Root architecture of prairie grasslands, which depends on plant phenology and edaphic conditions, strongly influences susceptibility to invasion by nonindigenous plant species. Field studies were conducted to compare in situ root growth patterns of warm-season (WS) and cool-season (CS) perennial grasses and musk thistle during a 2-yr period that included a drought in the second year. In 2 yr, CS grasses had the highest amount of roots (1,296 m roots m⁻² [395 ft roots ft⁻²]) across shallow (0 to 28 cm [0 to 11 in.]), medium (28 to 56 cm), and deep (56 to 98 cm) depths with 65% occurring in the shallow depths. However, roots of WS grasses were always greater at deeper depths compared to roots of CS grasses. The amount of new roots in CS grasses was statistically different in 2011 (F_2,43  =  33.3, P < 0.0001) at all depths for vegetative (April to May), inflorescence (June), and dormant (July to November) stages. In 2012, the amount of new roots in CS and WS grasses was statistically different (F_2,60  =  81.7, P < 0.0001 and F_2,37  =  8.0, P  =  0.0013), respectively, for vegetative (April to May), inflorescence (May to June), and dormant (June to November) stages. For both years, the amount of new roots in the CS grasses showed an interaction between the three growth stages and three soil depths (F_2,62  =  33.3, P < 0.0001 [2011]; F_4,60  =  18.6, P < 0.0001 [2012]). From germination to senescence, the total amount of musk thistle roots was 298 m roots m⁻², which was less than the CS (1,296 m roots m⁻²) and WS (655 m roots m⁻²) grasses. The largest proportion of new musk thistle roots (61%) (F_2,42  =  40.4, P < 0.0001) occurred during the bolting stage (April to June) of the second year. These results show the difference in root distribution of two grass types and the niches that are created underground by extraneous conditions (e.g., drought) in WS grass stands that may contribute to the establishment of musk thistle, an invasive plant species in many North American regions.

Nomenclature: Musk thistle, Carduus nutans L. CRUNU.

Management Implications: In established or newly restored grasslands, niches can occur that allow for the invasion of exotic plant species. This study examined root distribution patterns of cool-season and warm-season perennial grass species and musk thistle. Grown individually, cool-season perennial grasses had a greater number of active roots in the upper soil profile (0 to 28 cm), whereas warm-season perennial grasses had more roots that were active deeper (56 to 98 cm) in the soil. Musk thistle roots were found to dominate the upper soil profile (0 to 28 cm). Even though the two grasses and musk thistle were grown separately, predictions can be made relating to the potential for which grass type will be more susceptible to the invader. The lack of uniform root distribution in the upper soil profile by warm-season perennial grasses could contribute to the establishment of musk thistle. Further, under alternating years of normal and below-normal annual precipitation, musk thistle seedlings could germinate and grow as small rosettes in poorly managed grasslands during the first year (wet) and then continue rosette development, bolting, and flowering in the second year (drought) as roots are extended more fully throughout the soil profile. Therefore, land managers that have problems with musk thistle or an invasive plant species with similar life history (e.g., Scotch thistle, bull thistle) should consider (1) using a mix of perennial grass types and (2) not stressing grassland plants by overgrazing, especially during extreme drought conditions.

Cogongrass, an invasive grass native to Asia, has infested thousands of hectares in the southeastern United States. Although numerous studies have examined cogongrass control, no published studies, to our knowledge, have tested strategies for cogongrass eradication. Cogongrass has a persistent, thick rhizome mat but an ephemeral seedbank; therefore, successful eradication methods must largely focus on the rhizomes. A field study to evaluate specific herbicide treatments and application timings for cogongrass patch eradication was conducted at two locations in southwestern Alabama. Herbicide treatments included glyphosate at 4.48 kg ai ha⁻¹, imazapyr at 0.84 kg ai ha⁻¹, and a tank mix of glyphosate and imazapyr at the same rates. Treatments were applied in May, August, or October for 3 consecutive yr, and the May glyphosate treatment included a second annual application each October. Cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content were sampled during the course of the study. Cogongrass response to treatments varied by location but by 36 mo after initial treatment (MAIT), complete elimination of cogongrass shoot and rhizome biomass and 100% visual control was achieved in several herbicide treatment–timing combinations at both locations. These included glyphosate plus imazapyr at any application timing, imazapyr in August or October, and glyphosate applied in May and October each year. TNC levels of surviving healthy rhizomes were not affected by herbicide treatments, but a seasonal pattern was observed. The maximum live-rhizome depth was not influenced by any treatment, indicating that herbicides were not preferentially leaving deeper, surviving rhizomes. These results demonstrate, for the first time, that the entire rhizome layer of cogongrass can be eliminated within 3 yr with multiple treatment options and that cogongrass patch eradication is possible for many land managers.

Nomenclature: Glyphosate, glyphosate plus imazapyr, imazapyr, cogongrass, Imperata cylindrica (L.) Beauv. IMPCY.

