The genus Diorhabda (Coleoptera: Chrysomelidae) was recently revised, using morphological characters, into five tamarisk-feeding species, four of which have been used in the tamarisk (Tamarix spp.) biological control program in North America and are the subject of these studies. The taxonomic revision is here supported using molecular genetic and hybridization studies. Four Diorhabda species separated into five clades using cytochrome c oxidase subunit 1 sequence data with Diorhabda elongata separating into two clades. Amplified fragment length polymorphism (AFLP) analysis using genomic DNA revealed only four clades, which corresponded to the four morphospecies. Hybridization between the four species yielded viable eggs in F₁ crosses but viability was significantly lower than achieved with intraspecific crosses. Crosses involving Diorhabda carinulata and the other three species resulted in low F₂ egg viability, whereas crosses between D. elongata, Diorhabda sublineata and Diorhabda carinata resulted in > 40% F₂ egg viability. Crosses between D. carinulata and the other three species resulted in high mortality of D. carinulata females due to genital mismatch. AFLP patterns combined with principal coordinates analysis enabled effective separation between D. elongata and D. sublineata, providing a method to measure genetic introgression in the field.

Nomenclature: Northern tamarisk beetle, Diorhabda carinulata Desbrochers; Mediterranean tamarisk beetle, Diorhabda elongata Brullé; subtropical tamarisk beetle, Diorhabda sublineata Lucas; larger tamarisk beetle, Diorhabda carinata Faldermann; tamarisk species: Tamarix chinensis Lour.; Tamarix parviflora DC.; Tamarix ramosissima Ledeb.

Management Implications: Tamarisks (aka saltcedar) are invasive shrubs that have become a widespread problem in riparian and wetland areas in the western United States. Biological control utilizing tamarisk beetles (Diorhabda spp.) is an effective management option, but it has become clear that we need to know more about the beetles to use them effectively for control in the diverse ecological settings that tamarisks have invaded. In this study we use molecular methods to complement the taxonomic revision of the tamarisk-feeding Diorhabda. The four closely related species used in the North American tamarisk biological control program were separable using molecular methods. We performed interspecific crosses between these four species and found that hybrids could be formed and that genetic exchange between species is possible, particularly between the Mediterranean tamarisk beetle and the subtropical tamarisk beetle. We developed a molecular method for detection of interspecific hybrids and show that under some circumstances there has been interbreeding and introgression in populations of the Mediterranean tamarisk beetle and the subtropical tamarisk beetle used in the North American biological control program. This work will help determine the potential geographic distributions of these species and their hybrids.

We review chemical ecology literature as it relates to biological control of weeds and discuss how this means of controlling invasive plants could be enhanced by the consideration of several well-established research approaches. The interface between chemical ecology and biological control of weeds presents a rich opportunity to exploit potentially coevolved relationships between agents and plants where chemical factors mediating interactions are important. Five topics seem relevant, which if implemented could improve the predictability of host range determination, agent establishment, and impact on the target weed. (1) The host secondary plant chemistry and a potential biological control agent's response to that chemistry can be exploited to improve predictability of potential agent host range. (2) Evolutionary changes may occur in secondary plant chemistry of invasive weeds that have been introduced to novel environments and exposed to a new set of biotic and abiotic stressors. Further, such a scenario facilitates rapid evolutionary changes in phenotypic traits, which in turn may help explain one mechanism of invasiveness and affect the outcome of biological control and other management options. (3) Herbivores can induce production of secondary plant compounds. (4) Variability of weed secondary chemistry which, either constitutive or inducible, can be an important factor that potentially influences the performance of some biological control agents and their impact on the target weed. (5) Finally, sequestration of secondary plant chemistry may protect herbivores against generalist predators, which might improve establishment of a biological control agent introduced to a new range and eventually impact on the target weed. Recognition of these patterns and processes can help identify the factors that impart success to a biological control program.

Native forbs are important for plant community function and diversity, and provide food and cover for wildlife. Field studies have been conducted throughout the western United States to determine the impact of herbicides applied to control invasive weeds on native forbs. However, locating adequate populations of native forbs for evaluation of tolerance to herbicides is often difficult. The susceptibility of nine native prairie forbs to aminopyralid applied at 30 to 120 g ha⁻¹ was evaluated in a greenhouse study and results compared to the same or similar species in field trials. Forb susceptibility to aminopyralid varied by species. Of the forbs evaluated, azure aster, purple coneflower, and closed bottle gentian were the most tolerant to aminopyralid while prairie coneflower, great blue lobelia, harebell, and white prairie clover were the most susceptible and likely would be killed in the field. Blanket flower and showy goldenrod were moderately tolerant to aminopyralid even when applied at 120 g ha⁻¹. The susceptibility of greenhouse-grown forbs to aminopyralid was comparable to results for the same or similar species in the field. Results from greenhouse trials could be used to predict native forb tolerance in the field.

Nomenclature: Aminopyralid; azure aster, Symphyotrichum oolentangiense (Riddell) G.L. Nesom; blanket flower, Gaillardia aristata Pursh; closed bottle gentian, Gentiana andrewsii Griseb.; great blue lobelia, Lobelia siphilitica L.; harebell, Campanula rotundifolia L.; prairie coneflower, Ratibida columnifera (Nutt.) Woot. & Standl.; purple coneflower, Echinacea angustifolia DC.; showy goldenrod, Solidago speciosa Nutt.; white prairie clover, Dalea candida Michx. ex Willd.

