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Treatment Alternatives and Timing Affect Seeds of African Mustard ( Brassica tournefortii ), an Invasive Forb in American Southwest Arid Lands
Abstract
Developing management strategies for invasive plant species requires identifying effective treatment methods (e.g., physical or chemical treatments) and optimally timing their application. For invasive annual plants, effects of treatments on seed production and germinability are paramount to reduce seed banks and subsequent plant establishment. We compared effects of a range of physical and chemical treatments applied to plants containing seeds at different developmental stages at field sites in the Mojave Desert (Nevada and Arizona) for managing the exotic annual forb, African mustard. Effectiveness of physical treatments (hand pulling entire plants, breaking plants, or separating siliques from plants) for reducing African mustard seed size and germination varied by treatment and seed maturity stage at which treatments were applied. With all treated plant material remaining in the field (i.e., not bagged and transported off site), hand pulling or breaking plants resulted in 90 to 100% of developing and developed seeds still able to germinate. Separating siliques from plants, however, resulted in 0% germination of undeveloped and developing seeds. All three tested herbicides (glyphosate, 2,4-D, and metsulfuron) reduced germination to zero or near zero across all seed development stages. Results suggest that physical treatments are most effective at early stages of seed development, whereas several different herbicides are effective across seed developmental stages. Results also highlight the importance of considering the potential for continued seed development and germinability on treated plant material when choosing invasive plant treatment types and timing.
... Brassica tournefortii (Sahara mustard) is a xerophytic, self-pollinating annual endemic to North Africa, the Middle East, and Mediterranean regions of Europe, is a seed crop in Pakistan and India, and is invasive in Australia and North America (Abella, Suazo, Norman, & Newton, 2013;Berry, Gowan, Miller, & Brooks, 2014;Boutsalis, Karotam, & Powles, 1999;Dimmitt, 2009;Gorecki, Long, Flematti, & Stevens, 2012). In the western United States, B. tournefortii is an invasive plant that outcompetes native desert flora and impacts small animals (Hulton VanTassel et al., 2014). ...
... However, fruit production has been shown to contribute to successful establishment in this species (Abella et al., 2013;Bangle et al., 2008;Gorecki et al., 2012;Trader et al., 2006). In landrace populations, increased number of fruits is commonly selected by breeders, especially for seed crops (Tester & Langridge, 2010). ...
Varying environments can result in different patterns of adaptive phenotypes. By performing a common greenhouse experiment, we identified phenotypic differentiation on phenology, leaf morphology, branch architecture, size, and reproduction, among native, invasive, and landrace ranges of Brassica tournefortii. We first compared trait means and fitness functions among ranges, then we analyzed how trait means and selection strength of populations respond to varying aridity. Most traits varied such that landrace > invasive > native. Excluding reproduction, which was positively selected, most trait PCs experienced nonlinear selection in the native range but frequently shifted to directional selection in invasive and/or landrace ranges. The absence of strong clines for trait means in landrace and invasive populations suggest that agricultural practices and novel environments in source locations affected adaptive potential. Selection strength on faster reproductive phenology (negative directional) and leaf margin trait (disruptive) PCs coincided with increasing moisture. In native populations, higher aridity was associated with more days to reproduction, but landrace and invasive populations show stable mean time to reproduction with increasing moisture. A stable adaptive trait can increase range expansion in the invasive range, but stability can be beneficial for future harvest of B. tournefortii seed crops in the face of climate change. Varying environments can result in different patterns of adaptive phenotypes. By performing a common greenhouse experiment, we identified phenotypic differentiation in phenology, leaf morphology, branch architecture, size, and reproduction, among native, invasive, and landrace ranges of Brassica tournefortii (Sahara mustard). Understanding these differences may allow us to assess how native, agricultural, or invasive populations can be conserved, cultivated, or managed.
... In spite of these reports, there still remain concerns about adverse effects of glyphosate; with both farmers and scientist raising red flags regarding the effect of glyphosate on growth and pod production in young cocoa. Some authors have reported that drift during glyphosate application exert adverse effects on fruit and seed formation in other crops through the disruption of aromatic amino acid synthesis, necessary for fruit formation and retention (Magdal et al., 2012;Abella et al., 2013;Salem, 2013). It is possible therefore, that complains by farmers regarding the effect of glyphosate on the cocoa crop holds true. ...
... ha -1 ) which were very effective in killing weeds provided cheaper weed control options and increased dry bean yield, thus potentially increasing revenue and net benefits. These lower rates would also exert relatively less adverse effects on soil fauna and also lead to lower drift concentration which has been shown to affect fruit set and retention (Magdal et al., 2012;Abella et al., 2013;Salem et al., 2013). This probably explains why dry bean yields from plots treated with these lower rates were higher. ...
Weeds are a limitation to cocoa production, and herbicide use in cocoa cultivation is known to lower the cost of weed management and support better plant growth. As a result, glyphosate was recommended for use in cocoa cultivation following a two-year field trial at the Cocoa Research Institute of Ghana. Recent informal debates among scientists and farmers, however, point towards a disagreement regarding the effect of glyphosate on young cocoa. Consequently, an experiment was conducted from 2011 to 2013 at the Cocoa Research Institute of Ghana to re-evaluate the suitability of glyphosate (Isopropylamine) for weed management and its effects on growth and yield of young cocoa. Five rates of glyphosate viz: (i) 1,920 g active ingredient a.i. ha-1 using polyjet nozzle; (ii) 1,920 g a.i. ha-1 using very low volume (vlv) nozzle; (iii) 960 g a.i. ha-1 vlv; (iv) 720 g a.i. ha-1 vlv; (v) 480 g a.i. ha-1 vlv; and (vi) manual weeding were tested in a randomized complete block design with four replicates in the field. Effects of treatments on weeds, cocoa growth and yield were recorded for three years. In a gauze house study, cowpea and maize were used to determine residual effects of glyphosate. Emergence, survival and dry matter accumulation by these plants were recorded. Results from the gauze house study showed that glyphosate did not exhibit residual soil activity at these rates. Glyphosate at 960 g ha-1 significantly increased yield of three year old cocoa compared to the other rates and manual weeding. The 1,920 g ha-1 rates significantly reduced the initial yield of 3 year old cocoa compared to the other glyphosate rates. Cost analysis showed that glyphosate at 960 g a.i. ha-1 was Ghȼ 136.00 (11%) and Ghȼ 1,784.00 (61%) cheaper than the 1,920 g a.i. ha-1 rates and manual weeding respectively. It was therefore concluded that glyphosate can be applied at 960 g a.i. ha-1 (equivalent to 2.0 l ha-1 in 120 l of water) for effective weed management without significant adverse effects on growth and yield of young cocoa.
... The increase, which occurred at the moderately gravelly sand site which had the highest cover of non-native annuals, resulted from Sahara mustard. This forb produces copious seed and can dominate soil seed banks particularly on disturbed, sandy sites (Abella et al. 2013). Apparently where Sahara mustard was already abundant on or near the site, the activity of outplanting native species or perhaps the few irrigations of outplants somehow promoted this invasive, while implementing the abiotic treatments did not. ...
Two related concepts in restoration ecology include the relative interchangeability of biotic and abiotic restoration treatments for initiating recovery and bet hedging using multiple restoration approaches to increase the likelihood of favorable restoration outcomes. We used these concepts as a framework to implement a factorial experiment including biotic (outplanting greenhouse-grown individuals of three perennial species) and abiotic treatments (constructing microtopography or vertical mulch consisting of upright, dead plant material). These treatments were designed to stimulate native plant recruitment and reverse soil degradation at four disturbed sites in the Sonoran Desert, U.S.A. The first growing season after restoration treatments was the driest of the last 47 years, and 100% of outplants died. While the biotic treatment failed, the vertical mulch abiotic treatment increased native shrub seedling cover at the driest site and reversed soil loss across sites by increasing soil accumulation by 6× to 2 cm/year. Results revealed that i) inexpensive, minimal-input abiotic treatments outperformed resource-intensive biotic treatments; ii) the restoration effort withstood the total failure of a major component (outplanting) to nevertheless achieve key restoration benefits within 2-3 growing seasons; and iii) incorporating multiple treatment types served as a bet-hedging approach to buffer against treatment failures. Integrating minimal-input abiotic treatments in restoration warrants consideration given their low cost and bet-hedging potential.
