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Weeds
Kinds of Weeds Terms modified by Weeds Selected Abstracts"LONG LIVE THE WEEDS AND THE WILDERNESS YET": REFLECTIONS ON A SECULAR AGEMODERN THEOLOGY, Issue 3 2010STANLEY HAUERWAS While we are deeply appreciative of Taylor's A Secular Age, we nonetheless worry that his use of the immanent/transcendent duality may introduce a certain kind of Christian Constantinianism that he wants to disavow. In particular, we worry that the immanent/transcendent duality is far too formal in its character. In order to develop this concern, we draw on Talal Asad's account of the secular to suggest how liturgy may provide an alternative way of understanding as well as challenging Taylor's worries about "the immanent frame." [source] Lack of discontinuous gas exchange in a tracheate arthropod, Leiobunum townsendi (Arachnida, Opiliones)PHYSIOLOGICAL ENTOMOLOGY, Issue 2 2002John R. B. Lighton Abstract The discontinuous gas exchange cycle, characterized by stringent spiracular control and periods of near-zero external CO2 emission separated by ,bursts' of CO2 emission, has evolved independently in several taxa of tracheate arthropods. These include the hexapoda, diplopoda, and several arachnid taxa; ticks, pseudoscorpions and solphugids. This paper presents the first data on gas exchange kinetics in a harvestman (Arachnida; Opiliones). The experimental animal, Leiobunum townsendi Weed, from an arid area of the south-western United States, displayed a metabolic rate similar to those of other arthropods at 25 °C (129 ± 22 µW). Their CO2 emission kinetics showed, when the animals were motionless, only minor variations about a mean value of 0.0217 ± 0.0037 mL/h (n = 6, mean body mass 86 mg). Expressed on an intra-recording basis, the coefficient of variation of CO2 emission (= SD/MEAN), which is an index of short-term gas emission fluctuations and thus of spiracular control, had a mean value of only 0.082. In contrast, the coefficient of variation of animals employing a discontinuous gas exchange cycle is >,1.5. Gas exchange in opilionids, unlike the case with most other tracheate arthropods, may therefore be dominated by simple diffusion without a prominent role for wide modulations of spiracular conductance. Contributory to this conservative spiracular control strategy may be the weak degree of tracheation in opilionids, combined with circulating haemocyanin, which acts as both a transport medium and a buffering reservoir for respiratory gas exchange. [source] Susceptibility of invasive taxa of European blackberry to rust disease caused by the uredinial stage of Phragmidium violaceum under field conditions in AustraliaPLANT PATHOLOGY, Issue 3 2005K. J. Evans European blackberry (Rubus fruticosus agg.) is an aggregate of closely related taxa, with at least 15 taxa naturalized in Australia. Biological control of this Weed of National Significance, using the nonindigenous rust fungus Phragmidium violaceum, is effective when the weather is conducive to multiple cycles of infection, but some blackberry taxa escape severe disease. Thirty-one taxa of naturalized R. fruticosus agg. from southeastern Australia were isolated, their DNA phenotype determined and clones of each taxon inoculated with P. violaceum isolate SA1. Disease development was monitored for at least four generations of uredinia on large potted plants under field conditions. Although variation in mean disease severity appeared continuous over the range of Rubus clones tested, counts of uredinia and telia enabled identification of eight resistant taxa. Fine scale variation in susceptibility to rust disease was observed when different clones of R. leucostachys with the same DNA phenotype were found to express either resistance or susceptibility to P. violaceum (SA1). There were significant differences among 23 Rubus taxa rated as susceptible to rust disease in the mean number of leaves emerging per latent period of uredinia (LELPU). Mean LELPU appeared to account for some of the variation in two measures of mean disease severity observed among susceptible Rubus clones, although the correlation was insignificant (0·10 < P > 0·05). [source] A Novel Leaf-Movement Inhibitor of a Nyctinastic Weed, Sesbania exaltata Cory, Designed on a Naturally Occurring Leaf-Opening Substance and Its Application to a Potential, Highly Selective Herbicide.CHEMINFORM, Issue 2 2003Noboru Takada Abstract For Abstract see ChemInform Abstract in Full Text. [source] Impact of Soil Tillage and Crop Rotation on Barley (Hordeum vulgare) and Weeds in a Semi-arid EnvironmentJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2004H. Z. Ghosheh Abstract Experiments were conducted to evaluate the effect of mouldboard- or chisel-ploughing and rotations on barley crops and associated weeds in a semi-arid location. Two primary soil tillage operations and eight crop rotation-tillage operation combinations were evaluated over two successive seasons. Drought conditions prevailed (<152 mm annual precipitation) and affected the measured parameters. Barley grown in mouldboard-ploughed plots had higher biomass compared with chisel-ploughed plots. Barley grain yield was greater in mouldboard-ploughed plots in a fallow-fallow-barley rotation. Weed species densities varied between tillage systems and rotations. Density of Hordeum marinum, for example, was high in fallow-barley-fallow in chisel-ploughed plots, and was high under more continuous fallow in mouldboard-ploughed plots. Similar variations were also observed in weed fresh weights and in numbers of seed produced. The results describe the productivity of barley under extremely dry conditions, where an advantage for mouldboard ploughing was observed. The results also indicate the complexity of weed communities in their response towards different tillage-rotation combinations. [source] Pests, pesticide use and alternative options in European maize production: current status and future prospectsJOURNAL OF APPLIED ENTOMOLOGY, Issue 5 2010M. Meissle Abstract Political efforts are made in the European Union (EU) to reduce pesticide use and to increase the implementation of integrated pest management (IPM). Within the EU project ENDURE, research