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This page lists all time most cited articles for this title. Please use the publication date filters on the left if you would like to restrict this list to recently published content, for example to articles published in the last three years. The number of times each article was cited is displayed to the right of its title and can be clicked to access a list of all titles this article has been cited by.
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Geographic Origins and Genetic Diversity of Air-Potato (Dioscorea bulbifera) in Florida
- Matthew D. Croxton, Michael A. Andreu, Dean A. Williams, William A. Overholt, Jason A. Smith
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 22-30
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In Florida, air-potato is an invasive weed with high management priority, which may soon be targeted using classical biological control. This yam was introduced during the early 20th century by the United States Department of Agriculture (USDA) from areas throughout its extensive range. Our objectives were to characterize the genetic diversity of the invasive population in Florida and to identify the source regions of introduction. Authorities have often asserted the African provenance of the species in Florida, but our analyses, conducted using chloroplast markers, indicate that Florida air-potato is more similar to specimens examined from China than to those from Africa. Low intraspecific genetic diversity in Florida indicates that the invasive population was the result of at least two introductions becoming established in Florida.
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Effects of Picloram Application on Community Dominants Vary With Initial Levels of Spotted Knapweed (Centaurea stoebe) Invasion
- Yvette K. Ortega, Dean E. Pearson
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 70-80
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Broadleaf herbicides are commonly used to suppress exotic weeds with the intent of releasing native species from negative impacts of invasion. However, weed control measures can also have unintended consequences that should be considered along with intended effects. We conducted a controlled field experiment within bunchgrass communities of western Montana to examine if broadcast application of the broadleaf herbicide, picloram, may mitigate impacts of the exotic forb, spotted knapweed, on the dominant native grass, bluebunch wheatgrass, and forb, arrowleaf balsamroot. Local-scale relationships between native species and spotted knapweed cover served as a baseline for evaluating treatment effects at differing spotted knapweed invasion levels. To examine secondary invasion, we also measured treatment effects on the exotic grass, downy brome, relative to initial levels of spotted knapweed cover. Picloram application suppressed spotted knapweed cover by 70 to 80%. Treatment appeared to release cover and seed production of bluebunch wheatgrass, causing increases that varied positively with initial spotted knapweed cover. Bluebunch wheatgrass measures were elevated by as much as fourfold in treated vs. control plots, exceeding baseline levels in noninvaded plots. For arrowleaf balsamroot, negative effects of treatment prevailed, particularly where initial spotted knapweed cover was low. Arrowleaf balsamroot cover and fecundity variables were reduced by as much as 60% in treated vs. control plots, to levels typifying baseline conditions in highly invaded plots. In addition, treatment released downy brome, with cover increases from 2- to 20-fold. A controlled experiment selectively removing spotted knapweed showed similar release of downy brome. Our results show that picloram effects can depend on initial levels of weed invasion and may include substantial side effects, particularly when broadcast applications are used. Integrated approaches that include seeding of desirable species may be needed to enhance plant community resistance to secondary invaders and reinvasion by the target weed.
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Mapping Giant Reed (Arundo donax) Infestations along the Texas–Mexico Portion of the Rio Grande with Aerial Photography
- Chenghai Yang, James H. Everitt, John A. Goolsby
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 402-410
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Giant reed is an invasive weed throughout the southern half of the United States, with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. The objective of this study was to use aerial photography to map giant reed infestations and to estimate infested areas along the Texas–Mexico portion of the Rio Grande. Aerial color-infrared photographs were taken along the Rio Grande between Brownsville and El Paso, TX, in June and July 2002. Based on the aerial photographs and ground surveys, the portion of the river from San Ygnacio to Lajitas, which has a river length of 898 km (558 mi), was found to be infested with giant reed. To estimate infested areas along both sides of the river, 65 (13.5%) of the 480 aerial photographs taken between Lajitas and San Ygnacio were randomly selected. The aerial photographs were digitized, rectified to Google Earth imagery, and then classified using maximum-likelihood classification techniques. The infested areas on both sides of the river, as well as water area and river length, from each photographic image were determined. Based on the estimates from the 65 aerial photos, the ratio of giant reed area to water area and the ratio of giant reed area to river length were calculated. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio was estimated to be 5,981 ha (14,779 ac) with 3,714 ha or 62% on the U.S. side and 2,267 ha or 38% on the Mexican side. This study provides the first accurate estimates of giant reed infestations along the Texas–Mexico portion of the Rio Grande and will be useful for both land owners and government agencies for the estimation of water usage and economic loss and for the management and control of giant reed.
