South Texas is home to a high diversity of species due to its location at the confluence of subtropical, desert, and coastal ecoregions. Historical overgrazing of South Texas rangelands transformed the savanna and prairie to a landscape dominated by woody plants and shrubs interspersed with low seral grass species and bare ground. During the first half of the 20th century, exotic grass species, coupled with the application of industrial agricultural practices appeared to be the future of forage production in South Texas and elsewhere. Several of these exotic species, namely King Ranch bluestem [Bothriochloa ischaemum (L.) Keng], Kleberg bluestem [Dichanthium annulatum (Forssk.) Stapf], Angelton bluestem [Dichanthium aristatum (Poir.) C.E. Hubbard], buffelgrass [Pennisetum ciliare (L.) Link], guineagrass [Urochloa maxima (Jacq.) R. Webster], Lehmann lovegrass (Eragrostis lehmanniana Nees), and Bermudagrass [Cynodon dactylon (L.) Pers.], have escaped pasture cultivation. Additionally, the native grass tanglehead [Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult.] has begun displaying invasive behaviors. The monoculture growth habit of these species simplifies vegetation structure, reduces biodiversity, and decreases habitat for many species of wildlife. These grasses also alter natural fire regimes and nutrient cycling. This landscape-level transformation of vegetation composition and structure requires monitoring to quantify and assess the spatial and temporal distributions of invasive species as a basis to inform management practices. Current advances in remote sensing technologies, such as very high spatial resolution coupled with daily satellite imagery and unmanned aerial vehicles, are providing tools for invasive vegetation monitoring. We provide a synthesis of the natural history of these grasses, including their introductions, an overview of remote sensing applications in South Texas, and recommendations for future management practices.

Ornamental jewelweed (Impatiens glandulifera Royle) is an alien invasive plant in Europe. This annual plant often grows in riparian habitats where herbicides are prohibited. Several studies have reported the negative effect on ecosystem and ecosystem services by this species. However, limited research is published on control measures and the aim of our study was to explore use of hot water and cutting to control I. glandulifera. A lab experiment showed that the lethal water temperature for seed was between 45 and 50 C. In a pot experiment with seeds in soil, emergence of I. glandulifera was reduced by 78% and 93% compared with the untreated control with volumes of hot water (80 C) of 7.2 and 14.5 L m−2, respectively. When treatments were conducted on relatively tall plants (almost 60 cm) in late June, hot water gave significantly better control than cutting. Compared with an untreated control, I. glandulifera cover was reduced by 97% and 79% after hot water and cutting, respectively. Application of hot water to smaller (<40 cm) and less developed plants (BBCH 12–13) in early June and cutting of plants with visible flower buds (mid-July) led to no significant difference in cover. Compared with an untreated control, I. glandulifera cover was reduced by 99% (cut below first node) and 91% (hot water and cut above first node). When relatively tall plants (almost 60 cm) were treated, hot water use was high (31.1 L m−2) and required twice as many work hours (4.8 min m−2) as cutting (2.4 min m−2). When smaller plants (<40 cm) were targeted, work hours and hot water use were reduced to 2.1 min m−2 and 13.7 L m−2, respectively.

Glossy privet (Ligustrum lucidum W. T. Aiton) is a highly aggressive tree that has become globally invasive in a wide range of habitats and can quickly form dense thickets, shading and outcompeting native vegetation. Slowly decomposing slash following removal of dense infestations can create additional management challenges, including fire risk concerns, which curtailed planned invasive plant removal projects on certain tracts within the Balcones Canyonlands Preserve near Austin, TX. This prompted a pilot study to explore whether wood-decaying fungi could be used to hasten the recycling of L. lucidum logs back into the forest ecosystem. We inoculated 25 freshly cut L. lucidum logs with Trametes versicolor (Fr.) Pilat at two study sites and monitored the inoculated logs and 5 untreated control logs over a 3-yr period (February 2015 to March 2018). We found that inoculation significantly accelerated wood decay. By the end of our study, 100% of logs with >3 inoculation points were in advanced stages of decay, while only one of the control logs showed noticeable signs of decay. Inoculating logs in the field was easy and suitable for novices, requiring little or no previous experience to achieve successful results. An added benefit of using T. versicolor is its medicinal properties and potential for bioremediation. We have continued to inoculate logs with comparable success and are integrating them into forest restoration projects. Applied on a larger scale, these wood-decaying fungi have the potential to transform nonnative deadwood from a threat to an asset.

