Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Encroachment

  • bush encroachment
  • shrub encroachment

  • Selected Abstracts

    Encroachment of Echinococcus granulosus into urban areas in eastern Queensland, Australia

    DJ Jenkins
    Objective To investigate the prevalence of Echinococcus granulosus in wild dogs (dingos and dingo,domestic dog hybrids) living in and around human habitation on Fraser Island and in townships of the Maroochy Shire, on Queensland's Sunshine Coast, Australia. Design Wild dogs were humanely killed on Fraser Island and in the Maroochy Shire because they were deemed a potential danger to the public. Their intestines were collected and the contents examined for intestinal parasites. Procedure Intestines were removed as soon after death as possible, packed in plastic bags and kept frozen until examination. The intestinal contents were washed, sieved and examined microscopically for the presence of helminths, which were identified and counted. Results Intestines from 108 wild dogs, 7 foxes and 18 Fraser Island dingoes were examined. Echinococcus granulosus was only present in the wild dogs from Maroochy Shire (46.3%) with worm burdens of between 30 and 104,000. Other helminths included Spirometra erinacei, Dipylidium caninum, Taenia spp., Ancylostoma caninum and Toxocara canis. Two specimens of a trematode (Haplorchinae sp.) usually found infecting fish and seabirds were recovered from a Fraser Island dingo. Conclusion Dingoes on Fraser Island are not infected with E. granulosus and do not pose a hydatid disease public health risk to residents or visitors. However, wild dogs examined from the Maroochy Shire do present a potential hydatid disease public health risk. [source]

    Effects of Coastal Lighting on Foraging Behaviorof Beach Mice

    comportamiento de forrajeo; iluminación artificial; polución por luz; ratones de playa (Peromyscus polionotus leucocephalus) Abstract:,Introduction of artificial light into wildlife habitat represents a rapidly expanding form of human encroachment, particularly in coastal systems. Light pollution alters the behavior of sea turtles during nesting; therefore, long-wavelength lights,low-pressure sodium vapor and bug lights,that minimize impacts on turtles are required for beach lighting in Florida (U.S.A.). We investigated the effects of these two kinds of lights on the foraging behavior of Santa Rosa beach mice ( Peromyscus polionotus leucocephalus). We compared patch use and giving-up densities of mice for experimental food patches established along a gradient of artificial light in the field. Mice exploited fewer food patches near both types of artificial light than in areas with little light and harvested fewer seeds within patches near bug lights. Our results show that artificial light affects the behavior of terrestrial species in coastal areas and that light pollution deserves greater consideration in conservation planning. Resumen:,La introducción de luz artificial al hábitat de vida silvestre representa una forma de intrusión humana que se expande rápidamente, particularmente en sistemas costeros. Durante la anidación, la polución por luz altera el comportamiento de tortugas marinas; por tanto, para la iluminación de playas en Florida (E. U. A) se requieren luces de longitud de onda larga , luces de vapor de sodio de baja presión y contra insectos , que minimizan impactos sobre las tortugas. Investigamos los efectos de estos dos tipos de luces sobre el comportamiento de forrajeo de ratones de playa de Santa Rosa ( Peromyscus polionotus leucocephalus). Comparamos el uso de parches y las densidades de rendición de ratones en parches alimenticios experimentales establecidos a lo largo de un gradiente de luz artificial en el campo. Los ratones utilizaron menos parches de forrajeo cercanos a ambos tipos de luz artificial que en áreas con poca iluminación y cosecharon menos semillas en parches cercanos a luces contra insectos. Nuestros resultados muestran que la luz artificial afecta el comportamiento de especies terrestres en áreas costeras y que la polución por luz merece mayor consideración en la planificación de la conservación. [source]

    Fish utilisation of managed realignments

    Abstract, One area of ecological benefit not yet fully evaluated in European waters is the utilisation of restored saltmarsh habitats by fish species. This study examines the utilisation of managed realignments and relic saltmarsh by fish species. Factors affecting habitat heterogeneity and fish populations are discussed, and recommendations are made with respect to scheme design and management that will maximise the biological and socio-economic values. Fish populations in the high intertidal areas were assessed using a suite of techniques, including observations on feeding behaviour. Each microhabitat was discussed as a function of the extent of fish colonisation. A positive relationship between the degree of fish utilisation and habitat heterogeneity was ascertained using species richness, abundance and behavioural observations. This study will aid habitat valuation for economic justification of managed realignments, over and above existing drivers, such as compensatory habitat for encroachment, flood defence and the European Union Habitats Directive. The work now forms part of a wider European Interreg IIIb project, COMCOAST. [source]

    Ecological responses to altered flow regimes: a literature review to inform the science and management of environmental flows

    FRESHWATER BIOLOGY, Issue 1 2010
    Summary 1.,In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management. 2.,For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A ,qualitative' or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values. 3.,Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel. 4.,Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response; however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration. 5.,New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration,ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration. [source]

    The Perils of the Back Seat: Date Rape, Race and Gender in 1950s America

    GENDER & HISTORY, Issue 1 2008
    Lisa Lindquist Dorr
    Dating among white American teenagers in the 1950s caused parents considerable concern, as it represented disturbing developments in sexual expectations. While the rhetoric surrounding marriage celebrated traditional gender roles and monogamy, Americans bemoaned social and moral decay, caused in part by women's encroachment on male prerogatives. Sexual experience for boys increasingly became a defining gender characteristic and a means of achieving manhood as well. Ideas about proper marital norms and studies of dating practices among young people naturalised male aggression as proof of masculinity, which made girls, even ,respectable ones', vulnerable to violence from their dates. As teens' acceptance of going steady became more widespread, older racialised narratives of sexual danger evolved to incorporate new dating trends. Whereas American, and especially southern white, women knew the dangers of the supposed ,black beast rapist', they learnt during the 1950s that a special danger could confront them in the back seat of cars, despite the presence of their white, male date. Even with a white protector, white women remained vulnerable to violence on dates, whether from black men or from their white date. As dating conventions loosened, white women found that that the perils of the back seat only increased. [source]


