Bushkiller (Cayratia japonica) is a herbaceous, perennial vine that reproduces from seed and vegetative root structures within its native range. However, this species is considered invasive in the United States due to prolific shoot production, which can overtop surrounding vegetation. Cultural control practices, such as mulching, have been observed to further the spread of this species through regeneration of root fragments. Research was conducted to determine the regenerative capacity of bushkiller root fragments (1 to 7 cm; 2.5 to 18 inches) buried at various depths (0 to 40 cm). Root length and planting depth affected leaf number, shoot number, plant height, and shoot biomass. Bushkiller leaf density, shoot density, plant height, and dry weight increased as root fragment length increased from 1 to 7 cm; conversely, these variables decreased as planting depth increased from 0 to 40 cm. Results indicate bushkiller regeneration capacity from root fragments is extremely high and control practices that fragment roots should be avoided to reduce further spread.

Nomenclature: Bushkiller, Cayratia japonica (Thunb.) Gagnep

Management Implications: Bushkiller is an invasive, perennial vine that grows rapidly and overtops surrounding vegetation. It has invaded several states in the Southern United States and several recently reported infestations have elevated concern about this species. Research was conducted to determine the regenerative capacity of bushkiller roots. Bushkiller roots just 2.8 inches in length produced over 1 shoot around 10 inches in length with approximately 13 leaves by just 34 days after planting. Even though smaller roots produced fewer and shorter shoots, vegetative reproduction was observed down to the smallest root fragment evaluated, 0.4 inches in length. Root fragments were also able to reproduce when planted as deep as 16 inches. Based upon this data, established bushkiller would be extremely tolerant of single disturbance events including cultivation, mowing, mechanical removal of shoots, grazing, and application of non-systemic herbicides. Further, disturbance that results in root fragmentation may increase stem density. Our results also suggest that fragmented roots would readily form new infestations when moved as soil contact is maintained.

Greenhouse studies were conducted on two southern Illinois star-of-Bethlehem populations to determine the influence of chilling and bulb chipping on plant growth and reproduction. Chilling was not required for leaf emergence of dormant bulbs, but an increase to 10 wk of chilling proportionally delayed leaf emergence by 41 and 42 d for the Murphysboro and the Marion populations, respectively. Bulb chipping did reduce plant height when compared to plants from nonchipped bulbs. Also, chipped bulbs produced a greater number of small daughter bulbs compared to nonchipped bulbs; however, total bulblet production was variable and dependent on population, mother bulb size, and chipping treatment. Overall, bulb chipping did not have any negative influence on star-of-Bethlehem and might promote increased daughter bulblet production. Therefore, field operations, such as tillage, that cut and chip bulbs might actually accentuate both the spread and density of star-of-Bethlehem infestations.

Nomenclature: Star-of-Bethlehem, Ornithogalum umbellatum L. OTGUM

Management Implications: Star-of-Bethlehem is a persistent and aggressive invader of pastures and cropland. Although its movement to new fields is slow, once established in a field, star-of-Bethlehem populations can increase rapidly in area and density. Nonuniform leaf emergence in the spring makes foliar herbicide applications very difficult to plan while ensuring all plants have leaves emerged so no plants escape the foliar treatment. Additionally, very few herbicide options have proven effective on this pest. The results from this research show that star-of-Bethlehem does not require chilling to emerge; however, chilling can delay plant growth and leaf emergence. Therefore, the winter climate and exposure of a field might greatly determine star-of-Bethlehem leaf emergence, and subsequently, the timing of herbicide applications. Tillage also has been used as a control measure; however, due to Star-of-Bethlehem's perennial growth habit and propagation through bulb formation, it is probable that tillage could actually increase plant densities rather than decrease them. Greenhouse experiments simulating potential damage to star of-Bethlehem bulbs by tillage confirm that bulb chipping caused by tillage can increase production of bulblets, therefore enhancing the spread of this weed. From these findings, grower practices and future research should be focused on evaluating effective herbicide options and applications timings for management of star-of-Bethlehem.

