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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 12 yr 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.

Exotic plant invasions and chronic high levels of herbivory are two of the major biotic stressors impacting temperate forest ecosystems in eastern North America, and the two problems are often linked. We used a 4-ha deer exclosure maintained since 1991 to examine the influence of a generalist herbivore, white-tailed deer (Odocoileus virginianus), on the abundance of four exotic invasive (Rosa multiflora, Berberis thunbergii, Rubus phoenicolasius and Microstegium vimineum) and one native (Cynoglossum virginianum) plant species, within a 25.6-ha mature temperate forest dynamics plot in Virginia, USA. We identified significant predictors of the abundance of each focal species using generalized linear models incorporating 10 environmental and landscape variables. After controlling for those predictors, we applied our models to a 4-ha deer exclusion site and a 4-ha reference site, both embedded within the larger plot, to test the role of deer on the abundance of the focal species. Slope, edge effects and soil pH were the most frequent predictors of the abundance of the focal species on the larger plot. The abundance of C. virginianum, known to be deer-dispersed, was significantly lower in the exclosure. Similar patterns were detected for B. thunbergii, R. phoenicolasius and M. vimineum, whereas R. multiflora was more abundant within the exclosure. Our results indicate that chronic high deer density facilitates increased abundances of several exotic invasive plant species, with the notable exception of R. multiflora. We infer that the invasion of many exotic plant species that are browse-tolerant to white-tailed deer could be limited by reducing deer populations.

Rubus phoenicolasius Maxim. is a traditional Tibetan medicine and widely used in the clinical pharmacology. In current study, the complete chloroplast genome of R. phoenicolasius was reported. The total length of the genome was 155,144 bp with the GC content of 37.9%. We predicted 130 genes in the genome including 84 protein-coding genes, 37 tRNA genes, 8 rRNA genes and 1 pseudogene. 17 genes were duplicated in the IR regions including 7 tRNA, 4 rRNA and 6 protein-coding genes. Phylogenomic analysis revealed that R. phoenicolasius forms a strong supported branch with R. amabilis and R. coreanus under the Rosaceae clade.

Invasive plants in the riparian zone can negatively affect the characteristics and quality of a watershed. To support the development of a watershed management plan and foster public appreciation of the value of the riparian zone, Mohonk Preserve established a volunteer monitoring program surveying sites for invasive species. Between 2017 and 2019, citizen scientists repeatedly surveyed 20 sites in the Hudson River Valley in New York for 10 invasive plant species: purple loosestrife (Lythrum salicaria L.), common reed [Phragmites australis (Cav.) Trin. ex Steud], multiflora rose (Rosa multiflora Thunb.), garlic mustard [Alliaria petiolata (M. Bieb.) Cavara & Grande], dame's rocket (Hesperis matronalis L.), Japanese knotweed (Polygonum cuspidatum Siebold & Zucc.), wineberry (Rubus phoenicolasius Maxim.), barberry (Berberis spp.), Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], and Asiatic bittersweet (oriental bittersweet, Celastrus orbiculatus Thunb.). We found that the number of target species detected was higher on sites closer to paved roads and with increasing drainage area size, while lower with higher percentages of forested land in the basin. Our analysis results highlight variation in the presence of target invasive species across the Hudson River Valley region, highlighting sites and areas to monitor for future introductions and take action to prevent species' invasions. Our results highlight differences in the most relevant abiotic factors for hydrophytes and non-hydrophyte species, underscoring the importance of considering species' life-history traits before the development of management plans for invasive plant species in the riparian zone. Our case study of community-collected data in the Hudson River Valley region using a relatively simple monitoring protocol can provide a road map for other regions fostering volunteer engagement with invasive plants.

