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Vegetation Cover (vegetation + cover)
Kinds of Vegetation Cover Terms modified by Vegetation Cover Selected AbstractsPeriodic spotted patterns in semi-arid vegetation explained by a propagation-inhibition modelJOURNAL OF ECOLOGY, Issue 4 2001P. Couteron Summary 1,Vegetation cover regularly punctuated by spots of bare soil is a frequent feature of certain semi-arid African landscapes, which are also characterized by banded vegetation patterns (i.e. tiger bush). 2,The propagation-inhibition (PI) model suggests that a periodic pattern characterized by a dominant wavelength can theoretically establish itself through a Turing-like spatial instability depending only on a trade-off between facilitative and competitive interactions among plants. Under strictly isotropic conditions, spotted and banded patterns are distinct outcomes of a unique process, whereas anisotropy leads to a banded structure. The model predicts that spotted patterns will have a lower dominant wavelength than bands. 3,We test some outcomes of the PI model against vegetation patterns observable in aerial photographs from West Africa. Two sites with rainfall of c. 500,600 mm year,1 were studied: a 525-ha plain in north-west Burkina Faso and a 300-ha plateau in southern Niger. Digitized photographs were subjected to spectral analysis by Fourier transform in order to quantify vegetation patterns in terms of dominant wavelengths and orientations. 4,Spotted vegetation proved highly periodic. The characteristic range of dominant wavelengths (30,50 m) was similar at two sites more than 500 km apart. The PI model suggests that spots may occur as a hexagonal lattice but there is little evidence of such patterning in the field. A dominant wavelength was far quicker to establish in simulations (c. 102,103 years for annual grasses) than a hexagonal symmetry (c. 105 years), and observed patterns are therefore likely to be far from the asymptotic structure. 5,Elongated and smudged spots that locally became flexuous bands have been observed in southern Niger. This pattern that had a dominant wavelength of 50 m but lacked any dominant orientation can be interpreted as a transition from spots to bands under fairly isotropic conditions. 6,The PI model provides a framework for further investigation of patterns in semi-arid vegetation and may be of a broader ecological application. [source] Association of ecotones with relative elevation and fire in an upland Florida landscapeJOURNAL OF VEGETATION SCIENCE, Issue 3 2006E.A. Boughton Abstract: Question: What are the importance of elevation and fire in maintaining ecotones of Florida scrub assemblages along a gradual topographic gradient? Location: Archbold Biological Station (ABS), 12 km south of Lake Placid, Florida, USA. Methods: Vegetation cover of upland Florida shrublands was quantified using the line-intercept method along 20 transects traversing similar elevation gradients, stratified by time since fire (TSF). We objectively identified shrubland ecotones using a split moving windows boundary analysis (SMW) with three different window widths. Non-metric multidimensional scaling ordination was used to determine relationships among plant assemblages defined by SMW. Results: We located up to four ecotones per transect, the majority of which were wide, highly heterogeneous zones. Relative elevation controlled the distribution of plant assemblages in upland Florida shrublands. Ecotones in shrublands > 30 years TSF had relatively low dissimilarity values in SMW, indicating that previously discrete plant assemblages with longer TSF were becoming more similar with time. Conclusions Split Moving Windows (SMW) analysis identified ecotones relatively well although patches generated by oak clonal growth were sometimes identified as ecotones. Fire suppression caused ecotones to become more diffuse, suggesting that without fire at least every 30 years, discrete plant assemblages within upland Florida shrublands will be more continuous. [source] Prescribed Burning to Restore Mixed-Oak Communities in Southern Ohio: Effects on Breeding- Bird PopulationsCONSERVATION BIOLOGY, Issue 5 2001Vanessa L. Artman We studied the effects of repeated burning (1,4 years of annual burning) and recovery (1 year after burning,) on the breeding bird community. Burning resulted in incremental but temporary reductions in the availability of leaf litter, shrubs, and saplings, but it did not affect trees, snags, or understory vegetation cover. Of 30 bird species monitored, 4 were affected negatively and 2 were affected positively by burning. Population densities of Ovenbirds ( Seiurus aurocapillus), Worm-eating Warblers ( Helmitheros vermivorus), and Hooded Warblers ( Wilsonia citrina) declined incrementally in response to repeated burning and did not recover within 1 year after burning, suggesting a lag time in response to the changes in habitat conditions. Densities of Northern Cardinals ( Cardinalis cardinalis) fluctuated among years in the control units, but remained low in the burned units. Densities of American Robins ( Turdus migratorius) and Eastern Wood-Pewees ( Contopus virens) increased in response to burning, but these increases were apparent only after several years of repeated burning. In general, burning resulted in short-term reductions in the suitability of habitat for ground- and low-shrub-nesting birds, but it improved habitat for ground- and aerial-foraging birds. Overall, there were no changes in the composition of the breeding-bird community. Total breeding bird population levels were also unaffected by burning. Our results suggest that prescribed burning applied on a long-term basis or across large spatial scales is likely to have adverse effects on ground- and low-shrub-nesting bird species, but other changes in the composition of the breeding-bird community are likely to be minimal as long as the closed-canopy forest structure is maintained within the context of prescribed burning. Resumen: Se está reintroduciendo fuego artificialmente en los bosque del sur de Ohio para determinar su efectividad para restaurar y mantener comunidades de bosques mixtos de encino ( Quercus spp.). Estudiamos los efectos de quemas repetidas (1,4 años de quema anual,) y de recuperación (1 año después de la quema) sobre la comunidad de aves reproductivas. La quema resultó en reducciones temporales en la disponibilidad de hojarasca, arbustos y renuevos, pero no afectó a los árboles, tocones o la cubierta vegetal del sotobosque. De 30 especies de aves monitoredas, 4 fueron afectadas negativamente por la quema y 2 fueron afectadas positivamente. Las densidades de población de Seiurus aurocapillus, de Helmitheros vermivorus y de Wilsonia citrina declinaron incrementalmente