Boundary-based analysis for the assessment of coastal dune landscape integrity over time

Coastal dunes are transitional systems which offer manifold ecosystem services, including material and intangible benefits, whose relevance for human society has been little investigated to date. In order to plan a sustainable use of these threatened ecosystems, proper indicators to quantify ecological services and functions over time should be provided. Since the functionality of coastal dunes is affected by the specific contiguity among different dune habitat patches, in this paper we propose the use of landscape integrity, expressed by the number and length of boundary types among the aforementioned habitats, as an ecosystem functionality indicator. In particular, we aim at properly expressing the trend of coastal dune mosaic integrity in two Italian LTER sites over the last sixty years by applying a generalized diversity function on the number and length of boundary types. Such functions, unlike a traditional diversity index, allow a complete summarization of landscape diversity and structure. The proposed method has proved to be effective in the considered context, because it has adequately underlined the different landscape integrity trend recorded in the two sites. In particular, generalized diversity functions showed to efficiently express both rough and moderate anthropogenic transformations, which affected spatial heterogeneity and functionality of the considered coastal dune mosaic. Further applications at different scales and across different ecosystems are encouraged.     

Effects of dune stabilization on vegetation characteristics and soil properties at multiple scales in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however information on how dune stabilization influences vegetation and soil at different spatial scales...     

Desertification in the Eastern Province of Saudi Arabia

The problem of land degradation in the Eastern Province of Saudi Arabia is not a new phenomenon, but during the last decade it has grown to be a serious threat to the delicate desert ecosystems, and also to the urban and industrial areas, due to an increase in sand movement. The area under investigation is situated on the Gulf coast north of Jubail and is approximately 20 km in width centered along the coastline. The total area is almost 1000 km². Eight vegetation types were classified according to the dominant and co-dominant species. A comparative study of the vegetation in a fenced, non-grazed area and in an open grazed area showed that the impact of grazing and recreational activities have largely reduced the value of the rangelands. The reduction in species diversity and density leads to an increase in wind and sand dynamics. Exposed roots, giant ripples, changes in the extension of inland sabkhas and new active dunes could be observed in many parts of the study area. It could be proved that most inland sabkhas in the area are pure deflational features with considerable dynamic due to the reduction in vegetation cover during the recent years. The monitoring of vegetation density was carried out during helicopter flights with the help of GPS and a video camera. Image processing on a personal computer allowed accurate calculations of vegetation density. Observations on active dune fields in the area showed that the size of the dune fields almost doubled in 15 months. Tests in small enclosures showed that there is a potential for natural recovery even in severely damaged areas. In just one year without grazing and with average precipitation there is a significant difference in vegetation cover. Strict grazing management and camping regulations are required to prevent further degradation and allow the recovery of damaged ecosystems. Community involvement and education is necessary for the development of an understanding of regulations and the need for preservation.     

中美俄加陆域碳汇对人为增温的消减贡献

作为主要的气候强迫因子,CO2与人类活动密切相关,但很多研究往往忽视了陆地生态系统碳汇对人为排放CO2增温的消减作用.俄罗斯、加拿大、中国和美国是世界上地域面积最大、且社会经济处于不同发展阶段的4个国家,将短时期内CO2排放所引起的辐射强迫进行量化分析,对于评估人为和自然因素对气候的影响非常重要.本文基于CO2同化数据...     

沙质草原灌丛沙堆研究综述

灌丛沙堆是干旱、半干旱及半湿润荒漠地区风沙流遇到灌丛阻拦而堆积形成的一种地貌形态。普遍的研究表明灌丛沙堆是伴随人类不合理的土地利用和环境的变化而出现,是土壤风蚀和土地退化的标志,也是沙漠化的一种表现形式。灌丛沙堆在我国分布范围很广,但目前研究还不够深入。笔者主要阐述了国内外对灌丛沙堆形态、沉积物、演变及其环境意义等几个方面研究所取得的进展及其存在的争议,并提出了灌丛沙堆研究的发展趋势,以期引起国内对灌丛沙堆研究的关注。     

