Spatiotemporal heterogeneity of soil fertility in the Central Monte desert (Argentina)

In arid environments, soil fertility exhibits a high degree of spatial and temporal heterogeneity, which results from high climatic variability seasonally and heterogeneous plant distribution. However, because most desert areas have been altered by human activities, heterogeneous fertility would originate from grazing or logging activities. We evaluated spatial and temporal heterogeneity of soil fertility in cattle-excluded sites under and outside woody plant cover (Prosopis flexuosa and Larrea divaricata), and in sites disturbed by tree removal during wet and dry season in Ñacuñán Biosphere Reserve (Central Monte desert of Argentina). Soil organic matter, fulvic acids, bioavailable organic matter, and nitrate were lower outside plant canopy (8.9 mg g^?1, 0.03 mg g^?1, 8.2 mg g^?1, and 4.17 mg kg^?1, respectively). Total N, humic acids, and abundance of microbial functional groups did not show differences among sites. Most parameters differed between seasons, tending to be higher in the wet season. Overall soils of Ñacuñán Reserve are characterized by: a) more homogenous spatial pattern than expected from woody plant presence; b) very heterogeneous temporal pattern; and c) after two years, tree removal does not seem to induce infertile soil formation.     

Students' familiarity and initial contact with species in the Monte desert (Mendoza,Argentina)

This study investigates how familiarity and initial contact with species can be explained by social-demographic variables in an arid environment of Argentina. Our main objectives were to investigate which species children are familiar with, and analyse the effect of place of residence, sex and age on students' knowledge and initial contact with species. In total, 1746 students between 7 and 18 years old participated in the study, from 25 urban and 19 rural schools. Students were asked to write down ten animals and ten plants, and to indicate where they had seen them for the first time. Children were able to name an important number of species but they were mostly acquainted with exotic ones. Familiarity with species and the use of different sources of information can be explained by interactions between the studied factors, while place of residence was not as significant as we expected. Sex was an important explanatory variable, likely influenced by differences in roles and children activities' preferences. It is necessary to improve the knowledge on native species, particularly those with conservation problems by using information sources close to nature, without neglecting the knowledge of the exotic species that children showed more familiarity from everyday life.     

Abundance and diversity of small-bird assemblages in the Monte desert, Argentina

Assemblages of small bird species (<90 g body mass) from the Monte desert in Argentina were studied to analyze spatial and temporal variation in abundance and species richness. Mean species richness was higher during breeding season than in non-breeding season. The same pattern was observed in aerial insectivores, while granivores and substrate insectivores did not differ between breeding and non-breeding seasons. Overall bird abundance was similar across seasons. Species richness was positively correlated with bird abundance and negatively correlated with dominance; bird abundance and dominance were not correlated. These patterns could be explained by distinct responses of functional groups of birds; dominant species were granivores in the non-breeding season and aerial insectivores during the breeding season, and bird abundance in functional groups changed according to food supply. Most species are residents or regular migrants, while there are few nomadic and transient species. Predictable annual fluctuations in rainfall and resource availability should favor a migratory strategy more than nomadic movements. Similarly, breeding is strongly seasonal and most species start breeding when the first summer rains have generally not yet fallen. Finally, concordances in assemblage structure at local and regional scale suggest that similar mechanisms are acting on the local bird assemblages across the Monte.     

Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover

The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance.     

Short- and long-term effects of shrub management on vegetation in the Monte, Argentina

A comparison was made of plant cover, carrying capacity and diversity in areas of Monte vegetation at the Biosphere Reserve of Ñacuñán, Mendoza, Argentina, in 1982, 1984 and 1995. Treatments applied in 1981 were: control (untreated plots), selective hand-cutting, roller-chopping, and root-plowing. By 1995, woody cover was lower in root-plowed plots (27%) than in the others treatments (41–51%), and herbaceous cover was similar in treated (28–39%) and untreated areas (26%). Carrying capacity of treated areas (6–8 ha per Large Stock Unit (LSU)) was higher than in the control areas (12 ha LSU⁻¹). Woody species diversity, quantified by the Shannon index, for both areas was similar in the study period (0·62), except in root-plowed sites in 1982 (0·0) and 1995 (1·3). Herbaceous species diversity was similar on treated (0·81) and untreated sites (1·2) in 1995. We could recommend less drastic treatments to improve carrying capacity.     

Biological interactions at different spatial scales in the Monte desert of Argentina

In this review, we compiled published results on biological interactions at different spatial scales in the Monte desert of Argentina and identified gaps in current knowledge. We presented evidence of competitive and facilitative plant–plant conspecific and heterospecific interactions, and plant–soil–microbes interactions in relation to the abiotic environment at the fine patch-scale. We also showed evidence of animal–animal interactions and plant–animal interactions at the community scale through study cases involving both native and introduced herbivores. Moreover, we identified bottom-up and top-down forces governing the interactions between granivores (birds, ants, and small mammals) and seed availability/production at the community scale. At the landscape scale, we discussed feedbacks between domestic grazers and the spatial patterns of resources and their interrelationships with processes occurring at other scales. We concluded that research has steadily increased during the last 6 years but knowledge on biological interactions in the Monte desert is still scarce, particularly at a landscape scale.     

