Food habits of the Barn Owl (Tyto alba) in a steppe area of Tunisia

The diet of the Barn Owl (Tyto alba) is well known in different habitats but a lack of data persists for arid and subarid environments. We provide preliminary information on food selection of barn owls in Tunisia by the analysis of the composition of pellets. The diet consists largely of rodents and the three-toed Jerboa (Jaculus jaculus) that accounted for more than 50% of total prey biomass. Results suggest that barn owls show a nonrandom tendency toward rodent species especially small and young individuals.     

Differences in production and mortality of reproductive structures in two Prosopis L. (Mimosaceae) shrub species from Patagonia, Argentina

Prosopis L. pods have been proposed as a source of gum (galactomannans), with potential applications as a thickening agent in the food industry. The objective of this work was to compare, under field conditions, the production and mortality of reproductive structures in two sympatric shrub species of Prosopis: P. alpataco Phillipi and P. denudans Bentham. Our results indicate that fruit production in Prosopis denudans and P. alpataco is very low and erratic in non-irrigated lands. Although large quantities of flowers (15,000–25,000 flowers*0.40 m⁻²) can be found in one flowering season, 70–80% are shed before they reach anthesis and 20–28% are aborted between anthesis and fruit set. We conclude that the utilization of native populations of Prosopis denudans and P. alpataco for fruit production in Patagonian steppe, could not guarantee a consistent supply for the food industry.     

Tracking of saltating sand trajectories over a flat surface embedded in an atmospheric boundary layer

Saltation is a major mechanism for the transport of soil particles. In the present study, we carried out wind tunnel tests to examine the saltating trajectories of two types of natural sand collected from a beach (diameter, d = 300–500 μm and 200–300 μm respectively) as well as sand from the Taklimakan desert (d = 100–125 μm) in an atmospheric boundary layer. Consecutive images of saltating particles were recorded using a high-speed digital camera at a rate of 2000 fps with a spatial resolution of 1024 × 1024 pixels. The high temporal resolution of the acquired images enabled us to study the particle motion very close to the surface. The saltating particle trajectories were reconstructed from consecutive images, and the physical quantities characterizing the initial and final stages of the particle flight in the windward direction at friction velocities of about 10%–25% above the threshold friction velocity (u / u_t = 1.11–1.26) were analyzed statistically. In addition, the transverse deviation of the saltating particles from the main streamwise direction was evaluated. The results shed new light on the complicated motions involved in sand saltation and should prove useful in the evaluation and formulation of theoretical models.     

The response of drainage basins to the late Quaternary tectonics in the Sicilian side of the Messina Strait (NE Sicily)

Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (k_d) and critical shear stress (τ_c) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in k_d and τ_c from soil desiccation and freeze–thaw cycling. Soil erodibility and τ_c were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted k_d was 2.9 and 2.1 times higher (p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in k_d was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions (r² = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.     

Germination of Denmoza rhodacantha (Salm-Dyck) Britton & Rose (Cactaceae)

The germination response of Denmoza rhodacantha (Salm-Dyck) Britton & Rose to seed scarification and different calcium concentrations was analysed. Both scarified and unscarified seeds were treated with two different calcium concentrations (1.74 or 6.36 meq l⁻¹ calcium sulfate in distilled water). All treatments were conducted under a constant temperature (30 °C), and a photoperiodic regime of 12 h light and 12 h dark. Germination was initiated significantly sooner (3.6 days), and the rate of final germination was significantly higher (90.8%), for scarified seeds treated with a solution of 6.36 meq l⁻¹ Ca compared with all other treatments (9.0–11.4 days and 3.6–6.8%, respectively). There were no significant differences among the treatments for the time in which 50% of final germination occurred (6.9–13.6 days). The results suggest that both factors, scarification and calcium concentration, favor germination of Denmoza seeds.     