Recovery rates of microbiotic crusts within a dune ecosystem in the Negev Desert

Despite the important role played by microbiotic crusts in desert ecosystems, data concerning their recovery rates are scarce and are mainly based on estimates that fluctuate between several years to a few hundred years. In order to study the recovery rates of microbiotic crusts inhabiting sand dunes in the western Negev Desert, Israel, annual measurements of chlorophyll, protein, carbohydrates and moss counts were carried out during 1990–1995. Measurements were taken in two pairs of plots (1.5–6.3 m²) established in each north- and south-facing aspect from which the upper 10 cm surface from one plot of each pair was removed. Recovery of the crusts was fast with surface-removed plots showing a complete recovery of chlorophyll a within 6–7 years, of protein within 6–8 years and of carbohydrates within 8–9 years. Recovery of the mosses was slightly longer at 17–22 years. The data are higher than the lower estimates of recovery but much lower than the higher estimates proposed in the literature. The data also suggest that upon prohibition of goat and sheep grazing (and consequently trampling) a relatively rapid stabilization process may take place in the north-eastern Sinai dune field.     

民勤绿洲边缘带灌丛沙丘防风作用研究

对民勤天然绿洲边缘带的固定、半固定及半流动风速灌丛沙丘实地观测表明,气流通过单个固定灌丛沙丘时,近地面平均风速降低4.4%,在965 m观测样线内降低57%,且风是连续降低的,愈靠近内侧降低得愈多,到绿洲内部农田边缘处时,平均风速仅有对照点的21%。深入了解灌丛沙丘对绿洲的防护机理,对于合理保护和恢复绿洲边缘带灌丛沙丘,避免绿洲遭受风沙侵袭具有重要意义。     

中国干旱沙区的生态重建与恢复:沙坡头站60年重要研究进展综述

中国科学院沙坡头沙漠研究试验站建站60年来,服务于国家需求,推动了沙漠科学的发展。在沙害治理、沙漠生态重建与恢复、荒漠生态系统长期生态学、沙地生态水文学\,人工植被稳定性及干旱胁迫生理生态学方面取得了重要进展\.解决了在降水量小于200 mm的干旱沙漠地区植被建设的关键技术,证实了通过人为促进生态恢复是可行的,创造了人类活动(治理和利用)与沙漠自然和谐持续发展的模式;探讨了干旱沙区土壤水循环的植被调控机理,提出了生态恢复的关键技术及其应用模式;理论上探明了人工植被稳定性维持的生态学机理,提出了荒漠系统生态恢复的理论模型;揭示了荒漠生态系统碳、氮循环及其对环境因子的响应;引领了生物土壤结皮的生理生态功能及其水文学研究;拓展了干旱逆境生理生态学的研究。沙坡头站已成为国际沙漠科学与荒漠长期生态学研究的重要平台。     

Reconstructing the geomorphic evolution of large coastal dunes along the southeastern shore of Lake Michigan

Coastal dunes are common along the eastern shore of Lake Michigan, with the most common being large (>30 m high), parabolic dunes that mantle lake terraces south of Manistee, MI. Although these dunes are an important resource in Michigan, and thus intensely managed by various state agencies, their geomorphic history is poorly understood. This study examines four sites near Holland, MI, through stratigraphic and radiocarbon analyses and is the most detailed geomorphic reconstruction conducted of coastal parabolic dunes in the region. Results from this study could benefit the environmental agencies in their management of the coastal dune ecosystem.Deposition of Eolian sand apparently began 5500 cal. years BP (i.e., during the Nipissing high stand). Most (75%) dune building occurred between 4000 and 2500 cal. years BP but was punctuated by brief periods of stability that resulted in the development of Entisols (A/C horizonation). Entisol burial occurred because the sand supply apparently increased during both the receding and rising lake levels. Subsequently, each dune stabilized for 2000 years, allowing the formation of Inceptisols (i.e., A/E/Bs/C horizonation). This interval of dune stability correlates with sites south of Holland and occurred while Lake Michigan fluctuated slowly and the beach potentially prograded. These combined variables of slow fluctuation and potential beach progradation hypothetically protected the dunes from wave erosion. Dunes near Holland became active again 1000–500 cal. years BP and grew both vertically and laterally. This activity intensified in the past 500 cal. years BP and hypothetically occurred due to recession of the lake shore such that wave erosion at the modern bluff base resumed. Results from this study indicate that coastal dunes along Lake Michigan are similar to many coastal dunes around the world, including those along the intermediate beaches in SE Australia.     

