Desert vegetation distribution and species-environment relationships in an oasis-desert ecotone of northwestern China

Environmental heterogeneity significantly affects the structure of ecological communities.Exploring vegetation distribution and its relationship with environmental factors is essential to understanding the abiotic mechanism(s)driving vegetation succession,especially in the ecologically fragile areas.In this study,based on the quantitative analysis of plant community and environmental factors in 68 plots at 10 different transects in the Minqin oasis-desert ecotone(ODE)of northwestern China,we investigated desert vegetation distribution and species-environment relationships using multivariate analysis.Two-way indicator species analysis(TWINSPAN),detrended correspondence analysis(DCA),and canonical correspondence analysis(CCA)methods were used.A total of 28 species,belonging to 27 genera in 8 families,were identified.Chenopodiaceae,Zygophyllaceae,Gramineae,and Leguminosae were the largest families.Annual and perennial herbs accounted for 28.60%of the total number of plants,while shrubs(42.90%)were the most dominant.Nitraria tangutorum was the constructive species of the desert plant community.We divided the 68 plots surveyed in this study into 7 community types,according to the results of TWINSPAN.The distribution of these 7 communities in the DCA ordination graph showed that species with a similar ecotype were clustered together.Results of CCA indicated that groundwater was the dominant factor influencing vegetation distribution,while distance between plot and oasis(Dis)and soil electrical conductivity(EC)were the local second-order factors.Our study suggests that optimizing the utilization of groundwater in oases is key to controlling the degradation of desert vegetation.The favorable topographic conditions of sand dunes should be fully utilized for vegetal dune stabilization,and the influence of soil salinity on the selection of afforestation tree species should be considered.

Implications of tree species–environment relationships for the responsiveness of Himalayan krummholz treelines to climate change

Climate warming is expected to advance treelines to higher elevations. However, empirical studies in diverse mountain ranges give evidence of both advancing alpine treelines as well as rather insignificant responses. In this context, we aim at investigating the sensitivity and responsiveness of the near-natural treeline ecotone in Rolwaling Himal, Nepal, to climate warming. We analysed population densities of tree species along the treeline ecotone from closed forest stands via the krummholz belt to alpine dwarf shrub heaths （3700-4200 m） at 50 plots in 2013 and 2014. We quantified species - environment relationships, i.e. the change of environmental conditions （e.g., nutrient and thermal deficits, plant interactions） across the ecotone by means of redundancy analyses, variation partitioning and distance-based Moran＇s eigenvector maps. In particular, we focus on explaining the high competitiveness of Rhododendron campanulatum forming a dense krummholz belt and on the implications for the responsiveness of Himalayan krummholz treelines to climate change. Results indicate that treeline trees in the ecotone show species-specific responses to the influence of environmental parameters, and that juvenile and adult tree responses are modulated by environmental constraints in differing intensity. Moreover, the species - environment relationships suggest that the investigated krummholz belt will largely prevent the upward migration of other tree constrain the future response species and thus of Himalayan krummholz treelines to climate warming.

The influence of environmental variables on distribution patterns of Irano-Turanian forests in Alborz Mountains, Iran

Topographic and edaphic variables are the main ecological factor determining species spatial variability on mountainous forests. A field study was performed in central Alborz to investigate how the edaphic and topographic parameters can affect the tree and shrub communities. Initially, 27 forest stands were identified and the homogeneous units were separated regarding physiognomy. In each single homogeneous unit, one random sample plot （1000 m^2） and totally 43 plots were established. In each plot, the presence and abundance of all trees and shrubs were recorded and four soil samples were taken from depths of 0-5 and 5-20 cm. Concerning classification results, eight different forest communities were identified. The lowest and highest soil pH values were observed in Malus orientalis and pistacia-Amygdalus communities, respectively. The water saturation percent of pure- and mixed Juniperus excelsa and Rhus coriaria was the highest amongst communities. The clay content was the highest in pure J.excelsa. The 0-5 organic matter and Nitrogen content in mixed J. excelsa were significantly higher than pure J. excelsa and other communities. The CCA （Canonical Correspondence Analysis） altitude, precipitation, pH, results indicated that the EC, SP, clay and CaCO3 are the most important factors determine the distribution of trees and shrub in central Alborz.