A greenhouse study on root dynamics of cactus pears, Opuntia ficus-indica and O. robusta

Over the last 10 years a great interest in spineless cactus pear was shown in the drier areas in terms of both fresh fruit and fodder production. However, there is a lack of knowledge on quantitative data on root dynamics of these plants needed to fully understand its potential under water limiting conditions. This study aimed at quantifying the effects of water stress on the growth of tap roots, side roots and rain roots of the species Opuntia ficus-indica (L.) Miller (cultivar Morado—green cladode) and O. robusta Wendl. (cultivar Monterey—blue cladode). One-year-old cladodes were planted in root boxes and pots (2002/2003 season) that were kept in the greenhouse at day/night temperatures of 25–30 °C/15–18 °C. Placing the cladodes flat on the soil, more areoles came in contact with the soil and therefore more roots developed in both species with an average of only 3.4% areole complexes not rooting. Each areole complex formed on average 3 roots. The highest daily tap root growth was 42 and 36 mm for O. ficus-indica and O. robusta, respectively. Tap root growth increased in the morning with water stress for both species but decreased in the afternoon. Side root growth increased with water stress, with that of O. robusta more per tap root than O. ficus-indica. O. robusta showed a finer root system than O. ficus-indica. The side roots grew as much as 8 and 5 mm per day for O. ficus-indica and O. robusta, respectively. Whitish rain roots developed on the established roots within the first hour after rewetting the soil and grew for only 3 days. Rain roots grew up to 7 and 5 mm within a day for O. ficus-indica and O. robusta, respectively. Considering all studied aspects of their roots systems, O. robusta appears to be better adapted to drought (less sensitive to water stress) than O. ficus-indica.     

Sand transport under increased lateral jetting of raindrops induced by wind

Wind tunnel experiments for ‘Raindrop Detachment and Wind-Driven Transport’ (RD–WDT) process were conducted under improved lateral jetting induced by wind velocities of 6.4, 10, and 12 m s^− 1 at nozzle operating pressures of 75, 100, and 150 kPa. Wind-driven rainfalls were also incident on the windward and leeward slopes of 4° and 9° to have a broad variation in the angle of incidence. The objective of this experimental set-up was to distinguish the roles of both impact components of obliquely striking wind-driven raindrops on RD and wind on WDT. Raindrop impact components and reference horizontal wind were quantified by normal (E_tz) and horizontal (E_tx) kinetic energy fluxes and wind shear velocity (u), respectively, to physically model the process of RD–WDT. The results showed, at each level of u, differential sand transport rates by RD–WDT (q_m(RD–WDT)) occurred depending on the magnitude of raindrop impact components, and q_m(RD–WDT) increased as the relative contribution of E_tz increased. Although E_tx was more correlated with q_m(RD–WDT) than E_tz, the extreme increases in E_tx at the expense of E_tz brought about no increases but decreases in q_m(RD–WDT). An RD–WDT model was built under the process of examining the discrete effects of E_tz and E_tx on RD together with u and resulted in a better coefficient of determination (R² = 0.89) than only total kinetic energy (E_t) did alone with u (R² = 0.84). In this study, E_tx was strongly related to u and not to E_tz, which was the principal difference from the previous rainsplash studies, which relied on the compensatory lateral jet development by the compressive pressure build-up at the raindrop–soil interface. Including E_tx in the RD–WDT model both separated the distinct role of each raindrop impact component in RD and improved the performance of u in WDT by better distinguishing its interaction with E_tx, which was not explicitly separated in previous models of RD–WDT.     

Physical and chemical properties of soils under some piñon-juniper-oak canopies in a semi-arid ecosystem in New Mexico

Piñon (Pinus edulis)-juniper (Juniperus monosperma)-ecosystems increased substantially in the western USA during the 20th century. Sustainability of these ecosystems primarily depends on soil quality and water availability. This study was undertaken with the objective of assessing the effect of tree species on soil physical quality in a semi-arid region in the western part of Sugarite Canyon, northeast of Raton, Colfax County, NM (37°56′32″N and 104°23′00″W) USA. Three cores and three bulk soil samples were obtained from the site under the canopy of three juniper, Gambel oak (Quercus gambelii) and piñon trees for 0–10 and 10–20 cm depths. These samples were analyzed for particle size distribution, soil bulk density (ρ_b), water stable aggregation (WSA), mean weight diameter (MWD) of aggregates, pH, electrical conductivity (EC) and soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks. Sand content was greater under juniper (48%) than oak (32%), whereas clay content followed the opposite trend. The ρ_b, WSA, MWD, pH and EC were similar under juniper, piñon, oak canopies for both depths. Estimated (from Philip and Green and Ampt infiltration models) and measured water infiltration parameters did not vary among these sites and were in accord with the values for ρ_b, WSA and MWD. The SOC concentrations and stocks were greater under oak (43.1 Mg ha⁻¹ for 0–10 and 37.5 Mg ha⁻¹ for 10–20 cm depths) than piñon (23.3 Mg ha⁻¹ for 0–10 and 18.5 Mg ha⁻¹ for 10–20 cm depths). The TN concentrations were greater under oak (3.4 g kg⁻¹) than piñon (1.7 g kg⁻¹) for the 0–10 cm depth only. Accumulation of detritus material under tree canopies reduced soil compaction and crusting caused by raindrop impact and increased SOC, and TN concentrations, and water infiltration. Coefficients of variation ranged from low to moderate for most soil properties except infiltration rate at 2.5 h, which was highly variable. Overall, soil quality for each site was good and soil aggregation, water infiltration and SOC concentrations were high, and soil ρ_b was low.     