Rapid increases in herbicide resistance have highlighted the ability of weeds to undergo genetic change within a short period of time. That change, in turn, has resulted in an increasing emphasis in weed science on the evolutionary ecology and potential adaptation of weeds to herbicide selection. Here we argue that a similar emphasis would also be invaluable for understanding another challenge that will profoundly alter weed biology: the rapid rise in atmospheric carbon dioxide (CO2) and the associated changes in climate. Our review of the literature suggests that elevated CO2 and climate change will impose strong selection pressures on weeds and that weeds will often have the capacity to respond with rapid adaptive evolution. Based on current data, climate change and rising CO2 levels are likely to alter the evolution of agronomic and invasive weeds, with consequences for distribution, community composition, and herbicide efficacy. In addition, we identify four key areas that represent clear knowledge gaps in weed evolution: (1) differential herbicide resistance in response to a rapidly changing CO2/climate confluence; (2) shifts in the efficacy of biological constraints (e.g., pathogens) and resultant selection shifts in affected weed species; (3) climate-induced phenological shifts in weed distribution, demography, and fitness relative to crop systems; and (4) understanding and characterization of epigenetics and the differential expression of phenotypic plasticity versus evolutionary adaptation. These consequences, in turn, should be of fundamental interest to the weed science community.

Common practices for invasive species control and management include physical, chemical, and biological approaches. The first two approaches have clear limitations and may lead to unintended (negative) consequences, unless carefully planned and implemented. For example, physical removal rarely completely eradicates the targeted invasive species and can cause disturbances that facilitate new invasions by nonnative species from nearby habitats. Chemical treatments can harm native, and especially rare, species through unanticipated side effects. Biological methods may be classified as biocontrol and the ecological approach. Similar to physical and chemical methods, biocontrol also has limitations and sometimes leads to unintended consequences. Therefore, a relatively safer and more practical choice may be the ecological approach, which has two major components: (1) restoration of native species and (2) biomass manipulation of the restored community, such as selective grazing or prescribed burning (to achieve and maintain viable population sizes). Restoration requires well-planned and implemented planting designs that consider alpha-, beta-, and gamma-diversity and the abundance of native and invasive component species at local, landscape, and regional levels. Given the extensive destruction or degradation of natural habitats around the world, restoration could be most effective for enhancing ecosystem resilience and resistance to biotic invasions. At the same time, ecosystems in human-dominated landscapes, especially those newly restored, require close monitoring and careful intervention (e.g., through biomass manipulation), especially when successional trajectories are not moving as intended. Biomass management frequently uses prescribed burning, grazing, harvesting, and thinning to maintain overall ecosystem health and sustainability. Thus, the resulting optimal, balanced, and relatively stable ecological conditions could more effectively limit the spread and establishment of invasive species. Here we review the literature (especially within the last decade) on ecological approaches that involve biodiversity, biomass, and productivity, three key community/ecosystem variables that reciprocally influence one another. We focus on the common and most feasible ecological practices that can aid in resisting new invasions and/or suppressing the dominance of existing invasive species. We contend that, because of the strong influences from neighboring areas (i.e., as exotic species pools), local restoration and management efforts in the future need to consider the regional context and projected climate changes.

European swallowwort [Vincetoxicum rossicum (Kleopow) Barbarich] is found in the northeastern United States and southeastern Canada. It forms dense growth patterns that reduce plant and insect biodiversity, and lab assays show that it produces allelopathic compounds that affect microbial activity. Consequently, we hypothesized that V. rossicum alters soil microbiome composition and activity in invaded habitats, which may impact ecosystem properties and processes. We sampled soil from a similar time point within a growing season at each of five sites in New York State where V. rossicum was both present and absent. We measured bacterial and fungal microbiome composition, available soil nitrogen (N), soil respiration (CO2 flux), and soil extracellular enzyme activities. Microbial composition varied across field sites, but only fungal composition was affected by invasion. No significant differences were found between the invaded and uninvaded plots at any of the sites for available soil ammonium, nitrate, or respiration, though extractable N varied greatly between sites. Microbial hydrolytic extracellular enzyme activities suggest decreased protein degradation and increased oxidative enzyme activity with V. rossicum invasion, which is relevant to soil N and carbon cycling processes. Although V. rossicum impacted rhizosphere microbial composition and activity, it was not associated with large perturbations in ecosystem function when examined across multiple invasion sites during this short-term study.