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... Volunteers and American Conservation Experience crews, funded by the Desert Tortoise Preserve Committee, have pulled the mustards almost annually to limit spread. Herbicides are effective if used at the rosette stage (Marushia et al. 2012, Abella et al. 2013. Removing this species from the Natural Area and critical habitat units will require concentrated efforts of the government and non-profit organizations. ...
Feral Burros and Other Influences on Desert Tortoise Presence in the Western Sonoran Desert
KRISTIN H. BERRY1,4, JULIE L. YEE2, AND LISA M. LYREN3,5
1 U.S. Geological Survey, Western Ecological Research Center, 3621 Pinot Grigio Way, Reno, NV 89509, USA
2 U.S. Geological Survey, Western Ecological Research Center, 2885 Mission Street, Santa Cruz, CA 95060, USA
3 U.S. Geological Survey, Western Ecological Research Center, 2177 Salk Avenue, Suite 250, Carlsbad, CA 92008, USA
ABSTRACT: Across the globe, conflicting priorities exist in how land and resources are managed. In the American West, conflicts are common
on public lands with historical mandates for multiple uses. We explored the impacts of multiple uses of land in a case study of Agassiz’s Desert
Tortoises (Gopherus agassizii), a federally threatened species, in the western Sonoran Desert. The tortoise has declined for many reasons, most of
which relate to management of land and habitat. Frequently cited causes are livestock grazing, roads, vehicle-oriented recreation, predators, and
disease. In spring of 2009, we conducted a survey to evaluate relationships between desert tortoises, vegetation associations, topography,
predators, and anthropogenic uses. We sampled a 93-km2 area with 200 independent 1-ha plots. Density (6 SE) of adult tortoises was low, 2.0 6
1.0/km2, and the annualized death rate for adults during the 4 yr preceding the survey was high, 13.1%/yr. We observed tortoise sign, most of
which was recent, on 22% of the 200 plots, primarily in the southwestern part of the study area. More tortoise sign occurred on plots with
Brittlebush (Encelia spp.) vegetation at higher elevations. Most plots (91.0%) had �1 human-related impacts: feral burro scat (Equus asinus;
84.0%), recent vehicle tracks and trails (34.0%), trash (28.0%), burro trails and wallows (26.5%), and old vehicle tracks (24.0%). We used a
multimodel approach to model presence of tortoise sign on the basis of 12 predictor variables, and calculated model-averaged predictions for the
probability of tortoise presence. Importance values revealed two apparent top drivers: feral burros and vegetation association. This is the first
study to identify a negative association between presence of desert tortoises and feral burros.
Key words: Equus asinus; Gopherus agassizii; Trash; Vehicles; Vegetation association
... Volunteers and American Conservation Experience crews, funded by the Desert Tortoise Preserve Committee, have pulled the mustards almost annually to limit spread. Herbicides are effective if used at the rosette stage (Marushia et al. 2012, Abella et al. 2013. Removing this species from the Natural Area and critical habitat units will require concentrated efforts of the government and non-profit organizations. ...
Agassiz’s desert tortoise (Gopherus agassizii), a threatened species of the southwestern United States, has severely declined to the point where 76% of populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery of wild populations is low because females require 12–20 years to reach reproductive maturity and produce few eggs annually. We report on a 34‐year mark‐recapture study of tortoises initiated in 1979 at the Desert Tortoise Research Natural Area in the western Mojave Desert, California, USA, and provide substantive data on challenges faced by the species. In 1980, the United States Congress designated the Research Natural Area and protected the land from recreational vehicles, livestock grazing, and mining with a wildlife‐permeable fence. The 7.77‐km2 study area, centered on interpretive facilities, included land both within the Natural Area and outside the fence. We expected greater benefits to accrue to the tortoises and habitat inside compared to outside. Our objectives were to conduct a demographic study, analyze and model changes in the tortoise population and habitat, and compare the effectiveness of fencing to protect populations and habitat inside the fence versus outside, where populations and habitat were unprotected. We conducted surveys in spring in each of 7 survey years from 1979, when the fence was under construction, through 2012. We compared populations inside to those outside the fence by survey year for changes in distribution, structure by size and relative age, sex ratios, death rates of adults, and causes of death for all sizes of tortoises. We used a Bayesian implementation of a Jolly Seber model for mark‐recapture data. We modeled detection, density, growth and transition of tortoises to larger size‐age classes, movements from inside the protective fence to outside and vice versa, and survival. After the second and subsequent survey years, we added surveys to monitor vegetation and habitat changes, conduct health assessments, and collect data on counts of predators and predator sign. At the beginning of the study, counts and densities for all sizes of tortoises were high, but densities were approximately 24% higher inside the fence than outside. By 2002, the low point in densities, densities had declined 90% inside the fence and 95% outside. Between 2002 and 2012, the population inside the fence showed signs of improving with a 54% increase in density. Outside the fence, densities remained low. At the end of the study, when we considered the initial differences in location, densities inside the fence were roughly 2.5 times higher than outside. The pattern of densities was similar for male and female adults. When evaluating survival by blocks of years, survivorship was higher in 1979–1989 than in 1989–2002 (the low point) and highest from 2002 to 2012. Recruitment and survival of adult females into the population was important for growing the population, but survival of all sizes, including juveniles, was also critical. Major events and activities driving the decline in populations both inside and outside the fence included illegal collecting, upper respiratory tract disease, and hyperpredation by the common raven (Corvus corax) on juvenile tortoises. Other sources of death were gunshots, vehicles, and predation by mammals. Outside the fence, fragmentation and deterioration of habitat was a critical driver. Between the first and last surveys, 2 different ecosystem processes were underway: recovery of vegetation and soils from grazing and vehicles inside the fence and continued deterioration outside the fence. Habitat outside the fence became increasingly denuded of shrubs and fragmented by roads and trails, and habitat fragments increased 50‐fold. Outside the fence, biomass of non‐native annual plants was higher and the cover of shrubs was lower, a reflection of ongoing deterioration. These changes and losses of habitat resulted in loss of shrub cover and sites for burrows, reduction in preferred food plants, and greater exposure to predators and extremes in temperature. Overall, the tortoise population and habitat inside the fence appeared to benefit from protection and showed signs of recovery at the end of the study. Fencing, control of vehicular access, and removal of livestock grazing were among several recommended management actions for critical habitat in the first recovery plan in 1994. At the end of the study, the Natural Area remained as 1 of 2 fenced, official protected areas for the species in the geographic range. We attribute fencing to continuing higher densities of adults inside the fence compared with outside the fence and promising signs of recovery. Densities of adults at the Natural Area also were 2.3 to 5.5 times higher than in 16 of the 17 Tortoise Conservation Areas (critical habitat units) within the geographic range. © 2020 The Authors. Wildlife Monographs published by Wiley Periodicals, LLC on behalf of The Wildlife Society. La tortue du désert ou gophère d’Agassiz (Gopherus agassizii), une espèce menacée du sud‐ouest des États‐Unis, a subi une forte régression, au point que 76% des populations dans l’habitat essentiel (zones de protection des tortues) sont en dessous du seuil de viabilité. Le potentiel de régénération rapide des populations sauvages est faible, car les femelles n’atteignent leur maturité reproductive qu’après 12 à 20 ans, et même alors, elles ne pondent que peu d’œufs chaque année. Nous présentons ici une étude par marquage‐recapture sur les tortues, entreprise en 1979 et conduite pendant 34 ans dans la zone naturelle de recherche sur les tortues du désert, dans l’ouest du désert de Mojave en Californie, et nous fournissons des données concrètes sur les difficultés rencontrées par cette espèce. En 1980, le Congrès américain a délimité la zone naturelle de recherche et installé une clôture perméable à la faune pour protéger le terrain des véhicules récréatifs, du pâturage de bétail et de l’exploitation minière. La zone étudiée de 7,77 km2, située autour des installations didactiques, comprenait des terres à l’intérieur et à l’extérieur de la zone naturelle clôturée. Nous nous attendions