Impact Of Invasive Plant Species Research Articles

Plant invasion down under: exploring the below-ground impact of invasive plant species on soil properties and invertebrate communities in the Central Plateau of New Zealand

AbstractThe impacts of invasive plants on arthropod communities are often reported to be negative and have predominantly been explored aboveground, but there is a paucity of information regarding what happens belowground. To address this gap, we compared soil properties and soil fauna communities associated with two native plant species (Leptospermum scoparium—mānuka and Chionochloa rubra—red tussock) and two invasive species (non-N-fixing Calluna vulgaris—European heather and N-fixing Cytisus scoparius—Scotch broom) in the Central Plateau of New Zealand. We expected that (1) at individual plant level soil properties would be different under invasive and native plant species, with higher soil nutrient concentrations under invasive species, especially N-fixing broom; (2) total abundance of soil fauna would be higher under invasive plant species, as generally positive impact of invasive plants on soil invertebrates is indicated in the literature; (3) invasive plants, and especially N-fixing broom, will be associated with greater abundances of soil decomposer groups. We found that soil properties and soil fauna assemblages did not cluster by plant invasive status as initially predicted. At individual plant level, there was similarity in soil conditions between mānuka and broom, and between red tussock and heather. The invasive N-fixer (broom) had positive effects on soil N availability, with higher N pool and lower C/N ratio in soil under this species. There were no consistent differences in total soil fauna abundance between invasive and native plants. Broom and mānuka were associated with higher abundances of Collembola, Oligochaeta and Diplopoda; heather and red tussock had higher abundances of Hymenoptera and Hemiptera. Significantly more Oligochaeta and Collembola under broom matched the prediction of invasive plants (and especially N-fixing invasives) being associated with greater abundances of decomposers. However, another important decomposer group—oribatid mites—did not show the same tendency. These results evidence that simplified generalizations regarding the impacts of invasive plants are unlikely to be justified, since the ecological effects of plant invasions are complex and do not always follow the same pattern. Therefore, we need to take into consideration the ecological context and the traits of individual plant species and target organisms in an unbiased manner to fully understand the impacts of plant invasions.

Comparison of Machine Learning for Multispectral Signature Classification of Invasive Spathodea campanulata in Remote Sensing Imagery

Invasive plant species pose a significant threat to native ecosystems, and mapping their distribution is essential for effective management and conservation efforts. This study compared the performance of different machine learning techniques in the classification of multispectral signature of the invasive plant species Spathodea campanulata using remote sensing imagery. The ground-based locality data of vegetation was collected using a random sampling technique, and satellite imagery was acquired from Sentinel-2. The results showed that the blue, green, red, red- edge, and near-infrared bands were effective in distinguishing between invasive S. campanulata, non-vegetation, and other vegetation using machine learning techniques. The support vector machine (SVM) technique achieved the highest overall accuracy of 80%, followed by random forest (RF) with 73% and K-nearest neighbor (KNN) with 66%. The Gaussian mixture model (GMM) technique had the lowest overall accuracy of 53%. SVM and RF showed substantial agreement between predicted and observed classes, whereas KNN showed moderate agreement and GMM showed poor agreement. The maps generated by SVM depict a distribution of the invasive plant species that is characterized by isolated patches in the northern region of the study area. In contrast, the southern region – including the protected area of Mount Timolan – shows a dense presence of S. campanulata, indicating an ongoing invasion by the species. This highlights the need for effective management and conservation efforts to mitigate the negative impact of invasive plant species on native ecosystems.

An impact assessment of alien invasive plants in South Africa generally dispersed by native avian species

Invasive alien plant species have been identified as a major threat to biodiversity and the relationship with native avian dispersers may increase their invasion potential. The impact of invasive plant species needs to be quantified using comparable assessment tools across different habitats and species to allocate limited resources to high-priority species. Here, we used the Generic Impact Scoring System (GISS) to assess the impacts of 16 fleshy-fruited alien invasive plant species in South Africa generally dispersed by native avian species. The results showed that fleshy-fruited invasive species have both environmental and socio-economic impacts. The cumulated impact scores for lantana (Lantana camara) and the tree of heaven (Ailanthus altissima) were the highest, with scores of 42 and 32, respectively. Some species, such as white mulberry (Morus alba), camphor tree (Cinnamomum camphora), American bramble (Rubus cuneifolius) and Brazilian pepper tree (Schinus terebinthifolius), had low overall impact scores of 8, 18, 14 and 16, respectively, but scored the maximum impact of 5 for certain mechanisms. Environmental impacts of fleshy-fruited invasive plant species had a high impact magnitude through effects on the ecosystem and vegetation. Socio-economic impacts were mainly through effects on forest production, agriculture and human health. Species with large crop sizes, small seeds and fruit sizes had higher environmental and socio-economic impact magnitude. The information generated in this study is important for guiding resource allocation and preventing the uncontrolled introduction of invasive species in South Africa. The impact of the fleshy-fruited invasive species transcended sectors and, therefore, effective management of invasive species will require the collaboration of multiple and inter-sectoral stakeholders in South Africa.

