How special are Etendeka mesas? Flora and elevation gradients in an arid landscape in north-west Namibia

Seven mesas (i.e. flat-topped, isolated mountains) and the Grootberg mountain in arid north-west Namibia were investigated with regard to floristic relationships in relation to environmental gradients. Relationships between mesas and their surrounding, species richness and number of mesa specialists were used as measures to explore the influence of elevation on these floristic parameters. Also soil properties were investigated along these elevation gradients. The overall questions were designed to investigate the importance, i.e. ‘special status’, of these mesas in terms of contributing to species diversity and to elucidating ecological processes in this arid landscape.With regard to special floristic status, the tops of mesas supported different plant communities than their surrounding plains, while slopes indicated various levels of intermingling with plain vegetation. Differences between mesas and plains became more pronounced with increasing elevation. There were, however, no clear vegetation belts related to elevation. Plant species richness and number of mesa specialists showed a trend of increasing numbers with elevation, but these trends were statistically poorly supported, largely due to high variability between samples.Do soil gradients and elevation, as two important environmental variables, affect this ‘special’ status? Pronounced soil gradients were evident for many soil properties. These in combination with altitudinal effects of increased moisture and lower temperatures were believed to directly influence plant species composition and richness. The soil gradients may also indicate nutrient flow from the mesas to the surrounding lowlands, a process of ecological importance, particularly should degradation due to over grazing become a problem in the lowland areas.     

Ecological and species diversity of arid Mediterranean grazing land vegetation

This study was conducted in the arid Mediterranean Reserve located in northern Jordan, representing a continuous grazed arid rangeland ecosystem. Quantitative analyses on species diversity in addition to phytogeographical analysis were conducted. Some ecological parameters such as, life forms, growth forms, species density and frequency were investigated. A total of 93 vascular plant taxa belonging to 78 genera and 26 families were reported. This constitutes about 4.3% of the total flora of Jordan. Reported taxa include 13 species of grasses, 69 forbs and 10 shrubs and semi-shrubs. The botanical survey pointed to the presence of four rare species in Jordan. Plant species were classified into 28 functional groups. Pairwise correlation analyses among the most abundant species, showed that neutral associations dominated (75%) those communities, followed by positive associations (19%), while only (6%) showed negative association. Positive association may be attributed to direct facultative mutualism, or to physical environmental heterogeneity. Such a positive cooperation in the plant community can significantly maintain species diversity in adverse environments.The relationship between primary productivity and species richness showed a humpbacked pattern. Maximum richness corresponded to a biomass level of 300–400 g m⁻². However, a sinusoidal curve-fitting model explained the relationship between graminoids biomass and species richness. These findings pointed to the adaptation of plant taxa to livestock grazing and to the small-scale spatial and environmental heterogeneity in arid Middle Eastern Mediterranean rangelands. Results suggest that optimal biodiversity conservation for the arid Middle Eastern grazing lands should consider their high level of spatial heterogeneity. Rangeland managers should adopt grazing plans that apply a range of grazing pressure across the area so as to maintain diversity at local and regional scales.     

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?

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.     

Effects of grazing and climate change on species diversity in sandy grassland, Inner Mongolia, China

To understand the effects of animal grazing activities and climate change on sandy grassland vegetation in northern China, a field grazing and protected enclosure experiment was conducted from 1992 through 2006 in Horqin Sand Land, Inner Mongolia. The results showed that (1) the grazing was primary responsible for changes of the vegetation richness and diversity in the grazing grassland and that changing climate was the main reason for changes in the species richness and diversity in the grassland protected from grazing; (2) light and moderate grazing can promote restoration of the richness and the diversity in the degraded grassland, and heavy grazing could result in a decrease of the richness and diversity; (3) heavy grazing can result in significant decrease of the perennial diversity, and moderate and light grazing promotes increase of the perennial diversity; the grazing, whether heavy or moderate and light grazing, was beneficial to increase of the annual diversity; (4) heavy grazing was not beneficial to diversity of Graminean and Chenopodiaceae, and moderate and light grazing was favorable the diversity of Compositae and Chenopodiaceae; (5) the warm-humid climate was favorable to increase of the richness and the diversity, and the warm-drought climate could result in decease of the richness and the diversity; (6) increased precipitation was favorable to perennial diversity and the diversity of Graminean, Leguminosae, and Compositae, and decreased precipitation had few effects on the annual diversity and Chenopodiaceae diversity.     

