Coastal Change in Ras Al Khaimah (United Arab Emirates): a Cartographic Analysis

The coastline of Ras Al Khaimah, United Arab Emirates, has three main constructional complexes: Jazirat al Hamra, Julfah, and Jazirat Hulaylah. Archival information, air photographs and maps dating back to 1819, enable the history of coastal change to be reconstructed. Jazirat al Hamra has been much affected by recent reclamation and harbour works, but appears to have been relatively stable. Jazirat Hulaylah also appears to have changed relatively little. However, the Julfah complex, which includes the harbour mouth for Ras Al Khaimah city, has shown very considerable change as a result of coastal breaching and spit growth and decay.     

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.     

Financial appraisal of date-frond mat fence systems for wind erosion control and sand dune stabilization in the arid region of the United Arab Emirates

A discounted cash flow model was employed to assess the viability of four wind barrier systems. The systems were utilized for wind erosion control and sand dune stabilization in the Al-Ain region of the United Arab Emirates. These systems consisted of four densities of date-frond mat fences erected in the form of checker board grids between rows of two local tree species:Prosopis spicigeraandAcacia tortilis. Analysis of cost estimated was based on the annual equivalent value of costs for each system. The economic life of the systems varied as a function of the time needed for the different trees in the different systems to reach the self-support stage. Results indicated that the systems’ ranking according to the minimal costs varied among the different tree types and the number of fences; but there was a general decrease in cost with increased fence density using the same tree, and this was due mainly to the effect of the fence on reducing the cost of tree development and maintenance as a result of reducing accumulated eroded sand. The minimal cost was recorded in D-10 treatment (seven fences) usingProsopis spicigera.     

Textural attributes, mineralogy and provenance of sand dune fields in the greater Al Ain area, United Arab Emirates

Sand dunes and interdune sediments around Al Ain city have markedly high carbonate contents which increase towards Jabal Hafit mountain and the Arabian Gulf coast. The dunes are composed predominantly of well-sorted fine sands, consisting of unstrained quartz and carbonate grains together with minor proportions of chert and feldspars. Scanning electron microscope (SEM) examination reveals that quartz grains display various mechanically- and chemically-formed surface textures. The heavy minerals are dominated by opaques and pyroxenes with minor tourmaline, garnet, rutile, epidote, monazite, zircon, hornblende and staurolite.Interdune sediments consist of fine and very fine, poorly- to extremely poorly-sorted sands together with small concentrations of gravel, silt and clay. The light sand fractions compositionally resemble those of dunes but contain, in addition, gypsum, anhydrite, halite and celestite. Percentages of pyroxenes are higher whereas those of zircon, tourmaline and rutile are lower than in dunes. X-ray diffractometry reveals that the clay fractions consist solely of palygorskite. Generally, interdune sediments are much less mature texturally and mineralogically than dune sands; the maturity of both types of sediments decreases toward the NE of the study area.Sand dunes in the various districts of the greater Al Ain area are genetically related. Also, there is a partial genetic relationship between the dunes and interdune sediments; both are mainly multicyclic. Their major parts were brought mainly by the dominant north-west (El Shamal) winds from older dune fields in other localities in U.A.E., Qatar and El-Rub El-Khali. Local contributions to the dune fields from Jabal Hafit mountain, the Oman Mountains and the calcareous coast of the Arabian Gulf were, in cases, significant. Also, authigenesis by groundwater under highly evaporitic conditions played a major role in the formation of interdune sediments through the genesis of the clay and some nonclay minerals.     

The effects of grazing on the endangered Sinai Thyme (Thymus decussatus) in a hyper-arid environment

Herbivores play a key role in determining plant community composition. Historically grazing has been deemed detrimental for plants, but recent theoretical and empirical studies suggest that grazing may in fact be beneficial. Grazing is more likely to improve primary productivity in areas with a grazing history, where the plants are adapted to tolerate grazing, and also in arid environments because water stress and grazing select for comparable plant traits. Sinai Thyme (Thymus decussatus) in the arid St Katherine Protectorate of South Sinai has high apparent mortality rates and poor condition, both of which have detrimental consequences for its associated herbivores, particularly the Critically Endangered Sinai Baton Blue (Pseudophilotes sinaicus) whose larval stage feeds exclusively upon this plant. One recent conservation action banned grazing but there has been no obvious improvement in the thyme with continued high mortality, and local Bedu claim that grazing is in fact advantageous for plant health. We carried out a factorial experiment that manipulated simulated grazing, fertilizing and watering of thyme. This showed no evidence of any negative response to grazing or that watering or fertilizing had any effect either, presumably their impact is smaller than the current inter-annual variability caused by climatic fluctuations.     