en respuesta a quemas repetidas y no se recuperaron en un año después de la quema, sugiriendo un retraso en el tiempo de respuesta a los cambios en las condiciones del hábitat. Las densidades de Cardinalis cardinalis fluctuaron entre años en las unidades control, pero permanecieron bajas en las unidades quemadas. Las densidades de Turdus migratorius y de Contopus virens aumentaron en respuesta a la quema, pero estos incrementos fueron evidentes sólo hasta varios años después de quemas repetidas. En general, en el corto plazo la quema resultó en reducciones en la calidad del hábitat para aves que anidan sobre el suelo y en arbustos bajos, pero mejoró el hábitat para aves que forrajean en el suelo y el aire. En general, no hubo cambios en la composición de la comunidad de aves reproductivas. Los niveles totales de poblaciones de aves reproductivas tampoco fueron afectados por la quema. Nuestros resultados sugieren la posibilidad de que la quema prescrita aplicada a largo plazo o en escalas espaciales grandes tenga efectos adversos sobre especies de aves que anidan sobre el suelo y en arbustos bajos, pero la posibilidad de cambios en la composición de la comunidad de aves reproductivas es mínima. [source] Vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain areaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2009Armando Molina Abstract Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short-term (1,15 years) sediment deposition and gully stabilization. In well-vegetated gully systems ( , 30% of ground vegetation cover), 0.035 m3 m,1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short-term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd. [source] Evaluation of the PESERA model in two contrasting environmentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2009F. Licciardello Abstract The performance of the Pan-European Soil Erosion Risk Assessment (PESERA) model was evaluated by comparison with existing soil erosion data collected in plots under different land uses and climate conditions in Europe. In order to identify the most important sources of error, the PESERA model was evaluated by comparing model output with measured values as well as by assessing the effect of the various model components on prediction accuracy through a multistep approach. First, the performance of the hydrological and erosion components of PESERA was evaluated separately by comparing both runoff and soil loss predictions with measured values. In order to assess the performance of the vegetation growth component of PESERA, the predictions of the model based on observed values of vegetation ground cover were also compared with predictions based on the simulated vegetation cover values. Finally, in order to evaluate the sediment transport model, predicted monthly erosion rates were also calculated using observed values of runoff and vegetation cover instead of simulated values. Moreover, in order to investigate the capability of PESERA to reproduce seasonal trends, the observed and simulated monthly runoff and erosion values were aggregated at different temporal scale and we investigated at what extend the model prediction error could be reduced by output aggregation. PESERA showed promise to predict annual average spatial variability quite well. In its present form, short-term temporal variations are not well captured probably due to various reasons. The multistep approach showed that this is not only due to unrealistic simulation of cover and runoff, being erosion prediction also an important source of error. Although variability between the investigated land uses and climate conditions is well captured, absolute rates are strongly underestimated. A calibration procedure, focused on a soil erodibility factor, is proposed to reduce the significant underestimation of soil erosion rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] Field-based and spectral indicators for soil erosion mapping in semi-arid mediterranean environments (Coastal Cordillera of central Chile)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2007Renaud Mathieu Abstract The Coastal Cordillera of central Chile is naturally sensitive to soil erosion due to moderate to steep slopes, intense winter rains when the vegetation cover is scarce, and deeply weathered granitic rocks. In 1965, 60 per cent of its surface was moderately to very severely eroded. Today this process is still largely active, but no data are currently available to evaluate the real extent, distribution and severity of soil degradation on a regional scale. This information is vital to support efficient soil conservation plans. A multi-scale approach was implemented to produce regional land degradation maps based on remote sensing technologies. Fieldwork has shown that the surface colour or ,redness' and the density of coarse fragments are pertinent erosion indicators to describe a typical sequence of soil degradation in the context of mediterranean soil developed on granitic materials and micaschists. Field radiometric experiments concluded that both factors influence the reflectance of natural surfaces and can be modelled using radiometric indices accessible from most satellites operating in the optical domain, i.e. redness index and brightness index. Finally the radiometric indices were successfully applied to SPOT images to produce land degradation maps. Only broad classes of erosion status were discriminated and the detection of the degradation processes was only possible when most of the fertile layer had already been removed. This technology provides decision-making information required to develop regional soil conservation plans and to prioritize actions between catchment areas, especially in vast inter-tropical regions where spatialized data are not always readily available. Copyright © 2006 John Wiley & Sons, Ltd. [source] Overbank deposition along the concave side of the Red River meanders, Manitoba, and its geomorphic significanceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2005Gregory R. Brooks Abstract Slow earth sliding is pervasive along the concave side of Red River meanders that impinge on Lake Agassiz glaciolacustrine deposits. These failures form elongated, low-angled (c. 6 to 10°) landslide zones along the valleysides. Silty overbank deposits that accumulated during the 1999 spring freshet extend continuously along the landslide zones over hundreds of metres and aggraded the lower slopes over a distance 50 to 80 m from the channel margin. The aggradation is not obviously related to meander curvature or location within a meander. Along seven slope profiles surveyed in 1999 near Letellier, Manitoba, the deposits locally are up to 21 cm thick and generally thin with increasing distance from, and height above, the