Rain Splash Research Articles

Preliminary observation of genital secretions, growth rate and behaviour of caged cane rats

Cane rats are large terrestial rodents which have the potential to increase animal protein intake. There is paucity of information on the genital secretions and growth rate of caged cane rats. This study observed the genital secretions, growth rate, feeds, feeding and the behaviour of caged cane rats. When animals adjusted to cage conditions, they received feed (sugar cane) directly orally. Some of the cane rats captured around the stream did not adjust to the cage as they died 10 days after capture from the wild. The doe attained puberty at age 11weeks (2months 3weeks). At this age, reproductive activities commenced in the doe with a slight opening of the vulva and the presence of colourless mucous fluid in the vagina. At 11weeks, the vulva was opened for 3weeks plus 6days and by the 4th week the crust had covered the vulva. The vulva opened for a minimum of 1 week and maximum of 4 weeks. The vulva closed for a minimum of 3 weeks and maximum of 4½ weeks. During the intermittent opening between closures, there were always colourless mucous secretions or sometimes thick yellowish mucous and the buck did not chase the doe for mating. The buck withdrew completely from the doe. When the vulva opened and the vagina was dried, the buck made a chase of the doe. Environmental influences (rain splashes) do not affect the opening and closing activities of the vulva in the doe. At between 18 - 27 weeks, the doe had a better growth rate in cage and had gained 0.5kg. This study has revealed that cane rat has an estrous period hence it is a break through for the cane rat breeders and farmers. Breeders/farmers need not to keep the buck with the doe until it kits thus they would be able to maximize the useage of their breeding buck to serve many doe. This also calls for other studies on the physiological variations to be carried out in the intra and inter populations of cane rat.Key words: cane rat, feeding, mucous, vulva, vagina

Deposition patterns of Fusarium graminearum ascospores and conidia within a wheat canopy

Fusarium graminearum is the most important species in the fungal complex causing Fusarium head blight of small grain cereals. The fungus produces two types of spores on crop residues (ascospores and conidia), which are dispersed to ears by air currents and rain splashes, respectively. The distribution patterns of ascospores and conidia within a wheat canopy between booting and grain maturity were assessed by using leaf-like spore traps placed at 10, 30, and 60 cm height, and ear-like spore traps at 90 cm height. Maize residues were the inoculum source for both ascospores and conidia within the wheat plot. Of the total spores counted, 93 % were ascospores and 7 % were conidia. Approximately 41, 22, 19, and 18 % of the ascospores, and 77, 10, 8, and 5 % of the conidia were sampled at 10, 30, 60, and 90 cm height, respectively. Ascospore numbers did not significantly differ between those sampled on the upper or the lower sides of the leaf-like traps or among the four orientations (north, south, east, or west) of the ear-like traps. According to the index of dispersion (D), the spatial distribution of trapped ascospores was largely random (i.e., D ≤ 1) rather than aggregated (i.e., D > 1). The collective results (averaged across all traps and sampling periods) showed that the random distribution of the ascospores within the wheat canopy and at the ear level was associated with a clear vertical distribution pattern indicating an upward movement of ascospores from the maize residues on the ground.

Where have all the flowers gone? Postbloom fruit drop of citrus in the Americas.

Postbloom fruit drop (PFD), caused primarily by Colletotrichum acutatum, is a serious disease annually in the humid tropical citrus areas of the Americas and occurs more sporadically in the humid subtropics. The fungus infects flowers of all citrus species producing orange-brown lesions on petals that result in abscission of the fruitlets leaving the persistent calyx and floral disk attached to the twigs. C. acutatum also causes Key lime anthracnose and is morphologically identical to PFD, but the strains can be differentiated by molecular means and pathogenicity tests. C. acutatum produces abundant conidia on infected petals that are dispersed primarily by rain splash. After the bloom season, the fungus persists as appressoria on persistent calyces and other vegetative plant parts. Those appressoria are stimulated to germinate by flower extracts and produce secondary conidia to initiate a new disease cycle. Some cultural measures are useful in reducing disease severity, but control is based principally on application of fungicides. Benzimidazole fungicides and captafol were the best materials in the past but are no longer available. The QoI fungicides, folpet and tebuconazole + trifloxystrobin are the most effective among currently available materials. Forecasting systems based primarily on the availability of inoculum and recent rainfall were developed to aid growers on timing fungicide applications. The expert system, PFD-FAD, based on environmental conditions, inoculum, disease history, and varietal susceptibility is the most effective means currently available for scheduling fungicide applications.

