Although several invasive species have induced changes to the fire regime of invaded communities, potential intraspecific shifts in fire-related traits that might enhance the invasion success of these species have never been addressed. We assumed that traits conferring persistence and competitiveness in postfire conditions to downy brome, a quintessential invasive species of the Great Basin (North America), might be under selection in areas with recurrent fires. Therefore, we hypothesized that populations from frequently burned regions of the Great Basin would have (1) greater tolerance to fire at seed level, (2) higher relative seedling performance in postfire environments, and (3) greater flammability than unburned Central European populations that evolved without fire. Seeds were collected from three introduced populations from frequently burned regions in North America and three introduced populations of rarely or never burned sites from Central Europe. We performed (1) germination experiments with seeds subjected to the effect of different fire components (heat shocks, smoke, flame, ash), (2) pot experiments analyzing the effect of postfire conditions on the early growth of the seedlings, and (3) a series of flammability tests on dry biomass of plants reared in a common garden. All seeds tolerated the low-temperature treatments (40 to 100 C), but were destroyed at high heat shocks (140 and 160 C). Only the 100 C heat treatment caused a difference in reaction of seeds from different continents, as the European seeds were less tolerant to this heat shock. We found significantly increased seedling height and biomass after 4 wk of growth under postfire conditions in American populations, but not in European ones. American populations had enhanced flammability in three out of five measured parameters compared to European populations. In summary, these intraspecific differences in fire-related traits might contribute to the persistence and perhaps invasiveness of the frequently burned North American downy brome populations.

Nomenclature: Downy brome, Bromus tectorum L. BROTE.

Management Implications: We provide evidence that North American downy brome populations from frequently burned environments have enhanced postfire biomass accumulation and flammability compared to European populations that are rarely or never exposed to fire. Seeds of downy brome, however, do not tolerate severe fires with high heat shocks.

Our results suggest that management should focus on changing the fire regime toward less frequent, but more intense, fires to stop this highly invasive species. Therefore, lengthening the fire-return interval by creating firebreaks, which would amplify the intensity and size of subsequent fires, may be one option for controlling this invasive species. However, such bands of fuel breaks, where fuels are removed by cutting several swaths to reduce fire hazard, can serve as refuge and seed source of downy brome. The association of fuel breaks with roadways might minimize the total landscape impact.

To prevent the germination of downy brome, persistent cover of the ground by native vegetation must be achieved by reintroducing fire-tolerant perennial grasses and resprouting shrubs such as rabbitbrush, as closed vegetation makes for very limited alien seedling recruitment opportunities. The fire management practice should target the historical, natural fire regime that favors native species reestablishment. These native species would produce higher fuel loads and a continuous fuel bed that might also increase the intensity and decrease the frequency of fires.

Although our results may suggest that the introduction of European, non–fire-adapted populations of downy brome to the United States might be an option, they would perhaps be outcompeted in short tim

Dioscorea bulbifera is a serious invader of various ecosystems in Florida, where plants generated by its two morphotypes climb aggressively and smother supporting vegetation. There is a dearth of published research on its invasive biological attributes including vine growth and biomass production by plants generated from bulbils. Herein, we assessed these parameters in common garden studies by planting bulbils from four biomass categories (PBBCs I–IV) of both morphotypes. Vine lengths, longevity-based growth rates (VLGR), biomass, and quantities of leaves and daughter bulbils in both morphotypes showed positive correlation with the biomass of planted parental bulbils. This indicated similarity between corresponding attributes in two morphotypes. Total vine length showed strong positive correlation with VLGR, biomass, and quantities of leaves and bulbils. Overall vine longevity among plants from PBBCs I–IV did not significantly differ whereas the total vine lengths, VLGRs, number of branches, and quantities of leaves and bulbils increased with the biomass of the parental bulbils. Plants recruited by smaller bulbils allocated more biomass to leaves and tubers compared to stems and bulbils, whereas the plants recruited by larger bulbils allocated more biomass to leaves and bulbils compared to tubers and stems. Higher proportion of biomass allocation to leaves and bulbils presumably ensures immediate faster growth, longer vines, and a greater number of daughter bulbils for future recruitment of new plants. Vine length (associated with faster growth rate, capable of blanketing supporting structures and producing large quantities of bulbils) has been noted as the primary invasive biological attribute that facilitates D. bulbifera's status as a noxious exotic weed in Florida. Control measure that can reduce vine length should reduce or eliminate the invasive behavior of D. bulbifera in Florida.

Nomenclature: Air-potato, Dioscorea bulbifera L.