Management Implications: Invasion by noxious weeds has become a major threat to the conservation of biodiversity and ecosystem sustainability in remnant and restored prairies. Newly restored prairies are especially vulnerable to invasion by plants such as Canada thistle because there is not a well-established plant community that can compete for available resources. Chemical treatment remains the primary method of Canada thistle control used in rangeland and wildland sites because there are no cost-effective alternatives. Aminopyralid is often used to control Canada thistle and other invasive weeds on native and wildlands. Field studies have been conducted throughout the western United States to determine the impact of herbicides applied to control invasive weeds on native forbs. However, finding adequate populations of native forbs to evaluate tolerance to herbicides is often difficult. A greenhouse study evaluated tolerance of nine native prairie forbs to fall-applied aminopyralid. Of the forbs evaluated, azure aster, purple coneflower, and closed bottle gentian were the most tolerant to aminopyralid while prairie coneflower, great blue lobelia, harebell, and white prairie clover were the most susceptible and likely would be killed with fall applications in the field. Blanket flower and showy goldenrod were moderately tolerant to aminopyralid even when applied at 120 g ha⁻¹. The susceptibility of greenhouse-grown forbs to aminopyralid was comparable to results of the same or similar species in the field and suggests results could be used to predict native forb tolerance in the field. Forb species that were tolerant to aminopyralid in the greenhouse likely would be tolerant in the field as well because steps were taken to maximize potential injury. This information is valuable to land managers, who must balance the benefits of an aminopyralid application to control invasive weeds with the potential of unintentional injury to desirable plant species.

Buffelgrass, a highly competitive and flammable African bunchgrass, is spreading rapidly across both urban and natural areas in the Sonoran Desert of southern and central Arizona. Damages include increased fire risk, losses in biodiversity, and diminished revenues and quality of life. Feasibility of sustained and successful mitigation will depend heavily on rates of spread, treatment capacity, and cost–benefit analysis. We created a decision support model for the wildland–urban interface north of Tucson, AZ, using a spatial state-and-transition simulation modeling framework, the Tool for Exploratory Landscape Scenario Analyses. We addressed the issues of undetected invasions, identifying potentially suitable habitat and calibrating spread rates, while answering questions about how to allocate resources among inventory, treatment, and maintenance. Inputs to the model include a state-and-transition simulation model to describe the succession and control of buffelgrass, a habitat suitability model, management planning zones, spread vectors, estimated dispersal kernels for buffelgrass, and maps of current distribution. Our spatial simulations showed that without treatment, buffelgrass infestations that started with as little as 80 ha (198 ac) could grow to more than 6,000 ha by the year 2060. In contrast, applying unlimited management resources could limit 2060 infestation levels to approximately 50 ha. The application of sufficient resources toward inventory is important because undetected patches of buffelgrass will tend to grow exponentially. In our simulations, areas affected by buffelgrass may increase substantially over the next 50 yr, but a large, upfront investment in buffelgrass control could reduce the infested area and overall management costs.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link

Management Implications: Knowledge of where invasive species occur is often slim to nonexistent. In the face of this imperfect knowledge, land managers are still required to determine where to allocate their limited resources. Using a decision support model such as TELSA allows land managers to make a more informed decision on where to allocate funding. We addressed this imperfect knowledge in three ways. First, we acknowledged that there were many undetected buffelgrass plants on the landscape by stochastically adding and growing patches across the landscape throughout a 50-yr simulation. This is a way to see how populations that are not detected grow over time. We also developed a map of potentially suitable habitat to predict the future spread of buffelgrass patches. Finally, we calibrated spread rates by comparing past and current aerial photographs with simulation outputs. We found that areas invaded by buffelgrass may increase substantially over the next 50 yr, but that a large, upfront investment in buffelgrass control could reduce that area and overall management costs. The application of sufficient resources toward inventory is important because patches that remain undetected will tend to grow exponentially and, when eventually detected, will require substantially higher treatment efforts to control.

Determining the best strategy for allocating weed management resources across and between landscapes is challenging because of the uncertainties and large temporal and spatial scales involved. Ecological models of invasive plant spread and control provide a practical tool with which to evaluate alternative management strategies at landscape scales. We developed a spatially explicit model for the spread and control of spotted knapweed and leafy spurge across three Montana landscapes. The objective of the model was to determine the ecological and economic costs and benefits of alternative strategies across landscapes of varying size and stages of infestation. Our results indicate that (1) in the absence of management the area infested will continue to increase exponentially leading to a substantial cost in foregone grazing revenues; (2) even though the costs of management actions are substantial, there is a net economic benefit associated with a broad range of management strategies; (3) strategies a that prioritize targeting small new infestations consistently outperform strategies that target large established patches; and (4) inconsistent treatment and short-term delays can greatly reduce the economic and ecological benefits of management.

Nomenclature: Leafy spurge, Euphorbia esula L. EPHES; spotted knapweed, Centaurea stoebe L. CENMA.

Management Implications: Models of invasive plant spread and control provide a useful way to assess the performance of alternative management strategies and budget levels across broad temporal and spatial scales. To meet long-term goals for their landscape, managers should pursue strategies that are both ecologically effective and economically justified. Model results provide several insights for achieving that success.

Early detection and small-patch control strategies consistently outperformed large-patch strategies. Despite these results and previous recommendations for early detection and rapid response programs, managers are often mandated to focus on large infestations where weeds are well established and highly visible. Small infestations do not present an immediate loss of productivity and are often more remote and time-consuming to control. Consequently resources are directed toward locations where, based on our model results, treatment is less beneficial and long-term success is less likely. Our model results support the reallocation of resources to an effective early detection and treatment strategy.

Our results also indicate that managers should avoid delaying management or applying inconsistent treatment over time. In these cases, weed populations outpace management efforts and can reinvade previously treated areas, ultimately leading to a greater area invaded with greater economic costs. Preventative actions that reduce weed dispersal distances and spread rates will lower ultimate invasion levels and long-term management costs.

For landscapes with relatively few existing infestations of noxious weeds, managers should dedicate resources to detecting and controlling new infestations as early as possible to prevent the development of established populations. For invaded landscapes where large noxious weed infestations already exist, early detection and control remains a foundational strategy but managers should also maximize site-specific treatment success. At the broadest scale, resources should be allocated to landscapes with lower infestation levels and thus greater potential for long-term management success and return on investment, rather than highly invaded landscapes.