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Effect of Aminopyralid on Canada Thistle (Cirsium arvense) and the Native Plant Community in a Restored Tallgrass Prairie
- Travis L. Almquist, Rodney G. Lym
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- 20 January 2017, pp. 155-168
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Aminopyralid efficacy on Canada thistle (Cirsium arvense) and potential to injure native species was evaluated in a restored prairie at the Glacial Ridge Preserve managed by The Nature Conservancy in Polk County, MN. Canada thistle stem density was reduced from 17 to 0.1 stems m−2 10 mo after treatment (MAT) with aminopyralid applied in the fall at 120 g ha−1. Aminopyralid also altered the composition of both Canada thistle–infested and native plant communities. Aminopyralid controlled Canada thistle and removed or reduced several undesirable forb species from the restored prairie communities, such as absinth wormwood (Artemisia absinthium) and perennial sowthistle (Sonchus arvensis). A number of high seral forbs were also reduced or removed by aminopyralid, including maximilian sunflower (Helianthus maximiliani) and purple prairie clover (Dalea purpurea). Foliar cover of high seral forbs in the native plant community was reduced from 12.2 to 7% 22 MAT. The cover of high seral grass species, such as big bluestem (Andropogon gerardii) and Indiangrass (Sorghastrum nutans) increased after aminopyralid application in both the Canada thistle–infested and native plant communities and averaged 41.4% cover compared with only 19.4% before removal of Canada thistle. Species richness, evenness, and diversity were reduced after aminopyralid application in both Canada thistle–infested and native plant communities. However, the benefits of Canada thistle control, removal of undesirable species, and the increase in native grass cover should lead to an overall improvement in the long-term stability and composition of the restored prairie plant community, which likely outweigh the short-term effects of a Canada thistle control program.
- Cited by 23
Seed Mass, Viability, and Germination of Japanese Stiltgrass (Microstegium vimineum) under Variable Light and Moisture Conditions
- Cynthia D. Huebner
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- 20 January 2017, pp. 274-283
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The success of Japanese stiltgrass as an invader may be due to its ability to respond to stochastic events (e.g., by sexual reproduction via chasmogamous [CH] flowers) and to maintain a beneficial genetic make-up (e.g., by self-fertilizing via cleistogamous [CL] flowers) when conditions are stable. This paper evaluates the importance of Japanese stiltgrass seed type (chasmogamous seeds, cleistogamous seeds, and seeds originating from forest-interior [F-I] plants) in terms of seed mass, viability, and germination across variable moisture regimes (three regions in West Virginia) and at two light levels (roadside and forest interior). Seeds from nine populations were sampled in three site types in 2005 and 2008 and stored at 5 C until testing in April 2009. Seeds were tested for viability using a dye test. Seeds were germinated under both constant and fluctuating day/night temperatures. Additional samples of CH and CL seeds collected in 2008 were tested for viability again in September 2010 for a measure of seed longevity. CL and F-I seeds were smaller in mass than CH seeds. Seeds from the drier sites were smaller in mass than seeds from the more mesic sites. CL seeds, followed by F-I seeds, were less viable than CH seeds in 2005 and 2008. CL and F-I seeds had lower germination rates than CH seeds for each site type in 2005, but germination rates of the seed types did not differ in 2008. Differences in seed longevity for 2008 seeds were lower for CL compared to CH seeds, but only in the drier sites. Japanese stiltgrass' longer-lived and larger CH seeds from the roadsides may ensure population survival over the long term. Younger CL and F-I seeds differ less from CH seeds in terms of germination than older seeds, which may help Japanese stiltgrass to maintain populations under relatively stable conditions in the short term.
