Managing for biodiversity: impact and action thresholds for invasive plants in natural ecosystems

Plant networks are more connected by invasive brome and native shrub facilitation in Central California drylands

Dominant vegetation in many ecosystems is an integral component of structure and habitat. In many drylands, native shrubs function as foundation species that benefit other plants and animals. However, invasive exotic plant species can comprise a significant proportion of the vegetation. In Central California drylands, the facilitative shrub Ephedra californica and the invasive Bromus rubens are widely dispersed and common. Using comprehensive survey data structured by shrub and open gaps for the region, we compared network structure with and without this native shrub canopy and with and without the invasive brome. The presence of the invasive brome profoundly shifted the network measure of centrality in the microsites structured by a shrub canopy (centrality scores increased from 4.3 under shrubs without brome to 6.3, i.e. a relative increase of 42%). This strongly suggests that plant species such as brome can undermine the positive and stabilizing effects of native foundation plant species provided by shrubs in drylands by changing the frequency that the remaining species connect to one another. The net proportion of positive and negative associations was consistent across all microsites (approximately 50% with a total of 14% non-random co-occurrences on average) suggesting that these plant-plant networks are rewired but not more negative. Maintaining resilience in biodiversity thus needs to capitalize on protecting native shrubs whilst also controlling invasive grass species particularly when associated with shrubs.

Linear scaling – negative effects of invasive Spiraea tomentosa (Rosaceae) on wetland plants and pollinator communities

Invasive plants directly and indirectly disrupt the ecosystem functioning, of which indirect effects, for example, through trophic cascades, are particularly difficult to predict. It is frequently assumed that the impact of an invading species on the ecosystem is proportional (linearly related) to its density or abundance in a habitat, but this assumption has rarely been tested. We hypothesised that abundance and richness of plants and potentially pollinators of wet meadows change as a result of invasion of steeplebush Spiraea tomentosa and that these changes are proportional to the density of the shrub. We selected 27 sites amongst wet meadows habitats invaded by S. tomentosa with coverage ranging from 0% to 100% and examined the diversity of plants, as well as the abundance and diversity of flower visitors (bees, butterflies with moths and flies). Our results showed that the richness of plants, as well as the richness and number of individuals of flower visitors, decrease significantly and linearly with an increase of the S. tomentosa cover. This finding supports the hypothesis that the impact of an invasive species can be proportional to their population density, especially if this species is limiting the available resources without supplying others. Our study is the first to show such an unequivocal negative, linear effect of an invasive shrub on the abundance and richness of potential pollinators. It proves that the negative impact of S. tomentosa on the wetland ecosystem appears even with a minor coverage of the invader, which should be taken into account when planning activities aimed at controlling the population of this transformer species. The simultaneously detected linear dependence allows us to assume that the benefits of controlling secondary populations of the shrub can be proportional to the incurred effort.

The right tree in the right place? A major economic tree species poses major ecological threats

Tree species in the Pinaceae are some of the most widely introduced non-native tree species globally, especially in the southern hemisphere. In New Zealand, plantations of radiata pine (Pinus radiata D. Don) occupy c. 1.6 million ha and form 90% of planted forests. Although radiata pine has naturalized since 1904, there is a general view in New Zealand that this species has not invaded widely. We comprehensively review where radiata pine has invaded throughout New Zealand. We used a combination of observational data and climate niche modelling to reveal that invasion has occurred nationally. Climate niche modelling demonstrates that while current occurrences are patchy, up to 76% of the land area (i.e. 211,388 km2) is climatically capable of supporting populations. Radiata pine has mainly invaded grasslands and shrublands, but also some forests. Notably, it has invaded lower-statured vegetation, including three classes of naturally uncommon ecosystems, primary successions and secondary successions. Overall, our findings demonstrate pervasive and ongoing invasion of radiata pine outside plantations. The relatively high growth rates and per individual effects of radiata pine may result in strong effects on naturally uncommon ecosystems and may alter successional trajectories. Local and central government currently manage radiata pine invasions while propagule pressure from existing and new plantations grows, hence greater emphasis is warranted both on managing current invasions and proactively preventing future radiata pine invasions. We therefore recommend a levy on new non-native conifer plantations to offset costs of managing invasions, and stricter regulations to protect vulnerable ecosystems. A levy on economic uses of invasive species to offset costs of managing invasions alongside stricter regulations to protect vulnerable ecosystems could be a widely adopted measure to avert future negative impacts.

