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Community Change (community + change)

Distribution by Scientific Domains

Life Sciences	56%
Earth and Environmental Science	26%

Selected Abstracts

Tree Community Change across 700 km of Lowland Amazonian Forest from the Andean Foothills to Brazil

BIOTROPICA, Issue 5 2008
Nigel C. A. Pitman
ABSTRACT We describe patterns of tree community change along a 700-km transect through terra firme forests of western Amazonia, running from the base of the Andes in Ecuador to the Peru,Brazil border. Our primary question is whether floristic variation at large scales arises from many gradual changes or a few abrupt ones. Data from 54 1-ha tree plots along the transect support the latter model, showing two sharp discontinuities in community structure at the genus level. One is located near the Ecuador,Peru border, where the suite of species that dominates large areas of Ecuadorean forest declines abruptly in importance to the east. This discontinuity is underlain by a subterranean paleoarch and congruent with a change in soil texture. A second discontinuity is associated with the shift from clay to white sand soils near Iquitos. We hypothesize that the first discontinuity is part of an edaphic boundary that runs along the Andean piedmont and causes a transition from tree communities preferring richer, younger soils near the base of the Andes to those preferring poorer, older soils farther east. Because the floristic changes observed at this discontinuity are conserved for large distances to the east and west of it, the discontinuity is potentially key for understanding floristic variation in western Amazonia. The significant floristic turnover at the Ecuador,Peru border suggests that the only large protected area in the region,Ecuador's Yasuní National Park,is not adequate protection for the very diverse tree communities that cover vast areas of northern Peru. RESUMEN Describimos cambios en la comunidad de árboles a lo largo de un transecto de 700 km que atraviesa los bosques de tierra firme de la Amazonía occidental, desde la base de los Andes en Ecuador hasta la frontera Perú-Brasil. Nuestra pregunta principal es si la variación florística a grandes escalas es generada a base de muchos cambios graduales o en unos pocos cambios abruptos. Datos de 54 parcelas de árboles de 1 ha a lo largo del transecto apoyan el segundo modelo, mostrando dos discontinuidades bien definidas en la estructura de la comunidad a nivel de género. Una discontinuidad está localizada cerca de la frontera Ecuador-Perú, donde el grupo de especies que domina grandes áreas de la Amazonía ecuatoriana declina abruptamente en importancia hacia el este. Esta discontinuidad está asociada con un paleoarco subterráneo y es congruente con cambios en la textura del suelo. Una segunda discontinuidad está asociada con un cambio de suelos arcillosos a suelos de arena blanca cerca de Iquitos. Sugerimos que la primera discontinuidad es parte de un limite edáfico que corre a lo largo del piedemonte andino y causa una transición de comunidades de árboles que prefieren suelos más fértiles y jóvenes cerca de los Andes, a aquellos que prefieren suelos más pobres y antiguos hacia el este. Ya que los cambios florísticos observados en esta discontinuidad se conservan por grandes distancias hacia el este y oeste, la discontinuidad es potencialmente clave para entender la variación florística en la Amazonía occidental. El importante recambio florístico en la frontera Ecuador-Perú sugiere que la única gran área protegida en la región,el Parque Nacional Yasuní en Ecuador,no presta protección adecuada a las muy diversas comunidades de árboles en el norte del Perú. [source]

Abrupt community change on a rocky shore , biological mechanisms contributing to the potential formation of an alternative state

ECOLOGY LETTERS, Issue 6 2004
Robert T. Paine
Abstract The 1997/1998 El Niño initiated a major shift in the intertidal assemblage on the Washington State outer coast. A 25 year time series (1978,2003) shows stands of dominant canopy algae replaced by mussel beds. A prior experiment had indicated that mussels can become too large to be eaten by starfish; newly initiated starfish removals predict mussel attainment of a size refuge. Such escapes inhibit recovery towards prior community composition and enhance development of alternative community states which may persist long after the originating forcing has lessened or disappeared. [source]

Detecting active methanogenic populations on rice roots using stable isotope probing