Probabilistic modeling of soil moisture dynamics in a revegetated desert area

Soil moisture is the key link between land hydrological and ecological processes which plays an important role in the terrestrial water cycle. As extreme weather events have increased in recent years, the stochastic simulation of soil moisture has gradually become the focus of ecohydrology research. Based on continuous monitoring of soil moisture data from 2008 to 2011, and historical precipitation data from 1991 to 2011, combined with the Rodriguez-Iturbe soil moisture dynamic stochastic model, soil moisture dynamics and its probability density function in a revegetated desert area was simulated. Results show that annual soil moisture dynamic changes of the revegetated desert area during the growing season complied with rainfall distribution; soil moisture probability presents a single-peak distribution in the plant rhizosphere layer (0–60 cm). The peak width in the 20 cm topsoil was wider than in other soils, and the distribution presented the strong fluctuations and multiple aggregates. The peak widths of 40 cm and 60 cm soil moisture probability distribution were small, which are in accordance with simulated results of the Rodriguez- Iturbe model. This confirms that the Rodriguez-Iturbe model has good applicability and can well simulate the statistical characteristics of soil moisture in an arid revegetated desert area.     

The effects of the identity of shrub species on the distribution and diversity of ground arthropods in a sandy desert ecosystem of northwestern China

Shrub is an important factor on structuring ground arthropod communities in desert ecosystems. In this study, in order to determine how shrubs and their species influence ground arthropod distribution patterns in a sandy desert scrubland dominated by two different shrub species, Calligonum mongolicum and Nitraria sphaerocarpa, the ground arthropods were sampled with pitfall traps during spring, summer and autumn. At the community level, total arthropod abundance was shown to be significantly higher under shrubs than in intershrub bare areas in spring; similar patterns occurred in terms of the richness of arthropod groups in the spring and over three seasons, suggesting season-specific shrub presence effects on arthropod activity. In addition, more arthropods were found under N. sphaerocarpa shrubs than under C. rnongolicum shrubs in autumn, suggesting season-specific effects of shrub species of arthropod activity, whereas more arthropods taxa were captured under C. mongoIicum than N. sphaerocarpa. At the trophic group level, the abundances of predator and herbivore arthropods were significantly greater under shrubs than in intershrub bare habitats, whereas herbivore arthropods were more abundant under N. sphaerocarpa than C. rnongolicum, and an opposite rule was detected for predator arthropods At the family level, the mean abundances of Carabidae, Curculionidae, Gnaphosidae and Lycosidae were significantly higher in the shrub microhabitats than in the intershrub bare habitat, there was no significant difference between habitats on the mean abundances of Formicidae and Tenebrionidae. The study results suggested that shrub presence and shrub species variation are important determinants of ground arthropod assemblages in this desert ecosystem, but the responses of ar- thropods differed among trophic and taxonomic groups.     

Overview of the geography of the Monte Desert biome (Argentina)

The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.     

Seedling recruitment in a semi-arid steppe: The role of microsite and post-dispersal seed predation

Grasslands dominated by Stipa tenacissima are important ecosystems in the arid and semiarid climates of western Mediterranean, where they have originated by degradation of open dry forests and shrublands. At present, although the level of exploitation in these ecosystems is very low, succession processes seem to have stopped. In this study, we explore the role of microsite and post-dispersal seed predation on the seedling emergence of two species from advanced successional stages (Rhamnus lycioides, Quercus coccifera), three species from degraded stages (Cistus clusii, Helianthemum violaceum, Anthyllis terniflora), and of the dominant species (Stipa tenacissima). Seeds of these species were sown in plots divided into two microsites: (i) under tussocks of S. tenacissima and (ii) in the bare soil between tussocks. Soil moisture was significantly higher in the tussock microsites. The interaction observed between microsite and time, reflected the slower drying process under tussocks. Seed predation was in general high and differed significantly between species but not between microsites. Q. coccifera was especially affected by predation. The only germination detected in gap areas was that of H. violaceum. The results pointed to a direct facilitative effect of tussock grass on the germination in R. lycioides (20.4±8.0%) and S. tenacissima (41.3±5.7%) while the corresponding figures for bare ground were 0%. These results suggest that the recovery of potential vegetation in this ecosystem is not possible or, at least, is very slow because the residual shrub patches do not generate a sufficient number of seeds able to disperse to favorable germination microsites. S. tenacissima may act as facilitator of seedling recruitment if there is a supply of diaspores.     

