Neutral models and the deviation from neutral pattern metric

Ecological variables are inherently spatial with arrangement on the landscape often directly attributed to underlying processes. Historically, assumptions regarding the relationships among scale, pattern, and process have been used to characterize landscapes as well as compare multiple landscapes or changes in landscapes over time. Despite the utility of landscape comparisons, they often fail to adequately link scale, pattern, or process, and far too frequently are presented as logical interpretations leading to prediction of pattern to process relationships. Pattern metrics and measures of spatial autocorrelation have evolved to characterize and model landscape phenomena. Unfortunately, the two are quite often misapplied. This research presents an alternative metric, Deviation from Neutral (DFN), which permits the comparison of multiple landscapes.     

Can we measure ecological sustainability? Landscape pattern as an indicator for naturalness and land use intensity at regional,national and European level

European landscapes have been shaped over the centuries by processes related to human land use, which are reflected in regionally distinct landscape patterns. Since landscape pattern has been linked to biodiversity and other ecological values of the landscapes, this paper explores landscape pattern as a tool for ecological sustainability assessments at the regional (Austrian Cultural Landscapes), national (Austria) and European (European Union + Norway, Switzerland) level with focus on agricultural landscapes. A set of landscape metrics served as a basis to assess naturalness and geometrisation of Austrian and European landscapes as a proxy for their sustainability. To achieve an accurate spatially explicit assessment, we applied a spatial reference framework consisting in units that are homogeneous in biophysical and socio-economic contexts, adapted the regional approach for its application at European level, and developed relative sustainability thresholds for the landscape metrics. The analyses revealed that several landscape metrics, particularly the “Number of Shape Characterising Points” showed a high correlation with the degree of naturalness. The sustainability map of Austria based on an ordinal regression model revealed well-known problem regions of ecological sustainability. At the European level, the relative deviation from the average pattern showed clearly the simplification processes in the landscapes. However, a better spatial resolution of land cover data would add to the refinement of pattern analysis in regions and therefore the assessment of sustainability. We recommend the combination of information of different scales for the formulation and implementation of sustainability policies.     

Sensitivity of landscape measurements to changing grain size for fine-scale design and management

Landscape pattern quantities are affected by issues of scale, namely extent and resolution. The grain size (resolution) of fine-resolution geographic information system (GIS) data for two highly fragmented landscapes in USA and Italy were altered to evaluate the effect of grain size changes on landscape pattern metrics and cost-surface model outputs. Beginning with 3 m resolution data and resampling the data to 300 m resolution, we applied pattern metrics and cost-surface models (available in GIS software) and evaluated the types of behaviors in resulting quantities. Results showed that some pattern metrics are robust to changes in grain size (such as area, cohesion, interspersion and juxtaposition metrics), while others exhibit staircase-like or erratic responses. Compared to previous studies, we identified behavioral responses that differ from grain-size changes at coarser resolutions. Cost-surface models demonstrated robust or consistent responses to grain size changes in most cases. For both types of pattern measurement, however, we found that behaviors could differ contextually; that is, there could be different types of behaviors for different landscapes, classifications, or grain sizes. Results indicate that comparing spatial data collected at different scales (such as historical data to more recent, high-resolution sensed data) is complicated by different types of responses to changes in grain size. This may limit the applicability of tools for the measurement of landscape change over time if landscapes are represented by differently scaled data.     

Habitat quality of source patches and connectivity in fragmented landscapes

Because spatial connectivity is critical to dispersal success and persistence of species in highly fragmented landscapes, the way that we envision and measure connectivity is consequential for biodiversity conservation. Connectivity metrics used for predictive modeling of spatial turnover and patch occupancy for metapopulations, such as with Incidence Function Models (IFM), incorporate distances to and sizes of possible source populations. Here, our focus is on whether habitat quality of source patches also is considered in these connectivity metrics. We propose that effective areas (weighted by habitat quality) of source patches should be better surrogates for population size and dispersal potential compared to unadjusted patch areas. Our review of a representative sample of the literature revealed that only 12.5% of studies incorporated habitat quality of source patches into IFM-type connectivity metrics. Quality of source patches generally was not taken into account in studies even if habitat quality of focal patches was included in analyses. We provide an empirical example for a metapopulation of a rare wetland species, the round-tailed muskrat (Neofiber alleni), demonstrating that a connectivity metric based on effective areas of source patches better predicts patch colonization and occupancy than a metric that used simple patch areas. The ongoing integration of landscape ecology and metapopulation dynamics could be hastened by incorporating habitat quality of source patches into spatial connectivity metrics applied to species conservation in fragmented landscapes.     