ENVIRONMENTAL MICROBIOLOGY, Issue 3 2005
Yahai Lu
Summary Methane is formed on rice roots mainly by CO2 reduction. The present study aimed to identify the active methanogenic populations responsible for this process. Soil-free rice roots were incubated anaerobically under an atmosphere of H2/13CO2 or N2/13CO2 with phosphate or carbonate (marble) as buffer medium. Nucleic acids were extracted and fractionated by caesium trifluoroacetate equilibrium density gradient centrifugation after 16-day incubation. Community analyses were performed for gradient fractions using terminal restriction fragment polymorphism analysis (T-RFLP) and sequencing of the 16S rRNA genes. In addition, rRNA was extracted and analysed at different time points to trace the community change during the 16-day incubation. The Methanosarcinaceae and the yet-uncultured archaeal lineage Rice Cluster-I (RC-I) were predominant in the root incubations when carbonate buffer and N2 headspace were used. The analysis of [13C]DNA showed that the relative 16S rRNA gene abundance of RC-I increased whereas that of the Methanosarcinaceae decreased with increasing DNA buoyant density, indicating that members of RC-I were more active than the Methanosarcinaceae. However, an unexpected finding was that RC-I was suppressed in the presence of high H2 concentrations (80%, v/v), which during the early incubation period caused a lower CH4 production compared with that with N2 in the headspace. Eventually, however, CH4 production increased, probably because of the activity of Methanosarcinaceae, which became prevalent. Phosphate buffer appeared to inhibit the activity of the Methanosarcinaceae, resulting in lower CH4 production as compared with carbonate buffer. Under these conditions, Methanobacteriaceae were the prevalent methanogens. Our study suggests that the active methanogenic populations on rice roots change in correspondence to the presence of H2 (80%, v/v) and the type of buffer used in the system. [source]

Short-term climatic trends affect the temporal variability of macroinvertebrates in California ,Mediterranean' streams

FRESHWATER BIOLOGY, Issue 12 2007
LEAH A. BÊCHE
Summary 1. Long-term studies in ecology are essential for understanding natural variability and in interpreting responses to disturbances and human perturbations. We assessed the long-term variability, stability and persistence of macroinvertebrate communities by analysing data from three regions in northern California with a mediterranean-climate. During the study period, precipitation either increased or decreased, and extreme drought events occurred in each region. 2. Temporal trends in precipitation resulted in shifts from ,dry-year' communities, dominated by taxa adapted to no or low flow, to ,wet-year' communities dominated by taxa adapted to high flows. The abundance of chironomid larvae was an important driver of community change. Directional change in community composition occurred at all sites and was correlated with precipitation patterns, with more dramatic change occurring in smaller streams. 3. All communities exhibited high to moderate persistence (defined by the presence/absence of a species) and moderate to low stability (defined by changes in abundance) over the study period. Stability and persistence were correlated with climatic variation (precipitation and El Niño Southern Oscillation) and stream size. Stability and persistence increased as a result of drought in small streams (first-order) but decreased in larger streams (second- and third-order). Communities from the dry season were less stable than those from the wet-season. 4. This study demonstrates the importance of long-term studies in capturing the effects of and recovery from rare events, such as the prolonged and extreme droughts considered here. [source]

Variable sensitivity of plant communities in Iceland to experimental warming

GLOBAL CHANGE BIOLOGY, Issue 4 2005
Ingibjörg S. Jónsdóttir
Abstract Facing an increased threat of rapid climate change in cold-climate regions, it is important to understand the sensitivity of plant communities both in terms of degree and direction of community change. We studied responses to 3,5 years of moderate experimental warming by open-top chambers in two widespread but contrasting tundra communities in Iceland. In a species-poor and nutrient-deficient moss heath, dominated by Racomitrium lanuginosum, mean daily air temperatures at surface were 1,2°C higher in the warmed plots than the controls whereas soil temperatures tended to be lower in the warmed plots throughout the season. In a species-rich dwarf shrub heath on relatively rich soils at a cooler site, dominated by Betula nana and R. lanuginosum, temperature changes were in the same direction although more moderate. In the moss heath, there were no detectable community changes while significant changes were detected in the dwarf shrub heath: the abundance of deciduous and evergreen dwarf shrubs significantly increased (>50%), bryophytes decreased (18%) and canopy height increased (100%). Contrary to some other studies of tundra communities, we detected no changes in species richness or other diversity measures in either community and the abundance of lichens did not change. It is concluded that the sensitivity of Icelandic tundra communities to climate warming varies greatly depending on initial conditions in terms of species diversity, dominant species, soil and climatic conditions as well as land-use history. [source]