Comparison of different methods to measure soil erosion in the Central Ebro Valley

Fire is a natural factor of landscape evolution in Mediterranean ecosystems. Due to social and economical changes, wildfires have caused hydrological and geomorphological changes to be more pronounced, resulting in enhanced soil erosion. The study area is located in the Zuera Mountains, near the city of Zaragoza (Spain) in the Middle Ebro Valley. These mountains were affected by two wildfires in 2008 and 2009, burned around 2000 ha and 6000 ha, respectively. Middle Ebro Valley has extreme aridity, which results in a low plant cover and high soil erodibility enhanced by the fire effects. Soil infiltration is one of the properties affected by fire as a consequence of litter and vegetation removal, heating of and changes to the biological, chemical and physical soil properties. The objective was to compare two different methods –rainfall simulations and erosion plots–, to assess soil erosion after forest fires. We compared different measurements with rainfall simulators and erosion plots, applying a woodchip cover –in order to reduce the rain splash effect–, and to measure the erosion reduction. The work showed low sediment rates in both experiments covered with woodchips.

Thismiahongkongensis (Thismiaceae): a new mycoheterotrophic species from Hong Kong, China, with observations on floral visitors and seed dispersal.

A new species, Thismia hongkongensis S.S.Mar & R.M.K.Saunders, is described from Hong Kong. It is most closely related to Thismia brunonis Griff. from Myanmar, but differs in the number of flowers per inflorescence, the colour of the perianth tube, the length of the filaments, and the shape of the stigma lobes. We also provide inferences on the pollination ecology and seed dispersal of the new species, based on field observations and interpretations of morphology. The flowers are visited by fungus gnats (Myctophilidae or Sciaridae) and scuttle flies (Phoridae), which are likely to enter the perianth tube via the annulus below the filiform tepal appendages, and exit via small apertures between the filaments of the pendent stamens. The flowers are inferred to be protandrous, and flies visiting late-anthetic (pistillate-phase) flowers are possibly trapped within the flower, increasing chances of pollen deposition on the receptive stigma. The seeds are likely to be dispersed by rain splash.

Performance of the CalTOX fate and exposure model in a case study for a dioxin-contaminated site.

Soil with high levels of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) is found at contaminated sites all over the world. Transfer of PCDD/Fs from contaminated soil to the food chain could lead to elevated human exposure. As a complement to available monitoring data, multimedia fate and exposure modeling can be applied to support risk assessment of sites with PCDD/F contaminated soil. In this study, we evaluated the performance of the CalTOX fate and exposure model for 2,3,7,8-substituted PCDD/Fs against measured concentrations in air, soil, grass, carrots, potatoes, milk, meat, and eggs from a contaminated site in northern Sweden. The calculated total toxic equivalent (TEQ) concentrations agree with measurements within a factor of 10 for all exposure media but one. Results for individual congeners demonstrated that the model did not always perform well at describing key processes that mobilize PCDD/Fs out of soils, such as transfer into root crops and ingestion of soil by chickens. Uncertainty in only a small subset of input parameters affects the model output. Improved information and models describing transfer of soil particles onto leafy vegetation by rain splash and biotransfer factors for PCDD/Fs to milk, meat, and eggs are particular research needs to reduce uncertainties in model-based assessments.

Quantification of particle detachment by rain splash and wind-driven rain splash

A surface-hitting raindrop transfers a part of its kinetic energy onto the surface and thereby destroys aggregates and moves soil particles. The magnitude of interrill processes is largely determined by the intensity and kinetic energy of rainfall.Wind alters all erosion-relevant characteristics of a falling raindrop such as velocity, impact angle and kinetic energy. It also might capture and drag an airborne soil particle. To quantify the amount of raindrop erosion with and without the influence of wind, an experimental setting within the Portable Wind and Rainfall Simulator was developed and applied. The results on cohesionless sandy substrate suggest that wind considerably increases raindrop-erosion:1.The mean amount of detached substrate is increased by the factor 50.2.The covered distance is greater.3.The process splash-creep is intensified.The study highlights a potentially very strong impact of wind-driven rain on soil erosion. The evaluation of splash and splash-saltation is one important step towards the general understanding and realistic assessment of regional and global soil erosion rates and application in soil erosion models.

Direct splash dispersal prevails over indirect and subsequent spread during rains in Colletotrichum gloeosporioides infecting yams.