Gorgan Bay： a microcosm for study on macrobenthos speciesenvironment relationships in the southeastern Caspian Sea

The relationship between spatial patterns of macrobenthos community characteristics and environmental conditions（salinity, temperature, dissolved oxygen, organic matter content, sand, silt and clay） was investigated throughout the Gorgan Bay in June 2010. Principal components analysis（PCA） based on environmental data separated eastern and western stations. The maximum（4 500 ind./m2） and minimum（411 ind./m2） densities were observed at Stas 1 and 6, respectively. Polychaeta was the major group and Streblospio gynobranchiata was dominant species in the bay. According to Distance Based Linear Models results, macrofaunal total density was correlated with silt percentage and salinity and these two factors explaining 64% of the variability while macrofaunal community structure just correlated with salinity（22% total variation）. In general, western part of the bay showed the highest number of species and biodiversity while, the highest density was found at Sta. 1 and in the middle part of the bay. Furthermore, relationship between diversity indices and macrobenthic species with measured factors is also discussed. Our results confirm the effect of salinity as an important factor on distribution of macrobenthic fauna in south Caspian brackish waters.

驴运即人运--《环境、权力与不公》中的物种主义偏见分析

不同人群所拥有的权力真正决定着其所享用的客观环境条件,就是通过这样的机制,权力在不同种族、不同阶级和不同性别的人之间创造了现实生活中结构性的不平等、不公平,因此,权力是环境史上必不可少的考虑因素。令人意外的是,非洲土著在被殖民期间的境遇和当地的一种动物——驴子,演绎了相似的命运轨迹。他们的经历通常是:先被白人统治者借环境之由污名化、标签化,后被驱逐、强制搬迁,稍有反抗,就会被惩罚、被屠戮。驴子先是经历了各种抹黑,后遭到野蛮屠杀。间接统治手段方便白人殖民者实施暴力种族歧视行为,而当地的部族首领无力作为,又方便了白人殖民者推行自己理想化的经济模式。驴子和部族主体被虐待的原因须结合环境史史实进行透视和溯源:这是一种环境种族主义在南部非洲历史上的具体表现,而白人殖民者实施这一系列行为的背后心理逻辑动力则是其根深蒂固的物种主义偏见。

被掠夺的正义——《圆屋》的后殖民生态书写研究

美国印第安作家露易丝·厄德里克的获奖小说《圆屋》以当代印第安人遭遇的非正义现象为引,从生态的视角追溯社会问题背后的殖民历史根源,体现出鲜明的后殖民生态书写特色。小说强烈批判了以土地掠夺和动物滥杀为表现形式的环境种族主义和物种主义思维模式,反映出厄德里克作品中与日俱增的反殖民意识和生态意识,彰显其作为一名美国印第安作家为捍卫本民族家园所作出的不懈努力。

A multiscale analysis of herbaceous species richness in a Mediterranean ecosystem

Aims studies of species distribution patterns traditionally have been conducted at a single scale,often overlooking species-environment relationships operating at finer or coarser scales.Testing diversity-related hypotheses at multiple scales requires a robust sampling design that is nested across scales.our chief motivation in this study was to quantify the contributions of different predictors of herbaceous species richness at a range of local scales.Methods Here,we develop a hierarchically nested sampling design that is balanced across scales,in order to study the role of several envi-ronmental factors in determining herbaceous species distribution at various scales simultaneously.We focus on the impact of woody vegetation,a relatively unexplored factor,as well as that of soil and topography.light detection and ranging(liDAR)imaging enabled precise characterization of the 3D structure of the woody vegetation,while acoustic spectrophotometry allowed a particularly high-resolution mapping of soil CaCo3 and organic matter contents.Important Findings We found that woody vegetation was the dominant explanatory variable at all three scales(10,100 and 1000 m2),accounting for more than 60%of the total explained variance.in addition,we found that the species richness-environment relationship was scale dependent.many studies that explicitly address the issue of scale do so by comparing local and regional scales.our results show that efforts to conserve plant communities should take into account scale dependence when analyzing species richness-environment relationships,even at much finer resolutions than local vs.regional.in addition,conserving heterogeneity in woody vegetation structure at multiple scales is a key to conserving diverse herbaceous communities.