à ce que les tortues et leur habitat se trouvent davantage à l’intérieur qu’à l’extérieur de la zone. Nos objectifs étaient de mener une étude démographique, d’analyser et de modéliser les changements dans la population de tortues et leur habitat, et d’évaluer l’efficacité de la clôture sur la protection des populations et de l’habitat avec une comparaison entre l’intérieur et l’extérieur de la zone. Nous avons effectué des relevés au printemps de sept années entre 1979, lorsque la clôture était en construction, et 2012. Nous avons comparé les populations à l’intérieur et à l’extérieur de la clôture entre ces sept années: changements dans la distribution, structure selon la taille et l’âge relatif, proportion des sexes, taux de mortalité des adultes et causes de décès pour toutes les tailles de tortues. Nous avons utilisé une implémentation bayésienne d’un modèle Jolly‐Seber pour les données de marquage‐recapture. Nous avons modélisé la détection, la densité, la croissance et la transition des tortues vers les classes de taille‐âge supérieures, leurs mouvements de l’intérieur de la clôture de protection vers l’extérieur et vice versa, et leur survie. À partir de la deuxième année, nous avons ajouté des relevés pour surveiller les changements de la végétation et de l’habitat, évaluer la santé des tortues et recueillir des données sur le nombre de prédateurs et les signes de présence de prédateurs. Au début de l’étude, les dénombrements et la densité des populations de toutes les tailles de tortues étaient élevés, mais les densités étaient environ 24% plus élevées à l’intérieur de la clôture qu’à l’extérieur. En 2002, l’année où elles étaient les plus faibles, les densités avaient diminué de 90% à l’intérieur de la clôture et de 95% à l’extérieur. Entre 2002 et 2012, la population à l’intérieur de la clôture a montré des signes d’amélioration avec une augmentation de 54% de la densité. À l’extérieur de la clôture, les densités sont restées faibles. À la fin de l’étude, lorsque les différences initiales de localisation ont été prises en compte, les densités à l’intérieur de la clôture étaient environ 2,5 fois plus élevées qu’à l’extérieur. Les densités de population étaient similaires pour les adultes mâles et femelles. L’évaluation par périodes a montré que la survie était meilleure entre 1979 et 1989 qu’entre 1989 et 2002 (le niveau le plus bas), et encore meilleure entre 2002 et 2012. Le nombre et la survie des femelles adultes étaient des facteurs importants pour accroître la population, mais la survie de toutes les tailles de tortues, y compris des jeunes, était critique également. Les principaux événements et activités entraînant le déclin des populations à l’intérieur et à l’extérieur de la clôture étaient notamment le braconnage, les maladies des voies respiratoires supérieures et l’hyperprédation des jeunes tortues par le corbeau commun (Corvus corax). Les autres causes de mortalité étaient les tirs d’armes à feu, les véhicules et la prédation par des mammifères. À l’extérieur de la clôture, la fragmentation et la détérioration de l’habitat étaient un facteur critique. Entre le premier et le dernier relevé, deux processus écosystémiques différents étaient à l’œuvre: régénération de la végétation et des sols précédemment abîmés par les pâturages et les véhicules à l’intérieur de la clôture; poursuite de la détérioration à l’extérieur de la clôture. L’habitat à l’extérieur de la clôture était de plus en plus dépourvu de végétation et fragmenté par les routes et les sentiers, et les fragments d’habitat ont été multipliés par 50. À l’extérieur de la clôture, la biomasse de plantes annuelles non indigènes a augmenté et le couvert d’arbustes a été réduit, reflétant une détérioration continue. Ces changements et ces pertes d’habitat ont entraîné une réduction du couvert arbustif et des sites pouvant accueillir des terriers, une raréfaction des plantes dont se nourrissent les tortues et une plus grande exposition aux prédateurs et aux températures extrêmes. Dans l’ensemble, la population de tortues et l’habitat à l’intérieur de la clôture semblaient avoir bénéficié de la protection apportée et montraient des signes de régénération à la fin de l’étude. La clôture, le contrôle de l’accès des véhicules et la suppression des pâturages faisaient partie des mesures recommandées pour l’habitat essentiel dans le premier plan de régénération en 1994. À la fin de l’étude, la zone naturelle est demeurée l’une des deux zones officiellement protégées et clôturées pour l’espèce dans l’aire de répartition de l’espèce. Nous attribuons à la clôture la persistance de plus fortes densités d’adultes à l’intérieur par rapport à l’extérieur ainsi que les signes prometteurs de régénération. Les densités de population adulte dans la zone naturelle étaient également de 2,3 à 5,5 fois plus élevées que dans 16 des 17 zones de protection des tortues (unités d’habitat essentiel) de l’aire de répartition de l’espèce. We conducted a 34‐year demographic study of threatened Agassiz’s desert tortoises at the fenced Desert Tortoise Research Natural Area in the Mojave Desert, comparing a population inside the fence with one outside the fence. The fence successfully prevented habitat degradation but was insufficient in preventing a catastrophic decline caused by numerous anthropogenic activities, including an infectious disease and predation by common ravens. However, by 2012, the population inside the fence showed signs of increasing, whereas the population outside the fence was below viability.
... All rights reserved. targeted species, but also opens up unoccupied areas that could allow the subsequent establishment of either native or non-native species (e.g., Abella, Suazo, Norman, & Newton 2013;Hasselquist, Hasselquist, & Rogers 2013;Heckman, McColley, Slater, & Carr 2017). In contrast, burning involves the destruction of biomass of most if not all species inhabiting a site, has well-documented positive effects on native plant communities in North America (e.g., Brudvig et al. 2007;Bowles & Jones 2013), and also may favor the persistence of certain native species (e.g., Howe 2011;Young, Porensky, Wolf, Fick, & Young 2015). ...
Questions
Restoring native‐dominated plant communities often requires controlling invasive species, reintroducing native species, and implementing continued management practices. Can single herbicide applications to control Centaurea stoebe L. encourage establishment of seeded native species more effectively than a single mowing? Can annual hand pulling to control C. stoebe favor the persistence of seeded native species? Can mid‐spring burning reduce C. stoebe and increase native forbs and grasses? After 8 years, will the restored plant communities differ from those in untreated areas?.
Location
Bass River Recreation Area, Ottawa County, Michigan, USA.
Methods
We studied the effects of site preparation (mowing, clopyralid, glyphosate), hand pulling of C. stoebe, and burning on restoring native plant communities on a C. stoebe‐infested site. Over 8 years, we quantified the development of the plant communities on plots seeded with native grasses and forbs, and report on the second 4 years here.
Results
Native‐dominated plant communities developed using both herbicides, but while clopyralid provided longer control of C. stoebe, clopyralid‐treated plots had fewer native species than glyphosate‐treated plots. Native‐dominated plant communities also developed on plots that were only mowed once before seeding, achieving similar native species richness as the glyphosate treatment. Hand pulling controlled C. stoebe, burning increased relative cover of native graminoids and decreased that of non‐native grasses, and hand pulling and burning in combination increased relative cover of native forbs. After 8 years, the restored plant communities had greater native species cover and richness and higher mean Coefficient of Conservatism, Floristic Quality Index, and Shannon's Diversity Index values than untreated areas.
Conclusions
Site preparation, seeding, hand pulling of C. stoebe, and annual burning facilitated restoration of native‐dominated plant communities on a C. stoebe‐infested site. Effects accumulated over a period of 8 years, illustrating the importance of continued management and monitoring as part of similar restoration efforts.
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This datasheet on Brassica tournefortii covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
The purpose of this study was to determine the effects of different concentrations of crude ethanolic
extracts on two pathogenic bacterial strains. The various concentration of 10%, 5%, and 1% of crude
ethanolic extracts of 9 plants belonging to diverse families was estimated for antibacterial activity against
Staphylococcus aureus and Escherichia coli. The dried and ground plant materials were extracted in
absolute ethanol 99.9% by cold-soaking for 48 h. The in vitro antibacterial activity was done by disc
diffusion Assay (DDA). The zone of inhibition for the tested microbial strains was measured using the
disc diffusion method. Imipenem (Ipm 10) was used as the positive control, while DMSO was the
negative control. Among 9 medicinal plants used in this study, only (7) ethanolic extracts {H. stoechas L.,
M.parviflora (L.) Demonstr, S. arenariaForskal, P. rupestre L. M. longipetalaL., E. microcarpa and R.
