Search

Context: Dynamic feedbacks between physical structure and ecological function drive ecosystem productivity, resilience, and biodiversity maintenance. Detailed maps of canopy structure enable comprehensive evaluations of structure–function relationships. However, these relationships are scale-dependent, and identifying relevant spatial scales to link structure to function remains challenging. Objectives: We identified optimal scales to relate structure heterogeneity to ecological resistance, measured as the impacts of wildfire on canopy structure, and ecological resilience, measured as native shrub recruitment. We further investigated whether structural heterogeneity can aid spatial predictions of shrub recruitment. Methods: Using high-resolution imagery from unoccupied aerial systems (UAS), we mapped structural heterogeneity across ten semi-arid landscapes, undergoing a disturbance-mediated regime shift from native shrubland to dominance by invasive annual grasses. We then applied wavelet analysis to decompose structural heterogeneity into discrete scales and related these scales to ecological metrics of resilience and resistance. Results: We found strong indicators of scale dependence in the tested relationships. Wildfire effects were most prominent at a single scale of structural heterogeneity (2.34 m), while the abundance of shrub recruits was sensitive to structural heterogeneity at a range of scales, from 0.07 – 2.34 m. Structural heterogeneity enabled out-of-site predictions of shrub recruitment (R2 = 0.55). The best-performing predictive model included structural heterogeneity metrics across multiple scales. Conclusions: Our results demonstrate that identifying structure–function relationships requires analyses that explicitly account for spatial scale. As high-resolution imagery enables spatially extensive maps of canopy heterogeneity, models for scale dependence will aid our understanding of resilience mechanisms in imperiled arid ecosystems. [ABSTRACT FROM AUTHOR]

The purpose of this study was to compare two methods for assessing damage from the degradation of soils and agricultural lands located in the Kalachevsky district of the Volgograd Region. The amount of damage from soil and land degradation was calculated by the "Methodology for determining the amount of damage from soil and land degradation" (1994) and the cost of restoration (reclamation) of degraded soils was determined using the SmetaWizard estimate program (version 4.1.3). It was established that the most significant contribution to the total amount of damage from soil and land degradation (175 573 000 rubles or 64 955 rubles/ha) was made by the increase in the share of exchangeable sodium in soils (147 424 528 rubles or 54 541 rubles/ha), which is due to the development of the process of alkalinization in the soils of the studied agricultural sector in the region. This degradation process, which is harmful to the agricultural use of soils and lands, was found in areas that comprise 52% of the total farm area. This indicator's significant damage is also associated with extended periods of restoration (reclamation) work, 4 years. The cost of reclamation work amounted to 11 647 353 rubles or 4309 rub./ha. The maximum contribution (78%) to this was made by damage from soil organic matter losses (the amount of damage was 9 131 525 rubles or 3378 rubles/ha). The significant difference in the total values of the environmental and economic assessment of soil degradation and the land of the Donskoye agricultural enterprise in the Kalachevsky district, calculated in various ways, is associated with the methodological features of this assessment: the assessment of damage from degradation by the "Methodology ..." (1994) is a stricter approach than estimating the cost of reclamation (restoration) measures. Thus, soils may be degraded compared with a standard (considered when assessing damage), but this degradation is "insufficient" to justify reclamation. [ABSTRACT FROM AUTHOR]

Desertification processes in Central Asia are largely dependent on soil degradation induced by excessive livestock grazing, besides climate changes. Desertification represents a threat to wildlife species living in arid environments, since reduced accessibility to water strongly affects their distribution and behavior. Moreover, livestock presence exacerbates competition with wildlife for scarce water resources. Given their crucial importance to wildlife persistence, water sources in arid environments are critical to the study of wildlife behavior and interspecific competition. The Small Gobi A is one such environment of Mongolia, characterized by high grazing pressure despite low human presence. Between September and October 2017, we conducted camera trapping surveys at two waterholes identified as potential drinking sources for wildlife. We aimed to explore the spatio-temporal interactions among large domestic ungulates (e.g., Bactrian camel Camelus bactrianus), and wild ungulates (e.g., Asian wild ass Equus hemionus, and goitered gazelle Gazella subgutturosa), which are among the most iconic and threatened ungulates of Mongolia. The results showed a complete spatial segregation between domestic and wild ungulates, and a high temporal segregation among wild ungulates. This study confirms spatial and temporal niche partitioning as a strategy adopted by wild species to reduce competition and allow species coexistence. We recommend enhanced management measures of free-roaming livestock to reduce the pressure on wild species at drinking sites. [ABSTRACT FROM AUTHOR]

Urbanization usually reduces bat richness; however, the presence of green areas within cities and peripheral rural areas in arid ecosystems may provide microhabitats for some species. Light pollution is a major feature of urbanization, but its impact on bat behavior appears to be species-specific and previous studies have documented contrasting responses. Moreover, the effect of urbanization on bat species has been poorly studied in arid regions. We assessed the effect of artificial night light intensity (as a proxy of urbanization) on both bat occupancy and the acoustic space used (ASU) in an urbanization gradient in Peruvian central coast, based on passive acoustic recorders. We collected 26,169 recordings from 19 sites which resulted in 579 independent detections of 15 bat species. Variation in both ASU and species richness was best explained by artificial night light intensity. Species-specific effects of the artificial night light intensity based on a multi-species occupancy modeling showed that this covariate had a negative effect on occupancy for most of the bat species (12 species). ASU and both observed and posterior bat species richness were positively correlated, suggesting that ASU can be used as a proxy of bat richness. This study provides evidence that both bat richness and occupancy decrease with artificial light intensity; nevertheless, eight species used urban areas, similar to results found in other cities around the world. [ABSTRACT FROM AUTHOR]

