Fire is often used in northern grasslands to control invasive grass species but has unknown effects on Tamarix spp., more recent invaders. Temperature (using an oven as a fire surrogate) and duration combinations that would be most lethal to Tamarix seeds and seedlings were determined. Tamarix seeds were sown in soil-lined dishes, water added to saturation, and seedlings grown for 1 to 5 d. Seeds were also placed in water-saturated or dry soil just before temperature exposure (79 to 204 C [175 to 400 F]) by duration (1 to 5 min) treatments. After treatment, soil water loss was measured by weight difference, and surviving seedlings were counted for 6 d. Tamarix seedling establishment and survival decreased with increasing temperature and duration. The 5-d-old seedlings were the most affected. No 5-d-old seedlings survived 1- and 2-min exposures to 204 C, whereas 1-d-old seedlings had greater than 25% survival. If soils were saturated, two to four times more seedlings established following seed exposure to 177 and 204 C. Longer durations at lower temperatures were required to reduce Tamarix survival. Increasing duration from 2 to 5 min at 121 C decreased 5-d-old seedling survival from more than 80% to less than 10% and eliminated those seedlings at 149 C. Five minutes at 149 C decreased dry-soil seed viability to about 15%, whereas germination on saturated soils remained high (∼75%). No seeds survived the exposure to 177 and 204 C. Soil moisture loss values associated with 90% mortality of 5- and 1-d-old seedlings were 1.7 and 2.2%, respectively. On saturated soils, 90% of seeds died with 2.5% water loss. Under suitable conditions, fire can decrease Tamarix seedling survival. Fire may be useful for controlling Tamarix seedlings in northern grasslands and should be considered for management of new invasions.

Temperate and boreal forests in Canada and the northeastern United States have been invaded by several exotic species, including European earthworms (family Lumbricidae) and garlic mustard. Earthworms and garlic mustard co-occur and are both known to adversely impact some native plant species. However, relatively little is known about potential interactions between these two invaders. In a series of growth chamber experiments, we determined the palatability of garlic mustard and six native herbaceous forest species (shooting star, columbine, wild geranium, sweet cicely, butterfly milkweed, and yellow jewelweed) to the common nightcrawler. We also assessed the ability of the common nightcrawler to bury and digest garlic mustard and wild geranium. When offered seeds from garlic mustard and a native plant species, the earthworms ingested more garlic mustard seeds than seeds from four of the six native species. In a mesocosm experiment, the common nightcrawlers apparently digested 72 and 27% of garlic mustard and wild geranium seeds, respectively, that were placed on the soil surface. No seeds were observed on the soil surface at the end of the experiment but the majority of recovered seeds for both species were found within the top 10 cm (3.94 in). More seeds were recovered in 0- to 10-cm and 31- to 40-cm sections for wild geranium than for garlic mustard. No difference in seed recovery was detected at the other depths. Garlic mustard seed is readily consumed by common nightcrawlers and appears to be preferred over some native plant species suggesting that common nightcrawlers may reduce the size of the garlic mustard seed bank.

Cutleaf teasel is an invasive, biennial plant that poses a significant threat to native species along roadsides in Missouri. Flowering plants, together with understory rosettes, often grow in dense patches. Detection of cutleaf teasel patches and accurate assessment of the infested area can enable targeted management along highways. Few studies have been conducted to identify specific species among a complex of vegetation composition along roadsides. In this study, hyperspectral images (63 bands in visible to near-infrared spectral region) with high spatial resolution (1 m) were analyzed to detect cutleaf teasel in two areas along a 6.44-km (4-mi) section of Interstate I-70 in mid Missouri. The identified classes included cutleaf teasel, bare soil, tree/shrub, grass/other broadleaf plants, and water. Classification of cutleaf teasel reached a user's accuracy of 82 to 84% and a producer's accuracy of 89% in the two sites. The conditional κ value was around 0.9 in both sites. The image-classified cutleaf teasel map provides a practical mechanism for identifying locations and extents of cutleaf teasel infestation so that specific cutleaf teasel management techniques can be implemented.