    ABSTRACT. The census concept of total cropland is a better measure of effective agricultural land than is total farmland, which includes extensive areas of woodland owned by farmers. The cropland area of the United States dropped from 478 million acres in 1949 to 431 million acres in 1997, for a net loss of less than 1 million acres, or roughly one-fifth of 1 percent, per year. In the midwestern agricultural heartland most counties changed less than 5 percent in the half-century, and more counties gained than lost. The West was a crazy quilt of change, and in the East most counties lost more than 10 percent. Major metropolitan counties lost a few percentage points more than did adjacent areas, but at a lower rate per capita than the nation as a whole. Most of the loss of cropland was in marginal agricultural counties with soils of low inherent fertility and topography unsuited to modern farm machinery. The loss of cropland to suburban encroachment may be cause for intense local concern, but attempts to thwart development cannot be justified on grounds of a net national loss of good cropland. [source]


    ABSTRACT. A deficiency common to both the historical debates over loss of agricultural land and the current discussions of urbanization and sprawl is a limited understanding of land-use dynamics beyond the urban fringe. Data aggregated at the county level poorly capture the fine-grained pattern of land-use change beyond the dynamic urban-rural interface. Furthermore, current urban-based definitions are poorly suited to delineate these areas, and low-density, exurban land use is difficult to measure using existing land-cover databases. Urbanization and the conversion of once-agricultural or other natural resource lands to other uses has traditionally been tracked using urban areas, as delimited in the U.S. census. Urban densities are typically defined as areas with more than 1,000 people per square mile, or 1.6 people per acre (U.S. Census Bureau 2000). Assuming an average of 2.5 people per housing unit, this translates to roughly 0.7 units per acre, or approximately 1 unit per 1.6 acres. The analytical units used in the census, however, both overbound and underbound areas with urban densities. About one-third of urban areas in 1990 comprised lower-than-urban housing density, thanks to overbounding. But, then, one-third of locations that had urban-level housing densities failed to be included in urban areas as a result of underbounding, which, if counted, would have constituted another 18 million acres of urban area. An increase over time of the average number of acres required per housing unit in exurban and higher-density locations occurred in roughly one-third of U.S. counties from 1960 to 1990 and persisted from 1990 to 2000. In 2000 roughly 38 million acres were settled at urban densities, and nearly ten times that much land was settled at rates from low, exurban density (as low as one house per 40 acres) to higher rates (up to one per 10 acres). This represents a continuing encroachment on land previously given over to other uses,habitat or agriculture. Practitioners of natural resource management need to recognize the ubiquity of exurban development and better incorporate the fine-scale patterns of land use beyond the urban fringe. [source]

    Shrub expansion stimulates soil C and N storage along a coastal soil chronosequence

    Abstract Expansion of woody vegetation in grasslands is a worldwide phenomenon with implications for C and N cycling at local, regional and global scales. Although woody encroachment is often accompanied by increased annual net primary production (ANPP) and increased inputs of litter, mesic ecosystems may become sources for C after woody encroachment because stimulation of soil CO2 efflux releases stored soil carbon. Our objective was to determine if young, sandy soils on a barrier island became a sink for C after encroachment of the nitrogen-fixing shrub Morella cerifera, or if associated stimulation of soil CO2 efflux mitigated increased litterfall. We monitored variations in litterfall in shrub thickets across a chronosequence of shrub expansion and compared those data to previous measurements of ANPP in adjacent grasslands. In the final year, we quantified standing litter C and N pools in shrub thickets and soil organic matter (SOM), soil organic carbon (SOC), soil total nitrogen (TN) and soil CO2 efflux in shrub thickets and adjacent grasslands. Heavy litterfall resulted in a dense litter layer storing an average of 809 g C m,2 and 36 g N m,2. Although soil CO2 efflux was stimulated by shrub encroachment in younger soils, soil CO2 efflux did not vary between shrub thickets and grasslands in the oldest soils and increases in CO2 efflux in shrub thickets did not offset contributions of increased litterfall to SOC. SOC was 3.6,9.8 times higher beneath shrub thickets than in grassland soils and soil TN was 2.5,7.7 times higher under shrub thickets. Accumulation rates of soil and litter C were highest in the youngest thicket at 101 g m,2 yr,1 and declined with increasing thicket age. Expansion of shrubs on barrier islands, which have low levels of soil carbon and high potential for ANPP, has the potential to significantly increase ecosystem C sequestration. [source]

    Ecohydrological impacts of woody-plant encroachment: seasonal patterns of water and carbon dioxide exchange within a semiarid riparian environment

    Abstract Across many dryland regions, historically grass-dominated ecosystems have been encroached upon by woody-plant species. In this paper, we compare ecosystem water and carbon dioxide (CO2) fluxes over a grassland, a grassland,shrubland mosaic, and a fully developed woodland to evaluate potential consequences of woody-plant encroachment on important ecosystem processes. All three sites were located in the riparian corridor of a river in the southwest US. As such, plants in these ecosystems may have access to moisture at the capillary fringe of the near-surface water table. Using fluxes measured by eddy covariance in 2003 we found that ecosystem evapotranspiration (ET) and net ecosystem exchange of carbon dioxide (NEE) increased with increasing woody-plant dominance. Growing season ET totals were 407, 450, and 639 mm in the grassland, shrubland, and woodland, respectively, and in excess of precipitation by 227, 265, and 473 mm. This excess was derived from groundwater, especially during the extremely dry premonsoon period when this was the only source of moisture available to plants. Access to groundwater by the deep-rooted woody plants apparently decouples ecosystem ET from gross ecosystem production (GEP) with respect to precipitation. Compared with grasses, the woody plants were better able to use the stable groundwater source and had an increased net CO2 gain during the dry periods. This enhanced plant activity resulted in substantial accumulation of leaf litter on the soil surface that, during rainy periods, may lead to high microbial respiration rates that offset these photosynthetic fluxes. March,December (primary growing season) totals of NEE were ,63, ,212, and ,233 g C m,2 in the grassland, shrubland, and woodland, respectively. Thus, there was a greater disparity between ecosystem water use and the strength of the CO2 sink as woody plants increased across the encroachment gradient. Despite a higher density of woody plants and a greater plant productivity in the woodland than in the shrubland, the woodland produced a larger respiration response to rainfall that largely offset its higher photosynthetic potential. These data suggest that the capacity for woody plants to exploit water resources in riparian areas results in enhanced carbon sequestration at the expense of increased groundwater use under current climate conditions, but the potential does not scale specifically as a function of woody-plant abundance. These results highlight the important roles of water sources and ecosystem structure on the control of water and carbon balances in dryland areas. [source]