river. Local deposit thickness relates to distance from the channel, duration of inundation of the landslide surface, mesotopography, and variations in vegetation cover. Immediately adjacent to the river, accumulated overbank deposits are up to 4 m thick. The 1999 overbank deposits also were present along the moderately sloped (c. 23 to 27°) concave banks eroding into the floodplain, but the deposits are thinner (locally up to c. 7 cm thick) and cover a narrower area (10 to 30 m wide) than the deposits within the landslide zones. Concave overbank deposition is part of a sediment reworking process that consists of overbank aggradation on the landslide zones, subsequent gradual downslope displacement from earth sliding, and eventually reworking by the river at the toe of the landslide. The presence of the deposits dampens the outward migration of the meanders and contributes to a low rate of contemporary lateral channel migration. Concave overbank sedimentation occurs along most Red River meanders between at least Emerson and St. Adolphe, Manitoba. © Her Majesty the Queen in right of Canada. [source] The role of vegetation patterns in structuring runoff and sediment fluxes in drylandsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005Juan Puigdefábregas Abstract The dynamics of vegetation-driven spatial heterogeneity (VDSH) and its function in structuring runoff and sediment fluxes have received increased attention from both geomorphological and ecological perspectives, particularly in arid regions with sparse vegetation cover. This paper reviews the recent findings in this area obtained from field evidence and numerical simulation experiments, and outlines their implications for soil erosion assessment. VDSH is often observed at two scales, individual plant clumps and stands of clumps. At the patch scale, the local outcomes of vegetated patches on soil erodibility and hydraulic soil properties are well established. They involve greater water storage capacity as well as increased organic carbon and nutrient inputs. These effects operate together with an enhanced capacity for the interception of water and windborne resources, and an increased biological activity that accelerates breakdown of plant litter and nutrient turnover rates. This suite of relationships, which often involve positive feedback mechanisms, creates vegetated patches that are increasingly different from nearby bare ground areas. By this way a mosaic builds up with bare ground and vegetated patches coupled together, respectively, as sources and sinks of water, sediments and nutrients. At the stand scale within-storm temporal variability of rainfall intensity controls reinfiltration of overland flow and its decay with slope length. At moderate rainfall intensity, this factor interacts with the spatial structure of VDSH and the mechanism of overland flow generation. Reinfiltration is greater in small-grained VDSH and topsoil saturation excess overland flow. Available information shows that VDSH structures of sources and sinks of water and sediments evolve dynamically with hillslope fluxes and tune their spatial configurations to them. Rainfall simulation experiments in large plots show that coarsening VDSH leads to significantly greater erosion rates even under heavy rainfall intensity because of the flow concentration and its velocity increase. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effects of spatially structured vegetation patterns on hillslope erosion in a semiarid Mediterranean environment: a simulation studyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005Matthias Boer Abstract A general trend of decreasing soil loss rates with increasing vegetation cover fraction is widely accepted. Field observations and experimental work, however, show that the form of the cover-erosion function can vary considerably, in particular for low cover conditions that prevail on arid and semiarid hillslopes. In this paper the structured spatial distribution of the vegetation cover and associated soil attributes is proposed as one of the possible causes of variation in cover,erosion relationships, in particular in dryland environments where patchy vegetation covers are common. A simulation approach was used to test the hypothesis that hillslope discharge and soil loss could be affected by variation in the spatial correlation structure of coupled vegetation cover and soil patterns alone. The Limburg Soil Erosion Model (LISEM) was parameterized and verified for a small catchment with discontinuous vegetation cover at Rambla Honda, SE Spain. Using the same parameter sets LISEM was subsequently used to simulate water and sediment fluxes on 1 ha hypothetical hillslopes with simulated spatial distributions of vegetation and soil parameters. Storms of constant rainfall intensity in the range of 30,70 mm h,1 and 10,30 min duration were applied. To quantify the effect of the spatial correlation structure of the vegetation and soil patterns, predicted discharge and soil loss rates from hillslopes with spatially structured distributions of vegetation and soil parameters were compared with those from hillslopes with spatially uniform distributions. The results showed that the spatial organization of bare and vegetated surfaces alone can have a substantial impact on predicted storm discharge and erosion. In general, water and sediment yields from hillslopes with spatially structured distributions of vegetation and soil parameters were greater than from identical hillslopes with spatially uniform distributions. Within a storm the effect of spatially structured vegetation and soil patterns was observed to be highly dynamic, and to depend on rainfall intensity and slope gradient. Copyright © 2005 John Wiley & Sons, Ltd. [source] Integrating physiology, population dynamics and climate to make multi-scale predictions for the spread of an invasive insect: the Argentine ant at Haleakala National Park, HawaiiECOGRAPHY, Issue 1 2010Stephen Hartley Mechanistic models for predicting species' distribution patterns present particular advantages and challenges relative to models developed from statistical correlations between distribution and climate. They can be especially useful for predicting the range of invasive species whose distribution has not yet reached equilibrium. Here, we illustrate how a physiological model of development for the invasive Argentine ant can be connected to differences in micro-site suitability, population dynamics and climatic gradients; processes operating at quite different spatial scales. Our study is located in the subalpine shrubland of Haleakala National Park, Hawaii, where the spread of Argentine ants Linepithema humile has been documented for the past twenty-five years. We report four main