Interannual and seasonal variations in energy and carbon exchanges over the larch forests on the permafrost in northeastern Mongolia

The larch forests on the permafrost in northeastern Mongolia are located at the southern limit of the Siberian taiga forest, which is one of the key regions for evaluating climate change effects and responses of the forest to climate change. We conducted long-term monitoring of seasonal and interannual variations in hydrometeorological elements, energy, and carbon exchange in a larch forest (48°15′24′′N, 106°51′3′′E, altitude: 1338 m) in northeastern Mongolia from 2010 to 2012. The annual air temperature and precipitation ranged from −0.13 °C to −1.2 °C and from 230 mm to 317 mm. The permafrost was found at a depth of 3 m. The dominant component of the energy budget was the sensible heat flux (H) from October to May (H/available energy [R_a] = 0.46; latent heat flux [LE]/R_a = 0.15), while it was the LE from June to September (H/R_a = 0.28, LE/R_a = 0.52). The annual net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (RE) were −131 to −257 gC m⁻² y⁻¹, 681–703 gC m⁻² y⁻¹, and 423–571 gC m⁻² y⁻¹, respectively. There was a remarkable response of LE and NEE to both vapor pressure deficit and surface soil water content.     

Spatial precipitation and evapotranspiration in the typical steppe of Inner Mongolia,China – A model based approach using MODIS data

We present a simple method to derive spatial precipitation (P) and evapotranspiration (ET) for the typical steppe of the Xilin river catchment at 1 km and 8-day resolution during the main vegetation period (23 April to 28 August) of 2006. The hydrological model BROOK90 was parameterised from eddy covariance measurements. The daily model input data, precipitation, minimum (Ta_min) and maximum air temperature (Ta_max), were derived by manipulating MODIS leaf area index (LAI) and surface temperature data. P was estimated based on a linear regression of P measured at several sites against the mean gain of the MODIS LAI of surrounding 3 × 3 pixels areas (R² = 0.76). Ta_min and Ta_max were derived using a relationship between measured Ta_min and Ta_max and MODIS surface temperatures (R² = 0.92 and R² = 0.88, respectively). The mean precipitation was 145 mm; it varied between 52 mm in the north-western region and 239 mm in the eastern region. In spring, the modelled ET was low (<0.8 mm d⁻¹); evaporation dominated over transpiration and spatial differences were small. At the end of June, the mean ET reached its maximum (2 mm d⁻¹) and spatial differences were pronounced. From July on, transpiration dominated over declining evaporation, and spatial differences decreased in August.     

Moderate water supply and partial sand burial increase relative growth rate of two Artemisia species in an inland sandy land

Artemisia ordosica and Artemisia sphaerocephala seedlings were buried in sand to depths of 0, 0.25, 0.5, 0.75, 1 and 1.25 times the seedling height (H) and supplied with 2.5, 5.0, 7.5 and 10.0 mm of water every three days. For A. ordosica, the highest relative growth rate (RGR) and seedling height were achieved with 75 mm/month water supply and 0.5 H burial at 50 days, and the RGR decreased with 100 mm/month water supply. For A. sphaerocephala, the highest RGR was reached with 50 mm/month water supply and 0.5 H burial, but plants from this species had the greatest seedling height with 25 mm/month water supply and 0.75 H burial. A. ordosica and A. sphaerocephala have different proportions of their biomass in roots and shoots and thus are adapted to sandy environments in different ways. Partial sand burial significantly increased the RGR and growth height of the two Artemisia species, but complete burial lead to seedling death. Differences in the growth response to burial and moisture levels help explain why A. sphaerocephala is primarily found on drifting dunes and A. ordosica on semi-fixed and fixed dunes.     