Comparison of the effects of a broad-spectrum herbicide and a bio-herbicide on insect flower visitation in the Serengeti ecosystem, Tanzania

The functional role of insect visitors on flowering plants is crucial to both natural and agricultural ecosystems. While, few studies have addressed the impact of invasive plant species on insect visitors, even less is known about how management practices against invasive plants may affect plant-pollinator interactions. We assessed how natural versus chemical-based management against the invasive plant Gutenbergia cordifolia affected insect visitors in Mwiba area, Tanzania. We compared the number of insect visitors, diversity and richness, the number of inflorescences visited, inflorescences abundance and flower diversity across treatments of Desmodium uncinatum crude leaves extract (DUL), the chemical glyphosate (GLY), and none /control (CON). We found that more than half (55%) of the insect visitors observed were found visiting flowering plants in DUL plots, followed by CON with 26% and GLY plots with 19%. Further, DUL plots had almost twice as many inflorescences visited compared to CON and GLY plots. Inflorescence’s abundance and flower diversity were significantly higher in DUL plots compared to CON and GLY plots. Our study revealed that DUL treatment did not disrupt insect flower visitation but rather attracted more insects. We conclude that using the natural plant extract treatment is highly preferable to the chemical management of invasive plants such as G. cordifolia, as the DUL treatment maintained and even enhanced flower diversity while suppressing G. cordifolia and fostering insect visitors.

An invasive grass species has both local and broad‐scale impacts on diversity: Potential mechanisms and implications

AbstractQuestionsThe impact of invasive plant species on native diversity varies with spatial scale, with some invaders leading to broad‐scale diversity declines and others to only local declines. These discrepancies may reflect the invaders” capacity to reduce niche opportunities across spatial scales which can be associated with their functional traits. We investigated impact‐scale relationships and trait‐based mechanisms, in areas invaded by the exotic perennial grass species, Bothriochloa pertusa. We examine root traits specifically, as below‐ground competition was considered particularly important to the success of this species.LocationGrassy “ironbark” woodlands of eastern Queensland, Australia.MethodsWe examined plots with varying degrees of invasion by B. pertusa, at multiple spatial scales (up to 1,000 m2) and analysed changes to the species–area relationships (SARs) with increasing invader cover. Changes to SARs were assessed in relation to the invaders” effect on rare (low patch occupancy) and common species in the community. In a separate analysis within the same habitat, we collected root cores across a gradient of invader cover and analysed changes to community root traits that were considered important correlates of competition for space and nutrients.ResultsInvasion‐induced reductions in diversity were pervasive at all scales investigated, and this was associated with a proportionally greater effect on rare species in the community. In the separate root analysis, changes in community root traits with increasing invader cover were potentially indicative of more intense competition for resources rather than space.ConclusionsThe observed regional‐scale dominance of B. pertusa and associated declines in diversity warrant serious concern for the conservation of native plant communities and species in a region already at risk from other anthropogenic threats. Intense competition for below‐ground resources is likely a contributing mechanism to the success of B. pertusa in this study system. Experimental examination of this and other mechanisms would help to validate these findings.