Management Implications: The exotic invasive air potato vine D. bulbifera has become a serious problem for public and private land managers across Florida and beyond by blanketing and smothering native vegetation. Despite its common occurrence in Florida, there are no published research data related to the role of propagule biomass on the resulting vines' growth rate, biomass, and invasive biological traits. We conducted common garden studies using vegetative propagules (parent bulbils) ranging from small to large biomass and examined the growth and biomass of the plants generated from these bulbils. Biomass of the parent bulbils of both morphotypes was positively correlated with total vine lengths, growth rates, and the number of branches, leaves, and bulbils. The vine longevity of plants generated by bulbils of all sizes was not significantly different. However, the total vine length, vine growth rates, and the number of branches, leaves, and bulbils increased with the biomass of the parent bulbils. Plants recruited by smaller bulbils allocated a major proportion of total biomass to leaves and tubers compared to the stems and bulbils, whereas the larger bulbils allocated a greater proportion of total biomass to bulbils and leaves compared to tubers and stems. Total vine length was positively correlated with the total plant biomass. Reduced vine length should have concomitant negative impacts on leaf and bulbil production. These reductions should, in turn, negatively affect (1) plant biomass and the number of branches and leaves that are responsible for causing smothering effects on invaded plant communities and (2) bulbil production that will have direct negative impact on plant recruitment and invasion of the new areas. Therefore, control measures that reduce seasonal vine length should reduce the quantity of bulbils and hence invasiveness of D. bulbifera vines in Florid

Yellowflag iris, native to Europe, is a rhizomatous, emergent, invasive plant found in pond margins, ditches, and other wetland sites in much of the United States. In water depths up to approximately 50 cm, it forms dense stands, which displace native sedges and rushes, reducing waterfowl habitat and water flow. The rhizomes can reach 6 m in lateral spread, making it very difficult to control by mechanical methods. In addition, conventional boom-sprayer applications are often impractical in most aquatic systems. Drizzle application is a technique for directed treatment of hard-to-reach invasive plants. It uses low volumes (26 to 104 L ha⁻¹) of concentrated herbicide solution, applied using a spray gun emitting a thin stream of solution with an effective range of 6 m. In this study, conducted along the margins of two ponds at the University of California, Davis, we compared drizzle applications of glyphosate, imazapyr, and triclopyr to applications using a conventional boom sprayer. Although both glyphosate and imazapyr provided excellent control (> 96%) of yellowflag iris with either treatment technique, only the drizzle treatments of imazapyr at 2.26 and 4.52% ae (10 and 20% product) at spray volumes of 52 and 26 L ha⁻¹, respectively, were below the maximum labeled rate and still gave > 98% control. Furthermore, a cost analysis indicated that the most-economical application for effective control of yellowflag iris was a drizzle application of imazapyr at 4.52% ae (20% product) at 26 L ha⁻¹. This study demonstrates that drizzle application with imazapyr can be a practical application method for yellowflag iris control in aquatic systems in which broadcast treatments with conventional boom sprayers may be difficult.

Nomenclature: Glyphosate; imazapyr; triclopyr; yellowflag iris, Iris pseudacorus L.

Management Implications: Yellowflag iris is an invasive, rhizomatous, perennial plant of wetland and aquatic areas in many U.S. states. In shallow ponds, it can form a perimeter band 6 to 12 m wide. Infestations are difficult to control by mechanical methods, and very little has been published on chemical control options. Most chemical application techniques, particularly conventional hand-held boom sprayers, are difficult to use in yellowflag-infested areas because of the inability to reach plants growing in deeper water and at greater distance from the shore. In this study, we used a drizzle-application technique developed at the University of Hawaii for directed treatment of hard-to-reach, invasive plants along forest trails. We compared this technique to a conventional backpack boom sprayer using three herbicides, glyphosate, imazapyr, and triclopyr. Our results showed that glyphosate and imazapyr were both effective for control of yellowflag iris using either treatment method. However, the drizzle method gave outstanding control (> 98%) with 10 and 20% imazapyr product (Habitat) at spray volumes of 52 and 26 L ha⁻¹, respectively. These were the only treatments below the maximum labeled rate for either herbicide. Moreover, the 20% rate of imazapyr at 26 L ha⁻¹ was the most-economical treatment compared with any other rate, herbicide, or application method, primarily because of reduced labor costs. In addition to its control and cost effectiveness, the drizzle application method also reduces drift potential and provides easier access to difficult-to-reach aquatic sites.