蒙古人民共和国主要生态系统类型及动态

对蒙古国自然条件的特点、生态系统的主要类型的现状及变化趋势进行了阐述,并探讨了这些变化趋势对中国相近地区的借鉴意义。     

沼泽沉积剖面特征元素比值及其环境意义——盐碱化指标及气候干湿变化

沼泽发育过程中堆积的各类沉积物真实地记录下区域环境演变与沼泽发育过程的信息。以向海沼泽湿地为研究对象,由¹³⁷Cs、²¹⁰Pb法定年实现沉积层深度坐标向年代坐标的转换,对典型沉积剖面特征元素比值进行了综合剖析。结果表明: Sr/Ba、Rb/K、(CaO+K₂O+Na₂O)/Al₂O₃等比值具有盐碱化和气候干湿变化的指示意义。该区域的盐碱化并非只发生在近几十年,而是由来已久,只是近年来人类活动促进了盐碱化进程。霍林河流域近240年来气候存在冷干-暖湿-冷干的多次波动,1880年之前气候以冷干为主,并有小幅度波动;1880年后气候开始转暖,但仍以冷暖波动振荡为主。     

Effects of sand burial on dune plants: a review

Burial of different growth stages of plants （e.g., adult plants, seedlings and seeds） is frequent in dune ecosystems. The soil micro-environment, which differs from surface conditions, influences the survival and growth of dune plants. To sum up knowledge about the survival mechanisms of plants under sand burial and to promote practical rehabilitation of dune vegetation, we reviewed relevant published literature and concluded that： （1） Focus in recent years has been on impacts of sand burial on seed germination and seedling emergence. Generally, shallow burial increased seed germination and seedling emergence, but deeper burial was negative. Buried at the same depth, large seeds showed higher germination and seedling emergence rates, attributed to larger energy reserves. （2） Survival, growth and reproduction rates of dune plants show plasticity in response to sand burial. Long-term deep burial is fatal because it creates a physical barrier which overcomes the vertical growth of plants, reduces photosynthetic leaf area, and limits oxygen availability to roots. Modest burial, on the other hand, is advantageous for growth and reproduction of many dune plants, due to protection from excessive temperature and drought. （3） There are few reports concerning effects of sand burial on plant physiology, but a limited number of studies indicate that partial burial increases water use efficiency, chlorophyll content, transpiration rate and net photosynthetic rates. The antioxidant protective enzyme system and osmolyte balance were reported to be involved in the mechanisms of dune plant resistance to burial.     

干扰对生物土壤结皮及其理化性质的影响

生物土壤结皮作为荒漠地区特殊环境的产物,具有较强的抗风蚀、水蚀功能,也是干旱荒漠地区植被演替的重要基础。随着人类活动的加剧,生物土壤结皮也受到不同类型和不同程度的干扰,主要包括放牧、火烧、车辆碾压等形式。干扰对生物土壤结皮的影响主要表现在生物土壤结皮结构及盖度的变化、土壤理化性质的改变、土壤微生物数量及活性的变化等几个方面。放牧对土壤物理性质的影响还没有一致的结论,除了干扰的程度还与土壤含水量有关系。火烧虽然改善了土壤结构,但是破坏了地表植被的盖度,而且恢复比较困难,也加速了外界侵蚀的力度,对土壤化学性质也有显著影响。机械碾压的破坏力最强,且没有任何的积极意义。     