古尔班通古特沙漠沙丘主要灌木的种群数量动态

种群数量动态的研究是认识种群的生存现状及发展动态的前提。通过对古尔班通古特沙漠固定沙丘、半固定沙丘和流动沙丘上主要固沙灌木的样地调查,分析了固沙灌木的年龄结构,建立了3种沙丘上固沙灌木的静态生命表和存活曲线。结果表明：（1）固沙灌木的存活个体数呈逐级递减的趋势,幼龄个体占有很高的比例;固定沙丘上梭梭（Haloxylon ammodendron）呈现Ⅰ型存活曲线,种群退化,白梭梭（Haloxylon persicum）呈现Ⅱ型存活曲线,种群稳定;（2）半固定沙丘上白梭梭呈Ⅱ型存活曲线,种群相对稳定;沙拐枣（Calligonum mongolicum）和油蒿（Artemisia ordosica）均呈现Ⅰ型存活曲线,种群处于退化状态;（3）流动沙丘上沙拐枣呈现Ⅲ型存活曲线,种群有较大的增长潜力,白梭梭呈现出Ⅱ型存活曲线,种群相对稳定,油蒿呈现出Ⅰ型存活曲线,种群处于不稳定的退化状态。     

Exploring the potential of perennial crops in reducing soil erosion: A GIS-based scenario analysis in southern Tuscany,Italy

Preserving soils is a major challenge in ensuring sustainable agriculture for the future. Soil erosion by water is a critical issue in the Mediterranean regions and usually occurs when high-erosive precipitation is in temporal association with poor vegetation cover and density. Modelling soil erosion risks over large spatial scales suffers from the scarcity of accurate information on land cover, rainfall erosivity and their intra-annual dynamics. We estimated the soil erosion risk on arable land in a Mediterranean area (Grosseto Province, southern Tuscany, Italy) and investigated its potential reduction as a response to the change in intra-annual distribution of land cover due to the increase of perennial forage crops. A GIS-based (R)USLE model was employed and a scenario analysis was performed by setting criteria for raising the performance of perennial forage crops. Statistical data on agricultural crops provided an insight into current intra-annual land cover dynamics. Rainfall erosivity was computed on the basis of 22-year hourly precipitation data. The model was used to: i) quantify the potential soil losses of arable land in the study area, ii) identify those areas highly affected by erosion risks iii) explore the potential for soil conservation of perennial crops, thereby enabling appropriate preventive measures to be identified. The erosion rates, averaged over an area of about 140’000 ha, are estimated to 33.42 Mg ha⁻¹ y⁻¹. More than 59% of the study area was subjected to soil losses higher than 11 Mg ha⁻¹ y⁻¹ (from moderate to severe erosion) and the highest rates are estimated for steep inland areas. Arable land with severe soil erosion rates (higher than 33 Mg ha⁻¹ y⁻¹) represent about 35% of the whole study area. The risk of soil loss by water erosion in the study area is estimated to be reduced on average by 36% if perennial crops are increased in terms of 35% of the total arable land. The soil erosion data produced compared well with the published local and regional data. This study thus provides useful preliminary information for landscape planning authorities and can be used as a decision support tool in quantifying the implications of management policies.     

Effects of simulated storm sizes and nitrogen on three Chihuahuan Desert perennial herbs and a grass

Establishment and growth of three perennial herbs and a small tussock grass were studied in an experiment that provided simulated rainfall of 6 mm week⁻¹ or 25 mm once per month and nitrogen fertilization in combination with the different simulated rainfall regimes. Wild onion, Allium macropetalum, failed to establish in plots receiving 25 mm month⁻¹ simulated rainfall. The perennial composite, Bahia absinthifolia, occurred at higher densities in plots that were not irrigated but there were no differences in biomass in any of the irrigation or fertilization treatments. Desert holly, Perezia nana, failed to establish in nitrogen fertilized plots and developed higher abundance and biomass in plots receiving 25 mm month⁻¹. Nitrogen fertilization had either no effect or an adverse effect on the perennial herbs. The tussock grass, Dasychloa pulchella exhibited highest abundance and biomass with 6 mm week⁻¹ added water plus nitrogen. Since global climate change will affect both rain storm frequency and size and atmospheric nitrogen deposition, the results of this study are applicable to understanding vegetation responses climate change.     