priorities on pesticide reduction are defined. Using maize, one of the most important crops in Europe, as a case study, we identified the most serious weeds, arthropod pests, and fungal diseases as well as classes and amounts of pesticides applied. Data for 11 European maize growing regions were collected from databases, publications and expert estimates. Silage maize dominates in northern Europe and grain production in central and southern Europe. Crop rotations range from continuous growing of maize over several years to well-planned rotation systems. Weeds, arthropod pests and fungal diseases cause economic losses in most regions, even though differences exist between northern countries and central and southern Europe. Several weed and arthropod species cause increasing problems, illustrating that the goal of reducing chemical pesticide applications is challenging. Pesticides could potentially be reduced by the choice of varieties including genetically modified hybrids, cultural control including crop rotation, biological control, optimized application techniques for chemicals, and the development of more specific treatments. However, restrictions in the availability of alternative pest control measures, farm organization, and the training and knowledge of farmers need to be overcome before the adoption of environmentally friendly pest control strategies can reduce chemical pesticides in an economically competitive way. The complex of several problems that need to be tackled simultaneously and the link between different control measures demonstrates the need for IPM approaches, where pest control is seen in the context of the cropping system and on a regional scale. Multicriteria assessments and decision support systems combined with pest monitoring programs may help to develop region-specific and sustainable strategies that are harmonized within a EU framework. [source] A sterile-female technique proposed for control of Striga hermonthica and other intractable weeds: advantages, shortcomings and risk managementPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 5 2009Brian G Rector Abstract Weeds have posed intractable challenges to farmers since the dawn of agriculture. This article describes in detail a proposed control strategy based on the introduction of genes conferring female sterility into the genome of an intractable target weed. Spread of these genes through target populations via pollen would be facilitated by their incorporation within active transposable elements. Advantages (e.g. self-dissemination, self-proliferation, target specificity) and shortcomings (e.g. high cost, long project incubation period, limited range of possible targets) of this strategy are discussed in depth, as are assessment and management of its attendant biological and ecological risks, such as the risk of introduced genes spreading to non-target species. The parasitic weed Striga hermonthica (Del.) Benth. is examined as a potential target. Published 2009 by John Wiley & Sons, Ltd [source] Glyphosate-Resistant Weeds and CropsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 4 2008Stephen O. Duke No abstract is available for this article. [source] Primer and interviews: Gene regulation in Arabidopsis thalianaDEVELOPMENTAL DYNAMICS, Issue 9 2009Julie C. Kiefer Abstract The animal and plant kingdoms use many of the same molecular tools to build decidedly different multicellular organisms. Learning how plants approach challenges common to both kingdoms can inspire new ways of thinking in the animal biologist. This primer introduces how a weed from the mustard family, Arabidopsis thaliana, has been used to work through developmental problems. It also compares and contrasts gene regulation tools in animals and plants. Accompanying the primer is a discussion of current topics in root development with Arabidopsis researchers Philip N. Benfey, Ph.D., and Kenneth D. Birnbaum, Ph.D. Developmental Dynamics 238:2449,2458, 2009. © 2009 Wiley-Liss, Inc. [source] Comparing agglomerative clustering and three weed classification frameworks to assess the invasiveness of alien species across spatial scalesDIVERSITY AND DISTRIBUTIONS, Issue 6 2006Roger A. Lawes ABSTRACT To prioritize weed management at the catchment scale, information is required on the species present, their relatively frequency, abundance, and likely spread and impact. The objective of this study was to classify the invasiveness of alien species that have invaded the Upper Burdekin Catchment in Queensland, Australia, at three spatial scales. A combination of three published weed classification frameworks and multivariate techniques were employed to classify species based on their frequency and cover at a range of spatial scales. We surveyed the Upper Burdekin Catchment for alien species, and for each species determined the following distribution indices , site frequency, total cover, transect frequency per site frequency and quadrat frequency per site frequency, cover per quadrat when present, cover per transect when present, and cover per site when present. These indices capture the effect of species abundance and frequency between sites (site frequency and total cover), within sites (transect frequency per site and cover per transect when present), and within transects (quadrat frequency per site frequency and cover per site). They were used to classify the species into seven groups using a hierarchical cluster analysis. The relationship between the indices was explored to determine how effective the small scale, site-specific indices were at predicting the broader, landscape-scale patterns. Strong correlations were observed between transect frequency per site and frequency (r2 = 0.89) and cover per transect when present and total cover (r2 = 0.62). This suggests that if a weed is abundant at the site level, it has the potential to occupy large areas of the catchment. The species groupings derived from the application of the three published weed classification frameworks were compared graphically to the groupings derived from the cluster analysis. One of the frameworks classified species into three groups. The other two frameworks classified species into four groups. There was a high degree