Cutleaf teasel is an exotic weed that infests roadside environments in Missouri. As a growing biennial, the plant develops as a rosette during the first year and bolts during the second. Dense patches contain flowering plants with understory rosettes. The objective of this work was to develop approaches for detecting cutleaf teasel patches with accurate assessment in a complex of species along a roadside. Thus, management of cutleaf teasel could be located at specific sites. Two hyperspectral images (63 bands with 1-m spatial resolution) were analyzed to detect cutleaf teasel along the Interstate Highway I-70 in mid Missouri. Classification of cutleaf teasel reached a user's accuracy of 82 to 84% and a producer's accuracy of 89% at the two sites. The image-classified teasel map provides a practical mechanism for identifying the locations and extents of cutleaf teasel infestation so that specific management techniques can be implemented.

Invasive weed control within cleared, forested sites in the inland Northwest is complicated by the susceptibility of ponderosa pine to synthetic auxin herbicide injury, used to control broadleaf weeds. Herbicide injury may lead to decreased canopy volume and variable growth patterns of ponderosa pine, which is a commercially important tree species. Herbicide injury to ponderosa pine can be decreased with dormant-season applications, a timing suited to control many weeds that may occur within ponderosa pine sites. However, spring-timed herbicide applications are needed to control other weeds, such as meadow hawkweed, and that application timing coincides with active ponderosa pine growth. In this study, we determined the level of injury to ponderosa pine resulting from spring-timed aminopyralid, clopyralid, and picloram applications beneath ponderosa pine canopies. Herbicide injury to leader and lateral candles and needle elongation was evaluated 1 and 12 mo after treatment (MAT). Low rates of aminopyralid alone (0.05 kg ae ha−1 [3 fl oz ac−1]) and aminopyralid + clopyralid (0.05 + 0.10 kg ae ha−1) resulted in herbicide injury ratings that did not differ from untreated trees. The high rate of aminopyralid (0.12 kg ae ha−1) resulted in leader candle injury on 75% of treated trees, 5% of which were necrotic at 12 MAT. Herbicide injury was observed on 30% of lateral candles. In comparison, picloram (0.28 kg ae ha−1) treatments resulted in necrosis or mortality of leader and lateral candles on 65% and 40% of trees, respectively, at 12 MAT. Results suggest that use of low rates of aminopyralid alone or in combination with low rates of clopyralid minimizes the risk of nontarget injury to ponderosa pine (> 5 yr old) while controlling hawkweed with a spring application.

The use of benthic barriers alone or in combination with other control methods could initiate the eradication of pioneer populations of Eurasian watermilfoil and facilitate maintenance of acceptable population levels in water bodies where the weed is widely established. We evaluated the effects of duration of geotextile fabric panel placement on small Eurasian watermilfoil population control and nontarget plant abundance. In 2006, benthic barriers were placed over Eurasian watermilfoil infestations and removed at intervals of 4, 8, 10, and 12 wk. The 4-wk duration reduced Eurasian watermilfoil biomass 75%, and all other duration treatments reduced Eurasian watermilfoil biomass 100%. The 4-wk treatment had no effect on native plant biomass, whereas other treatments reduced native plant biomass by 79 to 93%. At the conclusion of the 12-wk study, Eurasian watermilfoil biomass had increased in the 4-wk treatment but did not reestablish within treatment plots of longer duration. Native plant biomass had increased to 21% of the untreated control in the 8-wk barrier treatment. Results suggest the 8-wk duration is sufficient for removal of Eurasian watermilfoil while allowing regrowth of native aquatic plants. A walk-in growth chamber experiment was established to evaluate the effect of sediment accumulation on the benthic barrier. Eurasian watermilfoil fragments grown on sediment depths of 0 to 3 cm (0 to 1.2 in) did not differ for shoot or root biomass. At sediment depths of 4 and 5 cm, Eurasian watermilfoil root and shoot biomass increased when compared with the control, suggesting benthic barrier maintenance should include sediment removal when sediment reaches a depth of 4 cm.

Early detection of an invading nonindigenous plant species (NIS) may be critical for efficient and effective management. Adaptive survey sampling methods may provide unbiased sampling for best estimates of distribution of rare and spatially clustered populations of plants in the early stages of invasion. However, there are few examples of these methods being used for nonnative plant surveys in which travelling distances away from an initial or source patch, or away from a road or trail, can be time consuming due to the topography and vegetation. Nor is there guidance as to which of the many adaptive methods would be most appropriate as a basis for invasive plant mapping and subsequent management. Here we used an empirical complete census of four invader species in early to middle stages of invasion in a management area to assess the effectiveness and efficiency of three nonadaptive methods, four adaptive cluster methods, and four adaptive web sampling methods that all originated from transects. The adaptive methods generally sampled more NIS-occupied cells and patches than standard transect approaches. Sampling along roads only was time-efficient and effective, but only for species with restricted distribution along the roads. When populations were more patchy and dispersed over the landscape the adaptive cluster starting at the road generally proved to be the most time-efficient and effective NIS detection method.

