There is great potential for integrating science and management to control or mitigate nonnative species, but such an integration faces substantial obstacles. Fundamental differences between science and management threaten the ability of scientists and managers to collaborate effectively. For example, science strives for generality, whereas management of natural resources is necessarily a site- and objective-specific endeavor. In addition, the literature on biological invasions is characterized by weak inference, relying mostly on post hoc, correlative research because of ethical and practical concerns associated with purposeful introductions. These obstacles notwithstanding, several patterns have been documented with respect to plant invasions and ecosystem processes. Unfortunately, documenting rates and patterns of spread has provided little predictive power and few clues about control strategies. It is clear, however, that predicting and controlling the spread of invasive species will require a concerted, holistic effort that integrates science and management.

Additional index words: Community structure, ecosystem function, plant invasions, resource management.

Abbreviation: NPS, National Park Service.

A strategic approach to weed management includes eradication of potential weed species before they become major problems where the only management options are containment or ongoing control—but which species should and can be eradicated? In this article, we describe a framework of quantitative methods to identify “sleeper weeds” for which eradication is a desirable and feasible strategy.

Additional index words: Cost, feasibility, invasive species, potential impact.

Abbreviations: PFE, profit at full equity; WRA, weed risk assessment.

Red quinine tree has been recognized as a serious weed in the Galapagos National Park for three decades. During this time, a variety of control methods have been implemented, initially with poor results. In this article, we reviewed past efforts to control red quinine tree and tested a variety of herbicides and selective application methods. A mixture of picloram and metsulfuron (240 and 15 g ai/L, respectively) killed 73 to 100% of trees when applied to connecting machete cuts around the circumference of tree trunks (hack and squirt [HS]) at concentrations of 5, 10, and 20% in water, with larger trees requiring higher concentrations for best results. Although this herbicide mixture also was effective when applied using other methods, HS was the least labor intensive and costly. The control methods developed could be used to combat this weed in other locations including Hawaii and Tahiti.

Nomenclature: Metsulfuron; picloram; red quinine tree, Cinchona pubescens Vahl.

Additional index words: Cinchona succirubra, Galapagos National Park, Hawaii.

Abbreviations: BB, basal bark; CDRS, Charles Darwin Research Station; CS, cut stump; DBH, diameter at breast height; GNP, Galapagos National Park; GS, girdle and squirt; HS, hack and squirt; H, hack only; MASL, meters above sea level; WS, wide-band hack and squirt.

The restoration and management of regulated rivers is important for sustaining all types of ecosystems across the world. The northern area of the Senegal River basin has endured major ecological change after the construction of the Diama and Manantali dams. Karibaweed has become a major problem in the region. Permanent availability of freshwater in the Diama reservoir and the blockage of the seasonal seawater intrusion induced the proliferation and the extension of many macrophyte species. The abundance and distribution of invasive species and their impacts were surveyed in September and October 2002. This monitoring was combined with a malacologic survey to establish a correlation between the densities of several weed species and mollusk populations. Cattail species increased in density between the two surveys. Presence of some mollusk species were correlated with water depth and current velocity, and others were correlated with abundance of aquatic plants. The invasive plants reduced flow of water in the irrigation channels, which aggravated the sedimentation process in the infrastructures. The delta ecosystem is weakened by the regulated infrastructures, and the exploitation of macrophytes has seriously reduced the agricultural potential of the region.

Nomenclature: Cattail, Typha latifolia (L.) and Typha domingensis Pers.; Karibaweed, Salvinia molesta Mitch. #³ SAVMO.

Additional index words: Bilharzias, dams, invasive plants, Senegal River.

Abbreviations: IRp, relative density index; SRB, Senegal River basin.

In India's Valley of Flowers National Park, the density of the Himalayan knotweed differed significantly between stable and unstable habitats. Manual removal of this aggressive and colonizer species will be counterproductive, resulting in replacement by another colonizer, balsam. Eradication of the Himalayan knotweed is also not recommended because it will initiate land instability and hinder the establishment of natural plant communities.

Nomenclature: Balsam, Impatiens sulcata Wall.; Himalayan knotweed, Polygonum polystachyum Wall. ex Meissn.

Additional index words: Colonizers, grazing, Himalayas, livestock, Valley of Flowers.

Abbreviation: VOF, Valley of Flowers.

Soil water availability is a primary determinant of successful plant establishment on western rangelands. Two major factors that determine water availability are seasonal and annual patterns of precipitation and the presence of competitive annual weeds. Seedbed microclimate and germination response models can be used to evaluate alternative management treatments and plant materials and to incorporate medium- and long-term weather forecasts into real-time management planning. To take full advantage of these tools it is necessary to separate short-term soil stabilization and longer-term biodiversity and restoration objectives. Emergency rehabilitation policies prioritize establishment of plants that will both stabilize the soil and compete successfully with invasive weeds. Weather forecast information and modeling may be more useful to longer term restoration planning where revegetation and weed control actions can be deferred to coincide with a favorable microclimatic forecast.

Additional index words: Big squirreltail, bluebunch wheatgrass, Bromus tectorum L., cheatgrass, Elymus multisetus (J. G. Smith) M. E. Jones, emergency rehabilitation, invasive weeds, Pseudoroegneria spicata (Pursh) Löve, restoration.

Biological processes and characteristics are important factors in the introduction, spread, and establishment of invasive weeds. These biological traits include reproduction, dispersal, phenology, physiology, protection from herbivores, tolerance to environmental extremes, and interspecific interactions. Measures and methods to prevent dispersal, establishment, and persistence of nonnative invasive weeds include knowledge of the most vulnerable growth stages, management strategies, maintenance of weed-free areas, and sanitation of vehicles, transportation equipment, animals, and other modes of dispersal.

Additional index words: Dispersal, ecology, invasive weeds, reproduction.

The objective of this paper is to provide insights into exotic and native invasive species dynamics using a conceptual model developed from the long history of research on native woody plant invasion into perennial grasslands in the southwestern United States. We first describe our new conceptual model that focuses on landscape characteristics (spatial configuration and connectivity) interacting with environmental drivers and biotic processes across multiple scales. We then provide support for the model using a long-term data set from southern New Mexico. Our results show that both local and spatially contagious processes can be important in generating temporal and spatial variation in native grass cover. Upland grass basal cover was related to both local (soil texture, precipitation, grazing by cattle) and spatial processes (shrub seed dispersal). Lowland grass basal cover was related to local processes associated with plant available water as well as grazing by cattle. We discuss new insights that this model has to offer for understanding, predicting, and managing exotic invasive species dynamics.

Additional index words: Chihuahuan Desert, conceptual model, landscape connectivity, landscape context.

A first inventory of the exotic flora of Chad has been compiled on the basis of the published literature, original distribution data collected by Global Positioning System field surveys (1999 to 2003), and plant exsiccata. A strictly geographical and conservative approach was adopted including only cultivated species and those with a native range separated from Chad territory. The reported aliens (131 taxa) represent approximately 6% of the total flora of the region (ca. 2,250 taxa). Most were introduced deliberately after 1823 (neophytes), from Central and tropical America. Agricultural weeds and ruderal species accounts for the 18%. Because source data may be underestimated, further assessments are proposed.

Additional index words: Chad, checklist, exotic flora, GPS survey, West Africa.

Abbreviations: GPS, Global Positioning System; IAS, invasive alien plants.

Exotic plant invasions can alter the stocks and flux rates of carbon, nutrients, and water within a wide range of ecosystems. In addition to direct changes in the distribution and amounts of biomass, these changes can be associated with known and suspected mechanistic pathways by which plants affect the structure and function of the soil biota. A variety of both aboveground and belowground plant traits can be identified that effect changes in nutrient stocks and fluxes. From a review of cases in which such traits have been compared between exotic species and co-occurring native species, several traits emerge as potentially useful for predicting the ecosystem-level effects and for screening the species for potential effects. These traits include overall size (biomass, height growth, and horizontal cover) much larger than any native; high growth rate (measured as relative growth rate or photosynthetic rate); the capacity to form dominating ground cover; high live tissue and litter nutrient contents, especially nitrogen; the presence of nitrogen-fixing symbioses; and root system size or morphology that contrasts strongly with native species. Although the usefulness of plant traits for assessing and predicting the effects of exotic species invasions on ecosystem processes requires further research on basic aspects of plant–soil interactions, these results suggest that such an approach may prove useful for managing invasions.

Additional index words: Ecosystems, exotic species, nitrogen, plant–soil interactions, plant traits.

Mathematical and process-based simulation models are powerful tools for synthesizing information about invasive species. However, there are a number of different types of models, ranging from simple to complex that can be selected for any given application. In this article, a model classification framework of three types of models is applied to studies of invasive species that allows the objective selection of a model type on the basis of its ability to capture key processes and dynamics, yet minimize the errors in prediction. Model selection is illustrated using a series of increasingly complex models.

Additional index words: Nonspatial models, spatially explicit models, spatially implicit models.

Three experimental designs for analysis and prediction of plant invasions from the traits of alien species and the traits of potentially invasible ecosystems were compared. Two designs that involve manipulation, i.e., mimicking conditions experienced by invaders in a growth chamber and simulating invasion in synthetic communities, are most useful for testing specific mechanisms of invasions, as well as for identifying traits of potential importance. Field designs without manipulation are more suitable to test the value of these traits for predictive frameworks.

Additional index words: Invasibility, invasion success, invasiveness, synthetic ecosystems.