    Historical shrub,grass transitions in the northern Chihuahuan Desert: modeling the effects of shifting rainfall seasonality and event size over a landscape gradient

    GLOBAL CHANGE BIOLOGY, Issue 10 2003
    Qiong Gao
    Abstract We use a spatially explicit landscape model to investigate the potential role of rainfall on shrub,grass transitions in the Jornada Basin of southern New Mexico during the past century. In long-term simulations (1915,1998) along a 2700 m transect running from a dry lake bed to the foothills of a small mountain, we test two hypotheses: (i) that wetter winters and drier summers may have facilitated shrub encroachment in grasslands, and (ii) that increases in large precipitation events may have increased soil water recharge at deeper layers, thus favoring shrub establishment and growth. Our model simulations generally support the hypothesis that wetter winters and drier summers may have played a key role, but we are unable to reproduce the major shifts from grass- to shrub-domination that occurred in this landscape during the early part of the 1900s; furthermore, the positive shrub response to wetter winters and drier summers was only realized subsequent to the drought of 1951,1956, which was a relatively short ,window of opportunity' for increased shrub establishment and growth. Our simulations also generally support the hypothesis that an increase in the number of large precipitation events may also have favored shrub establishment and growth, although these results are equivocal, depending upon what constitutes a ,large' event and the timing of such events. We found complex interactions among (i) the amount/seasonality of rainfall, (ii) its redistribution in the landscape via run-on and runoff, (iii) the depth of the soil water recharge, and (iv) subsequent water availability for the growth and reproduction of shrubs vs. herbaceous plants at various landscape positions. Our results suggest that only a mechanistic understanding of these interactions, plus the role of domestic cattle grazing, will enable us to elucidate fully the relative importance of biotic vs. abiotic factors in vegetation dynamics in this semiarid landscape. [source]

    Herbage mass and nutritive value of herbage of extensively managed temperate grasslands along a gradient of shrub encroachment

    GRASS & FORAGE SCIENCE, Issue 3 2009
    S. Kesting
    Abstract Semi-natural grasslands often serve as important reserves of biodiversity. In Europe extensive grazing by livestock is considered an appropriate management to conserve biodiversity value and to limit shrub encroachment. However, little is known about the influence of shrubs on agronomic values. A gradient analysis of shrub-invaded temperate grasslands (from shrub-free to pioneer forest) in Germany was carried out to test the hypothesis that herbage mass and variables describing nutritive value of herbage decrease with increasing shrub encroachment. The herbage mass of dry matter (DM), variables describing the nutritive value of herbage, composition of the vegetation and mean of Ellenberg's indicator values were analysed with respect to the extent of shrubs. There was a reduction of herbage mass of DM from 3570 to 210 kg ha,1 with increasing shrub encroachment. Metabolizable energy concentration of herbage ranged from 8·9 to 10·2 MJ kg,1 DM and crude protein concentration from 72 to 171 g kg,1 DM, both measures being positively correlated with shrub occurrence. Increasing shrub occurrence was associated with a decrease in water-soluble carbohydrates concentration (from 151 to 31 g kg,1) and a reduction in the indicator ,forage value'. The results indicate a potentially large agronomic value for shrub-encroached temperate grasslands. [source]

    Short-term transformation of matrix into hospitable habitat facilitates gene flow and mitigates fragmentation

    Summary 1Habitat fragmentation has major implications for demography and genetic structure of natural plant and animal populations as small and isolated populations are more prone to extinction. Therefore, many recent studies focus on spatial fragmentation. 2However, the temporal configuration of suitable habitat may also influence dispersal and gene flow in fragmented landscapes. We hypothesize that short-term switching of inhospitable matrix areas into suitable habitat can mitigate effects of spatial fragmentation in natural and seminatural ecosystems. 3To test our hypothesis, we investigated the hairy-footed gerbil (Gerbillurus paeba, Smith 1836), a ground-dwelling rodent, in fragmented Kalahari savannah areas. Here, rare events of high above mean annual rainfall suggest short-term matrix suitability. 4During the field survey in ,matrix' areas in the Kalahari (shrub encroachment by heavy grazing) we never observed the hairy-footed gerbil in years of average rainfall, but observed mass occurrences of this species during rare events of exceptionally high rainfall. 5In a second step, we developed an agent-based model simulating subpopulations in two neighbouring habitats and the separating matrix. Our mechanistic model reproduces the mass occurrences as observed in the field and thus suggests the possibly underlying processes. In particular, the temporary improvement in matrix quality allows reproduction in the matrix, thereby causing a substantial increase in population size. 6The model demonstrates further how the environmental trigger (rainfall) impacts genetic connectivity of two separated subpopulations. We identified seasonality as a driver of fragmentation but stochasticity leading to higher connectivity. 7We found that our concept of temporal fragmentation can be applied to numerous other fragmented populations in various ecological systems and provide examples from recent literature. We conclude that temporal aspects of fragmentation must be considered in both ecological research and conservation management. [source]

    The impact of cattle ranching on large-scale vegetation patterns in a coastal savanna in Tanzania