alba L.} Showed the range of inhibition zone between 7.66±0.57 to14.67±0.56 mm. However, the crude
ethanolic extract of L.resedifolia (L.) O. Kuntze, and B. tournefortiiGouan presented no activity at all
against pathogenic bacteria. Antibacterial susceptibility exposed that the most active antibiotics were
ciprofloxacin, chloramphenicol, imipenem, and ticarcillin against S. aureus; ciprofloxacin,
chloramphenicol, imipenem, and polymyxin against E. coli
Globally, invasion by non-native plants threatens resources that nature reserves are designated to protect. We assessed the status of non-native plant invasion on 1,662, 0.1-ha plots in Death Valley National Park, Mojave National Preserve, and Lake Mead National Recreation Area. These parks comprise 2.5 million ha, 23% of the national park land in the contiguous USA. At least one non-native species inhabited 82% of plots. Thirty-one percent of plots contained one non-native species, 30% two, 17% three, and 4% four to ten non-native species. Red brome (Bromus rubens), an 'ecosystem engineer' that alters fire regimes, was most widespread, infesting 60% of plots. By identifying frequency of species through this assessment, early detection and treatment can target infrequent species or minimally invaded sites, while containment strategies could focus on established invaders. We further compared two existing systems for prioritizing species for management and found that a third of species on plots had no rankings available. Moreover, rankings did not always agree between ranking systems for species that were ranked. Presence of multiple non-native species complicates treatment, and while we found that 40% of plots contained both forb and grass invaders, exploiting accelerated phenology of non-natives (compared to native annuals) might help manage multi-species invasions. Large sizes of these parks and scale of invasion are formidable challenges for management. Yet, precisely because of their size, these reserves represent opportunities to conserve large landscapes of native species by managing non-native plant invasions.
Introduced exotic plants can drive ecosystem change. We studied invasion and establishment of Brassica tournefortii (African mustard), a noxious weed, in the Chemehuevi Valley, western Sonoran Desert, California. We used long-term data sets of photographs, transects for biomass of annual plants, and densities of African mustard collected at irregular intervals between 1979 and 2009. We suggest that African mustard may have been present in low numbers along the main route of travel, a highway, in the late 1970s; invaded the valley along a major axial valley ephemeral stream channel and the highway; and by 2009, colonized 22 km into the eastern part of the valley. We developed predictive models for invasibility and establishment of African mustard. Both during the initial invasion and after establishment, significant predictor variables of African mustard densities were surficial geology, proximity to the highway and axial valley ephemeral stream channel, and number of small ephemeral stream channels. The axial valley ephemeral stream channel was the most vulnerable of the variables to invasions. Overall, African mustard rapidly colonized and quickly became established in naturally disturbed areas, such as stream channels, where geological surfaces were young and soils were weakly developed. Older geological surfaces (e.g., desert pavements with soils 140,000 to 300,000 years old) were less vulnerable. Microhabitats also influenced densities of African mustard, with densities higher under shrubs than in the interspaces. As African mustard became established, the proportional biomass of native winter annual plants declined. Early control is important because African mustard can colonize and become well established across a valley in 20 yr.
The United States created national parks to conserve indigenous species, ecological processes, and cultural resources unimpaired for future generations. Curtailing impacts of exotic species is important to meeting this mission. This synthesis identified 56 studies reported in 60 publications that evaluated effects of exotic plant treatments on National Park Service lands. Studies encompassed 35 parks in 20 states and one U.S. territory and included 157 exotic plant species. Eighty-seven percent of studies reported that at least one treatment reduced focal exotic species. Of 30 studies evaluating response of native vegetation, 53% reported that natives increased, 40% reported neutral responses, and 7% reported that natives decreased. For at least some of the neutral cases, neutrality was consistent with management objectives. In other cases, insufficient time may have elapsed to thoroughly characterize responses, or restoration might be needed. Nonfocal exotic species increased in 44% of the 16 studies evaluating them, but the other 56% of studies reported no increase. Results suggest that: (1) a range of exotic species spanning annual forbs to trees have been effectively treated; (2) developing effective treatments often required extensive experimentation and balancing nontarget impacts; (3) presence of multiple exotic species complicated treatment efforts, highlighting importance of preventing invasions; and (4) placing treatment objectives and outcomes in context, such as pretreatment condition of native vegetation, is important to evaluating effectiveness. Attaining the goal in national parks of conserving native species and ecological processes minimally influenced by exotic species will likely require comprehensive management strategies inclusive of treatment interactions with focal exotic species, other potential invaders, and native species.
The goal of this study was to evaluate the efficacy of four herbicides for controlling invasive Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) in idle grasslands by monitoring post-treatment plant communities. Experiments were conducted in two remnant savannas in central Kentucky. With the exception of domestic grazing, these sites were chosen because they were undisturbed by agriculture and development. Single treatments of 0.2 kg ai/ha imazapic, 0.2 kg ai/ha clethodim, 0.2 kg ai/ha imazapic + 1.1 kg ai/ha glyphosate, 0.03 kg ai/ha sulfosulfuron, and an untreated control were implemented in fall 2004 and spring and summer 2005 at each site in a randomized complete block design. Plant communities were monitored 3, 10, 12, 14, and 15 months after the final treatments were implemented. At 15 months post-treatment, tall fescue cover was reduced in all treatment plots relative to the untreated control, with the greatest reduction in tall fescue cover occurring in the summer treatment plots. Spring applications of each herbicide were more effective for Kentucky bluegrass control than summer or fall treatments. All herbicide treatments reduced Kentucky bluegrass compared to untreated plots. The most effective herbicide treatment was imazapic + glyphosate, which reduced Kentucky bluegrass cover to less than 7%. However, the resulting bare ground facilitated invasions by other aggressive exotic species, notably musk thistle (Carduus nutans L.). Spring applications of clethodim reduced Kentucky bluegrass cover relative to the untreated plots, and resulted in the highest number of native plant species compared to all other plots. This conservation of forb cover provided by clethodim may be of importance in managing areas impaired by this aggressive, invasive grass.
Invasive annual grasses have become increasingly impor-tant components of desert vegetation in North America. They are especially problematic because they increase the extent, severity, and frequency of fire in desert shrublands that normally experience fire very rarely, or not at all. After fire, invasive grasses and forbs are often dominant and restoration methods are required to promote native plant recovery. Three treatments to control invasive annual grasses and forbs were implemented in the first 3 years fol-lowing a fire in creosote bush scrub vegetation. Treatments included early season mechanical removal (raking) of all annuals, grass-specific herbicide (Fusilade II), and Fusilade II plus hand pulling of exotic forbs. In the first year, all treatments reduced invasive annual grass abundance by about half but had little effect on native annuals. Treatment effectiveness was minimal in the first year due to low and irregular distribution of rainfall. In the second year, insuf-ficient rainfall prevented the germination of any annual plants and no treatments were applied. In the third year, precipitation onset occurred later in the season and was above average. Although the raking treatment performed poorly, treatments utilizing Fusilade II nearly eliminated invasive grasses and forbs, achieved native annual dom-inance, and increased native perennial abundance. These results indicate that in the absence of invasive grasses and forbs, the native annual community can be resilient to fire disturbance and native perennials can recover. The results also suggest that burned creosote bush shrublands can be managed after fire to decrease the chance of invasive plant–fire feedback.
In the southwestern United States, Brassica tournefortii (Gouan) is a highly invasive plant that threatens native annuals. We conducted 5 experiments to help define the environmental limits for B. tournefortii germination. We found that this species germinates at a wide range of temperatures (16°C to 32°C), under moderate salt concentrations (up to 3.20 dS · m−1), in 24 hours of light or darkness, and after 10 weeks of submergence in water. These germination characteristics make B. tournefortii a potentially vigorous competitor of native annuals in the Mojave Desert. The fact that B. tournefortii can take advantage of and effectively reproduce in habitat altered by Tamarix spp. adds to management concerns for controlling this species. That B. tournefortii seeds remain viable after extended submergence, combined with our observation that B. tournefortii can float across large bodies of water with seed pods intact, indicates that this species is a highly successful invader and may be a threat to natural environments, including remote shoreline habitats. We can no longer assume that shoreline habitats experiencing little to no human contact will be safe from invasions initiated by humans.
