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Lower Slopes (lower + slope)
Selected AbstractsPositive and negative effects of livestock grazing on plant diversity of Mongolian nomadic pasturelands along a slope with soil moisture gradientGRASSLAND SCIENCE, Issue 3 2009Noboru Fujita Abstract To examine different effects of herbivorous large mammals' grazing pressure on plant diversity along a slope in a Mongolian nomadic pasture, we compared species richness, Simpson's index of diversity, and the total plant coverage of plants between protected pasture from livestock grazing and grazed pasture on the near ridge, upper slope, lower slope, foot slope and valley bottom. The species richness and Simpson's index of diversity decreased and the total coverage increased downwardly with increase in pasture soil moisture along the slope. The species richness of the protected pasture decreased, changed little, and increased on the near ridge and the upper slope, the lower slope and the foot slope, and the valley bottom, respectively. Simpson's index of diversity of the protected pasture decreased compared with the grazed pasture only on the valley bottom. The total coverage became lower in the grazed pasture. As the reason for our results, we discuss positive and negative effects of livestock grazing on the species diversity of plants. The positive effect is shown on the valley bottom, where soil moisture and plant growth becomes high with the total coverage over 100%, due to relaxing indirectly the competitive exclusion among plants due to the grazing of dominant plants. The negative effect is obtained on the near ridge and the upper slope, where the soil moisture and the plant growth are low, because of elimination of some plants from the pasture by direct grazing damage. [source] Applying discontinuous deformation analysis to assess the constrained area of the unstable Chiu-fen-erh-shan landslide slopeINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2007Jian-Hong Wu Abstract Chiu-fen-erh-shan landslide is a remarkable slope failure occurred during the Chi-Chi earthquake in 1999. In November of 2002, abnormal geomorphologic features, including buckling and ground subsidence, were observed on the lower slope of the Chiu-fen-erh-shan landslide. This study attempts to assess the constrained area of a future collapsing on the slope using a dynamic discrete numerical analysis method, discontinuous deformation analysis (DDA). The simulation results show that the depression in front of the toe of the slope provides a space for arresting the whole sliding rocks when only the unstable lower slope fails. However, as the whole slope slides, the rock fragments move farther into the memorial park and can impact other facilities resulting in the enlarging of constrained area. The authority should prohibit people from entrancing the constrained area in the rainy season. Copyright © 2006 John Wiley & Sons, Ltd. [source] How to test different density-dependent fecundity hypotheses in an increasing or stable populationJOURNAL OF ANIMAL ECOLOGY, Issue 1 2006MIGUEL FERRER Summary 1We report on a simulation study of increasing and stable populations working under two different hypotheses of density dependence of fecundity: the habitat heterogeneity hypothesis (HHH) and the individual adjustment hypothesis (IAH). Our aim is to find critical differences between the two regulatory hypotheses in natural populations. 2Populations under HHH show a strong negative relationship between fecundity and the coefficient of variation of fecundity. We also found a strong negative relationship between fecundity and skewness, demonstrating that, as fecundity decreases, the form of the distribution of brood sizes changes, being more left-skewed due to more territories failing to produce any offspring. 3This strong relationship was found only in the simulations of populations under HHH; whether increasing or stable, and under different ratios of good : poor territories and different population sizes. In contrast, no relationship between mean fecundity and skewness was found among simulations under IAH. 4Populations under IAH also showed a significant relationship between mean fecundity and the coefficient of variation of fecundity, but with a lower slope than in populations under HHH. 5In conclusion, skewness was found to be an adequate critical test that showed significant and strong relationships with mean fecundity only in populations under HHH, whether increasing or stable. This test is useful for species with a discrete distribution of offspring with a small number of integer categories, including most of the bird and mammal species. [source] Optimizing dispersal and corridor models using landscape geneticsJOURNAL OF APPLIED ECOLOGY, Issue 4 2007CLINTON W. EPPS Summary 1Better tools are needed to predict population connectivity in complex landscapes. ,Least-cost modelling' is one commonly employed approach in which dispersal costs are assigned to distinct habitat types and the least-costly dispersal paths among habitat patches are calculated using a geographical information system (GIS). Because adequate data on dispersal are usually lacking, dispersal costs are often assigned solely from expert opinion. Spatially explicit, high-resolution genetic data may be used to infer variation in animal movements. We employ such an approach to estimate habitat-specific migration rates and to develop least-cost connectivity models for desert bighorn sheep Ovis canadensis nelsoni. 