Implementing a community intervention to reduce young people's risks for getting HIV: Unraveling the complexities

JOURNAL OF COMMUNITY PSYCHOLOGY, Issue 2 2004
Maretha J. Visser
The ineffectiveness of community-based interventions can often be traced to problems that occur during implementation. In this study, we outline the implementation of a human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) prevention program in an educational setting in South Africa. An action research approach was used in the implementation of the intervention and a process and outcome evaluation, integrating qualitative and quantitative research methods, was made. The research illustrated the various levels of interaction in the community and the complexity of the processes involved in the implementation of interventions to facilitate community change. Social ecological theory, systems theory, and the social constructional approach are used to clarify the complexities of the implementation of community interventions. © 2004 Wiley Periodicals, Inc. J Comm Psychol 32: 145,165, 2004. [source]

Justice and local community change: Towards a substantive theory of justice

JOURNAL OF COMMUNITY PSYCHOLOGY, Issue 6 2002
Neil M. Drew
Justice is a core principle in community psychology, yet has been the subject of relatively little systematic research. In the social psychological literature on the other hand there is a long tradition of research on justice in social life. In this article the potential benefits of integrating the social justice aspirations of community psychology and the conceptualizations of procedural and distributive justice from social psychology are discussed in the context of planned community change. The benefits of exploring justice in this way are illustrated with reference to a research project examining public perceptions of the fairness of roadside tree lopping. Although the issue may appear trivial, it was seen by the local residents as important. The results support the development, application, and utility of a social community psychology of justice to issues of community change. © 2002 Wiley Periodicals, Inc. [source]

Linking physiological traits to impacts on community structure and function: the role of root hemiparasitic Orobanchaceae (ex-Scrophulariaceae)

JOURNAL OF ECOLOGY, Issue 1 2005
G. K. PHOENIX
Summary 1The hemiparasitic Orobanchaceae (ex-Scrophulariaceae) are characterized by a distinctive suite of ecophysiological traits. These traits have important impacts on host plants and non-host plants, and influence interactions with other trophic levels. Ultimately, they can affect community structure and functioning. Here, we review these physiological traits and discuss their ecological consequences. 2The root hemiparasitic Orobanchaceae form a convenient subset of the parasitic angiosperms for study because: they are the most numerous and most widely distributed group of parasitic angiosperms; their physiological characteristics have been well studied; they are important in both agricultural and (semi)natural communities; and they are tractable as experimental organisms. 3Key traits include: high transpiration rates; competition with the host for nutrients and haustorial metabolism of host-derived solutes; uptake of host-derived secondary metabolites; dual autotrophic and heterotrophic carbon nutrition; distinct carbohydrate biochemistry; high nutrient concentrations in green leaf tissue and leaf litter; and small (often hairless and non-mycorrhizal) roots. 4Impacts on the host are detrimental, which can alter competitive balances between hosts and non-hosts and thus result in community change. Further impacts may result from effects on the abiotic environment, including soil water status, nutrient cycling and leaf/canopy temperatures. 5However, for non-host species and for organisms that interact with these (e.g. herbivores and pollinators) or for those that benefit from changes in the abiotic environment, the parasites may have an overall positive effect, suggesting that at the community level, hemiparasites may also be considered as mutualists. 6It is clear that through their distinctive suite of physiological traits hemiparasitic Orobanchaceae, have considerable impacts on community structure and function, can have both competitive and positive interactions with other plants, and can impact on other trophic levels. Many community level effects of parasitic plants can be considered analogous to those of other parasites, predators or herbivores. [source]