The germination of seed is critical in deserts where annual plants are abundant and rely on seed buried in the soil for sustaining populations. The exotic annuals Bromus rubens and Brassica tournefortii threaten arid indigenous ecosystems such as the Mojave Desert, but little is known about the potential effects on seed emergence of different burial depths and substrates that could enhance or reduce emergence. Using seed from Mojave Desert populations, we conducted a three-factor greenhouse experiment testing the effects of species (Bromus or Brassica), burial depth (0, 2, 5, or 10 cm), and substrate (none, gravel, or litter) on seed emergence. Species and substrate interacted significantly with burial depth. Both species displayed the greatest emergence when seeds were sown on the soil surface (70% emergence for Bromus and 52% for Brassica), but Bromus emergence declined less at a 2-cm depth than Brassica. Emergence of surface-sown seed did not differ significantly among substrate types, but emergence of buried seed was significantly reduced below gravel substrates compared to no substrate or litter substrates. This suggests that seed fates in the soil (such as seed mortality by germination but not emergence from the soil) can be altered by manipulating soil surface conditions.
Summary 1. Restoration of habitats invaded by non-native plants should include both the removal of invasive plants and re-establishment of native plant communities. To develop appropriate restoration strategies and quantify the effects of invasions, experiments that evaluate multiple removal methods and native community responses to those removal methods are needed. 2. We evaluated the response of native plant communities to removal of the invasive grass Microstegium vimineum (Japanese stiltgrass) in eastern forests in the USA. At eight field sites in southern Indiana, we applied three common removal treatments and compared native community responses among treatments and to untreated reference plots. 3. After 2 years of treatment, native community responses to Microstegium removal varied significantly among methods and plant functional groups in autumn 2006. Graminoid richness was greater when the invader was removed with hand-weeding, while graminoid biomass was lower in plots treated with post-emergent herbicide compared to reference plots. Forb richness was greater with hand-weeding and post-emergent herbicide compared to plots treated with post-emergent plus pre-emergent herbicides or untreated plots. Forb biomass was greater across all removal treatments. Overall native community diversity was 24% greater when the invasion was removed with hand- weeding and 21% greater with post-emergent herbicide compared to reference plots. No positive response in plant diversity occurred with post-emergent plus pre-emergent herbicide. 4. By spring 2007, graminoid percentage cover was greater with hand-weeding but not with herbicide treatments compared to untreated plots. However, forb cover was greater across all removal treatments compared to plots where the invader was not removed. The density of native tree seedlings was 123% greater in post-emergent herbicide treated plots than in untreated plots, indicating that the invasion was inhibiting tree recruitment. 5. Synthesis and applications. Our results demonstrate that multiple techniques can be used to control invasive plants but that the responses of native plant communities vary among removal methods. Further, greater native plant diversity and biomass following removal shows that invasions were suppressing native plant communities. Management of plant invasions should consider not only the effectiveness of removal methods but also how different methods influence native plant responses.
Grasslands dominated by exotic annual grasses have replaced native perennial vegetation types in vast areas of California. Prescribed spring fires can cause a temporary replacement of exotic annual grasses by native and non-native forbs, but generally do not lead to recovery of native perennials, especially where these have been entirely displaced for many years. Successful reintroduction of perennial species after fire depends on establishment in the postfire environment. We studied the effects of vegetation changes after an April fire on competition for soil moisture, a key factor in exotic annual grass dominance. As an alternative to fire, solarization effectively kills seeds of most plant species but with a high labor investment per area. We compared the burn to solarization in a study of establishment and growth of seeds and transplants of the native perennial grass Purple needlegrass (Nassella pulchra) and coastal sage species California sagebrush (Artemisia californica). After the fire, initial seed bank and seedling densities and regular percent cover and soil moisture (0–20 cm) data were collected in burned and unburned areas. Burned areas had 96% fewer viable seeds of the dominant annual grass, Ripgut brome (Bromus diandrus), leading to replacement by forbs from the seed bank, especially non-native Black mustard (Brassica nigra). In the early growing season, B. diandrus dominating unburned areas consistently depleted soil moisture to a greater extent between rains than forbs in burned areas. However, B. diandrus senesced early, leaving more moisture available in unburned areas after late-season rains. Nassella pulchra and A. californica established better on plots treated with fire and/or solarization than on untreated plots. We conclude that both spring burns and solarization can produce conditions where native perennials can establish in annual grasslands. However, the relative contribution of these treatments to restoration appears to depend on the native species being reintroduced, and the long-term success of these initial restoration experiments remains to be determined.
Alien annual grasses in the genera Bromus and Schismus are widespread and abundant in the Mojave Desert, and negative correlations between these aliens and native annual plants suggest that competition may occur between them. Effects of competition were evaluated by thinning alien annual grass seedlings and measuring the responses of native annual plants at three sites in the central, southcentral and southwestern Mojave Desert during 2 y of contrasting plant productivity. Effects of Bromus and Schismus were evaluated separately in the microhabitat where each was most abundant, beneath the north side of creosote bushes (Larrea tridentata) for Bromus and in the open interspace between shrubs for Schismus. Thinning of Bromus and Schismus significantly increased density and biomass of native annuals at all three sites, only during a year of high annual plant productivity and species richness. Effects of thinning were greatest for Amsinckia tesselata and for a group of relatively uncommon native annuals. Thinning also significantly increased the density and biomass of the alien forb, Erodium cicutarium. These results show that alien annual grasses can compete with native annual plants and an alien forb in the Mojave Desert and that effects can vary among years.
Given the abundance of non-native species invading wildland habitats, managers need to employ informed triage to focus control
efforts on weeds with the greatest potential for negative impacts. Our objective here was to determine the level of threat
Sahara mustard, Brassicatournefortii, represents to meeting regional goals for protecting biodiversity. Sahara mustard has spread throughout much of the Mojave
and lower Sonoran Deserts. It has occurred in southern California’s Coachella Valley for nearly 80years, punctuated by years
of extremely high abundance following high rainfall. In those years the mustard has clear negative impacts on the native flora.
Using mustard removal experiments we identified reductions in native plant reproduction, shifting composition increasingly
toward Sahara mustard while decreasing the fraction of native species. High between-year variance in precipitation may be
a key to maintaining biodiversity as the mustard is less abundant in drier years. Sahara mustard impacts to the native fauna
were much less evident. Of the animal species evaluated, only the Coachella Valley fringe-toed lizard, Umainornata, demonstrated a negative response to mustard abundance; however the impacts were short-lived, lasting no more than a year
after the mustard’s dominance waned. Without control measures the long-term impacts to desert biodiversity may rest on the
changing climate. Wetter conditions or increased periodicity of high rainfall years will favor Sahara mustard and result in
reduced biodiversity, especially of native annual plants. Drier conditions will keep the mustard from becoming dominant but
may have other negative consequences on the native flora and fauna.
Habitat modification (i.e., disturbance) and resource availability have been identified as possible mechanisms that may influence
the invasibility of plant communities. In the Mojave Desert, habitat disturbance has increased dramatically over the last
50years due to increased human activities. Additionally, water availability is considered to be a main limiting resource
for plant production. To elucidate the effects of soil disturbance and water availability on plant invasions, we created experimental
patches where we varied the levels of soil disturbance and water availability in a fully crossed factorial experiment at five
replicated field sites, and documented responses of native and non-native winter annuals. The treatments did not significantly
affect the density (seedlingsm−2) of the non-native forb, Brassica tournefortii. However, the relationship between silique production and plant height differed among treatments, with greater silique production
in disturbed plots. In contrast to Brassica, density of the non-native Schismus spp. increased in soil disturbed and watered plots, and was greatest in disturbed plots during 2009 (the second year of the
study). Species composition of the native annual community was not affected by treatments in 2008 but was influenced by treatments
in 2009. The native forb Eriophyllum sp. was most dense on water-addition plots, while density of Chaenactis freemontii was highest in disturbed plots. Results illustrate that habitat invasibility in arid systems can be influenced by dynamics
in disturbance regimes and water availability, and suggest that invasiveness can differ between non-native annual species
and among native annuals in habitats undergoing changing disturbance and precipitation regimes. Understanding the mechanistic
relationships between water availability and non-native plant responses will be important for understanding the effects of
shifting precipitation and vegetation patterns under predicted climate change in arid ecosystems.
