The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches, which eventually lead to habitat fragmentation. The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood. To fill this knowledge gap, we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m² in a desertified grassland of the Horqin sandy land, Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches. Species composition and density of soil seed bank as well as aboveground vegetation composition, abundance and coverage were investigated. We then determined their relationships with in-situ habitat characteristics. Our observations showed that the studied area had low soil seed bank density and species richness, as well as depauperate soil seed bank communities. Consequently, local soil seed bank was not able to provide sufficient seed source for natural regeneration. This was indicated by the relationships between aboveground vegetation, soil seed bank and the in-situ habitat characteristics. For bare patches with an area between 300 m² and 900 m², increase the soil seed bank density and species richness should be the main restoration measures. For bare patches with a small area of less than 50 m², restoration of vegetation density should be the main measure. Our data highlighted that different extents of desertification, indicated by different bare patches, are requiring distinct restoration measures.     

半隐蔽式沙柳沙障的防风阻沙效益

对毛乌素沙地15,25和35cm的3个高度,1m×0.5m,1m×1m,1m×2m,2m×2m,2m×3m5种规格的半隐蔽格状沙柳沙障内近地表风沙流的活动过程进行了对比研究,分析了不同规格沙障的防风阻沙效益。结果表明,设置沙柳沙障后地表土壤中细粒物质含量明显增加;与裸沙丘相比,沙柳沙障内的相对输沙率明显减少。根据当地的自然条件和经济状况,认为毛乌素沙地适宜于当地铺设的沙柳沙障规格为2m×2m。     

流动沙丘造林对土壤物理组分有机碳分配的影响

(1)根据中国知网(CNKI)的《中国学术期刊影响因子年报(自然科学与工程技术.2010版)计量指标统计表》,《水土保持通报》综合统计源统计的总被引频次为3 446次(2009年版中为1 358次);复合影响因子为0.955;期刊综合影响因子为0.568(2008年为0.493),在所统计     

库布齐沙漠植被恢复对风沙土壤碳通量与碳储量的影响

为阐明库布齐沙漠植被恢复过程中土壤碳通量的时空动态特征及主控因子，明确土壤有机碳含量和储量的变化趋势，本研究以流动沙地、半固定沙地、藻结皮固定沙地和地衣苔藓混合结皮固定沙地为研究对象，运用静态暗箱–气相色谱法对风沙土壤碳通量及水热因子进行观测，并对土壤有机碳含量和密度进行测定和计算。结果表明，生长季内风沙土壤碳通量变异较大，季节动态与土壤温度基本一致，且随植被恢复碳通量呈递增趋势：混合结皮固定沙地(210.28 mg/(m~2·h))>藻结皮固定沙地(177.45 mg/(m~2·h))>半固定沙地(117.34 mg/(m~2·h))>流动沙地(65.61mg/(m~2·h))；土壤碳通量与各层土壤温度均显著正相关，除流动沙地土壤碳通量与深层土壤含水量显著负相关外，其余样地碳通量均与表层土壤含水量显著负相关；风沙土壤有机碳含量和密度随植被恢复而递增：混合结皮固定沙地(1.32 g/kg,0.94 kg/m~2)>藻结皮固定沙地(1.03 g/kg,0.74 kg/m~2)>半固定沙地(0.45 g/kg,0.36 kg/m~2)>流动沙地(0.27...     

Gully erosion,land use and topographical thresholds during the last 60 years in a small rangeland catchment in SW Spain

Gully erosion plays an important role in degradation processes of Mediterranean environments. In this paper aerial orthophotographs were used for (i) analysing the evolution of a valley bottom gully and its relation with land use and vegetation cover, (ii) exploring the role of land use and vegetation cover on the coefficients of the equation S = aA ^−b (where S is slope at the headcut and A is drainage area), which is based on the topographical threshold concept and is commonly used to predict gully initiation. The study was carried out in a small catchment (99·5 ha) located in the southwest of the Iberian Peninsula. Gullies and headcuts were mapped together with land use and vegetation cover using aerial photographs for the years 1945, 1956, 1989, 1998, 2002 and 2006, which had to be digitized and orthorectified in advance. The results showed an increase of the area affected by gullying from 695 m² in 1945–1009 m² in 2006, reaching a maximum of 1560 m² in 1956. Gullying was closely related with land use, especially with the amount of cultivated areas within the catchment and also with grazing intensity. No clear relationship was found between the evolution of the gullied area and rainfall amounts. Finally, the values of the exponent b obtained for different headcuts and different dates (close to 0·4) were similar to those proposed by other authors for gully erosion caused by Hortonian overland flow in semiarid environments. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of sediment connectivity from vegetation cover and topography using remotely sensed data in a dryland catchment in the Spanish Pyrenees