Successful control of invasive plants can have unexpected effects on native plants and wildland systems. Therefore, it is important for managers of invasive species to be concerned with ecological mechanisms and processes like invasion resistance, environmental heterogeneity, and succession that direct plant community dynamics. Augmentative restoration is a management approach for restoring desired species on wildlands dominated by invasive plants, where functioning ecological processes are maintained by selectively augmenting only those processes that are not operating sufficiently. The study was conducted within the Mission Valley, Montana, in an area where meadow vole disturbance provided site availability for colonization. In a split-plot design with four replications, eight factorial treatment combinations from three factors (shallow tilling, watering, and seeding) were applied to whole plots, and 2,4-D was applied to subplots. Cover and density of seeded species, spotted knapweed, and sulfur cinquefoil were sampled in July 2002 and 2003 to produce pretreatment and posttreatment data. Analysis of covariance was used to analyze cover and density data using pretreatment data as a baseline covariate. Data indicated that in areas with adequate site availability due to meadow vole disturbance, seeding and watering without tilling were required to increase seeded species. Spotted knapweed and sulfur cinquefoil decreased in response to 2,4-D. These data provided evidence that augmentative restoration may improve our ability to establish desired species on invasive plant–dominated wildlands.

Nomenclature: 2,4-D; spotted knapweed, Centaurea maculosa Lam.; sulfur cinquefoil, Potentilla recta L.

Additional index words: Environmental heterogeneity, invasive weeds, native plant establishment, successional management.

Abbreviations: ANCOVA, analysis of covariance.

Insect-mediated indirect interactions between native plant species recently have been shown to be important determinants of plant performance in a number of ecological communities. However, the potential indirect effects of exotic plant invasion on native plant species are not well understood. We examined whether the presence or proximity of the targeted exotic weed, musk thistle, influences the magnitude of attack on native thistles by the introduced biological control, flowerhead weevil. At the local scale, we quantified weevil egg densities on heads of the native wavyleaf thistle growing at different distances (0 to 100 m) from patches of the exotic thistle. Densities were significantly higher when the native thistle occurred within, vs. 30 to 50 m or 80 to 100 m from, patches of the exotic thistle, indicating a strong local “spillover effect.” At larger scales, we measured egg densities on wavyleaf thistle within grassland landscapes (2.4 × 2.4 km²) with varying infestation densities of the invasive musk thistle. We found that egg densities increased significantly with increasing invasive thistle densities measured at larger site and landscape scales. Because flowerhead weevil feeding substantially reduces seed production of wavyleaf thistle, exotic thistle populations are likely to have indirect negative effects on these native thistles. Our results provide strong empirical evidence that exotic plants can increase the attack on native plant species by maintaining populations of a shared insect herbivore. This finding suggests that persistence of exotic weeds in less-successful biocontrol programs will magnify the nontarget effects of weed biocontrol insects.

Nomenclature: Musk thistle, Carduus nutans spp. leiophyllus (Petrovic) Stoj. & Stef. #³ CRUNU; wavyleaf thistle, Cirsium undulatum (Nutt.) Spreng. # CIRUN; flowerhead weevil, Rhinocyllus conicus Frölich.

Additional index words: Associational susceptibility, biological control, indirect effects, nontarget effects, spillover effects, thistles.

The introduction and spread of exotic plant species is one of the most serious threats to biodiversity. It is estimated that over 40 million ha of U.S. land are already infested with invasive plants. Purple loosestrife is one such species that is currently invading wetlands and waterways in Midwestern states including 5,000 ha in Nebraska. Field studies were conducted in 2000 and 2001 at two locations in each year with the primary objective to evaluate performance of a single application of 16 herbicide treatments. A secondary objective was to document the impact of those herbicides on the total ground cover of local vegetation for two seasons after herbicide application. Evaluation at 10 wk after treatment showed that excellent season-long control (≥90%) of purple loosestrife was achieved with glyphosate at 3.36 kg ae/ha; 2,4-D dimethylamine at 2.66 kg ae/ha; triclopyr at 2.1 kg ae/ha; imazapyr at 1.68 kg ae/ha; and with the two mixtures of 2,4-D plus triclopyr at 1.33 1.26 kg/ha and 2,4-D plus metsulfuron at 1.33 ae/ha 0.042 kg ai/ha. Evaluation at 1 yr after treatment (YAT) showed excellent control (≥90%), with imazapyr at 0.33, 0.66, 1.12, and 1.68 kg/ha and metsulfuron at 0.084 and 0.168 kg/ha. Evaluation at 2 YAT suggested that excellent control (≥90%) was achieved with imazapyr at 1.12 and 1.68 kg/ha and metsulfuron at 0.084 and 0.168 kg/ ha. High rates of imazapyr caused negative effects on the local vegetation, indicating that use of these rates should be limited. Results suggest that a single application of more than half of the tested herbicides did not provide satisfactory control of purple loosestrife that lasts more than two seasons. However, the selective herbicides integrated with other control methods (e.g., mechanical, biocontrol) may be a valuable strategy for longer term control. Further studies are needed to evaluate the long-term effects of multiyear herbicide applications.

Nomenclature: 2,4-D; glyphosate; imazapyr; metsulfuron; triclopyr; purple loosestrife, Lythrum salicaria L. #³ LYTSA.

Additional index words: Integrated weed management, invasive species, noxious weeds.

Abbreviations: WAT, weeks after treatment; YAT, years after treatment.

Managing the risks posed by nonindigenous species can benefit from a consistent framework for bioeconomic risk assessment. Endogenous risk provides one framework that works to integrate the biological and economic circumstances. In this study, we explore how changes in manager's preferences for time (i.e., discounting) and for bearing risk affect the choice of optimal prevention and control in invasive species management. The results suggest invasive species managers who behave in a less myopic and less risk averse fashion are likely to invest more in prevention and less in control, which in turn requires less private adaptation, resulting in greater social welfare relative to more myopic and risk averse behavior.

Long-term ecological change is often hard to document without reliable baseline data. We obtained baseline data for and resurveyed 80 forest understory communities in Wisconsin first surveyed 50 yr ago. Sixty-two sites were in the forested region of northern Wisconsin, and 18 were in the agricultural region of southern Wisconsin. For 50 yr, the number of sites with nonnative plants increased from 4 to 62. Species richness in 1950 had little influence on nonnative species establishment by 2002, and nonnative species did not seem to influence rates of native species loss over time.

Additional index words: Ecologically invasive, forest, monitoring, plant, species loss, Wisconsin.

Although several successful examples of biocontrol using fungal pathogens exist, situations in which there is no discernable impact remain unacceptably high. This response may result from targeting inappropriate host life stages, failure of the control agent to establish and proliferate because of poor matching of host and pathogen life histories, or from broad environmental mismatching. At a genetic level, interactions between host and pathogen may determine the ultimate success of control programs. Here, we use a simulation model to illustrate that the optimal level of pathogen virulence is influenced by factors such as host longevity, as well as whether pathogen impacts on targets are through reduced fecundity or increased mortality. Importantly, the optimal pathogen in terms of effective long-term control of a target population is not necessarily the most virulent strain. In part, this is because the imposition of selection by a biocontrol agent may induce rapid increases in the frequency of resistance (if present) in host populations, ultimately leading to decreased effectiveness. Thus, appropriate matching of host and pathogen characteristics is an important consideration in trying to maximize impact on an invasive weed while minimizing the evolution of resistance.

Additional index words: Coevolution, host–pathogen dynamics, optimal biocontrol, resistance, virulence.

The development of effective linkages between science and management centers on the smooth integration of three pillars serving common objectives. Science, monitoring, and management all play a role in the overall success of managing natural areas. Control of invasive alien species (IAS) has generally followed rigid principles, built on a foundation of developing mechanisms for re-active, physical control techniques. As the numbers of IAS continue to grow, predictions are needed to manage the most serious species only. This approach requires a management framework that allows ecosystem flux and thus acceptance of invasive species as part of ecosystem dynamics. The management system must allow change within an envelope of predefined limits of acceptable change but must effectively highlight points exceeding these limits. A suitable framework needs flexibility to incorporate new research and thinking in a manner that is fundamentally proactive in approach. This article elucidates the development of the Kruger National Park strategic adaptive management system, allowing for the development of a conceptual framework for exploring science and management links for invasive species management.

Additional index words: Strategic adaptive management, thresholds of potential concern.

Abbreviations: KNP, Kruger National Park; SAM, strategic adaptive management; TPC, threshold of potential concern.

The exotic saltcedar occupies headwater, transitional, and depositional watershed portions, and revegetation strategies can be quite different depending on these locations. Regardless of specific socioeconomic or biological needs (or both), sites must often be revegetated after control to avoid reinfestation or invasion by other exotic species. Where natural riparian hydrologic processes continue to function, natural regeneration can be used as an effective restoration mechanism. However, in altered river systems, harsh environmental site characteristics may occur that severely limit revegetation potential after control, particularly in depositional areas. Because of high costs associated with saltcedar control, revegetation, and follow-up management, specific treatment areas should be evaluated and prioritized based on revegetation potential. Specific consideration should be given to the establishment of sustainable plant communities for long-term exclusion of saltcedar and other exotics.

Nomenclature: Saltcedar, Tamarix ramosissima Ledeb. #³ TAARA.

Additional index words: Acroptilon repens, Baccharis glutinosa, Distichlis spicata (L.) DISSP, Elaeagnus angustifoiia, ELGAN, imazapyr, Lepidium latifolium, perennial pepperweed, Populus deltoides, riparian restoration, Russian-olive, Salix exicjua, Salix gooddingii, saltgrass, triclopyr.