Background and aims: Vegetation patchiness is a distinctive feature of arid ecosystems that strongly shapes plant-soil interactions. While fertility islands are recognized as a critical plant legacy influencing ecosystem functioning, it is not clear whether there is a legacy associated with fungi symbionts in soils. We compared the legacies of arbuscular mycorrhizal fungi (AMF) and dark septate endophyte (DSE) inoculum potential in soil, to determine if they respond to the plant functional type (PFT, grasses and shrubs) and if they overlap spatially with the nutrient legacies.We estimated the soil inoculum potential of AMF and DSE and the soil organic carbon (C), phosphorus (P), and nitrogen (N) concentrations in the soil microsites occupied by the dominant grass and shrub species, and in bare soil microsites distributed in a 6-hectare grazing exclosure in the Patagonian steppe.The AMF inoculum potential was higher in soil microsites conditioned by grasses than in microsites conditioned by shrubs. Instead, the DSE inoculum potential did not differ among microsites and was higher than that of AMF. Furthermore, C and P concentrations were higher in microsites conditioned by shrubs, contrary to AMF inoculum potential.We found that grasses and shrubs have decoupled soil legacies that may alleviate nutrient limitation. While shrubs increase nutrient concentrations, grasses increase AMF inoculum potential. Moreover, the homogeneous distribution of DSE inoculum potential highlights the need to further investigate the role of this group of fungi and its interactions with AMF and soil nutrients in the plant-soil interface.Methods: Vegetation patchiness is a distinctive feature of arid ecosystems that strongly shapes plant-soil interactions. While fertility islands are recognized as a critical plant legacy influencing ecosystem functioning, it is not clear whether there is a legacy associated with fungi symbionts in soils. We compared the legacies of arbuscular mycorrhizal fungi (AMF) and dark septate endophyte (DSE) inoculum potential in soil, to determine if they respond to the plant functional type (PFT, grasses and shrubs) and if they overlap spatially with the nutrient legacies.We estimated the soil inoculum potential of AMF and DSE and the soil organic carbon (C), phosphorus (P), and nitrogen (N) concentrations in the soil microsites occupied by the dominant grass and shrub species, and in bare soil microsites distributed in a 6-hectare grazing exclosure in the Patagonian steppe.The AMF inoculum potential was higher in soil microsites conditioned by grasses than in microsites conditioned by shrubs. Instead, the DSE inoculum potential did not differ among microsites and was higher than that of AMF. Furthermore, C and P concentrations were higher in microsites conditioned by shrubs, contrary to AMF inoculum potential.We found that grasses and shrubs have decoupled soil legacies that may alleviate nutrient limitation. While shrubs increase nutrient concentrations, grasses increase AMF inoculum potential. Moreover, the homogeneous distribution of DSE inoculum potential highlights the need to further investigate the role of this group of fungi and its interactions with AMF and soil nutrients in the plant-soil interface.Results: Vegetation patchiness is a distinctive feature of arid ecosystems that strongly shapes plant-soil interactions. While fertility islands are recognized as a critical plant legacy influencing ecosystem functioning, it is not clear whether there is a legacy associated with fungi symbionts in soils. We compared the legacies of arbuscular mycorrhizal fungi (AMF) and dark septate endophyte (DSE) inoculum potential in soil, to determine if they respond to the plant functional type (PFT, grasses and shrubs) and if they overlap spatially with the nutrient legacies.We estimated the soil inoculum potential of AMF and DSE and the soil organic carbon (C), phosphorus (P), and nitrogen (N) concentrations in the soil microsites occupied by the dominant grass and shrub species, and in bare soil microsites distributed in a 6-hectare grazing exclosure in the Patagonian steppe.The AMF inoculum potential was higher in soil microsites conditioned by grasses than in microsites conditioned by shrubs. Instead, the DSE inoculum potential did not differ among microsites and was higher than that of AMF. Furthermore, C and P concentrations were higher in microsites conditioned by shrubs, contrary to AMF inoculum potential.We found that grasses and shrubs have decoupled soil legacies that may alleviate nutrient limitation. While shrubs increase nutrient concentrations, grasses increase AMF inoculum potential. Moreover, the homogeneous distribution of DSE inoculum potential highlights the need to further investigate the role of this group of fungi and its interactions with AMF and soil nutrients in the plant-soil interface.Conclusion: Vegetation patchiness is a distinctive feature of arid ecosystems that strongly shapes plant-soil interactions. While fertility islands are recognized as a critical plant legacy influencing ecosystem functioning, it is not clear whether there is a legacy associated with fungi symbionts in soils. We compared the legacies of arbuscular mycorrhizal fungi (AMF) and dark septate endophyte (DSE) inoculum potential in soil, to determine if they respond to the plant functional type (PFT, grasses and shrubs) and if they overlap spatially with the nutrient legacies.We estimated the soil inoculum potential of AMF and DSE and the soil organic carbon (C), phosphorus (P), and nitrogen (N) concentrations in the soil microsites occupied by the dominant grass and shrub species, and in bare soil microsites distributed in a 6-hectare grazing exclosure in the Patagonian steppe.The AMF inoculum potential was higher in soil microsites conditioned by grasses than in microsites conditioned by shrubs. Instead, the DSE inoculum potential did not differ among microsites and was higher than that of AMF. Furthermore, C and P concentrations were higher in microsites conditioned by shrubs, contrary to AMF inoculum potential.We found that grasses and shrubs have decoupled soil legacies that may alleviate nutrient limitation. While shrubs increase nutrient concentrations, grasses increase AMF inoculum potential. Moreover, the homogeneous distribution of DSE inoculum potential highlights the need to further investigate the role of this group of fungi and its interactions with AMF and soil nutrients in the plant-soil interface. [ABSTRACT FROM AUTHOR]