of subjectivity in applying the frameworks to the survey data. Some of the data were of no relevance to the classification frameworks and were therefore ignored. We suggest that the weed classification frameworks should be used in conjunction with existing multivariate techniques to ensure that classifications capture important natural variations in observed data that may reflect invasion processes. The combined use of the frameworks and multivariate techniques enabled us to aggregate species into categories appropriate for management. [source] The relative importance of latitude matching and propagule pressure in the colonization success of an invasive forbECOGRAPHY, Issue 6 2006John L. Maron Factors that influence the early stages of invasion can be critical to invasion success, yet are seldom studied. In particular, broad pre-adaptation to recipient climate may importantly influence early colonization success, yet few studies have explicitly examined this. I performed an experiment to determine how similarity between seed source and transplant site latitude, as a general indicator of pre-adaptation to climate, interacts with propagule pressure (100, 200 and 400 seeds/pot) to influence early colonization success of the widespread North American weed, St. John's wort Hypericum perforatum. Seeds originating from seven native European source populations were sown in pots buried in the ground in a field in western Montana. Seed source populations were either similar or divergent in latitude to the recipient transplant site. Across seed density treatments, the match between seed source and recipient latitude did not affect the proportion of pots colonized or the number of individual colonists per pot. In contrast, propagule pressure had a significant and positive effect on colonization. These results suggest that propagules from many climatically divergent source populations can be viable invaders. [source] Comparative seed ecology of the endangered shrub, Pimelea spicata and a threatening weed, Bridal Creeper: Smoke, heat and other fire-related germination cuesECOLOGICAL MANAGEMENT & RESTORATION, Issue 1 2003Anthony J. Willis SummaryPimelea spicata R. Br. is a nationally listed endangered Australian shrub threatened with extinction by habitat fragmentation and environmental weed invasion. Bridal Creeper (Asparagus asparagoides L. W. Wight) is the primary weed threat to the largest remaining populations of P. spicata in the Cumberland Plain. Fire, as part of an integrated pest management program, offers the potential to stimulate P. spicata populations while controlling Bridal Creeper. It is important, therefore, to understand how the components of fire affect the germination and growth of both species. Using laboratory experiments we investigated the effects of smoke, heat, ash and/or light on the germination of P. spicata and Bridal Creeper. We found a significant promotive effect of smoke and indication of an inhibitory heat shock (90°C for 10 min) effect on the germination of P. spicata seeds. The response of Bridal Creeper seeds to the same factors was complex; while the results of one experiment suggested an inhibitory effect of smoke and a promotive effect of heat, subsequent trials were contradictory, implying that Bridal Creeper, like many weeds, is able to germinate under a wide range of environmental conditions. Other experiments investigated the optimal germination temperature and innate dormancy of P. spicata in the absence of fire-related germination cues. Of the incubation temperatures investigated, the optimal diurnally fluctuating regime for P. spicata germinations was 10°C and 20°C in the night and day, respectively. The innate dormancy of freshly produced seeds disappeared after 3 months. In contrast to Bridal Creeper, we found a persistent germinable seed bank of about 97 P. spicata seeds/m2 located in the top 5 cm of the soil profile. While fire alone is unlikely to kill Bridal Creeper plants, fire may help to manage local infestations of the weed by limiting germination and providing opportunity for herbicide treatment of regrowth. [source] A novel host shift and invaded range of a seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), of an invasive weed, Leucaena leucocephalaENTOMOLOGICAL SCIENCE, Issue 1 2009Midori TUDA Abstract An endophagous seed predator, Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae: Bruchinae), utilizes Neotropical Leucaena (Fabaceae: Mimosoideae). One of its hosts, Leucaena leucocephala, is a fast-growing nitrogen-fixing tree that serves as a multipurpose beneficial plant but eventually becomes an aggressive invader where it was introduced. Herein, we report A. macrophthalmus invasion of the Far East, South Asian tropics and subtropics (Japanese Pacific Islands, Taiwan, Southern China, Northern Thailand and Southern India). Of other field-collected mimosoid legumes, an introduced tree, Falcataria moluccana, in Taiwan was found to be used by the seed predator. Conversely, our published work review revealed that the seed predator had retained high host specificity to Leucaena species in its native and introduced regions. Acanthoscelides macrophthalmus was able to utilize aphagously postharvest mature seeds for oviposition and larval development, which is a trait of post-dispersal seed predators. We confirmed that A. macrophthalmus that was reared on L. leucocephala was able to utilize F. moluccana as well. Although the relatively high host specificity of the oligophagous beetle is suitable for controlling the weedy L. leucocephala, the potential host range expansion confirmed by this study must be cautioned. [source] Degradation kinetics of ptaquiloside in soil and soil solutionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Rikke Gleerup Ovesen Abstract Ptaquiloside (PTA) is a carcinogenic norsesquiterpene glycoside produced in bracken (Pteridium aquilinum (L.) Kuhn), a widespread, aggressive weed. Transfer of PTA to soil and soil solution eventually may contaminate groundwater and surface water. Degradation rates of PTA were quantified in soil and soil solutions in sandy and clayey soils subjected to high natural PTA loads from bracken stands. Degradation kinetics in moist