Ventenata [Ventenata dubia (Leers) Coss.], an invasive winter annual grass, significantly reduces forage production in grassland systems and displaces species within both perennial- and annual-dominated grasslands within the Inland Northwest. The range of V. dubia is expanding into sagebrush steppe communities, an expansive habitat critical for forage production, wildlife, and recreation. Currently, there is limited knowledge of V. dubia’s distribution and abundance within sagebrush steppe communities. We performed field surveys at 15 locations in sagebrush steppe rangelands in southern Idaho and eastern Oregon to assess where V. dubia occurs, with the aim of providing insight about its niche in this new habitat. Specifically, we evaluated biotic and abiotic factors of the plant community as indicators of V. dubia presence. We also correlated species diversity measures with no, low (<12.5%), and high (>12.5%) V. dubia cover. Though widely distributed throughout the study region, V. dubia only appeared in 45% of the 225 plots, and foliar cover was typically less than 50%. It was primarily found in ephemerally wet microhabitats. Species richness and the Shannon diversity index were lowest in plots with high V. dubia cover. Nonmetric multidimensional scaling analysis revealed that V. dubia and medusahead [Taeniatherum caput-medusae (L.) Nevski] were closely associated. Furthermore, chi-square indicator analysis showed that T. caput-medusae was more prevalent, while mountain big sagebrush [Artemisia tridentata Nutt. spp. vaseyana (Rydb.) Beetle] was less prevalent, in plots containing V. dubia. Abiotic factors that explained variation in V. dubia abundance included rock cover, soil depth, and a north/south aspect. Higher V. dubia cover also correlated with higher clay content and lower phosphorus and potassium concentrations in the soil. We suggest that at this point, detection survey efforts to locate incipient infestations of V. dubia in sagebrush steppe communities should focus on moist areas and sites susceptible to invasion by T. caput-medusae.

Black swallowwort [Vincetoxicum nigrum (L.) Moench] and pale swallowwort [Vincetoxicum rossicum (Kleopow) Barb.] are perennial vines of European origin that invade natural areas and perennial cropping systems in the northeastern United States and southeastern Canada. Both species reproduce via wind-dispersed seeds in the form of achenes with comas, but little is known about the extent of dispersal of these seeds. We studied the relationship of seed release height (0.75 m, 2 m), wind speed at the time of release, seed mass, and settling rate on distance traveled. Vincetoxicum nigrum and V. rossicum seeds traveled up to 72.1 and 79.6 m, respectively. Seeds of both species released from 2 m traveled greater distances than seeds released from 0.75 m, which fell within 20 m of the release point. Release height was the most important factor influencing long-distance dispersal events. Wind speed also strongly interacted with release height for long-distance dispersal of V. nigrum. Vincetoxicum nigrum seed mass was greater and settling rates faster than for V. rossicum. Increasing seed mass generally increased settling rate, which in turn decreased distance traveled, except in V. rossicum, for which longer distance–dispersing seeds had a faster settling rate. Our findings suggest that management efforts focus on reducing the presence of these two vines, especially if there is potential for them to climb up taller vegetation such as trees. Seeds released from these greater heights are more likely to travel far from source populations and initiate new populations. Preventing seed production in small, nonclimbing patches will also help suppress the expansion of these two vines, as seeds can still disperse up to 20 m away from parent plants.

Invasive plants may dramatically impact forest ecosystems by establishing dense populations and suppressing the recruitment of native tree species. One invasive shrub currently spreading throughout eastern deciduous forests of North America, Japanese barberry (Berberis thunbergii DC), may be limiting tree recruitment in stands where it invades. Once established, B. thunbergii becomes densely populated within forest understories and suppresses native plants by competing for limited resources, altering soil conditions, and changing the understory microclimate. To quantify native seedling inhibition caused by B. thunbergii invasion, we conducted an observational study on seedling abundance within forest plots that were either invaded or not invaded by B. thunbergii and used survey data to generate Bayesian models of native seedling densities along gradients of increasing B. thunbergii stem counts and aboveground plant dry mass. Model outputs predicted that B. thunbergii–invaded plots had 82% lower seedling densities compared with uninvaded plots. Native tree seedling densities were very low even in areas with moderate B. thunbergii density, suggesting that reduced tree seedling densities are observed even at low densities of invasion. Our findings indicate that forests invaded with B. thunbergii harbor substantially lower densities of native tree seedlings, with potentially significant long-term consequences for forest ecological integrity, biodiversity, and ecosystem services.