Unified system describing factors related to the eradication of an alien plant species

Background

In the field of biological invasions science, a problem of many overlapping terms arose among eradication assessment frameworks. Additionally there is a need to construct a universally applicable eradication evaluation system. To unify the terminology and propose an eradication feasibility assessment scale we created the Unified System for assessing Eradication Feasibility (USEF) as a complex tool of factors for the analysis of eradications of alien (both invasive and candidate) plant species. It compiles 24 factors related to eradication success probability reported earlier in the literature and arranges them in a hierarchical system (context/group/factor/component) with a possibility to score their influence on eradication success.

Methodology

After a literature survey we analyzed, rearranged and defined each factor giving it an intuitive name along with the list of its synonyms and similar and/or related terms from the literature. Each factor influencing eradication feasibility is ascribed into one of four groups depending on the context that best matches the factor: location context (size and location of infestation, ease of access), species context (fitness and fecundity, detectability), human context (knowledge, cognition and resources to act) and reinvasion context (invasion pathways). We also devised a simple ordinal scale to assess each factor's influence on eradication feasibility.

Conclusions

The system may be used to report and analyze eradication campaign data in order to (i) prioritize alien species for eradication, (ii) create the strategy for controlling invasive plants, (iii) compare efficiency of different eradication actions, (iv) find gaps in knowledge disabling a sound eradication campaign assessment. The main advantage of using our system is unification of reporting eradication experience data used by researchers performing different eradication actions in different systems.

A Consideration of Wildlife in the Benefit-Costs of Hydraulic Fracturing: Expanding to an E3 Analysis

High-volume hydraulic fracturing (“fracking”) for natural gas in the Marcellus Shale (underlying about 24 mil ha in New York, Pennsylvania, Maryland, West Virginia, Ohio, and Virginia) has become a politically charged issue, primarily because of concerns about drinking water safety and human health. This paper examines fracking in the Marcellus region, and the tradeoffs between the energy and economic potential of natural gas extraction and the environmental impacts on wildlife. Therefore, we introduce a new E3 analysis that combines the costs and benefits as regards energy, economics, and the environment. The Marcellus Shale has the most proven reserves of natural gas of any basin in the United States, at 129 trillion cubic feet. Income from natural gas development comes primarily from direct and indirect jobs, and induced jobs (those created when direct workers spend their earnings in a community), taxes and fees, and royalty and lease payments to rights holders. Fracking, however, has detrimental effects on wildlife and wildlife habitats. Terrestrial habitat effects are primarily due to landscape fragmentation from the clearing of land for pipeline and well pad development, which often removes mature forest and creates open corridors and edge habitats. An increase in forest edge and open corridors is associated with shifts in the bird community, as generalist species that do well around people increase in abundance, while forest specialists decline. Invasive plants associated with disturbance further degrade forest habitats. Aquatic habitats are also affected, both directly and indirectly. Hydraulic fracturing requires up to 20 mil L of water per well fracture, most of which comes from surface water sources in the Marcellus region. The removal of water, especially in smaller headwaters, can increase sedimentation, alter water temperature and change its chemistry, resulting in reductions in aquatic biodiversity. Given the reality that hydraulic fracturing will continue, there is a need to develop practices that best minimize negative impacts on terrestrial and aquatic habitats, as well as policies and the resolve to enforce these practices. To achieve a more sustainable balance between economic, energy, and environmental costs and benefits, we recommend that industry, scientists, non-governmental organizations, mineral rights holders, landowners, and regulators work together to develop a set of best management practices that represent the best knowledge available.

Weeds harbor an impressive diversity of fungi, which offers possibilities for biocontrol