Watershed simulation in a sandy terrain of the Thar desert using GIS

The sandy landscape in a desert contains very few stream channels. This poses a problem for delineating watersheds for analysis. Since large-scale topographical sheets of sandy terrain also contain very little information on height, delineation of watersheds from topographical sheets often becomes difficult. In order to find a simple solution to the problem in the Thar desert of Rajasthan, India, the authors used the well-known ARC/INFO software for simulation of height and drainage network using the scarce topographical information for a sandy terrain near Jodhpur. Superimposition of data layers generated from remote sensing and secondary sources validated the simulation results, and suggested suitability of the method for application in similarly handicapped areas.     

Temporal dynamics and productivity of biogenic soil crusts in the central Karakum desert, Turkmenistan

Biogenic soil crusts (BSCs), consisting of different combinations of mosses, lichens, liverworts, fungi and cyanobacteria, are a widespread phenomenon in arid and semi-arid environments. BSCs are found throughout those areas unaffected by grazing and other anthropogenic activities. Current economic conditions in the newly Independent Central Asian States favor the development of BSCs, which may significantly influence plant communities. The data from 40-years of field observations in a protected area in the Karakum Desert, Turkmenistan, together with a sequence of aerial photographs of the same area may contribute to the study of the establishment of BSCs and understanding their role in vegetation communities. The fenced-off Karrykul area can serve as a model for the current processes in the vast desert areas in Central Asia, which are underused due to the financial constraints. It is hypothesized that after some 15 years, the role of BSCs changes from a positive (rehabilitating) effect on the first stages of protection, to a negative effect on the structure and biomass of vegetation communities. Therefore, undergrazing, as well as overgrazing, should be considered as a desertification factor.     

科尔沁沙质草甸土壤微生物数量的垂直分布及季节动态

通过对中国农牧交错带科尔沁沙质草甸土壤微生物数量的垂直分布及其季节动态的研究分析表明:(1)微生物总数、细菌和放线菌数量均表现出与降雨量同步的季节动态,即6月份较5月份有所减少,7月份增至最多,7月份以后微生物数量逐渐下降,真菌则表现出从5月份到8月份一直增加,9月份开始回落;(2)土壤微生物具有明显的垂直分布差异.细菌和放线菌的垂直分布表现出随土壤深度增加逐渐减少的趋势,真菌数量表层最高,20 cm以下变化不够规律;(3)土壤微生物的层化比率均大于2(5月份放线菌除外);(4)不同土壤生态因子对微生物的影响不同,相同因子对不同微生物类群的影响也不相同.细菌受水分影响较大,真菌与地温的变化趋势相近,放线菌与水热条件的共同作用有关.土壤养分(有机碳和全氮)与微生物数量呈显著的正相关.     

Dispersal and germination ofProsopis flexuosa(Fabaceae) seeds by desert mammals in Argentina

The ‘algarrobo’Prosopis flexuosais an important food resource in the Monte Desert of Argentina. Native, domestic, and exotic mammals consume the fruit of this legume and disperse the seed through faeces. In the present study we analyse the effect that different dispersal agents (cattle, horse, European wild boar, rodents, gray fox) have on seed damage, viability, and germination. Cattle increase germination at the expense of reduced viability, whereas horses maintain viability but do not contribute to a prompt germination response. Among native mammals, the gray fox maintains seed viability without increasing germination, whereas rodents affect seed viability but enhance germination rates. The European wild boar, however, damages all of the seeds it consumes.     

Diet of a fossorial rodent (Octodontidae), above-ground food availability,and changes related to cattle grazing in the Central Monte (Argentina)

Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle.     

Seed banks in a degraded desert shrubland: Influence of soil surface condition and harvester ant activity on seed abundance

We compared seed banks between two contrasting anthropogenic surface disturbances (compacted, trenched) and adjacent undisturbed controls to determine whether site condition influences viable seed densities of perennial and annual Mojave Desert species. Viable seeds of perennials were rare in undisturbed areas (3–4 seeds/m²) and declined to <1 seed/m² within disturbed sites. Annual seed densities were an order of magnitude greater than those of perennials, were one-third the undisturbed seed densities on compacted sites, but doubled on trenched sites relative to controls. On trenched sites, greater litter cover comprising the infructescences of the dominant spring annuals, and low gravel content, enhanced seed densities of both annuals and perennials. Litter cover and surface ruggedness were the best explanations for viable perennial seed densities on compacted sites, but litter cover and the presence of a common harvester ant explained annual seed densities better than any other surface characteristics that were examined. Surface disturbances can have a varied impact on the condition of the soil surface in arid lands. Nevertheless, the consistently positive relationship between ground cover of litter and viable seed density emphasizes the importance of litter as an indicator of site degradation and recovery potential in arid lands.     

