Giant reed (Arundo donax) is an invasive weed that is native to the Old World. Tens of thousands of hectares of riparian habitat in the Rio Grande Basin (RGB) in Texas and Mexico have been heavily affected by invasions of Arundo. Additionally, many other watersheds across the southwestern United States have also been affected. Giant reed is being targeted for biological control because it displaces native vegetation and consumes water that could potentially be used for agricultural and municipal purposes, especially in areas with limited access to water. Finding the best-adapted insects for biological control involves locating the origin(s) of this plant. To narrow down the proximal source(s) of invasion of giant reed in the RGB, 10 microsatellite markers were developed. An analysis of 203 Old World and 159 North American plants, with an emphasis on the RGB, indicated a reduction in the allelic diversity in the introduced range compared with the Old World. Clonal assignment, neighbor joining, principal coordinates analyses, and STRUCTURE analyses were consistent and implied multiple introductions in North America, with one (likely clonal) lineage responsible for the invasion of the RGB, northern Mexico, and other parts of the southwestern United States. Although no identical matches with the RGB lineage were found in the Old World, several close matches were found on the Mediterranean coast of Spain.

Prioritizing management of invasive plants is important for large land management entities, such as federal and state public land stewards, because management resources are limited and multiple land uses and management objectives are differentially impacted. Management decisions also have important consequences for the likelihood of success and ultimate cost of control efforts. We applied multi-criteria decision analysis methods in a geographic information system using natural resource and land use data from Fort Bragg, North Carolina. Landscape-scale prioritization was based on a hierarchical model designed to increase invasive plant management efficiencies and reduce the risk of impacts to key installation management goals, such as training-land management and protected species conservation. We also applied spatial sensitivity analyses to evaluate the robustness of the prioritization to perturbations of the model weights, which were used to describe the relative importance of different elements of the hierarchical model. Based on stakeholders' need for confidence in making management investments, we incorporated the results of the sensitivity analysis into the decision-making process. We identified high-priority sites that were minimally affected by the weight perturbations as being suitable for up-front management and evaluated how adopting this strategy affected management area, locations, and costs. We found that incorporating the results of the sensitivity analysis led to a reduced management area, different target locations, and lower costs for an equal area managed. Finally, we confirmed the distinctiveness of the approach by comparing this same subset of prioritized sites with locations representing species-centric strategies for three invasive plants and their aggregate distribution. By supplying pragmatic information about the localized effects of weighting uncertainty, spatial sensitivity analyses enhanced the invasive plant management decision-making process and increased stakeholder confidence.

Medusahead is a close relative of bread wheat that is native to Eurasia but has become a noxious, invasive weed in North America. Intergeneric use of primers for bread wheat simple-sequence repeat (SSR) markers was tested in medusahead in order to expand the pool of available genetic resources for study of this plant. Forty-two primer pairs were screened in medusahead, of which 29 produced visible bands in agarose gels. Amplicons from eight of these markers were sequenced and analyzed for the presence of SSRs and single-nucleotide polymorphisms (SNPs) among medusahead individuals from six populations in the western Great Basin. Of the eight sequenced amplicons, two contained SSRs, both of which were polymorphic and shared by the original bread wheat marker. Six of the eight markers combined to detect 33 SNP loci. BLAST comparisons of the eight amplicons revealed variable numbers of matching sequences from wheat and other grass species ranging from 0 to > 200 matches. Using data from the polymorphic loci, population genetic analysis of the six invasive medusahead populations indicated that they arose from two separate introductions with two additional subclusters possible within the two principal clusters. Extrapolating from these results, it is reasonable to expect that between 170 and 830 of the approximately 1,200 publicly available bread wheat SSRs would produce useful marker loci in medusahead.