Conservation and land management decisions often are based primarily on natural science, but could be more successful if human influences were effectively integrated into decision making. This is especially true for efforts to manage invasive plants, whose arrival is usually the product of deliberate human introduction. Risk-assessment models that predict the probability that a nonnative plant will naturalize or invade are useful tools for managing invasive plants. However, decisions based on such models could affect stakeholders differently. Careful assessment of risk-analysis methodologies should consider the importance of stakeholder participation. We surveyed the perceptions of four stakeholder groups (conservation professionals, master gardeners, professional horticulturists, and woodland landowners) in Iowa about invasive plants, general management approaches, and risk-assessment models. We also examined whether or not a stakeholder's nature relatedness plays a role in shaping his or her responses. Stakeholder perceptions varied less than expected across all four groups. Eighty-seven percent of respondents agreed invasive plants are a problem, and 88.4% agreed that we have a responsibility to manage them to protect natural areas. Support for the use of risk-assessment models also was high, with 78.7% of respondents agreeing that their use has potential to prevent plant invasions. Nature relatedness scores for all groups were correlated with respondent perspectives on invasive plants. Respondents believed biologically significant error rates (errors that might introduce a new invasive plant) should not exceed 5 to 10%. Respondents were more tolerant of horticulturally limiting errors (errors that restrict sale/use of a plant that would not have become invasive), reporting rates of 10 to 20% as acceptable. Researchers developing risk-assessment models might wish to aim for error rates within these bounds. General agreement among these stakeholder groups suggests potential support for future risk-management efforts related to invasive plants.

Japanese stiltgrass is one of the most aggressive, rapidly spreading invasive plants in the eastern United States. Management guidelines state that mowing can help manage Japanese stiltgrass but that mowing is most effective when done late in the season after the plants begin to flower and before they set seed. In this study, I tested the effectiveness of mowing at three different times between mid-June and early September in 2009 and 2010, as well as mowing twice in 1 yr and for two consecutive years. The effectiveness of mowing Japanese stiltgrass was determined by measuring percentage of cover, biomass, seed production, and the number of stems in the summer following mowing. All mowing treatments significantly reduced percentage of cover, biomass, seed production, and the number of Japanese stiltgrass stems the following year. In 2009, all of the mowing treatments significantly reduced biomass, percentage of cover, and seed production. The latest mow, at the end of August, resulted in a slightly greater reduction of cleistogamous seeds. In 2010, the earliest mowing treatment, in mid-June, did not reduce cover and biomass as much as the other mowing treatments. Overall, these results suggest that mowing can be an effective control method for Japanese stiltgrass and that mowing any time after June should be effectively equivalent, although later mowing may provide some marginal advantage.

Invasive species researchers often ask: Why do some species invade certain habitats while others do not? Ecological theories predict that taxonomically related species may invade similar habitats, but some related species exhibit contrasting invasion patterns. Brassica nigra, Brassica tournefortii, and Hirschfeldia incana are dominant, closely related nonnative species that have overlapping, but dissimilar, distributions. Brassica tournefortii is rapidly spreading in warm deserts of the southwestern United States, whereas B. nigra and H. incana are primarily limited to semiarid and mesic regions. We compared traits of B. tournefortii that might confer invasiveness in deserts with those of related species that have not invaded desert ecosystems. Brassica tournefortii, B. nigra and H. incana were compared in controlled experiments conducted outdoors in a mesic site (Riverside, CA) and a desert site (Blue Diamond, NV), and in greenhouses, over 3 yr. Desert and mesic B. tournefortii populations were also compared to determine whether locally adapted ecotypes contribute to desert invasion. Experimental variables included common garden sites and soil water availability. Response variables included emergence, growth, phenology, and reproduction. There was no evidence for B. tournefortii ecotypes, but B. tournefortii had a more rapid phenology than B. nigra or H. incana. Brassica tournefortii was less affected by site and water availability than B. nigra and H. incana, but was smaller and less fecund regardless of experimental conditions. Rapid phenology allows B. tournefortii to reproduce consistently under variable, stressful conditions such as those found in Southwestern deserts. Although more successful in milder, mesic ecosystems, B. nigra and H. incana may be limited by their ability to reproduce under desert conditions. Rapid phenology and drought response partition invasion patterns of nonnative mustards along a gradient of aridity in the southwestern United States, and may serve as a predictive trait for other potential invaders of arid and highly variable ecosystems.