Salinity tolerance in Schinopsis quebracho colorado: Seed germination, growth, ion relations and metabolic responses

Soil salinity is a major abiotic stress influencing plant productivity worldwide. Schinopsis quebracho colorado is one of the most important woody species in the Gran Chaco, an arid and salt-prone subtropical biome of South America. To gain a better understanding of the physiological mechanisms that allow plant establishment under salt conditions, germination and seedling growth of S. quebracho colorado were examined under treatment with a range of NaCl solutions (germination: 0–300 mmol l⁻¹ NaCl; seedling growth: 0–200 mmol l⁻¹ NaCl). The aim was to test the hypothesis that S. quebracho colorado is a glycophite that shows different salt tolerance responses with development stage. Proline content, total soluble carbohydrates and Na⁺, K⁺ and Cl⁻ concentrations in leaves and roots of seedlings, and the chlorophyll concentration and relative water content of leaves were measured. Germination was not affected by 100 mmol l⁻¹ NaCl, but decreased at a concentration of 200 mmol l⁻¹. At 300 mmol l⁻¹ NaCl, germination did not occur. Seedling growth decreased drastically with increasing salinity. An increase in NaCl from 0 to 100 mmol l⁻¹ also significantly reduced the leaf relative water content by 22% and increased the proline concentration by 60% in roots. In contrast, total soluble carbohydrates were not significantly affected by salinity. Seedlings showed a sodium exclusion capacity, and there was an inverse correlation between Cl⁻ concentration and the total chlorophyll concentration. S. quebracho colorado was more tolerant to salinity during germination than in the seedling phase. The results suggest that this increased tolerance during germination might, in part, be the result of lower sensitivity to high tissue Na⁺ concentrations. The significant increment of proline in the roots suggests the positive role of this amino acid as a compatible solute in balancing the accumulation of Na⁺ and Cl⁻ as a result of salinity. These results help clarify the physiological mechanisms that allow establishment of S. quebracho colorado on salt-affected soils in arid and semi-arid Gran Chaco.     

Processes and rates of rock fragment displacement on cliffs and scree slopes in an amba landscape, Ethiopia

Distinct rock fragment displacements occur on the ambas, or structurally determined stepped mountains of the Northern Ethiopian Highlands. This paper describes the rock fragment detachment from cliffs by rockfall, quantifies its annual rate, and identifies factors controlling rock fragment movement on the scree slopes. It further presents a conceptual model explaining rock fragment cover at the soil surface in these landscapes. In the May Zegzeg catchment (Dogu'a Tembien district, Tigray), rockfall from cliffs and rock fragment movement on debris slopes by runoff and livestock trampling were monitored over a 4-year period (1998–2001). Rockfall and rock fragment transport mainly induced by livestock trampling appear to be important geomorphic processes. Along a 1500-m long section of the Amba Aradam sandstone cliff, at least 80 t of rocks are detached yearly and fall over a mean vertical distance of 24 m resulting in a mean annual cliff retreat rate of 0.37 mm y^− 1. Yearly unit rock fragment transport rates on scree slopes ranged between 23.1 and 37.9 kg m^− 1 y^− 1. This process is virtually stopped when exclosures are established. Corresponding mean rock fragment transport coefficients K are 32–69 kg m^− 1 y^− 1 on rangeland but only 3.9 kg m^− 1 y^− 1 in densely vegetated exclosures. A conceptual model indicates that besides rockfall from cliffs and argillipedoturbation, all factors and processes of rock fragment redistribution in the study area are of anthropogenic origin.     