Sulfur cinquefoil is an invasive, perennial forb on rangelands of western Canada and the United States. Sulfur cinquefoil reproduces solely by seed and it is a prolific seed producer. Our 2-yr study (2006, 2007) investigated the optimal timing and intensity of defoliation to decrease aboveground productivity and seed production of sulfur cinquefoil plants on foothill rangeland in southwestern Montana. Each year, 150 sulfur cinquefoil plants within a 430-m² enclosure were tagged for identification and randomly assigned to one of 15 clipping treatments with 10 plants per treatment. Clipping treatments were conducted at three timings: (preflower [early June], flowering [late June], and seedset [mid-July]) and all possible combinations of timings for a total of seven timing treatments clipped to two stubble heights (7.5 cm or 15 cm), comprising 14 unique treatments. The final (15th) treatment consisted of an unclipped control. Response variables collected at senescence (late July) included aboveground biomass; number of buds, flowers and fruits on each plant; and number and viability of seeds produced. Results indicated that defoliation of sulfur cinquefoil can effectively reduce its yield and seed production. All clipping treatments reduced aboveground biomass of sulfur cinquefoil compared with control plants (P ≤ 0.05), except clipping to 15 cm during preflowering in the wetter year of 2006. Clipping to either 7.5 cm or 15 cm at all times or combinations of timings reduced the number of buds, flowers, fruits, and seeds produced by sulfur cinquefoil (P ≤ 0.05). Viable seed production was reduced 99 to 100% when plants were clipped once to either 7.5 or 15 cm during flowering or seedset. Results suggest that targeted livestock grazing or mowing applied one time per season during flowering or seedset could effectively suppress the biomass production and viable seed production of sulfur cinquefoil.

Nomenclature: Sulfur cinquefoil, Potentilla recta L. PTLRC

Management Implications: Sulfur cinquefoil is a nonnative, perennial, invasive weed that currently infests thousands of acres of rangeland and abandoned cropland in the western United States and Canada. This plant is a concern because it produces thousands of seeds and is capable of invading undisturbed rangeland. There are no approved biological controls, and herbicide treatment is expensive; therefore, we evaluated the potential for defoliation to reduce yield and seed production of sulfur cinquefoil. Hand-clipping treatments were applied at 14 different timing and intensity combinations to determine those most appropriate to suppress sulfur cinquefoil. Overall, clipped plants produced ∼ 80% less aboveground forage and > 90% fewer viable seeds than control plants. Clipping applied when sulfur cinquefoil plants were flowering or in early seedset had the greatest impact on forage and seed production. Plants clipped one time to either a 15- or 7.5-cm stubble height at flower or later were unable to produce any viable seed during the current growing season. Multiple defoliations were not necessary to decrease seed production if the first defoliation occurred at the flower stage or later. The intensity of the defoliation did not matter so long as the fruits were removed from the plant. Because of the longevity and abundant seed production of the plant, areas infested with sulfur cinquefoil likely have a large soil seed bank, and multiple years of uniform defoliation will be necessary before any noticeable change in the existing population can be determined. However, defoliation holds potential to reduce the competitive ability of sulfur cinquefoil as well as the ability of the plant to add to the seed bank. Targeted livestock grazing or mowing are two potential ways to defoliate sulfur cinquefoil at the appropriate timing and intensity to suppress the plant

We studied the response of naturalized kudzu plants to simulated herbivory at three locations: Delaware (DE), Pennsylvania (PA), and North Carolina (NC). At the DE and PA sites, plant mortality after the first yr was 14 and 50%, respectively, and was highest for plants that had a small starting root crown size. At both sites, 50 and 75% leaf and shoot clipping, and drilling one or two large holes from the root crown into roots, had no effect on aboveground biomass. In NC, all plants survived for 3 yr. Plants subject to 50% vine removal at this site showed significant decrease in aboveground biomass compared to the control, but 50% leaf cutting and root drilling had no effect. In the greenhouse, kudzu seedlings grown in 60 and 100% light compensated for 50% leaf removal, but 75% damage reduced aboveground biomass. Plants survived for 1 to 2 mo in 0% direct light, but only one of 53 plants survived to the end of the experiment. Results suggest that established kudzu plants are able to compensate for biomass removal, seedlings can survive for several weeks without light, and that effective biocontrol might require more than 2 to 3 yr of continuous damage.