The use of herbicides for weed control is very common, but some of them represent a threat to human health, are environmentally detrimental and stimulate herbicide resistance. Therefore, using microorganisms as natural herbicides appears as a promising alternative. The mycoflorae colonizing different species of symptomatic and asymptomatic weeds were compared to characterize the possible mycoherbicidal candidates associated with symptomatic weeds. A collection of 475 symptomatic and asymptomatic plants belonging to 23 weed species was established. A metabarcoding approach based on amplification of the internal transcribed spacer (ITS) region combined with high-throughput amplicon sequencing revealed the diversity of fungal communities hosted by these weeds: 542 fungal genera were identified. The variability of the composition of fungal communities revealed a dispersed distribution of taxa governed neither by geographical location nor by the botanical species, suggesting a common core displaying non-specific interactions with host plants. Beyond this core, specific taxa were more particularly associated with symptomatic plants. Some of these, such as Alternaria, Blumeria, Cercospora, Puccinia, are known pathogens, while others such as Sphaerellopsis, Vishniacozyma and Filobasidium are not, at least on crops, and constitute new tracks to be followed in the search for mycoherbicidal candidates. IMPORTANCE: This approach is original because the diversity of weed-colonizing fungi has rarely been studied before. Furthermore, targeting both the ITS1 and ITS2 regions to characterize the fungal communities i) highlighted the complementarity of these two regions, ii) revealed a great diversity of weed-colonizing fungi, and iii) allowed for the identification of potential mycoherbicides, among which unexpected genera.

Flight plan for the future: floatplane pilots and researchers team up to predict invasive species dispersal in Alaska

Aircraft can transport aquatic invasive species (AIS) from urban sources to remote waterbodies, yet little is known about this long-distance pathway. In North America and especially Alaska, aircraft with landing gear for water called floatplanes are used for recreation access to remote, often road-less wilderness destinations. Human-mediated dispersal of AIS is particularly concerning for the conservation of pristine wildlands, yet resource managers are often challenged by limited monitoring and response capacity given the vast areas they manage. We collected pathway data through a survey with floatplane pilots and used a Bayesian hierarchical model to inform early detection in a data-limited situation. The study was motivated by Alaska’s first known AIS, Elodea spp. (Elodea) and its floatplane-related dispersal. For 682 identified floatplane destinations, a Bayesian hierarchical model predicts the chance of flights originating from AIS source locations in freshwater and estimates the expected number of flights from these sources. Model predictions show the potential for broad spread across remote regions currently not known to have Elodea and informed monitoring and early detection efforts. Our result underlines the small window of opportunity for Arctic conservation strategies targeting an AIS free Arctic. We recommend management that focuses on long-distance connectivity, keeping urban sources free of AIS. We discuss applicability of the approach for other data-limited situations supporting data-informed AIS management responses.

Effects of Ailanthus altissima Invasion and Removal on High-Biodiversity Mediterranean Grasslands

Ailanthus altissima is one of the worst invasive plants in Europe in several habitat types, including high-biodiversity grasslands. The aim of this work was to evaluate the impact of the invasive A. altissima on high-biodiversity grassland vegetation and the effects of its removal on the recovery of native plant communities. The study area was within the Alta Murgia National Park (SE Italy). Seventeen vegetation quadrats were sampled in invaded grasslands and nine quadrats were sampled in nearby uninvaded areas. A. altissima was removed from six quadrats, which were sampled for two years after plant removal. Cluster analysis and non-metric multidimensional scaling ordination were used to identify and visualize the general vegetation pattern. Generalised Linear Models with different error structures were used to analyse the effects of A. altissima on native grasslands and vegetation recovery after removal. Results showed that the invasion of A. altissima changed drastically the community composition, reduced plant richness and diversity. Invaded stands had a greater presence of ruderal and widely distributed taxa, as opposed to a lesser presence of endemic and Mediterranean ones. The differences in the community composition between invaded and uninvaded quadrats became clearly detectable when A. altissima plants exceeded a threshold of 1 m of height and 50% of coverage. After A. altissima removal, the recovery of the grassland community was not completely achieved after two years.

Identifying thresholds in the impacts of an invasive groundcover on native vegetation