Dominant species have long been appreciated for their role in determining ecosystem attributes such as vegetation structure, successional patterns, soil characteristics, hydrology, and productivity. Exotic species may reach such high densities that they become community dominants, and it is in this role that exotics pose the greatest threat to native ecosystems. Four commonly observed patterns related to species dominance and their implications for understanding exotic invasions are discussed: the importance of scale in relationships between dominance and diversity, the positive correlation between local abundance and geographic range, the effects of dominants on ecosystem processes, and the mass effect of seed production in determining dominance. Understanding determinants of dominance will help us to better understand community invasibility.

Additional index words: Diversity, ecosystem effects, geographic range, mass effect.

In this article, we summarize previous and ongoing work examining the population and genetical consequences of the introduction of smooth cordgrass, a tidal marsh grass native to the Atlantic, into the range of California cordgrass in San Francisco Bay, CA, in the 1970s. The two species hybridized. A subset of hybrid genotypes outcompetes the native species, overgrows its niche space, produces much seed, and sires the majority of seed on native flowers. The result is the loss of existing native cordgrass plants and the usurpation of cordgrass regeneration sites by copious hybrid seed. These processes could lead to the extinction of the native species.

Nomenclature: California cordgrass, Spartina foliosa Trin.; Smooth cordgrass, Spartina alterniflora Lois.

Additional index words: Cordgrass, invasive Spartina, Spartina alterniflora, Spartina foliosa.

Abbreviations: MLW, mean low water; MSL, mean sea level; RAPD, random amplified polymorphic DNA.

New Zealand is a weedy place with more naturalized exotics than native plant species and 325 environmental weed species. Weed lists help us prioritize our weed work. Three New Zealand examples are described. (1) The National Pest Plant Accord lists 92 plant species banned from sale, distribution, or propagation throughout New Zealand. Predominantly, species listed have limited distributions but wide appeal to home gardeners. (2) Surveillance lists—short lists of new plant species to watch out for in a particular area because they are known invasive weeds that may well turn up for the first time in an area. (3) Weed-led and site-led approach—determining which weeds to tackle and where to control plants. The key criterion for weed-led projects: can you eradicate the species from the whole area? The critical criterion for site-led projects: is this a high-value place that is worth spending weed dollars on? Our strategic approach to weed management focuses on achieving the greatest conservation gain for the weed dollar spent.

Additional index words: Eradication feasibility, garden escapes, Pest Plant Accord, site-led control, surveillance lists, weed-led control.

Abbreviations: DOC, Department of Conservation; MAF, Ministry of Agriculture and Forestry.

Himachal Pradesh situated in the lap of northwestern Himalayas is one of the richest repositories of plant diversity in India. However, during the past three decades, because of the increased pace of development and interference of humans through introduction of invasive exotics, the ecology of the state has changed tremendously. Ragweed parthenium, billy goat weed, and lantana—the three exotics from South America—have caused much harm in the state because of their invasive potential. A study conducted to assess the changes in the structural composition and dynamics of vegetation shows that density and diversity of native flora were adversely affected because of invasion by these three exotics. Because all the three exotic weeds are known to exhibit allelopathy, it might be one of the major nonresource–based hypothesis for the successful invasion by these exotic species.

Nomenclature: Billy goat weed, Ageratum conyzoides L.; lantana, Lantana camara L.; ragweed parthenium, Parthenium hysterophorus L.

Additional index words: Diversity, dominance, ecological status, Importance Value Index, invasive weeds, species richness, vegetation analysis.

Abbreviation: IVI, Importance Value Index.

A framework was created based on the results of two experimental studies on invasiveness and invasibility. It shows us that grassland ecosystems are more invasible if the availability of nitrogen and light is high, whereas high aboveground biomass and high species richness reduce their invasibility. To restrict invasions, increasing the species richness of grasslands seems to be an appropriate management practice. A combined study of invader and ecosystem traits is needed to successfully predict invasions.

Various domestic and international initiatives have elevated invasive species issues onto the policy agenda. In the invasive plants arena, risk assessment efforts have focused on classifying the invasive potential of nonindigenous plants. Currently, however, the field of risk assessment for invasive species is in an early stage of development, and there is a lack of broad scientific principles or reliable procedures for identifying the invasive potential of plants in new geographic ranges. Furthermore, identifying potential hazards may be just the first step in a more comprehensive risk assessment. At least for those regulatory decisions that may be disputed internationally or domestically, scientifically ambitious risk assessment for invasive plants is not optional. Therefore, there is a pressing need to formulate adaptable, biologically plausible methods and approaches in this emerging field that strike an appropriate balance between the demand for accuracy and precision in predicting risks and the constraints of limited information, time, and other resources.

Additional index words: Regulatory analysis, Sanitary and Phytosanitary Agreement.

The Weed List Criteria Workshop consisted of four invited speakers and an animated discussion about the value of developing a standardized criteria system for developing lists of invasive plants. The presentations addressed the importance of having lists and criteria that are sufficiently robust to withstand legal challenges, the sophistication of a national prioritization system, some alternative strategies to the use of “one-size-fits-all” invasive plant lists, and the variety of lists that are already in use. Participants agreed that a standardized criteria system might need a modular format (e.g., agriculture or natural areas modules) with options for different thresholds for some criteria (e.g., rigor of documentation) to satisfy diverse listing objectives. Many participants expressed interest in future participation in this endeavor.

Additional index words: List standardization, status assessment, weed lists.

Invasive plants threaten not only natural habitats but also the native weed associations of the agricultural land. The segetal (arable) weed vegetation in Hungary has changed greatly in recent decades, mainly through the decrease of diversity of arable field flora. This study deals with the role of invasive weeds in transforming the segetal weed communities in South Hungary. It can be stated that these invasives have a serious transforming effect on the natural arable weed associations. Some of the investigated plants and their frequency in the examined region are common ragweed (84%), horseweed (22%), annual fleabane (14%), johnsongrass (36%), and Italian cocklebur (7%). These plants were all frequent and dominant on the studied area, both on arable land and in vineyards. Some of the weed associations already bear the names of these community-forming species.

Nomenclature: Annual fleabane, Erigeron annuus (L.) Pers. #³ ERIAN; common ragweed, Ambrosia artemisiifolia L. # AMBEL; horseweed, Conyza canadensis (L.) Cronq. # ERICA; Italian cocklebur, Xanthium italicum Moretti # XANIT; johnsongrass, Sorghum halepense (L.) Pers. # SORHA.

Additional index words: Arable weed flora, impoverishment, invasive weeds, segetal weed vegetation.

Genetic variability of invasive plant populations may create significant challenges to weed management through (1) selection for resistant genotypes and (2) differential efficacy of control methods resulting from genotypic variation. Effects of variation on management success may be particularly problematic for native invasive plants because they possess more genetic variation than bottlenecked exotic invasive species. We review the influence of genetic variation among populations and species on efficacy of chemical and biological control of select invasive rangeland plants. Population or genotype variation was more important for successful management when using biological agents than when using herbicides. Long-term success in weed control requires integrating multiple management strategies with attention to specificity of biological control agents to avoid selection for resistant genotypes.

Additional index words: Biological control, common garden, genetic variation, metsulfuron, native plants, picloram, rangeland plants.

The effect of a single fire event on the subsequent invasion dynamics of honey locust was studied in old-field and relict tussock grasslands of the Inland Pampa, Buenos Aires, Argentina. We added tree seeds to control (nonburned) and burned plots and monitored the recruitment and individual growth of three plant cohorts during 1999 to 2003. Burning increased seedling emergence during wet years, especially in tussock grassland. However, growth of establishing trees was significantly reduced in burned grassland plots. Without prior burning, tree growth was most strongly suppressed by the native tussock grass community. Thus, honey locust invasion into burned grasslands was a context-dependent process, which varied in response to interannual climate fluctuation and resident community structure.

Nomenclature: Honey locust, Gleditsia triacanthos L. #³ GLTR.

Additional index words: Competition, fire, seedling recruitment, woody plant invasions.

New Zealand has as many naturalized plant species as natives, and the invasion has yet to slow. The current composition and distribution of the naturalized flora are dominated by the time since species introduction and by human factors such as population density, at spatial scales from region to neighborhood.

Additional index words: Eradication, introduction effort, invasive plant, propagule pressure, weed.

Abbreviations: NZ, New Zealand; SE, standard error of the mean.

American Samoa, a U.S. territory in the South Pacific, has a history of invasive species problems and limited success managing them. Created to respond to these conditions, the American Samoa Invasive Species Task Force (ASSIST) includes researchers, management specialists, and concerned citizens. The group's goals are (1) to increase public awareness, (2) improve agency communication, and (3) coordinate management efforts on invasive species. ASSIST has created an invasive plant priority list, developed a manager's field guide to established invasive plants, and is making brochures to inform the public about plants to avoid bringing into the territory. There are significant biological, administrative, and cultural challenges to address, but ASSIST should be an effective means to overcome these obstacles.

Additional index words: Coordinated weed management, interagency collaboration, Pacific Islands, public awareness.

Abbreviations: ASG, American Samoa Government; ASSIST, American Samoa Invasive Species Task Force; NPAS, National Park of American Samoa.

Mathematical modeling is an important tool with which managers can understand, and hence plan to control, invasive species. A matrix model for the invasive musk thistle, derived from demographic studies in New Zealand, is used to conduct a retrospective analysis of the relative merits of three biological control agents released to control this species: Rhinocyllus conicus, Urophora solstitialis, and Trichosirocalus horridus. The analysis of musk thistle illustrates the utility of modeling approaches in management and demonstrates how model-derived information could shift the focus of future management efforts. By placing management in an adaptive framework, where active learning is used to improve management decisions, existing management strategies can be further improved to cope in situations where optimal control methods may depend on local conditions.