Keywords
Brassica tournefortii
–Invasibility–Invasiveness–Nitrogen–Precipitation–Resource pulse–
Schismus
Although glyphosate is typically used as a nonselective herbicide, low rates have the potential to provide selective control of seedling annuals in the understory of established perennial plants. In a repeated experiment on two adjacent sites at a single location near Alturas, CA (2009 and 2010), we evaluated the efficacy of glyphosate at several different rates on medusahead and nontarget species in northern California sagebrush scrub. We applied glyphosate at 10 rates ranging from 0 to 709 g ae ha(-1) (0 to 18 oz product acre(-1)) at three separate timings in each trial: mid-March (medusahead in early seedling stage), late April to early May (tillering), and late May to early June (boot to early head). Plots measured 3 m by 9 m (10 ft by 30 ft) and were arranged in randomized complete blocks with four replications for each rate and timing. We visually estimated vegetative cover for all dominant species in July before medusahead seed drop using three 1-m(2) quadrats per plot. Medusahead cover declined with increasing rates of glyphosate, and the middle application timing (at tillering) was the most effective. In rate series regression models, we achieved 95% control of medusahead with 160 g ae ha(-1) in midseason 2009, compared with 463 g ae ha(-1) in early season and 203 g ae ha(-1) in late season. In 2010, we achieved 95% control with 348 g ae ha(-1) in midseason, compared with > 709 g ae ha(-1) in early season. Medusahead seed production reflected changes in cover, though individual plants tended to produce more seed at low densities. We attribute reduced control early in the season and poorer overall control in 2010 to greater tolerance of medusahead to glyphosate at lower temperatures. Treatment effects on big sagebrush, as indicated by shoot tip vigor, were minor, although the midseason timing caused a slight reduction in vigor. These results show that low rates of glyphosate (158 to 315 g ae ha(-1)) at a treatment timing corresponding to medusahead tillering can give economical and effective control of medusahead without long-term damage to big sagebrush.
Invasive species researchers often ask: Why do some species invade certain habitats while others do not? Ecological theories predict that taxonomically related species may invade similar habitats, but some related species exhibit contrasting invasion patterns. Brassica nigra, Brassica tournefortii, and Hirschfeldia incana are dominant, closely related nonnative species that have overlapping, but dissimilar, distributions. Brassica tournefortii is rapidly spreading in warm deserts of the southwestern United States, whereas B. nigra and H. incana are primarily limited to semiarid and mesic regions. We compared traits of B. tournefortii that might confer invasiveness in deserts with those of related species that have not invaded desert ecosystems. Brassica tournefortii, B. nigra and H. incana were compared in controlled experiments conducted outdoors in a mesic site (Riverside, CA) and a desert site (Blue Diamond, NV), and in greenhouses, over 3 yr. Desert and mesic B. tournefortii populations were also compared to determine whether locally adapted ecotypes contribute to desert invasion. Experimental variables included common garden sites and soil water availability. Response variables included emergence, growth, phenology, and reproduction. There was no evidence for B. tournefortii ecotypes, but B. tournefortii had a more rapid phenology than B. nigra or H. incana. Brassica tournefortii was less affected by site and water availability than B. nigra and H. incana, but was smaller and less fecund regardless of experimental conditions. Rapid phenology allows B. tournefortii to reproduce consistently under variable, stressful conditions such as those found in Southwestern deserts. Although more successful in milder, mesic ecosystems, B. nigra and H. incana may be limited by their ability to reproduce under desert conditions. Rapid phenology and drought response partition invasion patterns of nonnative mustards along a gradient of aridity in the southwestern United States, and may serve as a predictive trait for other potential invaders of arid and highly variable ecosystems. Nomenclature: Black mustard, Brassica nigra (L.) Koch; Sahara mustard, Brassica tournefortii Gouan; shortpod mustard, Hirschfeldia incana (L.) Lagr.-Foss. Interpretive Summary: Sahara mustard (Brassica tournefortii), black mustard (Brassica nigra), and shortpod mustard (Hirschfeldia incana) are common invasive mustards throughout parts of the western United States. In particular, all three species are found in southern California, but they have different distributions. Brassica tournefortii is primarily an invader of warm desert ecosystems, black mustard is most common in more mesic regions, and shortpod mustard is most common in the arid Mediterranean-climate regions between the coast and warm deserts. We hypothesized that B. tournefortii's adaptations to arid North Africa might predispose it to successfully invade North America's arid, warm-desert ecosystems. Our objective was to identify which traits promote B. tournefortii's invasiveness. Mustards were compared by growing them in common gardens under both climatic and water availability treatments. Although all three species germinate in the same number of days, B. tournefortii has a more rapid development to seed set than B. nigra or H. incana under all conditions. B. tournefortii produced fewer seeds than H. incana under beneficial conditions, but the three species were not different under stressful conditions. All species produced seeds under sustained drought, suggesting that invasive mustards sustain populations with low reproduction rates even during drought years. Our results suggest that mortality before seed set is the limitation to invasion by B. nigra and H. incana in the desert ecosystem.
Control options for the nonnative common mullein are of increasing interest to land managers in the west. Common mullein is a prolific seed producer, with a single plant able to produce well over 100,000 seeds. We found that mechanical control of common mullein before mature seed capsules developed along the raceme significantly reduced viable seed production. Seeds from immature capsules had very low viability (early reproductive stage = 0.08%, 95% CI = 0.06%, 0.67%; mid reproductive stage = 1.52%, 95% CI = 0.49%, 3.11%). This information allows managers to time their management efforts so that they can reduce the amount of plant material that must be disposed of in order to control the spread of common mullein seeds. Nomenclature: Common mullein, Verbascum thapsus L. Management Implications: Common mullein is an increasing priority for control in natural areas of the western United States. This biennial species produces a large number of seeds that can lay dormant in the seed bank for at least 100 years. Managers detach reproductive flowering stalks in an effort to limit seed production but then must remove the reproductive portion from the field or risk adding seeds to the seed bank. At the request of land managers, the relationship between plant phenology and seed viability was studied to facilitate timing of the removal of reproductive stalks to minimize additions of common mullein seeds to the seed bank. This study provides specific information about the timing of removal of the reproductive inflorescences of common mullein to best limit seed set. If management efforts are carried out before seedpods turn brown on the stalk, seeds will not develop and the risk of adding additional seed to the seed bank is diminished. However, if seedpods have begun to mature, land managers should take precautionary measures by removal of stalks from the field, followed by proper disposal.
1. A field experiment compared the effects of herbicide treatments (picloram, clopyralid and clopyralid + 2,4-D, each at two timings, at the recommended rates for control of the exotic forb Centaurea maculosa) on the structure and species diversity of native plant communities during an 8-year period in western Montana, USA. 2. Floristic composition of replicated treatment plots was sampled before spraying and for 3 years after the initial herbicide applications at two grassland and two early seral forest sites. Following the third year post-spray measurements, half the treatment plots were randomly selected to be resprayed and community sampling was continued for two more years. Diversity was quantified as species richness and Shannon Diversity Index. 3. Standing crops by growth form were estimated by double sampling at the conclusion of the experiment. 4. Herbicide treatments had high efficacy on the target weed, shifting the plant communities back to a grass-dominated structure. 5. Depressions in plant community diversity were small and transitory. In the third year after the initial applications, there were no significant differences among treatments and some herbicide-treated plots had begun to surpass the untreated plots in community diversity measures. With most treatments, respraying 3-4 years after the initial applications did not reduce plant diversity compared to untreated levels. 6. Late season applications, made after most herbicide-susceptible forbs had entered summer drought-induced dormancy, minimized impacts on plant community diversity. 7. The behaviour of herbicide residues in the soil is described in relation to community-level effects. 8. Implications of the results for exotic weed management in conservation settings are discussed.
Semiarid regions are characterized by spatial heterogeneity with two patch types: (a) shrub patches with an annual vegetation understorey, and (b) biological soil crusts. Runoff as overland flow from the crust patch is a source of water and nutrients for the shrub patch and, thus, influences annual plant productivity. The aim of this study was to quantify the effects of the herbicide, simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], a photosynthesis inhibitor, on biological soil crusts and the consequences for the patchy desert landscape, in the northern Negev Desert, Israel. We studied the direct effect of the herbicide on the factors that compose the crusts (polysaccharides production, moss density, chlorophyll level), indirect effects on plant productivity (vegetation index and annual biomass), and resources (water, soil, organic matter and nutrients) on the landscape. We carried out a 2-year experiment, which entailed applying simazine on 20 (0.5 m) plots with combinations of crust and shrub patches, and 20 control plots. Results indicated that 41.3% of the runoff water that flow overland from the crust patches was intercepted and absorbed by the shrub patches. Destruction of live crust components, such as cyanobacteria and soil algae, reduce polysaccharide production (from 0.12 to 0.06 µg mL of crust extraction) and moss density (from 66 to 4 moss caulidia cm), which led to soil (12 g m yr), organic matter (0.5 g m yr) and nitrate (600 µg myr) erosion. Degradation of shrub patch productivity was due to the removal of annual vegetation by simazine. We conclude that applying simazine to biological soil crusts in this fragile semiarid ecosystem, affected the crust organisms and in turn, the flow of water, soil and nutrients.
