Characterization of spatial scaling relationships between vegetation pattern and topography at different directions in Gurbantunggut desert,China

Vegetation striped pattern is a common feature in semiarid and arid landscapes, which is seen as mosaics including vegetated and non-vegetated patches. Identifying scales of pattern in ecological systems and referring patterns to multi-scaled processes that create them are ongoing challenges. The aim of this paper is to study the vegetation patterns and their across-scale relationships between the vegetation and anisotropic topography (W–E and N–S) in 12 transects at Gurbantunggut desert. We used wavelet-based across-scale analysis for extracting information on scales of pattern for those transect data, evaluating their inherent structure, and inferring characteristics of the processes that imposed those patterns at across scales. The results show that, in W–E direction, the scales of vegetation pattern (C. ewersmanniana is at the scale 40 m, H. ammodendron, at 35 m) correspond to the dune ridge/dune valley sequences (appearing at distance of 40 m), and vegetation on mesoscale and large scale are significant cross-scale correlation with topography on mesoscale and large scale in all W–E transects. In N–S direction, there is an irregular pattern of vegetation along the N–S irregular topography, and no unified cross-scale relationships between topography and vegetation on different scales in different transects. Moreover, cross-scale correlation analysis between topography and vegetation provides further detail on hierarchical structure and specific scales in space that strongly influenced the larger patterns. Knowledge of the cross-scale relationships between topography and vegetation could lead to better understanding and management of biological resources in that region.     

红松存在/不存在数据的多尺度空间分布格局

红松属小兴安岭地区地带性植被优势种,该地区也是其分布的北缘。在景观尺度上开展红松的分布格局研究有利于进一步了解红松分布机理、未来迁移过程等问题,对其经营和保护有重要意义。将景观指数法与点格局分析法结合,设定8个空间尺度,利用红松存在/不存在数据,通过计算各空间尺度上红松聚集程度和景观指数,分析小兴安岭地区红松种群在多尺度上的分布格局。研究结果表明,小尺度上红松聚集分布明显,随机分布区多处于其聚集分布区的边缘,均匀分布区则散布在其聚集分布区内。景观指数研究表明,通过景观指数可判断红松聚集分布格局趋势,而不能判断均匀分布、随机分布格局趋势,因为它们在多尺度下景观指数波动大,不能用景观指数来描述分布格局。研究得出如下结论:1)红松主要分布在其分布区的核心区域内,在分布区边缘和过渡带上呈随机分布,2)存在/不存在数据能够用来分析种群的多尺度空间分布格局,3)空间尺度的变化会引起树种分布格局的变化,随机分布随尺度增加,边缘化程度加强,4)单一尺度上,景观格局指数不能完全描述种群分布格局;而在多尺度上,变化趋势稳定的景观指数表明聚集分布存在,而波动剧烈的景观指数常与随机分布和均匀分布联系在一起,5)地形因子中,红松对坡度和海拔两个因子变化敏感。     

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 environmental 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 CaCO 3 and organic matter contents.Important findings We found that woody vegetation was the dominant explanatory variable at all three scales (10, 100 and 1000 m 2), 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.     

Multiscale ordination: a method for detecting pattern at several seales

Multivariate analyses of vegetation data have been restricted to a single scale of sampling, or multiscale sampling has been restricted to a single species. However, vegetation scientists need to be able to explore spatial relationships of many species over many scales. We present a modification of Noy-Meir & Anderson's (1971) method of multiscale ordination by summing two-term local covariance matrices and smoothing the component profiles. The advantages of our method are: 1) results are less subject to the starting position of the transect, 2) matrices may be added at any block size, and 3) plots of factor scores are smoothed by a moving weighted average to better reveal patterns at a prescribed scale.This procedure provides statistical associations of species over a range of scales. The scales which exhibit the association to the maximum extent are then determined from multiscale ordination. The relationships of different associations and their scales can then be examined. The application of the method to fabricated data proved successful in recovering the structure built into the data. When used on real vegetation data, from a community and a landscape, the method revealed the details of species associations over a range of scales, and of the relationships among associations.Abbreviations PCA = Principal Components Analysis - DCA = Detrended Correspondence Analysis - TTLC = Two-Term Local Covariance     