Nomenclature: Musk thistle, Carduus nutans L. #³ CRUNU.

Additional index words: Adaptive management, biological control, nodding thistle, optimal management, uncertainty.

Abbreviation: AAM, active adaptive management.

For more than 50 yr, the European and Mediterranean Plant Protection Organization (EPPO) has made recommendations to its member countries for the protection of plants. In accordance with the revised International Plant Protection Convention (IPPC), the EPPO aims to prevent the entry and spread of organisms, including invasive alien plants, directly or indirectly harmful to both cultivated and wild plants. It considers damage to both the agricultural and the natural environment. For the assessment, if an invasive alien species can be regulated as a quarantine pest according to the IPPC and for the identification of measures to prevent risks posed to plants, a pest risk analysis should be conducted. Based on the relevant IPPC standards, an EPPO risk assessment scheme applicable to direct plant pests in cultivated land is now being revised in order to be also applicable to potentially invasive plants and to assess the effects that invasive alien species relevant for plants pose to the uncultivated environment. In 2003, the EPPO sent a questionnaire to its 44 member states asking for plants that have been intentionally or unintentionally introduced into EPPO countries and are considered to be listed as invasive. The member states reported hundreds of plant species, of which an initial 40 were selected for further assessment. These assessments may result in recommendations for regulations and measures against the introduction and spread of these or some of these plants. In this article, a description of the recently developing EPPO policy regarding invasive alien species is given by the German member of the EPPO expert panels on Invasive Alien Species and Pest Risk Analysis.

Additional index words: Invasive plants, International Plant Protection Convention, IPPC standards, pest risk analysis, quarantine pest.

Abbreviations: EPPO, European and Mediterranean Plant Protection Organization; IPPC, International Plant Protection Convention.

We conducted preliminary investigations into some of the potential effects of Australian swamp stonecrop, a nonnative invasive aquatic plant in the U.K., on native pond plants and newt populations. Four studies were carried out in the northwest of England, in the field and under controlled conditions, during the period 2002 to 2003. Six plant species, which are important to newts as an egg-laying substrate, showed significant germination suppression up to 83% under Australian swamp stonecrop. However, there was no significant effect of Australian swamp stonecrop on pond seed banks, and no significant loss of plant species was observed in ponds invaded by the weed. Smooth newt eggs hatched at a later developmental stage when laid on Australian swamp stonecrop compared with those laid on the native substrate watercress, generally considered to be a preferred species. No significant differences in developmental stage at hatching could be detected between substrates in the great crested newt, a protected species.

Nomenclature: Australian swamp stonecrop or New Zealand pigmyweed, Crassula helmsii (Kirk) Cockayne; watercress, Rorippa nasturtium-aquaticum (L.) Hayek; great crested newt, Triturus cristatus (Laurenti, 1768); smooth newt, Triturus vulgaris (Linnaeus, 1758).

Additional index words: Aquatic plants, invasive, nonnative, species interactions, urodele amphibians.

It was our objective to determine whether plant–soil feedbacks confer weed suppression to a shrub–steppe ecosystem in Washington State. We found that soils developed by native bluebunch wheatgrass communities reduced knapweed growth from 18 to 5% ground cover. A pairwise feedback model developed from our data successfully predicted the native and weedy plant distribution seen on the landscape. We suggest that endemic soil-based mechanisms of weed control may be common and will produce novel techniques for the management of invasive plants.

Nomenclature: Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh.); knapweed, Centaurea diffusa (Lam.).

Additional index words: Feedback, plant, shrub–steppe, soil, Washington State.

Abbreviation: SAS, Statistical Analysis Systems.

Perennial pepperweed is an invasive noxious weed spreading rapidly throughout a wide range of habitats in the western United States. Shoots form dense monotypic stands with high initial leaf area, dense inflorescences, and deep litter layers that inhibit the establishment of other plant species. Roots store large amounts of carbohydrates for future growth, establish deep into the soil, and are responsible for clonal expansion of populations. In sodic soils, increases in N, Mg, and Ca were observed in invaded compared with noninvaded areas. Several management methods are effective in controlling perennial pepperweed, but success is dependent on age and density of infestations. Knowledge of many factors, including perennial pepperweed's biology and specific characteristics of the infested area, will help in the development of the most appropriate, site-specific management and restoration plans.

Nomenclature: chlorsulfuron; glyphosate; 2,4-D; perennial pepperweed, Lepidium latifolium L. #³ LEPLA.

Additional index words: Amelioration, calcium, invasive, management, restoration, sodic soils, sodium adsorption ratio.

Exotic cool- and warm-season grasses have been used throughout the eastern United States as an improved forage in pastures and for wildlife habitat and erosion control. Several of these grasses, including tall fescue are invasive and diminish native grassland biodiversity. This article presents three strategies for reconstructing or rehabilitating native grasslands using herbicides. A variety of herbicides including glyphosate, imazapic, and clethodim, alone or in combination, are effective in killing tall fescue. Imazapic and clethodim show promise for removing tall fescue from native grasslands. Imazapic is more effective when applied with a surfactant and when tall fescue is burned before herbicide application. A standard recommendation for converting tall fescue to native warm-season grasses (NWSG) is to burn tall fescue in late winter, followed by application of 0.2 kg ai/ha imazapic with surfactant and a small amount of nitrogen a month later. The native grasses are seeded directly into the dying and dead sod with a no-till drill. An alternative method is to apply 2.2 kg ai/ha glyphosate to kill the fescue and use 0.067 kg ai/ha imazapic at seeding for weed control. NWSG can be effectively established using conventional tillage by preparing a firm seedbed, drilling or broadcasting the seed directly into the seedbed, and applying 0.067 kg ai/ha imazapic for weed control.

Nomenclature: Clethodim; glyphosate; imazapic; tall fescue, Festuca arundinacea Schreb. #³ 668 FESAR.

Additional index words: Bahiagrass, bermudagrass, fescue conversion, herbicides, native warm-season grasses, quackgrass.

Abbreviation: NWSG, native warm-season grasses.

To examine the effect of biological invasion by early-successional exotic plant species on the secondary succession of native plant species, we compared secondary forests with and without koa haole invasion, which became established in fields that were abandoned for 55 yr on Chichi-jima and Haha-jima in the Ogasawara (Bonin) Islands, in the northwestern Pacific. A comparison of the forest structure and the composition of secondary forest showed that the species richness of native plant species was significantly lower, and the basal area of late-successional alien plants (bischofia and Korean mulberry) was significantly larger in secondary forests with koa haole invasion than in those without koa haole invasion. The secondary forests in areas that had been invaded by koa haole had a significantly smaller basal area of native plant species and a greater area of late-successional alien plants in the understory than those in areas that had not been invaded by koa haole. These results suggest that in the Ogasawara Islands, the native species are incapable of replacing dense koa haole thickets directly and that invasion by koa haole promotes invasion and establishment of more aggressive alien plant species. Consequently, the invasion and expansion of koa haole has had a severe effect on the native plant community in the Ogasawara (Bonin) Islands and may alter the secondary succession.

Nomenclature: Bischofia, Bischofia javanica Blume; koa haole, Leucaena leucocephala (Lam.) de Wit; Korean mulberry, Morus australis

Additional index words: Early-successional alien species, late-successional alien species, secondary succession.

Eucalypts have been planted extensively beyond their natural range but few of these plantings have become invasive. The Kings Park bushland in Western Australia is an example of a native bushland in which a few nonlocal eucalypt species (Warted Yate, sugar gum, and lemon-scented gum) were introduced as ornamentals and have since spread into the bushland. Although the population expansion was obvious, little was known about the factors influencing this pattern, making management options unclear. The study objective was to investigate the factors facilitating the invasion of Kings Park by Warted Yate. The study has shown that ecological characteristics that may be facilitating the Warted Yate invasion in Kings Park include mass recruitment of seedlings subsequent to fire, high seedling survival rates, high levels of serotinous seed storage, and a high germination rate. It seems that this species has a high resilience in a fire-prone environment. However, it appears that Warted Yate is not as invasive as sugar gum. The Kings Park situation highlights the risks associated with planting introduced eucalypts at the interface between native and managed systems.

Nomenclature: Corymbia citriodora; Eucalyptus cladocalyx; Warted Yate, Eucalyptus megacornuta.

Additional index words: Ecological study of invasive eucalypts, restricted natural distribution.

Analysis of patterns and processes underlying the development of plant invasion patches may contribute to our general understanding of how invasive plants spread. The objective of this study was to reevaluate population development in formerly studied invasion patches of perennial forbs. Herb-chronology (analysis of annual rings in the roots of forbs) was used in this and in the former study to analyze the spatial age structure in stands of spotted knapweed and yellow foxglove in Michigan. Although invasion patches of the two species showed a pronounced spatial age structure in 1999, suggesting frontlike invasion, this pattern was largely or completely lost in 2003. These findings demonstrate how population growth trajectories in invasion patches may take a relatively sudden change because of altered growth conditions or consolidation of the population structure. In addition, they indicate the importance of the timing of a posteriori analyses into the development of plant invasion patches relative to successional stage.

Nomenclature: Spotted knapweed, Centaurea maculosa Lam. #³ CENMA; yellow foxglove, Digitalis grandiflora Mill.

Additional index words: Age determination, age distribution, annual rings, herbaceous perennials, herb-chronology, spatiotemporal invasion pattern.