Vegetation change from chronic stress events: Detection of the effects of tide gate removal and long-term drought on a tidal marsh

JOURNAL OF VEGETATION SCIENCE, Issue 3 2007
Paul R. Wetzel
Godfrey & Wooten (1979, 1981) Abstract Question: Chronic stress events are defined as disturbance events that exceed the lifespan of the dominant plant species, fluctuate in intensity and lack abruptness or physical destruction of biomass. Can the effects of chronic stress events be measured on vegetation communities? Did two chronic stress events, the removal of a tide gate and a four year drought, cause a temporary or permanent shift in the vegetation communities of a tidal marsh? Location: Tidal marsh in southeastern United States. Methods: Change in species composition and dominance and community change on a landscape level salinity gradient were measured between time periods ranging from four months to seven years to construct a statistical baseline reference community at freshwater, oligohaline, and mesohaline sections of a tidal marsh. Statistical shifts in the plant community were defined as changes in the plant community that fell outside of the defined baseline reference community. Results: Plant community changes outside of the reference community occurred in 13 out of 378 community comparisons. Removal of the tide gate had a greater effect on interstitial salinity levels than the drought and was most intense in the oligohaline marsh, where between 20 to 45% of the freshwa-ter/oligohaline community types permanently converted to oligohaline community types. However, community shifts in the freshwater and oligohaline marsh induced by the drought were temporary, lasting from 1 to 3+ years. Neither chronic stress event permanently altered the mesohaline plant communities. Conclusion: The effects of chronic stress events could be detected; an extended historical record of vegetation change (18 years) was necessary to identify community shifts outside of a reference condition of the community and to determine if those shifts were permanent or temporary. [source]

Restoration of Lake Geneva: Expected versus observed responses of phytoplankton to decreases in phosphorus

LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 2 2002
Orlane Anneville
Abstract Long-term phytoplankton responses in Lake Geneva to a decline in phosphorus (P) loading are examined in terms of summer (July,September) biomass and community structure. With the rapid development of human activity on its banks and within its catchment area in the 1960s, this large subalpine hydrosystem shifted from oligotrophy to eutrophy within approximately one decade. Measures to reduce P loading were initiated successfully in the mid-1970s, when total P concentrations in the winter overturn altered from 90 ,g/L in 1980 to 40 ,g/L in 1998. Until the 1990s, algal descriptors improved as expected (biomass decline, reappearance of diatom species, increased contribution of nanoplankton). Then, paradoxically, and in contrast to the reappearance of oligotrophic species, summer algal biomass began to increase. Pre-summer (period prior to the beginning of the clear water phase) dissolved inorganic phosphorus concentrations and summer phytoplankton composition presented similar interannual trends. However, the succession of phytoplankton structure during the reoligotrophication phase differed greatly from that during the eutrophication period, and a recent abnormal upward trend in algal densities is mainly the result of the development of large species that formerly were only common from late September until November. This community change, mainly triggered by filamentous (Mougeotia gracillima, Tribonema) or motile forms (Dinobryon sociale, Cryptophycea), seems to have been induced by the earlier and greater deepening of the P-depleted layer. In addition to milder summers, this massive development of larger forms seems to be favoured by four of their biological features: tolerance to warm temperatures, tolerance to low-light intensity (might exploit deeper layers where P is not yet limiting), shapes not only providing a large surface to volume ratio or motility (adaptation to low-nutrient concentrations), but increasing resistance to zooplankton grazing. This paradoxical trend, perhaps reinforced by the decline on roach Rutilus rutilus abundance (an opportunistic planktivore), is likely to remain until the P-depleted zone is extended below the layers that can be frequently resupplied in nutrients by hydrodynamic processes. [source]

Sustainable community change: A new paradigm for leadership in community revitalization efforts

NATIONAL CIVIC REVIEW, Issue 1 2005
2Article first published online: 28 MAR 200, Roger C. Mills
First page of article [source]

Determination of microbial community structures of shrimp floc cultures by biomarkers and analysis of floc amino acid profiles