Previous research showed growth regulator herbicides, such as picloram and aminopyralid, have a sterilizing effect on Japanese brome (Bromus japonicus Thunb.) that can reduce this invasive annual grass's seed production nearly 100%. This suggests growth regulators might be used to control invasive annual grasses by depleting their short-lived seed banks. The goal of this study was to extend the previous Japanese brome research to downy brome (Bromus tectorum L.), the most damaging invasive annual grass of U.S. grasslands. In a greenhouse, we found picloram did not greatly influence downy brome seed production, while point estimates suggest aminopyralid reduced seed production 55 to 80%. If not for a highly abnormal retillering response that we somewhat doubt would occur in the field, point estimates suggest aminopyralid would have reduced downy brome seed production approximately 90% when applied at the heading stage and approximately 98% when applied at three earlier growth stages. Our greenhouse study should encourage field studies designed to further explore the potential for using growth regulators to control downy brome and other invasive annual grasses.

Nomenclature: Picloram; aminopyralid; downy brome, Bromus tectorum L.; Japanese brome, Bromus japonicus Thunb.

Management Implications: Growth regulator herbicides, such as aminopyralid, picloram and dicamba, are widely used to control broadleaf weeds in grasslands. In recent studies, we discovered these herbicides interfered with reproductive processes in the invasive annual grass Japanese brome, thereby reducing its seed production nearly 100% in the greenhouse and field. This suggests growth regulators might be used to control invasive annual grasses by depleting their short-lived seed banks. Compared to currently used invasive annual grass herbicides, such as glyphosate and imazapic, growth regulators have the advantage of being less damaging to desirable perennial grasses, though all herbicides currently used for invasive annual grass control can severely damage desirable forbs and shrubs.

The objective of the current study was to extend our Japanese brome research to downy brome, a much more widespread and damaging congener of Japanese brome. In a greenhouse, we found that picloram was not effective against downy brome while aminopyralid greatly reduced downy brome seed production. This encouraging result should promote field studies designed to more fully evaluate the potential for using aminopyralid to control downy brome.

Our findings will perhaps prove most applicable to areas co-dominated by invasive annual grasses and invasive forbs, such as yellow starthistle, spotted knapweed, etc. Downy brome often dominates sites after herbicides are used to control invasive forbs. It may sometimes be possible to overcome this problem by using one appropriately timed growth regulator herbicide application to simultaneously target both invasive forbs and invasive annual grasses.

Buffelgrass is a non-indigenous, invasive, C₄ grass that was introduced throughout much of southern Texas, the Southwestern United States, and northern and central Mexico to improve degraded rangelands. The successful introduction and spread of buffelgrass follows a trajectory similar to that of other invasive C₄ grasses in arid and semiarid ecosystems. In the Plains of Sonora of the Sonoran Desert (Mexico) buffelgrass is favored by widespread removal of native vegetation and seeding, but, why, following initial introduction, the species persists remains unclear. In this study, we addressed two concerns associated with buffelgrass invasion in the Plains of Sonora. We hypothesized that under arid rangeland conditions, buffelgrass outcompetes native herbaceous species (1) through rapid acquisition of limiting nutrients (here assumed to be nitrogen) and (2) under conditions with high nitrogen input. In summer 2002, a 2 by 2 factorial experiment was established with buffelgrass removal and nitrogen addition in both intact desert and converted buffelgrass grassland habitats. In winter 2003, we found that, regardless of habitat type, buffelgrass removal had a positive effect on abundance, biomass, and richness of native herbaceous species while addition of nitrogen, as urea (at 50 kg N ha⁻¹yr⁻¹ or 9.18 lbs N ac⁻¹yr⁻¹), and disturbance resulted in reduction in abundance and biomass. Nitrogen addition did not negatively alter buffelgrass cover. Nitrogen addition had the expected result of increasing initial, peak and total NO₃ and NH₄ mineralization with the exception of NO₃ measures in intact desert. Removal of buffelgrass did not result in significant increases in soil NO₃ or NH₄ with the exception of peak NH₄ in intact desert. Results of this study support observations that native herbaceous species are displaced by buffelgrass invasion and that nitrogen pollution will likely favor buffelgrass over the native herbaceous species in this ecosystem.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link (Poaceae), formerly Cenchrus ciliaris L.

Management Implications: Buffelgrass is extensively planted in arid and semi-arid grassland ecosystems across the planet and has been useful in stabilizing soils and increasing productivity in rangelands where there has been widespread drought combined with overgrazing. Nonetheless, grassland conversion to accommodate buffelgrass plantings and invasion of the species itself has caused widespread and extreme collateral damage. In this study, we confirm that buffelgrass displaces native species. The study also demonstrates that high levels of nitrogen addition in low rainfall years results in neutral effects on buffelgrass and significantly negative effects on native herbaceous species. Given buffelgrass' significant negative impacts on biodiversity, its ability to alter fire regimes and establish a positive feedback loop, and its threat to the existence of ecosystems that have aesthetic and economic value in business sectors other than ranching (e.g., tourism in Arizona, United States), management of these rangelands for buffelgrass control is recommended as a high priority. Managers introducing buffelgrass to improve rangelands should take into consideration the species negative impacts on native forb and grass diversity, habitat for mammals and ground-dwelling birds, and the probable irreversible alteration of the ecosystem. In areas of conservation concern where biodiversity is a management goal we advocate (1) rigorous vigilance and immediate removal of nascent foci, (2) where established, an aggressive removal campaign (without the use of fire), (3) outreach to increase public awareness about the negative effects of the species, and (4) where possible, reduced