中国植物地理学研究进展与展望

中国植物地理学从20世纪20年代初创到当前繁荣经历了100年的发展,近30年来测序技术和生物信息技术的进步,促进了分类、进化和生态等学科交叉融合,中国植物地理学在诸多方面取得了突破性进展,主要包括：① 植物类群和区系在中国整体上按纬度、经度和海拔呈现出规律性;物种丰富度、系统发生多样性和特有性热点集中分布在南部山地,少数分布在北方山地和干旱地区。② 关于大尺度植物多样性格局及形成机制,多数热带起源科的物种多样性格局受冬季低温的限制,而多数温带起源科的物种多样性格局由末次冰期以来的气候变化主导;中国山地植物和群落具有显著的垂直地带性和空间分布异质性,热量因子是中国高山植物区系地理分异的首要气候因子。③ 中国大多数现生被子植物属（约66%）是在中新世及其以后分化;500 mm年等降水线是中国植物区系年龄和植被分区最重要的分界线;中国植物区系、区系中的特征或关键类群的起源和多样化与青藏高原抬升和亚洲季风加强密切相关。未来,时间和空间的结合仍是植物地理学研究的主旋律,类群、群落和区系分化时间的估算及物种分布数据的分辨率是研究者关注的焦点,植物大数据的持续积累和完善将为学科发展提供强大动力和广阔前景。     

洪河自然保护区湿地主要植被类型物种多样性与表层土壤性质的相关性研究

对洪河湿地主要植被类型物种多样性特征、土壤性质特征及二者之间的相互关系进行了研究。结果表明:按沼泽—沼泽化草甸—湿草甸—灌丛草甸—岛状林的序列,物种丰富度呈逐渐增加的变化格局,物种多样性、均匀度呈先下降后上升的格局,优势度呈先上升后下降的格局;而土壤性质特征则呈不规则变化格局。植物物种多样性与土壤性质之间只有均匀度与速效氮之间存在着极显著正相关,其他均无显著相关。这说明在洪河湿地,土壤性质不是决定上述序列的植被类型的物种多样性的主要因素,而土壤速效氮含量是影响物种均匀度的关键因素,同时,对其他物种多样性特征也有一定影响。     

Spatio-temporal variation in soil seed banks under contrasting grazing regimes following low and high seasonal rainfall in arid Namibia

In arid rangelands, soil seed bank characteristics vary with rainfall patterns, livestock pressure and habitat heterogeneity. We investigated this issue by assessing spatio-temporal patterns in soil seed bank density and richness in a degraded (heavy grazing) and non-degraded (light grazing) Nama Karoo ecosystem. To account for variation in seed distribution, different microsites were compared, and the effect of diaspore size on the patterning analyzed. Long-term heavy grazing increased seed densities and species richness of the soil seed bank by favoring small-seeded and tiny-seeded annual species. The spatial patterning of the soil seed bank was, however, similar to that found under sustainable grazing. The overall seed distribution was dictated by the small-scale environmental heterogeneity, which interacted with diaspore size. Our results suggest that the degraded environment is still efficient in controlling secondary dispersal and retaining seeds. This is through low stature barriers like surface rocks, which replace the function of grazing-sensitive perennial grasses in trapping and storing small diaspores. Soil seed banks were persistent and accumulated readily-germinable seeds over time. Observed temporal pattern across the study sites indicates that both condition and sequence of preceding rainfall seasons are likely to have a profound effect on soil seed banks of subsequent years.     

