Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact helpdesk@bioone.org with any questions.
Downy brome (Bromus tectorum L.), an invasive winter annual grass, may be increasing in extent and abundance at high elevations in the western United States. This would pose a great threat to high-elevation plant communities and resources. However, data to track this species in high-elevation environments are limited. To address changes in the distribution and abundance of downy brome and the factors most associated with its occurrence, we used field sampling and statistical methods, and niche modeling. In 2007, we resampled plots from two vegetation surveys in Rocky Mountain National Park for presence and cover of downy brome. One survey was established in 1993 and had been resampled in 1999. The other survey was established in 1996 and had not been resampled until our study. Although not all comparisons between years demonstrated significant changes in downy brome abundance, its mean cover increased nearly fivefold from 1993 (0.7%) to 2007 (3.6%) in one of the two vegetation surveys (P = 0.06). Although the average cover of downy brome within the second survey appeared to be increasing from 1996 to 2007, this slight change from 0.5% to 1.2% was not statistically significant (P = 0.24). Downy brome was present in 50% more plots in 1999 than in 1993 (P = 0.02) in the first survey. In the second survey, downy brome was present in 30% more plots in 2007 than in 1996 (P = 0.08). Maxent, a species–environmental matching model, was generally able to predict occurrences of downy brome, as new locations were in the ranges predicted by earlier generated models. The model found that distance to roads, elevation, and vegetation community influenced the predictions most. The strong response of downy brome to interannual environmental variability makes detecting change challenging, especially with small sample sizes. However, our results suggest that the area in which downy brome occurs is likely increasing in Rocky Mountain National Park through increased frequency and cover. Field surveys along with predictive modeling will be vital in directing efforts to manage this highly invasive species.
Nomenclature: Downy brome, Bromus tectorum L
Interpretive Summary: The data from field study plots sampled over the last 15 yr suggest that downy brome is spreading at high elevations in Rocky Mountain National Park. We applied a model that used environmental conditions where downy brome is found in the Park to predict where the plant was likely to spread. All three generated models showed a similar predicted distribution that was greater than the current distribution of downy brome in Rocky Mountain National Park. Many of the new locations of downy brome occurred where the earlier models predicted they would occur. This indicates that downy brome may likely continue spreading within this high-elevation region.
The models suggest that areas close to roads and trails, at lower elevations, and in shrubland plant communities in the park are most likely to be invaded by downy brome. Knowledge of both the high-risk areas and environmental factors that support the growth and spread of downy brome can greatly increase the efficiency of management efforts. Maxent is a geospatial model, so its mapping images can help focus weed management and control on areas with a high probability of spread as well as areas of high resource value. Using this or similar models can reduce the time and effort managers spend searching for weeds in areas of high priority but low probability of occurrence.
We evaluated the efficacy of the biological control agent, red-headed leafy spurge stem borer, against the nonnative invasive plant leafy spurge. Our three treatments were release of the biological control agent into uncaged plots, release of the biological control agent into plots caged to prevent agent escape, and control plots caged to prevent agent entry. These treatments were replicated three times at six sites in the western United States. We measured leafy spurge biomass for 1 or 2 yr following release. We also measured the percentage of leafy spurge stems showing evidence of red-headed leafy spurge stem borer oviposition for either 1 or 2 yr following agent release, depending on the site. Red-headed leafy spurge stem borer did not demonstrably reduce leafy spurge biomass in our study. Moreover, compared to the release year, evidence of red-headed leafy spurge stem borer oviposition declined with time, suggesting the agent population was diminishing. This suggests the agent is incapable of building large populations capable of controlling leafy spurge at the sites we studied. However, after being released, populations of biological control agents sometimes go through long lag phases and then begin rapid population increases, so we cannot completely dismiss the possibility that red-headed leafy spurge stem borer might become effective given more time.