results. First, at a microsite level, the accumulation of degree-days recorded in potential ant nest sites under bare ground or rocks was significantly greater than under a groundcover of grassy vegetation. Second, annual degree-days measured where population boundaries have not expanded (456,521,degree-days), were just above the developmental requirements identified from earlier laboratory studies (445,degree-days above 15.9°C). Third, rates of population expansion showed a strong linear relationship with annual degree-days. Finally, an empirical relationship between soil degree-days and climate variables mapped at a broader scale predicts the potential for future range expansion of Argentine ants at Haleakala, particularly to the west of the lower colony and the east of the upper colony. Variation in the availability of suitable microsites, driven by changes in vegetation cover and ultimately climate, provide a hierarchical understanding of the distribution of Argentine ants close to their cold-wet limit of climatic tolerances. We conclude that the integration of physiology, population dynamics and climate mapping holds much promise for making more robust predictions about the potential spread of invasive species. [source] Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in LaplandECOGRAPHY, Issue 4 2003Otso Suominen Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground-dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H') of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H'/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites. [source] Vegetation of the river Yamuna floodplain in the Delhi stretch, with reference to hydrological characteristicsECOHYDROLOGY, Issue 2 2009Tanveera Tabasum Abstract Vegetation in the Delhi stretch of the floodplain of the river Yamuna was examined in relation to hydrological characteristics. The floodplain was delineated into four zones based on hydrological interventions. Seventy-four plant species including forty-two aquatic/semi-aquatic were identified. The decrease in water discharge from Jhangola to downstream Okhla, led to reduction in species richness. Co-structures between hydrological characteristics and vegetational composition indicated that vegetation in the four identified zones was governed essentially by hydrological factors. Zones I and III exhibited near-perfect correspondence signifying that variation in vegetational composition in these zones could be explained, to a great extent, on the basis of variations in the hydrological conditions. Zone II and IV, with relatively weaker correspondence, indicated that there were gradients other than hydrological conditions, which caused variations in vegetational characteristics. The present study highlighted the importance of allocation of water for periodic inundation to maintain floodplain characteristics including aquatic/semi-aquatic vegetation cover as critical to the management of the river ecosystem. The current policy of water use focused entirely on human uses ignoring ecological requirements, and had clear adverse implications on the health of the river ecosystem. Copyright © 2009 John Wiley & Sons, Ltd. [source] Spatial variability of soil and nutrient characteristics of semi-arid grasslands and shrublands, Jornada Basin, New MexicoECOHYDROLOGY, Issue 1 2008Eva Nora Mueller Abstract Heterogeneity of vegetation and soil properties is characteristic of semi-arid and arid environments. The potential underlying causes of the dynamics that create this spatial variability, with consequent impacts on landscape connectivity and thus ecological and ecohydrological processes, are not clearly understood. An investigation was carried out into the spatial variability of ponded infiltration rate, soil moisture, soil-aggregate stability, vegetation cover, random roughness and nutrient content in the soil (ammonium, nitrate and phosphorus) at grassland and shrubland sites for two spatial scales in the Jornada Basin, in the northern part of the Chihuahua desert. At the plant-interplant scale, statistically significant differences exist between vegetated and non-vegetated sites for soil moisture and infiltration rate within both shrublands and grasslands. The spatial distributions of all other parameters follow a more complex scheme at this scale. At the landscape scale, distinct differences exist for most parameters between the grasslands and the shrubland sites. Geostatistical analysis revealed that the autocorrelation lengths are not simply a function of average shrub sizes, but may be caused by a more complex pattern probably related to the spatial layout of rill and inter-rill areas and other localized transfers of soil resources through the redistribution of water and wind. These results demonstrate the importance of understanding spatial linkages of processes within the landscape in understanding dryland ecosystem dynamics. Copyright © 2007 John Wiley & Sons, Ltd. [source] Patterns of bacterial diversity across a range of Antarctic terrestrial habitatsENVIRONMENTAL MICROBIOLOGY, Issue 11 2007Etienne Yergeau Summary Although soil-borne bacteria represent the world's greatest source of biological diversity, it is not well understood whether extreme environmental conditions, such as those found in Antarctic habitats, result in reduced soil-borne microbial diversity. To address this issue, patterns of bacterial diversity were studied in soils sampled along a > 3200 km southern polar transect spanning a gradient of increased climate severity over 27° of latitude. Vegetated and fell-field plots were sampled at the Falkland (51°S), South Georgia (54°S), Signy (60°S) and Anchorage Islands (67°S), while bare frost-sorted soil polygons were examined at Fossil Bluff (71°S), Mars Oasis (72°S), Coal Nunatak (72°S) and the Ellsworth Mountains (78°S). Bacterial 16S rRNA gene sequences were recovered subsequent to direct DNA extraction from soil, polymerase chain reaction amplification and cloning. Although bacterial diversity was observed to decline with increased latitude, habitat-specific patterns appeared to also be important. Namely, a negative relationship was found between bacterial diversity and latitude for fell-field soils, but no such pattern was observed for vegetated sites. The Mars Oasis site, previously identified as a biodiversity hotspot within this region, proved exceptional within the study transect, with unusually high bacterial diversity. In independent analyses, geographical distance and vegetation cover were found to significantly influence bacterial community composition. These results provide insight into the factors shaping the composition of bacterial communities in Antarctic terrestrial habitats and support the notion that bacterial diversity declines with increased