内陆河流域生态环境的空间分异特征

分析研究了内陆河流域气候条件,植被生态,土壤环境及水环境质量等生态环境要素的空间变异特征,探讨了流域不同地带的生态环境功能。结果表明：干旱内陆河流域气候条件,尤其是水热条件和地貌特征是植被生态,土壤环境及水环境形成与分异最主要的控制性因素,几大环境要素之间相互联系,相互制经久形成内陆流域生态环境空间带规律和生态系统功能在空间不同地带上的显著差异性,认识这种分带规律与不同区域的生态功能,是合理开发的     

Climate-induced change of environmentally defined floristic domains: A conservation based vulnerability framework

Global climate change is having marked influences on species distributions, phenology and ecosystem composition and raises questions as to the effectiveness of current conservation strategies. Conservation planning has only recently begun to adequately account for dynamic threats such as climate change. We propose a method to incorporate climate-dynamic environmental domains, identified using specific environmental correlates of floristic composition, into conservation strategies, using the province of KwaZulu-Natal, South Africa as a case study. The environmental domains offer an approach to conservation that conserves diversity under current and future climates, recognising that the species constituting diversity may change through time. We mapped current locations of domains by identifying their positions in a multi-dimensional environmental space using a non-hierarchical iterative k-means clustering algorithm. Their future locations were explored using an ensemble of future climate scenarios. The HadCM2 and GFDL2.1 models represented the extreme ranges of the models. The magnitude of change in each environmental domain was calculated using Euclidean distances to determine areas of greatest and least stability for each future climate projection. Domains occurring in the savanna biome increase at the expense of domains occurring in the grassland biome, which has significant negative consequences for the species rich grasslands. The magnitude of change maps represents areas of changed climatic conditions or edaphic disjunctions. The HadCM2 model predicted the greatest overall magnitude of change across the province. Species with specific soil requirements may not be able to track changing climatic conditions. A vulnerability framework was developed that incorporated climatic stability and habitat intactness indices. The mean magnitude of change informed the potential speed of transition of domains between the vulnerability quadrants. The framework informs appropriate conservation actions to mitigate climate change impacts on biodiversity. The study explicitly links floristic pattern and climate variability and provides useful insights to facilitate conservation planning for climate change.     

水热条件共同驱动新疆湿地植物丰富度空间分布格局

在地理空间尺度上,气候因素（如热量、降水量等）一直被认为是物种多样性的主要驱动因素。然而,气候因素能否解释湿地植物多样性格局仍不清楚。研究探讨了环境因素尤其水分和热量条件对湿地物种分布的影响,具体包括经度、纬度、海拔、年平均降水量、年平均气温、年平均蒸发量和年平均日照时数总计7个指标,研究对象涉及新疆3个二级流域的26处湿地公园,应用结构方程模型分析了各指标对湿地植物丰富度影响的相对大小及其相互作用关系。另外,还利用莫兰指数（Moran’s I）对各变量残差进行了空间相关性分析,以评估空间相关性的影响。结果表明：（1）结构方程模型总计解释了41.8%的物种丰富度变异,以年平均降水量对物种丰富度总效应最高,为0.47,其次是年平均日照时数,为-0.42,其中年平均降水量为正效应,年平均日照时数为负效应。其他各指标对物种丰富度的效应均不显著。（2）年平均降水量对植物丰富度的影响主要表现为直接效应,占总效应的92.86%,年平均日照时数对植物丰富度的影响主要是间接效应,占总效应的54.76%。（3）空间相关性分析表明年平均降水量和年平均日照时数的残差均不存在空间相关性,莫兰指数在-0.15～...     