Plant pathogens have evolved many dispersal mechanisms, using biotic or abiotic vectors or a combination of the two. Rain splash dispersal is known from a variety of fungi, and can be an efficient driver of crop epidemics, with infectious strains propagating rapidly among often genetically homogenous neighboring plants. Splashing is nevertheless a local dispersal process and spores taking the droplet ride seldom move farther than a few decimeters. In this study, we assessed rain splash dispersal of conidia of the yam anthracnose agent, Colletotrichum gloeosporioides, in an experimental setting using a rain simulator, with emphasis on the impact of soil contamination (i.e., effect of re-splashing events). Spores dispersed up to 50 cm from yam leaf inoculum sources, though with an exponential decrease with increasing distance. While few spores were dispersed via re-splash from spore-contaminated soil, the proportion deposited via this mechanism increased with increasing distance from the initial source. We found no soil contamination carryover from previous rains, suggesting that contamination via re-splashing from contaminated soils mainly occurred within single rains. We conclude that most dispersal occurs from direct splashing, with a weaker contribution of indirect dispersal via re-splash.

Recent insights into the pandemic disease butternut canker caused by the invasive pathogen Ophiognomonia clavigignenti‐juglandacearum

SummaryIn the 25 years following the initial 1967 report of the disease, butternut canker was able to quickly spread throughout the entire range of butternut (Juglans cinerea) in North America, from Minnesota in the upper Midwest to Tennessee in the south and Quebec in the north‐east. The speed of this dispersal is notable as butternut trees do not make up a significant proportion of any single forest type. Instead, they are usually found sparingly in most mixed hardwood forests. In this review, we synthesize the current knowledge of the invasion process of the butternut canker pathogen, Ophiognomonia clavigignenti‐juglandacearum, an invasive fungal pathogen, that as its emergence has spread across North America and is now found wherever butternut naturally occurs. Taxonomic studies have determined that the fungus belongs in the genus Ophiognomonia, which includes a number of saprophytes, endophytes and pathogens of members of the Fagales, rather than the genus Sirococcus, which includes several important pine pathogens. The ability of fungus to be dispersed by rain splash, transported on and in beetle vectors, transmitted by infected seed and successfully colonized several species of Juglans and Carya have all likely contributed to the rapid increase in abundance and severity of disease and tree mortality in the invaded forest ecosystems. Recent genomic and population genetic analyses have determined that there were at least three emergence events. A less virulent strain of the fungus likely has been present in the north eastern United States for over a century, but it was the emergence of a more virulent strain of the fungus in Minnesota and Wisconsin in the 1960s that resulted in range‐wide mortality and pushed butternut to be listed as an endangered species in Canada and a number of states in the United States.

Performance of transesterified jute rolled erosion-control products

ABSTRACT: Rolled erosion-control products (RECPs) made from natural fibres such as jute, coir and sisal are widely used for controlling soil erosion until vegetation growth is sufficient to reinforce the soil. The relatively high water retention of jute RECPs is responsible for its rapid degradation and limited use in areas of heavy rainfall. Among the various chemical treatments given to jute fibres to improve their durability, the transesterification process has been reported to be promising and free from toxic effects of chemicals used in the process. However, no researchers have reported the effect of the transesterification process on the performance of jute RECPs. In the present study, jute RECPs of 500 and 700 g/m2 masses were transesterified, and their erosion control performance was studied using Shiwalik range soil. Rain splash erosion tests were carried out at 15°, 30° and 45° slope angles, based on ASTM D 7101 using a bench-scale set-up with some modifications. Germination tests were performed according to ASTM D 7322. The transesterification of RECPs resulted in the improvement of erosion control, due to the improved percentage cover and reduced flexural rigidity. In the germination test, the total rooting, which improves the soil stability, was found to be higher for the transesterified RECPs. The chemical degradation of transesterified jute RECPs was tested using a saline solution at various pH values, and it was observed that the transesterified jute RECPs retained about 72% of their strength in comparison with 19% for jute untreated RECPs after 120 days of treatment.