Effects of the grazing systems on germinable soil seed bank of desert steppe

We studied a soil seed bank in the Stipa breviflora desert steppe under three grassland management systems, namely continuous grazing, rotational grazing, and no grazing, from 1999 until 2007. The germinable seed bank species in rotational, continuous and no grazing were 11, 9 and 8 species, respectively. Rotational grazing increased the number of seed bank plant species and perennial grasses. The density of germinal soil seed bank was significantly higher in the enclosed area (19,533.33 seeds/m²) than those in rotational (3,233.33 seeds/m²) and continuous grazing areas (2,553.60 seeds/m²). The vertical distribution of the soil seed bank had a similar trend: 75.06%–83.19% of the seeds are distributed in the top 0–5 cm soil layer, 14.16%–21.68% in the 5–10 cm layer, and 2.65%–4.95% in the 10–15 cm layer, which varied between the grazing treatments. Density of the soil seed bank was significantly higher in the enclosed area, and there was no significant difference between rotational and continuous grazing. The Margalef and Shannon-Wiener indices for the soil seed bank were higher for rotational grazing treatment than for continuous grazing. The Sorensen’s similarity index for the soil seed bank between the enclosed and rotational grazing areas reached 0.857.     

Effects of soil degradation on infiltration rates in grazed semiarid rangelands of northeastern Patagonia, Argentina

In grazed semiarid ecosystems, considerable spatial variability in soil infiltration exists as a result of vegetation and soil patchiness. Despite widespread recognition that important interactions and feedbacks occur between vegetation, runoff and erosion, currently there is only limited quantitative information on the control mechanisms that lead to differences in infiltration from different vegetation types. In this paper, we determine (i) the relationship between vegetation and soil surface characteristics and (ii) the soil infiltration rate by using rainfall simulations on runoff plots (0.60 × 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that vegetation and soil infiltration are closely coupled. Total infiltration was significantly higher in the GS (69.6 mm) compared with the DGS and DSS (42.9 and 28.5 mm, respectively). In the GS, soil infiltration rate declined more slowly than the others communities, reaching a terminal infiltration rate significantly greater (57.7 mm) than those of DGS and DSS (25.7 and 12.9 mm, respectively). The high rate of water losses via overland-flow may limit the possibilities for grass seedling emergence and establishment and favor the persistent dominance of shrubs.     

Effects of fire, grazing, and the presence of shrubs on Chihuahuan desert grasslands

Responses of herbaceous and suffrutescent species to fire, grazing, and presence of Prosopis glandulosa were examined in a Chihuahuan desert grassland in south-central New Mexico. Treatments were assigned randomly to eight 12×8 m plots within each of two blocks. Following fires in June 1995, unfenced plots were exposed to livestock grazing over 4 years. Plots were established that either included or excluded P. glandulosa. Perennial grass cover, primarilyBouteloua eriopoda , decreased by 13% in burned plots but increased 5% in unburned areas. Conversely, perennial forb cover was 4% greater after fire. Perennial grass frequency decreased 30% more and perennial forb frequency increased 10% more following burning. Further, increases in evenness after fire resulted in a 225% increase in species diversity. Grazing also resulted in a decrease in perennial grass cover while frequency decreased 22% more in grazed than ungrazed plots. Only frequency and not cover of perennial forbs and annual grasses increased more following grazing. Presence of P. glandulosa had no differential effect on responses of non-shrub species. Fires were conducted during near drought conditions while grazing occurred during years of precipitation equivalent to the long-term average. Precipitation immediately following fire may be critical for recovery of B. eriopoda -dominated desert grasslands; relationships between fire and post-fire precipitation patterns require future investigation.     