Nomenclature: Red-headed leafy spurge stem borer, Oberea erythrocephala Schrank.; leafy spurge, Euphorbia esula L
Interpretive Summary: Invasion of nonnative plants into forest and rangelands is of great concern to federal and state agencies, ranchers, and private land owners. The primary methods to control or manage invasive plants are the application of herbicides and biological control. Each of these methods is suited to application in differing situations. Insects as agents to biologically control plants are commonly employed to attack several areas of the plant (roots, stems, foliage, flowers, or seeds). Therefore, several different species of insects are introduced to manage a single species of plant. Some insect species can establish and quickly impact plant vigor and the overall population. Other insect species are slow to establish and take years to impact the host plant. We evaluated the impact of Oberea erythrocephala, the red-headed leafy spurge stem borer released in caged and uncaged plots of leafy spurge (Euphorbia esula). Our study indicated that within a 2-yr period, this insect does not demonstrably reduce the biomass of leafy spurge. Since large resources are spent in collecting and distributing O. erythrocephala this information is of importance and value to land managers throughout the West.
Smooth brome and Kentucky bluegrass are introduced cool-season perennial grasses known to invade grasslands throughout North America. During the fall of 2005 and spring of 2006, we implemented a restoration study at six native prairie sites in eastern South Dakota that have been invaded by smooth brome and Kentucky bluegrass. Treatments included five herbicide combinations, a fall prescribed burn, and an untreated control to determine the potential of each for renovation of invaded native grasslands. Herbicide treatments tested were sulfosulfuron, imazapyr, imazapic sulfosulfuron, and imazapyr imazapic, and were applied in late September 2005 and mid-May 2006. Untreated control plots averaged 64% (± 3.1) smooth brome cover and 38% (± 5.5) Kentucky bluegrass cover after the third growing season. Smooth brome cover in herbicide treated plots ranged from 6 to 23% and Kentucky bluegrass cover ranged from 15 to 35% after the third growing season. Smooth brome cover was 20% (± 2.9) and Kentucky bluegrass cover was 19% (± 4.0) in burned plots after the third growing season. Spring and fall treatments had similar native plant cover after three growing seasons. Spring and fall application of 0.33 kg ai ha−1 imazapyr and 0.10 kg ai ha−1 imazapic 0.16 kg ai ha−1 imazapyr had ≤ 10% smooth brome cover and increased native species cover after three growing seasons. Herbicides were effective at reducing cover of smooth brome and Kentucky bluegrass, and can be incorporated with other management strategies to restore prairie remnants.
Interpretive Summary: Smooth brome and Kentucky bluegrass are introduced forage grasses that are known to invade native grasslands throughout North America. Effective management strategies for controlling these species in native grasslands have not been developed. In this study we compared the efficacy of prescribed fire and multiple herbicide combinations to control smooth brome and Kentucky bluegrass while minimizing harm to native species. We evaluated spring and fall application of herbicides to determine if they have any significant effect (positive or negative) on these species, as well as native species. Our results indicate that several herbicide combinations show potential for restoring native prairie fragments, but prescribed fire did not provide adequate long-term control. Applications of imazapyr herbicide resulted in the most consistent control of smooth brome. Initial reductions in Kentucky bluegrass cover were observed during the study, but cover increased throughout the study and likely will require further management to achieve desired control. Spring-treated plots had much more bare ground and visible injury to surviving plants than did the fall treatments after the first growing season. These herbicide treatments reduced cover of smooth brome and Kentucky bluegrass and can be integrated with other strategies to restore native prairie remnants.
Black and pale swallowwort (BSW and PSW, respectively) are perennial, herbaceous vines in the Apocynaceae that are native to Europe. The species are becoming increasingly abundant in the northeastern United States and southeastern Canada and are difficult to manage. However, we know little about the demographic parameters of these species. We determined the survival, annual rate of vegetative growth, and fecundity of mature clumps of these swallowwort species. We selected four PSW sites (three of which comprised both old-field and forest habitats) in central New York and three BSW old fields in southeastern New York. BSW is largely restricted to higher light habitats in its introduced range. In each habitat, we followed the growth of 30 to 32 randomly selected clumps of similar size (2 to 5 stems clump−1 in the initial year) for 3 to 4 yr. Yearly survival was 99.6 ± 0.3% [mean ± standard error] for PSW and 100 ± 0% for BSW. In old fields, vegetative expansion varied from −0.01 ± 0.1 to 4.6 ± 0.4 stems clump−1 yr−1 for BSW and −0.02 ± 0.2 to 2.1 ± 0.5 stems clump−1 yr−1 for PSW. In forests, PSW growth was lower with vegetative expansion ranging from −0.01 ± 0.1 to 0.8 ± 0.2 stems clump−1 yr−1. Fecundity of PSW in 2007 and 2008 (130 ± 10 viable seeds stem−1 yr−1) was similar to BSW (100 ± 10 viable seeds stem−1 yr−1). Fecundity of PSW in forests was generally lower than PSW in old fields, but it varied greatly among sites (0 to 170 viable seeds stem−1 yr−1). We found that stem growth and fecundity did not vary with clump size (stems per clump). Since vegetative expansion and fecundity rates were high in old-field habitats, but were generally low or nonexistent in forest habitats, we suggest that management of these two invasive vines be focused in higher light environments to reduce overall seed production and its subsequent spread to surrounding areas.