Callery pear (Pyrus calleryana Decne.) was introduced to North America as an ornamental tree in the early 1900s. Due to widespread planting, P. calleryana has become common throughout the eastern United States and has invaded natural areas, especially disturbed areas. Prescribed fire is a common management technique in prairie ecosystems to mimic natural disturbances. We tested the effectiveness of prescribed fire as a control technique for P. calleryana in a managed prairie system. Fire top-killed all established P. calleryana individuals. However, these individuals responded to fire with 3 to 4 epicormic sprouts each. Similar sprouting behavior occurred in 2-yr-old seedlings. Exposed seeds, fruits, and 1-yr-old seedlings were killed by fire. Established P. calleryana were single-stemmed individuals before exposure to fire. After the prescribed fire, they all were multistemmed, which increased the potential flower-bearing stems within the prairie. We conclude that fire alone is not a suitable technique for managing P. calleryana invasion. Cut and herbicide application methods are labor-intensive. However, combining cut and spray methods with prescribed fire may be effective. Fire removes standing grass and forb biomass, leaving exposed P. calleryana stems, which would make locating individuals and directly applying herbicides easier.

Alien invasive species have strategies that can maintain fitness in a variety of environments. This flexibility is associated with environmental tolerance in several traits, such as allocation of resources to shoots versus roots, clonal versus sexual reproduction, and survival of seedlings. These traits were explored in the chandelier plant (Kalanchoe delagoensis Eckl. & Zeyh.), which has invasive populations in several countries. Light and water tolerance and herbicide treatments were tested on plantlet survival. Plantlet survival in the most extreme cases (full sunlight and no watering) was close to 30%, whereas in less severe conditions (water and shaded), it was close to 100%. Stress conditions triggered the onset of plantlet production from the margin of leaves, which increased clonality. Biomass was allocated primarily to aboveground structures. Although all herbicides resulted in high plantlet mortality (>85%), only 2,4-D and glyphosate+2,4-D amine achieved the maximum recorded mortality a few days after the chemical application. The high tolerance of K. delagoensis plantlets to varying conditions shows that under stress, plantlet production is enhanced as survival of established individuals decreases. Biomass is primarily aboveground, which can potentially alter nitrogen and carbon in poor arid environments, and the proportion of the biomass assigned to belowground roots increased with an increase in sunlight received. Even though the chemical treatments 2,4-D and glyphosate+2,4-D amine have been shown to be the only effective treatments, the 2,4-D treatment may be the most viable (cost+quantity) to reduce the propagation of K. delagoensis. Plantlets have become the main reason for population persistence, partially due to the plant’s environmental tolerance and ability to reproduce asexually in short time periods. Susceptibility of plantlets to the two herbicides presents a means to adequately manage invasions of K. delagoensis in Mexico.

Erect veldtgrass (Ehrharta erecta Lam.) is an invasive grass actively spreading in California that is capable of invading multiple habitats. Our objective is to contribute to a better understanding of the ecology, impacts, and potential for control of E. erecta in order to guide management practices. In a mixed-evergreen forest in Santa Cruz County, we measured impacts of E. erecta on native plant species richness and abundance in an observational comparison across 11 sites. Strikingly, we measured nearly four times greater total vegetation cover in plots invaded by E. erecta. However, native plants were not significantly less abundant in invaded plots than in reference plots, and native cover was not significantly predicted by E. erecta cover within invaded plots. We did, however, find evidence of change in community composition in response to E. erecta abundance. Our findings demonstrate that native species can persist in the presence of E. erecta, although the long-term impacts on populations of the perennial plants that dominate this forest understory are still unknown.

We also compared the effectiveness of mechanical (hand pulling with volunteers) and chemical (glyphosate) management methods. Twenty-two months following management treatments, we found substantial reductions in E. erecta using both mechanical and herbicide treatments, but herbicide application also produced greater reductions in native species cover and species richness. Transplanting native yerba buena [Clinopodium douglasii (Benth.) Kuntze] into management plots following treatment did not slow regrowth of E. erecta. It did, however, increase total native plant percent cover in herbicide and pull treatments, although largely by increasing C. douglasii cover. Effective management is possible using either manual or chemical removal methods; the optimal method may depend on the availability of manual labor and the sensitivity of the habitat to non-target effects on native plants.