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Seasonal Change in Forage Value of Rangeland Weeds in Northern Idaho
- Rachel A. Frost, Linda M. Wilson, Karen L. Launchbaugh, Elayne M. Hovde
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- 20 January 2017, pp. 343-351
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Prescribed grazing is an effective tool for controlling some rangeland weeds. Forage quality of eight nonnative rangeland weeds common to northern Idaho was determined. Five collection sites were established for each weed species: rush skeletonweed, meadow hawkweed, houndstongue, sulfur cinquefoil, yellow starthistle, Dalmatian toadflax, hoary cress, and tansy ragwort. Plants were collected at rosette, bolt, flower, and seed set stages; dried and separated into leaves, stems, flowers, or seed; and analyzed separately for crude protein (CP), neutral detergent fiber (NDF), and mineral content (ash). As expected, plants became more fibrous as they matured because stems increased in NDF value throughout the season and the leaf : stem ratio of most weeds we examined decreased throughout the season. In general, the weeds we examined expressed only moderate fiber levels, beginning the season with NDF values near 34% in the rosette stage and becoming near 52% NDF in the seed set stage. CP values were near 25% in the rosette stage for houndstongue, rush skeletonweed, and hoary cress whereas other weeds we examined had about 15% CP in the rosette. As the season advanced, all plants lost protein content and ended the season with CP values from 5 to 8% at seed set. Ash values declined for all species as the season progressed. Our results indicate that these weeds have forage values similar to many native plants and could be reasonable forage resources for livestock. We did not examine the content of secondary compounds in these weeds that may render them unpalatable and limit their forage value.
- Cited by 23
Prescribed Extreme Fire Effects on Richness and Invasion in Coastal Prairie
- Dirac Twidwell, William E. Rogers, Elizabeth A. McMahon, Bryce R. Thomas, Urs P. Kreuter, Terry L. Blankenship
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- 20 January 2017, pp. 330-340
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Widely-held, untested assumptions in many prairies are that high-intensity fires conducted during droughts will decrease native herbaceous species richness and lead to rapid invasions by alien species. We compared native and exotic herbaceous species richness and aboveground herbaceous biomass one year following the application of high-intensity growing-season fires in Texas coastal prairie. Fires were conducted in June 2008, when precipitation was 96% below the long-term monthly average, at the end of a severe 5-mo drought, resulting in high fire intensities within treatment units. Native forb species richness was greater in burned than unburned areas. In contrast, species richness of native grasses, exotic forbs, and the frequency of King Ranch (KR) bluestem [Bothriochloa ischaemum (L.) Keng.] did not significantly differ between burned and unburned treatments. The potential to use prescribed extreme fire to maintain native herbaceous species richness while not increasing KR bluestem provides preliminary evidence that growing season fires conducted during droughts can be a viable management strategy in coastal prairies.
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Comparing Effectiveness and Impacts of Japanese Barberry (Berberis thunbergii) Control Treatments and Herbivory on Plant Communities
- Jeffrey S. Ward, Scott C. Williams, Thomas E. Worthley
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 459-469
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Two factors that can degrade native plant community composition and structure, and hinder restoration efforts, are invasive species and chronic overbrowsing by ungulates such as white-tailed deer. Beginning in 2007, the effectiveness, costs, and impacts of Japanese barberry control treatments and herbivory on nonnative and native plant communities was examined at eight study areas over 4 to 5 yr. Prescribed burning and mechanical mowing by wood shredder or brush saw were utilized as initial treatments to reduce the aboveground portion of established barberry and were equally effective. Without a follow-up treatment, barberry had recovered to 56 to 81% of pretreatment levels 50 to 62 mo after initial treatment. Follow-up treatments in mid-summer to kill new sprouts included directed heating and foliar herbicide applications. Relative to untreated controls, follow-up treatments lowered barberry cover 50 to 62 mo after initial treatment by at least 72%. Although all follow-up treatments were equally effective, the labor cost of directed heating was four times higher than for herbicide applications. Follow-up treatment type (directed heating vs. herbicide) had minimal impact on species other than barberry. White-tailed deer herbivory had a larger impact on other species than did barberry control treatments. Native grass and fern cover was higher outside of exclosures. Areas inside exclosures had higher cover of Oriental bittersweet and multiflora rose, but not Japanese barberry. Thus, recovery of native communities will require more than simply removing the dominant invasive species where deer densities are high. Excellent reduction of Japanese barberry cover can be achieved using either directed heating or herbicides as follow-up treatments in a two-step process, but other invasive plants may become a problem when barberry is removed if deer populations are low.