毛乌素沙地风沙土粒径分布特征及其影响因素

为揭示毛乌素沙地风沙土粒径分布特征,推测其影响因素,以毛乌素沙地流动、半固定和固定沙丘风沙土为研究对象,利用激光衍射技术分析其粒度组成,并计算粒度参数,解析粒配曲线,研究结果表明：（1） 毛乌素沙地风沙土优势粒径组为细砂,其平均体积含量约为29.89%～32.46%,不同类型沙丘无显著差异（P>0.05）;少数粒径组分为粗砂、黏粒和极粗砂,其中流动沙丘与半固定、固定沙丘黏粒与粗砂含量均无显著差异（P>0.05）,从半固定到固定沙丘,黏粒含量显著增加（P<0.05）,粗砂含量显著减小（P<0.05）,从流动沙丘到固定沙丘,极粗砂含量显著减小（P<0.05）。（2） 毛乌素沙地风沙土平均粒径为3.35 Φ,粒度分布集中,分选性较差,偏度状况为正偏,尖窄峰态。在沙丘固定的过程中,平均粒径与标准偏差无显著变化（P>0.05）,峰态显著变宽平（P<0.05）,半固定沙丘偏态值与其他2种沙丘相比显著偏负（P<0.05）。（3） 流动、半固定与固定沙丘跃移组分的粒径区间分别为44～435 μm、63～500 μm和31～354 μm,风沙运动在半固定沙丘中最为强烈。毛乌素沙地风沙土优势粒径组分含量主要受物源影响,少数粒径组分含量主要受沙丘流动性影响,风沙运动强度随沙丘的固定呈先增大后减小的规律。     

新疆策勒绿洲-沙漠过渡带地表沙物质理化性质空间差异

植被盖度、地形等会对荒漠区风沙土壤理化性质产生影响.对策勒自流沙前沿沿主风向到绿洲边缘的柽柳沙堆顶部、流动沙丘顶部、裸露平沙地3种地貌部位表面沙物质理化性质分析,结果表明:流动沙丘顶部沙物质平均粒径3.47～2.6 Φ,明显粗于裸露平沙地和柽柳沙堆顶部沙粒,从流沙前沿到绿洲边缘沙物质有细化趋势,流沙前沿平沙地上沙粒平均粒径比绿洲边缘裸露平沙地沙粒平均粒径粗0.44 Φ;在空间上沙物质分选系数差异不大,分选性都为中等偏上-中等;平沙地和流动沙丘顶部沙粒偏度为-0.06～0.06,相对于平均值分布近对称.柽柳沙堆顶部沙粒偏度分布在0.05～0.25,大都属于极细偏;流动沙丘顶部和平沙地沙粒都表现为中等峰态,柽柳沙堆顶部沙粒大多表现为窄峰态.柽柳沙堆顶部大部分沙物质pH为酸性,其余地貌部位沙粒都表现为碱性,3种地貌单元含盐量与地形高低关系较密切.不同地貌部位地表沙物质总盐量表现为:柽柳沙堆顶部 > 裸露平沙地 > 流动沙丘顶部,流动沙丘顶部沙粒含盐量最少,越靠近绿洲柽柳沙堆顶部沙粒总盐量愈高.     

Comparison of soil physico-chemical properties under different land-use and cover types in northeastern China's Horqin Sandy Land

The Horqin Sandy Land of northeastern China was originally a grassland with plenty of water and lush vegetation dominated by palatable grass species along with sparsely scattered woody species. However, it has experienced severe desertification in recent decades due to its fragile ecology together with inappropriate human activities. Currently, the landscape of the Horqin Sandy Land is dominated by irrigated croplands and sand dunes with different degrees of vegetation cover, as the region has become the most important part of the semiarid agro-pastoral ecotone of northern China. In this study, we compared soil physical and chemical properties under different land-use and cover types (irrigated cropland, rainfed cropland, sandy grassland, fixed dunes, and mobile dunes). We found that soil particle size distribution; organic C, total N, and total mineral element, microelement, and available microelement and nutrient contents; pH; CEC; and bulk density differed significantly among the land-use and cover types. In general, soil quality was highest in the cropland, intermediate in the sandy grassland, and lowest in the dunes. The most important soil quality attribute, soil organic carbon (SOC) storage, decreased in the following order: irrigated cropland (5,699 g/m²) > sandy grassland (3,390 g/m²) > rainfed cropland (2,411 g/m²) > fixed dunes (821 g/m²) > mobile dunes (463 g/m²). SOC was significantly positively correlated with a large proportion of the other soil physico-chemical parameters. Our results suggest that the key issue in restoration of the degraded soils will be to increase SOC storage, which would also create a high potential for sequestering soil C in desertified areas of the Horqin Sandy Land.     