Management Implications: Cogongrass is one of the most difficult weeds to manage because of its aggressive growth and persistent rhizomes, which often survive initial herbicide treatments. Historically, research efforts have been focused on cogongrass control, but no published studies have tested strategies for eradication. The present study is the first documented research to demonstrate complete elimination of cogongrass in 18 to 36 mo using repeated, annual herbicide applications. Treatments included glyphosate, imazapyr, and a tank-mix of both applied in the spring, summer, or fall for 3 consecutive yr. Verification of eradication was based on a highly rigid criterion involving measurements of cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content over 3 yr. Cogongrass response to treatments varied by location. By 36 mo after initial treatment, the glyphosate plus imazapyr treatment applied at any timing, the imazapyr treatment applied in August or October, and the glyphosate treatment applied in May and October each year resulted in complete elimination of cogongrass shoot and rhizome biomass. The maximum live-rhizome depth (16 cm ± 2 SE) was not influenced by any treatment. During the 3-yr period, herbicides did not affect TNC levels of surviving rhizomes, indicating that repeated treatments directly killed rhizomes, rather than slowly exhausting energy reserves. We are not suggesting that cogongrass can be eradicated from the southeastern United States; however, with repeated glyphosate or imazapyr herbicide treatments, land managers do have a feasible means of eradicating cogongrass patches.

Because of disturbance and exotic plant invasions, ecological restoration is necessary for maintaining functional big sagebrush ecosystems in western North America. Downy brome control is often necessary in restoring this ecosystem type; however, many brome control measures hinder ecological restoration by limiting the types of plants which can be established. Microtopography manipulation may aid weed control by entrapping undesirable seeds. We undertook a field experiment at four sites in the Piceance Basin of western Colorado, USA to test the effects of microtopography (rough with brush mulch or flat with straw mulch), seed mix (high-forb or balanced), and herbicide (140 g ai ha⁻¹ imazapic ammonium salt or none) on downy brome control and perennial plant establishment following disturbance. Three years post-treatment, downy brome had become established at two of the four sites, one each with high (GVM) and low (MTN) downy brome seed rain. At GVM, the rough/brush treatment augmented the effectiveness of imazapic, reducing downy brome biomass six-fold. At MTN, the rough/brush surface reduced downy brome biomass 10-fold in the absence of imazapic. Across all four sites, forb and shrub biomass were higher with the high-forb mix, and there was no effect of seed mix on downy brome or annual forb biomass. Restoring a full complement of plant functional groups in big sagebrush ecosystems may be aided by increasing forbs in seed mixes, and manipulating soil microtopography.

Nomenclature: imazapic ammonium salt, big sagebrush, Artemisia tridentata Nutt. ARTR2, downy brome, Bromus tectorum L. BROTE.

Management Implications: Big sagebrush ecosystems in western North America are threatened by many factors, including downy brome invasion, conifer encroachment, and disturbance. Restoring downy brome-invaded ecosystems is difficult because many effective downy brome control measures, such as seeding competitive grasses or applying herbicides, impair the growth of desirable forbs and shrubs. Previous work has shown that downy brome seeds disperse more readily when the soil surface is flat or when vegetation is removed, such as following a fire or after the creation of an oil and gas well pad. In this study, we examined whether creating obstructions to seed dispersal could improve restoration. We tested three factors: (1) a rough soil surface, comprised of pothole-sized holes and mounds with brush mulch vs. a flat soil surface with straw mulch, (2) a high-forb seed mix, containing nearly 75% forbs by seed number, vs. a mix containing roughly equal numbers of forb, grass, and shrub seeds, and (3) imazapic herbicide at 140 g ai ha⁻¹ vs. no herbicide. Downy brome established at two of the four sites, and at both of these, the rough surface helped to control downy brome. The rough surface combined with imazapic was most effective at a site that had some downy brome prior to disturbance, while the rough surface alone was effective at another site which was not invaded prior to disturbance. It is possible that the rough surface makes downy brome less competitive because the seeds get trapped in the holes, which have higher soil moisture, as downy brome is typically less competitive in wetter environments. The high-forb seed mix resulted in higher forb and shrub establishment, and lower grass establishment, than the balanced mix. Even so, grass cover was still higher than forb cover at most sites, and was higher than in the undisturbed communities. There was no difference in downy brome or weedy annual forbs due to seed mix, and the high forb cover produced by the high-forb mix is beneficial for sage-grouse habitat restoration. Seeding mostly forbs and shrubs at a high rate, 1600 seeds m⁻², should be considered in areas where erosion is not a concern. The imazapic treatment did control downy brome, but it also had a negative

Studies were conducted to document that European starlings consume Russian olive fruits and determine subsequent effects on seed germination. In the first study, avian feeding patterns at Russian olive trees were monitored over a 1-yr period using motion activated digital photography. Starlings fed on Russian olive fruits with highest activity occurring in November and December. In a second study, 20 captive European starlings were fed Russian olive fruits and seed germination rates were determined for three categories: consumed by starlings, hulled fruits (pericarp removed), and whole fruits. Starlings readily consumed Russian olive fruits and most seeds were regurgitated 30 min after consumption. Germination rates of ingested/regurgitated seeds (57%) and pericarp-removed seeds (40%) were greater than whole fruits (0%). Viability tests confirmed that 85% of starling ingested seeds remained viable after consumption. Our data suggest that Russian olive dispersal may be dependent upon animals for effective spread.