黑河下游尾闾区植物群落物种多样性与稳定性格局

黑河下游尾闾区作为西北干旱区典型的脆弱生态系统,其植物群落物种多样性与稳定性对维持该地区生态安全和可持续发展具有重要意义。以黑河下游尾闾区荒漠植被为研究对象,采用K-Means聚类,基于距河道距离及其对应的土壤含水量数据,将黑河下游尾闾区垂直于河道0—4 km区域可分为距河0—0.3 km（T_0-0.3）、0.3—1.7 km（T_0.3-1.7）和1.7—4.0 km（T_1.7-4.0）3个距离梯度,研究不同距离梯度下植物群落物种组成、多样性和稳定性特征,并进一步探讨了黑河下游尾闾区主要植物最适宜土壤水分需求。结果表明：（1）近河0—0.3 km区域以耐湿耐盐碱的草本为主,优势种为芦苇（Phragmites communis）、盐爪爪（Kalidium foliatum）、苦豆子（Sophora alopecuroides）和冰草（Agropyron cristatum）;距河道0.3—1.7 km区域出现的植物种类数目最多,以乔木为主,兼有灌木和草本,优势种为柽柳和胡杨;距河道1.7—4.0 km区域出现的植物种类数目最少,以极耐旱的灌木和亚灌木等荒漠植被为主,优势种为红砂（Reaumuria songarica）和梭梭（Haloxylon ammodendron）。（2）3个距离梯度下Simpson指数、Pielou指数、Shannon-Wiener指数和丰富度指数R均表现为距河0.3—1.7 km>0—0.3 km>1.7—4.0 km,而植物群落稳定性与物种多样性间呈现出相反的变化趋势,即群落稳定性表现为距河1.7—4.0 km>0—0.3 km>0.3—1.7 km。（3）当黑河下游尾闾区距河0—0.3、0.3—1.7 km和1.7—4.0 km区域植被最适宜土壤含水量分别为27%—31%、15%—22%和4%—7%,有利于维持该区域植物群落物种多样性与稳定性。     

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...     

土地覆被变化与管理对土壤动物群落演变的耦合效应

以黑河中游人工绿洲边缘天然草地及其转变的人工梭梭灌木林（21 a）、人工杨树林（28 a）、人工樟子松林（33 a）和农田（开垦27 a和100 a）为研究对象,基于6种研究样地中小型土壤动物群落的调查数据,采用多变量排序和通径分析等方法,研究了土地利用/覆被变化与管理措施对中小型土壤动物群落及其主要类群演变的耦合效应。主要结果是:①将天然草地转变为未实施管理措施的人工梭梭灌木林后并未引起土壤动物群落组成、数量和物种多样性的显著变化,而转变为实施管理措施的杨树和樟子松人工林及农田后,导致了土壤动物群落组成、数量和物种多样性的变异,证实了土地覆被变化对中小型土壤动物群落的作用及其效应受管理措施的强烈调控。②土壤动物群落的演变过程受土地覆被变化与灌溉和施肥管理的共同影响,其中灌溉的贡献率最大,是关键驱动因子。③不同土壤动物类群对土地覆被变化和管理耦合作用的响应不同。灌溉对跳虫、甲螨和革螨的个体数量和物种丰富度的直接影响和总效应最大;施肥对辐螨的个体数量和物种丰富度的直接影响和总效应最大;灌溉和施肥对稀有类群的个体数量和物种丰富度的直接影响和总效应均较大,具同等重要的作用。结论是,土地覆被变化与管理耦合作用通过改变土壤水文和生态环境条件驱动了中小型土壤动物群落的演变过程。     

古尔班通古特沙漠纵向沙垄植被空间异质性

在古尔班通古特沙漠南部纵向沙垄上按5 m×10 m的网格测度植被样方100个,采集浅层风沙土样品184件。调查发现,乔灌木层片和草本层片的分布及相互关系明显受沙垄地形影响,并且在干旱环境下种群间的竞争和空间上的互补使两层片生态优势度具有显著的相关性。地统计分析结果显示,纵向沙垄上植被空间异质性表现为木本层片的物种多样性呈斑块状分布,草本层片物种多样性呈现平行沙垄的带状结构和斑块结构叠加的特点,而植被盖度则在垂直沙垄走向的方向上具有强烈的梯度性变化。和沙垄土壤理化性质空间格局特征相对比,植被盖度及物种多样性与风沙土浅层含水量在自相关空间（变程）及空间异质性程度上比较接近。这是纵向沙垄小生态系统中草本植物和浅层土壤水分耦合关系在空间上的反映,也是木本植物对水分和土壤资源在小尺度（m）上竞争及中小尺度（10～100 m）上互补的结果。     

