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Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] is an invasive plant, native to the New World, and an exemplary conflict species. It has been planted widely for its ornamental and soil fertility enhancement qualities and has become a notorious environmental weed in introduced habitats. Here we use a bioclimatic niche model (CLIMEX) to estimate the potential global distribution of this invasive plant under historical climatic conditions. We apply a future climate scenario to the model to assess the sensitivity of the modeled potential geographic range to expected climate changes to 2050. Under current climatic conditions, there is potential for substantial range expansion into southern Europe with moderate climate suitability, and in southern China with highly suitable climates. Under the near-term future climate scenario, there is potential for poleward range expansion in the order of 200 to 500 km. In the tropics, climatic conditions are likely to become less favorable due to the increasing frequency of supra-optimal temperatures. In areas experiencing Mediterranean or warm temperate climates, the suitability for T. diversifolia appears set to increase as temperatures warm. There are vast areas in North America, Europe, and Asia (particularly China and India) that can support ephemeral populations of T. diversifolia. One means of enjoying the aesthetic benefits of T. diversifolia in gardens while avoiding the unwanted environmental impacts where it invades is to prevent its spread into areas climatically suitable for establishment and only allow it to be propagated in areas where it cannot persist naturally.
Land managers require tools that improve understanding of suitable habitat for invasive plants and that can be incorporated into survey efforts to improve efficiency. Habitat suitability models (HSMs) contain attributes that can meet these requirements, but it is not known how well they perform, as they are rarely field-tested for accuracy. We developed ensemble HSMs in the state of Wisconsin for 15 species using five algorithms (boosted regression trees, generalized linear models, multivariate regression splines, MaxEnt, and random forests), evaluated performance, determined variables that drive suitability, and tested accuracy. All models had good model performance during the development phase (Area Under the Curve [AUC] > 0.7 and True Skills Statistic [TSS] > 0.4). While variable importance and directionality was species specific, the most important predictor variables across all of the species’ models were mean winter minimum temperatures, total summer precipitation, and tree canopy cover. Post model development, we obtained 5,005 new occurrence records from community science observations for all 15 focal species to test the models’ abilities to accurately predict results. Using a correct classification rate of 80%, just 8 of the 15 species correctly predicted suitable habitat (α ≤ 0.05). Exploratory analyses found the number of reporters of these new data and the total number of new occurrences reported per species contributed to increasing correct classification. Results suggest that while some models perform well on evaluation metrics, relying on these metrics alone is not sufficient and can lead to errors when utilized for surveying. We recommend any model should be tested for accuracy in the field before use to avoid this potential issue.
Pale swallowwort [Vincetoxicum rossicum (Kleopow) Barbar.; syn.: Cynanchum rossicum (Kleopow) Borhidi] and black swallowwort [Vincetoxicum nigrum (L.) Moench; syn.: Cynanchum louiseae Kartesz & Gandhi] are invasive perennial viny milkweeds that have become prevalent across natural and managed habitats in northeastern North America. Southern blight of V. rossicum caused by the fungus Athelia rolfsii (Curzi) C. C. Tu & Kimbr. was reported at a New York county park in 2008, resulting in a decline in V. rossicum stands. The disease outbreak and persistence of the pathogen highlighted the potential of A. rolfsii for Vincetoxicum spp. control. To better characterize A. rolfsii’s pathogenicity and biology, we studied virulence to adult Vincetoxicum spp., spatiotemporal attributes of the Southern blight epidemic at the discovery site over 4 yr, and sclerotial survival over 2 yr. Disease incidence and severity were high for both Vincetoxicum spp. in misting chamber experiments. The spatiotemporal spread patterns of Southern blight in V. rossicum suggest the epidemic in the first year of monitoring (2016) was already highly aggregated and that subsequent spread was limited and resulted in significant local aggregation. Sclerotial survival studies at two locations (Pittsford and Ithaca, NY) demonstrated the A. rolfsii isolates can overwinter in upstate New York and are pathogenic to Vincetoxicum spp. the subsequent season. However, shallow burial of sclerotia more rapidly reduced survival compared with placement on the soil surface. Overwinter survival of A. rolfsii sclerotia in New York is notable, as this pathogen is typically associated with subtropical and tropical regions. Broadcast applications of the pathogen would be needed for widespread Vincetoxicum control at a site, but even restricting releases to select locations would not prevent pathogen movement off-site via water or machinery. The known risks of the A. rolfsii isolate to other broadleaf plants in natural and agricultural settings suggest a low feasibility of use for the biological control of Vincetoxicum spp.