Nomenclature: Russian olive, Elaeagnus angustifolia L., European starlings, Sturnus vulgaris.

Management Implications: Our research clearly demonstrates that European starlings will consume Russian olive fruits. Most consumed seeds would be regurgitated and left on the soil surface in a more germinable state than whole fruits. This strongly suggests that Russian olive is dependent upon animals to disperse seeds and cause spread of this invasive species. Russian olive fruits are palatable to European starlings and many other bird and several mammal species that contribute to its effective spread. The change in germinability in fruits consumed by European starlings provides impetus for managing Russian olive particularly if passage through other animals' GI tracts has a similar effect. This interaction between two invasive species likely will change our collective impressions of their management importance.

Nonindigenous plant species (NIS) can affect individuals, communities, and ecosystems through numerous direct and indirect mechanisms. To synthesize the current understanding of how NIS cause impacts, we reviewed experimental research from the past decade. We found alteration of the microenvironment, such as incident light and air and soil temperature, was much more often a mechanism underlying NIS impacts than competition for soil water and nutrients. NIS litter frequently caused the alteration of microenvironments, and litter effects were often of greater consequence than the effects of live NIS plants. Results supported altered soil microbial communities and mycorrhizal associations as mechanisms underlying NIS impacts on native plant growth, community structure, and nutrient cycling. Impacts often could not be attributed to a single mechanism, highlighting the need for multi-factor studies that identify and distinguish between multiple, concurrently operating mechanisms. Overall, our synthesis indicates that effective management will require attention to legacy effects of NIS, that removing live NIS may not ameliorate impacts, and that removal of dead NIS biomass may be necessary for native species' survival. Furthermore, rehabilitating soil microbial and mycorrhizal communities may be crucial for successful post-NIS management revegetation.

Management Implications: The primary objective of most nonindigenous plant species (NIS) management is to reduce or eradicate live NIS plants using herbicides and manual removal. While this often is a sensible approach, it does not always achieve the desired outcome of reestablishing native plant cover. Through a review of experimental NIS impact studies, we found that consideration of the mechanisms, or ways, by which NIS cause impacts, may improve general approaches to NIS management. It is often assumed that the primary way NIS impact native plants is by robbing them of necessary resources, such as water and nutrients. However, the experimental research we reviewed shows that this often is not the underlying cause and that NIS impacts are more often traced to alterations of microenvironments, belowground communities, and plant-pollinator interactions. Additionally, many NIS impacts are attributable to NIS litter rather than live plants. Reducing NIS impacts and reestablishing native plant cover may be more successful if some resources typically spent on direct NIS treatment (i.e. spraying, pulling) are diverted to removal of NIS litter and applying mycorrhizal and microbial inoculations to improve or rebuild belowground communities. These communities are thought to be an important component of revegetation success. Another alternative management approach based on impact mechanisms is NIS flower removal, particularly when whole plant removal or chemical treatment is not feasible. Removing NIS flowers prevents native plant-pollinator interactions from being altered, increasing the chances of successful native plant reproduction. NIS flower removal has the additional benefit of eliminating NIS seed production, thereby lowering or stabilizing population growth rate. Our synthesis shows that fine-tuning management to address the mechanisms underlying NIS impacts will likely improve NIS control and increase the success of native revegetation.

Following large-scale herbicide spraying and burning on Assateague Island, a barrier bar island located in Maryland and Virginia, the invasive common reed (Phragmites australis) was largely reduced from vast monocultures to less dense patches interspersed within maritime shrublands. To improve the control of these remnant/reemerging infestations and limit further nontarget damage, we tested three new treatments: mechanical cutting followed by dripping imazapyr onto stems, cutting followed 2 wk later by the foliar spraying of regrowth, and simple cutting with and without the removal of Phragmites litter. All herbicide treatments and cutting paired with litter removal significantly reduced Phragmites coverage (P ≤ 0.01) when compared with untreated controls. Native plant coverage was significantly greater after the cut-stem treatment than after traditional foliar spraying (P ≤ 0.01) because of the former's reduced herbicide use and more direct contact limited to Phragmites stems; native coverage was also greater after litter removal than when litter remained (P ≤ 0.001). Cutting followed by stem applications of herbicide is an effective means of treating scattered common reed stands in sensitive habitats, and litter removal after cutting can provide native vegetation with an advantage at recolonization.