Millet (Pennisetum typhoides) yield and selected soil attributes as influenced by some tree types of the semi-arid tropics of Sudan

Two experiments were conducted in southern Kordofan State to determine the influence of Acacia senegal L., Balanites aegyptiaca L. and Azadirachta indica L. on millet (Pennisetum typhoides) yield, soil quality and to monitor decomposition and nutrients release from tree litters. Yield under A. indica (174.83 kg ha⁻¹) and B. aegyptiaca (173.09 kg ha⁻¹) were significantly higher than the control (121.43 kg ha⁻¹). The lowest yield (111.04 kg ha⁻¹) was recorded under A. senegal. Straw dry matter under B. aegyptiaca (1161.5 kg ha⁻¹) and A. indica (857.8 kg ha⁻¹) was significantly higher than both under A. senegal (321.8 kg ha⁻¹) and the control (454.8 kg ha⁻¹). Trees varied in their capacity to induce changes in soil properties whereas effects on soil N were not substantial. A. indica had a decomposition rate (0.6283 week⁻¹) 2.0 times higher than that of B. aegyptiaca (0.2057 week⁻¹) and A. senegal (0.267 week⁻¹). The highest rate of P and K release from A. indica and B. aegyptiaca litters has resulted in significant accumulation in the soil indicating these tree litters are potential sources for these elements. The capacity of trees to improve soil fertility could offer an alternative management system for improved cultivation of field crops.     

腾格里沙漠不同类型沙丘土壤水分含量与地形-植被因子关系研究

土壤水分是沙区主要的生态限制因子,其分布受气候、地形和植被等众多因素的影响。以腾格里沙漠沙坡头地区3种类型的沙丘（固定沙丘、半固定沙丘和流动沙丘）为研究对象,利用方差分析和冗余分析（RDA）等方法对沙丘不同部位和不同深度土壤水分的分布特征及其与地形-植被因子之间的关系进行了综合分析。结果表明：（1） 不同类型沙丘上0~300 cm的土壤水分随着深度的增加而增加,表层土壤水分的波动程度大于中层和深层。（2） 固定沙丘不同部位及不同深度的土壤水分之间没有明显的差异,半固定沙丘和流动沙丘迎风坡与丘底的土壤水分高于背风坡和丘顶。（3） 固定沙丘上的土壤水分受地形-植被因子的影响较半固定沙丘和流动沙丘小,影响固定沙丘土壤水分的主要因子有坡向、高差和灌木多度。（4） 地形-植被因子与研究区绝大多数半固定沙丘和流动沙丘的土壤水分均有负相关关系。研究揭示了腾格里沙漠土壤水分的分布规律及其与地形-植被因子的关系,对制定相应的防风固沙措施以及建立科学合理的植物固沙模式有积极的指导作用。     

Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.     

Nitrogen deposition effects on tissue chemistry and phosphatase activity in Cladonia foliacea (Huds.) Willd., a common terricolous lichen of semi-arid Mediterranean shrublands

In this article we evaluate the potential use of Cladonia foliacea tissue N content, C:N ratio, and phosphomonoesterase (PME) activity as biomarkers of N deposition by means of a field experiment. In order to do this, we continuously added NH₄NO₃ to a semi-arid shrubland at four rates: 0, 10, 20 and 50 kg N ha⁻¹ yr⁻¹ starting in October 2007. Tissue N content and C:N ratios, considered as N stress indicators, significantly increased and decreased, respectively, after 1.5 years. The response found suggests N saturation above 20 kg N ha⁻¹ yr⁻¹. After 2.5 years, extracellular PME activity increased with 20 kg N ha⁻¹ yr⁻¹ and this was attributed to an induced nutritional (N to P) imbalance. Above this threshold, PME significantly decreased as a consequence of the physiological stress caused by extra N. Effects on PME were dependent on the soil properties (pH and Ca and Mg availability) experienced by C. foliacea. PME response suggests a critical load of ∼26.4 kg N ha⁻¹ yr⁻¹ (20 kg N ha⁻¹ yr⁻¹ + background) for this lichen. Further tissue chemistry and PME evaluations in C. foliacea and soil surveys conducted along wide N deposition gradients will confirm the potential use of this species as a biomonitor of N pollution and the importance of soil properties on its ability to respond to atmospheric reactive N.     