Nomenclature: Kudzu, Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & S. M. Almeida

Management Implications: Kudzu is an exotic, invasive weed that covers two to seven million acres in the southern United States. As part of a biological control research program targeting this weed, we clipped leaves, removed or clipped stems, and drilled holes in roots to determine what kind of damage would reduce plant growth and/or survival. Near the edge of kudzu's invasive range (Delaware and Pennsylvania), many plants died following the first year, even where damage treatments were not applied. Near the center of the range (North Carolina), only plants that had half of their vines removed (simulating severe damage by stem-boring beetles) had reduced growth, and none of the plants died. In a greenhouse study, almost all kudzu seedlings grown in complete shade died after 80 d. When leaves were clipped, plants grown under low light conditions were more likely to die than those in full sun. Results suggest that biocontrol alone might not be sufficient to control kudzu, especially near the center of its range. Therefore, field practitioners should consider integrating multiple control tactics to stress the plant, including mechanical and chemical controls, or competition techniques such as planting canopy species with dense foliage. If kudzu patches in full sun are cleared, practitioners should implement additional management techniques such as revegetation to limit the recruitment of new kudzu plants from the seed bank.

The invasive annual grass downy brome is the most ubiquitous weed in sagebrush systems of western North America. The center of invasion has largely been the Great Basin region, but there is an increasing abundance and distribution in the Rocky Mountain States. We evaluated postfire vegetation change using very large–scale aerial (VLSA) and near-earth imagery in an area where six different fires occurred over a 4-yr period at elevations ranging from 1,900 to over 2,700 m. The frequency of downy brome increased from 8% in 2003 to 44% in 2008 and downy brome canopy cover increased from < 1% in 2003 to 6% in 2008 across the entire study area. Principal component analyses of vegetation cover indicate a shift from plant communities characterized by high bare soil and forbs immediately postfire to communities with increasing downy brome cover with time after fire. The highest-elevation sampling area exhibited the least downy brome cover, but cover at some midelevation locations approached 100%. We postulate that the loss of ground-level shade beneath shrubs and conifers, accompanied by diminished perennial vegetative cover, created conditions suitable for downy brome establishment and dominance. Without a cost-effective means of landscape-scale downy brome control, and with infestation levels and climate warming increasing, we predict there will be continued encroachment of downy brome at higher elevations and latitudes where disturbance creates suitable conditions.

Nomenclature: Downy brome, Bromus tectorum L

Management Implications: The annual grass known as downy brome or cheatgrass is one of the worst weeds of western North America infesting nearly 23 million hectares, reducing rangeland forage and habitat value and increasing wildfire risk. Downy brome is not only expanding across the landscape, but is also expanding to higher elevations, spreading the fire risk from sagebrush lowlands into higher-elevation rangeland systems. Downy brome cover in the foothills of the southern Wind River Mountains at elevations of 1,900 to 1,700 m averaged < 1% in 2002, but expanded to > 6% cover by 2008, approaching 100% cover at some individual sites. Local spring temperatures have increased into the range that supports early downy brome growth. We speculate that fire removed shading overstory, further increasing spring soil temperatures to allow downy brome to rapidly expand. Concurrently, longer, drier growing seasons are reducing native plant growth and competitiveness. We recommend that land managers be aware of the risk of downy brome expansion at higher elevations and adjust their management to address postfire downy brome infestations.