2Bighorn sheep dispersal is thought to be affected by distance and topography. We incorporated both factors into least-cost GIS models with different parameter values and estimated effective geographical distances among 26 populations. We assessed which model was correlated most strongly with gene flow estimates among those populations, while controlling for the effect of anthropogenic barriers. We used the best-fitting model to (i) determine whether migration rates are higher over sloped terrain than flat terrain; (ii) predict probable movement corridors; (iii) predict which populations are connected by migration; and (iv) investigate how anthropogenic barriers and translocated populations have affected landscape connectivity. 3Migration models were correlated most strongly with migration when areas of at least 10% slope had 1/10th the cost of areas of lower slope; thus, gene flow occurred over longer distances when ,escape terrain' was available. Optimal parameter values were consistent across two measures of gene flow and three methods for defining population polygons. 4Anthropogenic barriers disrupted numerous corridors predicted to be high-use dispersal routes, indicating priority areas for mitigation. However, population translocations have restored high-use dispersal routes in several other areas. Known intermountain movements of bighorn sheep were largely consistent with predicted corridors. 5Synthesis and applications. Population genetic data provided sufficient resolution to infer how landscape features influenced the behaviour of dispersing desert bighorn sheep. Anthropogenic barriers that block high-use dispersal corridors should be mitigated, but population translocations may help maintain connectivity. We conclude that developing least-cost models from similar empirical data could significantly improve the utility of these tools. [source] Vertical distribution of soil properties under short-rotation forestry in Northern GermanyJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2010Petra Kahle Abstract Short-rotation forestry (SRF) on arable soils has high potentials for biomass production and leads to long-term no-tillage management. In the present study, the vertical distributions of soil chemical and microbial properties after 15 y of SRF with willows and poplar (Salix and Populus spp.) in 3- and 6-year rotations on an arable soil were measured and compared to a pertinent tilled arable site. Two transects at different positions in the relief (upper and lower slope; transect 1 and 2) were investigated. Short-rotation forestry caused significant changes in the vertical distribution of all investigated soil properties (organic and microbial C, total and microbial N, soil enzyme activities), however, the dimension and location (horizons) of significant effects varied. The rotation periods affected the vertical distribution of the soil properties within the SRF significantly. In transect 1, SRF had higher organic-C concentrations in the subsoil (Bv horizon), whereas in transect 2, the organic-C concentrations were increased predominantly in the topsoil (Ah horizon). Sufficient plant supply of P and K in combination with decreased concentrations of these elements in the subsoil under SRF pointed to an effective nutrient mobilization and transfer from the deeper soil horizons even in the long term. In transect 1, the microbial-C concentrations were higher in the B and C horizons and in transect 2 in the A horizons under SRF than under arable use. The activities of ,-glucosidases and acid phosphatases in the soil were predominantly lower under SRF than under arable use in the topsoil and subsoil. We conclude, that long-term SRF on arable sites can contribute to increased C sequestration and changes in the vertical distribution of soil microbial biomass and soil enzyme activities in the topsoil and also in the subsoil. [source] Community structure of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean)MARINE ECOLOGY, Issue 2009Maria Cristina Follesa Abstract Community structure and faunal composition of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean) were investigated. Samples were collected during 32 hauls between 793 and 1598 m in depth over the 2003,2007 period. A total of 1900 decapod specimens belonging to 23 species were collected. Multivariate analysis revealed the occurrence of three faunistic assemblages related to depth: (i) an upper slope community at depths of 793,1002 m; (ii) a middle slope community at depths of 1007,1212 m and (iii) a lower slope community at depths greater 