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

Management Implications: Common reed (Phragmites) infestations that are interspersed throughout a shrubland of native vegetation pose a unique set of challenges. The most widespread methods for treating Phragmites involve the aerial and ground spraying of herbicide, mechanical clearing, and prescribed fire, all of which are impractical and extremely destructive to nontarget vegetation in this environment. Cutting Phragmites with a brush cutter, hand clippers, or both tools, and dripping imazapyr directly onto 5 to 25% of cut stems greatly limits the damage to nontarget vegetation relative to foliar spraying of herbicide and is equally effective at reducing Phragmites cover. Cutting followed by foliar spraying of Phragmites regrowth is as effective as treating 50% of cut stems with herbicide both in reducing Phragmites cover and limiting nontarget species damage. When accompanied by litter removal, cutting can significantly reduce Phragmites cover and greatly improve native plant regeneration in areas where herbicide cannot be applied, such as near open water or within sensitive areas containing rare or federally listed plant species. Cutting followed by stem-spraying generally requires less herbicide relative to the other methods tested, even in spite of this treatment's higher requisite herbicide concentration. The two alternative methods of applying herbicide tested herein require the same or slightly more person-hours to implement (relative to foliar-spraying of established stands), but they have an enhanced efficacy and utilize less herbicide.

We investigated the potential for an invasive sea lavender, Limonium ramosissimum subsp. provinciale (Algerian sea lavender; LIRA) to spread in San Francisco Estuary (SFE) tidal marshes by testing how two determinants of tidal marsh plant distribution, salinity and inundation, affect LIRA dispersal, germination, growth, and reproduction. Simulating dispersal in 0, 15, and 30 parts per thousand (ppt) salinity water, we found seeds remained afloat similarly regardless of salinity, and seed viability after floatation was high (88%); however, seeds in 0 ppt aquaria germinated after just 4 d, suggesting shorter dispersal distances in fresh than in brackish or saline water. Next, we compared LIRA and native halophyte seed germination in 0, 15, 30, and 45 ppt water. Percentage of germination was similar between species after 3 wk, but LIRA germinated faster in fresh water than all native species (90% vs. 5% germination after 4 d), suggesting a possible establishment advantage for LIRA at low salinities. Finally, we grew LIRA under crossed salinity and inundation levels in a tidal simulator for a growing season. LIRA growth and seed production increased when either salinity or inundation was reduced. We conclude that spread could be greatest among salt marshes due to high potential for seed dispersal in saline water, yet spread within marshes may be greatest in relatively lower salinity conditions where growth and reproduction are maximized.

Nomenclature: Algerian sea lavender, Limonium ramosissimum (Poir.) Maire subsp. provinciale (Pignatti) Pignatti.

Management Implications: Information regarding the potential for newly introduced nonnative species to invade wildland ecosystems is needed for resource managers to prioritize responses to multiple simultaneous plant invasions. Management decisions, such as which species or populations to prioritize for eradication or seed suppression, are aided by research that addresses how variation in environmental conditions affects a species' spread. This is true in tidal marshes of the San Francisco Estuary (SFE) where several invasive plants have been identified as priorities for management action because of their rapid spread and impacts, and where new nonnative species continue to establish, many with unknown potential for widespread invasion. This research provides timely information regarding how the spread of an invasive plant recently found in the SFE, Algerian sea lavender, is affected by two key environmental factors that vary within and among tidal salt marshes: salinity and inundation. Investigating the effects of these variables on key life history stages of Algerian sea lavender (dispersal, germination, growth and reproduction) permitted characterization of conditions where Algerian sea lavender propagule pressure will be greatest, and may serve as a model for predicting spread of other nonnative plants across a complex environmental gradient.

To investigate the relative importance of long-distance dispersal vs. diffusion in the invasion of a nonnative plant, we used age structure to infer the contribution to recruitment of external propagule rain vs. within-population reproduction. We quantified the age structure of 14 populations of Amur honeysuckle in a landscape where it recently invaded, in Darke County, OH. We sampled the largest honeysuckle individuals in each population (woodlots), and aged these by counting annual rings in stem cross sections. Individuals in the oldest four 1-yr age classes are assumed to be from external recruitment, given the minimum age at which shrubs reproduce. We used these recruitment rates to model external recruitment over the next 5 yr and used observed age structures to estimate total recruitment. We used the difference between total and external recruitment to infer the rate of internal recruitment. Our findings indicate that recruitment from within the population is of about the same magnitude as immigration in the fifth to seventh year after population establishment, but by years 8 to 9 internal recruitment dominates. At the landscape scale, the temporal-spatial pattern of population establishment supports a stratified dispersal model, with the earliest populations establishing in widely spaced woodlots, about 4 km from existing populations, and these serving as “nascent foci” for diffusion to nearby woodlots. Understanding the relative importance of long-distance dispersal vs. diffusion will inform management, e.g., whether it is more effective to scout for isolated shrubs or remove reproducing shrubs at the edge of invaded areas.

Nomenclature: Amur honeysuckle, Lonicera maackii (Rupr.) Herder.