Impacts of invasive species are often difficult to quantify, meaning that many invaders are prioritised for management without robust, contextual evidence of impact. Most impact studies for invasive plants compare heavily invaded with non-invaded sites, revealing little about abundance–impact relationships. We examined effects of increasing cover and volume of the non-native herbaceous groundcover Tradescantia fluminensis on a temperate rainforest community of southern Australia. We hypothesised that there would be critical thresholds in T. fluminensis abundance, below which the native plant community would not be significantly impacted, but above which the community’s condition would degrade markedly. We modelled the abundance–impact relationship from 83 plots that varied in T. fluminensis abundance and landscape context and found the responses of almost all native plant indicators to invasion were non-linear. Native species richness, abundance and diversity exhibited negative exponential relationships with increasing T. fluminensis volume, but negative threshold relationships with increasing T. fluminensis cover. In the latter case, all metrics were relatively stable until cover reached between 20 and 30%, after which each decreased linearly, with a 50% decline occurring at 75–80% invader cover. Few growth forms (notably shrubs and climbers) exhibited such thresholds, with most exhibiting negative exponential relationships. Tradescantia fluminensis biomass increased dramatically at > 80% cover, with few native species able to persist at such high levels of invasion. Landscape context had almost no influence on native communities, or the abundance–impact relationships between T. fluminensis and the plant community metrics. Our results suggest that the diversity of native rainforest community can be maintained where T. fluminensis is present at moderate-to-low cover levels.

Modelling the damage costs of invasive alien species

The rate of biological invasions is growing unprecedentedly, threatening ecological and socioeconomic systems worldwide. Quantitative understandings of invasion temporal trajectories are essential to discern current and future economic impacts of invaders, and then to inform future management strategies. Here, we examine the temporal trends of cumulative invasion costs by developing and testing a novel mathematical model with a population dynamical approach based on logistic growth. This model characterises temporal cost developments into four curve types (I–IV), each with distinct mathematical and qualitative properties, allowing for the parameterization of maximum cumulative costs, carrying capacities and growth rates. We test our model using damage cost data for eight genera (Rattus, Aedes, Canis, Oryctolagus, Sturnus, Ceratitis, Sus and Lymantria) extracted from the InvaCost database—which is the most up-to-date and comprehensive global compilation of economic cost estimates associated with invasive alien species. We find fundamental differences in the temporal dynamics of damage costs among genera, indicating they depend on invasion duration, species ecology and impacted sectors of economic activity. The fitted cost curves indicate a lack of broadscale support for saturation between invader density and impact, including for Canis, Oryctolagus and Lymantria, whereby costs continue to increase with no sign of saturation. For other taxa, predicted saturations may arise from data availability issues resulting from an underreporting of costs in many invaded regions. Overall, this population dynamical approach can produce cost trajectories for additional existing and emerging species, and can estimate the ecological parameters governing the linkage between population dynamics and cost dynamics.

A weed risk analytical screen to assist in the prioritisation of an invasive flora for containment

Prioritising weeds for control and deciding upon the type of control and its associated investment are fundamental to weed management planning. Risk analysis is central to this process, combining the activities of risk assessment, risk management and risk communication. Risk assessment methodology has a rich history, but management feasibility has typically been a secondary matter, dealt with separately or not at all. Determinants of management feasibility for weeds include the stage of invasion, weed biology, means of control and cost of weed control. Here, we describe a simple weed risk analytical screen that combines risk assessment with species traits that influence management feasibility. We consider stage of invasion, species biological/dispersal characteristics and plant community invasibility in a preliminary analysis of the risk posed by the non-native plant species on Christmas Island in the Indian Ocean. For each of 31 high-risk species considered to be ineradicable under existing funding constraints, we analyse the risk posed to two major plant communities: evergreen closed-canopy rainforest and semi-deciduous scrub forest. Weed risk ratings are combined with ratings for species-intrinsic feasibility of containment (based on a measure that combines time to reproduction with potential for long distance dispersal) to create preliminary rankings for containment specific to each community. These rankings will provide a key input for a more thorough analysis of containment feasibility – one that considers spatial distributions/landscape features, management aspects and the social environment. We propose a general non-symmetric relationship between weed risk and management feasibility, considering risk to be the dominant component of risk analysis. Therefore, in this analysis species are ranked according to their intrinsic containment feasibility within similar levels of risk to produce an initial prioritisation list for containment. Shade-tolerant weeds are of particular concern for the closed-canopy evergreen rainforest on Christmas Island, but a greater diversity of weeds is likely to invade the semi-deciduous scrub forest because of higher light availability. Nevertheless, future invasion of both communities will likely be conditioned by disturbance, both natural and anthropogenic. The plant communities of Christmas Island have undergone significant fragmentation because of clearing for phosphate mining and other purposes. With a substantial number of invasive plant species firmly established and having the potential to spread further, minimising future anthropogenic disturbance is paramount to reducing community invasibility and therefore conserving the island’s unique biodiversity.