Common reed [Phragmites australis (Cav.) Trin. ex Steud.] is an invasive plant that reproduces poorly by seed but regenerates vigorously by rhizomes. Because Phragmites australis propagates well through rhizome growth, invasion often occurs from transported rhizome tissue. We investigated both rhizome-fragment biomass and seasonal effects on survival and growth of ramets. Rhizomes were collected along roadside ditches during the fall of 2009 and 2010 and during the summer of 2010 and 2011. Fall and summer were chosen because the plants were either dormant or actively growing, respectively. Rhizomes were cut into fragments then grown in a greenhouse for 60 d in vermiculite with no added nutrients. Rhizomes collected in the fall had a survival rate of 71.1%, whereas only 15.6% of those collected in the summer survived. Within season, rhizomes with low initial biomass had lower survival rates and growth than did large rhizomes. There was no seasonal difference in the total biomass produced by the surviving plants; however, allocation of biomass did differ. Summer-collected rhizomes showed a higher belowground to aboveground biomass ratio than did those collected in the fall. Understanding the viability of Phragmites australis rhizome fragments provides land managers a greater awareness of the high-establishment risks of Phragmites australis. This information should be included in an integrated weed management program, and actions should be taken to reduce the spread of this weed during roadside maintenance. Although the risk of survival is lower during the summer, soil contaminated with Phragmites australis should not be transported or must be sifted with a screen to ensure all rhizome fragments are removed.

Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud.

Management Implications: Common reed [Phragmites australis (Cav.) Trin. ex Steud.] is one of the most problematic invasive species in the country, and it can be found growing in dense monocultures along roadside ditches and right-of-ways throughout the Midwest and eastern United States. It propagates clonally and is often spread when rhizome fragments are transported in soil during ditch maintenance. This research aims to contribute to integrated weed management plans by suggesting cultural practices to reduce the spread of Phragmites australis based on survival and growth rates as a function of rhizome biomass and the season in which the rhizomes are transported.

We determined that even though summer-collected rhizomes have depleted resource stores and the risk of survival and growth is lower, soil contaminated with Phragmites australis rhizome fragments should never be transported. Rhizomes should definitely not be transported in fall because the survival rates and growth are high at that time. We suggest that rhizomes be chipped and that any transported soil be screened to remove the rhizome fragments and thereby lessen any risk of producing a new clonal population.

Differing life histories contribute to difficulties establishing perennial grasses on lands dominated by exotic annual grasses. In a greenhouse study, we investigated to what extent allowing the perennial grass bluebunch wheatgrass to emerge before the exotic annual grass downy brome would increase its competitive ability and whether modifying nitrogen (N) would affect competition. We conducted an addition-series factorial experiment. In three cohort treatments, the two species were seeded concurrently or bluebunch wheatgrass was at the two- or four-leaf stage when downy brome was planted. N treatments were low (ambient) or high (N added to maintain 10 mg kg⁻¹ [0.1286 oz lb⁻¹]). Larger bluebunch wheatgrass avoided suppression by downy brome regardless of N. Under concurrent sowing, doubling downy brome density decreased bluebunch wheatgrass biomass by 22.6% ± 2.38 SE. In contrast, when bluebunch wheatgrass had a four-leaf size advantage, the same increase in downy brome density decreased bluebunch wheatgrass biomass by 4.14% ± 2.31. Larger bluebunch wheatgrass also suppressed downy brome more effectively, but N enrichment decreased the suppressive ability of bluebunch wheatgrass.

Nomenclature: Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) Á. Löve; downy brome, Bromus tectorum L.

Management Implications: This study demonstrated the importance of both order of emergence and nitrogen (N) availability in the competitive relationship between bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Á. Löve] and downy brome (Bromus tectorum L.). First, we found that larger bluebunch wheatgrass seedlings avoided suppression by downy brome more effectively and that they did so regardless of N availability. However, although larger bluebunch wheatgrass also suppressed downy brome more effectively, N enrichment decreased the ability of bluebunch wheatgrass to suppress downy brome. Our results suggest that order of emergence for desired perennial vs. exotic annual grasses may be an important aspect of revegetation planning and that avoiding conditions that lead to N increases, such as soil disturbance, could allow perennial grasses to better suppress downy brome. To establish an initial size difference that favors seeded species, managers could modify the standard timing of revegetation practices to ensure that perennial species receive a sufficient head start. Another way to promote an initial size difference would be to use transplants or plugs to restore critical sites.

Porcelain berry and bushkiller are confamilial, exotic, perennial vines in the Vitaceae family that are considered nuisance/invasive weeds of natural and riparian areas in the eastern United States. To better understand the competitive abilities of these aggressive weeds, greenhouse competition experiments were conducted on cuttings of porcelain berry, bushkiller, and Virginia-creeper, a native member of the Vitaceae family. Plants grown singly or in combination were monitored for stem growth and biomass production. In this research, porcelain berry and Virginia-creeper exhibited similar rates of stem growth, whereas bushkiller grew taller and faster than either of the other species. Porcelain berry stem growth was reduced in competition with bushkiller. All three species exhibited reduced stem biomass when grown with both other species. Root biomass of porcelain berry and Virginia-creeper were not affected by competition, but bushkiller, which produced the heaviest roots, exhibited reduced root biomass when grown with both other species. Porcelain berry root length was reduced by competition with both other species, but neither Virginia-creeper nor bushkiller root lengths were affected by competition. These results indicate that bushkiller is likely the strongest competitor of the three species studied. In these experiments, porcelain berry was less aggressive and vigorous than bushkiller but was similar to Virginia-creeper.

Nomenclature: Bushkiller,Cayratia japonica (Thunb.) Gagnep.; porcelain berry, Ampelopsis brevipedunculata (Maxim.) Trautv.; Virginia-creeper, Parthenocissus quinquefolia (L.) Planch.