- Cited by 22
Site Characteristics Determine the Success of Prescribed Burning for Medusahead (Taeniatherum caput-medusae) Control
- Guy B. Kyser, Morgan P. Doran, Neil K. McDougald, Steve B. Orloff, Ronald N. Vargas, Robert G. Wilson, Joseph M. DiTomaso
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 376-384
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Medusahead is one of the most problematic rangeland weeds in the western United States. In previous studies, prescribed burning has been used successfully to control medusahead in some situations, but burning has failed in other circumstances. In this study, trials were conducted using the same protocol at four locations in central to northern California to evaluate plant community response to two consecutive years of summer burning and to determine the conditions resulting in successful medusahead control. During 2002 through 2003 large-scale experiments were established at two low-elevation, warm-winter sites (Fresno and Yolo counties) and two higher elevation, cool-winter sites (Siskiyou and Modoc counties). Plant species cover was estimated using point-intercept transects, and biomass samples were taken in each plot. After 2 yr of burning, medusahead cover was reduced by 99, 96, and 93% for Fresno, Yolo, and Siskiyou counties, respectively, compared to unburned control plots. Other annual grasses were also reduced, but less severely, and broadleaf species increased at all three sites. In contrast, 2 yr of burning resulted in a 55% increase in medusahead at the coolest winter site in Modoc County. In the second season after the final burn, medusahead cover remained low in burned plots at Fresno and Yolo counties (1 and 12% of cover in unburned controls, respectively), but at the Siskiyou site medusahead recovered to 45% relative to untreated controls. The success of prescribed burning was correlated with biomass of annual grasses, excluding medusahead, preceding a burn treatment. It is hypothesized that greater production of combustible forage resulted in increased fire intensity and greater seed mortality in exposed inflorescences. These results demonstrate that burning can be an effective control strategy for medusahead in low elevation, warm-winter areas characterized by high annual grass biomass production, but may not be successful in semiarid cool winter areas.
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Invasion Potential of Chinese Tallowtree (Triadica sebifera) in California's Central Valley
- Michael J. Bower, Clare E. Aslan, Marcel Rejmánek
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- 20 January 2017, pp. 386-395
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The ecological effects of Chinese tallowtree are well documented in the southeastern United States, yet this known invasive plant continues to be planted extensively in California's Central Valley, where it has recently naturalized in several locations. Climate modeling suggests that most of California's lowland riparian habitat is susceptible to invasion by Chinese tallowtree; however, no field tests are available to corroborate this result for California or to identify local environmental constraints that might limit potential habitats. We used observational and experimental methods to evaluate invasion potential of Chinese tallowtree in riparian habitats in California's Central Valley. High invasion potential, indicated by an intersection of the maxima of dispersal probability, germination, and survivorship of seedlings, occurred at low elevations immediately next to perennial waters. The main factor limiting Chinese tallowtree invasion potential in more elevated habitats appears to be lack of seedling drought tolerance. These findings suggest that California's riparian habitats are vulnerable to invasion by Chinese tallowtree, especially downstream of current naturalized populations where water or bird dispersal will deposit seeds in environments ideal for germination and growth.