Management Implications: The relative importance of diffusion (expanding front) vs. long-distance dispersal can inform management of invasive species. If diffusion dominates, it will be most efficient to monitor for, and eradicate, new patches on the edges of existing patches. If long-distance dispersal dominates, one should scout for, and eradicate, initial colonists in previously uncolonized patches (Moody and Mack 1988). Furthermore, removing reproductive individuals at the edge of the current range would slow the spread of diffusing populations, but have little effect if long-distance dispersal dominates.

We assessed the relative importance of diffusion vs. long-distance dispersal in the invasion of Amur honeysuckle [Lonicera maackii (Rupr.) Herder] in forested patches in an agricultural landscape in southwest Ohio. We examined the age structures of woodlot populations, used these to estimate the importance of immigration vs. within-population recruitment, and examined the temporal-spatial pattern of population initiation.

Our findings indicate that long-distance dispersal dominates early in the invasion, and new populations grow slowly, until the original colonists begin reproducing. Thus, efforts to slow the spread of L. maackii should involve scouting for colonists in woodlots up to 4–5 km from existing populations. Fortunately, this is feasible, as even small honeysuckle shrubs are easily spotted during early spring and late fall, when native deciduous woody plants are not in leaf. These searches could be as infrequent as every 3 yr, given the lack of reproduction in the youngest age classes.

The purpose of this study was to determine the effect of whole-plant composting on the viability of seeds and other propagules of the invasive plant species waterhyacinth, waterlettuce, hydrilla, and giant reed while producing a valuable compost product. Invasive species were subjected to preliminary germination and growth tests and oven mortality tests to evaluate whether species distribution was via seeds, vegetative propagules, or both, as well as whether the composting process had the potential, through the high temperatures obtained, to kill seeds and other propagules. Germination and growth tests determined the means by which invasive species spread. Oven tests determined the temperatures at which unscarified and scarified seeds and propagules were rendered inviable. Achieving temperatures of at least 57.2 C was necessary within constructed compost piles to effectively kill the plants without the danger of redistribution. In the field, the study successfully developed a large-scale composting operation using invasive plant species as the primary feedstock. Analysis of field-scale composting showed final materials were within satisfactory to ideal levels for samples analyzed by the U.S. Compost Council's Seal of Testing Assurance Program and were, therefore, a valuable compost product.

Nomenclature: Giant reed, Arundo donax L., hydrilla, Hydrilla verticillata (L. f.) Royle, waterhyacinth, Eichhornia crassipes (Mart.) Solms, waterlettuce, Pistia stratiotes L.

Management Implications: The ecological impacts of invasive species are primarily due to their rapid growth, clogging waterways as well as outcompeting or completely displacing native species, which can result in the reduction of native population densities, species diversity, and richness (Chilton and Durocher 2009). Many exotic aquatic plants were introduced into the United State through the aquarium trade and through initial uses for erosion control (Chilton and Durocher 2009). However, most invasive aquatic plants are noxious weeds in aquatic environments nationwide (United States Congress 2006). In the past, biological control agents, chemical herbicides, and mechanical removal and harvesting were implemented to manage species in their various environments (Chilton and Durocher 2009). As a waste management system within agriculture, the composting process has been shown to kill plant pathogens and weed seeds if temperatures obtained are high enough and last long enough (Dougherty 1999; Wiese et al. 1998). Compost has also been used by the horticulture industry to decrease plant diseases, to increase plants' nutrient access, and as an effective weed-control agent (Faucette 2003). Some exotic plants have been successfully composted in the past, but the composting of invasive species has not been fully investigated to determine whether all plant seeds and propagules are inactivated during the composting process (Rogers 1983). This study investigated, and results demonstrated, the effectiveness of a large-scale composting operation in successfully rendering invasive plant seeds and propagules of waterhyacinth [Eichhornia crassipes (Mart.) Solms], waterlettuce (Pistia stratiotes L.), hydrilla [Hydrilla verticillata (L. f.) Royle], and giant reed (Arundo donax L.) inviable while producing a valuable compost product for the agricul

There is a limited understanding about the ecological mechanisms that enable certain plant species to become successful invaders of natural areas. This study was conducted to determine the soil and landscape characteristics that correlate with invasion of Chinese privet (CHP), and to develop a model to predict the probability of CHP invasion in Piedmont forests. A landscape ecosystem classification (LEC) system—based on the percentage of clay in the B horizon, depth to maximum clay (cm), exposure, terrain shape, and aspect (degrees)—was used to determine the soil moisture characteristics of invaded and uninvaded plots. Additional measurements included the cover classes of CHP and other species, litter depth (cm), slope (degrees), overstory basal area (m² ha⁻¹), and soil chemical properties. CHP invasion was negatively correlated with overstory basal area and slope and positively with litter depth and pH. A stepwise logistic regression model containing these four variables was highly sensitive, with an overall accuracy of 78%. Given the accuracy of this model, we propose that it can be used to calculate the probability of invasion in a given area, provided that some basic, readily obtainable site characteristics are known.

Nomenclature: Chinese privet, Ligustrum sinense Lour.