The influence of rainfall on PR radar measurement of ocean surface wind speed and its calibration

Rain can significantly degrade the wind vector retrieval from Precipitation Radar (PR) by three mechanisms, namely, two-way rain attenuation, rain volume-backscattering, and ocean surface roughening from the rain splash effect. Here we first derive the radar equation for PR in rainy conditions. Then we use the rain attenuation model for Ku band, volume backscatter model for spherical raindrops and PR-TMI (TRMM Microwave Imager, TMI) matchup datasets from June to August in 2010 to solve the radar equation, and quantitatively analyze the influence of rainfall on PR radar measurement of ocean surface wind speed. Our results show that the significant effect of rain on radar signal is dominated by two-way rain attenuation and rain splash effect, and the effect of rain volume-backscattering is relatively the weakest, which can even be neglected in rain-weak conditions. Moreover, both the two-way rain attenuation and rain splash effect increase with the increasing of integration rain rate and incident angle. Last, we combine volume-backscattering effect and splash effect into a simple phenomenological model for rain calibration and select three typhoon cases from June to August in 2012 to verify the accuracy of this model. Before calibration, the mean difference and mean square error (MSE) between PR-observed σ0 and wind-induced σ0 are about 2.95 dB and 3.10 dB respectively. However, after calibration, the mean difference and MSE are reduced to 0.64 dB and 1.61 dB respectively. The model yields an accurate calibration for PR near-nadir normalized radar cross section (NRCS) in rainy conditions.

Genetic Diversity and Population Structure of Fusicladium effusum on Pecan in the United States.

Fusicladium effusum causes pecan scab, which is the most destructive disease of pecan orchards in the United States. Conidia of the pathogen are spread by rain splash and wind. The fungus is pathogenically diverse; yet there is no information on its genetic diversity or population genetics. Universally primed polymerase chain reaction (UP-PCR) was used to investigate the genetic diversity and population structure on a hierarchical sample of 194 isolates collected from 11 orchard locations from Florida to Texas, consisting of three to four isolates from each of five to six trees at each location. Genetic variation was high throughout the region, with all but nine of the multilocus haplotypes being unique. Nei's average gene diversity ranged from 0.083 for a population from Mississippi to 0.160 for a population from Kansas. An analysis of molecular variance of the hierarchically sampled populations found that the majority of the genetic variability (82.6%) occurred at the scale of the individual tree and only relatively small amounts among populations in trees from an orchard (5.0%) or within groups (i.e., orchard location populations) (12.5%). The results suggest little population differentiation in F. effusum in the southeastern United States, although φpt values of genetic distance for pairwise comparisons indicated some populations could be differentiated from others. There was evidence of linkage disequilibrium in certain populations, and the common occurrence of asexual reproduction in F. effusum could lead to measurable linkage disequilibrium under certain circumstances. However, the degree of genetic diversity and the scale over which diversity is distributed is evidence that F. effusum undergoes regular recombination despite no known sexual stage.

Disease Incidence and Ascospore Dispersal from Cut Hazelnut Branches Colonized by Anisogramma anomala.

Hazelnut branches bearing stromata of Anisogramma anomala cut in December (2009 and 2010) were compared with branches cut prior to bud break in March to investigate these sources of inoculum. Branches were placed into brush piles (sources). Spore traps and potted hazelnut trees were placed adjacent to each source, 6.4 m upwind and downwind, and 20 m downwind from each source. Significantly more ascospores were detected near sources of branches cut in March compared with December in 2010 however, no differences were detected between pruning treatments in 2011. Ascospore viability, as assessed by trypan blue stain, averaged 50% for both pruning times each season. Significantly more ascospores were detected 6.4 m downwind compared with 6.4 m upwind or 20 m downwind of a source both years. All potted trees exposed to branches from both pruning treatments within sources became diseased both years. The proportion of potted trees that became infected was greater for the downwind group than the upwind for both years, suggesting that ascospores were dispersed beyond the rain splash dispersal range of sources. Ascospores from diseased branches pruned in December or March remained viable, infectious and were dispersed at least 20 m downwind.

Dispersal of conidia of Fusicladium eriobotryae and spatial patterns of scab in loquat orchards in Spain

Dispersal of conidia of Fusicladium eriobotryae, the causal agent of loquat scab, was investigated in two loquat orchards in Spain from 2010 to 2012. A volumetric spore sampler, horizontally and vertically orientated microscope slides, and rain collectors were placed in loquat fields to trap conidia of F. eriobotryae. No conidia were collected in the volumetric sampler, and highly variable numbers of conidia were collected in the rain gatherers. Large numbers of conidia were collected by microscope slides, particularly by those held in a horizontal orientation compared with those held in a vertical orientation. Approximately 90 % of the F. eriobotryae conidia were collected during rainy periods. Based on ROC and Bayesian analysis, using ≥ 0.2 mm rainfall as a cut-off value resulted in a high probability of correctly predicting actual conidial dispersal, and had a low probability of failing to predict actual conidial dispersal. Based on the index of dispersion and the binary power law, the incidence of loquat scab on fruit was highly aggregated in space between and within trees, and aggregation was influenced by disease incidence. Our results demonstrate, for the first time, that F. eriobotryae is dispersed mainly in rain splash. The results will be integrated into a mechanistic, weather-driven, disease prediction model that should help growers to minimize fungicide application for the management of loquat scab.