soil could be fitted with the sum of a fast and a slow first-order reaction; the fast reaction contributed 20 to 50% of the total degradation of PTA. The fast reaction was similar in all horizons, with the rate constant k1F ranging between 0.23 and 1.5/h. The slow degradation, with the rate constant k1S ranging between 0.00067 and 0.029/h, was more than twice as fast in topsoils compared to subsoils, which is attributable to higher microbial activity in topsoils. Experiments with sterile controls confirmed that nonmicrobial degradation processes constituted more than 90% of the fast degradation and 50% of the slow degradation. The lower nonmicrobial degradation rate observed in the clayey compared with the sandy soil is attributed to a stabilizing effect of PTA by clay silicates. Ptaquiloside appeared to be stable in all soil solutions, in which no degradation was observed within a period of 28 d, in strong contrast to previous studies of hydrolysis rates in artificial aqueous electrolytes. The present study predicts that the risk of PTA leaching is controlled mainly by the residence time of pore water in soil, soil microbial activity, and content of organic matter and clay silicates. [source] Biology, distribution and impacts of silverleaf nightshade (Solanum elaeagnifolium Cav.),EPPO BULLETIN, Issue 1 2007M. Mekki Silverleaf nightshade, Solanum elaeagnifolium, is listed as a noxious weed in its native range (Americas) and as an invasive alien plant in many countries across the world. Its local pattern of distribution in the EPPO region indicates that it is still in an establishment phase. S. elaeagnifolium invasiveness could be related to several biological traits: copious production of sexual and asexual propagules, its facility for long-distance dispersion, its ability to endure considerable drought and to dominate shallow-rooted vegetation, especially during summer dry periods, and its capacity to suppress more valuable species because it is unpalatable and toxic to cattle. Invasion of the Mediterranean semi-arid region by S. elaeagnifolium was mainly facilitated by irrigation and animal production. Low moisture stress may favour this invasive species and sheep are an important pathway for its long-distance dispersal. Once established, it is one of the most difficult weeds to eradicate because of its network of creeping horizontal and deep vertical roots. Its phenotypic plasticity enables it to adopt a rosette-like growth pattern to escape control by repeated slashing. Thus, S. elaeagnifolium monitoring in the EPPO region is vital in order to contain established populations and prevent invasion. [source] A NOVEL PREFERENCE FOR AN INVASIVE PLANT AS A MECHANISM FOR ANIMAL HYBRID SPECIATIONEVOLUTION, Issue 2 2007Dietmar Schwarz Homoploid hybrid speciation,speciation via hybridization without a change in chromosome number,is rarely documented and poorly understood in animals. In particular, the mechanisms by which animal homoploid hybrid species become ecologically and reproductively isolated from their parents are hypothetical and remain largely untested by experiments. For the many host-specific parasites that mate on their host, choosing the right host is the most important ecological and reproductive barrier between these species. One example of a host-specific parasite is the Lonicera fly, a population of tephritid fruit flies that evolved within the last 250 years likely by hybridization between two native Rhagoletis species following a host shift to invasive honeysuckle. We studied the host preference of the Lonicera fly and its putative parent species in laboratory experiments. The Lonicera fly prefers its new host, introduced honeysuckle, over the hosts of both parental species, demonstrating the rapid acquisition of preference for a new host as a means of behavioral isolation from the parent species. The parent taxa discriminate against each other's native hosts, but both accept honeysuckle fruit, leaving the potential for asymmetric gene flow from the parent species. Importantly, this pattern allows us to formulate hypotheses about the initial formation of the Lonicera fly. As mating partners from the two parent taxa are more likely to meet on invasive honeysuckle than on their respective native hosts, independent acceptance of honeysuckle by both parents likely preceded hybridization. We propose that invasive honeysuckle served as a catalyst for the local breakdown of reproductive isolation between the native parent species, a novel consequence of the introduction of an exotic weed. We describe behavioral mechanisms that explain the initial hybridization and subsequent reproductive isolation of the hybrid Lonicera fly. These results provide experimental support for a combination of host shift and hybridization as a model for hybrid speciation in parasitic animals. [source] Verbreitung und Differenzierung der mitteleuropäischen Unterarten von Buglossoides arvensis (L.) I. M. Johnst. (Boraginaceae),FEDDES REPERTORIUM, Issue 1-2 2003A. Clermont In Mitteleuropa sind zwei Unterarten des Ackersteinsamens (Buglossoidesarvensis subsp. arvensis, B. arvensis subsp. sibthorpiana) verbreitet. Die molekularbiologische Untersuchung der nucleären ITS1-Region von 55 mitteleuropäischen Belegen verdeutlicht die Eigenständigkeit der beiden Sippen. Innerhalb des 238 Basenpaare langen Markers unterscheiden sich die Unterarten durch 15 Substitutionen (6,4 %). Die Ergebnisse lassen den Schluss zu, dass die Unterarten bisher aufgrund ihrer morphologischen Plastizität oft verwechselt und Häufigkeit und Verbreitung der Subspecies sibthorpiana unterschätzt wurden. Morphologisch lassen sich die beiden Unterarten anhand folgender Merkmale unterscheiden: Buglossoides arvensis subsp. arvensis besitzt längliche Keimblätter, eine gerade Gynobasis, einen unverdickten, geraden Pedicellus sowie cremefarbene oder selten leicht rosa gefärbte Blüten. Buglossoides arvensis subsp. sibthorpiana zeichnet sich durch runde Keimblätter, eine zur Fruchtzeit leicht zur Blütenstandsachse geneigte Gynobasis, einen schiefen, verdickten Pedicellus an den unteren Früchten und blaue, rosa oder cremefarben gefärbte Blüten aus. Weiterhin unterscheiden sich die Unterarten in