A new contagion index to quantify spatial patterns of landscapes

A contagion index was proposed by O'Neill et al. (1988) to quantify spatial patterns of landscapes. However, this index is insensitive to changes in spatial pattern. We present a new contagion index that corrects an error in the mathematical formulation of the original contagion index. The error is identified mathematically. The contagion indices (both original and new) are then evaluated against simulated landscapes.     

Anuran responses to spatial patterns of agricultural landscapes in Argentina

Context

Amphibians are declining worldwide and land use change to agriculture is recognized as a leading cause. Argentina is undergoing an agriculturalization process with rapid changes in landscape structure.

Objectives

We evaluated anuran response to landscape composition and configuration in two landscapes of east-central Argentina with different degrees of agriculturalization. We identified sensitive species and evaluated landscape influence on communities and individual species at two spatial scales.

Methods

We compared anuran richness, frequency of occurrence, and activity between landscapes using call surveys data from 120 sampling points from 2007 to 2009. We evaluated anuran responses to landscape structure variables estimated within 250 and 500-m radius buffers using canonical correspondence analysis and multimodel inference from a set of candidate models.

Results

Anuran richness was lower in the landscape with greater level of agriculturalization with reduced amount of forest cover and stream length. This pattern was driven by the lower occurrence and calling activity of seven out of the sixteen recorded species. Four species responded positively to the amount of forest cover and stream habitat. Three species responded positively to forest cohesion and negatively to rural housing. Two responded negatively to crop area and diversity of cover classes.

Conclusions

Anurans within agricultural landscapes of east-central Argentina are responding to landscape structure. Responses varied depending on species and study scale. Life-history traits contribute to responses differences. Our study offers a better understanding of landscape effects on anurans and can be used for land management in other areas experiencing a similar agriculturalization process.

     

An aggregation index (AI) to quantify spatial patterns of landscapes

There is often need to measure aggregation levels of spatial patterns within a single map class in landscape ecological studies. The contagion index (CI), shape index (SI), and probability of adjacency of the same class (Qi), all have certain limits when measuring aggregation of spatial patterns. We have developed an aggregation index (AI) that is class specific and independent of landscape composition. AI assumes that a class with the highest level of aggregation (AI =1) is comprised of pixels sharing the most possible edges. A class whose pixels share no edges (completely disaggregated) has the lowest level of aggregation (AI =0). AI is similar to SI and Qi, but it calculates aggregation more precisely than the latter two. We have evaluated the performance of AI under varied levels of (1) aggregation, (2) number of patches, (3) spatial resolutions, and (4) real species distribution maps at various spatial scales. AI was able to produce reasonable results under all these circumstances. Since it is class specific, it is more precise than CI, which measures overall landscape aggregation. Thus, AI provides a quantitative basis to correlate the spatial pattern of a class with a specific process. Since AI is a ratio variable, map units do not affect the calculation. It can be compared between classes from the same or different landscapes, or even the same classes from the same landscape under different resolutions.     

The influence of thematic resolution on metric selection for biodiversity monitoring in agricultural landscapes

The objective of this paper is to investigate the relationship between landscape pattern metrics and agricultural biodiversity at the Temperate European scale, exploring the role of thematic resolution and a suite of biological and functional groups. Factor analyses to select landscape-level metrics were undertaken on 25 landscapes classified at four levels of thematic resolution. The landscapes were located within seven countries. The different resolutions were considered appropriate to taxonomic and functional group diversity. As class-level metrics are often better correlated to ecological response, the landscape-level metric subsets gained through exploratory analysis were additionally used to guide the selection of class-level metric subsets. Linear mixed models were then used to detect correlations between landscape- and class-level metrics and species richness values. Taxonomic groups with differing requirements (plants, birds, different arthropod groups) and also functional arthropod groups were examined. At the coarse scale of thematic resolution grain metrics (patch density, largest patch index) emerged as rough indicators for the different biological groups whilst at the fine scale a diversity metric (e.g. Simpson’s diversity index) was appropriate. The intermediate thematic resolution offered most promise for biodiversity monitoring. Metrics included largest patch index, edge density, nearest neighbour, the proximity index, circle and Simpson’s diversity index. We suggest two possible applications of these metrics in the context of biodiversity monitoring and the identification of biodiversity hot spots in European agricultural landscapes.     