Management Implications: Chinese privet (CHP) (Ligustrum sinense Lour) is one of the most common woody invasive alien plant species in the Appalachian Piedmont. An improved understanding of the factors that correlate with CHP invasion will benefit land managers in the region, as this species can reduce native diversity, alter forest structure, and be costly to control. We found CHP invasion to be negatively correlated with overstory basal area and slope and positively correlated with litter depth and pH. A model containing these four variables was highly sensitive, being able to predict CHP invasion 78% of the time. By identifying the areas that are most likely to be invaded, this model could facilitate early detection and control of CHP, thereby slowing its spread and helping to conserve native flora and fauna.

We assessed the ability of climatic, environmental, and anthropogenic variables to predict areas of high-risk for plant invasion and consider the relative importance and contribution of these predictor variables by considering two spatial scales in a region of rapidly changing climate. We created predictive distribution models, using Maxent, for three highly invasive plant species (Canada thistle, white sweetclover, and reed canarygrass) in Alaska at both a regional scale and a local scale. Regional scale models encompassed southern coastal Alaska and were developed from topographic and climatic data at a 2 km (1.2 mi) spatial resolution. Models were applied to future climate (2030). Local scale models were spatially nested within the regional area; these models incorporated physiographic and anthropogenic variables at a 30 m (98.4 ft) resolution. Regional and local models performed well (AUC values > 0.7), with the exception of one species at each spatial scale. Regional models predict an increase in area of suitable habitat for all species by 2030 with a general shift to higher elevation areas; however, the distribution of each species was driven by different climate and topographical variables. In contrast local models indicate that distance to right-of-ways and elevation are associated with habitat suitability for all three species at this spatial level. Combining results from regional models, capturing long-term distribution, and local models, capturing near-term establishment and distribution, offers a new and effective tool for highlighting at-risk areas and provides insight on how variables acting at different scales contribute to suitability predictions. The combinations also provides easy comparison, highlighting agreement between the two scales, where long-term distribution factors predict suitability while near-term do not and vice versa.

Nomenclature: Canada thistle, Cirsium arvense (L.) Scop., reed canarygrass, Phalaris arundinacea L, white sweetclover, Melilotus albus Medik.

Management Implications: Effective and proactive management of invasive species requires information on both current and potential future distributions. Alaska, similar to other high latitude areas, is relatively invasion free (Lassuy and Lewis, 2013). The rapidly changing climate in this region, however, is expected to increase the area suitable for establishment for a larger number of invasive species. Here, we present results for habitat suitability models of highly invasive plants in the southern coastal region of Alaska, creating climate driven models at a regional scale and physiographic and anthropogenic models for two local regions. Using these types of models for targeted sampling of invasive plants detected more locations with less effort than nontargeted sampling (Crall et al., 2013). Our local scale models can be thought of as predicting near term establishment and distribution (potential early detection locations for management), while longer term trends in distribution may be driven by climate, especially related to the future climate scenarios at the coastal scale (potential distributions). Locations where models at both scales indicate high habitat suitability values are more appropriate targets for current control and monitoring efforts than locations identified by a model that considers factors operating at a single scale. Additionally, evaluating the areas of future suitable habitat among early invaders can help prioritize which species should be targeted for control first. If two species have similar initial distributions and similar ecological impacts, management efforts should be directed to the species with the largest possible future distribution. These models, when incorporated into an iter

Meadow knapweed is a fertile European hybrid between black and brown knapweed that has expanded its North American distribution to 27 of the United States and four provinces in Canada. Two experiments were conducted on meadow knapweed in northwestern Washington to determine (1) whether meadow knapweed is similarly sensitive to several herbicides commonly used to control related knapweeds, (2) if herbicide application timing plays a role in control of meadow knapweed, and (3) whether mowing before, after, or instead of herbicide treatment can aid in meadow knapweed control. In the first experiment, herbicides were applied to meadow knapweed at rosette or bolting stages of growth, and again with the same herbicides in the autumn. In the summer following treatment, clopyralid alone or with 2,4-D, dicamba 2,4-D, and triclopyr ester 2,4-D ester provided 81 to 100% meadow knapweed control; the only other treatment providing similar control was glyphosate ammonium sulfate applied at bolting and in autumn in the 2004 to 2005 trial. In the second experiment, combinations of mowing and dicamba 2,4-D were applied at rosette or early flowering stages of growth. In the 2002 to 2003 trial, control when dicamba 2,4-D was used exceeded 90%, except when meadow knapweed was mowed at rosette and sprayed at early flowering (78% control). Mowing twice the previous year had only a slight effect on meadow knapweed (10% control). Grass biomass exceeded meadow knapweed biomass in all herbicide-treated plots. In the 2004 to 2005 trial, meadow knapweed control and grass biomass was maximized when plots were mowed at rosette and treated with dicamba 2,4-D at early flowering or when treated twice with these herbicides; these were the only treatments where grass biomass exceeded meadow knapweed biomass.

Nomenclature: Clopyralid, dicamba, glyphosate, imazapic, MCPP, triclopyr, 2,4-D, meadow knapweed, Centaurea debeauxii Gren. & Godr. CEDE5.