Management Implications: Porcelain berry and bushkiller are exotic, perennial, climbing vines in the grape family. Both species were likely introduced into the United States for horticultural purposes and have proven to be aggressive invaders in some areas. Porcelain berry is common throughout the eastern United States, whereas bushkiller is only known to occur in five states. One aspect of managing invasive species is to understand the threat posed by that species to other members of the invaded community. Competition studies are commonly used to measure the ability of a plant species to effectively garner resources, such as light, water, and nutrients, in the presence of competing neighboring plants. An understanding of the growth and competitive capabilities of these species may be helpful to determine regulatory policy in states with limited or no infestations of these species, for management recommendations of infested areas, and to predict potential environmental effects on invaded areas. Greenhouse competition studies between porcelain berry, bushkiller, and Virginia-creeper, a native perennial member of the grape family, indicate that bushkiller is by far the most successful competitor of the three, acquiring greater stem length and more stem and root biomass than the others. Porcelain berry showed similar growth and competitive abilities as Virginia-creeper, with the exception of having significantly higher inflorescence production than either other species. The results indicate that, although porcelain berry is a troublesome weed in many areas and may contribute intense propagule pressure, bushkiller has the potential to become a more significant threat, and infestations of this plant should be eliminated as soon as they are discovered.

Downy brome (cheatgrass) is a highly successful, exotic, winter annual invader in semi-arid western North America, forming near-monocultures across many landscapes. A frequent but poorly understood phenomenon in these heavily invaded areas is periodic ‘die-off’ or complete stand failure. The fungal pathogen Pyrenophora semeniperda is abundant in cheatgrass seed banks and causes high mortality. To determine whether this pathogen could be responsible for stand failure, we quantified late spring seed banks in die-off areas and adjacent cheatgrass stands at nine sites. Seed bank analysis showed that this pathogen was not a die-off causal agent at those sites. We determined that seed bank sampling and litter data could be used to estimate time since die-off. Seed bank patterns in our recent die-offs indicated that the die-off causal agent does not significantly impact seeds in the persistent seed bank.

Nomenclature: Downy brome, Bromus tectorum L.; black fingers of death, Pyrenophora semeniperda (Brittleb. & D.B. Adam) Shoemaker.

Management Implications: Cheatgrass is the most abundant exotic plant species in the natural landscapes of the western United States, occurring in near-monocultures over very large areas. Cheatgrass die-off occurs when a discrete area that is highly dominated by cheatgrass shows complete stand failure for one or more growing seasons. From a distance, these areas are most visible in late spring, when the matted, gray litter in failed stands contrasts sharply with the green of adjacent established stands. Die-offs have both positive and negative implications. In the short term, they present a rare situation in which formerly infested areas present much reduced cheatgrass competition for at least a year, suggesting that they may represent restoration opportunities. However, these sudden and unpredictable events also represent loss of spring forage for livestock and wildlife. In the longer term, areas experiencing prolonged or repeated die-offs may suffer increased erosion, resulting in soil loss and continued site degradation. Our study represents the first organized investigation of cheatgrass die-offs. Its goal was to determine whether the pathogen Pyrenophora semeniperda (also known as “black fingers of death”) played a role in nine die-offs in Nevada, Utah and Washington. This pathogen is omnipresent in cheatgrass seed banks and can kill large quantities of slow-germinating seeds. We found no evidence that this pathogen was a die-off causal agent at the studied sites, but we developed a greater understanding of the die-off process. Our seed bank data suggested that die-off mortality does not impact the persistent seed bank directly. Areas that have experienced die-off often show stand failure for multiple years, but most eventually revert back to cheatgrass dominance. Appropriate management of the sometimes large areas affected by cheatgrass die-off depends on a continuing research effort aimed at elucidating both causes and consequences of die-off events.

Seed dispersal is a crucial process in most plant invasions, but is notoriously difficult to study. One technique to identify the maternal source of dispersed seeds and newly established seedlings is labeling with a stable isotope. We tested whether foliar application of ¹⁵N-labeled urea would result in sufficient ¹⁵N enrichment to discriminate among seeds and seedlings grown from those seeds of the invasive shrub Lonicera maackii (Amur honeysuckle). We subjected mature L. maackii to all combinations of three concentrations of ¹⁵N-labeled urea (0.025 g L⁻¹ [0.003 oz gal⁻¹], 0.20 g L⁻¹, and a 0 g L⁻¹ control) and three temporal treatments (one application in August, one application in September, and five applications spaced every three weeks from June through August). Seeds were collected September to November; some of these were analyzed for %¹⁵N and others allowed to germinate and grow into seedlings under two treatments (in potting mix in greenhouse and in woodlot soil outdoors). Seedlings were harvested midway through the next growing season. We found that seeds from plants subjected to the three different concentrations had significantly different %¹⁵N levels, and there was a significant interaction between concentration and temporal treatment: the highest seed %¹⁵N levels were from plants sprayed five times with ¹⁵N-labeled urea, and the second highest from plants sprayed once in September. Similar patterns in %¹⁵N levels were found in seedlings, except that those from the 0.025 g L⁻¹ spray treatment were only distinguishable from controls for seedlings grown outdoors in woodlot soil. These findings demonstrate that a single foliar application of ¹⁵N in early September is sufficient to label both seeds and seedlings of this invasive shrub, enabling one to identify the source of field-collected seeds or seedlings. This provides a tool for studying patterns and processes in seed dispersal of Amur honeysuckle and potentially other invasive plants.

The continued threat of an invasive, annual brome (Bromus) species in the western United States has created the need for integrated approaches to postfire restoration. Additionally, the high germination rate, high seed production, and seed bank carryover of annual bromes points to the need to assay soil seed banks as part of monitoring programs. We sampled the soil seed bank to help assess the effectiveness of treatments utilizing the herbicide Plateau® (imazapic) and a perennial native seed mix to control annual Bromus species and enhance perennial native plant establishment following a wildfire in Zion National Park, Utah. This study is one of few that have monitored the effects of imazapic and native seeding on a soil seed bank community and the only one that we know of that has done so in a pinyon–juniper woodland. The study made use of untreated, replicated controls, which is not common for seed bank studies. One year posttreatment, Bromus was significantly reduced in plots sprayed with herbicide. By the second year posttreatment, the effects of imazapic were less evident and convergence with the controls was evident. Emergence of seeded species was low for the duration of the study. Dry conditions and possible interactions with imazapic probably contributed to the lack of emergence of seeded native species. The perennial grass sand dropseed outperformed the other species included in the seed mix. We also examined how the treatments affected the soil seed bank community as a whole. We found evidence that the herbicide was reducing several native annual forbs and one nonnative annual forb. However, overall effects on the community were not significant. The results of our study were similar to what others have found in that imazapic is effective in providing a short-term reduction in Bromus density, although it can impact emergence of nontarget species.