Effects of natural flooding and manual trapping on the facilitation of invasive crayfish-native amphibian coexistence in a semi-arid perennial stream

Aquatic amphibians are known to be vulnerable to a myriad of invasive predators. Invasive crayfish are thought to have eliminated native populations of amphibians in some streams in the semi-arid Santa Monica Mountains of southern California. Despite their toxic skin secretions that defend them from native predators, newts are vulnerable to crayfish attacks, and crayfish have been observed attacking adult newts, and eating newt egg masses and larvae. For 15 years, we have observed invasive crayfish and native California newts coexisting in one stream in the Santa Monica Mountains. During that period, we monitored the densities of both crayfish and newt egg mass densities and compared these to annual rainfall totals. After three seasons of below average rainfall, we reduced crayfish numbers by manual trapping. Our long-term data indicated that crayfish did not fare well in years when rainfall is above the historic average. This invasive predator did not evolve with high velocity streams, and observations indicated that southern California storm events washed crayfish downstream, killing many of them. Newts exhibit increased reproduction in years when crayfish numbers were reduced. A comparison with a nearby stream that does not contain crayfish indicated that newt reproduction positively responded to increased rainfall, but that fluctuations were much greater in the stream that contains crayfish. We suggest that rainfall patterns help explain invasive crayfish/newt coexistence and that management for future coexistence may benefit from manual trapping.     

Effects of fertilization on population density and productivity of herbaceous plants in desert steppe

In order to investigate the impacts of fertilization on population density and productivity on herbaceous plants in desert steppe, nitrogen （N）, phosphorus （P）, and N-P addition experiments were performed. Each fertilizer treatment included four addition levels, i.e., 0, 5, 10, and 20 g/m2. The results indicated that population density decreased as fertilization levels increased regardless of the sort of fertilizer. More specifically, total density as well as density ofArtemisia capillaris, Allium polyrhizum, and Enneapogon brachystachyus decreased significantly in 20 g/m2 treated plots, as compared with the control plots. Fertilization effects on aboveground and root biomasses were extremely similar to that found in population density; that is, both total aboveground biomass and aboveground biomasses for A. capillaris, A. polyrhizum, and E. brachystachyus were negatively correlated with increasing fertilization levels, with all determination coefficients （R2） greater than 0.80. Therefore, in the case of desert regions （annual precipitation 〈180 mm）, fertilization would inhibit population density and productivity of herbaceous plants.     

Rangeland management impacts on the properties of clayey soils along grazing gradients in the semi-arid grassland biome of South Africa

The grassland biome of South Africa is a major resource for livestock farming; yet the soils of these rangelands are stressed differently by various management systems. The aim of this study was to investigate how basic soil properties respond to different management systems. For this purpose we sampled rangeland management systems under communal (continuous grazing), commercial (rotational grazing) and land reform (mixture of grazing systems) farming. Within each of these systems a grazing gradient was identified with decreasing grazing pressure with increasing distance to the water points. Results showed that communal farms with continuous grazing were generally depleted in the respective nutrient stocks. The depletion increased with rising grazing pressure. Along that line there was a breakdown of macroaggregates with losses of the C and N stored therein. However, the commercial farms also exhibited a decline of macroaggregates and their associated C content nearby the water points. Aggregate fractionation is a sensitive indicator for detecting the beginning of soil degradation in this biome; yet, degradation was less pronounced under the rotational grazing of the commercial farms than under communal property right conditions. Hence, soil analyses confirm that fences and appropriate grazing periods are needed to manage these rangelands sustainably.     

Effects of grazing and climate change on sandy grassland ecosystems in Inner Mongolia

To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northern China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land, Inner Mongolia. The results showed that sustained heavy grazing resulted in serious degradation of the vegetation; moderate grazing can maintain vegetation stabilization; and light grazing can promote rapid restoration of degraded vegetation. The livestock productivity was the highest in the moderate grazing grassland, and sustained heavy grazing resulted in rapid decrease of the livestock productivity. Heavy grazing can cause a retrogressive succession of grassland vegetation, whereas moderate and light grazing may promote progressive succession of plant species. The effects of changing climate on succession processes were not significant in the short term; a warm-humid climate is favorable to restoration of degraded vegetation, whereas a sustained warm-drought climate may result in degradation of grassland vegetation. Heavy livestock grazing should be stopped for the sustainable use of grassland; the proper grazing intensity for sandy grassland is two to three sheep or sheep equivalents per hectare in Inner Mongolia.     