Calculating spatial configurational entropy of a landscape mosaic based on the Wasserstein metric

Landscape Ecology - Entropy is an important concept traditionally associated with thermodynamics and is widely used to describe the degree of disorder in a substance, system, or process....     

The influence of scale and the spatial characteristics of landscapes on land-cover mapping using remote sensing

Statistical analyses provide a means for assessing relationships between landscape spatial pattern and errors in the estimates of cover-type proportions as land-cover data are aggregated to coarser scales. Results from a multiple-linear regression model suggest that as patch sizes, variance/mean ratio, and initial proportions of cover types increase, the proportion error moves in a positive direction and is governed by the interaction of the spatial characteristics and the scale of aggregation. However, the standard linear model does not account for the different directions of scale-dependent proportion error since some classes become larger and others become smaller as the scene is aggregated. Addition of indicator variables representing class-type significantly improves the performance by allowing the model to respond differently to different classes. A regression tree model provides a much simpler fit to the complex scaling behavior through an interaction between patch size and aggregation scale. An understanding of the relationships between landscape pattern, scale, and proportion error may advance methods for correcting land-cover area estimates. Such methods could also facilitate high-resolution calibration and validation of coarse-scale remote-sensing-based land-cover mapping algorithms. Ongoing initiatives to produce global land-cover datasets from remote sensing, such as efforts within the IGBP and the EOS MODIS Land-Team, include significant emphasis on high level calibration and validation activities of this nature.     

The importance of spatial and temporal scale in describing hydrogeomorphic character of riverine landscapes

Landscape Ecology - Describing the hydrogeomorphic character of rivers in a holistic way is essential to understanding the processes whereby freshwater ecosystems maintain patterns of biodiversity...     

The use of native vegetation as a proxy for habitat may overestimate habitat availability in fragmented landscapes

Context

Native vegetation is often used as a proxy for habitat to estimate habitat availability in landscapes. This approach may lead to incorrect estimates of the impacts of habitat loss and fragmentation on species, which have not been thoroughly quantified so far.

Objectives

We quantified to what extent the loss of native vegetation reflect actual habitat loss by native species in landscapes. We tested the hypothesis that habitat availability declines at greater rates than native vegetation and thus is overestimated when it is quantified on the basis of native vegetation.

Methods

Using simulations, we quantified how the loss of native vegetation in artificial and real landscapes affects habitat availability for species with different habitat requirements. We contrasted a generalist species, which uses all native vegetation, with 10 habitat-specialist species classified into three categories (interior, patchy and riparian species).

Results

Habitat availability generally declined at greater rates than native vegetation for all specialist species. This pattern was apparent for different specialist species in a broad range of landscape types. Interior species always lost habitat availability more rapidly than the generalist species. Most riparian species lost habitat availability more rapidly than the generalist species. Responses of patchy species were more complex, depending on their dispersal abilities and landscape structure.

Conclusions

Habitat availability is likely to be overestimated when native vegetation is used as proxy for habitat, because habitat availability will generally decline at greater rates than native vegetation. Therefore, a species-centered approach should be adopted when estimating habitat availability in landscapes.

     

国家森林公园建设发展情况及其空间格局

为探索国家森林公园建设发展情况并揭示其空间分布规律,本研究采用知识图谱及GIS空间技术对我国国家森林公园的研究进展和空间格局进行了可视化的探索分析.结果 显示:(1)国家森林公园、生态旅游、森林旅游、风景园林、生物多样性、自然保护区、评价、群落结构等是我国森林公园的历史研究热点领域.(2)我国国家森林公园总体呈现东密西疏的空间格局,东北区域及西南区域公园分布较为集中,青海及西藏地区相反.(3)1992-2017年期间国家森林公园的面积得到了更为显著的提升,黑龙江、西藏、新疆、内蒙古4省贡献的面积较多,天津、上海、宁夏、海南4省市对全国国家森林公园建设面积的贡献较小.西部地区国家森林公园的数量有待提升,宁夏、海南2省的国家森林公园总面积有较大理论拓展空间,未来可以加强国家森林公园动态监测评价、森林公园管理制度保障、森林公园建设成效评价、智慧森林公园等方面的研究,以此来推动全国森林公园的全面健康发展.     