塔里木荒漠绿洲过渡带主要种群生态位与空间格局分析

于新疆塔里木盆地荒漠绿洲过渡带设置3条样带(长900 m×宽50 m)进行植物群落调查,运用生态位测度指标和点格局法对种群空间格局、空间关联性及生态位特征进行研究。结果显示,胡杨(Populus euphratica Oliv.)、多枝柽柳(Tamarix ramosissima Ledeb.)和甘草(Glycyrrhiza inflate Bat.)具有较大的重要值和生态位宽度,对其它生态位较窄的物种具有资源竞争和扩张优势,生态适应能力强,对群落结构和环境变化起决定性作用;生态过渡带植物的种间生态位重叠普遍较高,尤其是草本植物间更明显,此分配格局反映出荒漠植物长期适应旱化生境而发生趋同适应,生态位分化程度低,种间资源竞争激烈;优势种群空间格局呈明显的空间变异性,0~25 m尺度内多枝柽柳和甘草分别呈随机分布和聚集分布,胡杨种群在≤5 m尺度内呈聚集分布,并随尺度增大转为随机分布;胡杨与多枝柽柳、胡杨与甘草、多枝柽柳与甘草分别在4 m、≤16 m和≤25 m尺度内呈显著空间负关联,种间相互排斥。表明在匮乏环境资源条件下植物趋同适应与资源竞争是驱动荒漠植物群落演替和限制物种共存的主要原因。     

太白山牛皮桦-巴山冷杉混交林空间格局及关联性研究

采用改进的点格局分析法——邻域密度函数（Neighborhood Density Function,NDF）对太白山地区桦林-冷杉林交错区内主要树种的空间分布格局、种间空间关联性及其更新空间关联性进行了分析。结果表明：各树种所有个体整体上都呈随机分布,划分不同层级后,则各林层个体分布格局各异,各树种在较低的林层呈明显聚集分布,随林层增高,中、高层内个体聚集分布的空间尺度降低。两个主要竞争种牛皮桦（Betula albo-sinensis var．septentrionalis）和巴山冷杉（Abies fargesii）整体表现出显著空间负相关,巴山冷杉与玉皇柳（Salix yuhuangshanensis）未表现出明显相关性,而牛皮桦与玉皇柳间则有空间负相关的趋势。牛皮桦的更新格局仅依靠自身倒木扰动产生的机会,且被限定在较小尺度上。巴山冷杉在小尺度上会限制自身更新,此外与牛皮桦在小尺度上竞争激烈,可占据利用其空间位置进行更新。从空间格局分析角度认识牛皮桦和巴山冷杉的生态学特性,为进一步研究其共存机制,认识太白山桦林在秦岭植被垂直带中的作用和地位提供参考依据。     

山西太岳山兴唐寺红柄白鹃梅群落优势种的空间格局分析

使用点格局分析和分形分析(计盒维数、信息维数、关联维数)方法, 对山西太岳山兴唐寺红柄白鹃梅(Exochorda giraldii)群落进行了空间格局分析。结果表明: 1)红柄白鹃梅群落优势种在较小的尺度上呈现聚集分布的特点, 其中, 杠柳(Periploca sepium)和绣线菊(Spiraea salicifolia)在所有尺度上呈现聚集分布, 红柄白鹃梅和连翘(Forsythia suspensa)随着尺度的增加, 呈现聚集分布—随机分布—均匀分布的规律; 2)红柄白鹃梅群落优势种在不同尺度上表现出聚集分布的特点; 3)红柄白鹃梅群落优势种占据空间能力的大小为: 红柄白鹃梅>连翘>绣线菊>杠柳; 4)红柄白鹃梅群落优势种格局强度的尺度变化程度为: 杠柳>绣线菊>红柄白鹃梅>连翘; 5)红柄白鹃梅群落优势种个体空间相关程度为: 杠柳>红柄白鹃梅>连翘>绣线菊。点格局分析与分形分析结果一致, 揭示了暖温带落叶阔叶林遭到破坏后形成的次生灌丛的空间分布格局。     

Within‐stand spatial structure and relation of boreal canopy and understorey vegetation