Invasive saltcedar species have replaced native riparian trees on numerous river systems throughout the western United States, raising concerns about how this habitat conversion may affect wildlife. For periods ranging from 2 to 11 yr, I used live-trapping to monitor small mammal populations in paired saltcedar and native riparian woodlands at four sites in western Nevada and eastern California. Heteromyid rodents, such as Merriam's and Ord's kangaroo rats, were more likely to occur in saltcedar habitats, but other rodent species, particularly the montane vole and western harvest mouse, occurred more often in native habitats, and this balanced species richness in habitat comparisons. The most common species at all sites, the deer mouse, did not show any consistent differences in abundance or in mean body mass between the two habitat types. However, the ratio of captured male to female deer mice was higher in saltcedar than native habitats at two sites. Deer mice as well as Ord's kangaroo rats also had higher rates of being recaptured following initial capture in native habitats, which may have been due to fewer transient individuals occurring in these habitats. By contrast, Merriam's kangaroo rats may have been more transient in native habitats because they were more likely to be recaptured in saltcedar. Individuals of two species, pinyon mouse and white-tailed antelope ground squirrel, had greater mean body mass in native habitats than they did in saltcedar, implying that they may have maintained superior condition in native habitats.

Some plants being considered as bioenergy crops share traits with invasive species and have histories of spreading outside of their native ranges, highlighting the importance of evaluating the invasive potential before the establishment of large-scale plantings. The Asian grass Miscanthus × giganteus is currently being planted as a bioenergy crop in the north central region of the United States. Our goal was to understand the demographic rates and vegetative spread of this species in unmanaged arable lands in Illinois to compare with those of large-statured invasive grasses (LSIGs). We collected data from 13 M. × giganteus plantings in Illinois, ranging in age from 1 to 7 yr, recording tiller number, plant spatial extent, spikelet production, and plant survival over 4 yr. Additionally, to understand recruitment potential, we conducted a greenhouse germination experiment, and, to estimate establishment from rhizome fragments, field trials were performed. Miscanthus × giganteus demographic rates were age dependent. Spikelet production was high, with 1- and 4-yr plants producing an annual average of more than 10,000 and 180,000 spikelets plant−1, respectively; however, data from our germination trial suggested that none of these spikelets had the potential to yield seedlings. On average, plants expanded vegetatively 0.15 m yr−1. Tiller density within the center of a clone decreased with age, possibly leading to a “dead center” found among some LSIGs. Rhizome establishment increased with weight, ranging from 0 to 42%. Survival was low, 24%, for first-year plants but quickly climbed to an asymptote of 98% survival for 4-yr-old plants. Our results suggest that efforts should be made to eradicate plants that escape biomass production fields within a year of establishment, before the onset of high survival. Future work is needed to determine what types of natural and anthropogenic disturbances can fragment rhizomes, leading to regeneration.

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

Downy brome (Bromus tectorum L.)—dominated communities can remain as stable states for long periods, even with frequent disturbance by grazing and fire. The objective of this study was to determine the effectiveness of using targeted cattle grazing and late-season prescribed burning, alone and in combination, to reduce B. tectorum seed bank input and seed bank density and thus alter aboveground community dynamics (species composition) on a B. tectorum–dominated landscape in northern Nevada. Cattle removed 80 to 90% of standing biomass in grazed plots in May of 2005 and 2006 when B. tectorum was in the boot (phenological) stage. Grazed and ungrazed plots were burned in October 2005 and 2006. The combined grazing–burning treatment was more effective than either treatment alone in reducing B. tectorum seed input and seed bank density, and in shifting species composition from a community dominated by B. tectorum to one composed of a suite of species, with B. tectorum as a component rather than a dominant. This study provides a meso-scale precursor for landscape-scale adaptive management using grazing and burning methodologies.