Plant water relations of thornscrub shrub species, north-eastern Mexico

As an approach to understand how diurnal and seasonal plant water potentials (Ψ) are related to soil water-content and evaporative demand components, the responses of six thornscrub shrubs species (Havardia pallens, Acacia rigidula, Eysenhardtia texana, Diospyros texana, Randia rhagocarpa, and Bernardia myricaefolia) of the north-eastern region of Mexico to drought stress were investigated during the course of 1 year. All study species showed the typical diurnal pattern of variation in Ψ. That is, Ψ decreased gradually from predawn (Ψ_pd) maximal values to reach minima at midday (Ψ_md) and began to recover in the late afternoon. On a diurnal basis and with adequate soil water-content (>0.20 kg kg⁻¹), diurnal Ψ values differed among shrub species and were negatively and significantly (p<0.001) correlated with air temperature (r=−0.741 to −0.883) and vapor pressure deficit (r=−0.750 to −0.817); in contrast, a positive and significant (p<0.001) relationship was found to exist with relative humidity (r=0.758–0.842). On a seasonal basis, during the wettest period (soil water-content>0.20 kg kg⁻¹), higher Ψ_pd (−0.10 MPa) and Ψ_md (−1.16 MPa) values were observed in R. rhagocarpa, whereas lower figures (−0.26 and −2.73 MPa, respectively) were detected in A. rigidula. On the other hand, during the driest period (soil water-content<0.15 kg kg⁻¹), Ψ_pd and Ψ_md values were below −7.3 MPa; i.e. when shrubs species faced severe water deficit. Soil water-content at different soil layers, monthly mean relative humidity and monthly precipitation were significantly correlated with both Ψ_pd (r=0.538–0.953; p<0.01) and Ψ_md (r=0.431–0.906; p<0.05). Average soil water-content in the 0–50 cm soil depth profile explained between 70% and 87% of the variation in Ψ_pd. Results have shown that when gravimetric soil water-content values were above 0.15 kg kg⁻¹, Ψ_pd values were high and constant; below this threshold value, Ψ declined gradually. Among all shrub species, A. rigidula appeared to be the most drought tolerant of the six species since during dry periods it tends to sustain significantly higher Ψ_pd in relation to B. myricaefolia. The remaining species showed an intermediate pattern. It is concluded that the ability of shrub species to cope with drought stress depends on the pattern of water uptake and the extent to control water loss through the transpirational flux.     

Impacts of interrelated biotic and abiotic processes during the past 125 000 years of landscape evolution in the Northern Mojave Desert, Nevada, USA

Interrelated, biotic (flora and fauna) and abiotic (pedogenesis and hydrology) processes were examined at four sites (30, and approximately 1000–3000, 7000–12 000, and 125 000 years before present) in the northern Mojave Desert. Data collected at each included floral and faunal surveys; soil texture, structure, and morphology; and soil hydraulic properties. Separate measurements were made in shrub undercanopy and intercanopy microsites. At all sites, shrubs made up greater than 86 percent of total perennial cover, being least on the youngest site (4 percent) and most on the 7000–12 000-year-old site (31 percent). In the intercanopy, winter annual density was highest on the 1000- to 3000-year-old site (249 plants/m²) and lowest on the oldest site (4 plants/m²). Faunal activity, measured by burrow density, was highest on the 1000–3000- and 7000–12 000-year-old sites (0.21 burrows/m²) and density was twice as high in the undercanopy versus the intercanopy. Burrow density was lower at the two oldest sites, although density was not statistically greater in the undercanopy than intercanopy. At the older sites, the soil water balance was increasingly controlled by Av horizons in intercanopy soils in which saturated hydraulic conductivity (K_sat) decreased 95 percent from the youngest to the oldest site. No significant reduction in K_sat in undercanopy soils was observed. Decreases in the intercanopy sites correlated with decreases in annual plant density and bioturbation, suggesting these processes are interrelated with surface age.     