Analysis of the taxonomic structure of prokaryotic microbial complexes of the saline soils in the Lake Elton area and their comparative characteristics were carried out for a soil catena along the Khara River flowing into the hypersaline Lake Elton. High-throughput pyrosequencing detected 11 bacterial and 2 archaeal phyla. Comparative analysis of community structure revealed the differences between Solonchaks located at the river flood land and Kastanozems at the slope and top of the river terrace. The patterns of occurrence were described for six predominant phyla (Euryarchaeota, Thaumarchaeota, Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria). For the floodplain soils, the relations between the distribution of Euryarchaeota, Thaumarchaeota, Firmicutes, Actinobacteria, Proteobacteria and soil salinity as well as soil pH were described. Occurrence of members of the phyla Euryarchaeota, Thaumarchaeota, Firmicutes, Actinobacteria, and Proteobacteria in flood land soils was shown to depend on the soil salinity and pH. Members of the phyla Actinobacteria and Firmicutes were shown to predominate in Gleyic Kastanozems. Cloning of the 16S rRNA gene revealed high diversity within the genus Streptomyces (Actinobacteria). A number of the isolated streptomycete clones were homologous to the known antibiotic producers, which indicates that soils of this area are promising for further biotechnological screening. [ABSTRACT FROM AUTHOR]

Questions: How do fire frequency and fire size affect the long-term population dynamics of Mulinum spinosum? Which demographic parameters contribute most to the overall effect of fire on population growth? What is the relative importance of resprouting in sustaining population increase? Location: Grass-shrub northwestern Patagonian steppe, Argentina. Methods: We monitored five permanent plots excluded from grazing for 6 years. We measured shrub abundance, dimensions, reproductive status, seedling emergence, and the size structure of M. spinosum, a resprouting native shrub inhabiting the northwest Patagonian steppe. Data were used to parametrize a stochastic matrix model developed to explore the influence of fire frequency and fire size on long-term population dynamics. We analyzed hypothetical scenarios that included fire frequencies ranging from one per year up to exclusion. Results: Except for annual fires, projections show growing populations regardless of fire frequency. For fire return intervals greater than 50 years, the population becomes independent of fires, with an annual population growth rate of 5.6%. The results suggest two relevant aspects of the population dynamics of this species: M. spinosum is well adapted to the current fire frequency and its resprouting capability will allow M. spinosum to survive and persist in the community, even under frequent fires. Conclusions: Climate change models forecast an increase in summer temperature in NW Patagonia and, consequently, an enhanced fire frequency. Fire is a driver of M. spinosum encroachment that gets worse in overgrazed grasslands. Mulinum spinosum encroachment derivate in a relative replacement of palatable grasses by shrubs changes the ecosystem functionality and reduces productivity. Controlling this process is highly difficult and we suggest a change in the land use for the areas already deteriorated. [ABSTRACT FROM AUTHOR]

Background and aims: Irrigation-maintained artificial oases (AO) in arid regions of northwestern China provide vital human settlement sites. Recent human population increases has caused rapid AO expansion, mainly through transforming natural grassland to arable and afforested land. Here, we assessed how soil biodiversity is affected by various AO expansion strategies, each representing historical land-use regimes.Methods: We sampled six dominant functional groups of soil biota, covering multiple trophic levels: macrofauna consumers (predators and insect herbivores), mesofauna decomposers (Oribatida and Collembola), and microbial decomposers (bacteria and fungi). Sampling was carried out in three AO sites of northwestern China, each containing distinct land uses: natural grasslands (NG; non-irrigated), shrub (Haloxylon ammodendron) plantations (SP; non-irrigated), tree (Populus gansuensis) plantations (TP; irrigated), and arable lands (AL; irrigated).Results: The conversion of NG to SP, TP, and AL eliminated or reduced the abundance of some NG-adapted taxa. Their replacements were exotic species better suited for anthropogenic habitats. As a result, community composition shifted in all six functional groups, with greater differences between NG and TP and AL than between NG and SP. Based on taxonomic gains and losses within each group, we determined that NG to SP conversion positively affected diversity among predators, Collembola, and fungi, but negatively affected diversity of insect herbivores and Oribatida. Bacterial diversity remained unaffected. However, converting NG to TP and AL significantly promoted diversity in all six functional groups, although effect sizes differed.Conclusions: Our results suggest that different AO expansion strategies differentially affected the diversity and structure of belowground communities, which in turn, cascaded down to ecosystem functioning differently. These findings not only contribute to a better understanding of how the diversity and community composition within soil food-webs respond to land-use change but also provide key insights into the development of management strategies for AO ecosystems in drylands to mitigate the negative impact of land-use change on soil biodiversity and ecosystem functioning. [ABSTRACT FROM AUTHOR]

The results of monitoring of the climatic and natural conditions of the semidesert in the Dzhanybek station of the Institute of Forest Science of the Russian Academy of Sciences (IFS RAS) in the northern Caspian region are presented. Monitoring studies have been conducted since the middle of the past century. The goal of the observations was to determine the implications of climate change for the habitat, profile, and state of the animated nature of the ecosystem components. In the course of the process, the station's team observed an increase in the average annual air temperature by 2.2°C and the periodicity in the territory wetness caused by variations in the amount of precipitates. Moreover, in the period of increased wetness from 1980 to 1994, the ground water and water body levels increased, herbaceous communities and cereal crops became more yielding, and wild hoofed animals (saigas) proliferated as well. In the period of drought from 1995 to 2009, the spring melt water runoff attenuated, water bodies shoaled and dried, and dry spells repeated from year to year, which negatively affected the development of the ecosystem components. On the whole, the climate changes have not disturbed the dynamic balanced state of the natural ecosystems (e.g., yield of virgin land phytocenoses, wild animal stock); however, long dry spells have irreversibly aggravated the state of man-made forests and even caused their extinction and long-term cereal crop failures on zonal soils, which has led to unstable agricultural product outputs. The research results reveal the need to switch to adaptive fine-contour or focal farming suited most fitted for the climatic and natural condition of the region. [ABSTRACT FROM AUTHOR]