Management Implications: Meadow knapweed is a nonrhizomatous perennial hybrid of black and brown knapweed in the plant family Asteraceae that has been introduced from Europe into many of the United States and Canadian provinces. It is not as widespread in North America as certain other Centaurea species, so herbicides have not been widely tested for efficacy on this hybrid. Therefore, two experiments were conducted to determine (1) whether meadow knapweed is similarly sensitive to several herbicides commonly used to control related knapweeds, (2) if herbicide application timing plays a role in control of meadow knapweed, and (3) whether mowing before, after, or instead of herbicide treatment can aid in meadow knapweed control. Herbicides were applied either in spring autumn or in summer autumn in the first experiment; in the second experiment, dicamba 2,4-D was applied either before or after mowing and compared to one or two herbicide applications or two mowings. In the first experiment, clopyralid alone or in combination with other herbicides provided up to 100% control of meadow knapweed in the year following treatments. Triclopyr, dicamba, and glyphosate also resulted in control. These herbicides are often used at similar rates and timings to achieve control of other Centaurea species, which indicates that meadow knapweed is as susceptible to these products as other knapweeds. In the second experiment, combinations of mowing and herbicide applications at rosette or early flowering stages of growth generally reduced meadow knapweed biomass and increased grass biomass, although herbicide treatment alone achieved the same result. Mowing twice was an ineffective control strategy for this knapweed hybrid. Therefore, mowing is not recommended to augment control of meadow knapweed when using herbicides.

Japanese hedgeparsley is a biennial plant that invades roadsides, rights-of way, and forested areas in the midwestern United States. Interest in managing populations by mechanical or hand-clipping techniques exists, but no information is available on the appropriate timing to maximize mortality and prevent the production of viable seed. To assess that, we applied clipping treatments at five periods throughout the summer to three Japanese hedgeparsley populations in southern Wisconsin and measured the number and viability of seeds produced by each plant during the year of treatment and the survival of plants clipped. Japanese hedgeparsley plants began producing seed by mid-July, but production was not maximized until early August. Viable seeds were not produced until early or mid-August, coinciding with the presence of ripened brown fruit. Clipping at any timing resulted in > 95% mortality by the fall of the treatment year. All plants that resprouted were in the vegetative stage when clipped, and no plants survived the following year. Results indicate that clipping Japanese hedgeparsley plants when they are in a reproductive phase before fruit turns brown is an effective management strategy for this invasive plant.

Nomenclature: Japanese hedgeparsley, Torilis japonica (Houtt.) DC. TOIJA.

Management Implications: Japanese hedgeparsley is actively invading full sun and forested habitats in the midwestern United States. Little is known about how to manage populations, but mechanical or hand removal is of interest because populations are appearing along areas easily accessed by people or equipment. We compared the effectiveness of clipping populations at five timings in southern Wisconsin to determine when viable seed is produced and whether plants resprout after clipping requiring further management to prevent seed production. We found that Japanese hedgeparsley was capable of producing more than 6,000 seeds plant⁻¹, but viable seed were not present until the fruits turned brown in color. In Wisconsin, that occurred in early to mid-August, depending on the location. Clipping populations before that time not only prevented the production of viable seed, but < 5% of clipped plants resprouted. The few plants that did resprout were in the vegetative stage when clipped, but none produced viable seed. Results indicate that clipping is an effective control strategy for this invasive plant, and management should be conducted when plants are in the reproductive stage, but before fruit turn brown to avoid dispersal of viable seed. Although resprouting after clipping was minimal in Wisconsin, populations should be monitored carefully as the consistency of this response in other regions is unknown.

Miscanthus × giganteus, a widely planted biofeedstock, is generally regarded as a relatively low invasion concern. As a seed-infertile species, it lacks a consistent mechanism of long-distance dispersal, a key contributor to invasion rate, and constitutes a low risk for cultivation escape. However, agricultural production shelters plants from stochasticity and increases propagule pressure, enhancing the potential for low-risk species to take advantage of rare dispersal opportunities. Weed risk assessments of M. × giganteus assume the rarity of events such as scouring and flooding that would facilitate secondary dispersal of vegetative rhizome fragments and the long-term sexual inviability of escapes. Combining data from small-scale rhizome fragmentation and movement experiments, and estimates from the literature, we parameterized an individual-based model to examine M. × giganteus spread given three dispersal scenarios. We further evaluated our estimates in response to different field edge buffer widths and monitoring intensities, two key strategies advised for containing biofuel crops. We found that clonal expansion from the field edge alone was sufficient to allow the crop to outgrow buffers of 3 m or less within 11 to 15 yr with low monitoring intensities. Further, models that included the possibility of rhizome dispersal from fields and scouring at field edges demonstrate the potential for long-distance dispersal and establishment with inadequate management. Our study highlights the importance of considering minimum enforced management guidelines for growers to maintain the ecological integrity of the agricultural landscape.