Producers facing infestations of invasive annual grasses regularly voice the need for practical revegetation strategies that can be applied across broad landscapes. Our objective was to determine the potential for scaling up the single-entry approach for revegetating medusahead-infested rangeland to broader, more heterogeneous landscape-scale revegetation of winter annual grass–infested rangeland. We hypothesized, when applied on a highly variable landscape scale, the combination of imazapic and seeding would provide highest abundance of perennial grasses and lowest amount of annual grasses. Treatments included a control, seeding of crested wheatgrass (‘Hycrest’) and Sandberg's bluegrass, spraying (60 g ai ha⁻¹ imazapic), and a simultaneously applied combination of spraying and seeding. The HyCrest and Sandberg's bluegrass seeding rates were 19 and 3.4 kg ha⁻¹, respectively. The treatments were applied to large plots (1.4 to 8 ha) and replicated five times, with each replication located in different watersheds throughout southeastern Oregon. This study shows that the single-entry approach can be scaled up to larger landscapes, but variation within establishment areas will likely be high. This procedure should reduce the costs over multientry treatment applications and make revegetating annual grass–infested rangeland across landscapes more affordable.

Nomenclature: Imazapic, medusahead, Taeniatherum caput-medusae (L.) Nevski, crested wheatgrass, Agropyron cristatum (L.) Gaertn. × Agropyron desertorum Gaertn. ‘Hycrest’, Sandberg's bluegrass, Poa secunda J.S. Presl

Management Implications: Managing invasive annual grass infestations on a large scale remains a major impediment for successful rangeland restoration. The high cost of treatments and low percentage of success often keep managers from initiating management plans where large-scale infestations are present. In this experiment, we utilized a single-entry treatment of herbicide application and seeding on landscape-scale plots of medusahead- and cheatgrass-infested rangeland. We were interested in determining whether this method would provide acceptable levels of control for the invasive grasses and establishment of desired species. Our results suggest that the one-pass system might be a suitable method for restoring invasive annual grass infestations and lower the cost of treatment by completing an herbicide application and seeding in a single entry into the field.

Understanding the ecological characteristics of areas invaded and not invaded by exotic plants is a priority for invasive plant science and management. Buffelgrass is an invasive perennial species that managers view as a major threat to indigenous ecosystems of conservation lands in Australia, Mexico, the United States, and other locations where the species is not native. At 14 sites in Saguaro National Park in the Arizona Uplands of the Sonoran Desert, we compared the soil, vegetation, and soil seed bank of patches invaded and not invaded by buffelgrass. Abiotic variables, such as slope aspect and soil texture, did not differ between buffelgrass patches and patches without buffelgrass. In contrast, variables under primarily biotic control differed between patch types. Soil nutrients, such as organic C and NO₃–N, were approximately twofold greater in buffelgrass compared with nonbuffelgrass patches. Average native species richness was identical (14 species 100 m⁻²) between patch types, but native plant cover was 43% lower in buffelgrass patches. Unexpectedly, native seed-bank densities did not differ significantly between patch types and were 40% greater than buffelgrass seed density below buffelgrass canopies. Results suggest that (1) soil nutrient status should not be unfavorable for native plant colonization at buffelgrass sites if buffelgrass is treated; (2) at least in the early stages of buffelgrass patch formation (studied patches were about 10 yr old), native vegetation species were not excluded, but rather, their cover was reduced; and (3) native soil seed banks were not reduced in buffelgrass patches.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link