Purpose

Many Mediterranean drylands are characterized by strong erosion in headwater catchments, where connectivity processes play an important role in the redistribution of water and sediments. Sediment connectivity describes the ease with which sediment can move through a catchment. The spatial and temporal characterization of connectivity patterns in a catchment enables the estimation of sediment contribution and transfer paths. Apart from topography, vegetation cover is one of the main factors driving sediment connectivity. This is particularly true for the patchy vegetation cover typical of many dryland environments. Several connectivity measures have been developed in the last few years. At the same time, advances in remote sensing have enabled an improved catchment-wide estimation of ground cover at the subpixel level using hyperspectral imagery.

Materials and methods

The objective of this study was to assess the sediment connectivity for two adjacent subcatchments (~70 km²) of the Isábena River in the Spanish Pyrenees in contrasting seasons using a quantitative connectivity index based on fractional vegetation cover and topography data. The fractional cover of green vegetation, non-photosynthetic vegetation, bare soil and rock were derived by applying a multiple endmember spectral mixture analysis approach to the hyperspectral image data. Sediment connectivity was mapped using the index of connectivity, in which the effect of land cover on runoff and sediment fluxes is expressed by a spatially distributed weighting factor. In this study, the cover and management factor (C factor) of the Revised Universal Soil Loss Equation (RUSLE) was used as a weighting factor. Bi-temporal C factor maps were derived by linking the spatially explicit fractional ground cover and vegetation height obtained from the airborne data to the variables of the RUSLE subfactors.

Results and discussion

The resulting connectivity maps show that areas behave very differently with regard to connectivity, depending on the land cover and on the spatial distribution of vegetation abundances and topographic barriers. Most parts of the catchment show higher connectivity values in August as compared to April. The two subcatchments show a slightly different connectivity behaviour that reflects the different land cover proportions and their spatial configuration.

Conclusions

The connectivity estimation can support a better understanding of processes controlling the redistribution of water and sediments from the hillslopes to the channel network at a scale appropriate for land management. It allows hot spot areas of erosion to be identified and the effects of erosion control measures, as well as different land management scenarios, to be studied.     

甘肃秦王川灌区种植豆禾混播牧草的农田生态保育效应

以裸地(CK)、种植小麦(Triticum aestivum)和苜蓿/无芒雀麦(Medicago sativa/Bromus inermis)豆禾混播牧草地为研究对象,通过测定地表植被特征指标、土壤风蚀量及理化性质等指标,探究秦王川灌区农田风蚀规律及种植春小麦和牧草对土壤及养分流失的影响。结果表明:农田表土损失呈秋末冬初流失较多,冬季较少,春季又明显增强的"U"形曲线模式,从9月至翌年6月,出现2个风蚀高峰期(9—11月和3—5月);耕地裸露造成表土年均流失1.7 kg/m~2,即每年被风吹蚀1.3 mm厚表土,土壤有机质损失236.2 kg/hm~2,而种植小麦和牧草后在地表植被(根茬)覆盖作用下表土流失减少20.1%和52.3%,有机质损失减少12.2%和50.7%;由于风蚀季牧草植被(根茬)的盖度、高度和地表生物量均较小麦大,使得牧草地的地表粗糙度和湿度及表土(0—5 cm)含水率较小麦地高,从而造成土壤和有机质流失较小麦地少;相关和回归分析显示,地表植被特征指标与地表粗糙度和土壤含水率间呈显著正相关,而与地表土壤和有机质流失量呈极显著负相关;植被盖度每提高1%,将使表土和有机质流失减少4.1 g/m~2和59.3 mg/m~2,地表生物量每提高1 g/m~2,将使表土和有机质流失减少2.3 g/m~2和34.0 mg/m~2;春季春播小麦地的表土流失量与裸地相同,而种植多年生豆禾混播牧草可显著减少表土流失和有机质损失。综合以上,甘肃灌区农田春季播种农作物易引起土壤退化,而种植多年生豆禾混播牧草可实现农田生态保育,从而提高耕地质量和区域环境质量。     