ihren ökologischen Ansprüchen: B. arvensis subsp. arvensis kommt nur als Ackerunkraut vor, B. arvensis subsp. sibthorpiana wächst sowohl auf Ackerstandorten als auch auf Trockenrasen, sandigen Ruderalflächen oder in trockenen, lichten Wäldern. Distribution and differentiation of the Central European subspecies of Buglossoides arvensis (L.) I.M.Johnst. (Boraginaceae) The Corn Gromwell (Buglossoides arvensis) has two Central European subspecies, B. arvensis subsp. arvensis and B. arvensis subsp. sibthorpiana. The ITS1-region of 55 European samples was amplified and sequenced and it yielded a 238 bp fragment, which consistently differed by 15 substitutions between the two subspecies. The results suggest that the two subspecies indeed represent two independent taxa and have been confused mainly because of their morphological plasticity. Because of this confusion, distribution and abundance were poorly understood. The subspecies as here re-defined can be distinguished as follows: B. arvensis subsp. arvensis has oblong cotyledons, a horizontal gynobase, an unthickened pedicel in fruit, and a cream-coloured corolla. B. arvensis subsp. sibthorpiana has circular cotyledons, an oblique gynobase, an obliquely thickened pedicel in fruit, and a light blue to (more rarely) cream-coloured corolla. The two taxa show some degree of ecological differentiation: B. arvensis subsp. arvensis is only found as a weed in winter cereals, whereas B. arvensis subsp. sibthorpiana is occasionally found as a weed in fields, but also on dry grasslands, sandy waste sites and road sides, and in dry, open forests. [source] The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk streamFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2009W. D. RILEY Abstract, The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels. [source] Seasonal variation in habitat use by salmon, Salmo salar, trout, Salmo trutta and grayling, Thymallus thymallus, in a chalk streamFISHERIES MANAGEMENT & ECOLOGY, Issue 4 2006W. D. RILEY Abstract, A portable multi-point decoder system deployed in a tributary of the River Itchen, a southern English chalk stream, recorded the habitats used by PIT-tagged juvenile salmon, Salmo salar L., trout, Salmo trutta L. and grayling, Thymallus thymallus L., with a high degree of spatial and temporal resolution. The fishes' use of habitat was monitored at 350 locations throughout the stream during September/October 2001 (feeding period) and January/February 2002 (over-wintering period). Salmon parr tended to occupy water 25,55 cm deep with a velocity between 0.4 and 1.0 m s,1. During both autumn and winter, first year salmon (0+ group) were associated with gravel substrate during the daytime and aquatic weed at night. In autumn, 1+ salmon were strongly associated with hard mud substrates during the day and with marginal tree roots at night. In winter, they were located on gravel substrate by day and gravel and mud at night. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. During the autumn, 0+ trout were located along shallow (5,10 cm) and slow (,0.1,0.4 m s,1) margins of the stream, amongst tree roots by day and on silty substrates at night. During winter the 0+ trout occupied silty substrates at all times. As age increased, trout increasingly used coarse substrates; hard mud, gravel and chalk, and weed at night. All age groups of grayling (0+, 1+ and 2+) tended to occupy hard gravel substrate at all times and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40,70 cm deep with a velocity between 0.3 and 0.5 ms,1, whilst the 0+ groups showed a preference for shallower water with reduced velocity at night, particularly in the winter. There were greater differences in the habitats used between species and age groups than between the autumn and winter periods, and the distribution of fish was more strongly influenced by substrate type than water depth or velocity. The results are discussed in relation to the habitat requirements of mixed salmonid populations and habitat management. [source] Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in managementFRESHWATER BIOLOGY, Issue 5 2003J. F. Wright SUMMARY 1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50-m section of a chalk stream in Berkshire, England between June 1975,79 and June 1997,2001. 2. The site was part of a trout fishery in 1975,79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997,2001, the site was heavily shaded by trees and riparian vegetation. 3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat. 4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975,79 than in 1997,2001, total family richness for the site in each year did not differ significantly between sampling periods. 5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975,79 and 57 in 1997,2001. This small increase in site family richness may be due to the invading marginal plants. 6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation. 7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources. 8. Whereas macroinvertebrate family richness has been conserved under the recent ,no management' regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout. [source] COMPARING INVASIVE NETWORKS: CULTURAL AND POLITICAL BIOGRAPHIES OF INVASIVE SPECIES,GEOGRAPHICAL REVIEW, Issue 2 2004PAUL ROBBINS ABSTRACT. Under what cultural and political conditions do certain species become successful invaders? What impact does species invasion have on human culture and politics? The work assembled in this special issue of the Geographical Review suggests complex interspecies interactions that complicate any answer to these questions. It demonstrates the need to advance a more integrative human/environment approach to species invasion than has hitherto been seen. Reviewing the concepts demonstrated in these articles and applying them to case histories of Mimosaceae (a family that includes genera such as Acacia, Prosopis, and Mimosa) invasion, two general principles become clear. The status and identification of any species as an invader, weed, or exotic are conditioned by cultural and political circumstances. Furthermore, because the human "preparation of landscape" is a prerequisite for most cases of invasion, and because species