Mapping changes to vegetation pattern in a restoring wetland: Finding pattern metrics that are consistent across spatial scale and time

Tidal salt marshes in the San Francisco Estuary region display heterogeneous vegetation patterns that influence wetland function and provide adequate habitat for native or endangered wildlife. In addition to analyzing the extent of vegetation, monitoring the dynamics of vegetation pattern within restoring wetlands can offer valuable information about the restoration process. Pattern metrics, derived from classified remotely sensed imagery, have been used to measure composition and configuration of patches and landscapes, but they can be unpredictable across scales, and inconsistent across time. We sought to identify pattern metrics that are consistent across spatial scale and time – and thus robust measures of vegetation and habitat configuration – for a restored tidal marsh in the San Francisco Bay, CA, USA. We used high-resolution (20 cm) remotely sensed color infrared imagery to map vegetation pattern over 2 years, and performed a multi-scale analysis of derived vegetation pattern metrics. We looked at the influence on metrics of changes in grain size through resampling and changes in minimum mapping unit (MMU) through smoothing. We examined composition, complexity, connectivity and heterogeneity metrics, focusing on perennial pickleweed (Sarcocornia pacifica), a dominant marsh plant. At our site, pickleweed patches grew larger, more irregularly shaped, and closely spaced over time, while the overall landscape became more diverse. Of the two scale factors examined, grain size was more consistent than MMU in terms of identifying relative change in composition and configuration of wetland marsh vegetation over time. Most metrics exhibited unstable behavior with larger MMUs. With small MMUs, most metrics were consistent across grain sizes, from fine (e.g. 0.16 m²) to relatively large (e.g. 16 m²) pixel sizes. Scale relationships were more variable at the landcover class level than at the landscape level (across all classes). This information may be useful to applied restoration practitioners, and adds to our general understanding of vegetation change in a restoring marsh.     

The confounded effects of habitat disturbance at the local,patch and landscape scale on understorey birds of the Atlantic Forest: Implications for the development of landscape-based indicators

The search for surrogates of changes in species richness and community structure in fragmented landscapes involves not only the selection of predictors, such as landscape metrics or environmental variables, but also the identification of the spatial scale that is most relevant to the taxa in question. However the heavily intercorrelated nature of many structural features in fragmented landscapes complicates analyses, and the wide variation in species responses prevents the identification of a general trend. In this study, we used a two-tiered hierarchical variation partitioning to identify the unique and shared effects of: 1 – changes in vegetation structure at the plot scale, patch structure (size and shape), and forest cover at the landscape scale; and 2 – variables within these scales; as predictors of species richness and species’ abundances of birds in a fragmented landscape of Atlantic Forest; with the goal of aiding to the development of biodiversity indicators. Birds were sampled with mist-nets with a constant effort of 680 net-h at each of 23 sites, which resulted in almost 2600 captures. At the community level, regression models showed that changes in plot, patch and landscape scale variables explained a large proportion of the variation in species richness, but results from variation partitioning showed that the intercorrelation among predictors was so high that the unique contribution of each was non-significant. Our results point to a relatively large unique effect of local and landscape scale variables at the community level, but we also show that results vary greatly depending on the trophic guild being analysed. At the species level, multiple scale models also presented high explanatory power, however, species responses were so varied that we could not detect a general trend. We conclude that there is no single ‘best’ scale that could function as a proxy for changes in bird communities because each species and functional guild is uniquely affected by the environment, and suggest that efforts should be focused on finding indicators that encompasses all scales and the needs of different taxa.     