基于土地利用/覆盖的干旱绿洲区植被覆盖度变化--以新疆生产建设兵团第八师为例

为了探讨西北干旱绿洲区土地利用/覆盖类型景观格局特征,以及不同土地利用/覆盖类型植被覆盖度变化,本文以干旱典型绿洲区新疆生产建设兵团第八师为研究区,选取2000年、2005年的Landsat TM和2010年环境一号星CCD遥感影像数据,采用室内解译与野外核查相结合,运用RS和GIS技术分析了该区域的土地利用/覆盖和景观格局变化特征,并基于土地利用/覆盖类型选取3年的MODIS数据进行了植被覆盖度变化分析。结果表明:1)该研究区主要以耕地、草地和灌丛为主,占总面积的88.9%。在自然因素和人为因素的综合作用下,干旱绿洲区土地利用/覆盖类型发生明显变化,草地和灌丛呈减少趋势,面积分别由2000年的2 603.2 km2和1 166.2 km2减少至2010年的1 677.3 km2和933.8 km2;耕地和城镇逐步增加,面积分别由2000年的2 892.8 km2和209.2 km2增加至2010年的4 038.3 km2和259.1 km2;耕地主要由草地和灌丛转化而来,城镇主要由耕地转化而来,土地利用变化整体处于不平衡发展趋势。2)研究区景观特征趋于简单,土地利用变化改变了该区域景观格局,景观多样性、均匀度减少,优势度明显增大,破碎化程度降低,生物多样性也呈向单一方向转变的趋势。3)受气候等主要因素的影响,2000—2010年植被覆盖度呈先降低后逐步升高的趋势,不同土地利用/覆盖类型植被覆盖度表现为林地耕地草地灌丛荒漠,林地、灌丛、草地和耕地植被覆盖度分别增加6.7%、38.2%、15.6%和12.3%;较高和高等级植被覆盖面积增加,中、较低和低等级植被覆盖度面积减少。4)温度一定的条件下,降雨量是影响干旱绿洲区植被覆盖变化的关键因素。该研究结果可为新疆生产建设兵团生态环境保护管理以及合理规划生产模式提供科学的参考依据。     

Recovery of plant communities on coastal sand-dunes disturbed by human trampling

The resilience of plant communities to disturbance can be characterized by the ability of species and life-forms to recover, provided that the desired degree of naturalness is present. Results of a case study in two ecological types of Danish sand dunes, the grey and the white dune, show that dominant growth morphology and initial pattern of recovery are inter-related. The propagation of above-ground organs leads to progressive lateral recovery, while subterranean proliferation by means of rhizomes leads to erratic recovery. Species behave in different ways depending on the environment, and patches of bare ground generally grow over slowly, unlike well-established patches of vegetation where environmental conditions are more suitable. Because of this change of structure, vegetation recovery is not assessable by traditional recording of individual factors such as number of species or percentage cover, and a list of the key factors involved is given. The erratic pattern of recovery of rare species stresses the importance of long-term recording of vegetation to assess recovery.     

Landsliding related to land-cover change: A diachronic analysis of hillslope instability distribution in the Sierra Norte,Puebla, Mexico

This study examines mass movement associated with land use change, particularly deforestation, from multiple perspectives. The significance of such understanding is related to the degree of impact landsliding may cause on human settlements and economic activities, and on forest ecosystems. In this paper, the distribution of hillslope instability in the Sierra Norte, Puebla, Mexico is addressed by means of a diachronic analysis, which involves the development of vegetation indexes, as well as vegetation fragmentation derived from Landsat-5 (TM) and Landsat-7 (ETM+) satellite images from 1989 and 1999, respectively. The time period was chosen to compare vegetation cover conditions prior and after the extreme October 1999 rainfall event that triggered hundreds of slope failures in the study area. Results suggested there was a significant vegetation reduction from 1989 to 1999, which was strongly expressed by an increase of 809 km² of bare surfaces. Additionally, areas with highest vegetation density (91–100%) decreased considerably, from 1245 to 363 km², resulting in a net vegetation reduction of 70%. Furthermore, it was possible to highlight that landslide concentration was much higher on surfaces that were bare and had low vegetation density (0–50%), representing 85% of hillslope instability, than on surfaces having a greater density of vegetation cover. Land use change and land degradation are precursors to environmental hazards, such as mass movement events, that pose serious threats to regional population distributions and economic vitality.     

江西省鄱阳湖湖滨沙地蔓荆的固沙效益

 研究蔓荆植物在南方风沙化土地的阻沙、固沙作用,以及对土壤理化性状改良和小气候改善等方面的影响。结果表明:蔓荆植被覆盖率为10％～20％时,风蚀模数为2万4757t/（km2·a）,植被覆盖率达到40％时,年均风蚀模数只有2920t/（km2·a）;与裸沙地比较,5年生蔓荆地0～40cm土层的有机质、全N、全K、速效K分别增加了580％、100％、28.6％、67％;对于0～20cm土层,小于0.25mm的细沙粒增加98.7％;蔓荆地可降低地表最高温度10～12℃,增加空气湿度1.2％,有利于沙地植被的恢复。     

浅谈水土保持行政复议的基本原则

浅谈水土保持行政复议的基本原则茹建峰，李文（陕西省水土保持局，西安７１０００４）水土保持行政复议是指公民、法人或其他组织对水行政主管部门或水土保持机构作出的具体行政行为不服，依法向原作出具体行政行为的上一级机关提出申请，由上一级机关对该行政行为是否合...     