Nomenclature: Giant Miscanthus, Miscanthus × giganteus J. M. Greef and Deuter ex Hodk. and Renvoize.

Management Implications: Previous assessments of low invasion risk for sterile Miscanthus × giganteus are contingent on the rarity of events that would disperse plant rhizomes from the field edge. Our results demonstrate the importance of implementing monitoring strategies, augmented by field edge buffers that increase detection likelihood, to contain the invasion risk from large-scale cultivation of M. × giganteus. Early detection is key to increasing the success and decreasing the cost of invasive species control. Although opportunities for rhizomes to disperse should be rare, the accumulation of infrequent escapes from large-scale cultivation should be a matter of concern. The combination of field edge buffers and consistent monitoring should form a feasible strategy for containing cultivated plant escapes.

Lepidium latifolium (perennial pepperweed) is a weedy alien crucifer that has invaded wetlands throughout the western United States. We monitored L. latifolium invasion of an Elytrigia elongata (tall wheatgrass) community at the Honey Lake Wildlife Refuge in northeastern California. In 1993, a 40-m² plot was delineated, at which time only two single plants of L. latifolium were present. Beginning in 1994, L. latifolium stem density was measured yearly until 2011. From 1994 through 2000, the density of L. latifolium increased to greater than 120 stems m⁻². At its height of stem density and stature between 1998 and 2000, it appeared that E. elongata had been extirpated. From 2001 through 2006, stem density and plant stature of L. latifolium declined, but there were still areas of the plot where stem density exceeded 60 stems m⁻². From 2007 through 2009, stem density decreased considerably and averaged less than 30 stems m⁻² and a healthy recovery of E. elongata occurred. In the years 2010 and especially 2011, stem density increased, but individual plants were small in stature. Soil bicarbonate-extractable phosphorus data suggest that phosphorus availability may be crucial to the invasiveness of L. latifolium. Long-term biogeochemical cycling by L. latifolium may reduce soil phosphorus availability in deeper soil horizons and enrich availability in the soil surface, which alters the competitive relationship between L. latifolium and E. elongata.

Nomenclature: Perennial pepperweed. Lepidium latifolium L., tall wheatgrass, Elytrigia elongata Host (Nevski).

Management Implications: Over an 18-yr period, we monitored stem density of the exotic invasive crucifer Lepidium latifolium in an area at the Honey Lake Wildlife Refuge in northeastern California. Following a near record flood event in January 1997, in some areas density and stature of L. latifolium dramatically increased to form a near monoculture and appeared to have extirpated the perennial grass Elytrigia elongata planted in 1987 as nesting habitat. From its peak in 1998 to 2000, stem density and stature of L. latifolium has declined considerably and allowed E. elongata to once again assume dominance in many areas. The decline in stem density is not due to herbicide use or any management decisions. Instead, our evidence suggests that lowered precipitation and declining availability of soil phosphorous has tipped the competitive balance between L. latifolium and E. elongata. More research is needed to determine the range of soil phosphorus availability over soil depths that might constrain the invasiveness of L. latifolium. Our data, however, suggest that expensive control strategies for L. latifolium can be targeted to soils with high native levels of phosphorus availability; invasibility in areas with low phosphorus availability may naturally decline over time as phosphorus is bio-cycled by the plant.

Himalaya blackberry is a nonnative shrub that has invaded sites throughout the Pacific Northwest. Its persistent canopy and large underground crowns create a competitive environment that prevents desirable species from germinating, establishing, or both. Cutleaf blackberry grows in association with Himalaya blackberry, and control efforts frequently target these two species. Control of Himalaya blackberry is complicated by vigorous vegetative regrowth after mechanical control, including mowing, and variable response to chemical methods. Recent interest in the use of goat browsing for invasive plant control has led land managers to use a variety of browsing regimes to control unwanted species through disturbance by herbivory. This study examined changes in functional group percent cover in a perennial grass pasture invaded by Himalaya blackberry and cutleaf blackberry in the southern Willamette Valley of Oregon. The appearance of species and their functional group membership after three treatment protocols are evaluated. Changes in the percentage of cover by Himalaya and cutleaf blackberries, annual grasses, perennial grasses, annual forbs, and perennial forbs were examined after two annual treatments with (1) high-intensity–short-duration goat browsing, (2) mowing, and (3) high-intensity–short-duration goat browsing followed by mowing. These data were then compiled by functional group to assess trends in the plants' revegetating the pasture after treatment. All treatments caused a significant decline in the percent cover of the invasive blackberries (P < 0.0001), but differences among treatments were not significant. The increase in the percent cover of perennial forbs for plots treated with goat browsing followed by mowing was significantly greater (P  =  0.008) than it was in plots browsed only and those mowed only. Changes in percent cover of other functional groups were not significantly different with browsing or mowing treatments. Individual species within the perennial grass and perennial forb groups are discussed.

Nomenclature: Cutleaf blackberry (Rubus laciniatus Willd.), Himalaya blackberry (Rubus armeniacus Focke).