景观格局-土壤侵蚀研究中景观指数的意义解释及局限性

景观格局分析是景观生态学研究的重要组成部分。景观指数是景观格局分析的有力工具。近年来,景观格局与土壤侵蚀关系的相关研究增多,常规景观格局指数得到应用。但针对土壤侵蚀过程的景观指数意义解释不足,景观指数在刻画景观格局-土壤侵蚀过程关系存在局限。选择了连接性、多样性、边界/斑块密度、形状4个方面的12个常用景观指数,对这些指数在景观格局-土壤侵蚀过程关系研究中的意义进行阐述,对指数应用的局限性及其原因进行了分析。景观数据属性、景观指数本身性质和土壤侵蚀过程的复杂性使得常规景观格局指数在景观格局-土壤侵蚀关系研究中存在不足。这3方面的影响使得常规景观格局指数与土壤侵蚀表征变量之间不存在确定的关系,从而难以通过景观指数来表征景观土壤侵蚀特征。缺乏土壤侵蚀过程基础是常规景观指数在土壤侵蚀研究应用中存在局限的主要原因。因此,构建基于土壤侵蚀过程的景观指数是景观格局-土壤侵蚀关系研究的需要和新的发展方向。     

Evaluating the effectiveness of landscape metrics in quantifying spatial patterns

The effectiveness of landscape metrics in quantifying spatial patterns is fundamental to metrics assessment. Setting 36 simulated landscapes as sample space and focusing on 23 widely used landscape metrics, their effectiveness in quantifying the complexity of such spatial pattern components as number of patch types, area ratio of patch types and patch aggregation level, were analyzed with the application of the multivariate linear regression analysis method. The results showed that all the metrics were effective in quantifying a certain component of spatial patterns, and proved that what the metrics quantified were not a single component but the complexity of several components of spatial patterns. The study also showed a distinct inconsistency between the performances of landscape metrics in simulated landscapes and the real urban landscape of Shenzhen, China. It was suggested that the inconsistency resulted from the difference of the correlation among spatial pattern components between simulated and real landscapes. After considering the very difference, the changes of all 23 landscape metrics against changing of number of patch types in simulated landscapes were consistent with those in the real landscape. The phenomenon was deduced as the sign effect of spatial pattern components on landscape metrics, which was of great significance to the proper use of landscape metrics.     

基于移动窗口法的岷江干旱河谷景观格局梯度分析

以岷江干旱河谷为研究区,基于GIS技术和移动窗口法对其景观格局梯度变化进行分析,以期为区域的景观格局优化和管理提供支持。根据研究区的形状特征,分别沿干流和支流设置4条样带;选取景观水平下的景观指数,利用FRAGSTATS3.3软件分别采取标准法和移动窗口法获得不同尺度下的景观指数值;综合利用景观指数粒度效应分析、区域面积信息守恒评价方法和景观指数幅度效应评价曲线确定研究区景观格局梯度分析移动窗口尺寸,并计算了此窗口尺度下4条样带上的景观指数,得到沿样带方向的景观梯度格局。结果表明:岷江干旱河谷的景观基质是灌木林地,面积占73.82%。有林地和草地的景观异质性低,居民地和耕地斑块破碎化程度较大。确定了50m的栅格大小,250m的移动窗口尺寸为研究区景观格局梯度分析的窗口尺度;4条样带上各景观指数均随景观类型变化出现不同幅度的上下波动特征,梯度特征明显。处于景观类型过渡地带的区域,景观多样性和异质性增加,破碎化程度高;干旱河谷景观格局梯度变化主要受地形、水热因子,以及堤坝建设和土地开发利用影响。研究作为一种有益的尝试,更精细地分析了研究区的景观格局,能够为河谷地区景观格局量化分析提供参考,但也存在一定不足,需要在今后工作中继续深入研究。     

Landscape heterogeneity metrics as indicators of bird diversity: Determining the optimal spatial scales in different landscapes