Microfungal community associated with rhizosphere soil of Zygophyllum qatarense in arid habitats of Bahrain

Population density and species diversity of microfungal communities were investigated in the rhizosphere soil of the halophytic plant Zygophyllum qatarense inhabiting saline and nonsaline habitats of the arid desert environment of Bahrain. Unlike the nonsaline habitat which is situated in the physiographic zone of multiple escarpment and backslopes, the saline site is located in the coastal lowlands and is featured by high chloride content, electrical conductivity, total soluble salts and low organic matter. Soils of both habitats are sandy, slightly alkaline, poor in nutrient sources, low in water-holding capacity and mainly dominated by a salt-tolerant flora. Quantification of data for the recovery of fungi were based on colony identification and counts by a series of ten-fold dilutions plate method, using various natural, synthetic and selective media. A total of 2780 isolates, fluctuating between 25 and 1109 per sample, were recovered during the present study among all habitats, seasons and plant sizes. Grouping of these isolates has resulted in a maximum of 28 fungal taxa varied between 5 and 15 species, of which 24 were hyphomycetes, 3 ascomycetes and one was an unknown species. All the recorded species in this study, excluding the genus Fusarium, are newly reported from the arid terrestrial habitats of Bahrain. Of the encountered fungi,Cladosporium sphaerospermum was the most dominant and frequent genus, among all plant sizes, followed by Penicillium citrinam and Aspergillus fumigatus, a finding with consistent documented data from similar arid Sahara ecosystems. Examination of data, supported by analysis of relative density values, percentage recovery rates, polar ordination and diversity indices revealed that the nonsaline habitat during the dry period yielded the highest isolate frequency, species abundance, and diversity when compared with the saline habitat. Moreover, a progressive increase in colony occurrence and species diversity was equivalently associated with increment in plant size in the nonsaline habitat. Apparently, the vast majority (moderate to low occurrence class) of the reported species are rhizosphere indigenous saprophytic cellulose-decomposers, whilst the sparse taxa (high occurrence class), e.g. C. sphaerospermum, are regarded as thermo-osmotolerant. Comparison of species richness among samples suggests that small plants inhabiting nonsaline habitats during the wet and dry season were richest in species composition. It is proposed that inter- and intra-specific variation in fungal community between the above habitats reflect not only the influence of plant age and season but also extends to critical multi-soil edaphic and biotic factors involving essentially soil moisture, salinity and root growth dynamic and exudates.     

巴丹吉林沙漠南部高大沙丘包气带水分空间分布特征研究

水是影响沙漠生态系统的主要因子,决定着多年生植物的种类和数量。受恶劣的自然条件和研究手段限制,目前对沙漠地区包气带水分时空动态变化的研究相对薄弱。以巴丹吉林沙漠南部湖泊密集区为研究对象,通过随机采样和同一坡向剖面采样,综合运用DCCA和地统计学分析方法,揭示0～10 m较深层包气带沙丘水分的空间变化规律和局部控制因子对包气带水分的影响。结果表明,0～10 m沙丘包气带水分变化曲线呈指数、对数和对数正态分布3种类型,分别受地下水或下伏黏土层的毛管作用、湖心距和综合地形因子控制;影响沙漠包气带水分空间变化的主要局部控制因子与小流域的研究结果差异显著。地形、植被等局部控制因子影响对数分布型包气带水分的深度为表层1 m,而影响对数正态分布型的深度为3～4 m;沙丘水分随相对湖面高程空间变化差异显著,而空间相关距离则不显著。     