Seasonality and forest edge as drivers of Tradescantia zebrina Hort. ex Bosse invasion in the Atlantic Forest

As a result of biodiversity and ecosystem service losses associated with biological invasions, there has been growing interest in basic and applied research on invasive species aiming to improve management strategies. Tradescantia zebrina is a herbaceous species increasingly reported as invasive in the understory of disturbed forest ecosystems. In this study, we assess the effect of spatial and seasonal variation on biological attributes of this species in the Atlantic Forest. To this end, we measured attributes of T. zebrina associated with plant growth and stress in the four seasons at the forest edge and in the forest interior of invaded sites in the Iguaçu National Park, Southern Brazil. The invasive plant had higher growth at the forest edge than in the forest interior and lower leaf asymmetry and herbivory in the winter than in the summer. Our findings suggest that the forest edge environment favours the growth of T. zebrina. This invasive species is highly competitive in the understory of semi-deciduous seasonal forests all over the year. Our study contributes to the management of T. zebrina by showing that the summer is the best season for controlling this species.

Multiple comparisons of diversity indices invaded by Lantana camara

Current study assessed the impact of Lantana camara invasion on native plant diversity in Pothohar region of Pakistan. The approach used for study was random samplings and comparisons of diversity indices [number of species (S), abundance (N), species richness (R), evenness (Jꞌ), Shannon diversity index (Hꞌ) and Simpson index of dominance (λ)] with two categorical factors i.e., invaded and non-invaded (control). Control plots harboured by an average of 1.74 more species/10m2. The control category was diverse (Hꞌ=2.56) than invaded category (Hꞌ=1.56). The higher value of species richness in control plots shows heterogeneous nature of communities and vice versa in invaded plots. At multivariate scale, ordination (nMDS) and ANOSIM showed significant magnitude of differences between invaded and control plots at all sites. The decrease in studied diversity indices in invaded over control sites indicated that plant communities become less productive due to Lantana invasion.

Is There an Equivalence between Measures of Landscape Structural and Functional Connectivity for Plants in Conservation Assessments of the Cerrado?

Landscape connectivity can be assessed based on the physical connection (structural connectivity) or the maintenance of flow among habitats depending on the species (functional connectivity). The lack of empirical data on the dispersal capacity of species can lead to the use of simple structural measures. Comparisons between these approaches can improve decision-making processes for the conservation or restoration of habitats in fragmented landscapes, such as the Cerrado biome. This study aimed to understand the correspondence between the measures of landscape structural and functional connectivity for Cerrado plants. Three landscapes with cerradão patches in a pasture matrix were selected for the application of these metrics based on the functional connectivity of four profiles of plant dispersal capacity. The results showed divergent interpretations between the measures of landscape structural and functional connectivity, indicating that the assessment of biodiversity conservation and landscape connectivity is dependent on the set of metrics chosen. Structurally, the studied landscapes had the same number of cerradão patches but varied in optimal resource availability, isolation, heterogeneity, and aggregation. Functional connectivity was low for all profiles (based on the integral index of connectivity—IIC) and null for species with a low dispersal capacity (based on the connectance index—CONNECT), indicating that species with a medium- to long-distance dispersal capacity may be less affected by the history of losses and fragmentation of the Cerrado in the pasture matrix. The functional connectivity metrics used allowed a more robust analysis and, apparently, better reflected reality, but the lack of empirical data on dispersal capacity and the difficulty in choosing an indicator organism can limit their use in the management and planning of conservation and restoration areas.

Quantifying expert opinion with discrete choice models: Invasive elodea's influence on Alaska salmonids

Scientific evidence should inform environmental policy, but rapid environmental change brings high ecological uncertainty and associated barriers to the science-management dialogue. Biological invasions of aquatic plants are a worldwide problem with uncertain ecological and economic consequences. We demonstrate that the discrete choice method (DCM) can serve as a structured expert elicitation alternative to quantify expert opinion across a range of possible but uncertain environmental outcomes. DCM is widely applied in the social sciences to better understand and predict human preferences and trade-offs. Here we apply it to Alaska's first submersed invasive aquatic freshwater plant, Elodea spp. (elodea), and its unknown effects on salmonids. While little is known about interactions between elodea and salmonids, ecological research suggests that aquatic plant invasions can have positive and negative, as well as direct and indirect, effects on fish. We use DCM to design hypothetical salmonid habitat scenarios describing elodea's possible effect on critical environmental conditions for salmonids: prey abundance, dissolved oxygen, and vegetation cover. We then observe how experts choose between scenarios that they believe could support persistent salmonid populations in elodea-invaded salmonid habitat. We quantify the relative importance of habitat characteristics that influence expert choice and investigate how experts trade off between habitat characteristics. We take advantage of Bayesian techniques to estimate discrete choice models for individual experts and to simulate expert opinion for specific environmental management situations. We discuss possible applications and advantages of the DCM approach for expert elicitation in the ecological context. We end with methodological questions for future research.