invasions impact local culture and politics in ways that often feed back into the environmental system, specific power-laden networks of human and non-human actors tend to create the momentum for invasion. It is therefore possible to argue a more general cultural and political account of contemporary species expansion: It is not species but sociobiological networks that are invasive. [source] Effects of temperature and fertilization on nitrogen cycling and community composition of an urban lawnGLOBAL CHANGE BIOLOGY, Issue 9 2008NEETA S. BIJOOR Abstract We examined the influence of temperature and management practices on the nitrogen (N) cycling of turfgrass, the largest irrigated crop in the United States. We measured nitrous oxide (N2O) fluxes, and plant and soil N content and isotopic composition with a manipulative experiment of temperature and fertilizer application. Infrared lamps were used to increase surface temperature by 3.5±1.3 °C on average and control and heated plots were split into high and low fertilizer treatments. The N2O fluxes increased following fertilizer application and were also directly related to soil moisture. There was a positive effect of warming on N2O fluxes. Soils in the heated plots were enriched in nitrogen isotope ratio (,15N) relative to control plots, consistent with greater gaseous losses of N. For all treatments, C4 plant C/N ratio was negatively correlated with plant ,15N, suggesting that low leaf N was associated with the use of isotopically depleted N sources such as mineralized organic matter. A significant and unexpected result was a large, rapid increase in the proportion of C4 plants in the heated plots relative to control plots, as measured by the carbon isotope ratio (,13C) of total harvested aboveground biomass. The C4 plant biomass was dominated by crabgrass, a common weed in C3 fescue lawns. Our results suggest that an increase in temperature caused by climate change as well as the urban heat island effect may result in increases in N2O emissions from fertilized urban lawns. In addition, warming may exacerbate weed invasions, which may require more intensive management, e.g. herbicide application, to manage species composition. [source] Seedling recruitment dynamics of forage and weed species under continuous and rotational sheep grazing in a temperate New Zealand pastureGRASS & FORAGE SCIENCE, Issue 2 2005G. R. Edwards Abstract Understanding the grazing conditions under which plant populations are limited by seed availability (seed limitation) is important for devising management schemes that aim to manipulate the establishment of weed and forage species. Seeds of three weed species (Cirsium arvense, C. vulgare and Rumex obtusifolius) and five forage species (Lolium perenne, Lotus uliginosus syn. L. pedunculatus, Paspalum dilatatum, Plantago lanceolata and Trifolium repens) were broadcast sown into L. perenne,T. repens pastures in Manawatu, New Zealand and five sheep-grazing and two slug-grazing (with and without molluscicide) treatments were imposed in a split-plot design. Of the five sheep-grazing treatments, four compared continuous grazing with rotational grazing at intervals of 12, 24 and 36 d in spring, with all four grazed under a common rotation for the remainder of the year. The fifth treatment was continuous grazing all year. Seed sowing increased seedling emergence of C. vulgare, L. perenne, P. lanceolata, R. obtusifolius and T. repens under all sheep- and slug-grazing treatments, with differences in seedling densities persisting for at least 21 months. Seed sowing did not increase seedling densities of C. arvense, L. uliginosus or P. dilatatum. The effects of sheep-grazing management on seedling emergence and survival were uncoupled. For the five seed-limited species, seedling emergence was greater on pastures that were rotationally grazed during spring compared with those that were continuously grazed. However, seedling survival was lower in pastures grazed rotationally during summer, autumn and winter, so that after 21 months seedling numbers were greater on plots that were continuously grazed all year. Exclusion of slugs increased seedling recruitment of T. repens but had no impact on the other species. As weed and forage species responded in a similar way to sheep-grazing management (increased under continuous, decreased under rotational), it is unlikely that the goals of reducing weed invasions and enhancing forage species establishment could be carried out concurrently in established pastures with the same management. [source] Contrasting infection frequencies of Neotyphodium endophyte in naturalized Italian ryegrass populations in Japanese farmlandsGRASSLAND SCIENCE, Issue 2 2010Masayuki Yamashita Abstract Neotyphodium endophytes often confer benefits to their host grasses and may enhance invasiveness of some grasses. The knowledge of infection frequencies of endophytes among invading weed populations is necessary to understand the relationships between endophyte infection and invasiveness. Here we present data on infection frequencies of Italian ryegrass (Lolium multiflorum Lam.), an important weed in some farmlands in Japan, persisting in contrasting farmlands: a terraced paddy field and a wheat-soybean double-cropped field in the western region of Shizuoka prefecture, Japan. The terraced paddy site is a mosaic of several landscape elements such as paddy fields, levees, fallow and abandoned fields, with a high percentage of non-crop area. Rice (Oryza sativa L.) has been cultivated for more than a decade with no application of chemical fertilizers, pesticides and fungicides. The wheat-soybean field is characterized by the aggregation of large-scaled fields that were originally reconstructed paddy fields, showing a low percentage of non-crop area. Wheat and soybean have been grown as winter and summer crops, respectively, using chemical fertilizers and herbicides. We examined the presence or absence of endophytes in a total of 1200 seeds sampled from the two Italian ryegrass populations. The terraced paddy population exhibited a markedly high infection frequency (91.0%), due possibly to selective feeding of non-infected seeds by insects. In contrast, the wheat-soybean