Context: Arid rangelands have been severely degraded over the past century. Multi-temporal remote sensing techniques are ideally suited to detect significant changes in ecosystem state; however, considerable uncertainty exists regarding the effects of changing image resolution on their ability to detect ecologically meaningful change from satellite time-series. Objectives: (1) Assess the effects of image resolution in detecting landscape spatial heterogeneity. (2) Compare and evaluate the efficacy of coarse (MODIS) and moderate (Landsat) resolution satellite time-series for detecting ecosystem change. Methods: Using long-term (~12 year) vegetation monitoring data from grassland and shrubland sites in southern New Mexico, USA, we evaluated the effects of changing image support using MODIS (250-m) and Landsat (30-m) time-series in modeling and detecting significant changes in vegetation using time-series decomposition techniques. Results: Within our study ecosystem, landscape-scale (>20-m) spatial heterogeneity was low, resulting in a similar ability to detect vegetation changes across both satellite sensors and levels of spatial image support. While both Landsat and MODIS imagery were effective in modeling temporal dynamics in vegetation structure and composition, MODIS was more strongly correlated to biomass due to its cleaner (i.e., fewer artifacts/data gaps) 16-day temporal signal. Conclusions: The optimization of spatial/temporal scale is critical in ensuring adequate detection of change. While the results presented in this study are likely specific to arid shrub-grassland ecosystems, the approach presented here is generally applicable. Future analysis is needed in other ecosystems to assess how scaling relationships will change under different vegetation communities that range in their degree of landscape heterogeneity. [ABSTRACT FROM AUTHOR]

The water and hydrochemical balance of Shira and Itkul lakes, located in the arid (steppe) zone in the Republic of Khakassia (Russian Federation), has been calculated. It is shown that Lake Itkul can be considered a drained lake, which significantly determines the basic differences of the hydrochemical balance in the two water bodies. The outflow of water from Itkul to Shira is, on average, 6791000 m3/year, and the average outflow of dissolved salts is 35697 t/year. Lake Shira can be considered a drainless water body with an evaporation mechanism of formation of the chemical composition of its waters, and Lake Itkul is considered a flowing water reservoir. The salt concentration in Itkul is not as high as that in Shira due to the lower influence of evaporation on the formation of the chemical composition of waters and time of their interaction. It has been assumed that this phenomenon is regular, rather than exceptional, for the arid zone of Northern and Central Asia. [ABSTRACT FROM AUTHOR]

Changes in the state of Mongolian arid ecosystems revealed in long-term field studies have been analyzed in accordance with the developed concept of island-type desertification. Trends have been revealed in the development of climate aridity, drought frequency, and the anthropogenic load on pastures. Indicators of area moistening, anthropogenic desertification islands, and the overgrazing degree of arid pastures have been developed on the basis of satellite MODIS data. It has been shown that the effects of a sharp reduction in the number of livestock because of natural hazards (dzut, drought) are reliably manifested by a decrease in the surface albedo and an increase in the vegetation index. The dynamics of the islands of anthropogenic desertification has been analyzed. The degree of degradation of dry-steppe, desert-steppe, and desert ecosystems has been estimated snowstorms. [ABSTRACT FROM AUTHOR]

Measures to control populations of small mammals in natural ecosystems are taken because of their involvement in plague epizootics and probable competition for food with livestock in pastures. These measures are aimed at the keystone species of biocenosis, whose removal leads to breakage of biocenotic connections and reduction of species diversity. Moreover, available data show that these measures fail to restrain the development of epizootics in natural plague foci and do not bring expectable economic profit when applied in pastures. This is evidence that the practice of small mammal population control is inexpedient. [ABSTRACT FROM AUTHOR]

Large areas of public lands administered by the Bureau of Land Management and located in arid regions of the southwestern United States are being considered for the development of utility-scale solar energy facilities. Land-disturbing activities in these desert, alluvium-filled valleys have the potential to adversely affect the hydrologic and ecologic functions of ephemeral streams. Regulation and management of ephemeral streams typically falls under a spectrum of federal, state, and local programs, but scientifically based guidelines for protecting ephemeral streams with respect to land-development activities are largely nonexistent. This study developed an assessment approach for quantifying the sensitivity to land disturbance of ephemeral stream reaches located in proposed solar energy zones (SEZs). The ephemeral stream assessment approach used publicly-available geospatial data on hydrology, topography, surficial geology, and soil characteristics, as well as high-resolution aerial imagery. These datasets were used to inform a professional judgment-based score index of potential land disturbance impacts on selected critical functions of ephemeral streams, including flow and sediment conveyance, ecological habitat value, and groundwater recharge. The total sensitivity scores (sum of scores for the critical stream functions of flow and sediment conveyance, ecological habitats, and groundwater recharge) were used to identify highly sensitive stream reaches to inform decisions on developable areas in SEZs. Total sensitivity scores typically reflected the scores of the individual stream functions; some exceptions pertain to groundwater recharge and ecological habitats. The primary limitations of this assessment approach were the lack of high-resolution identification of ephemeral stream channels in the existing National Hydrography Dataset, and the lack of mechanistic processes describing potential impacts on ephemeral stream functions at the watershed scale. The primary strength of this assessment approach is that it allows watershed-scale planning for low-impact development in arid ecosystems; the qualitative scoring of potential impacts can also be adjusted to accommodate new geospatial data, and to allow for expert and stakeholder input into decisions regarding the identification and potential avoidance of highly sensitive stream reaches. [ABSTRACT FROM AUTHOR]