Interpretative Summary: Black swallowwort (BSW) and pale swallowwort (PSW) are climbing herbaceous perennials related to milkweeds. Although both vines were introduced from Europe into the northeastern United States and southeastern Canada in the latter 1800s, they increasingly have become problematic in the last 20 yr. Many gaps remain in our knowledge of swallowwort field biology, which can vary by plant species and habitat. We found that nearly all mature plants survived during a 4-yr field study in New York in which we tracked individual plants in relatively low-density stands in old fields (BSW and PSW) and forest understories (PSW only). We rarely have observed BSW in heavily shaded forests. Both species annually increased in size through the production of additional stems, and this was generally similar for PSW and BSW in old fields and much less for PSW in forests. BSW and PSW in old fields also produced the same amount of viable seed, but PSW in forests produced less seed. However, both reproduction and vegetative expansion by PSW in forests varied greatly, depending on the amount of light within the forest. Based on our findings in this study, it does not appear that the two species should require different strategies for management. We suggest that management of swallowwort should be focused in higher light environments, where vegetative growth and reproduction is greatest, to reduce seed production and thereby minimize its spread to other habitats.
Cogongrass invades forests through rhizomatous growth and wind-dispersed seeds. Increased density and abundance of woody vegetation along forest edges may strengthen biotic resistance to invasion by creating a vegetative barrier to dispersal, growth, or establishment of cogongrass. We evaluated differences in dispersal of cogongrass spikelets experimentally released from road edges into tallgrass-dominated and shrub-encroached longleaf pine forests (Pinus palustris). Average maximum dispersal distances were greater in the pine–tallgrass forest (17.3 m) compared to the pine–shrub forest association (9.4 m). Spikelets were more likely to be intercepted by vegetation in pine–shrub forests compared to pine–tallgrass forests. Results suggest that dense woody vegetation along forest edges will slow spread from wind-dispersed cogongrass seeds.
Interpretative Summary: It has been suggested that dense woody vegetation along forest edges may form a barrier to invasive species either through effects on microhabitat or effects on seed dispersal. This study evaluated use of dense woody vegetation along forest edges as a barrier to seed dispersal into forest interiors. In this study, more cogongrass spikelets dispersed farther into open longleaf pine forests with a tallgrass understory compared to longleaf pine forests with dense shrubby understories. Reduced wind speed and increased vegetative interception of spikelet in the shrub-encroached forests may have prevented greater dispersal into these forests. However, a few spikelets released into open or shrubby forests dispersed farther than could be measured. These results suggest that managers seeking to control cogongrass may benefit by maintaining dense woody edges along forests and prioritizing management techniques that prevent spread of or treat cogongrass growing near less densely wooded habitats. These results also suggest that although dense woody vegetation may slow spread of cogongrass into forest interiors, such vegetation is unlikely to completely prevent invasion. Therefore, managers will need to implement additional control techniques in order to protect these forested areas from invasion.