1420 m. In the upper and middle slopes the benthic (Polycheles typhlops) and epibenthic,endobenthic feeders (mainly Aristeus antennatus and Geryon longipes), which eat infaunal prey, were dominant, followed by the macroplankton,epibenthic feeders such as Acanthephyra eximia and Plesionika acanthonotus. In the deepest stratum, the most remarkable feature was the prevalence of macroplankton,epibenthic feeders (A. eximia and P. acanthonotus). A small percentage of the benthic deep-sea lobster Polycheles sculptus was also present. The biomass presented higher values in the middle slope and declined strongly in the lower slope. There was no general pattern of mean individual weight/size versus depth among decapods, and the changes seemed to be species-specific with different trends. [source] Erosional vs. accretionary shelf margins: the influence of margin type on deepwater sedimentation: an example from the Porcupine Basin, offshore western IrelandBASIN RESEARCH, Issue 5 2009M. C. Ryan ABSTRACT A 1000 km2 three-dimensional (3D) seismic data survey that extends out from the western margin of the Porcupine Basin, offshore western Ireland reveals the internal geometry and depositional history of a large Palaeogene (Palaeocene,Early Eocene) shelf-margin. Two wells intersect the margin thereby constraining the depositional environments. The 34/19-1 well (landward end) intersects slope, shelf, marginal marine to coastal plain facies. The 35/21-1 well (basinward end) intersects seismically imaged shelf-margin clinoforms where base of slope back up to coastal plain deposits (source-to-sink) are represented. The basin-fill stratal architecture of the Palaeogene succession reveals sediment deposition under two end member, basin physiographic styles: (1) an erosional margin style and (2) an accretionary or progradational margin style. Uplift of the western margin of the basin is suggested as the major cause of the initially oversteepened shelf-slope erosional profile. Key characteristics of an erosional margin include sediment bypass of the shelf, canyon formation, and the development of significant onlapping submarine fan deposits on the lower slope. Failure on the slope is also revealed by several mass,transport complexes (MTCs) that carve out major erosive features across the slope. Three-dimensional seismic analysis illustrates variations in size, geometry and depositional trend and transport mechanisms of the MTCs. Confined, thick chaotic seismic facies, erosional basal scours and syn-depositional thrusting (pressure ridges) at terminus as opposed to thin, high-amplitude discontinuous facies with an unconfined lobate terminus are interpreted to indicate slump- and slide-dominated vs. debris flow-dominated MTCs, respectively. The erosional margin was transformed into an accretionary margin when the gradient of the shelf-slope to basin-floor profile was sufficiently lowered through the infilling and healing of the topographic lows by the onlapping submarine-fan deposits. This shallowing of the basin allowed nearshore systems to prograde across the deepwater systems. The accretionary margin was characterised by a thick sediment prism composed of clinoforms both at the shoreface/delta (tens of metres) and shelf-margin (hundreds of metres) scales. Shelf-margin clinoforms, the focus of this study, are the fundamental regressive to transgressive building blocks (duration 10,100 kyr) of the stratigraphic succession and can be observed on a larger scale (,1 Myr) through the migration and trajectory patterns of the shelf-edge. Trajectory pathways in the accretionary margin are accretionary in a descending or ascending manner. The descending style was characterised by a shelf-slope break that migrated seawards and obliquely downwards as a result of a relative sea-level fall. The descending trajectory geometry is lobate along strike suggestive of a point source progradation. Internally, the descending trajectory consists of downward stepping, steeply dipping shelf-margin clinoforms that display extensive slumping and deposition of sediment on the lower slope indicative of rapid deposition. Furthermore, basin-floor fans and associated ,feeder' channels extend basinwards beyond toe of slope. The ascending trajectory reflects a shelf-slope break that is interpreted to have migrated seawards during steady or rising relative sea level. The ascending trajectory geometry is associated with significant lateral sediment dispersal along the shelf-edge, reflecting distributary systems that were less ,fixed' or a greater reworking and longshore drift of sediment. Accretion involving the ascending shelf-edge trajectory characteristically lacked significant basin-floor deposits. Variable ascending trajectories are recognised in this study, as read from the angle at which the shelf-slope break migrates. Horizontal to high angle ascending trajectories correspond to dominantly progradational and dominantly aggradational shelf-edge trajectories, respectively. The sequence stratigraphic analysis of the Porcupine