Comparing Negative Impacts of Prunus serotina, Quercus rubra and Robinia pseudoacacia on Native Forest Ecosystems

The introduction of invasive alien plant species (IAPS) can modify plant-soil feedback, resulting in an alteration of the abiotic and biotic characteristics of ecosystems. Prunus serotina, Quercus rubra and Robinia pseudoacacia are IAPS of European temperate forests, where they can become dominant and suppress the native biodiversity. Assuming that the establishment of these invasive species may alter native forest ecosystems, this study comparatively assessed their impact on ecosystems. This study further investigated plant communities in 12 forest stands, dominated by the three IAPS and native trees, Quercus robur and Carpinus betulus (three plots per forest type), in Northern Italy, and collected soil samples. The relationships between the invasion of the three IAPS and modifications of humus forms, soil chemical properties, soil biological quality, bacterial activity and plant community structure and diversity (α-, β-, and γ-diversity) were assessed using one-way ANOVA and redundancy analyses (RDA). Our comparative study demonstrated that invaded forests often had unique plant and/or soil properties, relative to native forests, and the degree of dissimilarity depended on the invasive species. Particularly, Q. rubra is related to major negative impacts on soil organic horizons and low/modified levels of microarthropod and plant biodiversity. R. pseudoacacia is associated with an altered base content of soil and, in turn, with positive feedback to the soil biological quality (QBS-ar) and plant diversity, but with a high cover compared with other alien plant species. P. serotina is associated with intermediate impacts and exhibits a plant species assemblage that is more similar to those of native forest stands. Our work suggests impact-based management decisions for the three investigated IAPS, since their effects on the diversity and composition of resident ecosystems are very different.

Management feasibility of established invasive plant species in Queensland, Australia: A stakeholders' perspective

Managing and monitoring invasive alien species (IAS) is costly, and because resources are limited, prioritization decisions are required for planning and management. We present findings on plant pest prioritization for 63 established invader species of natural and grazing ecosystems of Queensland, Australia. We used an expert elicitation approach to assess risk (species occurrence, spread, and impact) and feasibility of control for each IAS. We elicit semi-quantitative responses from diverse expert stakeholders to score IAS on three management approaches (biocontrol, chemical and mechanical) in relation to cost, effectiveness and practicality, and incorporate uncertainty in expert inputs and model outputs. In the process, we look for promising management opportunities as well as seek general trends across species' ecological groups and management methods. Stakeholders were cautiously optimistic about the feasibility of managing IAS. Taking into consideration all factors, the overall feasibility of control was uncorrelated with the stakeholders' level of confidence. However, within individual management criterion, positive trend was observed for the same bivariate traits for chemical control, and negative trends for biocontrol and mechanical controls. Utility and confidence in IAS management options were in the order: chemical > biocontrol = mechanical, with practicality and effectiveness being the main driver components. Management feasibility differed significantly between IAS life forms but not between habitats invaded. Lastly, we combined IAS risk assessment and management feasibility scores to create a risk matrix to guide policy goals (i.e. eradication, spread containment, protection of sensitive sites, targeted control, site management, monitoring, and limited action). The matrix identifies promising species to target for each of these policy outcomes. Overall, our general approach illustrates (i) the importance of understanding the feasibility of IAS control actions and the factors that drive it, and (ii) demonstrates how quantifying management feasibility can be used to enhance traditional risk assessment rankings to improve policy outcomes.