Natural forest in South Africa occurs in small, scattered patches. Many alien tree and shrub species have been recorded from the forest environments but few are true forest invaders. Concepts have been developed around the natural disturbance regimes affecting forests and how changes in these affect the invasion potential of invasive species. Natural fires in the landscape confined forests to fire refugia. Changing the fire regime through conservation, commercial forestry, intensive agriculture, and urban development allowed trees to grow back into the landscape. Invader plants, typical pioneers in their natural environment, were the first to become established. They are intolerant of shade but nurse the establishment of shade-tolerant forest species. Inside the forest, the natural small gaps (<150 m²) prevent the establishment of shade-intolerant invader plant species. This knowledge provides the basis for guidelines to manage plant invasions by controlling gap size inside the forest and to convert invasions to regrowth forest on the outside. This approach also gives the opportunity to combine invader plant control, forest rehabilitation, and small business in rural environments.

Additional index words: Forest rehabilitation, shade tolerance, small business, succession.

Leafy spurge has become a serious problem for ranchers and land managers in the northern Great Plains region. A bioeconomic model was developed to estimate the economic impacts of leafy spurge on grazing land and wildland in a four-state region (Montana, North Dakota, South Dakota, and Wyoming). Leafy spurge infestations on grazing land were estimated to result in a loss in regional grazing capacity sufficient to support a herd of 90,000 cows. Direct economic impacts on stock growers, landowners, and agribusiness firms were estimated to exceed $37 million annually, whereas secondary impacts throughout the regional economy totaled almost $83 million. Impacts on wildland were smaller but still substantial. Study results indicated the serious nature of the leafy spurge problem in the northern Great Plains region and helped to justify enhanced control efforts.

Nomenclature: Leafy spurge, Euphorbia esula L. #³ EPHES.

Abbreviations: AUM, animal unit month.

The wildfire model for invasive weed management is a simple yet effective strategic guide framed on the cornerstones of prevention, early detection, timely control, and vegetation restoration. These guidelines are the same fundamental ingredients that make up this nation's formula for effective wildfire management. Just as early detection is critical for success in fighting fires, early detection is also essential for minimizing ecological effects and to control costs associated with new weed invasions. Both active and passive detection are important in wildfire management, and the same is true for invasive weed management. Passive weed detection—the chance discovery of new infestations by individuals pursuing other outdoor activities—can be helpful but is generally haphazard and incomplete. Passive detection alone will almost certainly fail to find many weed infestations until they have grown too large for true eradication. However, passive detection should neither be discouraged nor its value minimized because it can provide a meaningful way to inform and include additional people who otherwise would not be concerned or involved in weed management. Active weed detection consists of periodic field surveys conducted by trained individuals having clearly defined objectives and using sound search and mapping methods. Traditional methods of on-the-ground weed surveys remain important, but new technology such as remote sensing now offers additional options. Systematic field surveys and other early detection efforts are as important to successful weed management as the organized network of fire lookouts and aircraft patrols are to modern wildfire management. Any wildland invasive weed management program that does not include an effective early detection component will most likely fail.

Melaleuca was first imported into the United States during 1886, and introduction records suggest that at least six sources have contributed to extant populations in Florida. Allozyme analyses found substantial genetic variation within and among populations, contributing to geographic structuring of melaleuca in southern Florida. The presence and distribution of two chemical phenotypes (chemotypes) contributed to this variation. Performance of the melaleuca snout beetle imported as a biological control agent differed dramatically in laboratory studies depending on which chemotype it was fed, with larval survivorship and growth substantially greater on an (E)-nerolidol chemotype. We are currently investigating whether these differences can be detected in the field.

Nomenclature: Melaleuca, Melaleuca quinquenervia (Cav.) Blake; melaleuca snout beetle, Oxyops vitiosa Pascoe.

Additional index words: Allozyme analysis, biological control, chemotype, herbivory, invasion history, insect–plant interactions.

Weed scientists and invasive plant biologists must find cost-effective, ecologically based methods to manage undesirable plants. Economic analyses are needed for management, policy making, and setting research priorities. The fundamental economic principle for weed management is simple: act only if the benefits exceed the costs. Implementation of the principle is difficult, however, with the many and typically uncertain costs and benefits of management. The economic threshold is a well-known but not practical implementation of this fundamental economic principle. However, adoption of the threshold concept has spurred the development of decision models and use of methods of decision analysis. With these tools, scientists have quantified some risks of management and the value of information about the weed population in a field for management decisions or the value of specific information about weed biology for identifying new management strategies. Meaningful analysis for economic weed management is currently limited by lack of understanding of weed population and spatial dynamics and problematic communication between weed scientists and agricultural economists.

Additional index words: Decision analysis, economic analysis, economic threshold, risk, value of information.

The adverse impacts of invading alien organisms are widely recognized as one of the major threats to biodiversity and are receiving growing recognition as a major socioeconomic threat. The hydrological impacts of alien plants have received less attention, despite growing evidence of their significance. The wide range in plant growth forms and physiology among invading species suggests that estimation of the hydrological impacts could be difficult. The concept of limits to evaporation was developed to help organize our general scientific understanding of the hydrological implications of changes in vegetation. It provides a way of reducing this complexity to the factors most likely to be the major determinants of evaporation from vegetation in a given situation. It distinguishes between physical factors (1) availability of energy from solar radiation and advection, (2) availability of soil moisture at landscape and habitat scales, and (3) raindrop size, and biological factors (4) plant size, including height and rooting depth, and (5) plant physiology, including seasonality of the leaves and drought tolerance. Studies of the hydrological impacts of vegetation change invasion show that changes in vegetation structure and seasonality can have significant impacts on water resources at both habitat and landscape scales. Invasions can also have significant impacts where the invaded habitat has more water available within the rooting depth than adjacent areas.

A literature review was conducted to summarize information on environmental, economic, and societal losses caused by 16 key invasive plants on rangeland and wildlands in the United States. Results of the literature review indicated that scope of published information ranged from narrow to comprehensive. Extensive quantitative information is published about environmental impacts caused by leafy spurge, downy brome, saltcedar, purple loosestrife, and several knapweeds or starthistle. For other species, quantitative information was limited and references to impacts were mainly anecdotal or observational. The economic impacts of most species were poorly documented. Comprehensive economic analyses conducted on either a state or regional basis were published about leafy spurge, saltcedar, and the knapweeds. Agricultural costs including loss of grazing value were quantified for several additional species, but environmental and societal costs were not included in the analyses. Additional research is needed to quantify economic and environmental losses of invasive nonnative plants on rangeland and wildland sites.

Nomenclature: Downy brome, Bromus tectorum L. #³ BROTE; leafy spurge, Euphorbia esula L. # EPHES; purple loosestrife, Lythrum salicaria L. # LYTSA; saltcedar or tamarisk, Tamarix spp., # TAASS; yellow starthistle, Centaurea solstitialis L. # CENSO.

Additional index words: Exotic plants, invasive plant impacts, noxious weed impacts.

Genetic analyses of invasive plants can provide information concerning the introduction dynamics of invasive species, the parameters associated with range expansion, the mechanisms of dispersal in the new range, and the identification of source populations. This information can give managers insights into the range of genotypes (and associated phenotypes) introduced, whether these genotypes may have experienced intermixing during range expansion, and the most efficacious locations in the native range to seek biological control agents. The invasive grasses downy brome and medusahead are now the predominant vascular plant species of degraded rangelands throughout arid and semiarid portions of western North America. In this article, I provide background information on the biology and history of introduction of downy brome and medusahead, summarize results of the allozyme analysis of populations of both species, and indicate the importance of these data to the management of invasive plant species. In addition, these data will be used to assess the introduction and spread of both downy brome and medusahead in their new ranges.

Nomenclature: Downy brome, Bromus tectorum L. #³ BROTE; medusahead, Taeniatherum caput-medusae (L.) Nevski # ELYCM.

Additional index words: Allozymes, genetic markers, invasive plants, multiple introductions.

Abbreviations: Got-4c, glutamate oxaloacetate transferase, locus 4, “c” allele.

Shoebutton ardisia is an invasive plant from Asia that infests subtropical forests and seasonal wetlands in southern Florida. Removal of invasive species is crucial to maintaining the ecological integrity of these habitats. This study tested the effectiveness of triclopyr applied in a cut-stump treatment to shoebutton ardisia in a forested seasonal wetland setting in southern Miami-Dade County, Florida. A total of 300 individuals of shoebutton ardisia were selected from three sites (100/ site); half were assigned to treatment and half to control groups. All plants were cut off at the base, and plants in the treatment group received an application of triclopyr (in amine form). Survival rates after 1 yr were 5.3% for treated vs. 97% for nontreated plants, indicating that triclopyr is effective at controlling shoebutton ardisia. However, results were significantly different at one site, indicating that further study is needed.

Nomenclature: Triclopyr; shoebutton ardisia, Ardisia elliptica Thunberg.

Additional index words: Herbicide effectiveness, seasonal wetlands.

The effect of mechanical clearing and litter removal on control of Sydney golden wattle was studied in areas of Portugal that had been invaded for either long or short periods. The plant species that emerged and soil parameters were monitored to assess the recovery potential and the soil status of these areas after Sydney golden wattle control. More plant species emerged in the plots where mechanical control in combination with litter removal was applied than in nontreated plots or in plots where mechanical control alone was used. More plant species emerged in the recently invaded areas than in those that had been invaded for a long time. More Sydney golden wattle seedlings were found in the long-invaded area than in the recently invaded one. Total litter, nitrogen and carbon content, and β-glucosaminidase activity were higher in the soil of the long-invaded compared with the recently invaded areas. Regarding the efficacy of the methods used to remove Sydney golden wattle, sprouting was not observed 10 mo after cutting the trees in both areas, although this was not the case in other parallel studies.

Nomenclature: Sydney golden wattle, Acacia longifolia (Andrews) Willd.