climatic severity. [source] Ecotoxicologic impacts of agricultural drain water in the Salinas River, California, USAENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2003Brian S. Anderson Abstract The Salinas River is the largest of the three rivers that drain into the Monterey Bay National Marine Sanctuary in central California (USA). Large areas of this watershed are cultivated year-round in row crops, and previous laboratory studies have demonstrated that acute toxicity of agricultural drain water to Ceriodaphnia dubia is caused by the organophosphate (OP) pesticides chlorpyrifos and diazinon. We investigated chemical contamination and toxicity in waters and sediments in the river downstream of an agricultural drain water input. Ecological impacts of drain water were investigated by using bioassessments of macroinvertebrate community structure. Toxicity identification evaluations were used to characterize chemicals responsible for toxicity. Salinas River water downstream of the agricultural drain was acutely toxic to the cladoceran Ceriodaphnia dubia, and toxicity to C. dubia was highly correlated with combined toxic units (TUs) of chlorpyrifos and diazinon. Laboratory tests were used to demonstrate that sediments in this system were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. Toxicity identification evaluations (TIEs) conducted on sediment pore water suggested that toxicity to amphipods was due in part to OP pesticides; concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d mean lethal concentration (LC50) for H. azteca. Potentiation of toxicity with addition of the metabolic inhibitor piperonyl butoxide suggested that sediment toxicity also was due to other non,metabolically activated compounds. Macroinvertebrate community structure was highly impacted downstream of the agricultural drain input, and a number of macroinvertebrate community metrics were negatively correlated with combined TUs of chlorpyrifos and diazinon, as well as turbidity associated with the drain water. Some macroinvertebrate metrics were also correlated with bank vegetation cover. This study suggests that pesticide pollution is the likely cause of ecological damage in the Salinas River, and this factor may interact with other stressors associated with agricultural drain water to impact the macroinvertebrate community in the system. [source] Nest Crypsis, Reproductive Value of a Clutch and Escape Decisions in Incubating Female Mallards Anas platyrhynchosETHOLOGY, Issue 8 2004Albrecht In cryptically coloured birds, remaining on the nest despite predator approach (risk-taking) may decrease the likelihood that the nest will be detected and current reproductive attempt lost. By contrast, flushing may immediately reveal the nest location to the predator. Escape decisions of incubating parents should therefore be optimized based on the risk-to-parent/cost of escape equilibrium. Animal prey may assess predation risk depending on a variety of cues, including the camouflage that vegetation provides against the predator. We examined interactive effects of nest crypsis and the current reproductive value of a clutch on flushing distances in incubating mallards (Anas platyrhynchos) approached by a human. Our results were consistent with predictions of parental investment theory: flushing distances were inversely correlated with measures of the reproductive value of the current clutch, namely with clutch size, stage of incubation and mean egg volume. Independently of a reproductive value of a clutch, nest concealment explained a significant portion of the variation in flushing distance among females; individual females tended to increase/decrease flushing distances according to change in nest cover. The results further suggest that vegetation concealment greatly influenced the risk of nest detection by local predators, suggesting that vegetation may act as a protective cover for incubating female. A female's ability to delay flushes according to the actual vegetation cover might thus be viewed as an antipredator strategy that reduces premature nest advertising to visually oriented predators. We argue, however, that shorter flying distances from densely covered sites might be maladaptive in areas where a predator's ability to detect incubating female does not rely on visual cues of nests. [source] Occurrence, prediction and hydrological effects of water repellency amongst major soil and land-use types in a humid temperate climateEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2006S. H. Doerr Summary Knowledge of soil water repellency distribution, of factors affecting its occurrence and of its hydrological effects stems primarily from regions with a distinct dry season, whereas comparatively little is known about its occurrence in humid temperate regions such as typified by the UK. To address this research gap, we have examined: (i) water repellency persistence (determined by the water drop penetration time method, WDPT) and degree (determined by the critical surface tension method, CST) for soil samples (0,5, 10,15 and 20,25 cm depth) taken from 41 common soil and land-use types in the humid temperate climate of the UK; (ii) the supposed relationship of soil moisture, textural composition and organic matter content with sample repellency; and (iii) the bulk wetting behaviour of undisturbed surface core samples (0,5 cm depth) over a period of up to 1 week. Repellency was found in surface samples of all major soil textural types amongst most permanently vegetated sites, whereas tilled sites were virtually unaffected. Repellency levels reached those of the most severely affected areas elsewhere in the world, decreased in persistence and degree with depth and showed no consistent relationship with soil textural characteristics, organic matter or soil moisture contents, except that above a water content of c. 28% by volume, repellency was absent. Wetting rate assessments of 100 cm3 intact soil cores using continuous water contact (,20 mm pressure head) over a period of up to 7 days showed that across the whole sample range and irrespective of texture, severe to extreme repellency persistence consistently reduced the maximum water content at any given time to well below that of wettable soils. For slightly to moderately repellent soils the results were more variable and thus hydrological effects of such repellency levels are more difficult to predict. The results imply that: (i) repellency is common for many land-use types with permanent vegetation cover in humid temperate climates irrespective of soil texture; (ii) supposedly influential parameters (texture, organic matter, specific water content) are poor general predictors of water repellency, whereas land use and the moisture content below which