The results are presented that have been obtained in studies on changes in the species composition, geobotanical characteristics, and productivity of natural vegetation in arid steppes of the Cisural region during the past few decades (1977-2012). Consideration is given to the significance of the soil factor in the processes of transformation of zonal vegetation. The increasing role of arid steppes as a natural barrier to desertification is demonstrated. [ABSTRACT FROM AUTHOR]

Background and aims: Our objective was to assess the effects of long-term continuous grazing on soil enzyme activities in relation to shifts in plant litter attributes and soil resources in an arid ecosystem, considering both spatial and temporal variations. Methods: We randomly extracted soil samples with the respective litter cover at 5 modal size plant-covered patches (PCP) and the nearest inter-canopy areas (IC) at Patagonian Monte sites with low, medium and high grazing intensity in winter and summer from 2007 to 2009. We analyzed enzyme activities (dehydrogenase, ß-glucosidase, protease, alkaline and acid phosphatase), microbial biomass-C, organic-C, total soil-N, and moisture in soil and mass and quality in plant litter. We assessed faeces density and plant cover in the field. Results and conclusions: Grazing led to reduced grass cover, decreasing plant litter mass with increasing soluble phenolics, and reduced phosphatases, ß-glucosidase and microbial biomass-C at PCP. A localized nutrient input from animal excreta seems to promote microbial biomass-C, alkaline phosphatase and dehydrogenase activities but only at IC from the site with high grazing intensity. Plant heterogeneous distribution, plant litter quantity and quality, nutrient inputs from grazers and seasonal variation in soil moisture, also affecting soil resources and microbial biomass, modulate soil enzyme responses to long-term grazing in the arid Patagonian Monte. [ABSTRACT FROM AUTHOR]

We have explored species-specific preferences for nitrate (NO) and ammonium (NH) as an alternative niche separation in ecosystems where nitrogen (N) is present mostly in inorganic forms. The Patagonian steppe is dominated by shrubs and grasses. Shrubs absorb water and nutrients from deep soil layers, which are poor in N, while grasses have the opposite pattern, absorbing most of their water and nutrients from the upper layers of the soil. We hypothesized that the preferences of shrub and grass for inorganic N forms are different and that the rate of potential N uptake is greater in shrubs than in grasses. To test this hypothesis, we grew individuals of six dominant species in solutions of different NH:NO concentration ratios. Nitrate uptake was found to be higher in shrubs, while ammonium uptake was similar between plant functional types. The NH:NO uptake ratio was significantly lower for shrubs than grasses. Shrubs, which under field conditions have deeper rooting systems than grasses, showed a higher N absorption capacity than grasses and a preference for the more mobile N form, nitrate. Grasses, which had lower N uptake rates than shrubs, preferred ammonium over nitrate. These complementary patterns between grasses and shrubs suggest a more thorough exploitation of resources by diverse ecosystems than those dominated by just one functional type. The loss of one plant functional group or a significant change in its abundance would therefore represent a reduction in resource use efficiency and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Investigation into the population of corsac fox in Dagestan enabled us to identify the animal's distribution, habitat, home ranges, forage base, and population size dynamics. A significant correlation has been established between the population size of corsac fox, annual precipitation, and the number of grazing livestock. Limiting factors that determine the population status of the corsac fox are studied. [ABSTRACT FROM AUTHOR]

Litter decomposition contributes to one of the largest fluxes of carbon (C) in the terrestrial biosphere and is a primary control on nutrient cycling. The inability of models using climate and litter chemistry to predict decomposition in dry environments has stimulated investigation of non-traditional drivers of decomposition, including photodegradation, the abiotic decomposition of organic matter via exposure to solar radiation. Recent work in this developing field shows that photodegradation may substantially influence terrestrial C fluxes, including abiotic production of carbon dioxide, carbon monoxide and methane, especially in arid and semi-arid regions. Research has also produced contradictory results regarding controls on photodegradation. Here we summarize the state of knowledge about the role of photodegradation in litter decomposition and C cycling and investigate drivers of photodegradation across experiments using a meta-analysis. Overall, increasing litter exposure to solar radiation increased mass loss by 23% with large variation in photodegradation rates among and within ecosystems. This variation was tied to both litter and environmental characteristics. Photodegradation increased with litter C to nitrogen (N) ratio, but not with lignin content, suggesting that we do not yet fully understand the underlying mechanisms. Photodegradation also increased with factors that increased solar radiation exposure (latitude and litter area to mass ratio) and decreased with mean annual precipitation. The impact of photodegradation on C (and potentially N) cycling fundamentally reshapes our thinking of decomposition as a solely biological process and requires that we define the mechanisms driving photodegradation before we can accurately represent photodegradation in global C and N models. [ABSTRACT FROM AUTHOR]

A steady and significant warming of the autumn-winter period and an increase in moisture supply during the growing season have taken place in the Northern Caspian Lowland, resulting in its general mesophytization. In particular, the dominant species in plant communities on solonchakous solonetzes have changed, with black wormwood ( Artemisia pauciflora) being replaced by forage kochia ( Kochia prostrata). However, these ecosystems remain in dynamic equilibrium, and their current changes and productivity fluctuations do not exceed natural limits and are reversible. [ABSTRACT FROM AUTHOR]