Background: Exotic species have been hypothesized to successfully invade new habitats by virtue of possessing novel biochemistry that repels native enemies. Despite the pivotal long-term consequences of invasion for native food-webs, to date there are no experimental studies examining directly whether exotic plants are any more or less biochemically deterrent than native plants to native herbivores. Methodology/Principal Findings: In a direct test of this hypothesis using herbivore feeding assays with chemical extracts from 19 invasive plants and 21 co-occurring native plants, we show that invasive plant biochemistry is no more deterrent (on average) to a native generalist herbivore than extracts from native plants. There was no relationship between extract deterrence and length of time since introduction, suggesting that time has not mitigated putative biochemical novelty. Moreover, the least deterrent plant extracts were from the most abundant species in the field, a pattern that held for both native and exotic plants. Analysis of chemical deterrence in context with morphological defenses and growth-related traits showed that native and exotic plants had similar trade-offs among traits. Conclusions/Significance: Overall, our results suggest that particular invasive species may possess deterrent secondary chemistry, but it does not appear to be a general pattern resulting from evolutionary mismatches between exotic plants and native herbivores. Thus, fundamentally similar processes may promote the ecological success of both native and exotic species.

Although allometric equations have been developed to predict aboveground biomass components for several shrub species, few efforts have been made to predict flower or fruit production. As numerous invasive Eurasian shrubs establish throughout eastern deciduous forests, it is becoming important to understand the ecosystem consequences of shifting dominance from native to nonnative shrub species, particularly with regard to fruit and nectar production. In this study, we created negative binomial hurdle models to predict flower production for Japanese barberry (Berberis thunbergii DC.), dogwoods (Cornus amomum Mill. and Cornus racemosa Lam.), border privet (Ligustrum obtusifolium Siebold & Zucc.), honeysuckle (Lonicera morrowii A. Gray, Lonicera X bella Zabel, and Lonicera tatarica L.), multiflora rose (Rosa multiflora Thunb.), and brambles (Rubus allegheniensis Porter, Rubus occidentalis L., and Rubus phoenicolasius Maxim.). The models effectively predicted flower production per ramet for 97-100% of the shrubs found at our study sites, but exhibited high predictive variability for the few stems in the largest diameter classes. This novel modeling approach can be used in a variety of ways to assist land managers in prioritizing invasive shrubs or trees for removal, determining a minimum replanting size for native plants to have reproducing individuals, estimating landscape-level sugar production, and better understanding shrub demography.

Traits associated with root morphology and nutrient uptake rate may contribute to the competitive ability of invasive species by determining their access to soil nutrients and their ability to extract those resources. Here, we tested the hypotheses that (a) exotic woody shrubs would be superior belowground competitors for nitrogen in heterogeneous soil resulting from key aspects of root architecture and (b) larger plants would be superior belowground competitors. We tested these hypotheses using two native shrubs, Rubus allegheniensis and Viburnum dentatum, and two invasive exotic shrubs, Rubus phoenicolasius and Berberis thunbergii, all four of which can become abundant in plant communities in the eastern United States. We grew replicate plants from each species with interspecific competitors, with intraspecific competitors, and individually in a randomized layout in a greenhouse in two temporal blocks. Each experimental container had a central soil patch amended with ¹⁵N-labeled litter. We measured above- and belowground growth, root morphology, and nitrogen uptake to assess the effects of intra- and interspecific competition on plant growth and nitrogen uptake. All species grew better in the second temporal block, but we did not detect any differences in the competitive ability or root traits for exotic versus native species; rather, plant size was the key trait that predicted competitive effects. Both Rubus species, which capitalized on the extended growing season offered by our greenhouse conditions, were stronger competitors and typically larger plants than B. thunbergii and V. dentatum. Both Rubus species exerted measurable competitive effects on other species, resulting in decreased aboveground size of competitors by 50% or more relative to control plants, but did not routinely decrease ¹⁵N uptake or root biomass of competitors. When competing with Rubus, leaf C:N ratios of all species except R. phoenicolasius were greater than when grown alone, suggesting that large Rubus plants did decrease the total nitrogen available to competitors. Our data suggest that belowground competitive ability in shrubs may be more closely associated with plant size and growth rate than plant origin. In addition, plant species that exhibit plastic growth phenology, such as those in the genus Rubus, may gain a competitive advantage during years with warmer autumn months by extending their growing seasons, facilitating their invasion and establishment in new habitats.