Assessment of grazing effect on sheep fescue (Festuca valesiaca) dominated steppe rangelands, in the semi-arid Central Anatolian region of Turkey

In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are patterns in examined vegetation; how dominant species contribute to these patterns; and how patterns differ between grazed and ungrazed vegetation. We determined that protection from grazing increased species richness. Grazing significantly changed composition through decreasing total plant, forb, grass and F. valesiaca covers, while substantially increasing T. sipyleus cover. Topography, soil and grazing appear to impact the dominance of plant communities where F. valesiaca and T. sipyleus prevail. These two dominant species had a significant effect in shaping vegetation patterns. Based on regression analysis, alterations in species richness with changes in cover of forbs and shrubs were evident, and spatial heterogeneity of F. valesiaca and T. sipyleus indicated unstable vegetative patterns in heavily grazed pastures and successional changes in protected pastures. Our study results identify F. valesiaca and T. sipyleus as indicator species of vegetation suppression in condition assessments of degraded steppe rangelands.     

Measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north-eastern Brazil

In this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north-eastern Brazilian coast. We extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index C of high resolution QuickBird panchromatic satellite images of the dune field. We then introduce the vegetation data into a continuous model for vegetated dunes, coupling sand erosion and vegetation growth, and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes. Finally, from the comparison of both, the measurements and the simulation results, we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow-out.     

未来气候变化对7种荒漠植物分布的潜在影响

利用CART(classification and regression tree,分类和回归树)模型,采用A2和B2气候情景,分析了气候变化对百花蒿、红砂、灌木亚菊、灌木小甘菊、戈壁藜、瓣鳞花和白梭梭分布范围及空间格局的影响.结果显示:气候变化下,就目前适宜分布范围,这些植物都呈现缩小趋势;就新适宜及总适宜分布范围,...     

模拟增雨对荒漠土壤古菌多样性的影响

为探讨生长季增雨对荒漠土壤中古菌群落结构的影响,根据内蒙古磴口多年平均降水量,设计了模拟增雨试验,包括对照、2个增雨时段（生长季前期与后期）、每个时段2个增雨梯度（50%与100%）共计5种处理。增雨后提取荒漠土壤总DNA,对古菌群落编码16S rRNA基因的V4区进行Hiseq测序,分析古菌群落丰度、多样性及结构组成等。结果表明：该地区荒漠土壤中古菌群落均以奇古菌门（Thaumarchaeota）和广古菌门（Euryarchaeota）为优势菌群。NMDS和3种非相似性分析（MRPP、ANOSIM和Adonis）表明,生长季前期增雨未显著改变古菌的群落结构,生长季后期增雨显著改变了古菌的群落结构,当生长季后期增雨量达到100%时,古菌丰富度和多样性显著降低。与氨氧化过程密切相关的奇古菌门（Thaumarchaeota）相对丰度在生长季后期100%增雨条件下显著增加,将促进荒漠土壤的硝化过程。Mantel检验发现荒漠土壤古菌群落结构受土壤湿度、土壤温度、土壤硝态氮含量的影响。未来全球变化背景下降水格局变化将会对荒漠土壤古菌群落结构产生影响,并可能影响氮循环过程。     

Effects of soil surface components on soil hydrological behaviour in a dry Mediterranean environment (Southern Spain)

Various researchers have studied the spatial pattern of soil surface components such as vegetation, rock fragments, bare soil, litter and surface crusts, as a key factor of hydrological behaviour in Mediterranean settings with heterogeneous patches of vegetation cover and strong human impact. The studies indicate that there is a mosaic of patches that generate run-off or infiltrate overland flow, distributed in various ways along hillslopes. Few of these studies, however, have looked at areas underlain by metamorphic rocks such as phyllites or schists. This study analysed the temporal and spatial variability of the effects of soil surface components on hydrological processes in a small dry Mediterranean catchment underlain by metamorphic rocks. A systematic sampling of multiple sites throughout a hydrological year was carried out.We related the hydrological behaviour of soil surface components to 1) their position along the hillslope, 2) the distance of existing vegetation tussocks from the line of run-off, 3) rainfall intensity and 4) the main physical/chemical soil properties affecting infiltration processes. Statistical analysis was used to check the validity of the relationships. The results show that soil surface components have highly variable effects, in both space and time, on soil hydrological behaviour. These effects particularly depend on the location along the line of maximum slope and the intensity of preceding rainfall, whose interaction defines soil hydrological status. These results are similar to those for other Mediterranean settings with different lithology, in that the succession of contributing patches are hydrologically interconnected along a hillslope. The variables used and the grouping of explanatory variables through principal component analyses were found to be suitable for discussing the spatial distribution of soil surface components in the hydrologically dynamic environment of the study area.     