Downstream hydraulic geometry of rivers in Victoria, Australia

Downstream variation of hydraulic geometry in rivers, characterized by fine textured banks and low width to depth ratios (7–25), is investigated in Victoria, Australia, with the aim of developing predictive models of channel geometry for large-scale spatial modeling applications. A one-dimensional hydraulic model is used to determine the mean bank-full geometry and discharge (Q_bf) for 93 sites which are investigated in relation to discharge of fixed average recurrence interval (ARI). The median bank-full ARI is estimated at 0.8 years with 75% of sites between 0.5 and 2.5 years. Exponents in the downstream hydraulic geometry relations for width, depth and velocity are respectively 0.43, 0.40 and 0.18 (Q = Q_bf) and 0.44, 0.38 and 0.03 (Q = Q₂, i.e., 2-year ARI), falling near the mode of global values. Q₂ and slope explain 66% of variance in Q_bf, while Q₂ explains 73% and 69% of the variance in width and depth relations, respectively: Q₂ provides a reliable substitute for Q_bf in spatial modeling applications. Spatial variation in hydraulic geometry relations within and between river basins remains largely unexplained. The W/D ratio characteristically decreases with increasing distance along the lower reaches of most rivers and this has contributed to the lower than expected value for the width exponent.     

Bedform morphology of salmon spawning areas in a large gravel-bed river

While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwest region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bedform types at the pool–riffle scale. A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool–riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool–riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (χ² = 57.5, df = 3, p < 0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at elevations greater than 80% of the difference in elevation between the nearest riffle crest and pool bottom. The analyses of bedform morphology will assist regional fish managers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.     

Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California

Debris flows generated during rain storms on recently burned areas have destroyed lives and property throughout the Western U.S. Field evidence indicate that unlike landslide-triggered debris flows, these events have no identifiable initiation source and can occur with little or no antecedent moisture. Using rain gage and response data from five fires in Colorado and southern California, we document the rainfall conditions that have triggered post-fire debris flows and develop empirical rainfall intensity–duration thresholds for the occurrence of debris flows and floods following wildfires in these settings. This information can provide guidance for warning systems and planning for emergency response in similar settings.Debris flows were produced from 25 recently burned basins in Colorado in response to 13 short-duration, high-intensity convective storms. Debris flows were triggered after as little as six to 10 min of storm rainfall. About 80% of the storms that generated debris flows lasted less than 3 h, with most of the rain falling in less than 1 h. The storms triggering debris flows ranged in average intensity between 1.0 and 32.0 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for floods and debris flows sufficiently large to pose threats to life and property from recently burned areas in south-central, and southwestern, Colorado are defined by: I = 6.5D^− 0.7 and I = 9.5D^− 0.7, respectively, where I = rainfall intensity (in mm/h) and D = duration (in hours).Debris flows were generated from 68 recently burned areas in southern California in response to long-duration frontal storms. The flows occurred after as little as two hours, and up to 16 h, of low-intensity (2–10 mm/h) rainfall. The storms lasted between 5.5 and 33 h, with average intensities between 1.3 and 20.4 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for life- and property-threatening floods and debris flows during the first winter season following fires in Ventura County, and in the San Bernardino, San Gabriel and San Jacinto Mountains of southern California are defined by I = 12.5D^−0.4, and I = 7.2D^−0.4, respectively. A threshold defined for flood and debris-flow conditions following a year of vegetative recovery and sediment removal for the San Bernardino, San Gabriel and San Jacinto Mountains of I = 14.0D^−0.5 is approximately 25 mm/h higher than that developed for the first year following fires.The thresholds defined here are significantly lower than most identified for unburned settings, perhaps because of the difference between extremely rapid, runoff-dominated processes acting in burned areas and longer-term, infiltration-dominated processes on unburned hillslopes.     

Growth response of three globose cacti to radiation and soil moisture: An experimental test of the mechanism behind the nurse effect

Cactus seedlings often establish under nurse plants which modify environmental conditions by increasing moisture and decreasing solar radiation, which may cause beneficial and detrimental effects, respectively, on seedling growth. Three soil moisture treatments (5%, 25% and 60%) and two solar radiation levels (100% exposure=243 μmol m⁻² s⁻¹, and 40%=102 μmol m⁻² s⁻¹) were used in a factorial design to analyze seedling growth response of three rare cactus species (Mammillaria pectinifera, Obregonia denegrii and Coryphantha werdermannii). The variables evaluated were relative growth rate (RGR), root/shoot ratio (R/S), and K (RGR_roots/RGR_shoot), obtained from an initial seedling harvest (6-month-old seedlings) and a final harvest 6 months after treatment application. All three species had slow RGRs (0.002–0.012 g g⁻¹ day⁻¹). O. denegrii had the lowest RGR values, but was the only species for which R/S and K varied with soil moisture. While all seedlings responded markedly to soil moisture, no response was observed to radiation treatments. The latter might have been related to the relatively low solar radiation levels present in the greenhouse. Yet, our results suggest that the main benefit nurse plants offer to seedlings is the increase in soil moisture.     