Ornamental grasses may become invasive weeds depending on their ability to naturalize and outcompete other species. Miscanthus sacchariflorus (Maxim) Franch. (Amur silvergrass) is a tall, self-incompatible, nonnative grass that has become naturalized in eastern North America, forming monospecific stands and raising concerns about its potential invasiveness. To understand the extent of clonal and sexual reproduction in feral populations, we examined their population genetic structure, seed production, and ploidy. We surveyed 21 populations in Iowa and Minnesota using eight polymorphic microsatellite markers. Only 34 multilocus genotypes (MLGs) were detected from a total of 390 samples. All of the study populations had more than one MLG, thereby allowing cross-pollination with near neighbors, but most were dominated by one or a few MLGs. Low genetic divergence suggests that all populations may have originated from similar cultivars. Cluster analysis showed that the six populations from Minnesota were extremely similar to each other, whereas the 15 populations from Iowa were somewhat more diverse. Seed production was quantified for 20 populations and ploidy for 11 populations. Average seed production was very low (< 0.30 seeds per panicle), although most populations did produce seeds. Because the populations were diploid (2x), they also may have the potential to hybridize with ornamental varieties of Miscanthus sinensis (Chinese silvergrass; eulaliagrass), a diploid close relative. Clonal growth, self-incompatibility, and spatial isolation of compatible clones may contribute to pollen-limited seed set in these populations. Low seed set may affect the rate of spread of feral M. sacchariflorus, which appears to disperse vegetatively as well as by seed. Although this species is not widely viewed as invasive, it is worth monitoring as a species that may become more widespread in the future.

Nomenclature: Amur silvergrass, silver banner grass, Miscanthus sacchariflorus (Maxim.) Franch.; Chinese silvergrass, Miscanthus sinensis Anderss.

Management Implications: Ornamental perennial grasses may have the potential to become invasive in areas where they can easily naturalize and disperse. In the nonnative genus Miscanthus, unwanted establishment of feral populations of ornamental M. sinensis (Chinese silvergrass) already has occurred in parklands and other areas, primarily in the eastern and southeastern United States. Its close relative, M. sacchariflorus (Amur silvergrass), also establishes feral populations, typically in more northern regions, but these stands are not as widespread as M. sinensis, nor do they produce abundant seeds. Low seed production could be a factor that limits population growth rates in feral M. sacchariflorus. The co-occurrence of genetically distinct individuals is a requirement for cross-pollination and seed set in this clonally reproducing, self-incompatible species. If several cross-compatible individuals occur in close proximity, this might lead to more abundant seed production and subsequent dispersal to other sites. In the current study, we found that feral populations of M. sacchariflorus in Iowa and Minnesota are genetically similar and highly clonal, but more than one genetic individual was present at each of our study sites. At present, we do not know whether M. sacchariflorus is in a temporary “lag phase” that precedes greater invasiveness. In any case, this tall, vigorously clonal perennial is able to establish extensive monospecific stands that crowd out other species, which is why managers of natural areas typically try to eradicate newly established populations. Ornamental plantings of M. sacchariflorus continue to be popular in northern areas of the United

An experiment was initiated to study the effects of rubber benthic barriers vs. aggressive cutting on the invasive aquatic emergent plant, yellow flag iris. Treatments were compared against a control at two locations within British Columbia, Canada (Vaseux Lake and Dutch Lake). Yellow flag iris response was significantly different between the two sites, but biologically the results were identical: the benthic barrier killed yellow flag iris rhizomes within 70 d of treatment. Over the extent of the research, at Vaseux Lake the effect of aggressive cutting was no different from the control, while aggressive cutting was statistically no different than the benthic barrier at Dutch Lake. Vegetation regrowth approximately 200 d after the benthic barriers were removed was not detected at either location. These results indicate that rubber benthic barriers may be an effective treatment for yellow flag iris and maybe suitable for other, similar species.

Nomenclature: Yellow flag iris, Iris pseudacorus L. IRPS.

Management Implications: Rubber matting (benthic barriers) appeared to work well on the emergent aquatic invasive plant yellow flag iris. In less than 3 mo, rhizomes that were treated with the benthic barrier had very few living cells. Additionally, no regrowth from rhizomes was documented the following growing season, further indication of the successful effects of the barriers. Aggressive cutting is also used as a yellow flag iris treatment. Our research found that depending on the site, aggressive cutting may be no different than the untreated control; or it may be no different than the benthic barrier. More research is required to understand how environmental parameters may affect aggressive cutting of yellow flag iris.

The abundant exposed soil following benthic barrier treatment, the presence of cattails, and the limited number of yellow flag iris germinants indicates that treated sites have a period of time posttreatment when restoration with desirable species could be implemented.