Effects of fire and environmental variables on plant structure and composition in grazed salt desert shrublands of the Great Basin (USA)

Fire in shrub-dominated portions of the Great Basin, largely fueled by non-native annuals such as Bromus tectorum, has become an important structuring force altering vegetation composition and soil characteristics. The extent to which fire affects native species in drier portions of the Great Basin, termed salt desert, is poorly documented. We conducted a survey of grazed salt desert habitat in northwestern Nevada 5 years after wildfires burned 650,000 ha, with the goal of investigating community response to fire and factors correlating with post-fire recovery. We found that recruitment of a dominant shrub, Artemisia spinescens, is severely restricted following fire: it occurred in only 2 of the 24 burned sites. The co-dominant shrub, Atriplex confertifolia, occurred in most burned sites although on average its percent cover was one-third lower than adjacent unburned sites. Biotic soil crust cover was four times lower, and non-native species cover 5 times higher, in burned sites compared to unburned. Ordination analyses confirmed differences among plant communities in burned versus unburned sites, with environmental variables soil conductivity, plant litter, soil potassium (K⁺) and pH explaining 38% of the variance in community composition. However, we found no environmental predictors of recovery for native species in burned sites. Future recruitment is likely to be further limited, as fire frequency in the salt desert is expected to increase with invasion by non-native annual grasses and with global climate change.     

利用MODIS/EVI数据分析干旱对西南地区植被的影响(英文)

2009年9月至2010年3月我国西南地区出现了有气象记录以来最严重的干旱,给当地的自然环境和生产、生活带来严重影响。本文利用多年MODIS/EVI数据求取距平植被指数来反映干旱对西南地区植被的影响。在此基础上,分析了西南地区植被受旱的时空格局及其可能影响因素。结果表明,我国西南地区植被受干旱影响的范围很大,超过地区总面积的50%,植被受旱程度时空差异显著。这种显著的差异除了受降水等气象因素影响外,还与不同植被类型对干旱的响应差异有很大关系。在西南地区三种主要的植被类型中,作物是最易受干旱影响的植被类型,草地次之,林地的抗旱能力最强。此外,植被干旱的空间分布与气象干旱也存在很大的差异,进一步证明了降水以外的其他因素对干旱程度的调节作用。研究证明与气象干旱指数相比,植被指数更能反映干旱的实际情况。但在使用植被指数衡量干旱影响时也要考虑到植被指数本身的局限性。     

Effects of an exceptional drought on daily activity patterns, reproductive behaviour, and reproductive success of reintroduced Arabian oryx (Oryx leucoryx)

Activity patterns, social behaviour, and reproductive success of Arabian oryx were monitored in a reintroduced population in Mahazat as-Sayd Protected Area, Saudi Arabia. During the first year of the study, precipitation was 38% lower than the long-term average, whereas rainfall in the following year resulted in precipitation that was 92.8% of the long-term average. These dramatically different rainfall conditions corresponded with distinct patterns in various environmental parameters (air and soil temperature, humidity, wind speed, solar radiation, air pressure). Daily activity patterns, the frequency of social behaviours, and foraging activity were significantly reduced during the drought period. The frequency of reproductive behaviour was significantly related to daytime, air temperature and radiation, with a pronounced reduction of reproductive activities during the drought. Monthly rates of conceptions were considerably lower during the drought. Our results substantiate the idea that extended dry periods affect the population development of Oryx, but also raise questions about habitat suitability and carrying capacity. Future management of Arabian oryx should consider extreme climatic events as factors influencing various aspects of the ecology and behaviour of this species. This aspect may become even more important in the face of climate change, including a future increase of extreme climatic events.