Bridal creeper has become a serious environmental weed in southern Australia. Historically the invaded areas had low soil nutrient levels. However, our field surveys indicate that soils in bridal creeper–invaded areas have higher phosphorus and iron levels than soils in nearby native reference areas regardless of the proximity to agriculture or other disturbances. A glasshouse experiment was undertaken to determine the influence of increased nutrients on plants that co-occur with bridal creeper in order to (1) assess the impact of changed soil conditions and (2) predict the response of dominant species following the biological control of bridal creeper. The relative growth rate (RGR) of bridal creeper, two native shrubs (narrow-leaved thomasia [Thomasia angustifolia] and bluebell creeper [Billardiera heterophylla]), and an invasive exotic grass (annual veldt grass [Ehrharta longiflora]) were determined in three soil types: soil collected within a bridal creeper stand, soil collected from a nearby reference area, and a potting mix with nutrient levels higher than that recorded in the field. The plant species were chosen due to their association with bridal creeper. For example, the native species narrow-leaved thomasia was identified in a previous survey as the most abundant shrub at the invaded site where the soil was collected. The two other species, bluebell creeper and annual veldt grass, were identified from a previous seedbank trial as being abundant (in the seedbank) and able to readily germinate in invaded areas. When grown in either the bridal creeper–invaded soil or reference soil, bluebell creeper had significantly lower RGRs than narrow-leaved thomasia and annual veldt grass. However, as all these species showed increases in RGRs between reference soil and bridal creeper soil, this study indicates that for at least these three species the impact of increased nutrients may not be a barrier to the recovery of invaded areas following the control of bridal creeper.
Interpretive Summary: In nutrient-poor environments, soil nutrient enrichment can favor invasions by exotic plant species (weeds) into native areas. The South African geophyte bridal creeper (Asparagus asparagoides) has become a serious environmental weed in southern Australia and field surveys indicate that bridal creeper–invaded areas have higher nutrient levels, especially available phosphorus (P) and relative iron (Fe). Many studies from outside Australia have investigated the relationship between exotic plants and soil nitrogen. However, P may be more important in many regions of Australia, and in other areas globally where P is low, given that native species richness has been found to be inversely related to P, whereas exotic species richness and cover has been reported to be positively correlated to P. It is unknown if bridal creeper originally invaded areas with higher nutrients; however, it could be the case that bridal creeper invades both P-rich and P-poor environments. Bridal creeper plants that survive in the poorer soils may slowly change the soil conditions, through changes to nutrient cycling or through the use of strategies to enhance the acquisition of normally unavailable P from soil. The high levels of soil nutrients below bridal creeper have not facilitated the invasion or expansion of other exotic plant species. As all the native and exotic species tested in this study showed increases in relative growth rates between relatively nutrient-poor reference soil and
Rehabilitation of downy brome–infested shrublands is challenging once this invasive grass dominates native communities. The effectiveness of imazapic herbicide in reducing downy brome cover has been variable, and there is uncertainty about the impacts of imazapic on native species. We used a before-after-control-impact (BACI) field experiment and greenhouse studies to (1) determine if imazapic herbicide applied at 132 g ai ha−1 (8 oz/ac−1) and seeding with two native shrub species (Wyoming big sagebrush [Artemisia tridentata] and Mexican cliffrose [Purshia mexicana]) reduced downy brome cover and promoted shrub establishment, (2) assess potential effects of imazapic on nontarget plant species and plant community composition, and (3) determine if imazapic affected downy brome or seeded shrub species when applied at different developmental stages. Seeding shrubs, alone, or in combination with imazapic application, did not significantly increase shrub density, possibly because of droughty conditions. In the field, imazapic reduced downy brome cover by 20% and nontarget forb cover by 25% and altered plant community composition the first year after treatment. Imazapic was lethal to downy brome at all growth stages in the greenhouse and reduced shrub germination by 50 to 80%, but older shrub seedlings were more tolerant of the herbicide. We conclude that a one-time application of imazapic combined with seeding shrubs was only slightly effective in rehabilitating areas with high downy brome and thatch cover and resulted in short-term impacts to nontarget species. These results highlight the need to treat downy brome infestations before they become too large. Also, removing thatch prior to treating with imazapic, although likely lethal to the native shrubs we studied, could increase the effectiveness of imazapic.
Nomenclature: Imazapic; downy brome, Bromus tectorum L.; Mexican cliffrose, Purshia mexicana (D. Don) Henrickson; Wyoming big sagebrush, Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young. Nomenclature of all plants follows the USDA-NRCS PLANTS database ( http://plants.usda.gov/), and common names of invasive plant species follow the WSSA database ( http://www.wssa.net/Weeds/ID/WeedNames/namesearch.php).