    M. W. Tobler
    Summary 1The success of large-scale cattle ranching in African savanna vegetation has often been limited by problems of bush encroachment and disease (in particular trypanosomiasis spread by tsetse flies). Mkwaja Ranch, occupying an area of 462 km2 on the coast of Tanzania, is a recent example of a large ranching enterprise that failed within the savanna environment. It was closed in 2000 after 48 years of operation. In this paper we describe the main vegetation types of the area (excluding closed forest vegetation) and relate their patterns of distribution to the former use of the ranch for cattle. 2The study area comprised the former ranch and parts of the adjacent Saadani Game Reserve, which had not been grazed by cattle for many years and had never been used for large-scale ranching. Following field surveys, 15 distinct types of grassland and bush vegetation were defined and a vegetation map was created using a Landsat TM satellite image. A multispectral classification using the maximum likelihood algorithm gave good results and enabled all 15 vegetation types to be distinguished on the map. 3Two main spatial trends were detected in the vegetation. One was a large-scale decrease in the cover of bushland from the most intensively used parts of the ranch through more extensively used areas to the game reserve; this trend was attributed to differences in management history as well as to climatic and topographic factors. A second trend was a radial vegetation pattern associated with the enclosures where cattle were herded at night. High amounts of three bushland types [dominated by (i) Acacia zanzibarica, (ii) Dichrostachys cinerea, Acacia nilotica or Acacia mellifera and (iii) Terminalia spinosa] occurred in a zone between 300 and 2500 m from the paddocks, with a peak in bush density at about 900 m (mean value for 18 paddocks). In contrast, bushland dominated by Hyphaene compressa was scarce close to the paddocks and became more abundant with distance. There was also a radial trend in the grassland communities: close to the paddocks there was short grass vegetation containing many ruderals and invasive weedy species, while the tall grassland types with species such as Hyperthelia dissoluta and Cymbopogon caesius occurred further away in the areas less affected by cattle. 4Synthesis and applications. The intensive modern livestock ranching as practised on Mkwaja Ranch proved to be unsustainable both economically and ecologically. In the end, the biggest problem faced by the ranch managers was not controlling disease, as had originally been feared, but preventing the spread of bush on pasture land. The results of our study demonstrate just how severe the problem of bush encroachment was, especially in areas close to paddocks. An important lesson for management is that grazing patterns need to be taken into consideration when determining the sustainable stocking rate for an area. To reduce the risk of bush encroachment in grazing systems with focal points such as paddocks or watering points, stocking rates need to be lower than in systems with a more uniform grazing distribution. [source]

    Comparative foraging and nutrition of horses and cattle in European wetlands

    Catherine Menard
    Summary 1Equids are generalist herbivores that co-exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co-existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary. 2In this paper we describe resource-use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski's index 0·58,0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition. 3Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 gDM kg W,0·75 day,1) than in cattle (88 gDM kg W,0·75 day,1). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 gDM kg W,0·75 day,1) than in cattle (51 gDM kg W,0·75 day,1). When food is limiting, horses should outcompete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons. 4Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species. [source]

    Forest progression modes in littoral Congo, Central Atlantic Africa

    Charly Favier
    Abstract Aim, To understand the persistence of a forest,savanna mosaic in places where rainfall data suggest that forest take-over should take place. To study the various modes of forest encroachment, and the role of human activities to hamper it. Location, Data were collected on several forest,savanna ecotones in the coastal region of the Republic of Congo. The sites were chosen to illustrate the differing principal modes of forest expansion, corresponding to different levels of anthropic pressure. Methods, The study sites were situated on five transects perpendicular to the ecotone (total sampled area: 1.7 ha) and 10 forest clumps in savanna (with diameters from 3 to 20 m). Along the transects botanical identification, diameter measurement and cartography were performed, while leaf area index was measured at a high resolution (every metre) along two of them. Collected data were analysed using a continuous quantification approach, which is much more useful than classical quadrat analysis. Time calibration of progression rates was performed using a simple model of the growth of the characteristic pioneer species, Aucoumea klaineana. Results, The two main different modes are reflected in different successional patterns. The edge diffusion is slow (its rate is evaluated to c. 1 m year,1) and is characterized by a progressive increase in large-diameter tree density and shade-tolerant tree density away from the ecotone. Conversely, savanna to forest phase transition by coalescence of clumps exhibits high tree density remnants distributed in established forest. The composition of these remnants is compatible with that of the forest clumps in savannas. Main conclusions, Three functional groups of pioneer trees are distinguished: some occupy the edge (edge pioneer), others establish clumps of forest in savanna (clump pioneers) and the longer-living A. klaineana ensures the transition to ,mature' forest. The two different observed patterns (linear edge progression and clump coalescence) can be understood with the use of a model of forest,savanna dynamics, ,FORSAT'. The two control parameters are the annual rainfall and the frequency of man-made fires in each savanna. In particular, an increase in the fire frequency can lead to a shift from the coalescence regime to the edge progression one. [source]

    A Novel Tetracycline Labeling Schedule for Longitudinal Evaluation of the Short-Term Effects of Anabolic Therapy With a Single Iliac Crest Bone Biopsy: Early Actions of Teriparatide,

    Robert Lindsay MD
    Abstract We describe a quadruple tetracycline labeling method that allows longitudinal assessment of short-term changes in bone formation in a single biopsy. We show that 1 month of hPTH(1-34) treatment extends the bone-forming surface, increases mineral apposition rate, and initiates modeling-based formation. Introduction: Iliac crest biopsy, with histomorphometric evaluation, provides important information about cellular activity in bone. However, to obtain longitudinal information, repeat biopsies must be performed. In this study, we show the capability to obtain short-term longitudinal information on bone formation in a single biopsy using a novel, quadruple labeling technique. Materials and Methods: Two tetracycline labels were administered using a standard 3 days on, 12 days off, 3 days on format. Four weeks later, the tetracycline labeling was repeated using the same schedule but with a different tetracycline that can be distinguished from the first by its color under fluorescent light. Iliac crest biopsies were performed 1 week later and prepared undecalcified for histomorphometry. Indices of bone formation 1 month apart were measured and calculated using the two sets of labels. We used this method to investigate the early effects of teriparatide [hPTH(1-34)] treatment on bone formation. The results were compared with those from a group of control subjects who were quadruple-labeled, but did not receive hPTH(1-34). Results: Treatment with hPTH(1-34) dramatically stimulated bone formation on cancellous and endocortical surfaces. This was achieved by both an increase in the linear rate of matrix apposition and extension of the bone-forming surface. New bone was deposited on previously quiescent surfaces (i.e., modeling-based formation), but a proportion of this could occur by encroachment from adjacent resorption cavities. Conclusions: A single transiliac crest bone biopsy, after sequential administration of two sets of tetracycline labels is a useful approach to study the short-term effects of anabolic agents on human bone. One month of hPTH(1-34) treatment extends the bone-forming surface, increases mineral apposition rate, and initiates modeling-based formation. [source]