Management Implications: Buffelgrass is a priority invasive, exotic species for managers of conservation lands in Australia, Mexico, and the United States because it can alter fire regimes and reduce native biodiversity. We compared ecological characteristics (soil, vegetation, and seed bank) of patches invaded and not invaded by buffelgrass at 14 sites in Saguaro National Park in the Arizona Upland Subdivision of the Sonoran Desert. Abiotic variables (e.g., aspect, soil texture) did not differ between patch types, whereas properties under biological control (e.g., soil organic C) differed between patch types. Soil nutrients, such as NO₃–N and organic C, were about twice as concentrated in buffelgrass compared with patches without buffelgrass. Given that the nutrient-rich soils below native, perennial plants are key locations for native plant recruitment and nutrient concentrations below buffelgrass were similar to those below native perennials reported in the literature, results suggest that soil nutrient status in buffelgrass patches should not be unfavorable for native plant recruitment. Native plant species richness and diversity were identical on average between patch types, but native cover was less by about one-half in buffelgrass patches. Unexpectedly, native-soil seed banks were not reduced in buffelgrass patches.

Understanding cause–effect mechanisms of buffelgrass invasion, temporal changes in the characteristics of buffelgrass-invaded sites, and responses of these characteristics to buffelgrass treatment are important research needs. If buffelgrass invasion is the principal driver of the observed reduced cover of native plants in patches invaded by buffelgrass, treatment of buffelgrass in its early stages of invasion might be important, before the exclusion of native species. To summarize, compared with nonbuffelgrass patches, buffelgrass patches exhibited higher soil nutrients, identical native plant species richness and diversity, lower native plant cover, and similar native species soil seed bank densities.

Chinese and European privets are among the most aggressive invasive shrubs in forestlands of the southern United States. We analyzed extensive field data collected by the U.S. Forest Service covering 12 states to identify potential determinants of invasion and to predict likelihood of further invasion under a variety of possible management strategies. Results of multiple logistic regression, which classified 75% of the field plots correctly with regard to species presence and absence, indicated probability of invasion is correlated positively with elevation, adjacency (within 300 m) to waterbodies, mean extreme maximum temperature, site productivity, species diversity, natural regeneration, wind disturbance, animal disturbance, and private land ownership and is correlated negatively with slope, stand age, site preparation, artificial regeneration, distance to the nearest road, fire disturbance, and public land ownership. Habitats most at risk to further invasion (likelihood of invasion > 10%) under current conditions occur throughout Mississippi, with a band stretching eastward across south-central Alabama, and in eastern Texas and western Louisiana. Invasion likelihoods could be reduced most by conversion to public land ownership, followed by site preparation, fire disturbance, artificial regeneration, and elimination of animal disturbance. While conversion of land ownership may be neither feasible nor desirable, this result emphasizes the opportunity for reducing the likelihood of invasions on private lands via increased use of selected management practices.

Nomenclature: Chinese privet, Ligustrum sinense Lour, European privet, Ligustrum vulgare L.

Management Implications: Biotic invasions have affected ecosystems worldwide. One of the greatest current challenges facing forest ecosystem management in the southern United States is the control of range expansions by invasive plant species. To move beyond reactive control efforts toward more proactive management requires prediction of potential ranges of invasive species on spatial scales relevant to forest managers. We drew upon extensive geo-referenced datasets on nonnative invasive plants maintained by the U.S. Forest Service to develop an invasion distribution model predicting possible range expansion of Chinese and European privets in forestlands of the southern United States. By identifying determinants of invasion and potential habitat, our analyses should assist land managers and restoration practitioners in planning proactive management strategies and control treatments.