Cogongrass [Imperata cylindrica (L.) Beauv.] is an invasive grass in the southeastern United States, and its impacts strongly affect the region, especially Florida. Herbicide strategies have been limited to glyphosate in natural areas and imazapyr in managed pine forests and non-crop areas where its soil residual activity is of less concern. This lack of options has raised concern for herbicide resistance, which has never been documented for I. cylindrica. Land managers have also reported variable I. cylindrica control, especially with glyphosate. To determine whether herbicide resistance was a possible explanation, we examined glyphosate response of I. cylindrica from 12 Florida populations. We also tested aminocyclopyrachlor with and without glyphosate and flumioxazin with glyphosate. Results indicated that herbicide performance was similar across I. cylindrica populations: glyphosate and aminocyclopyrachlor reduced I. cylindrica biomass by 78% and 76%, respectively, and the combined tank mix reduced cogongrass biomass by 91%. Flumioxazin tank mixed with glyphosate did not improve control compared with glyphosate alone. There were no differences in pretreatment I. cylindrica shoot height, with the exception of two panhandle populations that were shorter. Subsequent harvests indicated few differences in shoot and root plus rhizome weights among untreated controls for almost all populations, with the exception of one of the initially shorter panhandle populations. Our findings indicate that variability in glyphosate efficacy, as suggested by managers, is unlikely due to any conferred resistance. Other abiotic factors such as drought and shade and applicator factors such as carrier water quality should be examined to better understand this issue. Additional studies examining non-target impacts of aminocyclopyrachlor should be conducted to determine its potential fit into I. cylindrica management.

In the city of Tromsø in northern Norway, invasive Tromsø palm (Norwegian: Tromsøpalme; English: Persian hogweed) is widespread. Although Tromsø palm has negative impacts on biodiversity and contains a phototoxic sap that burns human skin, it is also considered to be a local symbol of Tromsø city and is appreciated by many inhabitants. This study examined private landowners’ characteristics, perceptions, and landowners’ regulation of invasive Tromsø palm on their parcels on Tromsø Island in 2012 (vegetation season: May–September) to provide information concerning which landowner groups could be assisted by official regulation. Eleven key informants and 17 landowners were interviewed. Afterward, Tromsø palm on Tromsø Island was mapped using aerial photos and street-level photos from Google Maps®/Google Street View® and fieldwork verification. This distribution map was superimposed on a property map in a geographic information system to produce a map showing private parcels that contained Tromsø palm and associated neighboring parcels that did not contain Tromsø palm. Questionnaires were mailed to the 441 owners of the selected parcels, and 199 of the returned questionnaires were analyzed. Tromsø palm was more likely to be fully regulated/absent on a parcel that was inhabited (particularly if the owner lived on-site) and less likely to be fully regulated/absent if the parcel was jointly managed by several households. These findings indicate that authorities could focus their management efforts on supporting regulation efforts of those private landowners who own currently uninhabited or rented-out parcels and landowners of parcels jointly managed by several households. Furthermore, those landowners who found regulation measures against the plant on Tromsø Island important tended to have partly or fully regulated Tromsø palm on their plots. This might imply that information campaigns from authorities might encourage more landowners to regulate Tromsø palm.

Local abiotic and biotic conditions can alter the strength of exotic species impacts. To better understand the effects of exotic species on invaded ecosystems and to prioritize management efforts, it is important that exotic species impacts are put in local environmental context. We studied how differences in plant community composition, photosynthetically active radiation (PAR), and available soil N associated with Russian olive presence are conditioned by local environmental variation within a western U.S. riparian ecosystem. In four sites along the South Fork of the Republican River in Colorado, we established 200 pairs of plots (underneath and apart from Russian olive) to measure the effects of invasion across the ecosystem. We used a series of a priori mixed models to identify environmental variables that altered the effects of Russian olive. For all response variables, models that included the interaction of environmental characteristics, such as presence/absence of an existing cottonwood canopy, with the presence/absence of Russian olive canopy were stronger candidate models than those that just included Russian olive canopy presence as a factor. Compared with reference plots outside of Russian olive canopy, plots underneath Russian olive had higher relative exotic cover (exotic/total cover), lower perennial C4 grass cover, and higher perennial forb cover. These effects were reduced, however, in the presence of a cottonwood canopy. As expected, Russian olive was associated with reduced PAR and increased N, but these effects were reduced under cottonwood canopy. Our results demonstrate that local abiotic and biotic environmental factors condition the effects of Russian olive within a heterogeneous riparian ecosystem and suggest that management efforts should be focused in open areas where Russian olive impacts are strongest.