deltaic complex reveals a long-term relative sea-level rise. [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] Selection on defensive traits in a sterile caste , caste evolution: a mechanism to overcome life-history trade-offs?EVOLUTION AND DEVELOPMENT, Issue 1 2009Estelle A. Roux SUMMARY During development and evolution individuals generally face a trade-off between the development of weapons and gonads. In termites, characterized by reproductive division of labor, a caste evolved,the soldiers,which is completely sterile and which might be released from developmental trade-offs between weapons and testes. These soldiers are exclusively dedicated to defense. First, we investigated whether defensive traits are under selection in sterile termite soldiers using allometric analyses. In soldiers of the genus Cryptotermes phragmotic traits such as a sculptured and foreshortened head evolve rapidly but were also lost twice. Second, we compared the scaling relationships of these weapons with those in solitary insects facing a trade-off between weapons and gonads. Defensive traits consistently had lower slopes than nondefensive traits which supports the existence of stabilizing selection on soldier phragmotic traits in order to plug galleries. Moreover, soldier head widths were colony specific and correlated with the minimum gallery diameter of a colony. This can proximately be explained by soldiers developing from different instars. The scaling relationships of these termite soldiers contrast strikingly with those of weapons of solitary insects, which are generally exaggerated (i.e., overscaling) male traits. These differences may provide important insights into trait evolution. Trade-offs constraining the development of individuals may have been uncoupled in termites by evolving different castes, each specialized for one function. When individuals in social insect are "released" from developmental constraints through the evolution of castes, this certainly contributed to the ecological and evolutionary success of social insects. [source] The Geologic Basis for a Reconstruction of a Grounded Ice Sheet in McMurdo Sound, Antarctica, at the Last Glacial MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2-3 2000George H. Denton A grounded ice sheet fed from the Ross Embayment filled McMurdo Sound at the last glacial maximum (LGM). This sheet deposited the little-weathered Ross Sea drift sheet, with far-traveled Transantarctic Mountains (TAM) erratics, on lower slopes of volcanic islands and peninsulas in the Sound, as well as on coastal forelands along the TAM front. The mapped upper limit of this drift, commonly marked by a distinctive moraine ridge, shows that the ice-sheet surface sloped landward across McMurdo Sound from 710 m elevation at Cape Crozier to 250 m in the eastern foothills of the Royal Society Range. Ice from the Ross Embayment flowed westward into the sound from both north and south of Ross Island. The northern flowlines were dominant, deflecting the southern flowlines toward the foothills of the southern Royal Society Range. Ice of the northern flowlines distributed distinctive kenyte erratics, derived from western Ross Island, in Ross Sea drift along the TAM front between Taylor and Miers Valleys. Lobes from grounded ice in McMurdo Sound blocked the mouths of TAM ice-free valleys, damming extensive proglacial lakes. A floating ice cover on each lake formed a conveyor that transported glacial debris from the grounded ice lobes deep into the valleys to deposit a unique glaciolacustrine facies of Ross Sea drift. The ice sheet in McMurdo Sound became grounded after 26,860 14C yr bp. It remained near its LGM position between 23,800 14C yr bp and 12,700 14C yr bp. Recession was then slow until sometime after 10,794 14C yr bp. Grounded ice lingered in New Harbor in the mouth of Taylor Valley until 8340 14C yr bp. The southward-retreating ice-sheet grounding line had penetrated deep into McMurdo Sound by 6500 14C yr bp. The existence of a thick ice sheet in McMurdo Sound is strong evidence for widespread grounding across the Ross Embayment at the LGM. Otherwise, the ice-sheet surface would not have sloped landward, nor could TAM erratics have been glacially transported westward into McMurdo Sound from farther offshore in the Ross Embayment. [source] ,Distribution of oxygen-18 and deuterium in river waters across the United StatesHYDROLOGICAL PROCESSES, Issue 7 2001Carol Kendall Abstract Reconstruction of continental palaeoclimate and palaeohydrology is currently hampered by limited information about isotopic patterns in the modern hydrologic cycle. To remedy this situation and to provide baseline data for other isotope hydrology studies, more than 4800, depth- and width-integrated, stream samples from 391 selected sites within the USGS National Stream Quality Accounting Network (NASQAN) and Hydrologic Benchmark Network (HBN) were analysed for ,18O and ,2H (http://water.usgs.gov/pubs/ofr/ofr00-160/pdf/ofr00-160.pdf). Each site was sampled bimonthly or quarterly for 