The ecology of urban landscapes: modeling housing starts as a density-dependent colonization process

Data on permits for new housing starts are a key source of information on recent changes in the urban landscape of central Arizona, USA. Drawing primarily on the conceptual parallels between the process of urban expansion and the spatial spread of non-human species, we outline a nested series of 'colonization' models that could be used to study changes in urban landscapes through simulations of housing starts.Within our probabilistic colonization framework, the ecological principle of density-dependence (operating simultaneously on different spatial scales) governs the positioning of new housing units. These simple models afford a great diversity of possible spatial patterns, ranging from tight clustering of houses to urban sprawl to more subtle patterns such as aversion of housing developments from (and aggregation near) different kinds of landscape features. These models can be parameterized from a variety of types of governmental housing data. Ultimately, such a framework could be used to contrast development patterns among cities and identify pertinent operational scales and factors influencing processes associated with urbanization.     

Consequences of spatial heterogeneity for ecosystem services in changing forest landscapes: priorities for future research

Changes in key drivers (e.g., climate, disturbance regimes and land use) may affect the sustainability of forest landscapes and set the stage for increased tension among competing ecosystem services. We addressed two questions about a suite of supporting, regulating and provisioning ecosystem services in each of two well-studied forest landscapes in the western US: (1) How might the provision of ecosystem services change in the future given anticipated trajectories of climate, disturbance regimes, and land use? (2) What is the role of spatial heterogeneity in sustaining future ecosystem services? We determined that future changes in each region are likely to be distinct, but spatial heterogeneity (e.g., the amount and arrangement of surviving forest patches or legacy trees after disturbance) will be important in both landscapes for sustaining forest regeneration, primary production, carbon storage, natural hazard regulation, insect and pathogen regulation, timber production and wildlife habitat. The paper closes by highlighting five general priorities for future research. The science of landscape ecology has much to contribute toward understanding ecosystem services and how land management can enhance—or threaten—the sustainability of ecosystem services in changing landscapes.     

Edge-mediated patterns of seed removal in experimentally connected and fragmented landscapes

While biological reserves remain central to biodiversity conservation, the amount of area available for terrestrial reserves may be inadequate for many taxa. Biodiversity spillover—the promotion of diversity in matrix areas surrounding reserves—might help address this shortfall in reserve area. However, the mechanistic underpinning of spillover remains uninvestigated. Two fundamental processes—seed dispersal and establishment—might generate plant biodiversity spillover. Here, we investigate the role of establishment in promoting spillover by assessing post-dispersal seed predation, a key component of establishment, in the matrix of a replicated, large-scale habitat fragmentation experiment, where spillover is elevated around patches connected by landscape corridors. Our results show that matrix seed predation may constrain the distance of this spillover effect by reducing establishment: seed removal was least at the matrix edge and increased further into the matrix. We found some support for matrix seed predation underpinning previously reported landscape-level variation in spillover. Of the three species we investigated, two showed evidence for elevated seed predation in the matrix surrounding the unconnected patches around which the lowest levels of spillover occur. However, seed predation did not explain connectivity-enhanced spillover, suggesting that seed dispersal likely drives this pattern. Management activities that increase seed deposition in the matrix may have beneficial effects via spillover. Our work also illustrates that matrix-mediated gradients in seed predation may be widespread, but likely vary depending upon matrix composition and the ecological system under consideration. In fragmented landscapes, this gradient could impact the distribution, abundance, and spread of plant species.     

Karst landscapes of China: patterns,ecosystem processes and services

Landscape Ecology - The karst region of southwestern China, one of the largest continuous karsts in the world, is known for its unique landscapes and rich biodiversity. This region has suffered...     

Southwestern ponderosa pine forest patterns following wildland fires managed for resource benefit differ from reference landscapes

Landscape Ecology - Managers aiming to utilize wildland fire to restore southwestern ponderosa pine landscapes require better understanding of forest cover patterns produced at multiple scales....     