Question: How do spatial patterns and associations of canopy and understorey vegetation vary with spatial scale along a gradient of canopy composition in boreal mixed‐wood forests, from younger Aspen stands dominated by Populus tremuloides and P. balsamifera to older Mixed and Conifer stands dominated by Picea glauca? Do canopy evergreen conifers and broad‐leaved deciduous trees differ in their spatial relationships with understorey vegetation? Location: EMEND experimental site, Alberta, Canada. Methods: Canopy and understorey vegetation were sampled in 28 transects of 100 contiguous 0.5 m × 0.5 m quadrats in three forest stand types. Vegetation spatial patterns and relationships were analysed using wavelets. Results: Boreal mixed‐wood canopy and understorey vegetation are patchily distributed at a range of small spatial scales. The scale of canopy and understorey spatial patterns generally increased with increasing conifer presence in the canopy. Associations between canopy and understorey were highly variable among stand types, transects and spatial scales. Understorey vascular plant cover was generally positively associated with canopy deciduous tree cover and negatively associated with canopy conifer tree cover at spatial scales from 5–15 m. Understorey non‐vascular plant cover and community composition were more variable in their relationships with canopy cover, showing both positive and negative associations at a range of spatial scales. Conclusions: The spatial structure and relation of boreal mixed‐wood canopy and understorey vegetation varied with spatial scale. Differences in understorey spatial structure among stand types were consistent with a nucleation model of patch dynamics during succession in boreal mixed‐wood forests.     

Vegetation establishment in post-fire Adenostoma chaparral in relation to fine-scale pattern in fire intensity and soil nutrients

At fine spatial scales (0.1–10m), chaparral communities have been shown to be strongly influenced by canopy-gap patterns, leading to periodicities in vegetation at 4–5 m spatial scales. Fine-scale variations in fire behavior and post-fire erosion can lead to changes in the patterning of viable seeds and nutrients and may alter the spatial patterning of post-fire chaparral communities. This study deals with the relationship among fire behavior, post-fire nutrient availabilities and vegetation patterns in a 1-yr old, post-fire Adenostoma fasciculatum chaparral community in the Sierra Nevada Mountains, California, USA. Variations in mineral soil exchangeable cations (Ca, Mg) and extractable phosphorus (P0₄-P) were correlated with ash distribution. Cations and measures of ammonium and nitrate were also correlated with fire intensity, measured by the diameter of the smallest remaining A. fasciculatum twigs following fire. Fire intensity was correlated with the pattern of post-fire vegetation establishment based on first axis DC A scores. However, ash PO4-P was more highly correlated with sample DCA scores, local species richness and total cover (p < 0.01), suggesting that small-scale variations in PO4-P which correlate with ash distributions may be important in structuring this community. Two- and three-term local variance analysis revealed a maximum of pattern intensity in DCA first axis scores at 4–5 m intervals that likely corresponds to pre-fire canopy-gap patterns. However, total cover showed pattern at spatial scales of 8–10 m, and was correlated at this scale with patterns of ash distribution and fire intensity. Microtopographic patterns also occur at similar spatial scales. Microtopographic patterns appear important in determining post-fire plant nutrient and water distributions and, thereby, patterns of plant establishment. Thus, the scale and intensity of post-fire vegetation pattern may differ considerably from pre-fire conditions.     

Spatial patterns of plant association in grazed and ungrazed shrublands in the semi‐arid Karoo,South Africa

Abstract. The investigation of vegetation pattern and plant association by spatial statistics has become increasingly popular among plant ecologists. Recently, Individual‐centered analysis (ICA) has been introduced as a new tool for analysis of multi‐species co‐occurrence patterns. We tested this new technique by applying it to spatial data from grazed and ungrazed shrub communities in the semi‐arid Great Karoo, South Africa. There were substantial but complex and scale‐dependent differences in pattern between grazed and ungrazed vegetation. Unpalatable species that increase in abundance in grazed vegetation possibly play a key role in the change of vegetation pattern. At small scales we found indications of aggregation (< 30 cm) at the ungrazed, but of repulsion (30 – 40 cm) at the grazed site. An additional non‐random pattern at 60 – 170 cm at the grazed site was probably due to the clumped distributions of some species on broader scales. We show that the interpretability of ICA results is improved when the actual observed and expected frequencies of species combinations are added to the program output. The main strength of ICA is that it has the potential to detect association patterns that involve more than two species.     