Interpretive Summary: Downy brome is a highly invasive annual grass that can outcompete native plant species and increase the frequency of fires. We examined if treatment with imazapic herbicide and/or seeding with native shrubs was effective in rehabilitating shrublands highly invaded by downy brome. We also determined the effects of imazapic on different growth stages of both downy brome and three shrub species in the greenhouse. Imazapic was lethal to downy brome at all growth stages in the greenhouse, yet only reduced downy brome cover by 20% for one season in the field, likely due to high thatch cover and the large amount of available downy brome seeds. Imazapic also altered plant community composition and reduced forb cover by 25% in the field the first year after treatment. Shrub establishment was low in all seeding treatments, probably because of droughty conditions. Shrub germination was reduced in the greenhouse by up to 80% by imazapic, yet remnant shrubs in the field and 4-mo-old shrubs in the greenhouse were tolerant of the herbicide, leading us to recommend that imazapic be applied after shrubs are established instead of at the time of seeding. We conclude that a one-time imazapic application and seeding treatment was minimally effective in reducing downy brome or increasing shrub density, but fortunately, the disturbances associated wi
Coral ardisia (Ardisia crenata) has been present in Florida for more than 100 yr as an ornamental and has become invasive in hammocks of natural areas. This plant forms dense understory cover, often greater than 90%, which can suppress native plant recruitment and growth. Results from herbicide trials at two sites in Florida indicate that a single foliar treatment applied as a spot application of triclopyr amine, triclopyr ester, glyphosate, imazapic, dicamba, triclopyr amine imazapic, or triclopyr ester fluroxypyr reduced Ardisia crenata to less than 13% at 12 mo after treatment (MAT). A single treatment of imazapic (2.4 g ae L−1) or imazapic (2.4 g ae L−1) triclopyr (10.8 g ae L−1) reduced cover of mature plants to less than 0.5% and seedlings to less than or equal to 4% at 12 MAT. Native plant cover was less than 5% prior to treatment indicating that dense infestations of Ardisia crenata may suppress native vegetation. In the dense infestations of Ardisia crenata observed in this study, nontarget damage was not a concern due to the rarity of native plants. However, applicators should use caution applying triclopyr and imazapic when small shrubs and trees are present in the treatment area. Additional follow-up treatments will be required for control of seedling and possible resprouts at 12 MAT.
Interpretive Summary: Coral ardisia (Ardisia crenata) is an invasive plant of natural areas throughout Florida that forms dense understory cover and suppresses native plants. This plant exhibits the potential to spread throughout all the southernmost states in the United States from North Carolina to California. These results from herbicide trials at two field sites in north-central Florida indicate that a single application of triclopyr, dicamba, imazapic, glyphosate, triclopyr imazapic, ortriclopyr fluroxypyr suppressed mature cover of Ardisia crenata for 12 mo. Seedling cover 12 mo after treatment was highly variable but tended to be very low in treatments containing imazapic. This study indicates that Ardisia crenata is effectively controlled with herbicides, but monitoring and retreatment at 12 mo or less following the initial treatment will be required for further suppression, especially for emerging seedlings. Longer studies are suggested to evaluate the response of native plant recovery following herbicide treatment of Ardisia crenata.
Smooth brome (Bromus inermis) is an introduced, cool-season perennial, sod-forming grass that has been shown to invade both native cool-and warm-season grasslands throughout North America. During the fall of 2005 through spring 2007, we implemented a smooth brome removal study at five sites in eastern South Dakota. Sites were selected to represent a range of soil and environmental conditions. Seven fall herbicide treatments, five spring herbicide treatments, an untreated plot that was planted with a native seed mix, and an untreated control that received no herbicide or seed addition were applied at each location in fall 2005/spring 2006 and fall 2006/spring 2007. Based upon first-year results, three fall herbicide treatments and two spring herbicide treatments were added in fall 2006/spring 2007. Sites were seeded with a native plant mix within 2 wk following spring herbicide treatment. Smooth brome cover in untreated plots ranged from 73 to 99% at the conclusion of the study. Smooth brome cover on herbicide-treated plots ranged from 0 to 84% on 2005/2006 plots and 0 to 98% on 2006/2007 plots after three growing seasons. Native plant response varied by site and treatment, possibly due to competition from exotic weeds. Although several herbicides show promise for control of smooth brome, future response of native plants will be important in determining the proper timing and herbicide combination.