Optical traits perform equally well as directly‐measured functional traits in explaining the impact of an invasive plant on litter decomposition

Abstract Functional traits can help elucidate and predict the impact of invasive plant species on ecosystem functioning. Yet, this approach requires comprehensive and labour‐intensive trait collection campaigns, covering intraspecific trait variation of both the invader and native species in the invaded community. One potential way to overcome these logistic constraints is using hyperspectral remote sensing technology to efficiently quantify functional trait values. Although such spectrally derived or ‘optical’ traits are known to closely link to directly measured functional traits, little research has explored how well these optical traits perform in assessing invader‐induced ecosystem impact. Here, we explored the trait‐mediated impact of the invasive Rosa rugosa on litter decomposition and evaluated whether optical traits perform equally well as directly measured traits in predicting litter decomposition variation. We collected data on species‐specific functional traits, leaf hyperspectral reflectance and standardized ‘tea bag index’ litter decomposition across 25 invaded and 25 uninvaded coastal grassland plots. The selected traits were all potentially related to litter decomposition and covered the leaf economics spectrum, additional leaf structural components and competitive ability. Optical traits were quantified through a combination of a physical radiative transfer model inversion and vegetation indices calculations. Invasion significantly increased the stabilization factor, i.e. the amount of resulting recalcitrant litter. Invader impact on litter decomposition could be entirely explained by changes it induced in the functional traits of the native community, rather than by the invader's traits itself. More specifically, the invader pushed the invaded community towards traits associated with high litter quality. Optical traits performed equally well as directly measured traits in explaining the invasion impact on the stabilization factor (R2 = 41.9% vs. 38.5%). Furthermore, the interpretation of the results based on optical traits resulted in a similar functional understanding of the invader impact. Synthesis. Our results indicate the potential of hyperspectral data to explain changes in ecosystem functioning. The combination of radiative transfer models and vegetation indices allowed to extract all relevant trait information from the hyperspectral data. This framework thus presents a practical shortcut to assess relevant leaf traits, requiring only a limited amount of field trait measurements.

Defoliation by a native herbivore, Omphalocera munroei, leads to patch size reduction of a native plant species, Asimina triloba, following small-scale removal of the invasive shrub, Amur honeysuckle, Lonicera maackii

Efforts to reduce the impact of invasive plant species, such as the Amur honeysuckle, Lonicera maackii, often involve the rapid removal of the invasive without any post-removal strategies. This has the potential to stimulate the rapid growth of some native plant species and their herbivores. How this rapid growth may affect plant–insect interactions is not well understood, and unintended consequences may arise. Here we assess how high defoliation rates caused by a native herbivore, Omphalocera munroei, impacted the population of a native understory tree, the common pawpaw, Asimina triloba, following small-scale L. maackii removal. High defoliation rates on A. triloba caused by O. munroei were first detected in two patches of A. triloba that had rapidly expanded following L. maackii removal. Defoliation of A. triloba was estimated throughout a 30-acre site and defoliation, survival, and stem growth were recorded in nine patches (two within the L. maackii removal areas and seven outside) for 6 years. Defoliation peaked during year 2 with near 100% defoliation on > 90% of A. triloba stems and remained higher than reference sites until year 5. Defoliation throughout the site led to > 50% stem mortality, with higher mortality rates observed outside L. maackii removal patches. Stem mortality was high across all age classes, with low recruitment and an unusually high mortality of well-established older plants. These results illustrate the potential for interactions among native species to be destabilized by the rapid colonization and population growth of native species that can occur following removal of an invasive species. Findings from this study highlight the need to consider post-removal restoration strategies following the removal of invasive plant species.

Impact of invasive plant species on the livelihoods of farming households: evidence from Parthenium hysterophorus invasion in rural Punjab, Pakistan

Invasive plant species often have negative impacts on agriculture and society in addition to their detrimental effects on biodiversity and environment. It is important to assess such impacts to devise effective management plans. A field survey study was carried out to assess the socio-economic effects of a highly invasive plant species, parthenium weed (Parthenium hysterophorus L.) across the three different cropping regions in Punjab province of Pakistan. The farming communities of different cropping regions reported significant effects of parthenium weed on their crop and livestock production, health and social well-being. The mixed cropping region was heavily infested and most affected region, whereas the cotton–wheat region was least affected. Farmers were well-aware of parthenium weed presence, its biology, habitat, and mode of dispersal across the landscape. All the major crops cultivated were infested by varying degrees of weed densities with potato, sugarcane and maize being the most infested crops. Farmers were generally good at managing the weed in crops which cost them significant amounts of money (ca. $205 per household). Parthenium weed also infested the fodder collection and grazing sites affecting the livestock production negatively. Each farmer lost an additional ca. $935 annually due to the weed infestations on fodder collection sites. A significant proportion of farmers also reported negative effects of the weed on animal health (22–36%) and human health (14–24%). The average annual costs associated with animal health and human health were ca. $2031 and $73 per household, respectively. Despite acknowledging the value of weed management in non-cropped areas, fewer farmers managed it practically in such areas. Most farmers reported parthenium weed as a very difficult-to-manage weed. About 37% of farmers were willing while 60% were likely to participate in a potential management program in future. A comprehensive management strategy is urgently needed to address the looming crisis of parthenium weed invasion across the province and similar approach must be implemented at the national and international level.