Determinants of bird species richness: role of climate and vegetation structure at a regional scale

We examined the respective roles of climate and vegetation structure on geographical variation in bird species richness. The Province of Buenos Aires (central-eastern Argentina) was divided into 146 squares of 50 km on a side. For each square we evaluated the number of bird species, the value of thirteen climatic variables, and the value of a vegetation strata index. The climatic matrix was analyzed by Principal Component Analysis (PCA), and the first factors resulting from PCA were considered as multifactorial climatic gradients. Simple and Partial Correlation Analysis among bird species richness, vegetation strata, and the first two factors derived from PCA (65% of total variation) indicated that bird richness distribution was determined by the availability of vegetation strata, associated with different vegetation types that, at the same time, were influenced by the climatic conditions summarized in the first climatic factor (a gradient of precipitation, relative humidity, annual termical amplitude, and frost occurrence). This relationships reflect the complexity of factors that can act directly as well as indirectly on the geographical patterns in species richness. Also, we evaluated the importance of study scale comparing our results with previous studies at macrogeographic and local scales, found out that the vegetation structure was the principal determinant of bird species richness at this three geographical scales.     

Population structure and spatial pattern of Caragana tibetica communities in Nei Mongol shrub-encroached grassland

Aims The community structure and function of the shrub-encroached grassland, as well as its formation mechanism, is one of hot scientific problems in vegetation science. The spatial pattern analysis is an important means for studying plant population interactions and the relationships between plant population and environment. The shrub-encroached grassland is one major vegetation type in Nei Mongol. Knowledge on the spatial pattern of shrub can improve our understanding on adaptive characteristics of shrub to steppe environment.
Methods We chose Caragana tibetica encroached grassland distributed in Ordos City as research objects. The spatial position of each C. tibetica individual in 64 m × 64 m study plot was determined by a method of “three-distance location method”, and then the spatial pattern and intraspecific associations of C. tibetica individuals was analyzed with the point pattern analysis.
Important findings The results showed that C. tibetica population was at the rising stage. The mature individuals showed a uniform distribution at the scale of less than 3.7 m, subsequently exhibiting a random distribution with an increased scale. The juvenile individuals showed an aggregation distribution at the scale of 0.3-20.4 m, but a uniform distribution at other scales. The dead C. tibetica individuals were distributed aggregately at the scale from 0.7 to 1.4 m, but randomly at other scales. An indistinctive positive association was found for live C. tibetica individuals to dead individuals at the scale of less than 9.9 m, but no associations was found between them at other scales. The mature individuals negatively interacted with juveniles at the scale of larger than 2.2 m, but unassociated at the other scales.     

珍稀濒危植物长蕊木兰种群的年龄结构与空间分布

珍稀濒危植物长蕊木兰为国家Ⅰ级保护植物。然而,由于受研究尺度和分析方法的限制,对其种群生态特征等方面仍不清楚。以云南高黎贡山原生的中山湿性常绿阔叶林4 hm2样地调查数据为基础,应用Ripley的L函数分析了长蕊木兰种群的年龄结构与空间分布格局。研究发现:(1)长蕊木兰种群的年龄结构为反"J"型,属稳定型种群。(2)长蕊木兰种群个体的空间分布格局与空间尺度关系密切,空间尺度小于75 m时为聚集分布,大于75 m时为随机分布。生境异质性在长蕊木兰种群空间分布格局的形成中可能发挥了重要的作用。(3)不同发育阶段个体的空间分布格局存在明显的差异,中树和小树阶段的分布格局在中、小尺度上呈聚集分布,在较大尺度上呈随机分布;大树阶段在整个空间尺度上均呈现随机分布。(4)长蕊木兰不同发育阶段的空间关联性主要表现为中、小尺度上的负相关,在较大尺度上则趋向于无关联。     

黄土高原马栏林区基于不同植被组织尺度的群落物种多样性

物种多样性格局随着时空尺度的变化而变化, 同时也与植被组织尺度的变化密切相关, 基于多组织尺度的研究能更好地揭示一个地区的物种多样性规律。在应用数量分类(TWINSPAN)和主成分分析法(PCA)确定黄土高原马栏林区不同组织尺度的群落类型及其相互关系的基础上, 采用加性分配法分析该区域物种多样性与植被型、群系和群丛3种植被组织尺度之间的关系, 结果表明: (1) 区域物种多样性(γ)可加性分配分为群丛内(α₁)、群丛间(β₁)、群系间(β₂)和植被型间(β₃) 4个多样性成分, 无论用物种丰富度指数还是Shannon-Wiener多样性或Simpson多样性指数, 乔木、灌木和草本植物的最大物种多样性都存在于群丛内(草本层的物种丰富度除外), 说明群丛尺度是度量该区物种多样性的最佳尺度。(2)植被型、群系和群丛3种组织尺度的Shannon-Wiener多样性百分比均大于Simpson多样性百分比, 说明稀有种的分布对马栏林区各植被组织尺度的物种多样性格局起主要作用。(3)各尺度间的β多样性大小顺序在乔木、灌木、草本植物3层以不同多样性指数表示时各不相同, 这与乔木、灌木、草本植物3层的物种组成和分布, 以及主导不同植被组织尺度的物种多样性的因素差异有密切联系。     