farmland population showed almost no infection (1.1%), whereas the putative source of the invasion in the proximity exhibited a relatively high infection rate (64.4%). Such a micro-scale variation in infection frequencies may be attributable to a loss in endophyte viability within the wheat-soybean field. The findings suggest that endophyte infection frequency may markedly differ among the Italian ryegrass populations even within the same region, presumably depending on the abundance of the seed-eating insects, farmland management regimes and/or environmental conditions such as soil humidity. [source] Response of Weed Communities to Legume Living Mulches in Winter WheatJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2007J. Hiltbrunner Abstract In order to obtain information about the impact of legume cover crops on the weed community in organic farming, winter wheat (Triticum aestivum L.) was directly drilled in rows 0.1875 and 0.3750 m apart in living mulches that consisted of Trifolium repens L. (TRFRE), T. subterraneum L. (TRFSU), Medicago truncatula Gaertner (MEDTR), and Lotus corniculatus L. (LOTCO). A control treatment without cover crops (NAT, the site-specific weed community) was also established. The vegetation between the wide rows was either mulched or left undisturbed. The effect of liquid farmyard manure (60 m3 ha,1) was also tested. TRFRE, TRFSU, and LOTCO effectively suppressed Poa annua L. and Matricaria recutita L. at site 1 and P. annua, Capsella bursa-pastoris (L.) Med., and Stellaria media (L.) Vill. at site 2 when compared with NAT. MEDTR, which died during the winter, provided little weed suppression. Mulching significantly suppressed dicotyledonous weed species, but favoured Poa trivialis L. No manure effect was observed. Winter hardy legume cover crops contribute to weed suppression in winter wheat. However, careful evaluation of cover crop × weed × management interactions is necessary to understand the risk for the establishment of problematic weeds. [source] Allelopathic Effects of Parthenium hysterophorus Extracts on Seed Germination and Seedling Growth of Eragrostis tefJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2002T. Tefera The present study was conducted to investigate the allelopathic effects of Parthenium hysterophorus weed on seed germination and seedling growth of tef. Flower, stem, root and leaf aqueous extracts of Parthenium at 0, 1, 5, and 10 % concentrations were applied to determine their effect on tef seed germination and seedling growth under laboratory conditions. Increasing concentrations of aqueous extracts of Parthenium from leaf and flower inhibited seed germination and complete failure of seed germination was recorded when the extract concentration from the leaf part was 10 %. In contrast, aqueous extracts from stem and root had no effect on tef seed germination. Roots appeared more sensitive to allelopathic effect than shoots. Extracts from flower, root and stem had a stimulatory effect on shoot length at all concentration levels, as against an inhibitory effect of leaf extracts. Root extracts at low concentration (1 %) greatly promoted root length but aqueous extracts from leaf and flower inhibited root length. [source] Interacting effects of management and environmental variability at multiple scales on invasive species distributionsJOURNAL OF APPLIED ECOLOGY, Issue 6 2009Jeffrey M. Diez Summary 1. The distribution and abundance of invasive species can be driven by both environmental variables and land management decisions. However, understanding these relationships can be complicated by interactions between management actions and environmental variability, and differences in scale among these variables. The resulting ,context-dependence' of management actions may be well-appreciated by ecologists and land managers, but can frustrate attempts to apply general management principles. 2. In this study, we quantify the effects of land management and environmental variability at different scales on the occurrence and abundance of Hieracium pilosella, a major agricultural weed in New Zealand. We used a hierarchical study design and analysis to capture relevant scales of variation in management actions and environmental heterogeneity, and test hypotheses about how these factors interact. 3. We show that fertilizing and grazing interact with environmental gradients at the scale of management application (farm paddocks) to influence the establishment and local abundance of H. pilosella. 4. We further show that H. pilosella's relationships with fine-scale abiotic and biotic factors are consistent with expected mechanisms driven by larger-scale management actions. Using data on occurrence and local abundance, we tease apart which factors are important to establishment and subsequent local spread. 5.Synthesis and applications. A major challenge for environmental scientists is to predict how invasive species may respond to ongoing landscape modifications and environmental change. This effort will require approaches to study design and analysis that can accommodate complexities such as interacting management and environmental variables at different scales. Management actions will be more likely to succeed when they explicitly account for variation in environmental context. [source] Influence of herbivory, competition and soil fertility on the abundance of Cirsium arvense in acid grasslandJOURNAL OF APPLIED ECOLOGY, Issue 2 2000G.R. Edwards Summary 1. ,The extent to which the weed Cirsium arvense (creeping thistle) may be controlled by manipulating interspecific competition and herbivory was examined in two factorial experiments in order to identify non-chemical herbicide-based control methods for the weed. 2. ,In the first experiment, a single spring cultivation of grassland intensively grazed by rabbits led to a 25-fold increase in C. arvense cover within 3 months, the effects of which were still present the following summer. As well as destroying the competing perennial vegetation, cultivation created and dispersed small root fragments (3,5 cm in length) from which almost all shoot recruitment occurred. 