Is the analysis of plant community structure better than common species-diversity indices for assessing the effects of livestock grazing on a Mediterranean arid ecosystem?     

Y. Pueyo  C.L. Alados  C. Ferrer-Benimeli 《Journal of Arid Environments》2006,64(4):698-712

Grazing in arid Mediterranean ecosystems brings about changes in species diversity, but the best way to measure such changes is unclear. In this study we compared various methods in order to identify indicators that might be useful for the management and conservation of grazed arid Mediterranean ecosystems.Changes in community structure and composition were compared along a previously studied grazing gradient in Cabo de Gata-Nijar Natural Park. Plant diversity was measured by calculating diversity (Shannon information index), evenness (Pielou index) and richness (species number). Rarefaction curves were used to measure plant species richness and the results were compared with traditional richness values. Community structure was measured as the percentage of bare ground and the coverage of overall perennial grasses, Stipa tenacissima L., perennial shrubs and annual plants. Our results showed that the proportion of bare ground, the cover of perennial shrubs and the relative abundance of S. tenacissima are good indicators of grazing effects on vegetation. Overall plant community structure was more sensitive to the grazing gradient than were the diversity indices. Finally, the adequacy of standardized methods for comparing species richness (i.e. rarefaction curves) along a grazing gradient are discussed.  相似文献   

塔里木河下游不同覆盖度灌木防风固沙功能野外观测研究   总被引：8，自引：1，他引：8  

程皓  李霞  侯平  裴玉亮 《中国沙漠》2007,27(6):1022-1026

 对塔里木河下游50%、25%、10%三种覆盖度灌木降低风速观测结果表明: 50%覆盖度灌木降低风速最明显，防风效能为49.21%；25%的覆盖度灌木降低风速较明显，防风效能为24.44%;10%的覆盖度灌木对风速降低有一定作用，防风效能为9.15%。在7.7 m.s-1风速下，植被覆盖度为10%、25%的沙地输沙率分别是无植被覆盖沙地的62.44%和8.37%；在10 m.s-1风速下，植被覆盖度50%的沙地仅有轻微的风蚀。根据塔里木河下游不同覆盖度植被与降低风速之间的定量关系，得出不同风速条件下的有效植被覆盖率，在研究区常见10～15 m.s-1风速条件下，要达到有效阻沙效果，植被覆盖率应在50%以上。  相似文献   

Biomass equations for shrub species of Tamaulipan thornscrub of North-eastern Mexico   总被引：1，自引：0，他引：1  

J. Nvar  E. Mndez  A. Njera  J. Graciano  V. Dale  B. Parresol 《Journal of Arid Environments》2004,59(4):269

Nine additive allometric equations for computing above-ground, standing biomass were developed for the plant community and for each of 18 single species typical of the Tamaulipan thornscrub of north-eastern Mexico. Equations developed using additive procedures in seemingly unrelated linear regression provided statistical efficiency in total biomass estimates at the scales of both individual species and at the plant community. A single equation for each species improves efficiency in biomass estimates by 12.5% in contrast to using a single equation for the plant community. Therefore, additive equations developed in seemingly unrelated linear regression of parameter estimation are recommended to compute biomass components and total biomass for the species described.  相似文献   

灌丛对沙质草地土壤结皮形成发育的影响及其作用机制   总被引：1，自引：0，他引：1  

赵哈林  郭轶瑞  周瑞莲 《中国沙漠》2011,31(5):1105-1111

为了了解灌丛对沙地土壤结皮的影响及其作用机制, 2006—2007年在科尔沁沙地调查了灌丛群落土壤结皮的发育特征, 并进行了田间模拟降尘、添加凋落物和结皮生物接种的试验。结果如下:①大气降尘、凋落物和微生物接种均可明显促进沙地土壤结皮的形成;②湿润、遮荫环境要比干旱、光照环境更有利于沙地土壤结皮的形成,但土壤结皮形成和发育对水分的敏感程度要大于对光照的敏感程度;③灌丛的存在对于流动沙地土壤结皮的形成发育具有明显的促进作用,沙地栽植灌木后通常会产生肥岛效应,在冠层下逐步形成结皮,并由灌丛内向外扩散;④灌丛促进沙地土壤结皮发育的主要机制是灌丛具有降风滞尘、拦截凋落物、遮荫保湿的功能,能使土壤黏粉粒、有机质、土壤养分和水分含量明显增加,为结皮的形成发育创造了良好物质条件和环境条件。  相似文献   