Species distribution models are often used to study the biodiversity of ecosystems. The modelling process uses a number of parameters to predict others, such as the occurrence of determinate species, population size, habitat suitability or biodiversity. It is well known that the heterogeneity of landscapes can lead to changes in species’ abundance and biodiversity. However, landscape metrics depend on maps and spatial scales when it comes to undertaking a GIS analysis.We explored the goodness of fit of several models using the metrics of landscape heterogeneity and altitude as predictors of bird diversity in different landscapes and spatial scales. Two variables were used to describe biodiversity: bird richness and trophic level diversity, both of which were obtained from a breeding bird survey by means of point counts. The relationships between biodiversity and landscape metrics were compared using multiple linear regressions. All of the analyses were repeated for 14 different spatial scales and for cultivated, forest and grassland environments to determine the optimal spatial scale for each landscape typology.Our results revealed that the relationships between species’ richness and landscape heterogeneity using 1:10,000 land cover maps were strongest when working on a spatial scale up to a radius of 125–250 m around the sampled point (circa 4.9–19.6 ha). Furthermore, the correlation between measures of landscape heterogeneity and bird diversity was greater in grasslands than in cultivated or forested areas. The multi-spatial scale approach is useful for (a) assessing the accuracy of surrogates of bird diversity in different landscapes and (b) optimizing spatial model procedures for biodiversity mapping, mainly over extensive areas.     

Towards more predictable and consistent landscape metrics across spatial scales

Habitat change and fragmentation are considered key drivers of environmental change and biodiversity loss. To understand and mitigate the effects of such spatial disturbances on biological systems, it is critical to quantify changes in landscape pattern. However, the characterization of spatial patterns remains complicated in part because most widely used landscape metrics vary with the amount of usable habitat available in the landscape, and vary with the scale of the spatial data used to calculate them. In this study, we investigate the nature of the relationship between intrinsic characteristics of spatial pattern and extrinsic scale-dependent factors that affect the characterization of landscape patterns. To do so, we used techniques from modern multivariate statistics to disentangle widely used landscape metrics with respect to four landscape components: extent (E), resolution (R), percentage of suitable habitat cover (P), and spatial autocorrelation level (H). Our results highlight those metrics that are less sensitive to change in spatial scale and those that are less correlated. We found, however, significant and complex interactions between intrinsic and extrinsic characteristics of landscape patterns that will always complicate researcher's ability to isolate purely landscape pattern driven effects from the effects of changing spatial scale. As such, our study illustrates the need for a more systematic investigation of the relationship between intrinsic characteristics and extrinsic properties to accurately characterize observed landscape patterns.     

Mediterranean drylands: The effect of grain size and domain of scale on landscape metrics

This study first sought to isolate a select group of landscape metrics particularly well-suited for describing dryland Mediterranean landscapes in Jordan. We examined the response of 50 landscape metrics to a large range of imagery grain sizes. Most of the metrics exhibited an expected behavior, similar to what has been previously reported in literature such as (a) a predictable (linear or power law) response to changing grain size, and (b) an unpredictable (staircase-like or erratic) response to changing grain size. Some metrics, however, exhibited a domain of scale effect, in particular the core area metrics. Using correlation analysis, the original 50 metrics were placed into 19 groups such that all metrics within a group were strongly correlated with each other, and were represented by a single representative metric. Using these representative metrics in the context of principal components analysis, we then found that six factors explained 95.35% of the total variation found in the landscape pattern. The highest loadings for these six factors, in order, were the number of patches (NP), mean proximity index (PROX_MN), largest patch index (LPI), patch cohesion index (COHESION), total core area (TCA), and the proximity index coefficient of variation (PROX_CV). It was concluded that east Mediterranean landscapes with a long history of anthropogenic-driven change showed a domain of scale for core area metrics. We also recommend that the majority of the pattern in dry Mediterranean landscapes, particularly those in Jordan, can be described with six metrics. We suggest that our procedure for landscape metric selection can be utilized in other regions of study as well.     

Patch occupancy and abundance of local populations in landscapes differing in degree of habitat fragmentation: a case study of the colonial black‐headed gull,Chroicocephalus ridibundus