    Effects of human,livestock,wildlife interactions on habitat in an eastern Kenya rangeland

    John Otuoma
    Abstract Human,livestock,wildlife interactions have increased in Kenyan rangelands in recent years, but few attempts have been made to evaluate their impact on the rangeland habitat. This study identified drivers of increased human,livestock,wildlife interactions in the Meru Conservation Area between 1980 and 2000 and their effects on the vegetation community structure. The drivers were habitat fragmentation, decline in pastoral grazing range, loss of wildlife dispersal areas and increase in livestock population density. Agricultural encroachment increased by over 76% in the western zone adjoining Nyambene ranges and the southern Tharaka area, substantially reducing the pastoral grazing range and wildlife dispersal areas. Livestock population increased by 41%, subjecting areas left for pastoral grazing in the northern dispersal area to prolonged heavy grazing that gave woody plant species a competitive edge over herbaceous life-forms. Consequently, open wooded grassland, which was the dominant vegetation community in 1980, decreased by c. 40% as bushland vegetation increased by 42%. A substantial proportion of agro pastoralists were encountered around Kinna and Rapsu, areas that were predominantly occupied by pastoralists three decades ago, indicating a possible shift in land use in order to spread risks associated with habitat alterations. Résumé Les interactions hommes-bétail-faune sauvage ont augmenté dans les pâturages kényans ces dernières années, mais il y a eu peu de tentatives pour évaluer leur impact sur cet habitat. Cette étude identifie quelles ont été les raisons sous-jacentes de ces interactions dans l'Aire de Conservation de Meru entre 1980 et 2000, et leurs effets sur la structure de la communauté végétale. Les raisons étaient la fragmentation de l'habitat, le déclin de la surface libre pour le pâturage pastoral, la perte d'aire de dispersion pour la faune sauvage et l'augmentation de la densité de population du bétail. L'envahissement agricole a augmenté de plus de 76% dans la zone ouest touchant les fermes de Nyambene et l'aire sud de Tharaka, réduisant substantiellement l'étendue du pâturage pastoral et les aires de dispersion de la faune sauvage. La population du bétail a augmenté de 41%, soumettant les étendues laissées au pâturage pastoral dans la région de dispersion nord à un pâturage intensif prolongé qui a donné aux espèces végétales ligneuses un avantage sur les formes herbeuses. Par conséquent, la prairie arborée ouverte, qui était la communauté végétale dominante dans les années 1980 a diminué de près de 40% alors que la végétation de broussailles a augmenté de 42%. Une proportion substantielle d'agropastoralistes se rencontraient autour de Kinlla et de Rapsu, des zones qui étaient principalement occupées par des pasteurs il y a trois décennies, ce qui indique une évolution possible de l'utilisation des sols afin de disperser les risques liés à l'altération des habitats. [source]

    Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlings

    Keletso Mopipi
    Abstract The effects of irrigation, nitrogen fertilization, grass competition and clipping were investigated for one growing season at the research farm of the University of Fort Hare in the Eastern Cape Province of South Africa. The aim of the experiment was to assess the short-term performance of Acacia karroo seedlings under different environmental conditions and the implications of such factors on the long-term recruitment of plant species in savanna rangelands. There were no significant treatment effects on the survival of A. karroo seedlings. Using stem length and basal diameter as growth parameters, it was observed that irrigation enhanced both variables, while nitrogen fertilization did not have any significant effects. Clipping, grass competition and their interaction greatly suppressed the growth of the seedlings. Clipping increased the mean stem length when they were irrigated and fertilized. Control and fertilized plants had the highest stem length in the absence of grass competition, while grass competition combined with clipping resulted in the lowest stem length in both irrigated and nonirrigated plants. It was concluded that in the presence of grass competition, controlled browsing could be a viable solution to the problem of bush encroachment in savanna rangelands. Résumé Les effets de l'irrigation, d'une fertilisation à l'azote, de la compétition avec l'herbe et de la taille ont étéétudiés pendant une saison de croissance dans la ferme expérimentale de l'Université de Fort Hare, dans la Province du Cap oriental, en Afrique du Sud. Le but de l'expérience était d'évaluer les performances à court terme de jeunes plants d'Acacia karroo dans différentes conditions expérimentales, et les implications de ces facteurs sur le recrutement à long terme d'espèces végétales dans des pâturages de savane. Il n'y a pas eu d'effet significatif des traitements sur la survie des plants d'A. karroo. En utilisant la longueur des troncs et le diamètre de la base comme indicateurs de croissance, on a observé que l'irrigation augmentait les deux variables, alors que la fertilisation à l'azote n'avait aucun effet significatif. La taille, la compétition avec l'herbe et leur interaction supprimait fortement la croissance des jeunes plants. La taille augmentait la longueur moyenne des troncs lorsqu'ils étaient irrigués et fertilisés. Les plants témoins et les plants fertilisés avaient les troncs les plus longs en absence de toute compétition avec des herbes, alors que cette dernière, combinée avec la taille, aboutissait à la longueur la plus petite des troncs, chez les plants irrigués ou non. On en a conclu qu'en cas de compétition avec des herbes, un pâturage contrôlé pourrait être une solution viable au problème de l'envahissement des broussailles dans les pâturages de savane. [source]