AQUACULTURE RESEARCH, Issue 2 2008
Zhi Yong Ju
Abstract Simple, rapid and reliable methods are required to monitor the microbial community change in aquatic pond for better animal performance. Four floc (suspended organic matter) samples were collected from outdoor raceways and tanks used for culturing Pacific white shrimp Litopenaeus vannamei. Twenty-two chlorophyll (Chl) and carotenoid pigments were separated, identified and quantified using high-performance liquid chromatography,ultraviolet/Vis-mass spectrometry in the freeze-dried floc samples. Algal community composition (diatoms, chlorophytes, cyanobacteria, dinoflagellates and cryptophytes) was determined by measuring concentrations of the respective taxonomic biomarkers (carotenoid fucoxanthin, lutein, zeaxanthin, peridinin and alloxanthin) as independent variables and Chl a as the dependent variable using a multiple regression model. This analysis found that the phytoplankton community of the floc samples from two groups of shrimp tanks (32 g L,1 -salinity) were diatom-dominated (81.7% and 84.4%); and two floc samples from shrimp raceways (5 and 18 g L,1 -salinity) were chlorophyte-dominated (75.4% and 82.3%). Assessment of total algal and bacterial biomass by quantification of Chl a and muramic acid, respectively, indicated that the 18 g L,1 -salinity raceway sample was bacteria-dominated, whereas the other three floc samples were algae-dominated. Sample protein quality was evaluated by its essential amino acid (AA) score and index. Arginine and lysine were found to be the two most limiting AAs for all floc samples. [source]

Tree Community Change across 700 km of Lowland Amazonian Forest from the Andean Foothills to Brazil

Responses of biofilms to combined nutrient and metal exposure

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2002
Núria Ivorra
Abstract Numerous studies have reported marked sensitivities of diatom species to phosphate and organic pollution but have ignored interactions with other common contaminants. The aim of the present study was to investigate the single and joint effects of increased phosphate and metal (cadmium, zinc) concentrations on benthic diatom communities. Microalgal biofilms from a relatively unpolluted stream were exposed in the laboratory to Zn, Cd, and P, separately and in combination, in concentrations found at a polluted stream in the same catchment. The Zn concentration reduced algal growth in biofilms more than the Cd concentration. Phosphate compensated for the single effect of each metal but not for their combined effects. Diatom community changes were evaluated using water quality indices based on the empirical sensitivities of taxa to nutrients (TDI) and organic pollution (%PTV). Phosphate exposure resulted in an increase of the eutrophy rank and presumed pollution-tolerant taxa. In contrast, exposure to Zn, Zn + Cd, and Zn + Cd + P caused a marked reduction of the TDI and %PTV community values. The successional trends in the laboratory matched the observed differences in microphyte communities in the reference and polluted river stations. However, the autoecology of the species present also revealed that the resulting composition of diatom communities cannot be attributed solely to the direct toxic effects of metal and nutrients and their interaction. Observed changes in the relative abundance of species are also determined by their growth form and microdistribution in biofilms. [source]

Vegetation responses in Alaskan arctic tundra after 8 years of a summer warming and winter snow manipulation experiment