中国北方农牧交错带鄂尔多斯高原段土壤表层粒度特征

土壤粒度是描述土壤性质的重要参数,研究农牧交错带土壤表层粒度对土壤质量和沙化程度评价具有科学意义。对不同沉积物类型及土地利用方式土壤表层(0~5 cm深度)粒度进行分析。结果表明:(1)沙黄土、覆沙黄土残积物、风化残积物中粉粒最多,其次为极细砂和细砂,这3个粒级含量之和表现为沙黄土(96.51%)>覆沙黄土残积物(88.29%)>风化残积物(77.58%);风成沙土壤表层以细砂(53.85%)和中砂(26.13%)为主。(2)平均粒径由小到大依次为沙黄土(4.78Φ)、覆沙黄土残积物(4.62Φ)、风化残积物(3.80Φ)、风成沙(2.46Φ);分选性由差到好依次为风化残积物、覆沙黄土残积物、沙黄土、风成沙;偏度呈现为正偏或极正偏;峰值表明风成沙(2.30)粒径分布最为集中。(3)同一地表沉积物中,砾石和极粗砂等粗颗粒在农田较多,粉粒在草地较多,极细砂在林地较多;风成沙中,粉粒在固定沙丘略多,细砂在半固定沙丘较多,砾石、极粗砂等粗颗粒仅在流动沙丘地中分布。(4)土壤颗粒分形维数表现为沙黄土(2.5242)>覆沙黄土残积物(2.4373)>风化残积物(2.3554)>风成沙(2.2815);地表沉积物类型不同,表层土壤分形维数与粒级含量相关性有着明显差异。     

The contribution of two common shrub species to aboveground and belowground carbon stock in Iberian dehesas

Shrubs play an important role in water-limited agro-silvo-pastoral systems by providing shelter and forage for livestock, for erosion control, to maintain biodiversity, diversifying the landscape, and above all, facilitating the regeneration of trees. Furthermore, the carbon sink capacity of shrubs could also help to mitigate the effects of climate change since they constitute a high proportion of total plant biomass. The contribution of two common extensive native shrub species (Cistus ladanifer L. and Retama sphaerocarpa (L.) Boiss.) to the carbon pool of Iberian dehesas (Mediterranean agro-silvo-pastoral systems) is analyzed through biomass models developed at both individual (biovolume depending) and community level (height and cover depending).The total amount of carbon stored in these shrubs, including above- and belowground biomass, ranges from 1.8 to 11.2 Mg C ha⁻¹ (mean 6.8 Mg C ha⁻¹) for communities of C. ladanifer and from 2.6 to 8.6 Mg C ha⁻¹ (mean 4.5 Mg C ha⁻¹) for R. sphaerocarpa. These quantities account for over 20–30% of the total plant biomass in the system. The potential for carbon sequestration of these shrubs in the studied system ranges 0.10–1.32 Mg C ha⁻¹ year⁻¹ and 0.25–1.25 Mg C ha⁻¹ year⁻¹ for the C. ladanifer and R. sphaerocarpa communities' respectively.     

Tree biomass and soil organic carbon densities across the Sudanese woodland savannah: A regional carbon sequestration study

Mean tree biomass and soil carbon (C) densities for 39 map sheet grids (1° lat. × 1.5° long.) covering the Acacia woodland savannah region of Sudan (10–16° N; 21–36° E) are presented. Data from the National Forest Inventory of Sudan, Harmonized World Soil Database and FAO Local Climate Estimator were used to calculate C densities, mean annual precipitation (MAP) and mean annual temperature (MAT). Above-ground biomass C and soil organic carbon (SOC, 1 m) densities averaged 112 and 5453 g C m⁻², respectively. Below-ground biomass C densities, estimated using root shoot ratios, averaged 33 g C m⁻². Biomass C densities and MAP increased southwards across the region while SOC densities were lowest in the centre of the region and increased westwards and eastwards. Both above-ground biomass C and SOC densities were significantly (p < 0.05) correlated with MAP (r_s = 0.84 and r_s = 0.34, respectively) but showed non-significant correlations with MAT (r_s = −0.22 and r_s = 0.24, respectively). SOC densities were significantly correlated with biomass C densities (r_s = 0.34). The results indicated substantial under stocking of trees and depletion of SOC, and potential for C sequestration. Up-to-date regional and integrated soil and forest inventories are required for planning improved land-use management and restoration.     