Japanese barberry is an important landscape shrub that has a demonstrated potential to be invasive in ∼30 states across the central and northern United States. Forty-six cultivars were evaluated for their potential to produce fruits and seeds in a randomized, replicated field planting. Seeds from a subset of cultivars were evaluated for their ability to germinate and survive as seedlings in a deciduous woodland. Seed production for cultivars varied from no seeds to more than 12,000 seeds plant⁻¹ and the number of seeds per fruit ranged from 0.1 to 1.8. Five cultivars produced fewer than 100 seeds plant⁻¹, and two cultivars failed to produce fruit. When plants were allowed to mature for 4 to 5 yr beyond the first evaluation time, cultivars exhibited significant increases in fruits per plant, producing as much as 35,000 fruits plant⁻¹ (‘Sparkle’). ‘Golden Devine’ and ‘Red Chief’, fruitless cultivars at the first evaluation, produced 165 and 20 fruit plant⁻¹, respectively, at the follow-up evaluation, demonstrating that long-term evaluation of cultivars is necessary to accurately assess sterility. Between 12.5 and 31% cultivar seed sown in a deciduous woodland germinated, and seedlings survived at rates between 5.6 and 29.3%. Coupling cultivar seed-production data with germination and survival data in a deciduous woodland suggests that even cultivars producing as few as 100 seeds annually have the potential to contribute a few seedlings each year to a natural area.

Nomenclature: Japanese barberry, Berberis thunbergii DC

Management Implications: Japanese barberry cultivars represent a substantial economic value to the nursery and landscape industries because they are popular, durable plants, widely used for landscaping. Unfortunately, Japanese barberry is also an invasive plant, and some states have imposed laws preventing the propagation and sale of the species and all cultivars. Cultivars of Japanese barberry look and behave differently from the species, with many being dwarf forms with purple or yellow foliage. The dramatic visual differences between cultivars of Japanese barberry and the species have led some to suggest that certain cultivars may be noninvasive or have a lower potential for rapid establishment in natural communities and could be exempted from species bans. The objective of this study was to evaluate the fecundity of a wide range of commercially available Japanese barberry cultivars to determine whether any could be considered noninvasive. We determined fruit production, seed production, and germination rates for 46 cultivars of Japanese barberry and its hybrids. Using seed from a representative subset of cultivars, we also determined the potential each cultivar had to germinate, survive, and grow in a deciduous woodland. Cultivars varied considerably in their seed production from more than 12,000 seeds to no seeds, and several cultivars produced fewer than 100 seeds plant⁻¹. When plants were allowed to mature for 4 to 5 yr beyond the first evaluation time, cultivars exhibited significant increases in fruits per plant. ‘Sparkle’ produced more than 35,000 fruits plant⁻¹ and ‘Golden Devine’ and ‘Red Chief’, which initially appeared to be fruitless, produced 165 and 20 fruit plant⁻¹, respectively. To accurately assess reproductive potential of cultivars, it is necessary to conduct evaluations for durations that are longer than those typically reported and to provide ample opportunities for cross-pollination. Cultivar seed germination rates were between 12.5 and 31% in a deciduous woodland, and seedlings survived at rates between 5.6 and 29.3%. By combining seed production data with establishment data in a deciduous woodland, even cultivars producing as few as 100 seeds yr⁻¹ in the landscape have the potential to co

The effects of annual, aerial and ground, herbicide treatments with glyphosate and metsulfuron were evaluated for control of Old World climbing fern (OWCF) and effects on native plants on tree islands in Arthur R. Marshall Loxahatchee National Wildlife Refuge during 2006 to 2009. Initial aerial herbicide treatments reduced OWCF cover by greater than 98% on metsulfuron-treated islands and greater than 88% on glyphosate-treated islands, but there was a concomitant decrease in native ground cover with both herbicides. Follow-up ground treatments, during years two and three of the study, were effective at maintaining low levels of OWCF. OWCF cover at the end of the study was 1 to 2% of pretreatment cover on metsulfuron-treated islands and 8 to 10% on glyphosate-treated islands. At the end of the study (3 yr after treatment), species richness was dominated by ruderal native species not typically found on tree islands. The survival rate of tree and shrubs was 65 to 93% on islands treated with metsulfuron and 6 to 20% on islands treated with glyphosate. Minimum effects were recorded for canopy cover on tree islands treated with metsulfuron compared with glyphosate. These data indicate that the aerial application of metsulfuron can be used for control of OWCF on tree islands. Follow-up ground treatments will be required for OWCF regrowth and new sporelings and should be conducted within 1 yr of the aerial application.