3. ,Fencing the cultivated plots against rabbits decreased the cover of C. arvense because ungrazed regrowth from palatable/grazing intolerant species reduced recruitment of C. arvense seedlings and shoots. Seedling competition, in the form of a wildflower seed mix sown soon after cultivation, reduced C. arvense cover on fenced plots to pre-cultivation levels. 4. ,In the second experiment, conducted in a permanent grassland, C. arvense shoot densities on plots fenced against rabbits and treated as a hay meadow were about one-eighth of those found on rabbit-grazed plots where competing vegetation was kept short. Adventitious shoot recruitment was greater on soil disturbances such as molehills and rabbit scrapes than in intact vegetation. Seedling recruitment occurred only on soil disturbances such as molehills. 5. ,Lime and nitrogen fertilizer application to the fenced grassland increased the standing biomass of competing species, which reduced C. arvense shoot density. Outside the fences, rabbit grazing was so concentrated on the competing species of the nitrogen-fertilized and limed areas that C. arvense benefited from competitive release, exhibiting increased shoot density. Cirsium arvense showed pronounced competitive release from grasses, with greater shoot densities where grasses were removed with selective herbicides than where no plant species were removed. 6. ,Exclusion of insects and molluscs with chemical pesticides had no effect on shoot or seedling recruitment or overall shoot density on cultivated soil or in permanent grassland. 7. ,It is concluded that combinations of management procedures that encourage interspecific competition, such as sowing crops soon after cultivation and delaying grazing of them, and nitrogen fertilizer application and non- or reduced grazing of intact grasslands, will help reduce C. arvense abundance. [source] Interactions between nutrient status and weevil herbivory in the biological control of water hyacinthJOURNAL OF APPLIED ECOLOGY, Issue 1 2000Tim A. Heard Summary 1.,Despite the widespread release of effective biocontrol agents, water hyacinth remains the world's most problematic aquatic weed, particularly in eutrophic waterbodies. However, understanding of the interaction between control and trophic status is still incomplete. 2.,Growth of water hyacinth plants was measured at two water nutrient concentrations (high and medium) and in the presence and absence of two insect biocontrol agents in a large circulating hydroponic system in a glasshouse. 3.,At the high nutrient concentration (1·6 mg l,1 N and 1·0 mg l,1 P), plants multiplied more quickly, attaining greater biomass. Both insect species reduced plant growth at both nutrient concentrations. Neochetina bruchi, however, performed better than N. eichhorniae at the high nutrient concentration by inflicting more damage on the plants and reducing biomass by a greater extent. 4.,Insect damage reduced the concentrations of nitrogen and phosphorus found in plants growing in high nutrient water but not in medium nutrient water (0·4 mg l,1 N and 0·025 mg l,1 P). 5.,The developmental and reproductive performance of N. bruchi was determined at both nutrient concentrations. Water hyacinth plants grown at higher nutrient concentration were superior hosts to N. bruchi than plants grown at medium concentrations. Net reproductive rate and intrinsic rate of increase were significantly greater at the high concentrations. Greater damage by N. bruchi to water hyacinth at the high nutrient concentration was due to the greater production of offspring, and hence greater larval damage. 6.,We predict that water hyacinth problems will be greater in eutrophic waterbodies, where N. bruchi will be a superior biocontrol agent to N. eichhorniae. In low-nutrient waterbodies, local nutrient enrichment of water may assist the establishment of control agents. These results illustrate the importance of wider ecological factors on the success of biological control. [source] Pests, pesticide use and alternative options in European maize production: current status and future prospectsJOURNAL OF APPLIED ENTOMOLOGY, Issue 5 2010M. Meissle Abstract Political efforts are made in the European Union (EU) to reduce pesticide use and to increase the implementation of integrated pest management (IPM). Within the EU project ENDURE, research priorities on pesticide reduction are defined. Using maize, one of the most important crops in Europe, as a case study, we identified the most serious weeds, arthropod pests, and fungal diseases as well as classes and amounts of pesticides applied. Data for 11 European maize growing regions were collected from databases, publications and expert estimates. Silage maize dominates in northern Europe and grain production in central and southern Europe. Crop rotations range from continuous growing of maize over several years to well-planned rotation systems. Weeds, arthropod pests and fungal diseases cause economic losses in most regions, even though differences exist between northern countries and central and southern Europe. Several weed and arthropod species cause increasing problems, illustrating that the goal of reducing chemical pesticide applications is challenging. Pesticides could potentially be reduced by the choice of varieties including genetically modified hybrids, cultural control including crop rotation, biological control, optimized application techniques for chemicals, and the development of more specific treatments. However, restrictions in the availability of alternative pest control measures, farm organization, and the training and knowledge of farmers need to be overcome before the adoption of environmentally friendly pest control strategies can reduce chemical pesticides in an economically competitive way. The complex of several problems that need to be tackled simultaneously and the link between different control measures demonstrates the need for IPM approaches, where pest control is seen in the context of the cropping system and on a regional scale. Multicriteria assessments and decision support systems combined with pest monitoring programs may help to develop region-specific and sustainable strategies that are harmonized within a EU framework. [source] | ||||||||||||||||||||||||||||||||||||||||||||||