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Distribution and Potential Spread of Japanese Knotweed (Polygonum cuspidatum) in Canada Relative to Climatic Thresholds
- Robert S. Bourchier, Brian H. Van Hezewijk
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- 20 January 2017, pp. 32-39
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Japanese knotweed (JK) is one of the most aggressive invasive plants known in the U.K., where its biology has been well-studied. It was introduced into Canada around 1900, but only recently has it become a serious concern in the province of British Columbia (BC). Climatic conditions, including annual degree days and mean-annual minimum temperatures at knotweed sites in British Columbia were modeled in BioSIM, using weather normals and long-term daily weather data, and compared to published thresholds (degree day = 2,505 DD, minimum temperature = −30.2 C, base temperature 0 C). The degree-day threshold was more limiting to JK in British Columbia than mean-minimum temperature (12.3% of province habitat was suitable for JK based on degree days compared with 26% for mean-minimum temperature). A new annual-precipitation threshold of 735 mm/year based on 95% of known knotweed sites in BC was identified. The best-fit logistic regression model included degree days and annual precipitation and predicted knotweed presence/absence with over 97% efficiency. Existing knotweed sites occupy just over half of the suitable habitat in BC, indicating there are still significant areas to be invaded. The limiting threshold for knotweed was reversed in Southern Ontario with between 35 to 53% of the habitat suitable based on minimum temperatures, whereas degree-day accumulations and annual precipitation were not limiting. Warmer temperatures from 2000 to 2008 resulted in an increase to 53% of the habitat in Southern Ontario being suitable for knotweed, compared to 35% when 1971 to 2000 weather normals were used. Different climatic thresholds among provinces might result in selection for different invasive knotweed genotypes. This could influence the success of biological control agents because of differential host suitability of knotweed genotypes. Habitat suitability maps generated will enable better targeting of knotweed surveys based on the risk of knotweed establishment.
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Perennial Pepperweed (Lepidium latifolium): Properties of Invaded Tidal Marshes
- Laura K. Reynolds, Katharyn E. Boyer
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- 20 January 2017, pp. 130-138
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Lepidium latifolium (perennial pepperweed) is recognized as a threat to wetland habitats throughout much of the western United States, but its role in tidal marshes has not been explored. Over three seasons in three regions of San Francisco Estuary (Suisun, San Pablo, and South San Francisco bays), we characterized locations in tidal marshes where monotypic stands of L. latifolium are replacing the native Sarcocornia pacifica (pickleweed). Soils within L. latifolium stands had significantly lower moisture, salinity, organic matter, and carbon : nitrogen (C : N) and higher pH than in adjacent S. pacifica stands at similar elevation and distance from channels. In addition, L. latifolium canopies were 2 to 3 times taller, thus increasing light reaching soils, and tended to support different insect/spider assemblages (sampled only at the Suisun site). Patterns were generally consistent across the three sites, although less pronounced for some measures at the South Bay site. Overall, these data suggest that L. latifolium invasion of tidal marshes is leading to modification of both structural and functional properties, several of which might further facilitate spread of the invader; however, additional study is needed to determine cause vs. effect for several soil characteristics.