    Impact of land use changes on water resources and biodiversity of Lake Nakuru catchment basin, Kenya

    Jackson Akama Raini
    Abstract Lake Nakuru, Kenya, is one of a series of saline,alkaline closed basin lakes in the eastern arm of the Rift Valley. The lake has been variously described as ,the lake of a million flamingos' and ,the Worlds greatest ornithological spectacle' and is bedrock to the areas' tourism. The lake was designated a bird sanctuary in 1960, a National Park in 1968, first rhino sanctuary in 1987, first Kenyan Ramsar site in 1990, an Important Bird Area in 1999 and a world-class national park in 2005. Over the last 40 years, its basin has been heavily settled, extensively cultivated, urbanized and industrialized. Environmental problems include poor agricultural practices, human encroachment, pollution, wildlife mortality/morbidity, human/wildlife conflicts, poverty, ethnic tensions and land clashes and lack of adequate legal and policy framework. Approaches to conservation have been initiated against identified existing problems and constraints. These approaches are (i) organizational and institutional development; (ii) hot spots and pollution loads management and (iii) catchment and park management. Constraints have been identified as unclear demarcation of responsibilities, lack of budget, skilled staff and know-how and lack of environmental standards and regulations. The impacts of ecosystem changes on people's lives and livelihoods are discussed. [source]

    Bush encroachment under three contrasting land-use practices in a mesic South African savanna

    B. J. Wigley
    Abstract This study determined the effects of land-use practice had on the rate and extent of bush encroachment in a mesic savanna in KwaZulu-Natal, South Africa. Changes in woody cover were measured for 1 km2 sites in areas under communal, commercial and conservation land-use systems for the period between 1937 and 2000. Land users from each area were interviewed to gain the histories of each area and to determine how the changes in woody cover had impacted them and whether anything was being done to counteract the spread of trees and shrubs on their land. Bush encroachment occurred across all three of the land-use types in the 67-year period between 1937 and 2000. The results showed that land-use practice had enormous impacts on the process of bush encroachment. The communal site showed a decrease in grass (21%) and tree (5%) cover and an increase in shrub cover (13%). At the commercial site, there was a considerable decrease in grass cover (46%) and moderate increase in shrub cover (10%) and a massive increase in tree cover (36%). The area under conservation showed a substantial decrease in grass cover (47%), a slight decrease in shrub cover (19%) and a massive increase in tree cover (66%). The perceived causes of these changes were fairly similar amongst the different land users. The changes were mostly not perceived to be a problem for the communal land users. The main advantages mentioned were increased woody resources for building and firewood and increased browse availability. The commercial and conservation land users perceived the changes to have significant negative connotations including the loss of grazing land and biodiversity and secondary invasion of encroached areas by alien plant species. Despite these perceptions, very little has been done to combat bush encroachment in the commercial and conservation land use systems. [source]

    Participatory planning, management and alternative livelihoods for poor wetland-dependent communities in Kampala, Uganda

    Robert Kabumbuli
    Abstract The paper is based on an on-going 3-year study in the wetland communities of Kampala. The study uses participatory methods and aims to contribute to (i) the development of low-income wetland communities, (ii) to prepare these communities to become less dependent on wetlands without receding into poverty, and (iii) the better management of the wetlands. The communities in direct dependence and intimate interaction with Nakivubo wetlands are mainly poor, live and work under hazardous conditions, and their activities pose a threat to the ecological function of the wetlands. Yet these wetlands are important for filtering the city's waste and storm water before it flows into Lake Victoria's Murchison Bay, which is Kampala's source of piped water. Government approaches to the problem of wetland encroachment have largely failed because they are confrontational, and are not consistent or participatory. The study has in the first year conducted a series of activities including stakeholder analysis, resource analysis, livelihood analysis, a questionnaire survey and action planning. Preliminary data show that wetland dependency is very high among the poor nearby communities. They practice cultivation, brick-making and harvesting of wetland vegetation. However, these activities are under threat because wetland resources are dwindling due to increasing population and over-use. Livelihoods are threatened not only by the decreasing productivity of the wetland, but also by the ever-present government threat to evict wetland encroachers to restore its ecology. The study therefore works with communities to prepare for less dependence on wetlands so that they do not suddenly recede into worse poverty if they are evicted. They formulate strategies to enhance alternative livelihood, and for management of the wetland. Action plans have been formulated to address the situation through a newly created association. [source]

    Land use affects rodent communities in Kalahari savannah rangelands

    Niels Blaum
    Abstract Shrub encroachment caused by overgrazing has led to dramatic changes of savannah landscapes and is considered one of the most threatening forms of rangeland degradation leading to habitat fragmentation. Although changes to plant assemblages are becoming better known, however, our understanding of how shrub encroachment affects rodent communities is low. In this study, we investigated relative abundance of five rodent species in sixteen southern Kalahari rangelands where shrub cover ranged from low (<5%) to high (>25%). Rodent abundance was determined on three trapping grids (40 × 100 m) for each site. Our results show that increasing shrub cover affected rodent species differently. The relative abundance of hairy-footed gerbil, short-tailed gerbil and bushveld gerbil declined with increasing shrub cover, whereas highveld gerbil and striped mouse exhibited hump-shaped relationships with shrub cover. Overall, species richness decreased with increasing shrub cover and a negative impact of high shrub cover above 15% on rodent abundance was congruent for all species. We conclude that our results support the hypothesis that long-term heavy grazing that results in area wide shrub encroachment, threatens the diversity of arid environments. Résumé L'envahissement de buissons dû au surpâturage a conduit à des changements spectaculaires des paysages de savane et on le considère comme une des menaces les plus dangereuses pour la dégradation des pâturages menant à la fragmentation de l'habitat. Bien que l'on connaisse mieux les changements qui touchent les associations de plantes, on comprend moins bien comment l'envahissement des buissons affecte les communautés de rongeurs. Ici, nous avons étudié l'abondance relative de cinq espèces de rongeurs dans seize prairies du sud du Kalahari où le couvert de broussailles allait de faible (<5%) àélevé (>25%). L'abondance des rongeurs était déterminée sur trois grilles-pièges (40 m × 100 m) pour chaque site. Nos résultats montrent que l'augmentation de la couverture des buissons affecte les espèces de rongeurs différemment. L'abondance relative de trois espèces de gerbilles (Hairy-footed gerbil, short-tailed gerbil et bushveld gerbil) diminuait avec l'augmentation du couvert buissonneux, alors que la highveld gerbil et la souris striée présentaient une relation <> avec le couvert buissonneux. Partout, la richesse en espèces diminuait avec l'augmentation du couvert des broussailles et l'impact négatif d'une forte couverture de broussailles, au-delà de 15%, sur l'abondance des rongeurs était comparable chez toutes les espèces. Nous concluons que nos résultats soutiennent l'hypothèse selon laquelle un pâturage intense de longue durée aboutit à un large envahissement de buissons et menace la diversité des environnements arides. [source]