Still no evidence that pathogen accumulation can revert the impact of invasive plant species

Fil: Chiuffo, Mariana Cecilia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Assessment of economic and environmental impact of invasive plant species

This article presents data from a review of published works on the economic damage caused by invasive plant species, their ecological and economical impact, and the legal regulation of biological invasions. It is concluded that it is necessary to elaborate and adopt a national strategy on alien species, federal regulatory acts concerning the policy on invasive organisms, and general approaches and criteria to evaluate the risk of their spread. Effective control of invasive species is only possible at the rational approach, which takes into consideration individual ecological-biological features of the species, their relations with other components of the community, the properties of the ecosystem invaded by them, expenditures for their control, and the period and consequences of their eradication.

Soil free-living nematodes as bio-indicators for assaying the invasive effect of the alien plant Heterotheca subaxillaris in a coastal dune ecosystem

The Israeli Mediterranean coastal dunes are considered to be a center of floral and faunal speciation and a natural habitat for rare endemic plants, with an extremely sensitive area for alien species invasion. The soil free-living nematode communities are one of the most important groups of soil biota, constituting an essential trophic link between primary decomposers, such as the soil microflora, and larger animals. Despite the fact that soil free-living nematodes play an important role in fundamental ecological processes and are sensitive bio-indicators for understanding processes of succession and nutrient flow in different ecosystems, little is known about the impact of invasive plant species on the soil free-living nematode communities. The present study was designed to fill this gap and evaluate the invasive effect of Heterotheca subaxillaris on the soil free-living nematode communities inhabiting the Mediterranean coastal dunes. Soil samples were collected from the upper (0–10cm) soil layer under H. subaxillaris (invasive perennial shrub) and Artemisia monosperma (native perennial shrub) at two different sites in the sea-sand ecosystem during the winter and summer seasons. Molecular analysis using the 18S rRNA gene for species determination, along with the traditional method, was a useful tool for evaluation of ecological conditions under the plant associations. The nematode communities, trophic diversity, and taxon composition were affected by the invasive plant at the study sites. Furthermore, this study showed that unfavorable seasonal conditions can also exacerbate the harmful effects of the invasive plants on nematode abundance and trophic and species diversity.

Linking functional traits to impacts of invasive plant species: a case study

Our understanding of the link between plant functional traits and ecological impact of invasive alien plant species is fragmentary and the mechanisms leading to impacts are poorly understood. Moreover, current knowledge is heavily biased to the temperate regions of the world and we know much less about traits and impacts of invaders in tropical and subtropical ecosystems. We studied two leaf traits of the invasive alien shrub Chromolaena odorata and the impacts of its invasion on native vegetation in savannas. We compared specific leaf area (SLA) and leaf area index (LAI) between C. odorata and native species and assessed how C. odorata differentially affects canopy light interception, soil moisture, soil nutrients, and litter accumulation compared to native species. We found that C. odorata has higher SLA and LAI than native species, lower light and moisture levels below its canopy, but higher nutrient levels and a higher litter accumulation rate. Because of its higher SLA, C. odorata grows faster, resulting in more biomass, increased litter accumulation and higher nutrient availability. Due to its high SLA and LAI, C. odorata intercepts more light and reduces available moisture more than do native trees due to higher transpiration rates, reducing the biomass of native understory vegetation. This study provides empirical evidence for strong links between plant functional traits and ecological impact of invasive plant species, highlighting the importance of traits in predicting ecosystem-level impacts of invasive plant species.

What is the “real” impact of invasive plant species?