Yellow-flag iris (Iris pseudacorus L.) is a nonnative, invasive wetland plant that disrupts riparian ecosystem processes and is widely distributed across the United States and Canada. Due to its physiological and morphological characteristics, I. pseudacorus has the capacity to exclude native vegetation and form extensive monocultures in both lotic and lentic wetland systems. Methods commonly used to manage I. pseudacorus include manual (e.g., hand pulling, digging) and mechanical (e.g., mowing) treatments for small populations and herbicide applications for larger populations; however, herbicide applications near water may be prohibited due to label restrictions. The objective of this research was to evaluate cattle trampling as a nonchemical method to reduce I. pseudacorus in riparian habitats. A greenhouse study was conducted to investigate the effects of inundation and two different timings of simulated trampling on I. pseudacorus density, height, and soluble sugar concentrations in the rhizomes. A complementary field demonstration was established on a ranch in northwestern Nebraska to evaluate cattle trampling effects on I. pseudacorus density and height after two consecutive years. Simulated cattle trampling in the greenhouse had no effect on I. pseudacorus density or height of non-inundated samples. However, combining trampling with inundation reduced I. pseudacorus density from a median of 10 I. pseudacorus per pot to 0 I. pseudacorus per pot and median height from 0.35 m to 0 m by the conclusion of the study. Additionally, the field demonstration resulted in reductions of both density and height of I. pseudacorus after two consecutive years (72% and 67% reduction, respectively). Soluble sugar concentrations were not impacted by any treatment.
Scientists and natural resource managers require suitable vegetation survey methods to assess the success of rangeland restoration projects. Visual estimation and point intercept methods are commonly used to evaluate vegetation cover. This study compared the performance of one visual (quadrat-based) and two line-point intercept (LPI, canopy and basal) methods to assess biodiversity and cover and to estimate biomass production on sites invaded by introduced annual grasses across Wyoming, USA. Greater species richness and higher Shannon index values were measured in quadrats, while introduced annual and native perennial graminoid cover values were higher in LPI canopy in general. Overall, these outcomes indicate quadrats as the most suitable survey method when biodiversity monitoring is the primary objective, while suggesting LPI canopy when monitoring vegetation cover is prioritized. Finally, our regression models indicated quadrat-based estimates as the most reliable to predict introduced annual and native perennial graminoid biomass.
Nonnative plant invasions can have devastating effects on native plant communities; conversely, management efforts can have nontarget and deleterious impacts on desirable plants. In the arid sagebrush steppe rangelands of the western United States, nonnative winter annual species affect forage production and biodiversity. One method proposed to control these species is to suppress the soil seedbank using the preemergent herbicide indaziflam. Our goal was to evaluate the efficacy of indaziflam to control nonnative annual mustards (Alyssum spp.) and to understand potential nontarget effects of management on the diverse mountain sagebrush steppe plant communities within Yellowstone National Park. Six sites were established along an elevation gradient (1,615 to 2,437 m), each with high and low Alyssum spp. infestations. We applied 63g ai ha−1 of indaziflam in late summer of 2018 and evaluated plant community cover in situ for 2 yr after treatment and emergence of forb species from the soil seedbank ex situ. Indaziflam was highly effective at controlling emergence of Alyssum spp. for 2 yr. Richness and Shannon’s diversity of the nontarget plant community were significantly lower in sprayed plots than in the control, and both decreased along the elevation gradient. These reductions were due to a decrease in perennial forbs and native annual forbs in the sprayed plots; perennial graminoids were not affected. Overall, the aboveground and seedbank community composition was negatively impacted by indaziflam, and these effects were strongest for the native annual forbs that rely on annual regeneration from the seedbank. The effects of this herbicide to the nontarget community should be evaluated beyond the length of our study time; however, we conclude that indaziflam should likely be reserved for use in areas that are severely invaded and have seedbanks that are composed of nondesirable species rather than diverse, native mountain sagebrush communities.