Significance of variations in the wind energy environment over the past 50 years with respect to dune activity and desertification in arid and semiarid northern China

Climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern China. The results show that at decadal time scales, erosivity varied greatly in this region. Most of arid and semiarid northern China was characterised by environments with moderate to low wind energy. After the 1980s, the erosivity was only 20 to 50% of that beforehand, and this difference had a significant impact on the environmental changes observed during the two periods. The dune mobility index was consistent with the observed dune activity. After the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s, after which only the crests were active. Some mobile dunes that had developed at the margins of mobile deserts were replaced by semi-anchored or anchored dunes. Because most desert areas with vegetated dune systems in arid and semiarid northern China are used for farming or grazing, the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region. Desertification was controlled much more by climatic changes than has previously been acknowledged, and especially by fluctuations in wind energy.     

我国干旱区绿洲城市研究进展

绿洲城市是干旱区内部人类活动最为集中、人地关系最为敏感的区域,绿洲城市研究具有积极的理论和实践意义。本文在回顾绿洲城市研究历程和不同时期研究重点的基础上,分析总结我国干旱区绿洲城市研究中的代表性论题及其主要结论,对绿洲城市不同空间尺度的组织结构特色、绿洲城市化影响因素和机制、绿洲城市发展扩张的区域环境响应以及在水资源约束下绿洲城市发展等方面的理论和实证研究进行了概括评述。今后绿洲城市研究面临良好机遇,通过研究内容扩展、学科交叉综合、新技术方法应用等途径能够得到进一步的发展和深入。     

腾格里沙漠沙坡头地区固沙植被对生物多样性恢复的长期影响

地处腾格里沙漠东南缘的沙坡头人工固沙植被始建于1956年,46 a来不仅确保了包兰铁路沙漠地段的畅通无阻,而且对区域生态环境的恢复产生了巨大的影响,成为我国干旱沙漠地区交通干线荒漠化防治与生态恢复的成功模式。长期定位监测结果表明:人工固沙植被建立4~5 a后,沙丘表面物理结构初步得到稳定,并由大气降尘形成的无机土壤结皮逐渐演变形成土壤微生物结皮。荒漠藻类、苔藓和地衣等隐花植物在结皮层中得到了大量的繁衍:固沙植被建立46 a后出现藻类24种;苔藓仅有5 种,少于天然固定沙丘结皮上的种类,此外,地衣也在植被区发现,这说明固定沙丘景观逐渐趋于稳定的状态;相对于流沙区,固沙植被区近地面风速降低了 40%,土壤有机质含量增加了60%,其中氮、磷、钾等荒漠生态系统主要限制养分因子及土壤理化性质得到了改善,沙丘表层成土过程明显;土壤水分循环的时空变异驱动了植被的演变,为大量的草本的侵入和定居创造了条件;此外,对鸟类、昆虫和土壤动物及荒漠动物的生存产生了积极的影响。46 a后,固沙植被区共有鸟类 28 种,昆虫 50 种,动物 23种。生物多样性的恢复使原有的相对单一的固沙植被演变成一个结构、组成和功能相对复杂的荒漠生态系统。沙坡头地区生态环境在人为促进下的恢复为我国西部生态建设提供了科学依据。     

用拱棚法对极干旱区沙地水分来源的定性分析

在潜水埋深超过200 m的敦煌莫高窟极干旱沙漠区,用拱棚法和微型空气湿度监测仪对流沙水分的时空分布格局进行监测,并对水分的来源进行分析。拱棚膜面凝结水分的持续抽取表明,在典型干旱气候条件下,有源源不断的沙地水分蒸发,其中1.25 g·m-2·d-1的水分在膜面凝结。沙地水分的时空动态分布格局表明,存在水分向上运移的温湿度条件。由此判定,除降水之外地下潜水蒸发是沙地水分最基础的来源。实验表明,干沙层虽然对沙地水分蒸发具有极强的抑制作用,但在升温过程中仍存在水分蒸发;在降温过程不但可从下层流沙吸收大量的水分,而且可吸收大气水分。沙地的蒸发量大于来自大气的吸湿量,总有少量的水分流失。沙地水分潜水来源的确定,不但对沙漠化的治理提供了新思路,而且对莫高窟文物的保护具有十分重要的意义。     