Introductions of biocontrol beetles (tamarisk beetles) are causing dieback of exotic tamarisk in riparian zones across the western United States, yet factors that determine plant communities that follow tamarisk dieback are poorly understood. Tamarisk-dominated soils are generally higher in nutrients, organic matter, and salts than nearby soils, and these soil attributes might influence the trajectory of community change. To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, we conducted separate germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. Focal species were two common native (red threeawn, sand dropseed) and two common invasive exotic plants (Russian knapweed, downy brome), planted alone and in combination. Nutrient, salinity, wood chip, and litter manipulations examined how tamarisk litter affects the growth of other species in a context of riparian zone management. Tamarisk litter, tamarisk litter leachate, and fertilization with inorganic nutrients increased growth in all species, but the effect was larger on the exotic plants. Salinity of 4 dS m−1 benefitted Russian knapweed, which also showed the largest positive responses to added nutrients. Litter and wood chips generally delayed and decreased germination; however, a thinner layer of wood chips increased growth slightly. Time to germination was lengthened by most treatments for natives, was not affected in exotic Russian knapweed, and was sometimes decreased in downy brome. Because natives showed only small positive responses to litter and fertilization and large negative responses to competition, Russian knapweed and downy brome are likely to perform better than these two native species following tamarisk dieback.

Corallita (Antigonon leptopus) is a perennial vine, lauded as an ornamental for its vigorous growth, and plentiful (usually) pink flowers, and even its ability to smother unsightly landscapes. In the United States it thrives in horticultural zones 8 to 10, and also is successfully grown worldwide in tropical climates. When corallita is neglected, it can grow quickly over other vegetation, spreading beyond its area of introduction. Once established, it is difficult to eradicate because it produces many tuberous roots that can propagate vegetatively. Its fruits are buoyant, allowing for successful seed dispersal in water. The islands of Guam (South Pacific Ocean) and St. Eustatius (Caribbean Sea) represent two regions where corallita has become so pervasive that it threatens local diversity. In Florida, already it is classified as a Category II invasive. Our report reviews the literature and past studies of corallita, in addition to adding new taxonomic and distribution information from herbarium specimens to clarify the identity and geographic range. It is recommended that introductions of this plant by the horticultural industry in both tropical and temperate regions be closely monitored to prevent spread. On tropical island nations, we advise against any new introductions.

Nonnative Spartina species (cordgrasses) are widely distributed along the West Coast of North America, but have not invaded all bays with susceptible habitat. We used drift cards to assess the patterns and rates of potential Spartina propagule dispersal by ocean currents from estuaries with significant populations of one or more Spartina species. Cards were released monthly for 1 yr from Willapa Bay, Washington; Humboldt Bay, California; and San Francisco Bay, California; with recovery information reported by volunteers. Recovery rates averaged 37% for all release sites. Cards were commonly recovered close to their bay of release but were repeatedly found hundreds of kilometers both north and south of their release location. Cards most generally traveled northward from the release sites. Cards from Humboldt and Willapa bays were commonly recovered along the British Columbia coast, particularly in the winter. Cards released from Humboldt Bay were found farthest from their release sites. One card from Humboldt Bay traveled 2,800 km to Kodiak Island, Alaska. The timing of seed production, combined with prevailing currents, puts bays currently uninfested by Spartina at risk of repeated propagule loading by ocean currents. A coordinated coast-wide strategy for eradication of all nonnative Spartina will be critical to the success of individual bay-wide eradication efforts.

Models have been developed to simulate the long-term effects of weed treatments across a landscape to determine effective management strategies, but those models might not be suitable for evaluating short-term action plans of weed treatments that are specific in time and place. In this study, we developed a simulation model to build and evaluate 5-yr weed treatment plan options in terms of their cost and effectiveness in minimizing total infestation areas over the short-term planning horizon. In an iterative, interactive process, 5-yr treatment plan options are developed based on user-defined weed treatment preferences, and evaluated in terms of total projected infestation areas at the end of the planning horizon. The simulation model was applied to a study area of 24,867 ha (61,447 ac) located in the Salmon River watershed in Idaho. Eight treatment plan options were developed using two treatment priority strategies and four increasing budget levels, and compared for their effectiveness. The application results showed that regardless of budget levels, site priority strategies were more cost-effective than the species priority strategies in reducing total infestation areas over time. This simulation model can provide weed managers with a useful tool to evaluate short-term treatment options, and thus support informed decision-making for effective weed management. Although the availability and quality of input data may be a practical limitation of using the simulation model, more data would become available and improved as more invasive species monitoring programs are implemented.