GLOBAL CHANGE BIOLOGY, Issue 4 2005
C.-H. A. Wahren
Abstract We used snow fences and small (1 m2) open-topped fiberglass chambers (OTCs) to study the effects of changes in winter snow cover and summer air temperatures on arctic tundra. In 1994, two 60 m long, 2.8 m high snow fences, one in moist and the other in dry tundra, were erected at Toolik Lake, Alaska. OTCs paired with unwarmed plots, were placed along each experimental snow gradient and in control areas adjacent to the snowdrifts. After 8 years, the vegetation of the two sites, including that in control plots, had changed significantly. At both sites, the cover of shrubs, live vegetation, and litter, together with canopy height, had all increased, while lichen cover and diversity had decreased. At the moist site, bryophytes decreased in cover, while an increase in graminoids was almost entirely because of the response of the sedge Eriophorum vaginatum. These community changes were consistent with results found in studies of responses to warming and increased nutrient availability in the Arctic. However, during the time period of the experiment, summer temperature did not increase, but summer precipitation increased by 28%. The snow addition treatment affected species abundance, canopy height, and diversity, whereas the summer warming treatment had few measurable effects on vegetation. The interannual temperature fluctuation was considerably larger than the temperature increases within OTCs (<2°C), however. Snow addition also had a greater effect on microclimate by insulating vegetation from winter wind and temperature extremes, modifying winter soil temperatures, and increasing spring run-off. Most increases in shrub cover and canopy height occurred in the medium snow-depth zone (0.5,2 m) of the moist site, and the medium to deep snow-depth zone (2,3 m) of the dry site. At the moist tundra site, deciduous shrubs, particularly Betula nana, increased in cover, while evergreen shrubs decreased. These differential responses were likely because of the larger production to biomass ratio in deciduous shrubs, combined with their more flexible growth response under changing environmental conditions. At the dry site, where deciduous shrubs were a minor part of the vegetation, evergreen shrubs increased in both cover and canopy height. These changes in abundance of functional groups are expected to affect most ecological processes, particularly the rate of litter decomposition, nutrient cycling, and both soil carbon and nitrogen pools. Also, changes in canopy structure, associated with increases in shrub abundance, are expected to alter the summer energy balance by increasing net radiation and evapotranspiration, thus altering soil moisture regimes. [source]

Variable sensitivity of plant communities in Iceland to experimental warming

Chronic fishing disturbance has changed shelf sea benthic community structure

JOURNAL OF ANIMAL ECOLOGY, Issue 3 2000
M. J. Kaiser
Summary 1.,Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2.,In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3.,Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4.,Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state. [source]

Plant community properties predict vegetation resilience to herbivore disturbance in the Arctic

JOURNAL OF ECOLOGY, Issue 5 2010
James D. M. Speed
Summary 1.,Understanding the impact of disturbance on vegetation and the resilience of plant communities to disturbance is imperative to ecological theory and environmental management. In this study predictors of community resilience to a simulated natural disturbance are investigated. Responses to disturbance are examined at the community, plant functional type and species level. 2.,Field experiments were set up in seven tundra plant communities, simulating disturbance based on the impact of grubbing by an increasing herbivore population of pink-footed geese (Anser brachyrhynchus). The short-term resilience of communities was assessed by comparing community dissimilarity between control plots and plots subject to three disturbance intensities based on the foraging impact of these geese. Potential for long-term recovery was evaluated across different disturbance patch sizes. 3.,Resilience to disturbance varied between communities; those with higher moss cover and higher soil moisture, such as wetlands and mires, were most resilient to disturbance. 4.,The wetter communities demonstrated greater long-term recovery potential following disturbance. In wetland communities, vegetative recovery of vascular plants and moss was greater in smaller disturbed patches and at the edges of patches. 5.,The response of vegetation to disturbance varied with intensity of disturbance, plant community and plant species. The use of functional type classifications only partially explained the variation in species responses to disturbance across communities, thus their use in predicting community changes was limited. 6.,Synthesis. The impact of disturbance is shown to be plant-community specific and related to the initial abiotic and biotic properties of the community. By showing that resilience is partly predictable, the identification of disturbance-susceptible communities is possible, which is of relevance for ecosystem management. [source]

Vegetation change from chronic stress events: Detection of the effects of tide gate removal and long-term drought on a tidal marsh

A conceptual model of plant community changes following cessation of cultivation in semi-arid grassland