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Nonchemical and Herbicide Treatments for Management of Japanese Stiltgrass (Microstegium vimineum)
- Jeffrey Stuart Ward, Todd L. Mervosh
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- 20 January 2017, pp. 9-19
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Japanese stiltgrass, an annual grass species native to eastern Asia, has become a serious invasive-plant problem in the eastern United States. We compared the efficacy of herbicides and nonchemical options found effective for controlling stiltgrass in earlier studies, with organic herbicides and herbicides used at reduced rates in a wooded floodplain along the lower Connecticut River. We compared the effect of 2 yr of conventional and alternative treatments on cover of other nonnative and native species. Four blocks of 18 plots (3 by 4 m [9.8 by 13.1 ft]) were established in May 2008. Treatments included directed heating with a propane torch (June, July), hand-pulling (July), mowing with a string trimmer (July, August), foliar applications of household vinegar [5% acetic acid] (June, July) and the herbicides imazapic (June), pelargonic acid (June, July), and pelargonic acid plus pendimethalin (June). The following herbicides were applied at labeled doses and at one-fourth labeled doses: fenoxaprop-p-ethyl (July), glufosinate (August), and glyphosate (August). Stiltgrass cover and height were evaluated periodically, and plant samples were collected in autumn of 2008 and 2009 to determine the number of viable seeds produced. Final evaluations were conducted in June 2010 after 2 yr of treatment. Stiltgrass cover averaged 88% on untreated plots in fall. All treatments reduced stiltgrass cover and seed production. The least-effective treatments were hand-pulling, pelargonic acid, and vinegar in July. Direct heating, mowing, and vinegar in June reduced seed production by more than 90%. All treatments containing imazapic, pelargonic acid plus pendimethalin, fenoxaprop-p-ethyl, glufosinate, and glyphosate completely prevented stiltgrass seed production in the second year of treatment. Effective control of stiltgrass can be achieved during a 2-yr period with a variety of herbicides, including herbicides at one-fourth of the labeled dose, and through nonchemical treatments.
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Invasive shrub removal benefits native plants in an eastern deciduous forest of North America
- Erynn Maynard-Bean, Margot Kaye
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- 01 May 2019, pp. 3-10
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In eastern deciduous forests of North America, invasive shrubs are increasing in richness and abundance at the expense of native species across taxa. Invasive shrubs create an understory that is more dense than both recent and historical preinvasion conditions. Interest in invasive shrub removal to restore native habitat is growing, but our understanding of natural regeneration following treatment of a diverse invasive shrub community is lagging. Using an invasive shrub removal experiment, we provide insight into the effect of repeated removal of a suite of 18 invasive shrub species dominated by border privet (Ligustrum obtusifolium Siebold & Zucc.). In 2009, invasive shrubs were removed from five 20-m-diameter treatment plots, each with a paired control plot. Seven years later, we find an increase in plant diversity, native understory species abundance, and overstory tree species regeneration for individuals under a meter in height. For plants 1 to 4 m in height, the removal treatment has a positive effect on understory woody species, but there has been no change in regenerating overstory trees. A lack of overstory tree regeneration to greater heights is not surprising, given the time frame and the closed-canopy conditions. However, other factors, such as white-tailed deer (Odocoileus virginianus Zimmermann) browse, could be serving as an impediment to taller tree regeneration in the forest understory. An ambient sampling approach in unmanaged, invaded, and uninvaded forest has been used in other studies to estimate the potential impacts of invasive shrub species to native plant communities. However, in this study the ambient sampling approach underestimated the impacts of invasive shrubs compared to their experimental removal. Overall, invasive shrub removal increased plant diversity and allowed passive natural regeneration of native plants that exceeded native cover in the unmanaged, ambient forest under minimal invasive shrub abundance.
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Corallita (Antigonon leptopus): Intentional Introduction of a Plant with Documented Invasive Capability
- Janelle M. Burke, Antonio DiTommaso
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- 20 January 2017, pp. 265-273
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Corallita (Antigonon leptopus) is a perennial vine, lauded as an ornamental for its vigorous growth, and plentiful (usually) pink flowers, and even its ability to smother unsightly landscapes. In the United States it thrives in horticultural zones 8 to 10, and also is successfully grown worldwide in tropical climates. When corallita is neglected, it can grow quickly over other vegetation, spreading beyond its area of introduction. Once established, it is difficult to eradicate because it produces many tuberous roots that can propagate vegetatively. Its fruits are buoyant, allowing for successful seed dispersal in water. The islands of Guam (South Pacific Ocean) and St. Eustatius (Caribbean Sea) represent two regions where corallita has become so pervasive that it threatens local diversity. In Florida, already it is classified as a Category II invasive. Our report reviews the literature and past studies of corallita, in addition to adding new taxonomic and distribution information from herbarium specimens to clarify the identity and geographic range. It is recommended that introductions of this plant by the horticultural industry in both tropical and temperate regions be closely monitored to prevent spread. On tropical island nations, we advise against any new introductions.