Egg production rates of two common copepods in the Barents Sea in summer

Small copepod species play important roles in the pelagic food webs of the Arctic Ocean, linking primary producers to higher trophic levels. The egg production rates (EPs) and weight-specific egg production rates (SEPs) of two common copepods, Acartia longiremis and Temora longicornis, were studied under experimental conditions in Dalnezelenetskaya Bay (southern Barents Sea) during summer. The average EP and SEP at 5–10 °C were 4.7 ± 0.4 eggs female⁻¹ day⁻¹ and 0.025 ± 0.002 day⁻¹, respectively, for A. longiremis and 13.1 ± 0.9 eggs female⁻¹ day⁻¹ and 0.075 ± 0.006 day⁻¹, respectively, for T. longicornis. EP and SEP were significantly higher at 10°C than at 5°C for both species. The mean egg diameter correlated positively and significantly with female prosome length (PL) in each species. SEP of T. longicornis correlated negatively and significantly with PL. Daily EP and SEP were similar to rates recorded for other Acartia and Temora species in temperate and warm regions. The influence of environmental factors (temperature, salinity, and phytoplankton concentration) on EP of both species is discussed. We conclude that temperature is the main factor determining the reproduction rate and timing in A. longiremis and T. longicornis in the Barents Sea.     

Vegetation diversity and its application in sandy desert revegetation on Tibetan Plateau

The dry and cold Tibetan Plateau is, by its nature, sensitive to desertification, and now human impacts and overexploitation makes things worse. One of the most important things involved in combating desertification is to stabilize mobile sandy land and facilitate revegetation. A study was conducted on shifting sand dunes of Tibetan Plateau to investigate the relationships among sand control, vegetation restoration and diversity dynamics of seed plant species. It was found that a positive correlation lay between sand stabilizing shrubs (Caragana korshinskii and Artemisia ordosica) and Leymus secalinus, a species of dominant and perennial grass in well-restored vegetation, but a negative correlation occurred between those shrubs and Agriophyllum arenarium indicator of shifting dunes. Secondly, sand stabilization facilitated revegetation, and total cover and cover of L. secalinus rose continuously from the beginning of restoration, but diversity indices showed a complex tendency. Based on these results, it was reasoned that on alpine shifting dunes of desertified regions, continual sand drifting caused by gales was the limiting factor for plant to survival. If sand barriers were established, sand drifting would be effectively controlled, then many native plant species could colonize shifting dunes gradually, so the process of revegetation was facilitated.     

Community succession along a chronosequence of vegetation restoration on sand dunes in Horqin Sandy Land

Species diversity influences plant community structure and function. This paper examines the patterns and dynamics of species diversity along a chronosequence of vegetation recovery on sand dunes in a semi-arid region to assess the probability of vegetation recovery via succession, and provides some implications for revegetation practices in this region. Species richness and diversity indices gradually increased with succession, except for a decline in the community of 18 years, which is attributed to the strong dominance of Artemisia halodendron. In each stage of the restoration process, there was a dominant species with particular life history traits which contribute to the dominance of this species. Species replacement and habitat changes were the main drivers of succession, while plant species and community succession drove the process of vegetation recovery. Results showed that restoration via succession holds promise for vegetation recovery and desertification control within protected, fenced enclosures.     

Beach–dune interactions on the dry–temperate Danube delta coast

Beach–dune seasonal elevation changes, aeolian sand transport measurements, bathymetric surveys and shoreline evolution assessments were used to investigate annual and seasonal patterns of dune development on Sfântu Gheorghe beach, the Danube delta coast, from 1997 to 2004. Dune volume increased consistently (1.96 m³ m^− 1 y^− 1 to 5.1 m³ m^− 1 y^− 1) over this 7-year period with higher rates in the southward (downdrift) direction. Dune aggradation is periodically limited by storms, each of which marks a new evolutionary phase of the beach–dune system. As a consequence of the variable beach morphology and vegetation density during a year, foredune growth occurs during the April–December interval while between December and April a slightly erosive tendency is present. The pattern of erosion and deposition shown by the topographical surveys is in good agreement with the sand transport measurements and demonstrates the presence of a vigorous sand flux over the foredunes which is 20–50% smaller than on the beach. This high sand flux, due to low precipitation and sparse vegetation cover, creates an aerodynamically efficient morphology on the seaward dune slope. The seaward dune face accretes during low to medium onshore winds (5.5–12 m s^− 1) and erodes during high winds (> 12 m s^− 1).