Aim This study investigated whether habitat fragmentation at the landscape level influences patch occupancy and abundance of the black‐headed gull, Chroicocephalus ridibundus, and whether the response of the species to environmental factors is consistent across replicated landscape plots. Location Water bodies (habitat patches) in southern Poland. Methods Surveys were conducted in two landscape types (four plots in each): (1) more‐fragmented landscape, in which habitat patches were small (mean size 2.2–6.2 ha) and far apart (mean distance 2.5–3.1 km); and (2) less‐fragmented landscape, in which habitat patches were large (mean size 9.2–16.5 ha) and separated by short distances (mean 0.9–1.4 km). Observations were performed twice in 284 potential habitat patches during the 2007 breeding season. Results Colonies were significantly more frequent and larger in the less‐fragmented landscapes than in the more‐fragmented ones. Probability of patch occupancy and number of breeding birds were positively related with patch size and these relationships were especially strong in the more‐fragmented landscapes. In the less‐fragmented landscapes, the occurrence of black‐headed gulls was negatively related to the distance to the nearest local population, but in the more‐fragmented landscapes such a relationship was not detected. As distance to the nearest habitat patch increased, the probability of the patch occupancy decreased in the more‐fragmented landscapes. Moreover, abundance was negatively influenced by distance to the nearest habitat patch, especially strongly in more‐fragmented landscapes. Proximity of corridors (rivers) positively influenced the occupation of patches regardless of landscape type. The number of islets positively influenced occupancy and abundance of local populations, and this relationship was stronger in the more‐fragmented landscapes. Main conclusions Our results are in agreement with predictions from metapopulation theory and are the first evidence that populations of black‐headed gulls may have a metapopulation structure. However, patch occupancy and abundance were differentially affected by explanatory variables in the more‐fragmented landscapes than in the less‐fragmented ones. This implies that it is impossible to derive, a priori, predictions about presence/abundance patterns based on only a single landscape.     

景观生态学的学科前沿与发展战略

根据美国景观生态学2001年年会关于景观生态学的关键议题和研究领域特别专题的讨论,综合16位国际知名专家所发表的关于深化理论、整合协调和方法改进等方面的意见,深入论述了景观生态学的6项关键议题和10个优先研究领域。包括通过景观镶嵌体的生态流,土地利用和土地覆被变化的过程、机制,非线性动态和景观复杂性,尺度转换方法论的发展,景观指标与生态过程,人类活动与景观生态,景观格局的优化,景观保育与可持续性,资料获取与准确性评价。并对构建中国景观生态学的理论框架提出了初步的想法,即发展以格局——过程关系为中心的生态空间理论,以人类活动有序化为中心的景观生态建设理论,以发挥景观多重价值为中心的景观规划理论。     

景观指数耦合景观格局与土壤侵蚀的有效性

景观格局分析是景观生态学中揭示景观变化及其生态效应的主要方法,而景观指数是景观格局分析中广泛使用的工具。土壤侵蚀是土壤物质在景观中的迁移和再分配过程,受地形、植被和人类活动及其空间格局的调控。运用景观格局分析揭示景观格局变化特别是土地利用/覆被格局变化对土壤侵蚀的影响是土壤侵蚀研究中应用景观生态学原理和方法的典型。在当前的研究中,斑块-廊道-基质范式下建立的景观指数对侵蚀过程的解释能力不断受到质疑,建立筛选适用的景观指数的原则和方法十分必要。以延河流域碾庄沟小流域为例,利用WATEM/SEDEM模型模拟多个年份流域侵蚀产沙和输沙量;基于土地利用/覆被数据,利用Fragstat4.2软件,计算了相应年份流域斑块、边界密度、形状、集聚与分散和斑块类型多样性4个方面的代表性景观指数。在此基础上,分析了景观指数与流域侵蚀产沙和输沙之间的关系,讨论了景观指数在土壤侵蚀研究中的有效性,在景观和斑块类型水平上分析了景观指数表达"源"、"汇"两大类景观类型的空间格局与侵蚀产沙和输沙之间的关系的一致性。结果表明:斑块-廊道-基底范式下发展的景观指数在指示景观格局的土壤侵蚀效应时存在局限。相对而言,斑块类型尺度的景观指数更能有效表达景观格局与土壤侵蚀的关系。基于景观类型在土壤侵蚀过程中的"源"、"汇"功能,提出了在土壤侵蚀研究中筛选适用的景观指数的原则:(1)对"源"、"汇"两类景观类型,景观指数与土壤侵蚀状况表征变量的相关系数符号相反;(2)对同为"源"或"汇"景观类型的多个景观类型,景观指数与土壤侵蚀表征变量的相关系数应具有符号一致性。尽管景观指数在斑块类型水平上具有一定的有效性,但用其预测景观格局变化的侵蚀效应有很大的不确定性。因此,基于土壤侵蚀过程与景观格局的作用机制发展新型的景观指数是增强景观格局分析预测土壤侵蚀过程的能力的途径。     