Live shearing free-ranging guanacos (Lama guanicoe) in Patagonia for sustainable use

Guanaco (Lama guanicoe) populations declined after the introduction of domestic sheep and the emerging conflicts with sheep breeders and their livestock. Apart from conflicts with sheep ranching, guanacos have declined due to poaching, legal overhunting, and lack of sound management schemes. Guanacos have been proposed as a key species for rural development in Latin America, so research on tools for their sustainable use is required. We tested a mobile corral trap (MCT) designed for live-trapping and shearing free-ranging guanacos at four ranches along Patagonia. We assessed mortality and injury rates related to our procedures and calculated and compared roundup and capture efficiencies. We captured a total of 55 guanacos (13 females, 38 males, and 4 calves), and live-sheared 30. No mortalities were recorded. Average roundup and capture efficiencies were 11.9 guanacos roundup⁻¹ (range 8–20) and 11% (range 0.3–31.5%), respectively. Mean fleece weight was 307±15 g for females and 338±12 g for males. The MCT employed seems promising for capturing and shearing free-ranging guanacos for their sustainable use. Management implications include: (1) sheep ranches may obtain benefits, generating a positive perception toward guanacos; (2) guanaco populations may increase and even colonize devoid areas due to an increased protection level.     

Representative rainfall thresholds for landslides in the Nepal Himalaya

Measuring some 2400 km in length, the Himalaya accommodate millions of people in northern India and Pakistan, Nepal, Bhutan, and parts of other Asian nations. Every year, especially during monsoon rains, landslides and related natural events in these mountains cause tremendous damage to lives, property, infrastructure, and environment. In the context of the Himalaya, however, the rainfall thresholds for landslide initiation are not well understood. This paper describes regional aspects of rainfall thresholds for landslides in the Himalaya. Some 677 landslides occurring from 1951 to 2006 were studied to analyze rainfall thresholds. Out of the 677 landslides, however, only 193 associated with rainfall data were analyzed to yield a threshold relationship between rainfall intensity, rainfall duration, and landslide initiation. The threshold relationship fitted to the lower boundary of the field defined by landslide-triggering rainfall events is I = 73.90D^− 0.79 (I = rainfall intensity in mm h^− 1 and D = duration in hours), revealing that when the daily precipitation exceeds 144 mm, the risk of landslides on Himalayan mountain slopes is high. Normalized rainfall intensity–duration relationships and landslide initiation thresholds were established from the data after normalizing rainfall-intensity data with respect to mean annual precipitation (MAP) as an index in which N_I = 1.10D^− 0.59 (N_I = normalized intensity in h^− 1). Finally, the role of antecedent rainfall in causing landslides was also investigated by considering daily rainfall during failure and the cumulative rainfall to discover at what point antecedent rainfall plays an important role in Himalayan landslide processes. Rainfall thresholds presented in this paper are generalized so they can be used in landslide warning systems in the Nepal Himalaya.     

Resting cells of microorganisms in the 20–100 μm fraction of marine sediments in an Antarctic coastal area

We investigated the morphological features, vertical sinking fluxes, and number densities of the resting cells of ice-associated microorganisms in the 20–100 μm fraction of natural marine sediments collected from ice-covered and ice-free areas around Syowa Station, Lützow-Holm Bay, East Antarctica. We identified the resting cells of various taxonomic groups, including the spores of a diatom, cysts of three dinoflagellates, cysts of five oligotrich ciliates, and the eggs of a mesozooplankton. This is the first report of oligotrich ciliate cysts from Antarctic waters. The resting spores of Thalassiosira australis (diatom), cysts of Polarella glacialis (dinoflagellate), and egg type 1 sink to the bottom sediment during summer. Our results suggest that some planktonic and ice-associated microorganisms in Antarctic coastal areas send their resting cells to the bottom sediments as seed populations for the following generation.     

Growth, ionic and osmotic relations of an Allenrolfea occidentalis population in an inland salt playa of the Great Basin Desert

Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7·3–8·3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m⁻¹, and soil moisture, ranging from drought (9·2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na⁺and Cl⁻ions were accumulated in plant tissues in much greater amounts than K⁺, Ca²⁺, and Mg²⁺. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (F_v/F_mratio) was more affected by salinity and irradiation levels during the summer period.