repellency can occur seem more reliable; and (iii) infiltration and water storage capacity of very repellent soils are considerably less than for comparable wettable soils. [source] Edaphic and physiographic factors affecting the distribution of natural gamma-emitting radionuclides in the soils of the Arnás catchment in the Central Spanish PyreneesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2002A. Navas Summary Gamma-emitting radionuclides are a natural source of radiation that can be a concern for human health, therefore it is important to know the radionuclide backgrounds in soils and to assess their mobility and transfer in ecosystems. Concentrations of natural radionuclides were determined in soils from a small catchment in the middle mountain environment of the Central Spanish Pyrenees. Radioisotope activities were well within the natural ranges for soil, averaging 27, 26, 32 and 500 Bq kg,1 for 238U, 226Ra, 208Tl and 40K, respectively. Their distributions in the soil profile were analysed along three transects of contrasting physiography and soil type. Uranium was depleted in upper layers of the soil and slightly enriched in deeper sections, while 226Ra, 40K and 208Tl were more uniformly distributed. Radionuclide activities in the Calcaric Regosols on the shrub slope were less than those in the deeper and better developed Haplic Kastanozems under forest and in Calcaric Fluvisols in the valley bottom. These spatial patterns seem to be affected by the soil type; other landscape features, such as slope orientation and vegetation cover, appeared to have an indirect effect. The results indicate that the depth distribution of the radionuclides is affected by some soil properties, including pH, carbonates, organic matter and particle size, and soil processes, such as leaching and adsorption. [source] Modelling patterned ground distribution in Finnish Lapland: an integration of topographical, ground and remote sensing informationGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2006Jan Hjort Abstract New data technologies and modelling methods have gained more attention in the field of periglacial geomorphology during the last decade. In this paper we present a new modelling approach that integrates topographical, ground and remote sensing information in predictive geomorphological mapping using generalized additive modelling (GAM). First, we explored the roles of different environmental variable groups in determining the occurrence of non-sorted and sorted patterned ground in a fell region of 100 km2 at the resolution of 1 ha in northern Finland. Second, we compared the predictive accuracy of ground-topography- and remote-sensing-based models. The results indicate that non-sorted patterned ground is more common at lower altitudes where the ground moisture and vegetation abundance is relatively high, whereas sorted patterned ground is dominant at higher altitudes with relatively high slope angle and sparse vegetation cover. All modelling results were from good to excellent in model evaluation data using the area under the curve (AUC) values, derived from receiver operating characteristic (ROC) plots. Generally, models built with remotely sensed data were better than ground-topography-based models and combination of all environmental variables improved the predictive ability of the models. This paper confirms the potential utility of remote sensing information for modelling patterned ground distribution in subarctic landscapes. [source] Detailed geomorphological survey of a small mountain drainage area, Abisko, northern Swedish LaplandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002Lena Rubensdotter A thorough geomorphological survey of a small (2km2) drainage area has been conducted using digital magnification of aerial photographs in conjunction with field visits. The result presented is a geomorphological map where individual geomorphological features down to metre size can be identified. The study was done in connection with a project focusing on the relationship between geomorphological processes and lacustrine sedimentation. Good knowledge of the geomorphological setting and the related process activity in the catchment is important in studies using lacustrine sediments as environmental archives. The survey reveals a small,scale geomorphology dominated by a number of different periglacial upfreezing forms together with bedrock,controlled slope processes. Three different geographically separated geomorphological assemblages were recognised with few sediment transportation pathways connecting them. Composition of substrate, soil water content and vegetation cover combined with different slope angles are probably the most important factors controlling the distribution of the geomorphological features. [source] Water availability controls microbial temperature responses in frozen soil CO2 productionGLOBAL CHANGE BIOLOGY, Issue 11 2009MATS G. ÖQUIST Abstract Soil processes in high-latitude regions during winter are important contributors to global carbon circulation, but our understanding of the mechanisms controlling these processes is poor and observed temperature response coefficients of CO2 production in frozen soils deviate markedly from thermodynamically predicted responses (sometimes by several orders of magnitude). We investigated the temperature response of CO2 production in 23 unfrozen and frozen surface soil samples from various types of boreal forests and peatland ecosystems and also measured changes in water content in them after freezing. We demonstrate that deviations in temperature responses at subzero temperatures primarily emanates from water deficiency caused by freezing of the soil water, and that the amount of unfrozen water is mainly determined by the quality of the soil organic matter, which is linked to the vegetation cover. Factoring out the contribution of water limitation to the CO2 temperature responses yields response coefficients that agree well with expectations based on thermodynamic theory concerning biochemical temperature responses. This partitioning between a pure temperature response and the effect of water availability on the response of soil CO2 production at low temperatures is crucial for a thorough understanding of low-temperature soil processes and for accurate predictions of C-balances in northern terrestrial ecosystems. [source] Microscale vegetation-soil feedback boosts hysteresis in a regional vegetation,climate systemGLOBAL CHANGE BIOLOGY, Issue 5 2008RUUD H. H. JANSSEN Abstract It has been hypothesized that a positive feedback between vegetation cover and monsoon circulation may lead to the existence of two alternative stable states in the Sahara region: a vegetated state with moderate precipitation and a desert