Additional index words: Invasive plants, mechanical control, native species recovery, soil properties.

Abbreviations: A, with Acacia longifolia; AR, Acacia longifolia removed; ALR, Acacia longifolia and litter removed; NAG, N-acetyl-β-d-glucosaminidase (NAGase EC 3.2.1.30); NRSJD, Natural Reserve of São Jacinto Dunes.

Because of the severe environmental and economic costs of invasive plants, organizations and individuals importing plants into new regions should evaluate plant introductions for their potential to escape cultivation and invade natural areas. Current weed risk assessment (WRA) models used in the United States are not precise enough to provide a definitive answer for woody taxa and have not yet been developed specifically for annuals and herbaceous perennials. We tested several WRA models to determine their effectiveness for the Chicago region and selected one for use in the invasive screening protocol at Chicago Botanic Garden that includes the use of regional invasive plant lists, commercial availability, WRA, and on-site evaluation of plants. By using this integrated approach, we have implemented a screening protocol that has increased our confidence in predicting invasiveness, is time and space efficient, and is user-friendly.

Additional index words: Alien plants, botanic garden, Chicago, evaluation, horticulture, invasive plants, weed risk assessment.

Abbreviations: CBG, Chicago Botanic Garden; NISC, National Invasive Species Council; WRA, weed risk assessment.

Species lists are important tools for managing biodiversity, including controlling nonnative species, but they are either incomplete or lacking for many areas. Our objective was to illustrate how the synergy of disparate data sets can increase knowledge of species distributions while minimizing further field expenditures. We compared five different data types (two species lists, weed surveys, vegetation plots, and weed maps) of nonnative plant locations at the county level from 45 data sets covering Colorado. Species lists captured the highest number of species, but they missed many of the noxious weeds recorded by weed-mapping data. The number of species recorded per county increased by 30% on average with data synergy even in the most intensively surveyed areas. Each data type also followed the same pattern of survey intensity, leaving some areas in the state consistently unsurveyed or undersurveyed. On average, there was a 44% increase in species recorded per county with all data types included. Overall, inclusion of more data types greatly increased knowledge of the nonnative species in Colorado. Therefore, harnessing the synergy of disparate data sets seems to be a cost-effective first step to increase knowledge of species richness (presence) in an area.

Additional index words: Data bias, data synergy, nonnative species, species richness.

Abbreviations: BONAP, Biota of North America Program; GPS, global positioning system; QQ, quarter quad.

In India, exotic weeds, especially Parthenium hysterophorus in urban areas, Lantana camara in forestlands, and Ageratum conyzoides in croplands, have assumed the proportion of noxious biological pollutants. Each of these three natives of tropical America has wide ecological amplitude. Because of ecological, agricultural, environmental, and health hazards for cattle and man, the respective governments of the states as well as the union government of India are trying hard to assess the damage and find a solution for their control. Considerable effort is allocated to top research and development projects involving integrated management through physical, biological, and chemical means, as well as making people aware of the problem. However, success remains elusive, primarily on account of the reluctance of the community because of the health hazards of these weeds. Apart from presenting the hazards and efforts toward control measures tried, it is proposed to share how the success in their management could be achieved through community mobilization.

Nomenclature: Billy goat weed, Ageratum conyzoides L.; lantana, Lantana camara L.; ragweed parthenium or congress grass, Parthenium hysterophorus L.

Additional index words: Community participation, ecological hazards, invasive weeds.

Ambiguity exists in the use of the terms “survey,” “inventory,” and “monitoring” as related to adaptive weed management. Misunderstanding can lead to poor planning and inefficient use of limited budgets. Adaptive weed management includes developing an objective-based weed management plan, implementing the plan, monitoring to measure progress toward objectives, evaluating the plan or practices, making any necessary adjustments, and then repeating the cycle. Monitoring involves the repeated collection and analysis of site-specific data to evaluate progress toward management objectives. Surveys and inventories are field searches to determine the location and relative abundance of weeds on a landscape scale. Surveys are representative samples of an overall weed population, whereas inventories attempt to account for all weed infestations or individual plants within a specified area. Weed surveys and inventories are as basic to preserving land health as medical exams are to maintaining human health, and weed maps are as vital to land managers as X-rays are to medical professionals. Weed surveys are especially critical for success in early detection and rapid response. Area-wide weed surveys or inventories should be conducted as part of planning long-term weed management strategies and control tactics. Attempts to survey and monitor weeds simultaneously can result in data ill suited to the objectives.

Additional index words: Definitions, invasive, inventory, monitoring, survey.

In the area of the Białowieża Forest (an extremely well-preserved forest complex in Central–Eastern Europe), despite the planted 49 conifer taxa, only jack pine and white pine show expansional tendencies. The reasons for this response can be grouped as follows: (1) climatic conditions, (2) biological properties of the plants, (3) late introduction of conifers for plantation and their small contribution among the planted species, (4) competition from the existing plant cover, and (5) the activity of herbivores and pathogens.

Nomenclature: Jack pine, Pinus banksiana Lamb., white pine, Pinus strobus L.

Additional index words: Cultivation, invasion, naturalization, Pinophyta.

Resource managers realize the potential of remote sensing and geographic information system (GIS) operations for detecting, monitoring, mapping, and modeling distributions of invasive plants. However, to make wise decisions, imagery must be evaluated in terms of geometric fidelity, spatial resolution, spectral resolution, area coverage, and cost. These data characteristics are discussed relative to mapping vegetation distributions and detecting exotic plants. Examples are drawn from projects conducted during the past 20 yr by the Department of Geography's Center for Remote Sensing and Mapping Science at the University of Georgia using remotely sensed data, GIS, and Global Positioning System techniques to produce detailed vegetation maps and databases for study areas in the southeastern United States. Many of these projects include a component of invasive plant detection and distribution mapping for monitoring spread and effectiveness of control.

Additional index words: Hyperspectral image data, national parks, natural resource management, photo interpretation, satellite imagery.

Abbreviations: ASTER, Advanced Spaceborne Thermal Emission and Relection Radiometer; AVHRR, Advanced Very High Resolution Radiometer; AVIRIS, Airborne Visible/Infrared Imaging Spectrometer; CIR, color infrared; DMC, Digital Modular Camera; GIS, geographic information system; GPS, Global Positioning System; GR, ground resolution; LIDAR, light detection and ranging; lprs/mm, line pairs per millimeter; MODIS, Moderate Resolution Imaging Spectroradiometer; PAN, panchromatic; SPOT, System Probatoire d'Observation de la Terre; USGS, United States Geological Survey; XS, multispectral.

Ecosystem ecologists and restoration practitioners have become increasingly interested in the effects that invading species might have on soil processes. Invading species, particularly ones that differ from native species in traits that are likely to influence soil processes, may influence nitrogen cycling to such an extent that the legacy of the invasion persists long after invaders have been removed. We suggest that exotic species that are capable of altering soil nitrogen (N) pools, whether by augmenting ecosystem N through fixation of atmospheric N or by increasing rates of N losses, have the greatest capacity to interfere with restoration efforts. In contrast, cases where more subtle differences in tissue quality or quantity alter soil N fluxes but not total N pools may not exhibit a legacy long after removal of the exotic species. Given the challenges that invading species' effects on soils present to restoration efforts, it is important to develop predictions as to which invaders are likely to influence N dynamics after their removal and to develop techniques to minimize the influence of exotics on restored ecosystems.

Currently, the Federal Interagency Committee for the Management of Noxious and Exotic Weeds is leading a national effort to develop and implement a National Early Detection and Rapid Response System for Invasive Plants in the United States. Ultimately, the system will be part of an All Taxa Early Detection and Rapid Response System under the National Invasive Species Management Plan. The overall purpose of developing such a system for invasive plants is to provide a coordinated framework of public and private partners to more effectively address new invasive plants through: (1) early detection and reporting of suspected new plants to appropriate officials, (2) identification and vouchering of submitted specimens by designated botanists, (3) verification of suspected new state, regional, and national plant records, (4) archival of new records in designated regional and plant databases, (5) rapid assessment of confirmed new records, and (6) rapid response to new records that are determined to be invasive. Currently, the U.S. Geological Survey is cooperating with state and regional partner groups in New England, the Gulf Coast, and the West to develop and field-test elements and processes that were identified in the Conceptual Design Plan. Once fully implemented across the nation, the proposed system will provide an important second line of defense against invasive plants that complements federal efforts to prevent unwanted introductions at the ports of entry.

Additional index words: Early detection, invasive plants, rapid assessment, rapid response.

Abbreviations: EDRR, early detection and rapid response; FICMNEW, Federal Interagency Committee for the Management of Noxious and Exotic Weeds.

The Hawaiian island of Maui, with highly diverse habitats and 80 federally endangered plant species, provides a microcosm for addressing the threats of plant invasions to endemic biological diversity through partnerships for research and management. An evolving vision of what is needed involves an accelerated, balanced program involving exclusion of potential new invaders, early detection and rapid response, biological control, control to protect local populations, and public education.

Additional index words: Biological control, Clidemia hirta, early detection, Hedychium gardnerianum, interagency cooperation, Miconia calvescens, Psidium cattleianum, public education, rapid response, weed exclusion.

Abbreviation: MISC, Maui Invasive Species Committee.