    Ecological recovery of an afromontane forest in south- western Uganda

    J. B. Lejju
    Abstract A study of the regeneration of an afromontane forest was carried out in Mgahinga Gorilla National Park (MGNP), south-western Uganda. The area landscape has been subjected to agricultural encroachment for the last 50 years. The landscape was changed by terracing and removing the indigenous vegetation and replacing it with exotic tree species. Stratified random sampling was employed in sampling the vegetation. There was a significant difference in species richness and density in the three habitat types. The natural forest supported the highest stem density (75%) and the lowest stem density (4%) was recorded under exotic woodlots. Seedlings (<2 cm, diameter at breast height) accounted for the majority of juveniles in the three habitats. The natural forest had the highest density (24,625 seedlings ha,1) and exotic woodlots supported the lowest stem density (1350 seedlings ha,1). The level of regeneration in the encroachment area is influenced by the intensity of cultivation and soil nutrients. The advanced growth beneath the exotic woodlots, especially black wattle (Acacia mearnsii) and Eucalyptus sp. stands is relatively impoverished. This condition beneath the exotic species suggests that a low diverse community of native species is able to exploit this environment. [source]

    The production, storage and viability of seeds of Acacia karroo and A. nilotica in a grassy savanna in KwaZulu-Natal, South Africa

    Michele Walters
    Abstract African Acacias are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. They produce large quantities of seed and may have large soil-stored seed banks. In Hluhluwe,Umfolozi Park, the number of adult Acacia nilotica trees per hectare far exceed that of A. karroo adults. The relative dominance is reversed in the juvenile stage with A. karroo outnumbering A. nilotica threefold outside closed woodlands. Acacia karroo trees were smaller than A. nilotica trees on average, but produced more seeds for a given basal diameter size class. Acacia karroo showed less bruchid infestation than A. nilotica at all stages of pod development. Unlike A. nilotica, a proportion of A. karroo seeds was able to germinate after bruchid attack. We detected no difference between the two species in the soil-stored seed bank or in the viability of seeds found in the seed bank. Résumé Les acacias africains sont souvent des contributeurs majeurs de l'augmentation progressive des composants ligneux de la savane, un phénomène connu comme l'envahissement du bush. Ils produisent de grandes quantités de semences et il peut y avoir de grands stocks de semences dans le sol. Dans le Parc de Hluhluwe-Umfolozi, le nombre d'Acacia nilotica adultes par hectare dépasse de loin celui d'A. karroo adultes. Cette dominance relative est inversée au stade juvénile, les A. karrooétant trois fois plus nombreux que les A. nilotica en dehors des forêts fermées. Les Acacia karroo sont en moyenne plus petits que les A. nilotica, mais ils produisent plus de graines pour une classe de diamètre donnée. Les A. karroo présentent une moindre infestation par les bruchidés que les A. nilotica, à tous les stades de développement de la gousse. Contrairement aux graines d'A. nilotica, une certaine proportion de celles d'A. karrooétaient capables de germer après une attaque de bruchidés. Nous n'avons décelé aucune différence entre les deux espèces en ce qui concerne le stock de graines dans le sol ou la viabilité des semences que l'on y trouve. [source]

    Pharmacist prescribing in the UK , a literature review of current practice and research

    A. P. Tonna MRPharmS MSc
    Abstract Objective:, To review the research literature to date on pharmacist prescribing in the United Kingdom (UK) and to explore the main areas of care and practice settings including any benefits and limitations. Findings:, There are two models of pharmacist prescribing in the UK: pharma\cist supplementary prescribing (SP) introduced in 2003, involving a voluntary partnership between the responsible independent prescriber (a physician or a dentist), the supplementary prescriber and the patient, to implement an agreed patient-specific clinical management plan; and pharmacist independent prescribing (IP) introduced in 2006, responsible for the assessment and consequent management, including prescribing of both undiagnosed and diagnosed conditions. There have been narrative reports of pharmacist SP in different health care settings including primary care, community pharmacies, secondary care and at the primary/secondary care interface; published research within these areas of care is conflicting as to which setting is more suitable for pharmacist prescribing. Initial research reports that almost 50% of pharmacist supplementary prescribers self-reported prescribing with both benefits of and barriers to implementing SP. Research involving other healthcare professionals has indicated that encroachment of traditional roles is likely to occur because of the advent of pharmacist prescribing. A small-scale study has concluded that patients are likely to accept pharmacist prescribing favourably, with another study showing pharmacist prescribing leading to improved adherence to guidelines. There is no published research yet available about practices involving pharmacist IP. Discussion:, Most of the literature focuses on pharmacists' perceptions of SP, with little information referring to other stakeholders, including patients. There is also limited published research focusing on clinical and economic outcomes of pharmacist SP. Conclusion:, This is a rapidly changing aspect of pharmacy practice in the UK, particularly with the more recent introduction of pharmacist IP. It is likely that this area of research will expand rapidly over the coming years. [source]

