Cuban club-rush is an invasive aquatic weed that is spreading northward in the southeastern United States. It is reported for the first time from Mississippi and from significantly farther northward in Alabama than was previously known. Cuban club-rush dissemination and rapid population growth are attributed to two types of reproduction: corky floating achenes and asexual reproduction by fragmentation. An illustration of Cuban club-rush and photos of its habit and habitat are provided.

The invasive grass Bromus tectorum (cheatgrass, downy brome) has extensive ecological breadth in its introduced range, and is increasing in abundance at high elevations. As a predominantly selfing species with high potential population growth rates, it is a likely candidate for having general-purpose genotypes that facilitate its invasion into high elevations. We evaluated evidence for general-purpose genotypes by examining phenotypic and molecular variation in B. tectorum from low- and high-elevation sites in the Rocky Mountains. Common garden experiments revealed that plants from high elevations germinated faster, but no other phenological, morphological, or physiological differences were found between elevations. Leaf length was longer for low-elevation sites in a common garden using field-collected seeds, but this was not found in a common garden using greenhouse-grown seeds, suggesting maternal effects. For most traits, there was significant phenotypic variation among sites and individuals. Using microsatellites, we genotyped individuals from low- and high-elevation sites. We found no indication of genetic differentiation at these loci between high and low elevations, but there was significant variation within and among sites. No single genotype was common across sites. The success of B. tectorum is not due to a few general-purpose genotypes, but rather many genotypes associated with many different phenotypes. Understanding the mechanisms behind the success of invaders enhances our knowledge of basic evolutionary and ecological processes and is crucial to our ability to manage ongoing, and prevent future, invasions, especially into new habitats.

Understanding the ecological processes that foster invasion and dominance by medusahead is central to its management. The objectives of this study were (1) to quantify and compare interference between medusahead and squirreltail under different concentrations of soil nitrogen (N) and phosphorous (P) and (2) to compare growth rates of medusahead and squirreltail under field soil N and P availabilities. We grew medusahead and squirreltail in an addition series in a greenhouse and applied one of four nutrient treatments weekly: (1) low N low P (no N or P added), (2) low N high P (added 250 ml of 600 µM P solution in the form of calcium phosphate), (3) high N low P (added 250 ml of 8,400 µM N solution in the forms of calcium nitrate and potassium nitrate), and (4) high N high P (added solutions as listed above for high N and high P). After 70 d density and biomass by species were sampled. We also grew individual medusahead and squirreltail plants in control soil conditions. Biomass, leaf area, and root length were determined for each species at 14-d intervals over 72 d. Regression models for medusahead and squirreltail suggested N appeared to be playing a much larger role than P in interference between the species. The high N treatment did not increase medusahead's interference ability relative to squirreltail as we had hypothesized. Medusahead typically imposed a two-to-seven-times stronger influence on interference relationships than squirreltail. Medusahead accumulated biomass, leaf area, and root length twice as fast as squirreltail. Results from our study suggest that medusahead seedlings will likely dominate over squirreltail seedlings. To restore squirreltail to medusahead-infested rangeland, medusahead densities should be reduced with integrated weed management strategies. On medusahead-free rangeland, prevention and early detection and eradication programs are critical.

Invasive plants are a common problem in the management and restoration of degraded lands in the semiarid western United States, but are often not the primary focus of restoration ecologists. Likewise, restoring native vegetation has not been a major concern of weed scientists. But trends in the literature demonstrate increasing overlap of these fields, and greater collaboration between them can lead to improved efficacy of restoration efforts. Succession and ecosystem development are the products of complex interactions of abiotic and biotic factors. Our greatest restoration and invasive plant management successes should result when we take advantage of these natural processes. Recent shifts in management objectives have generated approaches to directing plant community development that utilize species that are strong competitors with invasive species as a bridge to the establishment of native perennial vegetation. Soil water and nutrient characteristics and their interactions can affect desired and undesired plant species differentially and may be manipulated to favor establishment and persistence of desired perennial plant communities. Selection of appropriate plant materials is also essential. Species assemblages that suppress or exclude invaders and competitive plant materials that are well adapted to restoration site conditions are important keys to success. We provide guidelines for restoration based on the fundamental ecological principles underlying succession. Knowledge of the complex interactions among the biotic and abiotic factors that affect successional processes and ecosystem development, and increased collaboration between weed scientists and restoration ecologists hold promise for improving restoration success and invasive species management.

Preamble: Executive Order (EO) 13112—defines an invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” In the Executive Summary of the National Invasive Species Management Plan (NISMP) the term invasive species is further clarified and defined as “a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” To provide guidance for the development and implementation of the NISMP, the National Invasive Species Council (NISC) and the Invasive Species Advisory Committee (ISAC) adopted a set of principles outlined in Appendix 6 of the NISMP. Guiding Principle #1 provides additional context for defining the term invasive species and states “many alien species are non-invasive and support human livelihoods or a preferred quality of life.”