2·5 to 3 years between 1984 and 1987. The ability of this dataset to serve as a proxy for the isotopic composition of modern precipitation in the USA is supported by the excellent agreement between the river dataset and the isotopic compositions of adjacent precipitation monitoring sites, the strong spatial coherence of the distributions of ,18O and ,2H, the good correlations of the isotopic compositions with climatic parameters, and the good agreement between the ,national' meteoric water line (MWL) generated from unweighted analyses of samples from the 48 contiguous states of ,2H=8·11,18O+8·99 (r2=0·98) and the unweighted global MWL of sites from the Global Network for Isotopes in Precipitation (GNIP) of the International Atomic Energy Agency and the World Meteorological Organization (WMO) of ,2H=8·17,18O+10·35. The national MWL is composed of water samples that arise in diverse local conditions where the local meteoric water lines (LMWLs) usually have much lower slopes. Adjacent sites often have similar LMWLs, allowing the datasets to be combined into regional MWLs. The slopes of regional MWLs probably reflect the humidity of the local air mass, which imparts a distinctive evaporative isotopic signature to rainfall and hence to stream samples. Deuterium excess values range from 6 to 15, in the eastern half of the USA, along the northwest coast and on the Colorado Plateau. In the rest of the USA, these values range from ,2 to 6,, with strong spatial correlations with regional aridity. The river samples have successfully integrated the spatial variability in the meteorological cycle and provide the best available dataset on the spatial distributions of ,18O and ,2H values of meteoric waters in the USA. Published in 2001 by John Wiley & Sons, Ltd. [source] A test of the metapopulation model of the species,area relationshipJOURNAL OF BIOGEOGRAPHY, Issue 8 2002Stephen F. Matter Abstract Aim The species,area relationship is a ubiquitous pattern. Previous methods describing the relationship have done little to elucidate mechanisms producing the pattern. Hanski & Gyllenberg (Science, 1997, 275, 397) have shown that a model of metapopulation dynamics yields predictable species,area relationships. We elaborate on the biological interpretation of this mechanistic model and test the prediction that communities of species with a higher risk of extinction caused by environmental stochasticity should have lower species,area slopes than communities experiencing less impact of environmental stochasticity. Methods We develop the mainland,island version of the metapopulation model and show that the slope of the species,area relationship resulting from this model is related to the ratio of population growth rate to variability in population growth of individual species. We fit the metapopulation model to five data sets, and compared the fit with the power function model and Williams's (Ecology, 1995, 76, 2607) extreme value function model. To test that communities consisting of species with a high risk of extinction should have lower slopes, we used the observation that small-bodied species of vertebrates are more susceptible to environmental stochasticity than large-bodied species. The data sets were divided into small and large bodied species and the model fit to both. Results and main conclusions The metapopulation model showed a good fit for all five data sets, and was comparable with the fits of the extreme value function and power function models. The slope of the metapopulation model of the species,area relationship was greater for larger than for smaller-bodied species for each of five data sets. The slope of the metapopulation model of the species,area relationship has a clear biological interpretation, and allows for interpretation that is rooted in ecology, rather than ad hoc explanation. [source] Spatial and temporal variation of fire regimes in a mixed conifer forest landscape, Southern Cascades, California, USAJOURNAL OF BIOGEOGRAPHY, Issue 8 2001R. Matthew Beaty Aim In this study, we evaluated the fire-forest mosaic of a mixed conifer forest landscape by testing the hypothesis that pre-fire suppression fire regime parameters vary with species composition (tree species), and environment (i.e. slope aspect, slope position, elevation). Location Our study was conducted in the 1587 ha Cub Creek Research Natural Area (CCRNA), Lassen National Forest, CA, USA. Methods We quantified the return interval, seasonal occurrence, size, rotation period, and severity of fires using dendroecology. Results Slope aspect, potential soil moisture, forest composition, and fire regime parameters in our study area co-vary. Median composite and point fire return intervals (FRI) were longest on higher, cooler, more mesic, north-facing (NF) slopes covered with white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii),white fir, and red fir (A. magnifica),white fir forests, shortest on the dry, south-facing (SF) slopes covered with ponderosa pine (Pinus ponderosa),white fir forests and intermediate on