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Legacy effects of invasive grass impact soil microbes and native shrub growth
- Brooke Pickett, Irina C. Irvine, Eric Bullock, Keshav Arogyaswamy, Emma Aronson
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- 01 May 2019, pp. 22-35
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In California, invasive grasses have displaced native plants, transforming much of the endemic coastal sage scrub (CSS) to nonnative grasslands. This has occurred for several reasons, including increased competitive ability of invasive grasses and long-term alterations to the soil environment, called legacy effects. Despite the magnitude of this problem, however, it is not well understood how these legacy effects have altered the soil microbial community and, indirectly, native plant restoration. We assessed the microbial composition of soils collected from an uninvaded CSS community (uninvaded soil) and a nearby 10-ha site from which the invasive grass Harding grass (Phalaris aquatica L.) was removed after 11 yr of growth (postinvasive soil). We also measured the survival rate, biomass, and length of three CSS species and P. aquatica grown in both soil types (uninvaded and postinvasive). Our findings indicate that P. aquatica may create microbial legacy effects in the soil that likely cause soil conditions inhibitory to the survival rate, biomass, and length of coastal sagebrush, but not the other two native plant species. Specifically, coastal sagebrush growth was lower in the postinvasive soil, which had more Bacteroidetes, Proteobacteria, Agrobacterium, Bradyrhizobium, Rhizobium (R. leguminosarum), Candidatus koribacter, Candidatus solibacter, and rhizophilic arbuscular mycorrhizal fungi, and fewer Planctomycetes, Acidobacteria, Nitrospira, and Rubrobacter compared with the uninvaded soil. Shifts in soil microbial community composition such as these can have important implications for restoration strategies in postinvasive sites.
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Soil–Occupancy Effects of Invasive and Native Grassland Plant Species on Composition and Diversity of Mycorrhizal Associations
- Nicholas R. Jordan, Laura Aldrich-Wolfe, Sheri C. Huerd, Diane L. Larson, Gary Muehlbauer
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- 20 January 2017, pp. 494-505
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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.
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Susceptibility of Exotic Annual Grass Seeds to Fire
- Sara B. Sweet, Guy B. Kyser, Joseph M. DiTomaso
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- 20 January 2017, pp. 158-167
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Prescribed burning can control invasive annual grasses that threaten the biological and economic value of California grasslands. Susceptibility of grass seed to burning can depend on burn timing, exposure time, and type of exposure (direct flame heat or convective heat); thus, these factors can influence the success of a prescribed burning program. To further investigate these factors, laboratory simulations were conducted on barb goatgrass, medusahead, and ripgut brome at several stages of seed maturity, as determined by percent moisture of the inflorescences. Seeds were exposed either to direct flame using a Bunsen burner or to heated air in a muffle furnace. Flame treatments were conducted at one temperature (∼400 C) and several exposure times (0 to 14 s), depending on the species. Furnace treatments included four temperatures (150, 200, 250, and 300 C) and seven exposure times (0, 10, 20, 30, 40, 60, or 80 s). Seed germination was analyzed for each temperature series to determine the LD50 and LD90 in seconds of exposure time. Susceptibility to furnace treatments, which simulated heat exposure of seeds on the soil surface, was not statistically different within a range of seed moisture levels for all three species. The LD50 values at 250 C (typical soil temperature with grassland fire) ranged from 28 to 49 s, which far exceeds the time of exposure during a typical grassland fire. Susceptibility to flame showed a similar lack of change over maturation of medusahead and barb goatgrass seeds, with LD90 values ranging between 4.8 and 7.4 s for all seed moisture levels. In contrast, ripgut brome seeds exposed to flame showed increasing susceptibility with reduced seed moisture content. The LD90 values for exposure were less than one second for seed moisture levels at or below 10%, compared to 3.7 s for seeds at 55 to 60%. Although flame susceptibility increased for ripgut brome, seeds at all maturation stages were more sensitive than medusahead and barb goatgrass. Additionally, the LD90 values for all three species are attainable under field conditions. Thus, burn prescriptions for these three species are not constrained by maturation stage, but should occur prior to seed drop and when fuel loading is high. This will maximize exposure time of seeds to direct flame.