Nomenclature: Imazapic, brome, Bromus, sand dropseed, Sporobolus cryptandrus Torr.

Management Implications: Invasive annual bromes threaten native diversity across vast areas of the western United States. A variety of techniques have been employed to control these species, yet populations continue to persist and expand. Recently, some success had been achieved through use of the herbicide imazapic. This study sampled the soil seed banks to evaluate the ability of imazapic and a native seed application to reduce brome occurrence and promote native species reestablishment following a wildfire at Zion National Park, Utah. This study is one of the few that has monitored the effects of imazapic and native seeding on a soil seed bank community. Target brome species were significantly reduced during the first year following application, but not during the second and third years. Several nontarget species were also reduced, but overall, the effect on the entire soil seed bank community was not significant. Our results also suggest that imazapic may have had an adverse effect on the emergence of at least two of the seeded native species. However, in general the seeded native species made only a minimal contribution to the soil seed bank and had a minimal effect on reducing brome species, although the increase in sand dropseed during the last year of study suggests that it may become a more substantial component of the seed bank in the next few years. Further research needs to be conducted both on the susceptibility of native species and on the timing of seeding additions in relation to imazapic applications. Finding additional site-adapted natives that can quickly replenish fire-impoverished seed banks would also be beneficial. Finally, the increase in nonnative species in the last year of the study suggests that further steps need to be taken to insure native establishment during the first year of imazapic application.

Understanding the ecological distribution range of exotic trees in an arboreal ecosystem is essential to managing natural forest resources sustainably. Forest resource mapping can be applied as a powerful tool in the identification of forest resource threat patterns, and in monitoring ongoing changes associated with a landscape. This study offers an insight on Russian-olive and its impact on a spatially bound ecosystem, namely, Bismarck–Mandan Wildland–Urban Interface (BMWUI). Data from the National Agricultural Imagery Program collected in 2005 and 2010 and in situ reference data were used to estimate the potential habitat of Russian-olive using ArcGIS ArcInfo® 9.3 (ESRI, Redlands, CA). Russian-olive plants are discernible on aerial photographs with a fine spatial resolution because of silvery gray-green leaves in the upper strata of their canopies. Results showed that Russian-olive occupied 110 ha (272 acres) in BMWUI in 2005 and of that, 13 ha (12%) was in inundated habitats. In addition, Russian-olive in 2010 covered 125 ha within the BMWUI and of that, 25 ha (20%) was in inundated habitats. Russian-olive showed a close association with the silt loam and silty clay soil type, which occurs along the Missouri River floodplain. Our findings revealed that the species is well established in riparian habitats and other open habitats such as roadside and agricultural lands. There is a greater likelihood of lateral spread of Russian-olive throughout the BMWUI that may require active management to avert undesirable conservation impacts.

Nomenclature: Russian-olive, Elaeagnus angustifolia L.

Management Implications: Understanding vulnerable habitats for rapid invasions by exotic species is crucial for land managers to identify and implement successful management strategies. Habitat suitability modelling is useful for identifying critical arboreal ecosystems that can be targeted with surveillance, prevention and eradication measures to avoid wide-scale infestations. This study provides valuable baseline information of preferred habitats for current and potential future distribution of Russian-olive within the Bismarck-Mandan Wildland Urban Interface (BMWUI) on the banks of Missouri River. For example, we found that riparian habitats are more suitable for establishment of Russian-olive than terrestrial habitats. Forest managers can use our distribution data to monitor how Russian-olive colonization of an area may impact growth and survivability of native trees such as cottonwood and willow at similar sites. North Dakota Parks and Recreation Department's Natural Heritage Inventory (NDNHI) has carried out botanical surveys, for example, creating an inventory of rare plants, and our results are important to evaluating whether Russian-olive has also been threatening rare plants in this region. Weed managers in other regions of the Missouri River can compare our results with their data to create strategies to manage Russian-olive regionally through prescribed restoration programs. This study also provides valuable information from which city and wildlife managers can make better management plans to conserve native plants, protecting them from the invasive species in the riparian and upland regions.

Common reed (Phragmites australis) is a nonnative invasive perennial grass that is problematic in aquatic and riparian environments across the United States. Common reed often forms monotypic stands that displace native vegetation which provide food and cover for wildlife. To help maintain native habitats and manage populations of common reed in the United States, an understanding of its life history and starch allocation patterns are needed. Monthly biomass samples were harvested from sites throughout the Mobile River delta in southern Alabama, USA from January 2006 to December 2007 to quantify seasonal biomass and starch allocation patterns. Total biomass of common reed throughout the study was between 1375 and 3718 g m⁻² depending on the season. Maximum aboveground biomass was 2200 ± 220 g m⁻² in October of 2006 and 1302 ± 88 g m⁻² in December of 2007. Maximum belowground biomass was seen in November of 2006 and 2007 with 1602 ± 233 and 1610 ± 517 g m⁻² respectively. Biomass was related to ambient temperature, in that, as temperature decreased aboveground biomass (p  =  0.05) decreased. Decreases in aboveground biomass were followed by an increase in belowground biomass (p < 0.01). Starch comprised 1 to 10% of aboveground biomass with peak temporary storage occurring in July and August 2006 and September to November of 2007. Belowground tissues stored the majority of starch for common reed regardless of the time of year. Overall, belowground tissues stored 5 to 20% of total starch for common reed with peak storage occurring in December 2006 and October 2007. Starch allocation to belowground tissues increased as temperatures decreased. Understanding seasonal life history patterns can provide information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed.

Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud PHRCO.

Management Implications: Common reed is an invasive grass that continues to spread across the United States. The genetic haplotype I is the dominant form of this species along the Gulf Coast of the United States. During this two year study, common reed biomass fluctuated seasonally, though maximum biomass exceeded 3700 g m⁻². Biomass allocation was influenced by seasonal temperatures in that aboveground biomass peaked in early fall, followed by a peak in belowground biomass. The peak in belowground biomass allocation corresponded to increased starch allocation to underground tissues. Understanding these seasonal life history patterns can provide information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed. Based on these data it may be beneficial to implement management techniques in early spring when starch reserves in belowground tissues are being used to support shoot growth. Aboveground biomass during this time would be reduced as plants would be small, and therefore, may be more susceptible to management.

Flea beetles (Aphthona spp.) were released in the Little Missouri National Grasslands (LMNG) in western North Dakota in 1999 to control leafy spurge. The changes in leafy spurge density and soil seedbank composition were evaluated on two ecological sites 10 yr (2009) after Aphthona spp. release to monitor the effectiveness of the insects on weed control and the associated changes in plant communities. In 2009, leafy spurge stem density averaged 2 and 9 stems m⁻² (0.19 to 0.84 ft⁻²) in the loamy overflow and loamy sites, respectively, compared with 110 and 78 stems m⁻², respectively, in 1999. Leafy spurge constituted nearly 67% of the loamy overflow seedbank in 1999, compared with 2% in 2009. In the loamy seedbank, the weed represented nearly 70% in 1999, compared with approximately 15% in 2009. As leafy spurge abundance was reduced, native species richness and seed count increased 10 yr after Aphthona spp. release. Late seral species represented 17% of the loamy overflow seedbank in 2009, an increase from 5% in 1999. However, Kentucky bluegrass, a nontarget weedy species, increased more than 250% in the loamy overflow seedbank. Late seral species were 38% of the loamy seedbank in 2009, compared with 13% in 1999. The number of native species increased from 31 in 1999 to 39 in 2009 in the loamy overflow seedbank, but only changed from 32 to 34 species in the loamy site during the same period. The reestablishment of native species has been slow, but seedbank analysis indicates the number and type of species found before the leafy spurge infestation have increased. Planting native species in selected areas may have reduced the lag time in these species return to the seedbank and reduced invasion from other nondesirable species, such as Kentucky bluegrass.

Nomenclature: Leafy spurge flea beetle, Aphthona spp.; Kentucky bluegrass, Poa pratensis L.; leafy spurge, Euphorbia esula L. EPHES.

Management Implications: The leafy spurge (Euphorbia esula L.) biological control agents Aphthona nigriscutis and Aphthona lacertosa were introduced to the Little Missouri National Grasslands (LMNG) in western North Dakota in 1999 to control the invasive weed. At the same time, 12 sites each on loamy overflow and loamy soils were established for evaluation of change in leafy spurge density and soil seedbank. In 2009, 10 yr after Aphthona spp. release, leafy spurge stem density had decreased by an average of 94% in the loamy overflow and loamy sites. At the same time leafy spurge seed decreased in the loamy overflow seedbank from 67% in 1999 to only 2% in 2009 and from 70% in 1999 to approximately 15% after 10 yr at the loamy site. As leafy spurge was successfully controlled in the LMNG, native species richness increased in the soil seedbank. Prairie Junegrass was a prevalent native species in the loamy overflow seedbank in 2009, and some late seral species that appeared by 2009 included textile onion (Allium textile A. Nels. & J.F. Macbr.), shy wallflower [Erysimum inconspicuum (S. Wats.) MacM.], locoweed [Oxytropis campestris (L.) DC.], and prairie groundsel [Packera plattensis (Nutt.) W.A. Weber & A. Löve]. However, from 2004 to 2009, there was a substantial increase in Kentucky bluegrass (Poa pratensis L.) in the loamy overflow seedbank. The increase in Kentucky bluegrass was most likely enabled by the reduction in leafy spurge and above-average precipitation, which provided a favorable habitat for growth and invasion. Although Kentucky bluegrass may become a problem species in the LMNG, an increasing trend in native species was observed in the soil seedbank following the reduction of leafy spurge. Desirable forb species and native grasses could be seeded within 5 yr following leafy spurge reduction to reduce opportunistic i

Hardwood forests in eastern North America are being colonized by multiple nonnative plant and animal species. Colonization rates can be affected by stand structure and distance from edge. We sampled earthworm densities and understory plant species cover in transects located in paired old- and second-growth forests in Indiana. Two 100-m transects were established within each forest stand during late April to early May in each year. One transect was placed parallel to and within 5 m of a south- or west-facing edge. The second transect was placed parallel to the first. but at no less than 100 m from any edge. Nonnative earthworms and plants were found in forest edge and interior regardless of structural stage (second-growth vs. old-growth). The number of native plant species decreased linearly as the densities of adult Lumbricus and Aporrectodea earthworms and the percent cover of multiflora rose (an invasive plant species) increased. Densities of L. terrestris and Aporrectodea earthworms and percent cover of multiflora rose cumulatively explained 39% of the variation in the number of native plant species found in transects across the state. However, multivariate analyses suggested that the species composition of Indiana understory plant communities was affected more by geography than by earthworm densities. Our results suggest that nonnative earthworms and plants are ubiquitous in Indiana hardwood forests and that they may reduce the number of native plant species.

Nomenclature: Multiflora rose, Rosa multiflora Thunb. ex Murr. ROSMU; nightcrawler, Lumbricus terrestris L.