Invasive plants impact native plant and animal species, communities, and ecosystems. We explore the role of treefall gaps in facilitating invasive species growth. We measured the frequency and density of different life stages of three invasive species: Rubus phoenicolasius, Berberis thunbergii, and Rosa multiflora in an eastern deciduous mature forest. Gaps were important for the establishment, growth, and reproduction of R. phoenicolasius, growth of R. multiflora and reproduction of B. thunbergii. We present several hypotheses as to why we observed a species-specific response of invasive plants to treefall gaps, including propagule rain as a driver of invasive plant establishment.

Traits associated with root morphology and nutrient uptake rate may contribute to the competitive ability of invasive species by determining their access to soil nutrients and their ability to extract those resources. Here, we tested the hypotheses that (a) exotic woody shrubs would be superior belowground competitors for nitrogen in heterogeneous soil resulting from key aspects of root architecture and (b) larger plants would be superior belowground competitors. We tested these hypotheses using two native shrubs, Rubus allegheniensis and Viburnum dentatum, and two invasive exotic shrubs, Rubus phoenicolasius and Berberis thunbergii, all four of which can become abundant in plant communities in the eastern United States. We grew replicate plants from each species with interspecific competitors, with intraspecific competitors, and individually in a randomized layout in a greenhouse in two temporal blocks. Each experimental container had a central soil patch amended with 15N-labeled litter. We measured above- and belowground growth, root morphology, and nitrogen uptake to assess the effects of intra- and interspecific competition on plant growth and nitrogen uptake. All species grew better in the second temporal block, but we did not detect any differences in the competitive ability or root traits for exotic versus native species; rather, plant size was the key trait that predicted competitive effects. Both Rubus species, which capitalized on the extended growing season offered by our greenhouse conditions, were stronger competitors and typically larger plants than B. thunbergii and V. dentatum. Both Rubus species exerted measurable competitive effects on other species, resulting in decreased aboveground size of competitors by 50% or more relative to control plants, but did not routinely decrease 15N uptake or root biomass of competitors. When competing with Rubus, leaf C:N ratios of all species except R. phoenicolasius were greater than when grown alone, suggesting that large Rubus plants did decrease the total nitrogen available to competitors. Our data suggest that belowground competitive ability in shrubs may be more closely associated with plant size and growth rate than plant origin. In addition, plant species that exhibit plastic growth phenology, such as those in the genus Rubus, may gain a competitive advantage during years with warmer autumn months by extending their growing seasons, facilitating their invasion and establishment in new habitats.

One explanation for the success of exotic plants in their introduced habitats is that, upon arriving to a new continent, plants escaped their native herbivores or pathogens, resulting in less damage and lower abundance of enemies than closely related native species (enemy release hypothesis). We tested whether the three exotic plant species, Rubus phoenicolasius (wineberry), Fallopia japonica (Japanese knotweed), and Persicaria perfoliata (mile-a-minute weed), suffered less herbivory or pathogen attack than native species by comparing leaf damage and invertebrate herbivore abundance and diversity on the invasive species and their native congeners. Fallopia japonica and R. phoenicolasius received less leaf damage than their native congeners, and F. japonica also contained a lower diversity and abundance of invertebrate herbivores. If the observed decrease in damage experienced by these two plant species contributes to increased fitness, then escape from enemies may provide at least a partial explanation for their invasiveness. However, P. perfoliata actually received greater leaf damage than its native congener. Rhinoncomimus latipes, a weevil previously introduced in the United States as a biological control for P. perfoliata, accounted for the greatest abundance of insects collected from P. perfoliata. Therefore, it is likely that the biocontrol R. latipes was responsible for the greater damage on P. perfoliata, suggesting this insect may be effective at controlling P. perfoliata populations if its growth and reproduction is affected by the increased herbivore damage.