Interpretive Summary: Smooth brome (Bromus inermis) is an introduced, cool-season perennial, sod-forming grass that has been widely planted as a forage species. However, it is also an aggressive grass that can rapidly invade native cool-and warm-season grasslands throughout North America. Much work has been devoted to developing management strategies for smooth brome. Many of the past studies utilized herbicides that are no longer labeled for use in certain situations, or required conversion of invaded areas to agriculture for several years prior to planting native species. New herbicides have the potential to allow direct conversion of smooth brome–dominated areas to native plant communities without prior conversion to agriculture. In this study we compared the efficacy of several herbicide combinations to control smooth brome, while allowing the establishment of planted native species. We also evaluated spring and fall application timings to determine if they have any significant effect (positive or negative) on smooth brome control, as well as native plant establishment. Several herbicide combinations show potential for controlling smooth brome and allowing establishment of planted native species. Treatments with sulfosulfuron glyphosate and imazapyr provided the most consistent smooth brome control during the study. Treatments that showed the greatest reduction in smooth brome also tended to have the highest cover of planted species. Caution still has to be exercised when using high rates of imazapyr, as it can cause injury to planted species. These results will allow managers to convert smooth brome–dominated fields to native plant communities without first converting them to agriculture, decreasing the amount of time necessary to achieve a successful conversion.
A total of 24 pre-and posttreatment plant frequency data sets were analyzed from 15 Wisconsin lakes treated with granular 2,4-D BEE herbicide for the control of Eurasian watermilfoil (Myriophyllum spicatum). Six data sets from four untreated control lakes were analyzed for comparison. The data sets included the results of line-transect aquatic plant surveys and point-intercept aquatic plant surveys. The results from these two survey methods were analyzed separately. Analysis of pre-and posttreatment changes in frequency of occurence for 46 species of aquatic plants indicated Eurasian watermilfoil was the only species to show significant declines in all the surveys. At application rates of 112 kg ha−1, Eurasian watermilfoil declined an average 65.9% among the line-transect surveys; and 58.0% among the point-intercept surveys. At application rates of 168 kg ha−1, Eurasian watermilfoil declined by 94.4% and 76.5% among line-transect and point-intercept surveys, respectively. Among the control lakes, Eurasian watermilfoil increased an average of 77% in year 1 and 24% in year 2. Northern watermilfoil (Myriophyllum sibiricum), a closely related native plant, underwent declines in frequency at the higher 2,4-D application rate (20.0%) but showed an increase (88.9%) at the lower rate among the line-transect surveys. Northern watermilfoil exhibited declines at both rates among the point-intercept surveys (48 and 50%, respectively); however, the plant also exhibited declines in the control lakes in year 2. Most other native aquatic plant species were unaffected or showed increases following treatment with 2,4-D BEE. The high degree of selectivity to Eurasian watermilfoil found in this survey of operational treatments with 2,4-D BEE suggests that this herbicide is an important tool for restoring plant communities that have been degraded by Eurasian watermilfoil.
On the west coast of North America and in Australia, there have been parallel cases of sequential invasion and replacement of the shoreline plant American sea-rocket by European sea-rocket. A similar pattern has also occurred in New Zealand. For 30 to 40 yr, from its first recording in 1921, American sea-rocket spread throughout the eastern coastlines of the North and South Islands of New Zealand. European sea-rocket has so far been collected only on the North Island. From its first collection in 1937, European sea-rocket spread to the northern extremity of the island by 1973, and by 2010, it had reached the southernmost limit. In the region where both species have occurred in the past, American sea-rocket is now rarely found. This appears to be another example of congeneric species displacement.
Nomenclature: American sea-rocket, Cakile edentula (Bigelow) Hook.; European sea-rocket, Cakile maritima Scop
This article is only available to subscribers. It is not available for individual sale.
Access to the requested content is limited to institutions that have
purchased or subscribe to this BioOne eBook Collection. You are receiving
this notice because your organization may not have this eBook access.*
*Shibboleth/Open Athens users-please
sign in
to access your institution's subscriptions.
Additional information about institution subscriptions can be foundhere