state with low precipitation. This could explain the sudden onset of desertification in the region about 5000 years ago. However, other models suggest that the effect of vegetation on the precipitation may be insufficient to produce this behavior. Here, we show that inclusion of the microscale feedback between soil and vegetation in the model greatly amplifies the nonlinearity, causing alternative stable states and considerable hysteresis even if the effect of vegetation on precipitation is moderate. On the other hand, our analysis suggests that self-organized vegetation patterns known from models that only focus at the microscale plant,soil feedback will be limited to a narrower range of conditions due to the regional scale climate-feedback. This implies that in monsoon areas such as the Western Sahara self-organized vegetation patterns are predicted to be less common than in areas without monsoon circulation such as Central Australia. [source] Combined statistical and dynamical assessment of simulated vegetation,rainfall interactions in North Africa during the mid-Holocene,GLOBAL CHANGE BIOLOGY, Issue 2 2008MICHAEL NOTARO Abstract A negative feedback of vegetation cover on subsequent annual precipitation is simulated for the mid-Holocene over North Africa using a fully coupled general circulation model with dynamic vegetation, FOAM-LPJ (Fast Ocean Atmosphere Model-Lund Potsdam Jena Model). By computing a vegetation feedback parameter based on lagged auto-covariances, the simulated impact of North African vegetation on precipitation is statistically quantified. The feedback is also dynamically assessed through initial value ensemble experiments, in which North African grass cover is initially reduced and the climatic response analyzed. The statistical and dynamical assessments of the negative vegetation feedback agree in sign and relative magnitude for FOAM-LPJ. The negative feedback on annual precipitation largely results from a competition between bare soil evaporation and plant transpiration, with increases in the former outweighing reductions in the latter given reduced grass cover. This negative feedback weakens and eventually reverses sign over time during a transient simulation from the mid-Holocene to present. A similar, but weaker, negative feedback is identified in Community Climate System Model Version 2 (CCSM2) over North Africa for the mid-Holocene. [source] Productivity of high-latitude lakes: climate effect inferred from altitude gradientGLOBAL CHANGE BIOLOGY, Issue 5 2005Jan Karlsson Abstract Climate change is predicted to be dramatic at high latitudes. Still, climate impact on high latitude lake ecosystems is poorly understood. We studied 15 subarctic lakes located in a climate gradient comprising an air temperature difference of about 6°C. We show that lake water productivity varied by one order of magnitude along the temperature gradient. This variation was mainly caused by variations in the length of the ice-free period and, more importantly, in the supply of organic carbon and inorganic nutrients, which followed differences in terrestrial vegetation cover along the gradient. The results imply that warming will have rapid effects on the productivity of high latitude lakes, by prolongation of ice-free periods. However, a more pronounced consequence will be a delayed stimulation of the productivity following upon changes of the lakes terrestrial surroundings and subsequent increasing input of elements that stimulate the production of lake biota. [source] Net changes in regional woody vegetation cover and carbon storage in Texas Drylands, 1937,1999GLOBAL CHANGE BIOLOGY, Issue 3 2003GREGORY P. ASNER Abstract Although local increases in woody plant cover have been documented in arid and semiarid ecosystems worldwide, there have been few long-term, large-scale analyses of changes in woody plant cover and aboveground carbon (C) stocks. We used historical aerial photography, contemporary Landsat satellite data, field observations, and image analysis techniques to assess spatially specific changes in woody vegetation cover and aboveground C stocks between 1937 and 1999 in a 400-km2 region of northern Texas, USA. Changes in land cover were then related to topo-edaphic setting and historical land-use practices. Mechanical or chemical brush management occurred over much of the region in the 1940,1950s. Rangelands not targeted for brush management experienced woody cover increases of up to 500% in 63 years. Areas managed with herbicides, mechanical treatments or fire exhibited a wide range of woody cover changes relative to 1937 (,75% to + 280%), depending on soil type and time since last management action. At the integrated regional scale, there was a net 30% increase in woody plant cover over the 63-year period. Regional increases were greatest in riparian corridors (33%) and shallow clay uplands (26%) and least on upland clay loams (15%). Allometric relationships between canopy cover and aboveground biomass were used to estimate net aboveground C storage changes in upland (nonriparian) portions of regional landscapes. Carbon stocks increased from 380 g C m,2 in 1937 to 500 g C m,2 in 1999, a 32% net increase across the 400 km2 region over the 63-year period. These plant C storage change estimates are highly conservative in that they did not include the substantial increases in woody plant cover observed within riparian landscape elements. Results are discussed in terms of implications for ,carbon accounting' and the global C cycle. [source] Landscape modification and habitat fragmentation: a synthesisGLOBAL ECOLOGY, Issue 3 2007Joern Fischer ABSTRACT Landscape modification and habitat fragmentation are key drivers of global species loss. Their effects may be understood by focusing on: (1) individual species and the processes threatening them, and (2) human-perceived landscape patterns and their correlation with species and assemblages. Individual species may decline as a result of interacting exogenous and endogenous threats, including habitat loss, habitat degradation, habitat isolation, changes in the biology, behaviour, and interactions of species, as well as additional, stochastic threats. Human-perceived landscape patterns that are frequently correlated with species assemblages include the amount and structure of native vegetation, the prevalence of anthropogenic edges, the degree of landscape connectivity, and the structure and heterogeneity of modified areas. Extinction cascades are particularly likely to occur in landscapes with low native vegetation cover, low landscape connectivity, degraded native vegetation and intensive land use in modified areas, especially if keystone species or entire functional groups of species are lost. This review (1) demonstrates