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Reviewing the Role of Wildfire on the Occurrence and Spread of Invasive Plant Species in Wildland Areas of the Intermountain Western United States
- Lisa J. Rew, Mara P. Johnson
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 347-364
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Fire is unlikely to be a simple, deterministic process that will result in increased rates of invasion by nonnative plants. Relative dominance of nonnative plants at any postfire site likely results from a combination of factors, including propagule pressure (aboveground and belowground), time since invasion, interspecific competition, disturbance history, rainfall patterns, soil nutrients, environmental heterogeneity, land use, plus the actual fire dynamics. Consequently, the role different factors play in nonnative plant invasion is still relatively unexplained, and the possibility that wildfire may promote nonnative plant species remains a concern. Our aim was to evaluate the state of knowledge concerning how nonnative plant species establish, survive, and spread following wildfire in wildland areas for the main vegetation types of the Intermountain West. Although the particular invading species varied with vegetation type, the most frequently reported species were annual grasses (e.g., downy brome [Bromus tectorum], Japanese brome [Bromus japonicus]) and long-distance, dispersing forbs (e.g., Canada thistle [Cirsium arvense], common dandelion [Taraxacum officinale], and prickly lettuce [Lactuca serriola]). Overall, many of the reviewed studies found an increase, followed by a long-term decline, in nonnative species after wildfire, particularly when other disturbances were minimal. Regardless of this finding, many people consider rapid detection and control of new, nonnative plant populations after wildfire one of the most effective management activities. That axiom may be correct, if the nonnative propagule pressure is high and the anthropogenic disturbances are frequent, but if this is not the case the question to answer is whether immediate management, including reseeding, will benefit the system or whether off-target effects could make that approach undesirable. Continued investigation and increased quantitative analysis of the complex factors that likely contribute to changes in nonnative plants dynamics following wildfire should improve our understanding of the issue and assist managers in allocating limited resources.
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Evaluating Restoration Methods across a Range of Plant Communities Dominated by Invasive Annual Grasses to Native Perennial Grasses
- Priscilla A. Nyamai, Timothy S. Prather, John M. Wallace
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- Published online by Cambridge University Press:
- 20 January 2017, pp. 306-316
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Prairies are imperiled habitats, with remnants being generally small and often existing in isolation. Invasive plants have the potential to invade not just the edge of small remnants but also the interior because smaller remnants experience greater edge effects than do large, contiguous prairies. Additionally, invasive plants limit recruitment of native plants, which can arrest secondary succession. We proposed to assess techniques for restoration that included removing annual grasses and supplementing native species recruitment with seeding of native grass and forb species. We also assessed the effect of specific factors affecting recruitment: soil moisture and seed predation. Treatments included broadcast, spot, or no application of the herbicides imazapic and glyphosate and with or without seeding plus mulch. With treatments nested within each of three plant communities, ranging from annual- to perennial-dominated communities, in four blocks per community, plant characteristics (percentage of cover and plant density), soil moisture availability, and seed-predation losses were measured along a plant community gradient within one season at two locations. A combination of broadcast herbicide application and seeding with mulching was found to be more effective in reducing annual grasses and enhancing the establishment of native grass species in predominately annual and mixed communities (annuals and perennials). Spot herbicide application was effective in predominately perennial communities, whereas only seeding native species did not improve recruitment. Although seed predation reduced seedling recruitment, mulch provided seed protection and enhanced soil moisture retention. Plant community response to imposed treatments differed among communities, suggesting that a decision support tool would facilitate management decisions tailored for each plant community. The decision tool would be useful to ensure that appropriate treatments are applied and that specific factors affecting recruitment, such as seed predation and soil moisture, are addressed.