Fine-scale spatial organization of tallgrass prairie vegetation along a topographic gradient

Fine-scale spatial patterns of native tallgrass prairie vegetation were studied on Konza Prairie, Kansas, USA. Three sites, upland, slope, and lowland, were sampled in an ungrazed watershed. Presence of vascular plant species was recorded in two 25.6 m long transects of contiguous 5×5 cm micro-quadrats on each topographic position. Spatial patterns of species and functional groups were analyzed by information theory models ofJuhász-Nagy. Within-community variability of coexistence was expressed by the diversity and spatial dependence of local species combinations. Considerable diversity in the local coexistence of species was found on each site. Upland and hillside communities were richer and more diverse in species combinations than lowland. Spatial scale effected coexistence relationships. The maxima of information theory estimates varied between 15 and 30 cm. There was no trend in the variation of characteristic scales along the topographical gradient. Above 10 m, all sites tended to be homogeneous. The analysis of spatial associations revealed that variability in the local coexistence of species was strongly constrained in all topographic positions. Overall spatial association of species was the lowest on lowland. The characteristic scales of maximum association were between 1.2 m and 3 m at all sites. The maxima of information theory estimates for the functional group-based data appeared at smaller plot sizes than for the species based analyses. Only weak spatial associations were detected among the functional groups indicating that individuals of functional groups coexist well at small scales, and form combinations close to random expectations. The length of transects did not effect the relative associations. Strong positive correlations were found between the number of components (species or functional groups) and the maxima, of information theory models suggesting that richness is a good predictor of within-community coexistence relations. However, there was no relationship between richness and the characteristic scales of community patterns.     

Limited benefits of non-crop vegetation on spiders in Australian vineyards: regional or crop differences?

In crops, invertebrate natural enemies such as spiders have been documented as responding to non-crop vegetation at the local and landscape scales, particularly in northern Europe. Much of this information is based on data from arable or annual crops and it is possible that spider numbers in more persistent perennial systems including vineyards may be less dependent on non-crop vegetation. To test the relationship between spider abundance and non-crop vegetation within the context of Australian vineyards, we sampled spiders in 54 vineyards with adjacent non-crop vegetation, from three different regions. Landscape composition in the area surrounding each of the 54 sites was characterized at 11 spatial scales from 95?m to 3?km radius and spiders were sampled monthly using canopy sticky traps and ground pitfall traps. There were only weak relationships between pasture or woody vegetation and the abundance of spiders in vineyards at all spatial scales. At the local scale, abundance of most spider families tended to be greater in vineyards with adjacent pasture. At the landscape scale there were inconsistent patterns. We discuss possible reasons for these apparent contrasting patterns between perennial and annual crops and European compared to Australian agroecosystems.     

Effect of woody vegetation at the landscape scale on the abundance of natural enemies in Australian vineyards

Undisturbed vegetation within agricultural areas, especially woody vegetation, has been documented to enhance natural invertebrate enemies within adjacent crops, particularly in northern Europe. To test this idea within the context of Australian vineyards, we considered 44 landscapes from two regions, and sampled invertebrates in vineyards central to each landscape five times at monthly intervals using canopy sticky traps. Landscape composition was characterized at 11 spatial scales from 95 m to 3 km radius. We found only weak relationships between woody vegetation and the abundance of invertebrate groups including coccinellids at any spatial scale, regardless of whether the contribution of each scale was considered independently or together using a multiple regression approach. The only consistent pattern was that several families of parasitoids were influenced by woody vegetation at the landscape scale; the abundance of Eulophidae increased with woody vegetation in the landscape, while two families of smaller parasitoids, Trichogrammatidae and Mymaridae, were negatively affected by woody vegetation. We discuss possible reasons for these apparent contrasting patterns between Australian and European studies.     