Open grasslands in California and Washington are being invaded by two closely related European shrubs, French broom and Scotch broom, that are considered among the most invasive and damaging of wildland species in those habitats. In this study, we present evidence of their effects on soil nitrogen (N) and the implications for restoration. Using natural abundance ¹⁵N signatures of leaves, we show that N fixation by brooms varies across sites and may depend on a suite of site-specific factors. Nonetheless, in sites in both California and Washington, we observe up to a twofold increase in soil N availability, as assayed in the laboratory. Across a range of sites, we determined that burning decreases total soil N by nearly 40%. We found burning to have the simultaneous effect of decreasing the broom seedbank by 68% after one burn. In a separate experiment, we removed broom and added sawdust to the soil to test whether a N-immobilization effect would help slower growing native perennial grasses in competition with European annual grasses. We found that although sawdust effectively decreased N availability after a 2-yr application period, we could not effectively target which group of species would benefit most.

Nomenclature: French broom, Genista monspessulana L. Link; Scotch broom, Cytisus scoparius L. Link.

Additional index words: Grassland, nitrogen fixation, restoration, shrub.

There is a significant positive association between exotic plant species richness of an area and the human population size of that area. This association is notable not only for its high correlation (r² = 0.69) but also because it spans five orders of magnitude for human population size. The correlation is apparently caused by the introduction of increasing numbers of exotic species as human population size grows. As population grows, so does exotic propagule importation and habitat disturbance. The regression is clearly asymptotic, indicating that per capita rates of exotic species introductions decline as human population continues to increase. A main implication for exotic species control is that efforts to limit exotic species will be most effective and least costly in areas (at many scales) where human population size is still relatively small. Another implication is that because human population size will continue to increase in many areas, educating the general public about harmful exotic species may be the only way to reduce rates of introduction, i.e., the slope of the regression.

Additional index words: Introduced species, exotic, weeds, human.

Pathways are any means that lead to entry or spread of pests. Pathway risk analysis entails identifying pathways and assigning the probability of entry, spread, introduction, establishment, or outbreak of a pest through the various pathways, along with the consequences of their introduction. As an example, a schematic quantitative pathway analysis for the number of infested imported avocados entering susceptible areas of the United States annually is presented.

Nomenclature: Avocado, Persea americana Mill. ‘Hass’; soybean, Glycine max (L.) Merr.

Additional index words: Introduction, outbreak, pest entry, spread.

Abbreviations: PERAL, Plant Epidemiology and Risk Analysis Laboratory; CPHST, Center for Plant Health Science and Technology; APHIS-PPQ, Animal and Plant Health Inspection Service–Plant Protection and Quarantine.

Although evolution has been neglected in invasive species work, evolutionary theory can be used to guide invasive species management, and research on exotic species can be used to test evolutionary theory. One substantial challenge in invasive plant management is the evolution of resistance to herbicides, biological control, and other treatments. We show how the tools of quantitative genetics and selection analysis can be used to investigate the potential for evolution of resistance, which can aid in the management of invasive plant populations. We also illustrate how invasive species research can be used to test theory, such as the evolution of increased competitive ability hypothesis. We outline the methods to investigate this theory and recommend including evolutionary considerations in invasive species management.

Additional index words: Biological control, genetics, herbivory, natural enemies, Melaleuca quinquenervia MLAQU.

Abbreviation: EICA, evolution of increased competitive ability.

Invasive alien plant species represent an ecological risk to indigenous plants and ecosystems. In this study, the dichotomous system is suggested to assess the ecological risk of invasive plant species. Case studies of noxious alien plants in South Korea were used to develop the system based on environmental risk factors. Assessing ecological risk of invasive alien plants was considered with the following factors: harmful effects to animals or humans, ecological characteristics, invasion time, present state after invasion (dispersion), and availability of resources. Invasive plant risk assessment was based on the methodology for predictive risk assessment used to manage and monitor invasive alien plants in South Korea. Our system enabled us to classify invasive plants in Korea into four grades: (1) noxious species (three categories), (2) monitoring species (five categories), (3) harmless species (innocuous species), and (4) beneficial species. Our assessment system can help land managers monitor invasive alien plant species.

Additional index words: Dichotomous system, ranking system.

This study was carried out to obtain basic data for alien plant management in South Korea. Field surveys were conducted in forests, fields, islands, industrial complexes, landfill areas, and so forth from 1995 to 2002. The number of naturalized alien plants recorded in Korea was 39 families and 281 taxa through 2002. Members of the Asteraceae and Poaceae families were the most frequently growing alien plants in Korea and comprise 23 and 17% of the total population, respectively. Most of them invaded South Korea from Europe and North America. Ministry of Environment in Korea designated six alien plants as harmful nonindigenous plants on ecosystems by the Natural Environment Conservation Act, considering their possible negative effect on the ecosystem. Those species were ragweed, giant ragweed, white snakeroot, joint grass, knotgrass, and horsenettle. On the basis of the research, we constructed a database titled An Illustrated Internet Guide to Alien Plants in Korea ( http://alienplant.nier.go.kr). We expect the database to help increase public awareness and encourage citizens to participate in the management of alien plants.

Nomenclature: Giant ragweed, Ambrosia trifida; horsenettle, Solanum carolinense L.; joint grass, Paspalum distichum var. distichum L.; knotgrass, Paspalum distichum var. indutum; Shinners ragweed, Ambrosia artemisiifolia var. elatior (L.) Desc.; white snakeroot, Eupatorium rugosum Houtt.

Additional index words: Alien plants, database, harmful nonindigenous plant.

In agricultural systems, weed seedbanks provide insights into cropping and management history as well as potential weed problems. Seedbank management is an integral part of a long-term weed management system. In this article, we propose a framework for managing weed seedbanks by putting weed seedbanks into the context of populations and communities. Early in the plant invasion process, it is possible to eradicate or contain the weed species through intensive focused management. Weed populations that become established and pose unique or extreme problems should be managed using population-based strategies such as targeted removal or trap crops. Established weed populations that pose no specific problem should be managed as part of the weed community using a variety of strategies such as tillage, crop rotation, cover crops and mulches, soil solarization, and microorganisms.

Invasive species are increasingly being acknowledged as one of the most serious environmental problems of our times. Many such species were introduced intentionally. Codes of conduct among groups that contribute to the introduction and spread of invasive species may alleviate some of the problems and contribute to educational efforts. Because a majority of invasive plants appear to be introduced for horticultural purposes, representatives from nurseries, botanical gardens, landscape architecture, the gardening public, and government have developed such codes. The process included building consensus and mutual respect, providing clear feedback, and finding common ground. Implementation of the codes has proven to be challenging for most of the groups but is still moving forward.

Plants growing on ancient buildings and archaeological remains pose a severe threat to their conservation. Controlling such weeds is costly, and the use of herbicides may lead to serious ecological problems. We surveyed 20 archaeological sites in Mediterranean Italy and estimated the relative effect of alien and native weeds on archaeological remains on the basis of their abundance, frequency, and danger index (DI), which is a measure of the potential damage that each species can cause to buildings and remains. DI is assessed according to plant morphology, vigor, and life-form. The results show that, although alien plant species are potentially harmful, as revealed by their significantly higher DI, they rarely grow on remains, whereas native plants thrive. Despite human disturbance and abundant propagule supply, factors that generally enhance the establishment of aliens, the flora growing on archaeological remains was relatively resistant to alien invasion. Among the aliens observed, only tree-of-heaven turned out to be relatively harmful. Although this invasive tree is not frequent on remains, it is expected to become more widespread on them, as areas surrounding archaeological sites become increasingly urbanized.

Nomenclature: Tree-of-heaven, Ailanthus altissima (Mill.) Swingle #³ AILAL.

Additional index words: Biodeterioration, invasion resistance, Mediterranean Basin.

Abbreviations: DI, danger index.

During the past decade, as the issue of plant invasion gained recognition in the public domain, both ecologists and weed scientists voluntarily or by mandate moved to provide their expertise to the management of invasive plants on public lands. Diverse views of nature carried to the table by ecologists and weed scientists have resulted in different priorities and opinions on management strategies. However, both groups share the goal of protecting natural resources for the public good. Efforts to achieve consensus among ecologists and weed scientists should acknowledge and resolve how and why the two groups come to different views of nature. Then, areas of mutual strength need to be identified so that improved management or restoration plans can be developed.

Additional index words: Ecosystem management, restoration.

The largest grasslands in Indiana and Illinois are on reclaimed surface coal mines, which are numerous in the Illinois Coal Basin. The reclamation goal of establishing a vegetation cover with inexpensive, hardy exotic grass species (e.g., tall fescue, smooth brome) inadvertently created persistent, large grassland bird refuges. We review research documenting the importance of these sites for native prairie birds. On mines, grassland specialist birds (restricted to grassland throughout their range) prefer sites dominated by exotic grasses to those rich in forbs, whereas nonspecialist bird species show no significant preference. Midwestern mine grasslands potentially could be converted into landscapes that include native warm-season grasses and forbs adapted to the relatively dry, poor soil conditions, in addition to the present successful exotic grass stands. A key question is whether native mixtures will resist conversion to forb-rich or woody growth over the long term, as the exotic grasses have done.

Nomenclature: Smooth brome, Bromus inermis Leyss.; tall fescue, Festuca arundinacea Schreb.

Additional index words: Avian conservation, grassland birds, mine grasslands.

Molecular data are becoming easier to collect and can help us address many important questions in invasion biology. However, for most organisms, the connection between molecular loci and phenotypic traits is not direct. Here, I review some fundamentals of population and ecological genetics and point out limitations of molecular data, particularly when the data are from loci without a known connection to the phenotype. I then discuss the ways that molecular data may facilitate management of invasive weeds, despite the limitations. Key uses of molecular data in invasive weed management include identifying species, determining their origins, and understanding mechanisms and rates of spread.

Additional index words: Biological invasions, ecological genetics, phylogeography.