Invasive plant species should be evaluated and prioritized for management according to their impacts, which include reduction in native diversity, changes to nutrient pools, and alteration of fire regimes. However, the impacts of most invasive species have not been quantified and, when measured, those impacts are based on a limited number of response metrics. As a result, invasion ecology has been overwhelmed by speculation and bias regarding the ecological consequences of invasive plants. We propose a quantitative mathematical framework that integrates any number of impact metrics as a function of groundcover and geographic extent. By making relative comparisons between invaded and uninvaded landscapes at the population scale, which results in a percent change for each metric, we overcome previous limitations that confounded the integration of metrics based on different units. Our model offers a quantitative approach to ecological impact that may allow identification of the transition from benign introduction to impactful invader, while also allowing empirical comparisons at the species and population levels that will be useful for management prioritization.

Invasive Plant Species in the National Parks of Vietnam

The impact of invasive plant species in national parks and forests in Vietnam is undocumented and management plans have yet to be developed. Ten national parks, ranging from uncut to degraded forests located throughout Vietnam, were surveyed for invasive plant species. Transects were set up along roads, trails where local people access park areas, and also tracks through natural forest. Of 134 exotic weeds, 25 were classified as invasive species and the number of invasive species ranged from 8 to 15 per park. An assessment of the risk of invasive species was made for three national parks based on an invasive species assessment protocol. Examples of highly invasive species were Chromolaena odorata and Mimosa diplotricha in Cat Ba National Park (island evergreen secondary forest over limestone); Mimosa pigra, Panicum repens and Eichhornia crassipes in Tram Chim National Park (lowland wetland forest dominated by melaleuca); and C. odorata, Mikania micrantha and M. diplotricha in Son Tra Nature Conservation area (peninsula evergreen secondary forest). Strategies to monitor and manage invasive weeds in forests and national parks in Vietnam are outlined.

Spatiotemporal Analysis of Three Common Wetland Invasive Plant Species Using Herbarium Specimens and Geographic Information Systems

Abstract The negative ecological impact of invasive plant species has been widely reported in recent years. Herbarium specimens can allow for the study of spatiotemporal spread of invasive species in order to understand distribution characteristics and patterns which can then be utilized for management decisions. In this study, three common wetland invasive plant species (Phragmites australis, Lythrum salicaria and Rorippa nasturtium-aquaticum) were chosen and analyzed via two previously published methods to determine the historic rate and pattern of spread as well as to identify periods of invasiveness. Performance of these methods varied in scale with a general, area-corrected approach covering the entire southeastern United States and an associate species-corrected method covering smaller, regional areas of dense historical specimen collection. Results showed positive spread over time for these three species in both methods; however, periods of invasiveness did not coincide between the two methods. The...

Forest floor plant community response to experimental control of the invasive biennial, Alliaria petiolata (garlic mustard)1

The impact of invasive plant species on native plants is largely assumed to be negative, but supporting evidence is sparse. A common control method of non-native plants is herbicide application, but little is known about the effects of these chemicals on non-target plant populations, or differences in these populations before and after control measures are taken. We examined the response of the forest floor plant community to herbicide-mediated reduction of Alliaria petiolata in an old-growth and a second-growth forest stand in Hueston Woods State Park, Preble and Butler Counties, OH. Fifty 1 × 1 m plots were established in each stand, and 25 plots per stand were treated with Round-up© each November 2000–2004, which reduced cover of adult Alliaria petiolata but did not suppress recruitment. Percent cover of herbs and woody plants ≤0.85 m tall was assessed in May and June, 2000–2005. To determine compositional differences between sprayed and unsprayed plots in each stand we ordinated plots based on peak cover of each species using nonmetric multidimensional scaling, tested for differences in community composition with a multiple response permutation procedure, and compared total cover of growth forms with Kruskal-Wallis tests.Five years of Alliaria petiolata control only modestly affected the forest floor vegetation. Neither species richness nor diversity differed significantly between sprayed and unsprayed treatments in any year of the study. Community composition differed each year between stands, but treatments differed significantly only in 2002 (in the second-growth stand), and marginally in 2004 and 2005 (in the old-growth stand). Treatment affected cover of some growth forms during the study, but only in some years: in the second-growth stand sprayed plots had significantly greater cover of spring perennials and graminoids in 2003 and marginally lower cover of annuals in 2005; in the old-growth stand sprayed plots had marginally more spring perennials in 2005. Wintergreen species, particularly the exotic annual Stellaria media, had lower cover in sprayed plots in the old-growth stand in 2005. We attribute the compositional differences we observed in the forest floor community to competitive impacts of Alliaria petiolata, but suggest that effects were modest due to the persistence of rosettes in the sprayed plots.