Effects of controlled fire on hydrology and erosion under simulated rainfall

Mediterranean forests are frequently subject to wildfires, inducing risks of high runoff and loss of nutrient-rich topsoil. The mechanisms influencing these post-fire effects are spatially variable due to differences in vegetation density, litter composition, soil texture and structure, and fire intensity, and therefore difficult to separate. The characteristics of the soil surface in the immediate post-fire period are of critical importance to the hydrological response and erosion susceptibility of the burnt hillslope and catchment. In laboratory experiments, uniform soil, controlled temperature and rain regimes were used to create a controlled environment to isolate the impact of certain influencing parameters. In this study, for a Rendzina soil, we investigated the post-fire impacts of laboratory fire and two successive rainfall (rotating disktype) simulation experiments to evaluate short-term effects of fire on soil hydrological and erodibility parameters by examining (i) soil water repellency (WR) levels and distribution, (ii) surface cover features, and (iii) infiltration, runoff and erosion responses to simulated rain on control (bare and pineneedle covered) and burnt (with and without ash cover) samples. Fire-induced surface WR tested in the laboratory by grid-wise Water Drop Penetration Time tests (WDPT), revealed moderate WR, which decreased for all treatments after rainfall. The response to rain (33 mmh-1) differed for the two simulation runs. The rates of drainage and runoff of the burnt samples in the first run varied between the values of cover (low runoff, high infiltration) and bare (high runoff, low infiltration). Drainage in the ash-covered samples was twice as high as ashremoved samples. In the second run, both samples showed a similar response compared to bare conditions. These laboratory observations suggest that WR and protection by ash are factors to consider in assessing the erosion susceptibility of a burnt forest soil. Furthermore, possible management implications based upon this research are that: 1) ash can have several important roles immediately after a forest fire by protecting the forest soil from rain splash erosion, and with its high water holding capacity, absorbs rainfall, thereby reducing runoff; and 2) ash has no negative influence upon soil infiltration demonstrating the important benefits of ensuring the longer term maintenance of post-fire ash within the burnt landscape. Finally, management actions including mulching further enhance soil stability and minimize soil erosion.

Rangeland hydrology and erosion model (RHEM) enhancements for applications on disturbed rangelands

AbstractThe rangeland hydrology and erosion model (RHEM) is a new process‐based model developed by the USDA Agricultural Research Service. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a run‐off event because of declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination (R2) and Nash–Sutcliffe efficiency were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modelling approach, the model was enhanced to be a practical tool that utilizes readily available vegetation and soil data for quantifying erosion and assessing erosion risk following rangeland disturbance. Copyright © 2014 John Wiley & Sons, Ltd.

Spatiotemporal characterization of citrus postbloom fruit drop inBrazil and its relationship to pathogen dispersal

Citrus postbloom fruit drop (PFD) is caused byColletotrichum acutatumandC. gloeosporioides. These pathogens attack the flowers and cause premature fruit drop and the retention of fruit calyces. This study was designed to characterize the spatial and temporal dynamics ofPFDin commercial citrus‐growing areas to better understand the disease spread. Experiments were carried out in three young orchards (500 trees each) in two municipalities in Sao Paulo State,Brazil. Symptoms ofPFDon the flowers and presence of persistent calyces were assessed in each of three orchards for three years. Logistic, Gompertz and monomolecular models were fitted to the incidence data over time from the trees with symptoms. The spatial pattern of diseased trees was characterized by a dispersion index and by Taylor′s power law. An autologistic model was used for the spatiotemporal analysis. The logistic model provided the best fit to the disease incidence data, which had a fast progress rate of 0·53 per day. During the early epidemic ofPFD, the spatial pattern of diseased trees was random, which suggested that inoculum spread was due to mechanisms other than rain splash. As the disease incidence increased (up to 12·6%), the spatial pattern of diseased trees became aggregated. The rapid rate of disease progress and the distribution ofPFDsuggest that dispersal of the pathogen is possibly related to a mechanism other than splash dispersal, which is more typical of other fruit diseases caused byColletotrichumspp.