湖南省种子植物物种丰富度与地形的关系

为探讨区域尺度物种丰富度与地形的关系,利用湖南省地方植物志资料和地形图,借助GIS软件等手段,在定量分析湖南省地形的海拔分异特征的基础上,研究了湖南省种子植物的物种丰富度和物种密度沿海拔梯度的变化趋势,以及他们与地形复杂度的关系,得到如下结果：(1) 随着海拔的升高,科、属、种丰富度和物种密度均呈现先增大后减小的趋势,也即物种丰富度和物种密度均在中海拔地区达到最高;(2) 随地形复杂度的增加,物种丰富度和物种密度呈现先增大后减少的趋势,即中等复杂程度的地形,具有较高的丰富度和物种密度。     

岷江干旱河谷豆科植物多样性及其空间格局

为研究岷江干旱河谷的豆科植物物种多样性及其在纬度和海拔梯度上的分布格局,在从四川汶川到松潘的干旱河谷两岸选择了7个地点,通过204个样方 (2 m×2 m) 调查,分析了不同纬度和海拔豆科物种组成、高度、盖度与根系结瘤的空间分布特点.结果表明:(1) 在所有样方中共出现乡土豆科植物16属,38种,其中灌木7属19种;草本植物7属17种,1或2 a生草本 6种,多年生草本11种.仅刺槐 (Robinia pseudoacacia L.) 和葫芦巴 (Trigonellae foenum-graecum L.) 为栽培物种.灌木在该地区豆科植物中占较大优势,50%以上灌木的频度与盖度均＞10%,尤其白刺花 (Sophora davidii)、小马鞍羊蹄甲 (Bauhinia brachycarpa var.microphylla)、岷谷木蓝 (Indigofera lenticellata) 等灌木频度＞20%,而所有草本植物的频率及盖度都＜10%. (2) 豆科植物丰富度及生长具有较为明显的空间差异,干旱河谷核心地区的干热、贫瘠环境中,总物种丰富度较高,但是其盖度与高度较小.随着纬度升高,灌木丰富度和频度均减少,草本丰富度与和频度增加.随着海拔上升,灌木丰富度与总物种丰富度都减小,草本植物丰富度变化不明显;植物平均高度与盖度高度也无明显的垂直变化规律.(3) 植物根系结瘤能力很低,66%物种未结瘤,并且幼苗结瘤能力显著大于成株.这一结果可为豆科植物资源的保护和开发利用提供科学依据.     

科尔沁沙地草地植被对围封和放牧的响应

研究了科尔沁沙地疏林草地、针茅草原和草甸植被盖度、地上和地下生物量、物种多样性对围封和放牧的响应。结果表明：（1）围封与放牧草地的优势植物不同,围封草地植物群落优势植物为多年生禾本科植物,放牧草地中一年生植物和小半灌木优势明显。（2）围封和放牧草地的植物盖度、凋落物量、地上生物量和物种丰富度存在明显差异（P<0.05）;围封显著提高了植被盖度和地上生物量,由疏林草地、针茅草原到草甸,植物盖度和地上生物量逐渐增加,而3种草地植被凋落物量大小顺序为针茅草原> 疏林草地> 草甸;放牧条件下植物盖度、凋落物量和物种丰富度差异不显著（P>0.05）。（3）3种草地之间的地下生物量无显著差异（P>0.05）,但围封与放牧之间、不同土壤层次之间地下生物量存在明显差异（P<0.05）;围封显著提高草地的地下生物量（P<0.05）;草地地下生物量随着土壤深度表现出下降趋势（P<0.05）。长期放牧增加了草地一年生植物和小半灌木植物的优势,消除了不同草地之间植被盖度和物种丰富度的差异;而围封能提高草地多年生禾本科植物的优势、增加其物种丰富度,对于草地质量和植物多样性的恢复和保育具有积极作用。