Nomenclature: Glyphosate, metsulfuron, Old World climbing fern, Lygodium microphyllum (Cav.) R. Br

Management Implications: The use of herbicides can effectively control Old World Climbing Fern (OWCF) on Everglade tree islands but results in substantial nontarget damage to ground cover. Aerial applications of metsulfuron limited shrub and tree mortality and reductions in canopy cover compared with glyphosate treatments. Monitoring and follow-up treatments on an annual basis would be required for control of OWCF. Without herbicide management, OWCF will continue to form monocultures on tree islands and other habitats resulting in lower native-species richness, evenness, and canopy cover. Follow-up treatments will reduce OWCF growth and spore production, limiting the ability of OWCF to infest new sites from wind blown spores. It is likely that OWCF cover can return to pretreatment levels less than 6 yr following a single herbicide treatment. The best management strategy for OWCF on tree islands is an initial aerial application with metsulfuron over large infestations and annual monitoring and follow-up ground treatments as needed. Managers using aerial application of herbicides for control of OWCF can expect to observe shifts from late-successional vegetation, typical of tree islands, to ruderal species, typical of disturbed sites.

There is growing interest in whether invasive species may be controlled by utilizing management strategies that target vulnerable life stages. We manipulated the timing of fire and measured its effects on sericea lespedeza germination and seedling survival. Although fire strongly decreased germination in the laboratory, fire increased germination under field conditions. Additionally, fire caused small decreases in seedling survival in the field. Therefore, controlled burns are likely to encourage spread of sericea lespedeza and are unlikely to effectively control this invasive species. Although targeting vulnerable life stages is a promising strategy for invasive species control, our results illustrate that system-specific studies may be needed to unravel potentially complex interactions between biotic and abiotic factors before effective control strategies can be devised.

Nomenclature: Sericea lespedeza, Lespedeza cuneata (Dum. Cours.) G. Don

Management Implications: Sericea lespedeza is a noxious invader capable of suppressing native species in grasslands and prairies in the Great Plains. Currently, repeated herbicide application is the only effective method of controlling sericea lespedeza; however, herbicides are cost prohibitive for many land managers. Fire has been considered as a potential management tool for controlling this weed but it is not currently recommended because adult plants may resprout. However, controlled burns might be useful to control recolonization from seed after adult plants have been killed with herbicides. Our results show that burning seedlings in the growing season immediately following germination slightly reduces sericea lespedeza survivorship but creates a large flush of germination that more than offsets this reduction in survivorship. While it remains possible that other burning treatments may reduce the spread of this noxious weed, the treatments we tested suggest that fire will encourage sericea lespedeza invasion.

Diversified grasslands that contain native plant species can produce biofuels, support sustainable grazing systems, and produce other ecosystem services. However, ecosystem service production can be disrupted by invasion of exotic perennial plants, and these plants can have soil-microbial “legacies” that may interfere with establishment and maintenance of diversified grasslands even after effective management of the invasive species. The nature of such legacies is not well understood, but may involve suppression of mutualisms between native species and soil microbes. In this study, we tested the hypotheses that legacy effects of invasive species change colonization rates, diversity, and composition of arbuscular-mycorrhizal fungi (AMF) associated with seedlings of co-occurring invasive and native grassland species. In a glasshouse, experimental soils were conditioned by cultivating three invasive grassland perennials, three native grassland perennials, and a native perennial mixture. Each was grown separately through three cycles of growth, after which we used T-RFLP analysis to characterize AMF associations of seedlings of six native perennial and six invasive perennial species grown in these soils. Legacy effects of soil conditioning by invasive species did not affect AMF richness in seedling roots, but did affect AMF colonization rates and the taxonomic composition of mycorrhizal associations in seedling roots. Moreover, native species were more heavily colonized by AMF and roots of native species had greater AMF richness (number of AMF operational taxonomic units per seedling) than did invasive species. The invasive species used to condition soil in this experiment have been shown to have legacy effects on biomass of native seedlings, reducing their growth in this and a previous similar experiment. Therefore, our results suggest that successful plant invaders can have legacies that affect soil-microbial associations of native plants and that these effects can inhibit growth of native plant species in invaded communities.