Fire is an important natural disturbance process in arid grasslands but current fire regimes are largely the result of both human and natural processes and their interactions. The collapse of the Soviet Union in 1991 spurred substantial socioeconomic changes and was ultimately followed by a rapid increase in burned area in southern Russia. What is unclear is whether this increase in burned area was caused by decreasing livestock numbers, vegetation changes, climate change, or interactions of these factors. Our research goal was to identify the driving forces behind the increase in burned area in the arid grasslands of southern Russia. Our study area encompassed 19,000 km in the Republic of Kalmykia in southern Russia. We analyzed annual burned area from 1986 to 2006 as a function of livestock population, NDVI, precipitation, temperature, and broad-scale oscillation indices using best subset regressions and structural equation modeling. Our results supported the hypothesis that vegetation recovered within 5-6 years after the livestock declined in the beginning of the 1990s, to a point at which large fires could be sustained. Climate was an important explanatory factor for burning, but mainly after 1996 when lower livestock numbers allowed fuels to accumulate. Ultimately, our results highlight the complexity of coupled human-natural systems, and provide an example of how abrupt socioeconomic change may affect fire regimes. [ABSTRACT FROM AUTHOR]

Arid ecosystems receive precipitation pulses of different sizes that may differentially affect nitrogen (N) losses and N turnover during the growing season. We designed a rainfall manipulation experiment in the Patagonian steppe, southern Argentina, where we simulated different precipitation patterns by adding the same amount of water in evenly spaced three-small rainfall events or in one-single large rainfall event, three times during a growing season. We measured the effect of the size of rainfall pulses on N mineralization and N losses by denitrification, ammonia volatilization, and nitrate and ammonia leaching. Irrigation pulses stimulated N mineralization ( P < 0.05), with small and frequent pulses showing higher responses than large pulses ( P < 0.10). Irrigation effects were transient and did not result in changes in seasonal net N mineralization suggesting a long-term substrate limitation. Water pulses stimulated gaseous N losses by denitrification, with large pulses showing higher responses than small pulses ( P < 0.05), but did not stimulate ammonia volatilization. Nitrate leaching also was higher after large than after small precipitation events ( P < 0.05). Small events produced higher N transformations and lower N losses by denitrification and nitrate leaching than large events, which would produce higher N availability for plant growth. Climate change is expected to increase the frequency of extreme precipitation events and the proportion of large to small rainfall events. Our results suggest that these changes would result in reduced N availability and a competitive advantage for deep-rooted species that prefer nitrate over ammonia. Similarly, the ammonium:nitrate ratio might decrease because large events foster nitrate losses but not ammonium losses. [ABSTRACT FROM AUTHOR]

Ring-shaped growth patterns commonly occur in resource-limited arid and semi-arid environments. The spatial distribution, geometry, and scale of vegetation growth patterns result from interactions between biotic and abiotic processes, and, in turn, affect the spatial patterns of soil moisture, sediment transport, and nutrient dynamics in aridland ecosystems. Even though grass ring patterns are observed worldwide, a comprehensive understanding of the biotic and abiotic processes that lead to the formation, growth and breakup of these rings is still lacking. Our studies on patterns of infiltration and soil properties of blue grama ( Bouteloua gracilis) grass rings in the northern Chihuahuan desert indicate that ring patterns result from the interaction between clonal growth mechanisms and abiotic factors such as hydrological and aeolian processes. These processes result in a negative feedback between sediment deposition and vegetation growth inside the bunch grass, which leads to grass die back at the center of the grass clump. We summarize these interactions in a simple theoretical and conceptual model that integrates key biotic and abiotic processes in ring formation, growth and decline. [ABSTRACT FROM AUTHOR]

We compared the size and spatial pattern of the germinable soil seed bank (GSB) of the three dominant perennial-grass species in the arid Patagonian Monte of Argentina. These species differ in plant functional traits, seed morphology, and in their preference by grazers. During three consecutive years, we sampled the soil seed bank at 1 m intervals and the intercepted diameter of perennial-grass species and shrub patches along 50-m linear transects at three sites with different grazing pressure. Soil samples were incubated at field capacity during 12 weeks and emerged seedlings counted. The largest-seeded and most xerophytic Stipa speciosa did not form a GSB. The other two grass species with more mesophytic traits and smaller seeds than S. speciosa formed different GSB. Poa ligularis formed a smaller and more heterogeneous GSB than Stipa tenuis. Grazing had not effect on GSB size of P. ligularis but increased the proportion of seeds under dense shrub canopies. In contrast, grazing reduced the size and also increased the proportion of the GSB of S. tenuis under shrub canopies. We conclude that the size and the spatial pattern of the GSB of the dominant perennial-grass species in the arid Patagonian Monte were related not only to seed and plant traits but also to the spatial distribution of grass plants and their exposure to grazers. [ABSTRACT FROM AUTHOR]

Studies of the effects of precipitation on litter decomposition and nitrogen mineralization in arid and semiarid environments have demonstrated contradictory results. We conducted a manipulative experiment with rainout shelters in the semiarid Patagonian steppe, aimed at assessing the direct effects of water availability on litter decomposition and net nitrogen mineralization while isolating the indirect effects. We created four levels of precipitation input: control and three levels (30, 55 and 80%) of precipitation interception and we examined litter decomposition and nutrient release of a dominant grass species, Stipa speciosa, inorganic soil nitrogen, and in situ net nitrogen mineralization over two consecutive years. Litter decomposition rates ( k, year−1) varied significantly ( P < 0.001) among precipitation interception treatments and were positively correlated with incoming annual precipitation (APPT, mm/year) ( k = 0.0007 × APPT + 0.137). In contrast, net N mineralization was not correlated with incoming precipitation. Soil NO significantly decreased with increasing precipitation input, whereas soil NH concentration did not differ among precipitation interception treatments. Controls of water input on litter decomposition appear to be different from controls on N mineralization in the semiarid Patagonian steppe. We suggest that although water availability affects both the mineralization of C and N, it differentially affects the movement and fate of the inorganic products. A consequence of the accumulation of inorganic N during dry episodes is that periods of maximum water and soil nutrient availability may occur at different times. This asynchrony in the availability of N and water in the soil may explain the observed lags in the response of primary production to increases in water availability. [ABSTRACT FROM AUTHOR]