古尔班通古特沙漠灌丛雾凇的生态水文学效应   总被引：1，自引：0，他引：1  

郑新军  李嵩  吴林峰  李彦  秦海波 《冰川冻土》2012,34(4):942-949

对生长于古尔班通古特沙漠东南边缘的梭梭和白梭梭两种植物的小枝与灌丛雾凇量进行了观测, 并结合植被调查估算这两种植物对群落雾凇量的贡献量, 探讨群落雾凇量与气象要素之间的关系.研究结果表明: 在小枝水平上, 白梭梭雾凇量是梭梭的1.5倍, 但是在灌丛和群落尺度上, 梭梭却是白梭梭的1.5和3.6倍.小枝粗细及其生长位置、 灌丛形态结构和相对种群密度的差别共同造成两种植物雾淞量不同水平的差异.积雪、 低风速、 逆温和高湿是形成雾凇的最主要原因, 日最高气温(T_ma)与群落雾凇量(Rime)相关性最显著, 它与日最小比湿(q_mi)组成的二元线性方程可以解释Rime 98.50%的变异.在观测期, 当T_ma>-11.48 ℃时, Rime随T_ma的变化率较大, 当T_ma < -11.48 ℃时, Rime随T_ma的变化率较小, 前者是后者的3.59倍.总之, 雾凇能部分补偿雪面蒸发造成的积雪量减少, 间接地保护了浅薄的地表积雪, 是古尔班通古特沙漠冬季极重要的生态水文学过程.  相似文献   

The measurement and modelling of stemflow in an alpine Myricaria squamosa community          下载免费PDF全文

Si‐Yi Zhang  Xiao‐Yan Li  Liu Li  Yong‐Mei Huang  Guo‐Qin Zhao  Hui‐Ying Chen 《水文研究》2015,29(6):889-899

Stemflow is an important hydrological process of rainfall partitioning, but it has rarely been studied in the alpine riparian shrub Myricaria squamosa in the Qinghai–Tibet Plateau. This study aimed to measure and model the stemflow of the unstudied M. squamosa and to identify the key controlling factors of stemflow yield. Correlations and stepwise regression analysis between stemflow and five meteorological and ten biological factors indicated that the rainfall amount and the aboveground biomass were the best variables for modelling and predicting stemflow. We used the best model to estimate annual and stand stemflow, as well as rainfall threshold for stemflow generation. Annual stemflow accounted for 2.3 to 10.2% of the annual rainfall amount, varying with different vegetation coverage and leaf area index. The annual stemflow percentage increased linearly with the annual total rainfall amount of events > 7.3 mm. For M. squamosa stands, branches with diameters of 10 to 25 mm were less frequent but contributed much more stemflow than branches with diameters smaller than 10 mm. The stemflow percentage increased sharply with increasing rainfall amounts when the rainfall amounts were less than 4, 8 or 13 mm for the M. squamosa stands with coverage of 32.6, 47.6 or 56.1%, respectively, but increased gently when the rainfall amounts were greater than these values. The rainfall threshold for stemflow generation decreased as the branch aboveground biomass increased, and the estimated median value of the rainfall threshold was 0.8 mm for M. squamosa stands, with a range of 3.0 to 0.4 mm for branches weighing 10 to 300 g, respectively. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

荒漠草原带沙源及灌丛对灌丛沙堆形态的影响   总被引：3，自引：0，他引：3  

谢国勋  罗维成  赵文智 《中国沙漠》2015,35(3):573-581

灌丛沙堆是干旱区一种典型的景观类型,经常出现在靠近流沙地带。在地处荒漠草原带的宁夏盐池北部的流沙边缘就发育有典型的白刺(Nitraria tangutorum)灌丛沙堆。本文对不同沙源距离和灌丛生长状况下的白刺灌丛沙堆形态特征进行了研究。结果表明:荒漠草原带白刺灌丛沙堆的高度0.2～4.8 m,90.05%的高度小于3.0 m;体积0.11～805.17 m³,6.08%的体积小于150 m³;面积0.86～333.3 m²,72.26%的小于50 m²。灌丛沙堆长轴长和短轴长、高度和面积、高度和体积、面积和体积间都存在很好的幂函数关系,随着灌丛沙堆高度的增加,其面积和体积也增加。沙源对白刺灌丛沙堆的分布特征有显著影响,灌丛沙堆的高度、面积和体积和沙源距离都有很好的抛物线形关系。白刺灌丛的生长状况对灌丛沙堆的形态特征也有明显的影响,即白刺灌丛生长状况越好,灌丛沙堆的高度、面积和体积也增大。  相似文献   