Since its introduction to the United States in 1852, Chinese privet (Ligustrum sinense Lour.) has spread throughout the Southeast, invading many natural areas. Manual control by cutting or shredding is one of the most common strategies many land managers employ. However, rapid sprouting from the root collar and lateral roots commonly results in poor control. Cutting followed by either glyphosate or triclopyr application to the stumps is generally effective, but the efficacy of these herbicides in relation to treatment timing and L. sinense root collar diameter has not been evaluated. The objective of this experiment was to determine the effectiveness of glyphosate and triclopyr cut stump treatments compared with cutting alone at spring and fall timings across a range of L. sinense size classes. Studies were conducted at two locations in Auburn, AL. Treatments included cut stump+no herbicide, cut stump+ glyphosate (120 g L−1), or cut stump+triclopyr (90 g L−1). Treatments were applied to at least 50 experimental units each at April and November timings. Root collar diameter was recorded for each stem, stems were cut 2.5 cm above the ground, and herbicide treatments were applied within 30 s. Ligustrum sinense mortality and sprouting were quantified 6, 12, and 18 mo after treatment. Both glyphosate and triclopyr amine were very effective in controlling L. sinense at both spring and fall timings. However, glyphosate provided slightly better results than triclopyr when lateral sprouting was included. Application timing also was significant, with a lower percentage of sprouting following November treatments than April treatments. Stem size influenced treatment success, as larger stumps tended to sprout more than smaller stumps. These results indicate L. sinense can be controlled with cut stump herbicide treatment using either glyphosate or triclopyr with spring or fall timings at concentrations much lower than typically used.

Native forbs are an essential component in the functioning and diversity of prairie communities. Aminocyclopyrachlor (AMCP) will effectively control many noxious weeds that invade prairie communities; however, its efficacy on desirable broadleaf plants is relatively unknown. Few field studies have been reported, and locating adequate populations of native forbs for evaluation of tolerance to herbicides is difficult. The susceptibility of 10 prairie forb species to AMCP was evaluated in the greenhouse. Species were chosen to correlate with a field study of AMCP and a previous greenhouse experiment. AMCP was applied at 0, 35, 70, and 105 g ha−1 with a methylated seed oil (MSO) plus silicone-based non-ionic surfactant (NIS) blend at 0.25% v/v when plants reached the growth stage simulating a spring treatment for weed control. Blueflag iris (Iris versicolor L.) and harebell (Campanula rotundifolia L.) were relatively tolerant and would likely be unharmed following an application of AMCP in the field. Wild licorice (Glycyrrhiza lepidota Pursh), prairie wild rose (Rosa arkansana Porter), purple prairie clover (Dalea purpurea Vent.), and wild bergamot (Monarda fistulosa L.) were moderately susceptible to AMCP; however, plants might regrow in the field, since some survived at the highest AMCP application rate (105 g ha−1) evaluated. Skyblue aster [Symphyotrichum oolentangiense (Riddell) G. L. Nesom], Canada goldenrod (Solidago canadensis L.), blue cardinal-flower (Lobelia siphilitica L.), and blacksamson echinacea (Echinacea angustifolia DC.) were susceptible to AMCP even when applied at 35 g ha−1. The susceptibility of greenhouse-grown forbs to AMCP was the same or similar to species evaluated in the field and can be used to predict native forb tolerance in the field.

Exotic annual grasses such as medusahead [Taeniatherum caput-medusae (L.) Nevski] and downy brome (Bromus tectorum L.) dominate millions of hectares of grasslands in the western United States. Applying picloram, aminopyralid, and other growth regulator herbicides at late growth stages reduces seed production of most exotic annual grasses. In this study, we applied aminopyralid to T. caput-medusae to determine how reducing seed production in the current growing season influenced cover in the subsequent growing season. At eight annual grassland sites, we applied aminopyralid at 55, 123, and 245 g ae ha−1 in spring just before T. caput-medusae heading. The two higher rates were also applied pre-emergence (PRE) in fall to allow comparisons with this previously tested timing. When applied in spring during the roughly 10-d period between the flag leaf and inflorescence first becoming visible, just 55 g ae ha−1 of aminopyralid greatly limited seed production and subsequently reduced T. caput-medusae cover to nearly zero. Fall aminopyralid applications were less effective against T. caput-medusae, even at a rate of 245 g ae ha−1. The growing season of application, fall treatments, but not spring treatments, sometimes reduced cover of desirable winter annual forage grasses. The growing season after application, both spring and fall treatments tended to increase forage grasses, though spring treatments generally caused larger increases. Compared with other herbicide treatment options, preheading aminopyralid treatments are a relatively inexpensive, effective approach for controlling T. caput-medusae and increasing forage production.