Dalmatian toadflax is listed as a noxious weed in most of the western United States, but control of this species has not been extensively studied in California. Studies in other states show effective control of Dalmatian toadflax with picloram, but this herbicide is not registered for use in California. In addition, reports vary as to the optimal timing for herbicide applications. In this study we evaluated several herbicides with combined foliar and soil-residual activity at two times of application: postsenescence (fall) and rosette (winter to early spring). We applied two series of treatments (2008 and 2009 to 2010) on adjacent sites in high desert scrub of southern California. In the year of treatment and the following year, we evaluated Dalmatian toadflax cover and presence/absence of associated dominant species (≥ 5% cover). Although time of application, treatment, and timing by treatment interaction all produced significant differences in Dalmatian toadflax cover in the 2008 trial, only the high rate of aminocyclopyrachlor (280 g ae ha−1) applied to dormant plants in fall consistently reduced cover through the second year. No treatments at the rosette stage consistently produced 2 yr of control. In 2009 to 2010, treatments were more effective, probably owing to higher precipitation in spring. In both dormant and rosette applications made in 2009 to 2010, aminocyclopyrachlor (140 and 280 g ae ha−1) and aminocyclopyrachlor + chlorsulfuron (140 g ae ha−1 + 53 g ai ha−1) gave second year control; chlorsulfuron at the dormant stage (105 and 158 g ai ha−1) and aminopyralid at the rosette stage (245 g ae ha−1) also gave 2 yr of control. The treatments had only minor effects on grass species. The response of broadleaf species varied among treatments, with aminocyclopyrachlor at the high rate increasing Eriogonum spp., but greatly reducing Asteraceae species. These results provide options for the management of Dalmatian toadflax in California and other western states.

Understanding seed characteristics and seedling establishment patterns is essential for the development of effective management strategies for invasive annual species. Dittrichia graveolens (stinkwort) has increased its range rapidly within California since 1995, yet its biology is not well understood, which has led to poorly timed management. In this study, seed viability, germination, longevity, and dormancy, as well as seedling emergence characteristics of D. graveolens were evaluated in field, greenhouse, and laboratory experiments in Davis, CA, over a 2-yr period (fall 2010 to summer 2012). In the laboratory, seed germination of D. graveolens occurred at a wide range of constant temperatures (12 to 34 C). Cumulative germination was comparable to total seed viability (80 to 95%) at optimal germination temperatures, indicating that primary (innate) dormancy is likely absent. The base temperature for germination was identified using a thermal time model: 6.5 C and 4 C for 2010 and 2011 seed populations, respectively. In the field, seedlings emerged from fall through spring following precipitation events. A very low percentage of seedlings (2.5%) emerged in the second year after planting. Equivalent seedling emergence was observed over a wide range of light conditions (100, 50, 27, and 9% of available sunlight) in a greenhouse experiment, indicating that seed germination is not limited by high or low light. Results from these seed experiments improve our understanding of the reproductive biology of this rapidly expanding exotic annual and provide valuable information for developing effective timing and longevity of management programs.

Effective control techniques for pale swallowwort (PSW), an invasive herbaceous vine of old fields and forest understories, are limited. We conducted a 3-yr cutting and herbicide study on an adjacent old-field and forest understory site near Ithaca, NY, for control of PSW. Plants in experimental plots were cut in early July and cut again or sprayed in late August for two seasons with the isopropylamine salt of glyphosate, or one of two rates (low or high) of either triclopyr triethylamine salt (i.e., SL, SH) or triclopyr butoxyethyl ester (EL, EH). The herbicide treatments were effective in reducing PSW cover, plant (stem) density, and aboveground biomass in the old-field site, but in several cases, only after 2 yr of cutting plus herbicide application. Only the cutting plus SH treatment did not reduce PSW cover relative to the unmanaged control in the forest understory and no treatment reduced biomass. In general, the cutting plus EH treatment was most effective in reducing PSW stem densities in the forest site. The most effective herbicide treatments differed between sites. Cutting plus EH reduced PSW cover by 84% and stem density (> 5 cm) by 86% in the old-field site. Cutting plus SH effectively decreased long and short (≤ 5 cm) stem densities by 86 and 96%, respectively. Cutting plants twice during each of two seasons increased PSW cover by 301% and density of stems > 5 cm by 73% at this site. In the forest site, cutting plus glyphosate, or cutting plus EH or cutting plus SL and EL resulted in the greatest reductions in PSW cover (80, 76, 66, and 56%, respectively). Cover in plots cut twice per year decreased by 19%. The EH or SL treatments decreased long-stem densities by 78 and 71%, respectively. The EH treatment decreased short-stem density by 37%. These findings suggest that integrated techniques may control PSW but that effective management strategies may be habitat constrained.

