eichhorniae and Neochetina bruchi were released in 1970s, while Megamelus scutellaris was released in 2010. Assessing the impact of these biocontrol agents is crucial in evaluating efficacy, distribution, and overall progress in management efforts. The traditional survey and monitoring methods used to evaluate the impact of biocontrol present numerous challenges in data acquisition, especially in remote areas and aquatic habitats. This study aimed to detect damage caused by Neochetina spp. and M. scutellaris on P. crassipes using hyperspectral remote sensing. Plants were exposed to varying levels of Neochetina spp. and M. scutellaris herbivory for 2 and 4 wk under laboratory conditions. After the exposure period, the plants were scanned using a visible and near-infrared hyperspectral imaging system. Two classification algorithms, partial least-squares discriminant analysis (PLS-DA) and support vector machine (SVM) were employed for classification. SVM achieved high classification accuracy at both low and high damage levels, with overall training and validation accuracies of 84.9% and 78.79%, respectively, while PLS-DA only achieved high classification accuracy at high damage levels, with overall training and validation accuracies of 56.3% and 60.38%. Based on the observed performance metrics, both algorithms demonstrated improved classification accuracy as damage increased over time. The results indicated that hyperspectral remote sensing can be used to monitor and assess biocontrol agents damage on P. crassipes.
Boneseed [Chrysanthemoides monilifera subsp. monilifera (L.) Norl.; syn. Osteospermum moniliferum subsp. moniliferum L.] is a perennial shrub native to the southwestern and southern coasts of South Africa. It was introduced to Australia in about 1852 and now represents a significant threat to natural ecosystems. Despite C. monilifera subsp. monilifera being listed as a Weed of National Significance, momentum on improving its management has dissipated at a national level, beginning in 2008 (when a national research initiative finished) and increasingly after 2013 (when funding for national coordination ceased). A recent synthesis of past management for C. monilifera subsp. monilifera and recommendations for guiding future priorities has rekindled interest in Western Australia. To complement this synthesis and to identify improvements for program efficiency and effectiveness, we reviewed research and management findings on this weed with a focus on the past two decades. We collated information across the ecology and biology of C. monilifera subsp. monilifera, and the near relative, bitou bush [Chrysanthemoides monilifera subsp. rotunda (DC.) J.C. Manning & Goldblatt; syn. Osteospermum moniliferum subsp. rotundatum (DC.)], as well as useful insight from C. monilifera subsp. monilifera management programs applied elsewhere. As part of this review, we assessed the classical biological control work that has been done on C. monilifera subsp. monilifera, focusing on likely explanations for why, despite nine agents and a naturalized fungus, biological control is not an effective management tool. Our synthesis suggests that for the limited populations with low-abundance plants in Western Australia, eradication from the state remains a realistic target. This objective, however, needs to build on the collated baseline of past management efforts and deploy a carefully planned management program over the coming two decades. Systematic surveillance using the latest techniques, combined with manual or herbicide removal and controlled burns where possible, remain the most suitable methods to deploy. The long-lived soil seedbank requires detailed monitoring following initial plant removals and long-term funding to ensure the sustained effort required to deliver the goal of eradication of C. monilifera subsp. monilifera in Western Australia.
The invasive plant species Japanese hop (Humulus japonicus Siebold & Zucc.) and reed canarygrass (Phalaris arundinacea L.) are increasing in cover in Upper Mississippi River (UMR) floodplains, where they negatively impact native vegetation. This study evaluated novel reforestation methods to rapidly close canopy openings colonized by invasives and reduce their cover at four study sites ranging from southern Wisconsin to southwestern Illinois. Each site contained three replicates of four 20 by 20 m plots comprising four tree-planting treatments. These included two using large-diameter willow (Salix) cuttings planted at different densities, one using container stock of American sycamore (Platanus occidentalis L.) and eastern cottonwood (Populus deltoides W. Bartram ex Marshall), and a control plot with no planted trees. Half of each planting treatment also received maintenance treatments for invasives control. Results indicated that planting and maintenance had significant effects on tree survival, invasives cover, and plant community diversity. Specifically, trees that received maintenance had higher survival than those that did not, and Salix cuttings had higher survival than container stock. Annual tree height growth was greatest in Salix cuttings planted at the highest density. Invasive species cover declined significantly in maintenance treatments and Salix plantings. Change in plant community diversity was greater in maintenance treatments and in Salix plantings, but was still extremely low at the northernmost site. Vegetation patterns were strongly influenced by invasives and reinforced the general inverse relationship between plant community diversity and invasives cover. Overall, results indicated that tree plantings using large Salix cuttings can be an effective method to quickly reforest areas along the UMR that have been colonized by invasive plant species and that incorporating tree-planting maintenance activities in early years can lead to better survival.