Jubatagrass is one of the most invasive plants along the California and southern Oregon coast. It establishes dense populations that can severely impact native plant diversity and conifer seedling recruitment following forestry operations. This goal of this study was to evaluate the effectiveness of both manual removal and several herbicide control options and application techniques. In addition, a cost analysis was also conducted for the most successful herbicide control methods. Results demonstrate that mechanical removal through digging is effective, although labor intensive. Among the herbicides tested, glyphosate applied as a high-volume (spray-to-wet) application (0.6% ae) in early summer, low-volume application (2.4% ae) in early summer or fall, and ropewick technique in early summer or fall (> 9.9% ae) all provided ≥ 88% jubatagrass control, but the low-volume treatments were the most cost effective. Although the graminicide sethoxydim at the highest rate (0.36% ai) did not give effective control, fluazifop applied in the fall in a low-volume treatment (0.98% ai) gave 87% control of jubatagrass. Imazapyr gave some level of control but does not appear to provide an economical option for jubatagrass management. Results of this study demonstrate that in addition to the more conventional methods of mechanical removal and spray-to-wet glyphosate (0.6% ae), control of jubatagrass can also be equally or more effective with low-volume and ropewick applications of glyphosate.

Limited data exist on the affect of downy brome invasion on biogeochemical cycling. Biogeochemical cycling was quantified in a winterfat community in northeastern, CA that was separated into three invasion classes: noninvaded (NI), invaded for 3 yr (I3), and 10 yr (I10) by downy brome. On each plot, all aboveground vegetation was harvested and separated by species, dried, weighed, and tissue nutrients quantified. In addition, soil samples were collected from 0- to 30-, 30- to 60-, and 60- to 100-cm depths and various nutrient pools quantified. Aboveground biomass g/m2 was significantly greater, with downy brome averaging over 90% of the plant mass on the I10 plots (280 g) compared to the NI plots (148 g). In comparison to the NI plots, vegetation fluxes (g/m2/yr) of carbon (C) were significantly greater, and fluxes of Ca, Fe, and Cu were significantly less on I10 plots. Soils occupied for 10 yr by downy brome have significantly greater total N and organic C, and greater availability of Fe, Mn, Cu, ortho-P, Ca, and K compared to NI soil. For the I10 plots, available soil N (dominantly NO3 −) was greatest in the 60- to 100-cm-depth increment, whereas for the other plots, N availability was greatest in the 0- to 30-cm-depth increment. Net N soil mineralization potential was near 0 on the I10 plots at all depth increments. These data suggest that invasion by downy brome facilitates elevated nutrient availability, possibly increases system leakiness of N, and fosters differential plant nutrient cycling relative to a native noninvaded community. Elevated nutrient availability promulgated by downy brome invasion might increase its competitive stature. Long-term occupation of environments by downy brome might affect the vertical distribution of nutrients, which can alter soil evolution and plant successional patterns.

Jamaican nightshade is a prickly, perennial, invasive shrub in central and southern peninsular Florida. It was first seen in Florida in 1930 near St. Cloud, and has since been reported at several other locations in the state. Jamaican nightshade is primarily found in wooded habitats, where it can quickly become dominant in the understory, but it also occasionally grows in isolated patches in the open. Although the distribution of Jamaican nightshade does not appear to be rapidly expanding in Florida, land mangers should be made aware of the potential of this weed to establish at new sites, and initiate control efforts during the early stages of colonization at newly invaded sites.

Weed Management Areas (WMAs) are an important approach for managing invasive plants. However, most WMAs are relatively recent, and little is known about how these active partnerships can be maintained over the long term. This case study of the Estes Valley WMA examined the early community support that led to the establishment of a WMA and reasons why the Estes Valley WMA did not continue as a collaborative process. The analysis uncovered four factors that were critical to the early success of the Estes Valley WMA group: community education/awareness, key participants, a community sense of responsibility, and economic/aesthetic values. The analysis also uncovered four factors explaining why the Estes Valley WMA did not continue: a lack of group structure, unclear boundary definitions, availability of funding, and decline in motivation. Residents of the Estes Valley now rely more on the county and private contractors to provide weed management services. While this approach is meeting basic weed management needs, some interviewees feel that community involvement has declined. Recommendations are given for the reestablishment of a collaborative weed management group in the Estes Valley.

The rate at which plant invasions occur is accelerating globally, and a growing amount of recent research uses genetic analysis of invasive plant populations to better understand the histories, processes, and effects of plant invasions. The goal of this review is to provide natural resource managers with an introduction to this research. We discuss examples selected from published studies that examine intraspecific genetic diversity and the role of hybridization in plant invasion. We also consider the conflicting evidence that has emerged from recent research for the evolution of increased competitiveness as an explanation for invasion, and the significance of multiple genetic characteristics and patterns of genetic diversity reported in the literature across different species invasions. High and low levels of genetic diversity have been found in different invading plant populations, suggesting that either selection leading to local adaptation, or pre-adapted characteristics such as phenotypic plasticity, can lead to aggressive range expansion by colonizing nonnative species. As molecular techniques for detecting hybrids advance, it is also becoming clear that hybridization is a significant component of some plant invasions, with consequences that include increased genetic diversity within an invasive species, generation of successful novel genotypes, and genetic swamping of native plant gene pools. Genetic analysis of invasive plant populations has many applications, including predicting population response to biological or chemical control measures based on diversity levels, identifying source populations, tracking introduction routes, and elucidating mechanisms of local spread and adaptation. This information can be invaluable in developing more effectively targeted strategies for managing existing plant invasions and preventing new ones. Future genetic research, including the use of high throughput molecular marker systems and genomic approaches such as microarray analysis, has the potential to contribute to better understanding and more effective management of plant invasions.