Abbreviations: AFLP, amplified fragment length polymorphisms; cpDNA, chloroplast DNA; RFLP, restriction fragment length polymorphisms.

The link between science and management of invasive plants in natural areas appears to be the strongest at the “field crew” level, with historically high levels of research on control materials and methods, survey techniques, and monitoring strategies, and with a high rate of incorporation of science into field practices. Less scientific support is given to higher level managers, for example, those managing a whole ecosystem while attempting to determine invasive weed priorities. Although whole-ecosystem management concepts (e.g., adaptive management, integrated pest management) may be supported individually by a great deal of field research and careful thought, scientists have not conducted the experimental studies necessary to compare outcomes and provide practical means of implementation. In other words, the “science of management” in readily implementable form has not reached the upper levels of resource managers. The link between science and management may be the weakest where decisions are made about the amount of funding to allocate to the many competing parts of what should be a complementary management program, including public education, economic and ecological impact studies to document actual effects, early detection, and rapid response, and many others.

Additional index words: Economic and ecological justification, public education, science-based management, terminology.

This article reviews and summarizes data sets that attempt to compare performance, population dynamics, and herbivory of invasive plant species. Specifically, we review results from studies comparing (1) individual and population parameters of plant invaders in their native and exotic range, (2) herbivore pressure and natural enemy guilds associated with plant invaders in their native and exotic range, and (3) performance and defense levels of native and exotic populations of the invasive under standardized conditions and the performance of selected herbivores. We found a total of 39 published and 2 unpublished studies, investigating 40 plant species. The majority of studies within the first category showed that invaders form larger populations, grow denser, have higher reproductive output, larger seed banks, and higher regeneration rates in the exotic compared with the native range. In contrast, plant vigor was not always greater, presumably because of increased intraspecific competition. Nearly all studies within the second category showed that herbivory (percentage of attack, species number and load) was reduced and, if investigated, that the herbivore community shifted from specialists to generalists and from endophagous to exophagous species in the exotic compared with the native range. Under standardized conditions (category 3), an equal number of studies found increased vigor or no significant differences between plants from the exotic and native range. In a few cases, plants from the exotic range grew less vigorous. Specialist herbivores generally preferred or developed better on plants from exotic compared with native populations, which were also better defended. Studies comparing plant invaders at field sites in their native and exotic range or under standardized conditions can help identify factors facilitating successful invasions, which in turn can improve the selection and efficiency of biological control agents and the development of integrated management strategies. We therefore suggest to include comparative studies more frequently in biological control programs and to extend them to include manipulative experiments and comparisons of control agents.

Additional index words: Biological weed control, comparative studies, enemy release hypothesis, evolution of increased competitive ability hypothesis.

Abbreviations: EICA, evolution of increased competitive ability; ERH, enemy release hypothesis.

Saltcedar invasion has many economic and environmental effects, including displacement of native riparian vegetation and associated wildlife. A biological control program led to the approval in 1994 of two insects for introduction but was delayed by the presence of the endangered southwestern willow flycatcher (SWWF) in saltcedar. In 2001, the saltcedar leaf beetle was released in six states but not where the SWWF was present. Delays circumvent the benefits that saltcedar suppression could have for other declining species, including many rare or absent in ecosystems dominated by saltcedar. Numerous birds forage within saltcedar vegetation but in lower numbers and diversity than in native stands that provide better habitat and insect resources. Successful establishment by saltcedar leaf beetle resulted in extensive saltcedar defoliation, and observations of wildlife feeding on the beetles in an otherwise depauperate system suggest that biocontrol may enhance habitat quality for many species, including the SWWF. Consideration of the multiple species affected by saltcedar would have allowed more effective invasive plant management in this case, but delays also reflect drawbacks in federal administrative structures related to invasive species management in ‘natural areas’ as much as problems with a narrow focus on a single species. A functionally integrated approach where research and management decisions are made cooperatively would allow more rational management of invasive species in wildland ecosystems.

Nomenclature: Saltcedar, Tamarix ramosissima Ledeb. #³ TAARA, complex also includes T. chinensis Lour. # TAACH, T. parviflora DC. # TAAPA; saltcedar leaf beetle, Diorhabda elongata; southwestern willow flycatcher, Empidonax traillii extimus Phillips.

Additional index words: Biodiversity, ecological restoration, ecosystem management, riparian habitat.

Abbreviations: APHIS, Animal and Plant Health Inspection Service; SWWF, southwestern willow flycatcher; USDA, U.S. Department of Agriculture; USFWS, U.S. Fish and Wildlife Service.

We compared distributions of native nonweed, native weed, and exotic weed species based on a weed checklist for Mexico and for each of the 32 federal states. The national checklist contains 2,197 native and 617 exotic weed species. We calculated floristic similarity between states for native and exotic weeds and grouped the state floristic similarities by cluster analysis. The exotic and native weed species show different patterns both for distribution size and for geographic groupings. About 64% of the exotic species occur in eight or less states, whereas 36% of the native weed species occur in this limited range. Only 5.3% of the exotic species but 8.5% of the natives are recorded from 25 or more states. Native nonweed species have even more limited distributions than exotic weeds. The cluster analysis shows that the groupings based on the native weed flora are mostly coherent with general phytogeographical classifications. The grouping of the states for exotic weeds was different, and we propose that it may be related to climatic factors (particularly extreme minimum temperatures) and to management. The data do not support the hypothesis that exotic species have a superior, more general-purpose genotype than members of a well-developed, native weed flora.

Additional index words: Invasive plants, weed distribution, weed phytogeography.

Weed science is a diverse field that relies upon many fundamental disciplines to generate theories and empirical information about weedy plants. This information is used to develop and improve technology designed to manage weeds. Weed management includes three components— prevention, eradication, and control of weeds or undesirable plants—as well as protecting crops or fostering beneficial vegetation. The tools of weed control include biological, chemical, cultural, and mechanical tools as well as integrated weed management, which is the integration of effective and environmentally safe weed control methods within the context of a managed ecosystem. Invasive species may be viewed as a subset of the larger category of plants we call weeds; as such, the knowledge, concepts, and tools of weed management are highly applicable to the understanding and management of invasive plant species.

Additional index words: Integrated weed management, invasive species, vegetation management, weed control.

Abbreviations: IPM, integrated pest management; IWM, integrated weed management.

Modern weed science combines basic and applied sciences in the study of weeds, typically defined as plants that are objectionable or interfere with the activities or welfare of humans. Although weeds have been associated with human activity since the beginning of crop cultivation, the history of weed science parallels the history of modern day agriculture and is less than 100 yr old. From an early emphasis on chemical weed control, the field of weed science now integrates preventive, mechanical, chemical, cultural, and biological tactics in the management of weeds. Weeds cause tremendous economic costs to agriculture and natural resources in terms of crop loss, loss of land utility, health-related problems, and the costs of control. Weed science is now expanding its focus to include invasive plants in natural systems, which are undesirable from an ecological perspective rather than just an economic one.

Additional index words: Integrated weed management, invasive plants.

Abbreviations: IWC, integrated weed control; WSSA, Weed Science Society of America.

Categorizing species according to their functional traits, such as spatial and temporal patterns of resource use, effects on ecosystems, and responses to environmental perturbations, can facilitate successful restoration of plant communities. Functional guilds condense species lists by grouping species according to similarities in characteristics we believe to be important in a particular context. These groupings can allow us to (1) ensure community and ecosystem structural and functional attributes, (2) increase competitiveness of the community to deter the establishment of undesirable species, (3) simplify and test models of community assembly including resistance to invasion, succession, and species coexistence, and (4) facilitate cross-site comparisons. As useful as functional guilds can be, we must not overlook the potentially important roles of individual species. In restoration, including multiple species that represent each functional type within a target community may provide a buffer against environmental change. Functional guilds provide realistic conceptual units to ensure that restored plant communities include species that confer the ecological functions of most importance the majority of the time.

Additional index words: Community assembly, competition, functional traits, invasion, resource use, stability.

Abbreviations: CCNHA, Cedar Creek Natural History Area; CO₂, carbon dioxide; N, nitrogen; NO₃, nitrate.

Ecological resistance refers to the biotic and abiotic factors in a recipient ecosystem that limit the population growth of an invading species. Although there is interest in applying this concept to the management and restoration of habitats influenced by damaging, invasive species, practical difficulties in restoring resistance have inhibited its broad-scale incorporation. Also, some ecologists have argued that resistance is unimportant in generating landscape pattern casting doubt on its potential usefulness in large-scale management. In this study, we argue that despite temporal and spatial fluctuations in resistance being the norm, the concept provides a valuable foundation for a more sustainable approach to long-term weed management. This goal should be achievable through identification and manipulation of successional processes in natural communities.

Additional index words: Biotic resistance, community invasibility, ecological restoration, weed control.

Managers are faced with considerable uncertainty about the systems they manage; yet, they are still expected to optimize weed management. A wide variety of mathematical models can be used to improve the efficacy and implementation of biocontrol for invasive plants. In this article, applied insights that have been generated by mathematical models of biological control systems are described. First, the ways in which models can be used to help choose appropriate agents for biocontrol are outlined. In particular, a novel example showing how demographic and dispersal models can be linked to address the life-history stage to target to reduce either local abundance or spatial spread of weeds is presented. Second, the use of stochastic optimization models to improve biological control release and redistribution strategies is reviewed. The discussion outlines the way in which learning about uncertainties can be explicitly included in the management process. These two topics demonstrate the use of ecological models for improving the targeting and implementation of biological control of weeds.

Additional index words: Optimization, release strategies, spatial spread, uncertainty.

Abbreviation: AAM, active adaptive management.

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