Downy brome is a problematic invasive annual grass throughout western rangeland and has been increasing its abundance, spread, and impacts across Montana during the past several years. In an effort to develop effective management recommendations for control of downy brome on Montana rangeland, we compiled data from 24 trials across the state that investigated efficacy of imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC) applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We ran a mixed-model ANOVA to test for main effects and interactions across application rate (70, 105, 141, 176, and 211 g ai ha−1), application timing (preemergent [PRE], early postemergent [EPOST, one- to two-leaf growth stage], and postemergent [POST, three- to four-leaf growth stage]), and adjuvant (MSO, NIS). Application timing and rate interacted to affect downy brome control (P = 0.0033). PRE imazapic application resulted in the lowest downy brome control (5 to 19%), followed by POST application (25 to 77%) and EPOST application (70 to 95%). Downy brome control remained fairly consistent across rates within application timing. Adjuvant (MSO or NIS) did not affect downy brome control (P = 0.2789). Our data indicate that POST application at 105 to 141 g ai ha−1 provides the most-consistent, short-term control of downy brome. Furthermore, applying imazapic to downy brome seedlings shortly after emergence (one- to two-leaf growth stage) provided better control than applying it to older downy brome seedlings (three- to four-leaf growth stage).

Japanese hedgeparsley is an annual (or sometimes biennial) forb introduced from Eurasia and found throughout much of the eastern United States and parts of extreme southern Canada. In North America, Japanese hedgeparsley is commonly found in ruderal habitats, such as roadsides, railroad rights-of-way, forest edges, and urban waste spaces. This species has not yet been listed as a noxious invasive, but its expanding populations have caused concern in several Midwestern states. The primary threat from Japanese hedgeparsley is its vigorous growth habit, which creates dense patches, and its dispersal ability, facilitated by its clinging, burr-like fruits. Some confusion on identification exists within the Torilis genus, with similar species (particularly T. arvensis) frequently misidentified in herbaria and the literature. Here, we review aspects of the etymology, taxonomy, biology, distribution, and management of Japanese hedgeparsley with the objective of increasing awareness of the potential threat posed by this species and its closely related congeners.

Energy-extraction disturbances entail soil handling and often have large edge-to-area ratios. These characteristics should be considered when designing weed-control strategies. In western North America, many energy developments coincide with infestations of downy brome, an annual grass that severely curtails productivity, diversity, and habitat value of invaded areas. Downy brome is sensitive to soil compaction and seed burial, both of which may occur when soil is handled. In this study, I examined the effect of soil-density manipulations and herbicide application (105 g ai ha−1 imazapic with 280 g ai ha−1 glyphosate) on six simulated pipeline disturbances in a Wyoming big sagebrush ecosystem invaded by downy brome. Disturbances occurred at the end of the growing season, after ambient downy brome seed rain in the study areas had abated. Treatments and seeding occurred shortly after disturbances. The following spring, downy brome seedling density was 10-fold lower within disturbances than in control areas, but seedling density quickly rebounded in disturbed areas where no herbicide had been applied. In herbicide plots, downy brome seedling density remained low during the first growing season, and shrub cover after 3 yr was eight times higher than in no-herbicide plots. Soil density manipulations via disking and rolling treatments had little effect on downy brome. Prior research has shown that imazapic is more effective when combined with disturbances, such as fire. This study demonstrates that imazapic may also be effective in combination with a disturbance that is timed to bury downy brome seeds.

Giant reed is an invasive weed throughout the southern half of the United States, with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. The objective of this study was to use aerial photography to map giant reed infestations and to estimate infested areas along the Texas–Mexico portion of the Rio Grande. Aerial color-infrared photographs were taken along the Rio Grande between Brownsville and El Paso, TX, in June and July 2002. Based on the aerial photographs and ground surveys, the portion of the river from San Ygnacio to Lajitas, which has a river length of 898 km (558 mi), was found to be infested with giant reed. To estimate infested areas along both sides of the river, 65 (13.5%) of the 480 aerial photographs taken between Lajitas and San Ygnacio were randomly selected. The aerial photographs were digitized, rectified to Google Earth imagery, and then classified using maximum-likelihood classification techniques. The infested areas on both sides of the river, as well as water area and river length, from each photographic image were determined. Based on the estimates from the 65 aerial photos, the ratio of giant reed area to water area and the ratio of giant reed area to river length were calculated. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio was estimated to be 5,981 ha (14,779 ac) with 3,714 ha or 62% on the U.S. side and 2,267 ha or 38% on the Mexican side. This study provides the first accurate estimates of giant reed infestations along the Texas–Mexico portion of the Rio Grande and will be useful for both land owners and government agencies for the estimation of water usage and economic loss and for the management and control of giant reed.