In 1994, a general population survey was conducted to evaluate Montanans’ knowledge about noxious weeds, and results from that survey launched an ongoing statewide education campaign. In 2019, we conducted another general population survey to assess the views and behaviors of Montanans as they relate to noxious weeds and to identify new approaches for disseminating noxious weed information. We also asked questions to evaluate changes over the 25-yr period, although our ability to make direct comparisons is subject to limitations. We implemented a mail-based survey in March through May 2019. The response rate was 18%, with 830 responses from 4,582 valid mailing addresses. Just under half (48%) of respondents report “little” or “no” knowledge about noxious weeds, which would constitute a 19-point improvement since 1994. A large majority (68%) of respondents indicate that noxious weeds are a “serious” or “very serious” problem, and appreciation for the range of negative impacts associated with noxious weeds is considerable. Most respondents (61%) identify humans as contributing “a lot” to noxious weed spread, and respondents report that their behaviors to prevent the spread of noxious weeds have increased over time. While the 1994 respondents rated television, newspaper, and radio as the best ways to disseminate information about noxious weeds, respondents now also recognize methods such as websites and social media pages as effective. Our survey identifies a need for increased educational messaging for women and people in the 18 to 39 age group. Overall, our results indicate that individuals who have seen different forms of advertisements and have participated in educational programs are more likely to consider noxious weeds a serious problem and to engage in behaviors to stop their spread.
Invasive winter annual grasses, such as cheatgrass (Bromus tectorum L.) are considered serious threats to regional biodiversity. Pollinator populations that depend on the native flora are likely to be negatively impacted as these native species may be displaced by the invasive grass species. Colonization by cheatgrass is also predicted to increase risk of wildfires, as dead plant parts provide fuel in the already dry and arid regions of the western United States. Biocontrol, grazing, prescribed burning, or use of broad-spectrum nonselective herbicides have been suggested as possible means to control B. tectorum. Efficient control may facilitate regrowth of native flora that could in turn support other ecosystem functions. Reporting our findings as a case study, we describe here the results of the application of a preemergent herbicide, indaziflam, that limits germination of B. tectorum seeds. Herbicide was applied to the study locations during the months of December 2016, January 2017, and February 2017. The data reported here on the diversity of flowering plants were collected between May through September 2018. Herbicide-treated plots showed an increase in diversity and abundance of flowering plants compared to the untreated control within two seasons after cheatgrass control was implemented, suggesting that effective reduction of the population of the invasive annual cheatgrass may help facilitate the growth of native forbs. Further studies are necessary to understand mechanisms that facilitate reestablishment of native flowering species, the long-term consequences of reducing invasive annual grasses and to document any residual effects of the herbicide on ground-nesting pollinators.
Individual plant treatment (IPT) techniques (e.g., basal bark, cut stump, hack and squirt) are used for woody invasive plant management and often rely on small trigger-pump spray bottles as an economical and efficient way to deliver a herbicide to the target species. Worldwide, plastic suppliers produce many models and designs with a wide range of uses, including pesticide application. However, spray bottle performance has rarely been examined in relation to IPT techniques for operational invasive plant management. We tested 10 commonly available spray bottles for trigger output and variation over repeated strokes. We also examined sustained trigger sprayer performance over a 6-wk period for spray bottles containing water or basal oil carriers blended with amine and ester formulations of triclopyr, respectively. In the first study, we found significant differences in spray output per stroke between almost every bottle tested. Almost all spray bottle brands yielded outputs greater than 1.0 ml per stroke, which exceeds the maximum application amount specified for hack and squirt. Several bottles produced an output of greater than 2.5 ml per stroke. In the second study, the output per stroke was reduced for basal oil mixes, with significant reductions measured for two brands by 21 d and for all three brands tested by 42 d after mixing. These results indicate that consumer-grade trigger sprayers are likely to depreciate rapidly with routine operational use without proper hygiene maintenance. Even then it is likely that these application devices may need to be replaced several times annually. Trigger-pump spray bottles are an economical and practical solution for remote field operations and volunteer weed control activities. These sprayers are most suitable for spray-to-wet techniques such as basal bark and cut-surface treatments but may potentially be less suited for hack and squirt application, which often requires sub-milliliter precision.