Serpentine grasslands are relatively free of the invasive species that typify other California grasslands, but recently are threatened by the spread of barb goatgrass, a Eurasian annual that is unique in its tolerance of serpentine soils. We evaluated two graminicides (clethodim and fluazifop), one broad-spectrum herbicide (glyphosate), mowing, and hand pulling for their effectiveness in controlling barb goatgrass and for restoring native species cover and diversity. We also evaluated application timing for the graminicides: before goatgrass flowering (early season), at flower initiation (midseason), and at early seed development (late season). Glyphosate was applied at early seed development. The 10 treatment combinations were applied to 10 blocks of 4-m2 (43-ft2) experimental plots in an inner Coast Range serpentine grassland with high cover of barb goatgrass but few other nonnative species. After 2 yr of treatment, all treatments except glyphosate reduced goatgrass frequency. Hand pulling, fluazifop, and mowing were most effective at controlling goatgrass, reducing frequency by 60, 51, and 48%, respectively (compared to a 30% increase on control plots). Midseason applications of clethodim and fluazifop were more effective than those applied early or late. Hand pulling, fluazifop, and clethodim increased native forb frequency by 31, 46, and 74%, respectively, with the benefit of the graminicides decreasing with later applications. Native grasses were at least partially resistant to the graminicides. Cover of one sided blue grass (Poa secunda), the most widespread native grass, might have been reduced slightly by early-season applications but was increased by late-season applications. Cover of soft brome (Bromus hordeaceus), the only other widespread nonnative species in the study, was reduced by early-season applications of the graminicides. Clethodim and fluazifop show great potential to selectively remove barb goatgrass and other nonnative annual grasses in grasslands that are otherwise dominated by native grasses and forbs. Mowing is a less selective, but viable alternative. Nomenclature: Clethodim; fluazifop; glyphosate; barb goatgrass, Aegilops triuncialis L.; Sandburg bluegrass, Poa secunda J. Presl. Interpretive Summary: Few studies have addressed the management of barb goatgrass, which is a recent and aggressive invader of serpentine grasslands in California. In nonserpentine grasslands, 2 successive yr of prescribed fire can control barb goatgrass, but the slow fuel build up in serpentine grasslands generally prevents a complete burn in the second year. As a potential alternative or follow up to fire, we evaluated two graminicides (clethodim and fluazifop), one broad-spectrum herbicide (glyphosate), mowing, and hand pulling for their effectiveness in controlling barb goatgrass and restoring diversity and cover of native species. We also evaluated application timing for the graminicides: before barb goatgrass flowering (early season), at flower initiation (midseason), and at early seed development (late season). Glyphosate was applied at early seed development and mowing occurred at flowering. Hand pulling, which is impractical at a large scale, was included purely as a reference for the most selective possible control. All treatments except glyphosate reduced the frequency of barb goatgrass, but the best control (besides hand pulling) was provided by fluazifop and mowing. Clethodim and fluazifop are most effective when applied midseason. Clethodim provides poor control early-season, but adequate control midseason. Application of graminicides early in the season provides the most benefit to native forbs (probably because of their early release from competition), but can reduce populations of native grasses, which benefit more from applications later in the season when they have set seed or are nearer to dormancy. Early-season application can also provide control of other nonnative annual grasses, such as Bromus hordeaceus, that mature earlier than goatgrass. Mowing provides acceptable goatgrass control, but less benefit to native forbs. Late-season application of glyphosate failed to control goatgrass, eliminated the native grass Nassella pulchra, and reduced the cover of some native forbs that were still actively growing at the time of application. For all treatments, significant barb goatgrass cover remains after 2 yr of treatment. Outside of this study, experience suggests that 5 to 6 yr of hand pulling is necessary to deplete the seed bank. To avoid selection for herbicide resistance, graminicides should be part of a integrated strategy that includes prescribed fire and mowing.
Our main objective was to improve understanding of herbicide effects on community dynamics to refine the use of technology and advance the development of ecologically based weed management strategies. We hypothesized that native grasslands would exhibit reductions in culturally sensitive forb cover, biomass, and density relative to the rate of application of selective rangeland herbicides, and that hand-removal of sulfur cinquefoil (Potentilla recta L.) would increase indigenous species cover, biomass, density, species richness, and diversity. Treatments consisted of 3 rates each of 2,4-D + clopyralid (0.28 kg ai · ha−1 + 0.0532 kg ai · ha−1, 0.56 kg ai · ha−1 + 0.1064 kg ai · ha−1, 0.84 kg ai · ha−1 + 0.1596 kg ai · ha−1); 2,4-D amine (0.532 kg ai · ha−1, 1.064 kg ai · ha−1, 1.596 kg ai · ha−1); metsulfuron (0.0042 kg ai · ha−1, 0.021 kg ai · ha−1, 0.032 kg ai · ha−1); picloram (0.14 kg ai · ha−1, 0.28 kg ai · ha−1, 0.56 kg ai · ha−1); and clopyralid (0.05025 kg ai · ha−1, 0.21 kg ai · ha−1, 0.42 kg ai · ha−1). This experiment was replicated 3 times at 2 late-seral, noninfested sites in southeastern Montana. In a companion study, sulfur cinquefoil was removed adjacent to paired nonremoved controls in 5 replicates at 2 sites in 1-m2 plots for 2 growing seasons. Canopy cover, density, and biomass were collected 24 months after initial treatment at all sites. Indigenous perennial grass cover and biomass increased with herbicide application; however, picloram, metsulfuron, and clopyralid reduced native forb density at 1 site, and picloram reduced forb cover at both sites regardless of rate. Effects of herbicides on species richness or diversity were not detected. Hand-removing sulfur cinquefoil increased total plant richness, especially that of native forbs. Restoring species richness and diversity may be difficult using selective broadleaf herbicides because key functional groups, such as forbs, appear to be at risk.
Plant biomass and seed production were quantified for Brassica tournefortii Gouan, Brassicaceae (Sahara mustard) from 3 sites spanning the Mojave and Sonoran deserts, in the Southwestern United States. We found strong linear relationships between plant biomass and seed production, with larger plants producing more seeds per plant (R2 = 0.93) and greater seed biomass per plant (R2 = 0.94). Both seed count (R2 = 0.93) and seed biomass (R2 = 0.90) were also greater in 0.25 m2 plots that had higher plant biomass. These results and the law of constant final yield indicate that biomass and seed production of individual Sahara mustard plants can be higher in plots with lower densities. These data suggest that control efforts that do not remove all individuals may reduce densities but inadvertently increase net seed production within treated areas.
1. Exotic annual plants are an increasingly important ecological issue and new, creative approaches to management are required. In desert ecosystems of the southwestern USA, the forbs Brassica tournefortii, Erodium cicutarium and Schismus spp. dominate and alter native annual communities. Hand weeding B. tournefortii is currently the most common control method employed, but weeding is inadequate and expensive for managing large-scale invasions. New methods must be developed to conserve and restore desert ecosystems.
2. Exotic annuals in desert systems have rapid germination and phenology compared to natives, indicating that a window for selective control of exotic annuals may occur immediately after exotic seedling emergence. We tested the role of timing in control methods by comparing a cotyledon-stage glyphosate application to a bolting-stage application and to hand weeding B. tournefortii, plus an untreated check. Treatments were tested at two sites dominated by either exotic or native annuals and followed for 2 years; early application was repeated the second year. Cover and richness were evaluated during seedling and peak flowering stages underneath and between shrubs.
3. Early glyphosate application did not affect native cover, but did reduce exotic cover. Late herbicide negatively impacted both exotics and natives. Natives had little positive response, and then only through hand weeding under shrubs, but the same treatment caused an increase in the exotic E. cicutarium.
4.Synthesis and applications. The rapid phenology of exotic annuals may be exploited to control exotics while minimizing impacts on native plants in desert communities. This approach may be useful for other invasions in other ecosystems by species with rapid, early germination, or may act as a supplement to improve the efficacy of existing management regimes.