    Phenology of fine roots and leaves in forest and grassland

    JOURNAL OF ECOLOGY, Issue 6 2008
    Diego F. Steinaker
    Summary 1The phenology of temperate vegetation is advancing in association with climate warming. Most phenology data, however, comes from flowers and tree leaves. We tested the generality of results from shoot phenology by expanding data collection in two new directions. We related forest leaf phenology to root phenology, and to phenology in a second habitat, grassland. 2We measured leaf and root phenology simultaneously in aspen forest and adjacent native grassland. Root growth accounts for 80,90% of productivity in these habitats. Seasonal variation in soil moisture and temperature were also measured. 3Forest leaf production was greatest about 45 days before peak root production, resulting in a significant negative correlation between leaf and root production in forest. Grassland leaf production was greatest about 15 days before peak root production, and grassland leaf and root production were significantly positively correlated. The duration of root production was 40% greater than that of shoot production. 4Forest leaf production increased significantly with increasing soil moisture, but not temperature. In contrast, the production of forest roots, grassland roots and grassland leaves increased significantly with soil temperature. 5Synthesis. The most commonly measured aspect of phenology, forest leaves, is out of step with the majority of production in forest, as well as phenology in grassland. The invasion of grassland by woody vegetation is characterized by a decoupling of root and shoot phenology, a result that has not been reported previously. Given the global nature of woody plant encroachment, this decoupling may influence our general understanding of productivity and carbon sequestration in response to warming. [source]

    Disturbance history of a European old-growth mixed-species forest,A spatial dendro-ecological analysis

    Bernhard E. Splechtna
    Abstract Question: We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old-growth forest in Central Europe. Location: The forest, co-dominated by Fagus sylvatica, Picea abies and Abies alba, is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe. Methods: We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1-ha plots distributed across the old-growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic. Results: The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s and 1980s). Peaks and gaps in the disturbance chronologies widely agreed with peaks and gaps in the age distributions. Most disturbance events during single decades showed a random spatial distribution. Conclusions: There is considerable variation in disturbance frequency and/or severity over time. Most disturbance events will rather thin the stand than clear larger areas at once. Following scattered disturbance two pathways occur: (1) gap expansion leading to creation of larger gaps, and (2) gap closure by lateral encroachment or by subcanopy trees growing into the canopy. [source]

    Shrub encroachment in Argentinean savannas

    A.C. Cabral
    Zuloaga et al. (1994, 1996a, b). Some native names were included using quotation marks Abstract. In the Wet Chaco region of Argentina, increasing shrub encroachment in savannas over the last few decades has led to important changes in the structure and functioning of the landscape. Some sectors of this territory are characterized by the appearance of circular clusters of woody patches, dispersed throughout the grassland matrix. The increasing size of these patches leads to a gradual change from grassland to dense shrubland. We studied these circular woody patches in the eastern region of the Argentine province of Formosa and characterized the variation in terms of floristic composition, diversity and predominant seed dispersal mode in different size patches. We observed an increase in species richness, diversity and compositional heterogeneity among patches with increasing patch size. Seed dispersal by animals, especially birds, is an important factor in the expansion of these woody vegetation patches within the grassland matrix. [source]

    Mechanisms blocking Pinus sylvestris colonization of Mediterranean mountain meadows

    Jorge Castro
    Tutin et al. (1964,1980) Abstract. In southern Mediterranean Pinus sylvestris forests there are grassy meadows that resist invasion of trees despite the proximity to seed sources. In this study, we investigate the mechanisms blocking colonization by Pinus sylvestris of the meadows. Two experiments were conducted in which seeds were sown either at 1 cm depth or on the surface to simulate dispersal, and three treatments of vegetation removal were applied: Disturbed (where the herbaceous layer was eliminated, exposing the mineral soil), Clipped (vegetation cut at ground level) and Control (no disturbance of the herbaceous layer). In addition, the effect of seed predators was controlled by using wire cages in the case of the surface sown experiment. When seeds were sown at 1 cm depth, seedling emergence was not reduced by the herbaceous layer. In contrast, when seeds were surface sown and predators were excluded, the rate of emergence was low in the Control treatment, intermediate in Clipped and high in Disturbed. Seedling emergence was, however, minimal when predators were not excluded, irrespective of the disturbance level. Seedling survival and growth after three years of study were similar among treatments. The results show that the seed predation and the physical barrier created by the herbaceous layer are the two mechanisms blocking the encroachment of Pinus sylvestris onto these Mediterranean mountain meadows, limiting the regeneration and potential expansion of the forest. [source]

    Effects of browsing and grazing on cyclic succession in nutrient-limited ecosystems

    Jan Bokdam
    van der Meijden (1990) Abstract. This paper deals with browsing and grazing as forces driving cyclic succession. Between 1989 and 1994 reciprocal transitions between the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa were monitored in permanent plots in a cattle grazed grass-rich Dutch heathland on podsolic soils in which tree encroachment was prevented. Heather beetles killed Calluna in four of the nine plots during 1991/1992. The monitoring revealed reciprocal transitions and cycles between Calluna and Deschampsia on a subplot scale. Beetles and cattle had additional and complementary effects on the two competing species. Defoliation by beetles and trampling by cattle-killed Calluna and favoured grass invasion. Grazing and gap creation by cattle in Deschampsia favoured the establishment and recovery of Calluna. Analysis of the causal mechanisms suggests that indirect, resource-mediated herbivory effects may be as important for the replacement processes as direct effects of defoliation and trampling. Herbivory created differential light and nutrient levels in Calluna and Deschampsia gaps. Grazing and browsing improved the resource-capturing abilities of Calluna and its resistance to herbivory and abiotic disturbances. The emerged Calluna-Deschampsia cycle and its driving forces are summarized in a conceptual triangular resource-mediated successional grazing cycle (RSGC) model, a limit cycle involving herbivore-plant-plant resource interactions. It offers a deterministic equilibrium model as alternative for stochastic transitions between the meta-stable states with dominance of Calluna and Deschampsia respectively. The validity range of the RSGC model and its management implications are briefly discussed. [source]