Bacterial predator–prey dynamics in microscale patchy landscapes

Soil is a microenvironment with a fragmented (patchy) spatial structure in which many bacterial species interact. Here, we explore the interaction between the predatory bacterium Bdellovibrio bacteriovorus and its prey Escherichia coli in microfabricated landscapes. We ask how fragmentation influences the prey dynamics at the microscale and compare two landscape geometries: a patchy landscape and a continuous landscape. By following the dynamics of prey populations with high spatial and temporal resolution for many generations, we found that the variation in predation rates was twice as large in the patchy landscape and the dynamics was correlated over shorter length scales. We also found that while the prey population in the continuous landscape was almost entirely driven to extinction, a significant part of the prey population in the fragmented landscape persisted over time. We observed significant surface-associated growth, especially in the fragmented landscape and we surmise that this sub-population is more resistant to predation. Our results thus show that microscale fragmentation can significantly influence bacterial interactions.     

Anthropogenic Habitats Facilitate Dispersal of an Early Successional Obligate: Implications for Restoration of an Endangered Ecosystem

Landscape modification and habitat fragmentation disrupt the connectivity of natural landscapes, with major consequences for biodiversity. Species that require patchily distributed habitats, such as those that specialize on early successional ecosystems, must disperse through a landscape matrix with unsuitable habitat types. We evaluated landscape effects on dispersal of an early successional obligate, the New England cottontail (Sylvilagus transitionalis). Using a landscape genetics approach, we identified barriers and facilitators of gene flow and connectivity corridors for a population of cottontails in the northeastern United States. We modeled dispersal in relation to landscape structure and composition and tested hypotheses about the influence of habitat fragmentation on gene flow. Anthropogenic and natural shrubland habitats facilitated gene flow, while the remainder of the matrix, particularly development and forest, impeded gene flow. The relative influence of matrix habitats differed between study areas in relation to a fragmentation gradient. Barrier features had higher explanatory power in the more fragmented site, while facilitating features were important in the less fragmented site. Landscape models that included a simultaneous barrier and facilitating effect of roads had higher explanatory power than models that considered either effect separately, supporting the hypothesis that roads act as both barriers and facilitators at all spatial scales. The inclusion of LiDAR-identified shrubland habitat improved the fit of our facilitator models. Corridor analyses using circuit and least cost path approaches revealed the importance of anthropogenic, linear features for restoring connectivity between the study areas. In fragmented landscapes, human-modified habitats may enhance functional connectivity by providing suitable dispersal conduits for early successional specialists.     

Importance of estimating matrix quality for modeling species distribution in complex tropical landscapes: a test with Atlantic forest small mammals

Information to guide decision making is especially urgent in human dominated landscapes in the tropics, where urban and agricultural frontiers are still expanding in an unplanned manner. Nevertheless, most studies that have investigated the influence of landscape structure on species distribution have not considered the heterogeneity of altered habitats of the matrix, which is usually high in human dominated landscapes. Using the distribution of small mammals in forest remnants and in the four main altered habitats in an Atlantic forest landscape, we investigated 1) how explanatory power of models describing species distribution in forest remnants varies between landscape structure variables that do or do not incorporate matrix quality and 2) the importance of spatial scale for analyzing the influence of landscape structure. We used standardized sampling in remnants and altered habitats to generate two indices of habitat quality, corresponding to the abundance and to the occurrence of small mammals. For each remnant, we calculated habitat quantity and connectivity in different spatial scales, considering or not the quality of surrounding habitats. The incorporation of matrix quality increased model explanatory power across all spatial scales for half the species that occurred in the matrix, but only when taking into account the distance between habitat patches (connectivity). These connectivity models were also less affected by spatial scale than habitat quantity models. The few consistent responses to the variation in spatial scales indicate that despite their small size, small mammals perceive landscape features at large spatial scales. Matrix quality index corresponding to species occurrence presented a better or similar performance compared to that of species abundance. Results indicate the importance of the matrix for the dynamics of fragmented landscapes and suggest that relatively simple indices can improve our understanding of species distribution, and could be applied in modeling, monitoring and managing complex tropical landscapes.