Invasive plants disperse to new areas via numerous pathways. Study of these pathways helps to focus limited budgets toward prevention and early detection. This study examined potentially invasive seed contaminants in imported crops and grass seed as pathways for plant dispersal to Alaska. Crop and grass seed were purchased from 13 Alaska retail outlets representing 14 seed suppliers. Seed bags were sampled using federally mandated protocols and were analyzed for crop seeds that were not supposed to be included and for weed contaminants. Ninety-five weed and 36 contaminant crop taxa were found. Crop seed contained 43 weed taxa and 15 other crop species contaminants, a mean of 6.4 taxa and 3,844 contaminant seed kg−1. Grass seed samples contained 73 weed taxa and 21 crop contaminants, a mean of 3.5 contaminant species and 1,250 seeds kg−1. Two species prohibited by the Alaska seed law were found: Canada thistle was found in a single crop sample, and quackgrass was found in two grass samples. There were no significant relationships between either seed type or supplier and either the number of contaminant species or number of seeds. Labels of 33% of crop samples and 8% of grass samples claimed 0.00% weed seeds, but low (0.007% by weight, 2 species) to high (1.18% by weight, 13 species) amounts of weed contaminants were found. Importation of crop seed is a large pathway for seed movement, causing significant propagule pressure and an increased likelihood of establishment by new invasive plant populations. Prevention of spread via this pathway would be enhanced by changes to seed laws, by greater regulatory enforcement, and by including on the label, the names of all weed and contaminant crop species found in the law-required samples. Consumers could then make decisions on whether to purchase seed based on the potentially invasive species that would be planted with the desired seed.

To better understand the response of Ipomoea cairica (Cairo morningglory) to herbivory, the compensatory growth and photosynthetic characteristics of plants were measured after simulated herbivory by leaf trimming at four intensities: 25, 50, 75, and 100% removal, starting from the apex. Defoliation at 25% had no significant influence on plant biomass, but the total biomass (−19 to −66%) and root biomass (−31 to −75%) of the plants decreased significantly when defoliation intensity was ≥ 50% (P < 0.05). Photosynthetic rates (Pn) increased with defoliation intensity (P < 0.01), and Pn values in the defoliated plants were 10 to 72% greater than those in the control plants, a relationship that could be attributed to a decrease in stomatal limitation (−11 to −34%) and the increase in rubisco content (9 to 18%) as well as higher photosynthetic efficiency and less light energy dissipated as heat. At defoliation intensities up to 50%, plants needed more energy to compensate photosynthetically, which could influence the plant photosynthetic characteristics as well as the allocation of assimilates, resulting in less root development. Since the spread of I. cairica depends primarily on clonal growth, smaller roots could limit uptake of nutrients from the soil. These direct and indirect effects indicate that leaf-feeding herbivores may have potential for biological control of I. cairica but to have any effect the herbivores would need to consume ≥ 50% of the leaf biomass.

The aim of this study was to evaluate the effect of the macrophyte waterhyacinth on the water quality of a reservoir in Colombia. Postinvasion water quality assessments were performed during three different hydrological periods and compared with preinvasion data. The results show that water quality has improved, especially in terms of transparency, showing an increase in Secchi disk values from 0.3 to 2 m (1 to 6.6 ft). The analysis strongly suggests that the improvement in water quality is due to the filtering and precipitation effects provided by waterhyacinth. This case highlights the dilemma of managing an invasive species that provides a beneficial ecological service while posing a high ecological risk.

Invasive weed management in wildland areas is often challenging due to the need to protect and preserve the integrity of natural ecosystems. Russian knapweed is an aggressive, deep-rooted, creeping perennial forb that was first identified as a problematic species in Dinosaur National Monument in 1977. From 2002 to 2005, extensive nonnative plant inventories were conducted in portions of the monument. Results were used to develop and implement an aggressive weed management program beginning in 2005. Emphasis was placed on reducing Russian knapweed infestations around Josie's Ranch in the Cub Creek Watershed. Several other species were targeted as well. In 2010, a reinventory was conducted in selected areas to evaluate how implemented management strategies affected the overall distribution and abundance of targeted species on the landscape. Comparisons between inventories indicate that management strategies were successful in reducing the total infested area of Russian knapweed by 79%. Treatments used for other targeted species also appear to have been effective in reducing their overall distribution and abundance on the landscape. In addition, the reinventory identified several new species with the potential to become problematic in the area. Although this case study documents the substantial progress that has been made at Dinosaur National Monument toward obtaining specific weed management objectives, it more importantly illustrates the process and benefits of an adaptive approach in sustaining long-term invasive plant species management efforts.