Sediment disentrainment and the concept of local versus nonlocal transport on hillslopes

A local formulation of the sediment flux on a hillslope describes the flux as a unique function of local hillslope conditions at any contour position x, whereas a nonlocal formulation must take into account nonlocal (upslope or downslope) conditions that influence the flux at x. Local formulations are reasonable when particle motions involve small length scales associated with localized bioturbation of the soil column or with proximal surface transport such as rain splash. Nonlocal formulations may be more appropriate in steeplands where patchy, intermittent motions involve large travel distances, mostly over the surface. Once sediment motions are initiated, the disentrainment process determines the distribution of particle travel distances, which, in turn, forms the basis of nonlocal formulations that involve a convolution of hillslope surface conditions, for example, the land‐surface slope. The kernel in the convolution integral, which weights the effect of land‐surface conditions (e.g., slope) at all positions upslope or downslope of x, derives from the formulation of the disentrainment rate and characterizes whether particle travel distances depend on conditions at the position where motions originate or vary as particles experience changing surface conditions during their downslope motions. If hillslope properties controlling transport (e.g., surface slope) are defined or measured at a specified resolution, then motions smaller than this resolution cannot be attributed to these properties resolved at a smaller scale. In essence, the relative importance of local and nonlocal transport depends on the scale of particle motions compared to the relevant scale of hillslope properties that drive transport.

Small-scale effects of annual and woody vegetation on sediment displacement under field conditions

Abstract Interactions between desert vegetation and erosive forces are prominent and are part of landscape evolution in deserts. The role of annual herbaceous plants in these processes is usually overlooked. Likewise, the interactions and relative contributions of the different erosive forces are rarely studied. We examined the effects of mound-forming shrubs and annual plants on sediment dispersal at small spatial scales in the semi-arid shrubland of the northern Negev Desert of Israel. We conducted a field experiment to test the displacement of dyed sediment by wind, runoff and rain splash in 5 × 5 cm areas on shrub-mounds, placed under the canopy and on mound margins, and on the biological soil crust-covered intershrub space. As experimental treatments, we used artificial rain covers and removal of annuals and their litter. We found that 1) most sediment displacement was caused by rain splash, which was effectively reduced by shrub canopy and less so by annual plant cover, and 2) runoff effects were limited to a fraction of rain events, took place only in the intershrub space, and were significantly reduced by annual plants and their litter. The combined effect of shrubs, annuals, and litter on sediment movement was significantly stronger than the effect of any single element. Accordingly, we conclude that, in addition to shrubs, herbaceous annual plants play a significant role in shrub-mound growth and maintenance, and thus also, in erosion control and vegetation pattern formation in dryland landscapes. Since herbaceous plants enhance mound formation, which in turn enhances shrub growth, our findings are further evidence of the crucial feedback interactions that are central to understanding ecosystem functioning, dynamics and pattern formation in water-limited ecosystems.

Water flux and sediment transport within a forested landscape: the role of connectivity, subsurface flow, and slope length scale on transport mechanism

AbstractThe connectivity and upscaling of overland runoff and sediment transport are important issues in hillslope hydrology to identify water flux and sediment transport within landscape. These processes are highly variable in time and space with regard to their interactions with vegetation and soil surface conditions. The generation of overland runoff and its spatial connectivity were examined along a slope to determine the variations in the transport mechanism of runoff and soil particles by rain splash and overland runoff. Field experiments were conducted by erosion plots on a steep hillslope at lengths of 5, 10, and 15 m. The overland runoff connectivity and flow transport distance decreased with the slope length, while spatial variability of infiltration increased significantly with the slope length. Observation of subsurface flow revealed that surface soil and litter layer could have important role in water transport. However, the surface soil water content and water flux transport along the slope was highly variable for different storm events; the variability was related to the complexity of the system, mainly by way of the initial wetness conditions and infiltration characteristics. Only net rain‐splashed soil was measurable, but examination of the water flux, overland runoff and sediment transport connectivity, characteristics of sheetwash, and the variability in spatial infiltration indicated an increase in the contribution of the rain splash transport mechanism along the slope. Copyright © 2013 John Wiley & Sons, Ltd.