Common deficiencies of actions for managing invasive alien species: a decision-support checklist

Despite the increasing number of invasive species, protocols devoted to assess the feasibility (i.e., probability of success or failure) of management actions in the field are scarce, yet success depends on a broad scope of issues beyond the biology of species and the ecosystem to be managed. In this paper we make a retrospective analysis of 90 actions and management proposals developed in Andalusia (southern Spain) in 2004 to 2018. Actions included 59 terrestrial and aquatic taxa. We identified items that in case of deficiency were responsible for either the rejection of action proposals (n = 44) or failure of implemented actions for which the goal was not achieved (n = 22). The most frequent deficiencies included the absence of funding during the necessary time to achieve the goals, the risk of reinvasion and an insufficient removal rate to achieve the specific objective. Based on the deficiencies found, we built a comprehensive, broad-scope compliance checklist to assist decision-makers to identify deficiencies before action. In addition, implemented actions for which the goal was achieved (n = 24) were used for validating the checklist. The checklist contains 40 items related to IAS features, administrative features, methodology effectiveness, efficiency and impacts of the action, and invaded ecosystem features. The checklist is valid across all taxa and habitats. The use of this checklist will help reduce the degree of arbitrariness and subjectivity of actions aimed at managing IAS, and a more efficient use of resources.

Non-native plants have greater impacts because of differing per-capita effects and nonlinear abundance-impact curves

Invasive, non-native species can have tremendous impacts on biotic communities, where they reduce the abundance and diversity of local species. However, it remains unclear whether impacts of non-native species arise from their high abundance or whether each non-native individual has a disproportionate impact - that is, a higher per-capita effect - on co-occurring species compared to impacts by native species. Using a long-term study of wetlands, we asked how temporal variation in dominant native and non-native plants impacted the abundance and richness of other plants in the recipient community. Non-native plants reached higher abundances than natives and had greater per-capita effects. The abundance-impact relationship between plant abundance and richness was nonlinear. Compared with increasing native abundance, increasing non-native abundance was associated with steeper declines in richness because of greater per-capita effects and nonlinearities in the abundance-impact relationship. Our study supports eco-evolutionary novelty of non-natives as a driver of their outsized impacts on communities.

Invasive shrub re-establishment following management has contrasting effects on biodiversity

Effective control of an invasive species is frequently used to infer positive outcomes for the broader ecosystem. In many situations, whether the removal of an invasive plant is of net benefit to biodiversity is poorly assessed. We undertook a 10-year study on the effects of invasive shrub management (bitou bush, Chrysanthemoides monilifera ssp. rotundata) on native flora and fauna in a eucalypt forest in south-eastern Australia. Bitou bush eradication is a management priority, yet the optimal control regime (combination of herbicide spray and fire) is difficult to implement, meaning managed sites have complex management histories that vary in effectiveness of control. Here we test the long-term response of common biodiversity indicators (species richness, abundance and diversity of native plants, birds, herpetofauna and small mammals) to both the management, and the post-management status of bitou bush (% cover). While average bitou bush cover decreased with management, bitou bush consistently occurred at around half of our managed sites despite control efforts. The relationship between biodiversity and bitou bush cover following management differed from positive, neutral or negative among species groups and indicators. Native plant cover was lower under higher levels of bitou bush cover, but the abundance of birds and small mammals were positively related to bitou bush cover. Evidence suggests that the successful control of an invader may not necessarily result in beneficial outcomes for all components of biodiversity.

Identifying thresholds and ceilings in plant community recovery for optimal management of widespread weeds

A substantial body of work underlies the theory and practice of early intervention in the management of invasive alien plants, but less attention has been paid to the strategic management of widespread weeds, especially in the context of natural asset recovery. The assumption lingers amongst some researchers and land managers that removing weeds will automatically lead to positive biodiversity outcomes, with the more weed removed, the better the outcome. However, this is often not the case, particularly for long-established weed species whose dominance has created impoverished communities with little capacity for passive recovery. A common result may be wasted investment in weed control and, in the extreme, net negative impacts upon asset values. We present a conceptual model for the management of weed-impacted assets, plus guidance for its application, with a view to improving asset recovery practice. Weed removal should be calibrated by asset recovery, which may mean not seeking to completely remove a weed at a given spatial scale. Our model focusses on weed removal that is enough to initiate asset recovery, but not more than is necessary to promote maximum expression of asset resilience, particularly in the context of secondary invasions. Optimal management efficiency will involve a proportional allocation of resources to control, monitoring and revegetation activities that is appropriate to the stage of asset recovery, as well as a willingness to revise a management goal if the original one cannot be achieved within existing constraints on resources.