Smooth bromegrass (Bromus inermis Leyss.) is an introduced, perennial, cool-season invasive grass that has invaded native rangelands in the Great Plains. Defoliation at specific growth stages may reduce the abundance of B. inermis, but information is limited about when this should occur. Between 2018 and 2020 we assessed how defoliation at four different phenological stages influenced the amount of outgrowth on B. inermis tillers near Mandan, North Dakota, USA. In three replicated plots, we evaluated axillary buds, tillers, and rhizome outgrowth. Treatments consisted of defoliating B. inermus at a height of 5 cm at one of the following phenological stages: (1) once in the vegetative stage, (2) twice in the vegetative stage, (3) once in the elongation stage, (4) once in the reproductive stage, and an undefoliated control. Individual tillers were collected in the fall following defoliation and processed in the laboratory. Each year 10 tillers were defoliated at each phenological stage for a total of 50 tillers plot-1 year-1. The total number of crown positions was determined for each tiller and outgrowth (tillers and rhizomes), and the number of axillary buds was counted on each tiller. A double-staining technique was used to determine active, dead, and dormant axillary buds. Tillers defoliated twice in the vegetative stage had less outgrowth per tiller than tillers defoliated once in the reproductive stage or the undefoliated controls (new outgrowth of 1.2, 2.2, and 1.8 per tiller for twice vegetatively, reproductive, and control respectively). Results show that defoliating tillers in the elongation or reproductive stage resulted in nearly complete tiller mortality. Our data suggest managers who wish to reduce B. inermis abundance should focus on defoliating it twice in the vegetative stage and avoid defoliating B. inermis in the reproductive stage to limit outgrowth.
Tree of heaven [Ailanthus altissima (Mill.) Swingle] is an invasive tree that inhibits regeneration of forests. Management of forests invaded by A. altissima often includes chemically treating it and leaving dead boles behind. Verticillium wilt (Verticillium nonalfalfae) infects some populations of A. altissima, leading to localized mortality. Areas with population-wide A. altissima mortality may increase as this disease spreads or is used as a biocontrol agent. Ailanthus altissima has documented allelopathic compounds; stems left to decompose may result in soil legacy effects that negatively impact native plant restoration. The goal of this study was to determine whether soil under decomposing A. altissima wood has negative impacts on native perennial plant germination and growth. Ailanthus altissima was grown in a garden for 4 yr, basally cut, and treated with herbicide. The stems were sectioned and stacked into piles to decompose for 18 mo on grass and garden fabric, after which the wood was mulched. Soil from cores taken under each woodpile was added over potting media in pots in which seeds of three native perennials (purple coneflower [Echinacea purpurea (L.) Moench], dogbane (Apocynum cannabinum L.), and false nettle [Boehmeria cylindrica (L.) Sw.]) were planted. Seeds for half the pots were covered with potting media or mulch, respectively. The plants were grown under high- and low-light conditions in a greenhouse for 3 mo. Germinations were tallied, and dry shoot biomass was determined. Pots with woodpile soil had lower germination and biomass production for two of the native species, but mulch reduced the impact. Biomass was greater for all soil treatments with mulch added compared with treatments with no mulch. Plants growing in soil under garden fabric had germination values similar to plants in woodpile soil. This study reveals that soil under decomposing A. altissima wood is likely to negatively impact germination and growth of some newly seeded species for at least 18 mo.