The expansion of populations of invasive species continues to compromise the ecological and economic integrity of our natural resources. The negative effects of invasive species on native biota are widely reported. However, less is known about how the duration (i.e., age of oldest invaders) and intensity (i.e., density and percent cover) of an invasion influences native plant diversity and abundance at the microsite scale. We examined the influence of density, percent cover, and age of Amur honeysuckle (a nonnative invasive shrub), and several environmental factors on native plant taxa at 12 mixed hardwood forests in Indiana, USA. Overall, study sites with the greatest taxonomic diversity (Shannon's Diversity; H′), richness (S), percent cover, and density of native vegetation also had the lowest percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m). Based on linear mixed model analyses, percent cover of Amur honeysuckle in the upper vertical stratum was consistently and negatively correlated with H′, S, total percent cover, and woody seedling density of native taxa at the microsite scale (P < 0.05). Duration of Amur honeysuckle at the microsite scale was not significant when percent cover of Amur honeysuckle in the upper vertical stratum was included in models. However, duration of Amur honeysuckle invasion was significantly correlated with dependent variables and with upper-stratum honeysuckle cover, suggesting that older Amur honeysuckle in a microsite resulted in greater light competition from above for native understory plant species. Beyond increased cover and shading, our results do not provide evidence of duration-related effects from long-term dominance of honeysuckle in our sampled mixed hardwood forest sites.

The United States is charging toward the largest expansion of agriculture in 10,000 years with vast acreages of primarily exotic perennial grasses planted for bioenergy that possess many traits that may confer invasiveness. Cautious integration of these crops into the bioeconomy must be accompanied by development of best management practices and regulation to mitigate the risk of invasion posed by this emerging industry. Here I review the current status of United States policy drivers for bioenergy, the status of federal and state regulation related to invasion mitigation, and survey the scant quantitative literature attempting to quantify the invasive potential of bioenergy crops. A wealth of weed risk assessments are available on exotic bioenergy crops, and generally show a high risk of invasion, but should only be a first-step in quantifying the risk of invasion. The most information exists for sterile giant miscanthus, with preliminary empirical studies and demographic models suggesting a relatively low risk of invasion. However, most important bioenergy crops are poorly studied in the context of invasion risk, which is not simply confined to the production field; but also occurs in crop selection, harvest and transport, and feedstock storage. Thus, I propose a nested-feedback risk assessment (NFRA) that considers the entire bioenergy supply chain and includes the broad components of weed risk assessment, species distribution models, and quantitative empirical studies. New information from the NFRA is continuously fed back into other components to further refine the risk assessment; for example, empirical dispersal kernels are utilized in landscape-level species distribution models, which inform habitat invasibility studies. Importantly, the NFRA results in a relative invasion risk to known species (e.g., is giant reed a higher or lower invasion risk than johnsongrass). This information is used to design robust mitigation plans that include record keeping, regular scouting and reporting, prudent harvest and transport practices that consider species biology, and eradication protocols as an ultimate precaution. Finally, a socio-political balance must be struck (i.e., a cost-benefit analysis) among our energy choices that consider the broader implications, which includes the risk of future invasions.

Data on 111 environmental weed eradication programs carried out by the New Zealand Department of Conservation (DOC) have been collected and summarized. A total of 21 programs were discontinued, and 90 are ongoing. Within the ongoing programs, four have been successful in that no plants remain at any known infestations. All four of the successful eradications had a total area across all infestations of less than 1 ha (2.5 ac); however, many similar-sized programs were not successful. Correctly assessing the extent of infestations appears to be a major problem for discontinued programs. Some of the ongoing programs are progressing toward eradication, but this is taking much longer than initially anticipated. The strongest determinant of progress toward eradication was found to be the identity of the DOC administrative area, for reasons that are only speculative. The number and area of initial infestations had no effect on progress toward eradication. However, the rate at which new infestations were located was negatively correlated with progress. Across many programs, progress was restricted by inconsistent infestation visitation. After running for a decade, DOC's weed eradication strategy has yet to provide significant dividends. Environmental weed eradication is clearly more difficult than has previously been acknowledged in New Zealand.