1. Theories of plant succession are poorly developed in arid lands, hindering our understanding of how long communities may take to recover after disturbances such as fire. In desert landscapes vulnerable to fire, information about vegetation recovery is important when deciding whether land managers should facilitate vegetation recovery. The deserts of the southwestern USA are increasingly subject to unprecedented fires, facilitated by fuel from exotic grasses, yet management strategies are unclear.
2. We evaluated post‐fire recovery patterns of perennial plant species richness and diversity, compared the rate and direction of succession between two major community types, and explored the relationship of time since fire (TSF) and other environmental factors with vegetation recovery. We sampled perennial plant communities and environmental variables (e.g. soil N) on 32 burns, ranging from 2 to 29 years TSF and each paired with their own unburned area, within a 1·8 million ha landscape in the Mojave Desert, USA.
3. Species richness, diversity and composition exhibited different post‐burn recovery patterns, and recovery rates differed between community types. Specifically, diversity in Coleogyne ramosissima communities was greater in burned than unburned areas, but diversity did not differ in Larrea tridentata communities. Species composition in Larrea communities exhibited trajectories that indicate convergence with unburned community composition after 19 years TSF. Conversely, burned and unburned Coleogyne communities lacked convergence irrespective of TSF. Environmental variables (e.g. soil texture and P) accounted for 79–83% of the variation in burned species composition, suggesting environmental characteristics in part control recovery patterns.
4. Synthesis and applications . The results indicate that geographically similar vegetation types within the same landscape can have markedly different post‐disturbance successional rates and trajectories. Furthermore, the persistence of fire effects varied depending on the community measure, with fire effects on species composition more long‐lasting than the effects on species diversity. This work supports (i) the use of post‐disturbance successional analyses for helping to prioritize management where it is most needed (e.g. communities not recovering naturally) and (ii) the need to assess whether persistent, early successional desert communities meet functional management objectives.
The first step in restoration often involves the removal of invasive plants, but few studies have determined if the response of plant communities matches management goals. The shrub Morrow’s honeysuckle (Lonicera morrowii Gray) is one of a suite of exotic bush honeysuckle species that have become pervasive woody invaders in eastern North America. In 2004, we tested four control methods (cut, mechanical removal, stump application of glyphosate, and foliar application of glyphosate) during late spring and early autumn within a degraded meadow at Fort Necessity National Battlefield, Pennsylvania, U.S.A. Our restoration goals are to control Morrow’s honeysuckle, restore native vegetation, and mimic the conditions present in the mid-1700s. We established forty-five 5 × 5–m plots to measure woody species; five plots of each treatment method were treated in spring, whereas the remaining five were treated in autumn. We maintained five control plots. Before control, mean density of Morrow’s honeysuckle was 67,920 ± 4,480 shrubs/ha. Foliar application of herbicide and mechanical removal were most effective at reducing the number of shrubs (≥62%). Overall, our treatments were less successful (26–68% reduction) than reported control efforts of other bush honeysuckle species; the sheer number of shrubs coupled with their open habitat made control efforts difficult. Spring treatments, particularly cut and mechanical treatments, had higher metrics of herbaceous community quality. However, continued restoration efforts, including follow-up treatments, White-tailed deer (Odocoileus virginianus) control, and the planting of native seeds and saplings, should be employed to favor the establishment of native seedlings and herbs.
Conservation of North American grasslands is hampered by the impact of invasive herbaceous species. Selective control of these plants, although desirable, is complicated by the shared physiology and phenology of the invader and the native components of the invaded plant community. Fortunately, there is evidence that some management practices, such as prescribed fire, herbicide, and mowing, can cause differential responses in native and invasive grassland species. However, timing of treatment is critical, and fire has been shown to increase rates of invasion when implemented during the dormant season. Bothriochloa ischaemum, an introduced C4 Eurasian grass is an increasing problem in grasslands, particularly in southern and central regions of North America. To date, there has been little success in effective selective control. Two invaded grassland sites representative of Blackland Prairie and Edwards Plateau ecoregions were subjected to two growing-season prescribed fire treatments, single and double herbicide applications, and single and double mowing treatments. Mowing had no effect on either B. ischaemum or other dominant species at either site one-year posttreatment. However, growing-season fire and herbicide were both effective at reducing the abundance of B. ischaemum, with other codominant species responding either negatively to herbicide or neutrally or positively to fire. The vulnerability of B. ischaemum to growing-season fire may be associated with the ecology of its native range. The negative growth response to growing-season fire, combined with its lower implementation costs, indicates that this method warrants further investigation as a selective management tool for other problematic species in invaded grasslands.
We develop a geometric model predicting that maximum seedling emergence depth should scale as the cube root of seed weight.
We tested the prediction by planting seeds from 17 species ranging in weight from 0.1 to 100 mg at a variety of depths in
a sand medium. The species were spread across 16 genera and 13 families, all occurring in fire-prone fynbos shrublands of
South Africa. Maximum emergence depth was found to scale allometrically with seed weight with an exponent of 0.334, close
to the predicted value. We used the allometry to predict recruitment response to experimentally simulated variation in fire
intensity. Five species with small (<2 mg) seeds and five with large (>10 mg) seeds were planted at ≤20-mm and 40-mm depths
and exposed to low and high heat treatments and a control. The allometric equation predicted that species with large seeds
would be able to emerge from a depth of 40 mm but those with small seeds would not. Only 1% of 481 seedlings from small-seeded
species emerged from the 40-mm planting compared with 40% of 626 seedlings from the large-seeded group. The simulated fire
treatments killed seeds in shallow, but not deeper, soil layers. At simulated high fire intensities, seedling emergence was
poor in small-seeded species but good in large-seeded species, with most seedlings emerging from the 40-mm planting depth.
Seed size could be a useful general predictor of recruitment success under different fire intensities in this system. We suggest
that allometric relationships in plants deserve wider attention as predictive tools.
Land managers are concerned about the negative effects of alien annual plants on native plants, threatened and endangered species such as the desert tortoise (Gopherus agassizii), and ecosystem integrity in the Mojave Desert. Management of alien plants is hampered by a lack of information regarding the dominance and environmental correlates of these species. The results of this study indicate that alien plant species comprised a small fraction of the total annual plant flora, but most of the annual plant community biomass. When rainfall was high in 1995, aliens comprised 6% of the flora and 66% of the biomass. When rainfall was low in 1999, aliens comprised 27% of the flora and 91% of the biomass. Bromus rubens, Schismus spp. (S. arabicus and S. barbatus), and Erodium cicutarium were the predominant alien species during both years, comprising 99% of the alien biomass. B. rubens was more abundant in relatively mesic microhabitats beneath shrub canopies and at higher elevations above 800–1000 m, whereas Schismus spp. and E. cicutarium were more abundant in the relatively arid interspaces between shrubs, and, for Schismus spp., at lower elevations as well. Disturbance variables were more reliable indicators of alien dominance than were productivity or native plant diversity variables, although relationships often varied between years of contrasting rainfall. The strongest environmental correlates occurred between dirt road density and alien species richness and biomass of E. cicutarium, and between frequency and size of fires and biomass of B. rubens.
Exotic species can threaten native ecosystems and reduce services that ecosystems provide to humans. Early detection of incipient populations of exotic species is a key step in containing exotics before explosive population growth and corresponding impacts occur. We report the results of the first three years of an exotic plant early detection and treatment program conducted along more than 3,000 km of transportation corridors within an area >1.5 million ha in the Mojave Desert, USA. Incipient populations of 43 exotic plant species were mapped using global positioning and geographic information systems. Brassica tournefortii (Sahara mustard) infested the most soil types (47% of 256) surveyed in the study area, while Nicotiana glauca (tree tobacco) and others currently occupy less than 5% of soil types. Malcolmia africana (African mustard) was disproportionately detected on gypsum soils, occurring on 59% of gypsum soil types compared to 27% of all surveyed soils. Gypsum soils constitute unique rare plant habitat in this region, and by conventional wisdom were not previously considered prone to invasion. While this program has provided an initial assessment of the landscape-scale distribution of exotic species along transportation corridors, evaluations of both the survey methods and the effectiveness of treating incipient populations are needed. An exotic plant information system most useful to resource mangers will likely include integrating planning oriented coarse-scale surveys, more detailed monitoring of targeted locations, and research on species life histories, community invasibility, and treatment effectiveness.
Controlling African mustard: evaluation of herbicide and mechanical treatments (California)
- Brooks