Factors controlling regeneration in a rare desert tree Acacia peuce: Limits to soil seed bank accumulation in time and space

We assessed reasons for rare recruitment in Acacia peuce, an Australian arid zone tree, by testing recruitment-limitation hypotheses relating to seed bank inputs and losses. Viable seed occurred in low density in the soil (<1 seed m²) whereas freshly produced seed was non-dormant and germination was high and fast, indicating small rain events can deplete seed banks without providing sufficient moisture for seedling survival. Seed bank seed had lower viability than fresh seed. Insect predation of seed was negligible but seed pod production and seed number/pod were low. Thus, seed bank accumulation is limited by low inputs and continual high seed losses through germination and potentially seed death. No seed shadow effect under adult canopies was found, but dispersal beyond existing stands was negligible. Seed dispersal from parent plants occurred by wind movement of unopened pods whereas the resident ant fauna did not transport seed. Microsite parameters strongly influenced horizontal distribution of buried seed, with all seed being retrieved from vegetated sandy mounds. Overall, we found that seedling recruitment is likely to be confined to large above average rainfall events because the species is unlikely to maintain a seed bank in below-average and average rainfall phases.     

Diet of the desert lizard Liolaemus pseudoanomalus (Iguania: Liolaemini) in northern La Rioja Province, Argentina

The diet of a species can help us to understand its natural history, ecological requirements, and strategies involved in searching for food. Liolaemus pseudoanomalus is a rare desert lizard where previous studies showed no seasonal, ontogenetic or sexual differences observed in microhabitat use; however the sexual dimorphism is evident in the number of precloacal pores and in the snout-vent length. In this work, we investigate if there are differences in the diet composition between sexes and age groups. Herein we describe the diet of L. pseudoanomalus, of the Central West Monte desert of Argentina, based on the analysis of 63 stomach contents. We found that ants are the most important food item and some characteristics of foraging behavior suggest similarities with other ant-eating lizards.     

Use of the revised universal soil loss equation (RUSLE) for soil and nutrient loss estimation in long-used rainfed agricultural lands,North Ethiopia

This study was conducted to quantify agricultural land degradation in the Ruba Gered watershed, Ethiopia. The watershed was divided into 12 land mapping units (LMU) after superimposing maps of soil, slope, land use/cover, and elevation. Subsequently, cultivated land was delineated to assess degradation types and severity based on standard approaches. Sheet erosion was estimated using the revised universal soil loss equation. Composite soil samples were collected from each LMU to quantify key soil nutrients (OM, total nitrogen, available phosphorus, and available potassium) lost by sheet erosion. The annual average soil loss due to sheet erosion was estimated to be 17.4 t ha^?1 yr^?1, with average annual nutrient losses estimated as 246.5 kg ha^?1 organic matter, 12.4 kg ha^?1 total nitrogen, 0.1 kg ha^?1 available phosphorus, and 1.6 kg ha^?1 available potassium. The study revealed that substantial quantities of soil and nutrients are lost every year in the study area due to severe sheet erosion. This amount of nutrient loss severely degrades soil and reduces soil fertility.     

Responses of photosynthesis and water relations to rainfall in the desert shrub creosote bush (Larrea tridentata) as influenced by municipal biosolids

Responses of photosynthesis (P_n), stomatal conductance (g_s), pre-dawn leaf water potential (Ψ_lp) and leaf water content (ω_l) of creosote bush to 10 rainfall events in the Chihuahuan Desert were investigated. Infiltration of rainwater was manipulated by applying municipal biosolids. The responses of P_nand water relation parameters to rainfall (>10 mm) were mainly dependent upon drought severity: (1) following a moderate drought, P_n, g_s, Ψ_lpand ω_lrecovered to corresponding values of irrigated plants within 2 days after a 23-mm rainfall; (2) Ψ_lpand g_sresponded to a 15-mm rainfall within 2 days, following a 25-day drought, whereas responses of P_nand ω_lwere delayed for several days; (3) responses of P_n, g_s, Ψ_lpand ω_lto a 14·7-mm rainfall were all delayed for several weeks following a 110-day drought, but the delay was longer in P_n, g_sand ω_lthan in Ψ_lp. Creosote bush responded to small rainfall events (approximately 6 to 8 mm) with an increase in Ψ_lp, but without noticeable changes in g_sand P_n, suggesting a strong stomatal control of water loss even though xylem embolism was reduced. Biosolids applied at high rates (3·4 and 9 kgm⁻²) decreased the soil water by 2 to 4 mm following rainfall events, and this in turn delayed and decreased the responses of P_nand water relation parameters to rainfall.P_nand g_swere linearly related to ω_land exponentially related to Ψ_lp. With the generally coincidental responses of P_nor g_sand ω_lto rainfall, we concluded that the responses of P_nand g_sto rainfall were dependent on leaf rehydration which resulted from restored hydraulic conductance following drought.