that species-oriented and pattern-oriented approaches to understanding the ecology of modified landscapes are highly complementary, (2) clarifies the links between a wide range of interconnected themes, and (3) provides clear and consistent terminology. Tangible research and management priorities are outlined that are likely to benefit the conservation of native species in modified landscapes around the world. [source] Effect of distance from farm periphery on the risk of forage damage by sika deer (Cervus nippon)GRASSLAND SCIENCE, Issue 4 2009Hideharu Tsukada Abstract The foraging behavior of deer can be influenced by both food availability and the "critical distance" from protective vegetation cover. The effect of the distance from the farm periphery on the risk of forage damage by sika deer was investigated in a public pasture in Tochigi Prefecture in central Japan from May to November 2006 and in May 2007. The risk of forage damage by sika deer, evaluated by deer pellet group density, was compared along three line transects at different distances from the farm periphery (10, 110 and 210 m) and among 18 paddocks at different distances from the farm periphery. Deer pellet group abundance in the line transects did not differ significantly with the distance from the periphery but decreased significantly with the distance from the nearest escape cover. The transect-based deer pellet abundance was more significantly influenced by other factors such as paddock identity and survey month in a generalized linear model. Deer pellet group abundance in the paddocks showed a significant albeit weak negative correlation with distance from the periphery in May 2007, but not in November 2006. The paddock-based deer pellet abundance was more influenced by sward height than by the distance from the periphery in a generalized linear model. Furthermore, a high density of deer pellet groups was exclusively observed in the paddock just after pasture renovation. These results show that the foraging behavior of sika deer was influenced partially by the distance from the nearest escape cover but largely by other factors such as herbage quality and seasonality. [source] Grazing exclusion as a conservation measure in a South Australian temperate native grasslandGRASSLAND SCIENCE, Issue 2 2009Nicholas J. Souter Abstract Many of South Australia's remnant temperate native grasslands are degraded by introduced livestock grazing. As a conservation measure, grazing was excluded from three 50 × 50 m exclosures in grazed native grassland. After 4 years, grazing removal had a noticeable effect on the grassland structure, increasing basal vegetation cover. Grazing removal had no significant effect on either native or exotic species richness, rather differences in richness changed as a result of interannual differences, such as the amount of rainfall that fell in the growing season. The percent cover of the native tussock grass Austrostipa spp. and the introduced annual grass Avena barbata, whilst fluctuating from year to year, both increased following the removal of grazing. Multivariate analyses showed that whilst only interannual differences affected community taxon richness, changes in structure were affected by the interaction between grazing treatment and year. Excluding livestock from a degraded grassland resulted in limited recovery and restoration of these endangered plant associations will require active rehabilitation efforts. [source] 3D float tracking: in situ floodplain roughness estimationHYDROLOGICAL PROCESSES, Issue 2 2009Menno Straatsma Abstract This paper presents a novel technique to quantify in situ hydrodynamic roughness of submerged floodplain vegetation: 3D float tracking. This method uses a custom-built floating tripod that is released on the inundated floodplain and tracked from shore by a robotic total station. Simultaneously, an acoustic Doppler current profiler (ADCP) collects flow velocity profiles and water depth data. Roughness values are derived from two methods based on (1) run-averaged values of water depth, slope and flow velocity to compute the roughness based on the Chézy equation, assuming uniform flow, (2) the equation for one-dimensional free surface flow in a moving window. A sensitivity analysis using synthetic data proved that the median value of the roughness, derived using method 2, is independent of (1) the noise in water levels, up to 9 mm, (2) bottom surface slope, and (3) topographic undulations. The window size should be at least 40 m for a typical lowland river setup. Field measurements were carried out on two floodplain sections with an average vegetation height of 0·030 (Arnhem) and 0·043 m (Dreumel). Method 1 resulted in a Nikuradse roughness length of 0·08 m for both locations. Method 2 gave 0·12 m for Arnhem and 0·19 m for Dreumel. In Arnhem, a spatial pattern of roughness values was present, which might be related to fractional vegetation cover or vegetation density during the flood peak. 3D float tracking proved a flexible and detailed method for roughness determination in the absence of waves, and provided an unrestricted view from shore. Copyright © 2008 John Wiley & Sons, Ltd. [source] Estimating the evolution of vegetation cover and its hydrological impact in the Mekong River basin in the 21st centuryHYDROLOGICAL PROCESSES, Issue 9 2008Hiroshi Ishidaira Abstract The terrestrial biosphere plays a key role in regional energy and water cycles. Thus, for long-term hydrological predictions, possible future changes in vegetation cover must be understood. This study examined the evolution of vegetation cover in the 21st century and its estimated impact on river discharge in the Mekong River basin. Based on climatic predictions (TYN SC 2·03) under the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC SRES) A1FI, A2, B1, and B2, changes in vegetation type and the leaf area index (LAI) were simulated using a Lund-Potsdam-Jena-Dynamic Global Vegetation Model (LPJ-DGVM) and Terrestrial Biogeochemical Cycle Model (BIOME-BGC). The estimated LAI was then used in the rainfall-runoff analysis in the Yamanashi Distributed Hydrological Model (YHyM). The simulation results indicated a significant change in vegetation type mainly on the Tibetan Plateau and in mountainous areas, with the degree of change differing for each SRES scenario; LAI increases around the edge of the Tibetan Plateau and decreases in the lower reaches of the basin; and more conspicuous changes in river discharge in upstream areas than in the middle to lower reaches, mainly due to increases in precipitation in the plateau region. After the 2050s, the results suggested changes in river discharge will be slowed due to changes in evapotranspiration. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||