小冰期福建海岸沙丘的沉积环境

选取福建东南沿海典型海岸沙丘——东海沙丘,运用GPR（Ground Penetrating Radar）技术探测海岸沙丘内部构造,辅助天然剖面和人工探槽观测,进行系统的年代采样与OSL（Optically Stimulated Luminescence）测年,并选择物理意义明确的粒度参数作为主要环境代用指标,获得了亚热带季风区砂质海岸带典型海岸沙丘的沉积年代和沉积结构。结果表明：（1）东海沙丘是由若干灌丛沙丘组成的横向沙丘,0～6 m主要是～0.45 ka BP以来形成的海岸风成沙丘,可以划分为～0.45 ka BP和0.22～0.12 ka BP两个阶段。（2）东海沙丘沉积过程是多因素共同作用的结果,冷干的气候环境是沙丘发育的适宜条件,入境台风频率增加可能加快了风沙的沉积过程。对比历史文献资料发现,气候异常期往往与社会动荡期、重要历史事件相对应。     

Nitrogen limitation in arid-subhumid ecosystems: A meta-analysis of fertilization studies

Evidence supporting water limitation in arid-semiarid ecosystems includes strong correlations between aboveground net primary production (ANPP) and annual precipitation as well as results from experimental water additions. Similarly, there is evidence of N limitation on ANPP in low precipitation ecosystems, but is this a widespread phenomenon? Are all arid-semiarid ecosystems equally limited by nitrogen? Is the response of N fertilization modulated by water availability?We conducted a meta-analysis of ANPP responses to N fertilization across arid to subhumid ecosystems to quantify N limitation, using the effect-size index R which is the ratio of ANPP in fertilized to control plots. Nitrogen addition increased ANPP across all studies by an average of 50%, and nitrogen effects increased significantly (P = 0.03) along the 50-650 mm yr⁻¹ precipitation gradient. The response ratio decreased with mean annual temperature in arid and semiarid ecosystems but was insensitive in subhumid systems. Sown pastures showed significant (P = 0.007) higher responses than natural ecosystems. Neither plant-life form nor chemical form of the applied fertilizer showed significant effects on the primary production response to N addition. Our results showed that nitrogen limitation is a widespread phenomenon in low-precipitation ecosystems and that its importance increases with annual precipitation from arid to subhumid regions. Both water and N availability limit primary production, probably at different times during the year; with frequency of N limitation increasing and frequency of water limitation decreasing as annual precipitation increases. Expected increase N deposition, which could be significant even in arid ecosystems, would increase aboveground net primary production in water-limited ecosystems that account for 40% of the terrestrial surface.     

Elongation and migration of sand dunes

Two distinct processes are known to act on dynamic dunes, the process of migration by erosion on the windward side and deposition on the lee side, typical for transverse dunes, and the process of elongation typical for linear dunes. These two processes are determined by wind direction relative to the dune alignment. This article reviews the assertion that linear dunes experience lateral displacement in addition to elongation. Fieldwork on vegetated linear dunes (VLDs) and GIS work on seif dunes indicates no lateral migration for these dunes. Linear dunes can shift laterally only when a slip face, formed on the lee side, reaches the plinth of the dune. The winds from both sides of the seif dune are never symmetric; usually winds from one direction are more dominant and effective. The outcome is the formation of peaks and saddles along the dune. The strongest winds create a slip face on the lee side of the peak segments of the dune, oblique to the dune alignment, which reaches the base of the dune and displaces the peak downwind along the dune alignment. The internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally. On the other hand, there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes. In such cases, both processes act on the dune, which subsequently experiences migration as well as elongation.