west-facing slopes dominated by white fir,sugar pine (P. lambertiana),incense cedar (Libocedrus decurrens) forests. The spatial pattern for length of fire rotation (FR) was the same as that for FRI. Fires in CCRNA mixed conifer forests occurred mainly (90%) in the dormant season. Size of burns in CCRNA mixed conifer forests were generally small (mean=106 ha), however, during certain drought years widespread fires burned across fuel breaks and spread throughout the watershed. Fire severity was mainly high on upper slopes, low on lower slopes and moderate and low severity on middle slopes. Patterns of fire severity also varied with slope aspect. Fire frequency decreased dramatically in CCRNA after 1905. Conclusions In CCRNA, fire regime parameters [e.g. FRI, fire extent, FR, fire severity] varied widely with species composition, slope aspect and slope position. There was also temporal variation in fire extent with the most widespread fires occurring during drought years. The important contributions of topography and climate to variation in the fire regime indicates that exogenous factors play a key role in shaping the fire-forest structure mosaic and that the fire-forest structure mosaic is more variable, less predictable and less stable than previously thought. Finally, some characteristics of the fire regime (i.e. fire severity, season of burn) in CCRNA are different than those described for other mixed conifer forests and this suggests that there are geographical differences in mixed conifer fire regimes along the Pacific slope. [source] Repolarization Abnormality in Idiopathic Ventricular Fibrillation:JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 1 2004Assessment Using 24-Hour QT-RR, QaT-RR Relationships Introduction: We evaluated the characteristics of QT-RR and QaT (apex of T wave)-RR relationships in patients with idiopathic ventricular fibrillation (IVF) compared with control subjects. We hypothesized that IVF patients have unique repolarization dynamics related to a reduced fast Na current and a prominent transient outward current. Methods and Results: The study group consisted of 9 men (age 47 ± 10 years) with IVF (6 with Brugada type and 3 with non-Brugada type) who had experienced nocturnal episodes of VF. The control group consisted of 28 healthy age-matched men (age 44 ± 12 years). The relationships between QT and RR intervals and between QaT and RR intervals were analyzed from 24-hour Holter ECG data using an automatic measurement system. Both QT and QaT at RR intervals of 0.6, 1.0, and 1.2 seconds were determined from QT-RR and QaT-RR linear regression lines. Both QT-RR and QaT-RR slopes were lower in the IVF group than in the control group (QT-RR: 0.092 ± 0.023 vs 0.137 ± 0.031, P < 0.001; QaT-RR: 0.109 ± 0.025 vs 0.153 ± 0.028, P < 0.001). QT at an RR interval of 0.6 second did not differ between two groups, but QT at RR intervals of either 1.0 or 1.2 seconds was significantly shorter in the IVF group than in the control group (RR 1.0 s: 0.384 ± 0.018 vs 0.399 ± 0.017, P < 0.05; RR 1.2 s: 0.402 ± 0.019 vs 0.426 ± 0.020, P < 0.01). QaT at RR intervals of either 1.0 or 1.2 seconds also was shorter in the IVF group (RR 1.0 s: 0.289 ± 0.022 vs 0.312 ± 0.021, P < 0.01; RR 1.2 s: 0.311 ± 0.024 vs 0.343 ± 0.024, P < 0.01). In four patients, oral administration of disopyramide (300 mg/day) was effective in suppressing VF episodes and increased slopes of QT-RR and QaT-RR relationships. Conclusion: IVF patients had lower slopes of QT-RR and QaT-RR regression lines and impaired prolongation of QT and QaT at longer RR intervals compared with control subjects. These unique repolarization dynamics may be related to the frequent occurrence of VF episodes at night. (J Cardiovasc Electrophysiol, Vol. 15, pp. 59-63, January 2004) [source] Holocene solifluction, climate variation and fire in a subarctic landscape at Pippokangas, Finnish Lapland, based on radiocarbon-dated buried charcoal,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2005John A. Matthews Abstract A large number of radiocarbon dates from charcoal layers buried beneath stacked solifluction lobes at Pippokangas, in the northern boreal zone of Finnish Lapland, are used to reconstruct a Holocene history of solifluction. Although the site is surrounded by Scots pine forest, the solifluction lobes occur on the lower slopes of a kettle hole, the microclimate of which prevents the growth of trees. Samples from the upslope end of charcoal layers have enabled the recognition of four synchronous phases of solifluction lobe initiation: 7400,6700, 4200,3400, 2600,2100 and 1500,500,cal.,yr,BP. Rates of lobe advance are shown to be lobe-dependent and age-dependent: initially, average rates were commonly 0.14,0.19,cm yr,1, later falling to 0.02,0.07,cm,yr,1 or less as the lobes approached the bottom of the slope. The absence of charcoal prior to 8000,cal.,yr,BP, together with single IRSL and TL dates, indicate a relatively stable early Holocene landscape. The onset of solifluction around 7400,cal.,yr,BP. appears