Small-scale pattern: an evaluation of techniques with an application to salt marsh vegetation

This paper examines the outcome of four different procedures for quantifying small-scale association patterns in vegetation, with respect to data from Church Island salt marsh, Menai Bridge, N. Wales. A main aim is the evaluation of two plot-less techniques, proposed by Stowe & Wade (1979). The first examines frequencies of juxtaposition, the second the frequencies of target species in the regions of occurrence of other species. The results of these analyses are compared with those of two plot-based techniques. A Reciprocal averaging ordination is also employed to describe medium-scale distributional pattern within the data set.Of the two plot-less methods, the species-region method is found to be more useful, particularly because it is capable of detecting asymmetric relationships. When using the recommended collapsed data format the plot-less methods operate at an inconsistent spatial scale approximating to the mean run or clump size of species along the sampling transects. This allows detection of sociological patterns but may obscure environmental relationships. The small-scale relationships depicted by the plot-less methods are in cases in accord with the plot-based results at a range of scales, in other cases they differ: in each circumstance providing insights into the nature of interspecific relationships.Inter-specific pattern in salt marsh vegetation has rarely been studied. The methodology employed here shows that relationships do exist at the small scale, and may allow hypothesis generation with respect to their causality and their role in the dynamics of the marsh system.     

Complex effects of scale on the relationships of landscape pattern versus avian species richness and community structure in a woodland savanna mosaic

Landscape pattern metrics are widely used for predicting habitat and species diversity. However, the relationship between landscape pattern and species diversity is typically measured at a single spatial scale, even though both landscape pattern, and species occurrence and community composition are scale‐dependent. While the effects of scale on landscape pattern are well documented, the effects of scale on the relationships between spatial pattern and species richness and composition are not well known. Here, our main goal was to quantify the effects of cartographic scale (spatial resolution and extent) on the relationships between spatial pattern and avian richness and community structure in a mosaic of grassland, woodland, and savanna in central Wisconsin. Our secondary goal was to evaluate the effectiveness of a newly developed tool for spatial pattern analysis, multiscale contextual spatial pattern analysis (MCSPA), compared to existing landscape metrics. Landscape metrics and avian species richness had quadratic, exponential, or logarithmic relationships, and these patterns were generally consistent across two spatial resolutions and six spatial extents. However, the magnitude of the relationships was affected by both resolution and extent. At the finer resolution (10‐m), edge density was consistently the best predictor of species richness, followed by an MCSPA metric that measures the standard deviation of woody cover across extents. At the coarser resolution (30‐m), NDVI was the best predictor of species richness by far, regardless of spatial extent. Another MCSPA metric that denotes the average woody cover across extents, together with percent of woody cover, were always the best predictors of variation in avian community structure. Spatial resolution and extent had varying effects on the relationships between spatial pattern and avian community structure. We therefore conclude that cartographic scale not only affects measures of landscape pattern per se, but also the relationships among spatial pattern, species richness, and community structure, often in complex ways, which reduces the efficacy of landscape metrics for predicting the richness and diversity of organisms.     

Spatial associations and patterns of perennial vegetation ina semi-arid steppe: a multivariate geostatistics approach

We investigated the spatial patterns of perennial species (Stipa tenacissima, Anthyllis cytisoidesGlobularia alypum, Brachypodium retusum and chamaephytes) in a 50 m × 50 m semi-arid steppe by using the combination of a linear model of coregionalization (LMC) and sampling units of varying size (1.25 m × 1.25 m, 2.5 m × 2.5 m, and 5 m × 5 m). The data-adjusted LMC showed the patchy structure of the vegetation, which was especially evident with the highest resolution grid. It also detected a periodic pattern in the distribution of S. tenacissima, as well as autocorrelation at two spatial scales for A. cytisoides and G. alypum. The latter species was negatively associated with the other species at both short and long distances. These negative associations were consistent for all sampling grids and suggest the presence of interference between G. alypum and the rest of the evaluated species. Despite species-specific differences, the LMC was fitted satisfactorily to all of them. This suggests a common variation pattern for all the species, which may be caused by an underlying environmental property driving the patterns of all the species or, alternatively, by the dominance of some species’ spatial pattern, or another kind of species association, over the rest. The spatial patterns found were profoundly affected by the observational scale. Our results reveal that the multivariate geostatistical approach introduced in this paper is a suitable technique for the spatial analysis of semi-arid plant communities. It allows plant ecologists to evaluate if the species forming the plant community of interest share a common spatial pattern, and to assess the spatial covariation between the species forming a plant community at different spatial scales independently.