A stochastic numerical approach was developed to model the actual standing biomass in the sand dunes of the northwestern Negev (Israel) and probable boundary conditions that may be responsible for the vegetation patterns investigated in detail. Our results for several variables characteristic for the prevailing climate, geomorphology, hydrology and biologicy at four measurement stations along a transect from northwest to southeast allowed for the development of a stochastic model for biomass distribution over the entire sand dune field (mesoscale) and at Nizzana experimental station (microscale). With this equation it was possible to compute and interpolate a biomass index value for each grid point on the mesoscale and micro scale. The spatial distribution of biomass is negatively linked to distance from the sea, to rainfall and relief energy. [ABSTRACT FROM AUTHOR]

In arid ecosystems, the ability to rapidly capture nitrogen (N) from brief pulses is expected to influence plant growth, survival, and competitive ability. Theory and data suggest that N capture from pulses should depend on plant growth rate and availability of other limiting resources. Theory also predicts trade-offs in plant stress tolerance and ability to capture N from different size pulses. We injected K15NO3, to simulate small and large N pulses at three different times during the growing season into soil around the co-dominant Great Basin species Sarcobatus vermiculatus, Chrysothamnus nauseosus ssp. consimilis, and Distichlis spicata. Soils were amended with water and P in a partial factorial design. As predicted, all study species showed a comparable decline in N capture from large pulses through the season as growth rates slowed. Surprisingly, however, water and P availability differentially influenced the ability of these species to capture N from pulses. Distichlis N capture increased up to tenfold with water addition while Chrysothamnus N capture increased up to threefold with P addition. Sarcobatus N capture was not affected by water or P availability. Opposite to our prediction, Sarcobatus, the most stress tolerant species, captured less N from small pulses but more N from large pulses relative to the other species. These observations suggest that variation in N pulse timing and size can interact with variable soil water and P supply to determine how N is partitioned among co-existing Great Basin species. [ABSTRACT FROM AUTHOR]

Riparian corridors of eastern Oregon and Washington, like those in other regions, comprise small portions of river drainages but provide disproportionately important ecosystem functions. However, most riparian and fluvial (streams and rivers) systems have been greatly altered. Degraded ecosystems commonly reflect influences of land-uses (e. g., mining, logging, road construction, fire suppression, livestock grazing), hydro-developments (e.g., dams, irrigation, flood control) and other human actions. Some important consequences include: degradation and fragmentation of habitats, changes in riparian plant associations, isolated fish populations, and altered flow and sediment regimes. This synthesis paper evaluates some major environmental factors that can influence the sustainability of riparian corridors and fluvial systems along lowland-arid to mountain gradients within river drainages of eastern Oregon and Washington. Four tributary rivers of the Columbia River, the Grande Ronde and John Day Rivers in northeastern Oregon, and the Yakima and Methow Rivers on the eastside of the Cascade Mountains in Washington, provide perspectives on environmental conditions. Factors evaluated include: a) dominant riparian plant associations and distributions in relation to differences in precipitation and temperature regimes along elevation gradients; b) ecological and physiochemical functions of riparian and fluvial systems along elevation gradients; c) long-term historical and contemporary cumulative impacts of human actions; and d) management provisions that could restore and sustain ecosystem functions. Ecological functions of riparian and fluvial systems are viewed as being closely coupled because of their dependence on hydrological (surface and sub-surface) and sediment routing regimes. From a river landscape perspective, achieving greater connectivity can be a key objective for analyzing and integrating the management of riparian and fluvial ecosystems. Effective management should include ensuring the delineation of major limiting factors (e.g., erosion, water shortages and temperatures) and identification of streamside and channel networks that link critical habitats at multiple landscape scales (e. g., locations and spacing of refuge habitats for fish and wildlife). Management actions should encourage the connectivity of reaches and habitats and maintenance of riparian and fluvial functions so interactions can occur. Efforts should include renewal of natural flood and sediment routing regimes and the reestablishment of habitats adjacent to ecologically intact habitats. [ABSTRACT FROM AUTHOR]

The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 µmol NOg-1 FW h-1). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 µM NO. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the15N natural abundance method and was a significant component of the N-requirement of the legumeAlhagi, the average contribution of biologically fixed nitrogen inAlhagiwas 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through development of root systems that access groundwater to satisfy demands for both water and nutrients. This is an ecologically favourable strategy since only groundwater is a predictable and stable resource. [ABSTRACT FROM AUTHOR]