Management Implications: European earthworms, which are not native to eastern temperate and boreal forests in North America, have been linked to changes in forest soils and to declines in native plant diversity in invaded areas. Earthworm densities appear to be greater under several invasive plant species and researchers have speculated that these earthworms might facilitate plant invasions and vice versa. We sampled six old- and second-growth pairs in Indiana for earthworms and understory plants in 2009 and 2010. The number of native plant species decreased as the densities of adult Lumbricus and Aporrectodea earthworms and the percent cover of multiflora rose (an invasive plant species) increased. We found little evidence that stand structure or distance from edge strongly affected earthworm distributions (with the possible exception of L. rubellus). It seems apparent from this study that nonnative earthworms and plants can establish in the interior of old-growth forest. Consequently, land managers should anticipate changes in nutrient availability, organic matter decomposition, and arbuscular mycorrhizal fungi populations that are associated with earthworms in hardwood forests irrespective of stand age. These changes, which constitute a substantial disturbance to North American hardwood forest ecosystems, seem likely to promote the further colonization of hardwood forests by nonnative plant species. It is unlikely that earthworm invasions can be prevented or reversed and in some areas, such as Indiana, the colonization of forests by introduced earthworms might be largely complete. This study highlights the importance of invasive plant management within the context of multiple plant and animal invaders.

Invasion of closed canopy forests by shade-tolerant alien plants has the potential to modify species composition, stand structure, ecosystem function, and long-term forest development patterns. Ligustrum sinense is a shade-tolerant alien shrub that has invaded bottomland forests throughout the southeastern United States. This species has received comparatively little attention in the literature despite its potential to drastically alter invaded sites. The overarching goal of our study was to document the relationships between Ligustrum sinense invasion and woody plant biodiversity and development patterns in an intact southeastern U.S. bottomland forest. The forest was dominated by Quercus nigra and Liquidambar styraciflua. Ligustrum sinense ranked fifth in basal area contribution, occurred in 97% of our plots, and represented 95% of all understory stems. Spearman's rho for dominance (based on basal area of stems > 5 cm diameter at breast height [dbh]) of L. sinense and woody plant species richness for each plot revealed a significant negative relationship (r_s  =  −0.69, P < 0.01). A similar relationship was revealed between L. sinense density and woody plant species diversity (r_s  =  −0.78, P < 0.01) and evenness (r_s  =  −0.82, P < 0.01). Spearman's rho for L. sinense density and native understory stem density (individuals ≥ 1 m height, < 5 cm dbh) also revealed a significant negative association (r_s  =  −0.48, P < 0.01). Under the current disturbance regime and without active management, we projected the forest would shift to support a stronger component of L. sinense and that structure would transition from tree to shrub dominance for sites within the forest.

Nomenclature: Chinese privet, Ligustrum sinense Lour; sweetgum, Liquidambar styraciflua L.; water oak, Quercus nigra L.

Management Implications: Invasion of Ligustrum sinense on bottomland sites may inhibit forest regeneration and shift structure of invaded stands from tree to shrub dominance. Scatterplots of L. sinense density and woody plant diversity measures revealed that 0.05-ha plots with greater than ca. 200 L. sinense stems (4,000 stems ha⁻¹) had relatively low evenness and Shannon diversity values. Although low biodiversity might not be the result of L. sinense invasion, if abiotic conditions of invaded sites are similar to nearby sites with higher biodiversity, then such severely invaded sites may be prioritized for L. sinense control. Restoration efforts might be best if focused on sites with mature L. sinense stems that have ascended to the uppermost forest stratum and lack the multi-stemmed growth form common for the species in smaller size classes. These areas may be those considered most impacted by L. sinense establishment and may be considered priority restoration areas by managers. Based on the potential density of L. sinense stems, even relatively small invaded forests might need to be compartmentalized by field crews.

We examined relationships between land disturbance and the extent and abundance of exotic buffelgrass (Pennisetum ciliare) at the interface of cultivated pastures and native desert lands in Sonora, Mexico. Plot and transect surveys of lands inside and outside pasture fences and general linear mixed models revealed complex relationships among buffelgrass, native vegetation, distance from pasture fences, and three categories of land disturbance (undisturbed, moderate, and severe). Results illustrate that buffelgrass invasion is extensive in lands surrounding pastures, and that buffelgrass abundance declines steeply with distance from pasture fences. The role of disturbance is weak but significant in its interaction with distance from the fence. Buffelgrass is more successful at colonizing severely disturbed lands than native vegetation, and its decline in abundance on severely disturbed lands is relatively more gradual than on other disturbance regimes, so landscapes where severely disturbed lands are interspersed with buffelgrass pastures could become centers of extensive buffelgrass invasion. In light of its potential to transform the Sonoran Desert, buffelgrass outside pastures warrants attention in a region-wide control scheme, as well as in future research, which ideally would involve remote sensing.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link.

Management Implications: Buffelgrass (Pennisetum ciliare) is widely understood to be a threat to the Sonoran Desert because of its ability to outcompete native vegetation and introduce a new wildfire regime. Conservationists and land managers tend to focus on buffelgrass as it impinges on protected and urbanized areas, neglecting unprotected rural lands such as ranches. In Sonora, Mexico, ranchers aggressively cultivate buffelgrass, and the resulting pastures serve as large seed sources. Furthermore, buffelgrass pastures in Sonora tend to be surrounded by mixed-use landscapes, with soils disturbed in different ways and to different degrees. This research demonstrates that buffelgrass extends far beyond pasture boundaries, and its invasion of the Sonoran landscape is associated with disturbed (particularly severely disturbed) lands. These findings suggest that an integrated region-wide buffelgrass control scheme must take seriously the existing widespread invasion from Sonoran pastures, as well as the great potential for further invasion facilitated by disturbance in Sonora's heterogeneous and dynamic landscapes. Land managers should not continue to neglect the important role of pastures and their interactions with their surrounding lands in promoting buffelgrass invasion in Sonora, Mexico.