Wind velocity and algal crusts in dune blowouts

In two saucer-shaped blowouts wind velocity was measured at 0.18 m height and compared to the wind velocity data from the nearest standard meteorological station at Valkenburg about 3.5 km to the northeast. In blowout 1 relative velocities are highest when the wind blows from directions between E and SSE. In blowout 2 winds blowing from directions between S and WSW are relatively stronger. In general the wind speed increases as its moves along the surface inside the blowout, because the aerodynamic roughness of the blowout surface is less than that of the surrounding area. Less important are the influence of the configuration of the terrain surrounding the blowout and the influence of the slopes within the blowout.The frequency distribution of the general wind at Valkenburg is analysed and combined with the horizontal wind velocity pattern within blowouts. A simulation model, producing the spatial distribution of the wind power shows that the prevalence of algal crusts at the SW side of blowouts agrees well with the location which reaches the lowest wind power values. In other parts of the blowouts algal crusts are damaged by moving sand at times of high wind velocity.     

甘肃省沿黄灌区春小麦与披碱草/苜蓿混播对土壤盐渍化的影响

[目的] 研究甘肃省沿黄灌区耕地撂荒、种植春播作物与豆禾混播牧草对土壤盐渍化的影响,为该区生物措施防治土壤盐碱提供科学依据。[方法] 以裸地（CK）、小麦（Triticum aestivum）、披碱草和苜蓿（Elymus nutans/Medicago sativa）混播为研究对象,测定地表植被和微环境相关指标及表土（0-5 cm）水、盐含量,分析植被与盐含量间定量关系。[结果] 裸地盐含量全年呈W形变化,初春、夏末和秋末为3个高峰期;麦地呈U形变化趋势,高峰在初春和秋末;混播牧草地仅初春盐含量较高。秋末,麦地盐含量较裸地高18.4%,而牧草地较裸地低55.9%。对比2 a 3月的土壤盐含量,裸地和小麦地分别提高了23.7%和14.8%,而牧草地却降低了28.2%。植被特征指标与表土盐含量间呈极显著负相关（p<0.01）,其中植被盖度与盐含量间相关性最强（达-0.916）。植被的盖度、高度和生物量每提高1%,1 cm和1 g/m²,将使表土盐含量分别降低0.031,0.139,0.014 g/kg。[结论] 甘肃省沿黄灌区耕地撂荒和种植生育期较短春播作物易造成表土积盐和引发土壤次生盐渍化危害,而种植多年生豆禾混播牧草可降低表土盐含量和预防土壤盐渍化。     

Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Application of scientific principles to sand dune stabilization in New Zealand: past progress and future needs

Sand dune management involves stabilization techniques designed to prevent erosion and deposition of sand. Recognition of the problems facing New Zealand's coastal landowners during the last century led to the development of a government sand stabilization strategy based on foredune maintenance, successional planting of the dune complex with appropriate species, and the establishment of a sequence of vegetation zones parallel to the coast. Large areas were reclaimed and converted to productive forest and farmland. A review of research and practice shows that stability of all dune land, and particularly the strip within 0·5 km of the shoreline, is dependent on the continued application of knowledge already gained. Decentralization of responsibility for problems associated with drifting sand, coupled with specific requirements of the 1991 Resource Management Act, has generated a need for the principles of sand stabilization to be understood more widely. This information must be made available to individual managers to assist their decisions about potential land-use options. © 1998 John Wiley & Sons, Ltd.     

库姆塔格沙漠及周边地表覆被变化监测

[目的]研究库姆塔格沙漠及周边区域地表覆被变化状况。[方法]通过遥感技术对库姆塔格沙漠及周边区域的地表覆被变化状况进行监测,并对该区1990年代、2000年代和2010年代的TM影像进行处理和分类,而后应用ArcGis软件对3期数据进行对比分析。[结果](1)该地区植被面积一直在增长,但仍然占很小比重,戈壁与裸地则占很大比重;(2)沙漠面积经历一个先增长后减少的过程,总体仍是增长;(3)湿地的稳定性最差,湿地的变动取决于水分的积聚与流失。[结论]人类已经着手改善该地生态环境,并取得一定效果。山地和库姆塔格沙漠南缘是绿化和防沙治沙的重点区域。     