均匀配置的两种仿真灌木林防风效应野外观测   总被引：1，自引：1，他引：0  

刘虎俊  袁宏波  郭春秀  徐先英  王多泽  李学敏  刘开琳 《中国沙漠》2015,35(1):8-13

建立灌木林是一种有效的防风固沙方法,灌木林空间配置是防护林体系研究与建设取得最佳效益的关键.应用两种仿真固沙灌木,建立株行距相等的均匀配置灌木林,观测林内与林前不同风速,比较其防风效能.结果表明:在风速为4.6～10.7 m·s^-1时,侧影面积为0.25 m²的无叶仿真灌木林比侧影面积为0.39 m²的有叶仿真灌木林防风效能低10%～20%.仿真固沙灌木林风速与高度变化关系呈指数函数关系,但在风沙流中拟合系数更高.仿真固沙灌木林空气动力粗糙度平均值是流沙地的5倍多,但不同风速下的粗糙度值差异较大.对相同配置的防风固沙林,调节灌丛结构可以提高其防风固沙效能.  相似文献   

Age of the Jombolok lava field (East Sayan): evidence from dendrochronology and radiocarbon dating     

S.G. Arzhannikov  A.V. Ivanov  A.V. Arzhannikova  E.I. Demonterova  M. Jolivet  V.I. Voronin  V.A. Buyantuev  V.A. Oskolkov 《Russian Geology and Geophysics》2017,58(1):20-36

Dendrochronology and radiocarbon dating, with reference to remote sensing, digital elevation modeling, geological, and geomorphological data, provide new age constraints for the Jombolok lava field in the East Sayan Mountains (Siberia). The Jombolok lava field originated in the latest Late Pleistocene and underwent at least four phases of volcanic activity recorded in lava flows. Two earliest phases followed shortly one after another more than 13 kyr ago. The third phase corresponding to eruptions of Kropotkin volcano can be timed only relatively. The fourth phase has been dated by dendrochronology and AMS ¹⁴C of well-preserved wood buried under the youngest lava which occurs among older lavas near the Jombolok River mouth. The age of this activity is bracketed between the death of trees caused by eruptions 1268-928 years ago and the beginning of new tree growth on the surface of the most recent lavas 900 years ago.  相似文献   

西鄂尔多斯地区5种荒漠优势灌丛生物量分配格局及预测模型     

党晓宏  高永  蒙仲举  高君亮  王珊  包蕾  余新春  王祯仪  王则宇 《中国沙漠》2017,37(1):100-108

以西鄂尔多斯地区5种荒漠优势灌丛（沙冬青（Ammopiptanthus mogolicus）、四合木（Tetraena mongolica）、霸王（Zygophyllum xanthoxylum）、红砂（Reaumuria songarica）、半日花（Helianthemum songaricum））为研究对象,采用平均标准灌丛全部收获法测定灌丛各营养器官（枝条、叶片、根系）生物量,并分别以丛高（H）和冠幅（C）的复合因子（CH）及基径（D）和丛高（H）的复合因子（D²H）为自变量建立单株灌丛生物量预测模型。通过决定系数（R²）、估计值的标准误差（SEE）和F检验显著水平筛选出各灌丛种最佳生物量预测模型。结果表明：（1）5种荒漠灌丛单株总生物量干鲜比差异性显著（P<0.05）,各营养器官间差异性也达到显著水平（P<0.05）;灌丛根冠比种间差异显著（P<0.05）,红砂（1.05）> 霸王（1.01）> 半日花（0.92）> 沙冬青（0.90）> 四合木（0.49）;（2）根系和枝条是荒漠灌丛生物量的主要贡献者,其生物量占灌丛总生物量比例之和均在80%以上,根系生物量分配随根系径级的增加而增加;（3）5种荒漠优势灌丛单株灌丛生物量预测模型R²值均在0.85以上,且在0.05水平上显著,生物量模型预测精度较高。  相似文献