Soil engineering by downy brome may be a facet of its competitiveness. Using rhizotrons in the greenhouse, we compared the growth and plant–soil relationships of downy brome grown in two field soil types: soil invaded for 12 yr by downy brome and a similar soil not yet invaded. For each soil type, downy brome was grown for two growth cycles. At harvest, root mass and soils were sampled at depths of 10, 40, and 80 cm (4, 16, and 32 in); aboveground biomass was also sampled. After the first growth cycle, downy brome grown in invaded soil had 250% greater aboveground biomass and nearly double the root mass per soil volume at 10 cm relative to downy brome grown in noninvaded soil; root mass per volume was similar at depths of 40 and 80 cm. For the second growth cycle, aboveground biomass declined, but was twice greater for downy brome grown in invaded soil; however, root mass per volume was similar between soil types for each depth. Soil attributes that positively related to aboveground biomass included bicarbonate-extractable P, DTPA (diethylentriamene pentaacetate)-extractable Mn, and solution-phase (80-cm depth). We conclude that the data support our hypothesis that downy brome has engineered the soil to increase its growth potential, but proof will require a more robust experimental design. Plant competition is affected by myriad interactions; however, a plant that can increase the availability of soil nutrients for itself and its growth potential, relative to competing plants, would appear to be at an advantage. The mechanistic underpinnings involved are inconclusive, but may involve increased availability of soil N, P, and Mn.

Throughout the world, the invasion of nonnative plants is an increasing threat to native biodiversity and ecosystem sustainability. Invasion is especially prevalent in areas affected by land transformation and disturbance. Surface mines are a major land transformation, and thus may promote the establishment and persistence of invasive plant communities. Using the Shale Hills region of Alabama as a case study, we assessed the use of landscape characteristics in predicting the probability of occurrence of six invasive plant species: sericea lespedeza, Japanese honeysuckle, Chinese privet, autumn-olive, royal paulownia, and sawtooth oak. Models were generated for invasive species occurrence using logistic regression and maximum entropy methods. The predicted probabilities of species occurrence were applied to the mined landscape to assess the probable prevalence of each species across the landscape. Japanese honeysuckle had the highest probable prevalence on the landscape (48% of the area), with royal paulownia having the lowest (less than 1%). Overall, 67% of the landscape was predicted to have at least one invasive plant species, with 20% of the landscape predicted to have two or more species, and 3% of the landscape predicted to have three or more species. Japanese honeysuckle, sericea lespedeza, privet, and autumn-olive showed higher occurrence on the reclaimed sites than across the broader region. We found that geospatial modeling of these invasive plants at this scale offered potential for management, both for identifying habitat types at risk and areas that need management attention. However, the most immediate action for reducing the prevalence of invasive plants on reclaimed mines is to remove invasive plants from the reclamation planting list. Three (sericea lespedeza, autumn-olive, and sawtooth oak) out of the six most common invasive plants in this study were planted as part of reclamation activities.

English ivy (Hedera helix) is an evergreen, perennial vine that was introduced from Europe and Asia and is not endemic in much of the United States. English ivy can be invasive and difficult to control once established. Four similar, but not identical, experiments were conducted in sequence to evaluate selected, POST-applied herbicides for English ivy control. English ivy plants were propagated from cuttings and container-grown to obtain a large population of uniform plants. Aminopyralid and fluroxypyr applied at 1.34 and 0.71 kg ae ha−1, which is more twice the maximum registered rate for either herbicide, were ineffective. Glyphosate and 2,4-D amine were generally more effective, but neither herbicide provided a level of control that could be deemed consistently acceptable. Glyphosate applied at 8.51 kg ae ha−1 (the highest rate evaluated) provided 69, 98, and 89% control in the second, third, and fourth experiments as determined by foliage fresh-weight reduction relative to a nontreated control. Treatment with 2,4-D at 5.60 kg ae ha−1 (the highest rate evaluated) controlled English ivy 28, 98, and 89% in the second, third, and fourth experiments, respectively. Mixtures of 2,4-D and glyphosate were generally no more effective than were the components applied alone. Metsulfuron was the most effective herbicide. Metsulfuron applied at 0.168 kg ai ha−1 controlled English ivy ≥ 97% across the three experiments in which this treatment was included. This treatment also prevented regrowth.