Management Implications: In the midwestern US, regulatory, market and policy pressures could convert large areas from annual agriculture to semi-natural grassland agroecosystems, e.g., as part of a national effort to produce energy crops. Native grassland perennials could be used in these grasslands to reduce production costs, conserve soil quality, conserve native biodiversity, and enhance carbon sequestration in grassland agroecosystems. However, producer interest in semi-natural grassland systems is reduced by current difficulties in reliable and cost-effective establishment of these species, and weed management during establishment is a major concern. Many lines of evidence suggest that weedy exotic species can alter soils physically and/or microbially, creating a “legacy” that persists after control or removal of these species. This legacy effect may contribute significantly to the risk of additional weed invasion and poor performance of desirable species during grassland establishment. In smooth brome, crested wheatgrass and leafy spurge, three exotic perennials that are highly invasive in grasslands, we examined legacy effects on AMF associations of a set of native and invasive species in these grasslands. Smooth brome, crested wheatgrass and leafy spurge had legacy effects that altered AMF colonization rates and community composition in seedling roots of native and invasive species, In a previous analysis of these data (Jordan et al. 2011), we found that these invasive species also had legacy effects that reduced growth of some native species. However, these legacy effects on growth and AMF colonization of natives varied substantially among these invasive species, suggesting that such effects are not uniform. Taken together, these legacy effects on AMF associations and growth sugges

Tree-of-heaven is an invasive, nonnative species that invades newly disturbed areas and forms large monospecific stands. It was surveyed from a vehicle along 5,175 km of roads in Virginia in 2004, 2005, 2010, and 2011. Fifty-eight percent of every 1.6-km road segment had at least one tree-of-heaven. Mean density of tree-of-heaven throughout the roads surveyed in Virginia was 39 km⁻¹. The interaction between road classification (interstate, primary, and secondary) and physiographic region (mountain, piedmont, and tidewater) was significant; consequently, the density of tree-of-heaven along the different road classifications depended on the effect of the physiographic region and vice versa. Tree-of-heaven was fairly evenly distributed throughout Virginia ranging from 39 to 78% of 1.6-km road segments infested, but had a greater variation in density. Current areas with low densities could increase in density in the future. The highest density of tree-of-heaven was along interstate highways in the mountains (85 km⁻¹), followed by the tidewater (63 km⁻¹), and piedmont (46 km⁻¹) regions. Primary roads had a moderate density of tree-of-heaven with a range of 24 to 36 km⁻¹. Secondary roads had lower densities with 12 km⁻¹ and 41 km⁻¹ in the tidewater and mountain regions, respectively. Tree-of-heaven spreads primarily by wind-dispersed seeds from female trees, and populations bordering roadsides could serve as seed sources for further local and landscape spread.

Nomenclature: Tree-of-heaven, Ailanthus altissima (P. Mill.) Swingle

Management Implications: The invasive nonnative tree-of-heaven invades newly disturbed areas and forms large monospecific stands. The mean density of tree-of-heaven throughout the 5,175 km of roads surveyed in Virginia was 39 km⁻¹ with mean infestation of 58% of 1.6-km road segments. Interstate highways had the highest tree-of-heaven densities and high infestation frequencies. Populations bordering the roads serve as seed sources for further dispersal along roads and into open and forested areas. Efforts to minimize the impact and spread of tree-of-heaven should be concentrated along the leading edge of infestations. Chemical applications and felling of mature female trees would reduce seed dispersal along roads and into adjacent forests. Reducing the amount of disturbed soil and quickly reseeding with native seeds would help in reducing new invasions of tree-of-heaven.