to have followed the immigration of pine around the site, which increased the frequency of forest fires. Phases of solifluction activity seem to have been triggered by millennial-scale variations in effective moisture (the climatic hypothesis), rather than episodic burning of the surface vegetation cover (the geoecological hypothesis), although climate may also have affected fire frequency and severity. Copyright © 2005 John Wiley & Sons, Ltd. [source] Water-Yield Reduction After Afforestation and Related Processes in the Semiarid Liupan Mountains, Northwest China,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2008Yanhui Wang Abstract:, The increase of coverage of forest/vegetation is imperative to improve the environment in dry-land areas of China, especially for protecting soil against serious erosion and sandstorms. However, inherent severe water shortages, drought stresses, and increasing water use competition greatly restrict the reforestation. Notably, the water-yield reduction after afforestation generates intense debate about the correct approach to afforestation and forest management in dry-land areas. However, most studies on water-yield reduction of forests have been at catchment scales, and there are few studies of the response of total evapotranspiration (ET) and its partitioning to vegetation structure change. This motivates us to learn the linkage between hydrological processes and vegetation structure in slope ecosystems. Therefore, an ecohydrological study was carried out by measuring the individual items of water balance on sloping plots covered by different vegetation types in the semiarid Liupan Mountains of northwest China. The ratio of precipitation consumed as ET was about 60% for grassland, 93% for shrubs, and >95% for forestland. Thus, the water yield was very low, site-specific, and sensitive to vegetation change. Conversion of grassland to forest decreased the annual water yield from slope by 50-100 mm. In certain periods, the plantations at lower slopes even consumed the runon from upper slopes. Reducing the density of forests and shrubs by thinning was not an efficient approach to minimize water use. Leaf area index was a better indicator than plant density to relate ET to vegetation structure and to evaluate the soil water carrying capacity for vegetation (i.e., the maximum amount of vegetation that can be supported by the available soil water for an extended time). Selecting proper vegetation types and plant species, based on site soil water condition, may be more effective than the forest density regulation to minimize water-yield reduction by vegetation coverage increase and notably by reforestation. Finally, the focuses in future research to improve the forest-water relations in dry-land areas are recommended as follows: vegetation growth dynamics driven by environment especially water conditions, coupling of ecological and hydrological processes, further development of distributed ecohydrological models, quantitative relation of eco-water quota of ecosystems with vegetation structures, multi-scaled evaluation of soil water carrying capacity for vegetation, and the development of widely applicable decision support tools. [source] Wheat field erosion rates and channel bottom sediment sources in an intensively cropped northeastern Oregon drainage basin,LAND DEGRADATION AND DEVELOPMENT, Issue 1 2004G. N. Nagle Abstract Sediment tracers were used to quantify erosion from cultivated fields and identify major source areas of channel bottom sediment within the Wildhorse Creek drainage, an intensively cropped tributary of the Umatilla River in northeastern Oregon, USA. Available data indicated that Wildhorse Creek was one of the largest sediment yielding tributaries of the Umatilla River. Carbon, nitrogen and the nuclear bomb-derived radionuclide 137Cs were used as tracers to fingerprint sediment sources. Sediment was collected from the stream bottom and active floodplain and compared to samples from cultivated fields and channel banks. Samples were characterized on the basis of tracer concentrations and a simple mixing model was used to estimate the relative portion of bottom sediment derived from cultivated surface and channel banks. The results indicate that the amount of bottom sediment derived from cultivated surface sources was less than 26,per,cent for the 1998 winter season, although this estimate has a high margin of error. Cesium-137 was also used to estimate surface erosion from three cultivated fields in the watershed. Annual estimates of erosion since 1963 from the three sampled fields were from 3 to 7,5,t,ha,1 yr,1. For the 1998 season, it appears that most channel-bottom sediment was of subsurface origin with much of it likely coming from channel and gully banks indicating that significant reductions in sediment in Wildhorse Creek might be accomplished by the stabilization of eroding riparian areas and swales on the lower slopes of agricultural fields. Published in 2004 by John Wiley & Sons, Ltd. [source] | |||||||||||||||||||