Exotic plants have the ability to modify soil seed banks in habitats they invade, but little is known about the legacy of invasion on seed banks once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following its removal: a return of native plants, or a secondary invasion of other exotic plants. It is unknown, however, if this difference in plant communities following leafy spurge control is due to seed bank differences. To answer this question, we monitored seed banks and standing vegetation for 2 yr in mixed-grass prairies that were previously invaded by leafy spurge but controlled within 5 yr of our study. We found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community, and leafy spurge invasion history had a larger impact on cover and diversity of the vegetation than on the seed banks. Differences in plant communities following leafy spurge control do not appear to be related to the seed banks, and soil conditions may be more important in determining trajectories of these postinvasion communities.

We assessed pre- and posteradication nitrogen and phosphorus dynamics in longleaf pine sandhill stands severely affected by cogongrass. Across a 7-yr posteradication (glyphosate + imazapyr) “recovery chronosequence,” which included untreated cogongrass, uninvaded reference, and treated plots, we analyzed soils for total N, potentially available P (Mehlich-1 [M1]), pH, and organic matter content. We also used resin bags to assess fluxes of plant available N and P in the soil solution. Additionally, we used litterbags to monitor the decomposition and nutrient mineralization patterns of dead rhizome and foliage tissue. Our results indicate similar total N and M1-P contents in both cogongrass-invaded and uninvaded reference plots, with levels of M1-P being lower than in cogongrass plots for 5 yr after eradication. Soil organic matter did not differ between treatments. Resin bag analyses suggest that cogongrass invasion did not affect soil nitrate availability, although a pulse of NO2 + NO3 occurred in the first 3 yr after eradication. No such trends were observed for ammonium. Resin-adsorbed PO4 was lowest 3 yr after eradication, and pH was highest 5 yr after eradication. Our litterbag study showed that approximately 55% of foliar biomass and 23% of rhizome tissue biomass remained 18 mo after herbicide treatment. Substantial N immobilization was observed in rhizomes for the first 12 mo, with slow mineralization occurring thereafter. Rapid P mineralization occurred, with 15.4 and 20.5% of initial P remaining after 18 mo in rhizomes and foliage, respectively. Overall, our findings indicate that cogongrass invasion has little to no effect on soil nutrient cycling processes, although some significant—but ephemeral—alterations develop after eradication.

To investigate the impacts of long-term targeted invasive plant stewardship projects on students' subsequent stewardship attitudes, an experiment using pre and post-tests to understand program effects and using post-test only comparisons to understand school effects was conducted. The resulting scores from two science classes that participated in year-long invasive plant and restoration activities were compared with those from three comparable classes at a linked school that did not participate in any of these activities. Students in the experimental classes showed overall significantly higher scores compared with the control classes. These attitude scores were then divided into two indexes: sense of personal effectiveness and attitudes of caring for particular places. Students in the experimental group showed increases in both, as compared with the controls. Parent and student focus groups were conducted at the end of the academic year. The resulting comments provide evidence for actual behavior change outside of the school environment. Analysis showed that any student, especially those in the control classes in the traditional middle school, indicating they had prior exposure to nature stewardship projects showed significantly higher scores than students who did not. The results underscore the value of having students involved in real-world stewardship projects, especially those of a long-term nature.

Desert grasslands of the southwestern United States have experienced an increase in the abundance and distribution of woody plant species over the past century. Shrub encroachment has caused a substantial loss of grasslands in the northern Chihuahuan Desert. The Chihuahuan Desert has also been invaded by Lehmann lovegrass, a fire-adapted species from southern Africa. In 1999, the U.S. Department of Agriculture–Agricultural Research Service burned a remnant desert grassland to determine the effects of prescribed fire on shrub–perennial grass dynamics. The grassland also contained the nonnative perennial grass Lehmann lovegrass. I am reporting on a study that was initiated to determine whether prescribed burning would alter the vegetative community within and proximal to a Lehmann lovegrass–dominated patch. Cover of Lehmann lovegrass showed no significant response to the burn treatment. Of the dominant native species, only black grama and broom snakeweed had a significant year by treatment interaction. No species or growth form had a significant vegetation type by year by treatment interaction. After 6 yr, differences between burned and unburned transects were not significant for any species or growth form.