Distribution of earthworms and influence of soil properties across a successional sand dune ecosystem in NW England

An investigation of earthworms across a sand dune system in NW England examined species distribution and abundance with respect to soil physico-chemical conditions and management. Replicated 0.1 m² quadrats were examined every 50 m along 700 m transects across areas of vegetation succession and samples were then taken every 10 m where earthworms were first encountered. A translocation of Aporrectodea longa assessed the ability of this species to live in soils with a high sand content and laboratory work examined growth, maturation and survival of this species in soils with increasing proportions of sand (0–100%). Nine earthworm species were found on the dunes, but none in yellow dunes where organic matter (OM) content was <1%. Dendrobaena octaedra and Lumbricus rubellus were located 300 m from the strand line in grey dunes with an OM content of 3.9%. Allolobophora chlorotica and Lumbricus castaneus occurred within a wet dune slack at 340 m (OM content 11%). In areas of human disturbance (dune car park), A. longa, Aporrectodea caliginosa and Lumbricus terrestris were present, and in soil below pine trees L. castaneus and L. rubellus were present in litter. Laboratory growth of A. longa demonstrated significant (p < 0.05) increases in growth (2–2.75 g) with 25 and 50% sand compared with 0, 75 and 100% over 24 weeks and a greater rate of maturation. Initial results show earthworm colonisation to be influenced by dune successional stage. Laboratory findings suggested A. longa could exist in higher sand content areas but experimental design needs development. The translocation was unsuccessful. Future investigations could examine soil properties more closely and undertake monitoring on site throughout the year.     

Impact of protection and free grazing on sand dune vegetation in the Rajasthan Desert,India

In the Thar (Rajasthan) Desert of India, sand dunes and sandy plains dominate the landscape. Livestock raising and marginal land cultivation are the main occupations. Owing to the high growth rates of human and livestock populations and a decrease in pasture area and its primary productivity, these lands bear acute grazing pressure. Average rainfall is low and vegetation growth is restricted to the short rainy season of two to four months duration. Often there are years of lower than normal rainfall. In these circumstances, fenced areas, established to stabilize formerly active sand dunes, are increasingly opened to grazing to prevent high stock mortality during droughts. This study was conducted in four fenced and one open site, representative of the region's different vegetation types and grazing pressures. The impact of 2 and 5 per cent free grazing pressure on protected sand dune vegetation density and cover was tested in the two fenced sites. The vegetation data for grazed sites are compared with those for the two ungrazed fenced (protected) and one unfenced (open) site subjected to unlimited grazing pressure throughout the year. The vegetation sampling was carried out by the qaudrat and line-transect method before and after grazing from November 1984 to October 1986. It shows a significant reduction in the density and cover of many palatable species and an increase of unpalatable plants. The effect of vegetation degradation is greater in the unfenced area. The low grazing pressure on the fenced sand dunes sites can still cause drastic changes in the vegetation density and cover. Protection resulted in reduced sand erosion and enhanced growth of palatable plants in the fenced sites under similar climatic and edaphic conditions to the unfenced sites. The grazing pressure in the unfenced areas remains high to extreme during the year, due to low land productivity and high feed demand. The regeneration rate is very slow under the constant (3rd to 5th degree) overgrazing. Low intensity grazing pressure on the fenced sites during droughts can cause heavy utilization and mortality of palatable vegetation.     

雅鲁藏布江江当宽谷区固沙措施对流沙理化性质的改良效应

[目的]分析雅鲁藏布江江当宽谷区流沙治理技术(砾石覆盖+人工植被+围封)对流沙理化性质的改良效应,为区域荒漠化治理工作提供理论指导。[方法]对比分析固沙区和流动沙丘土壤机械组成、有机质和养分等指标开展研究。[结果]采用植物和工程相结合的固沙措施,在流沙表面覆盖砾石、播种固沙植物,并对该区域进行围封后,沙丘表面植被盖度增加,流沙基本固定。与流动沙丘相比,固沙区土壤的黏粒、粉粒明显增多。固沙区土壤的有机质、全氮、碱解氮、全磷、速效磷、速效钾含量比流动沙丘高;尤其是土壤表层0—5cm,分别比流动沙丘高出634.3%,268.0%,506.5%,38.3%,343.8%,66.7%。固沙区0—5cm土层的pH值比流动沙丘降低了11.5%;电导率比流动沙丘增加了268.1%。[结论]该项流沙治理技术(砾石覆盖+人工植被+围封)的固沙和改良土壤理化性质作用明显,适宜在该区推广使用。