Field manipulative experiments represent a straightforward way to explore temporal relationships between annual precipitation and productivity. Water exclusion usually involves the use of rainout shelters, which are in general formed by a complete roof that intercepts 100% of the rainfall and require complicated mechanisms to move the shelter into place. The rainout-shelter design described here is a fixed-location shelter with a roof consisting of bands of transparent acrylic that blocks different amounts of rainfall while minimally affecting other environmental variables. We constructed thirty 3.76-m2 shelters in an arid steppe near Río Mayo, Argentina (at 45°41′S, 70°16′W), to impose 30%, 55%, and 80% of rainfall interception. We tested the effectiveness of the design by collecting all the intercepted water in storage tanks and we evaluated changes in soil water content with the time domain reflectometry technique. We also measured soil water content in regular grids to assess the magnitude of the edge effect. We analysed the microclimate impact of the shelters by measuring photosynthetically active radiation and air and soil temperature inside and outside shelters. We did not detect significant differences between the observed and the expected rainfall interception for the 30% and 55% interception treatments but the 80% shelters intercepted 71% of incoming rainfall, which was significantly (P<0.05) lower than the expected value. Soil water content was significantly (P<0.05) higher in the control plots than in the plots with rainout shelter at all dates, except in January (summer). Radiation was not affected by the 30% interception treatment, but the roof with the largest number of acrylics bands (80% interception treatment) reduced incident radiation throughout the day by 10%. Air and soil temperatures were lower under than outside the shelters during the period of highest radiation but the opposite occurred with low radiation but with smaller differences. The two characteristics of the shelter, fixed design and low cost, allow for proper replication in space, which is required in ecological field experiments. [ABSTRACT FROM AUTHOR]

We examined soil and vegetation N isotopic composition (δ15N) and soil inorganic N availability in an intact Mojave desert ecosystem to evaluate potential effects of elevated atmospheric CO2 on N cycling. Vegetation from the dominant perennial shrub Larrea tridentata under elevated CO2 was enriched in 15N. Over a 7-month sampling period, Larrea δ15N values increased from 5.7±0.1‰ to 9.0±1.1‰ with elevated CO2; under ambient conditions, δ15N values of shrubs increased from 4.9±0.3‰ to 6.6±0.7‰. No difference was found in soil δ15N under elevated and ambient CO2. Soil δ15N values under the drought deciduous shrubs Lycium spp. were greatest (7.2±0.3‰), and soil under the C4 perennial bunchgrass Pleuraphis rigida had the lowest values (4.5±0.2‰). Several mechanisms could explain the enrichment in 15N of vegetation with elevated CO2. Results suggest that microbial activity has increased with elevated CO2, enriching pools of plant-available N and decreasing N availability. This hypothesis is supported by a significant reduction of plant-available N under elevated CO2. This indicates that exposure to elevated CO2 has resulted in significant perturbations to the soil N cycle, and that plant δ15N may be a useful tool for interpreting changes in the N cycle in numerous ecosystems. [ABSTRACT FROM AUTHOR]

We contrasted the seasonal use of simulated large rain events (24 mm) by three native species of the arid Colorado Plateau: the perennial grass Hilaria jamesii and two shrubs Artemesia filifolia and Coleogyne ramosissima. Deuterium-enriched water was used to distinguish shallow "pulse" water from water in deeper soil layers that were unaffected by the water input. We also measured the leaf gas exchange rates of watered and unwatered control plants for 5 days after the rain event. H. jamesii had twice the pulse water proportion in its xylem than the two shrubs in spring (approx. 70% vs 35%). In summer, the pulse water proportions of all species were around 70%. The increase in the relative pulse water uptake of the two shrubs was caused primarily by a reduction in the rate of water uptake from deeper sources, consistent with the decrease in the availability of stored winter water. Rain increased the rates of gas exchange in C. ramosissima in both seasons, in H. jamesii only in summer and had no significant effect on A. filifolia. In H. jamesii, summer rain also increased water use efficiency. This suggests three principle mechanisms for rainwater use: (1) immediate increase in gas exchange via stomatal opening (C. ramisissima), (2) immediate increase in water use efficiency through restoration of the photosynthetic apparatus (H. jamesii) and (3) conservation of deeper soil water, potentially extending photosynthetic activity into later drought periods (A. filifolia). On a ground-area basis, A. filifolia was by far the largest consumer of spring and summer rain, due to its greater ground cover, while rain use by H. jamesii was negligible. We hypothesize that a population's fraction of the total community Leaf Area Index, more than species identity, determines which species takes up most of the spring and summer precipitation and we discuss this idea in the context of Walter and Stadelmann's (1974, In: Brown JW Jr (ed) Desert biology. Academic Press, New York, pp 213–310) water partitioning hypothesis. [ABSTRACT FROM AUTHOR]

Most arid ecosystems have suffered from severe overexploitation by excessive wood harvesting, overgrazing, and agriculture, resulting in depletion of vegetation biomass and soil erosion. These changes are often difficult to reverse due to positive feedbacks that tend to stabilize the new situation. In this paper, we briefly review evidence for the idea that different states in these ecosystems might represent alternative equilibria and present a graphic model that summarizes the implications for their response to changing environmental conditions. We show how, in the light of this theoretical framework, climatic oscillations such as El Niño Southern Oscillation (ENSO) could be used in combination with grazer control to restore degraded arid ecosystems. We also present evidence that, depending on grazing pressure, ENSO episodes can trigger structural and long-lasting changes in these ecosystems. [ABSTRACT FROM AUTHOR]

Interactions between changing precipitation regimes and other aspects of global change are likely to affect natural and managed terrestrial ecosystems. Relatively little research has focused on understanding how ecosystems respond to changes in precipitation regimes, which are expected to have significant impacts for ecosystem functioning, species distribution, species richness and biodiversity especially in arid ecosystems. There is a need for integrated studies to understand the functional ecology of different species in order to predict their success under changing environmental conditions. One example for such an integrated assessment is a study by Xu and Li (this issue) on water-use strategies of desert shrubs. By combining investigations of morphological traits, such as root architecture, with ecophysiological measurements Xu and Li were able to elucidate the differing adaptive strategies of three desert shrubs in their arid environment. The plant physiological response of the plants was closely related to their water-use strategy and was coupled with the functional type of the root system. Integrated research such as this will lead to a more complete understanding of the water and carbon economy of plant species and ecosystems and will allow a more accurate prediction of plant responses to changing environmental conditions. [ABSTRACT FROM AUTHOR]