APPLIED VEGETATION SCIENCE, Issue 4 2010
Nathan K. Wong
Abstract Question: Can vegetation changes that occur following cessation of cultivation for cereal crop production in semi-arid native grasslands be described using a conceptual model that explains plant community dynamics following disturbance? Location: Eighteen native grasslands with varying time-since-last cultivation across northern Victoria, Australia. Methods: We examined recovery of native grasslands after cessation of cultivation along a space for- time chronosequence. By documenting floristic composition and soil properties of grasslands with known cultivation histories, we established a conceptual model of the vegetation states that occur following cessation of cultivation and inferred transition pathways for community recovery. Results: Succession from an exotic-dominated grassland to native grassland followed a linear trajectory. These changes represent an increase in richness and cover of native forbs, a decrease in cover of exotic annual species and little change in native perennial graminoids and exotic perennial forbs. Using a state-and-transition model, two distinct vegetation states were evident: (1) an unstable, recently cultivated state, dominated by exotic annuals, and (2) a more diverse, stable state. The last-mentioned state can be divided into two further states based on species composition: (1) a never-cultivated state dominated by native perennial shrubs and grasses, and (2) a long-uncultivated state dominated by a small number of native perennial and native and exotic annual species that is best described as a subset of the never-cultivated state. Transitions between these states are hypothesized to be dependent upon landscape context, seed availability and soil recovery. Conclusions: Legacies of past land use on soils and vegetation of semi-arid grasslands are not as persistent as in other Australian communities. Recovery appears to follow a linear, directional model of post-disturbance regeneration which may be advanced by overcoming dispersal barriers hypothesised to restrict recovery. [source]

Effects of raised water levels on wet grassland plant communities

APPLIED VEGETATION SCIENCE, Issue 3 2009
Sarah E. Toogood
Abstract Questions: What are the effects of raised water levels on wet grassland plant communities and dynamics? To what extent do time since raised water levels, vegetation management and water regime influence community composition? Location: Pevensey Levels, southeast England, UK. Methods: Plant communities and hydrology were monitored during 2001-03 within 23 wet grassland meadows and pastures where water levels had been raised for nature conservation at different times over 21 years. Community variations were examined using species abundance and ecological traits. Results: Water regime, measured as duration of flooding, groundwater level and soil moisture was significantly related to plant community variation. Communities were divided into grasslands where inundation was shallow (,8 cm) and relatively short (,3 months) and sites where deeper flooding was prolonged (,5 months), supporting a variety of wetland vegetation. With increasing wetness, sites were characterised by more bare ground and wetland plants such as sedges, helophytes and hydrophytes, and species with a stress-tolerating competitive strategy. All sites showed considerable annual dynamics, especially those with substantially raised water levels. There were no significant relationships between time since water levels were raised and plant community composition. Grassland management exerted a limited influence upon vegetation compared to water regime. Conclusions: Grassland plant communities are responsive to raised water levels and have potential for a rapid transition to wetland vegetation, irrespective of grazing or cutting management. Creation or restoration of wet grasslands by (re)wetting is feasible but challenging due to the high dynamism of wetland plant communities and the need for substantially raised water levels and prolonged flooding to produce significant community changes. [source]

Long-term plant community changes in managed fens in Ohio, USA

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2008
Matthew J. Barry
Abstract 1.Long-term studies are necessary to describe effects of restoration efforts on plant communities and invasive species in North American fen communities. In 1986, 1999 and 2000, wetland plant communities and abiotic factors were sampled in two fens in Ohio that were actively managed as a state nature preserve since 1986. The correlation between plant species and environmental conditions was examined in 1986 to 2000, and changes in woody plant cover were measured on aerial photographs from 1938 to 1997 to analyse long-term effects of management practices. 2.142 vascular plant species and 32 bryophyte taxa were found in these rich fens, including 13 rare (i.e. state-listed as endangered, threatened or potentially threatened) and 14 alien species. TWINSPAN analyses identified nine plant community types, and species distributions were correlated with several abiotic factors (groundwater depth, pH, soil organic content, distance from wetland edge and depth of peat). Communities along the wetland edge in deep peat had higher richness, more woody species, more alien species and fewer rare species than communities in areas near sources of flowing groundwater with more marl and less peat. 3.There was little change in species richness, evenness, and Shannon's diversity from 1986 to 2000. However, plant species assemblages changed during the study, and changes were different in unmanipulated transects compared with those where habitat managers removed invasive woody plants. An aerial photograph analysis indicated that woody plant cover increased by about 1% each year during 1938 to 1997 despite current management efforts to remove invasive trees and shrubs. Additional strategies should be directed toward reducing shrub encroachment and invasive species while promoting rare species. Copyright © 2007 John Wiley & Sons, Ltd. [source]