Streambed landscapes: evidence that stream invertebrates respond to the type and spatial arrangement of patches

The availability and spatial arrangement of habitat patches are known to strongly influence fauna in terrestrial ecosystems. The importance of patch arrangement is not well-studied within running-water systems where flow-induced movements of patches and of fauna could decouple habitat characteristics and faunal habitat preferences. Using small, stream-dwelling invertebrates, we asked if fauna in such systems can distinguish among patch types and if patch arrangement at their `landscape scale' (i.e., within a streambed across which they move and forage) can be linked to faunal abundance. We quantified the spatial distribution of sand and leaf patches at multiple sites on a streambed at regular intervals over a 1 yr period, estimated faunal abundance in the two patch types, and experimentally determined if faunal colonization varied among leaf patches that were similar structurally but differed in their potential microbial food resources. We show that despite their small size and limited swimming abilities, these stream invertebrates did respond to patch type, that specific characteristics of an individual patch influenced faunal colonization, and that the spatial arrangement of patches on the streambed was linked to field abundances. Larval chironomids and adult copepods were more abundant in leaves than in sand and preferentially colonized leaf patches made with rapidly decomposing leaves that harbored higher microbial (bacteria and fungi) abundances over leaf patches with more refractory leaves and lower microbial abundances. Further, statistical models that included spatially-explicit data on patch arrangement (e.g., patch contagion, distance between patches) explained significantly more variation in faunal abundance, than models that included only nonspatial information (e.g., date, time since last flood). Despite the fact that these fauna live in a highly dynamic environment with variable flow rates during the year, unstable patch configurations, and seasonal changes in total abundance, our findings suggest a need for aquatic ecologists to test the hypothesis that small-scale landscape attributes within streams (e.g., leaf patch aggregation) may be important to faunal dynamics. If patch aggregation has negative consequences for stream biota, streambed `landscapes' may be fundamentally different from many terrestrial landscapes due to the inherent connectivity provided by the water and the over-riding importance of patch edges. Regardless of these differences, our findings suggest that the spatial configuration of patches in a landscape may have consequences for fauna even in highly dynamic systems, in which patches move and fauna periodically experience high levels of passive dispersal.     

Measuring the impacts of climate change on the spatial structure of grasslands in urban landscapes of North America

Although the importance of biodiversity conservation has been acknowledged in urban landscapes of many forest, desert, and coastal biomes, urbanization in grasslands and its negative/positive impacts on biodiversity is understudied. We designed a pilot, spatio-temporal study to envision the impacts of land-use and vegetation change on the composition and configuration of grasslands in urban landscapes of the Upper Missouri River Basin under four climate-change scenarios (A1B, A2, B1, and B2) from 2020 to 2070 with respect to the IPCC’s high-level and mid-level Representative Concentration Pathways (RCP 8.5 w/m² and RCP 4.5 w/m²). We show that under the most climate-change scenarios, the rate of grassland conversion into other land cover classes from 2020 to 2070 was greater in urban landscapes than the whole region but this trend was not correlated with urban expansion. Conversely, habitat proximity was negatively correlated with urban expansion. The capacity of habitat patches to function as wildlife refugia in urban landscapes was substantially greater under the B2 scenario, where social equality and environmental conservation are highly prioritized. On the basis of the results of this study, we demonstrate that measuring the changes in the composition and configuration of habitat patches, combined with an understanding of the rate of grassland conversion can provide more detailed information about opportunities and limitations for biodiversity conservation in this region and beyond. If managed strategically, urban landscapes can play a positive role in conserving biodiversity and preserving ecosystems in regions predominantly used for agricultural lands.     

Trees outside forests in agricultural landscapes: spatial distribution and impact on habitat connectivity for forest organisms

Context

Various species of forest trees are commonly used for ornamental purposes and are therefore frequently found in nonforest ecosystems. They constitute an important component of the so-called trees outside forests (TOF). Not much is known, however, about the drivers of TOF spatial distribution either in urbanized or in agricultural landscapes since they are generally absent from forest inventories.

Objective

The present study focused on the spatial distribution of TOF across agricultural landscapes and their potential role in the dispersal of a forest pest insect, the pine processionary moth, Thaumetopoea pityocampa (PPM).

Methods

All the TOF belonging to the genera Pinus, Cedrus and Pseudotsuga were considered as potential hosts and inventoried within a 22 × 22 km study window. We fitted a nonstationary Poisson process to the empirical data and used the distance to the nearest building as a covariate.

Results

Both empirical and simulated data indicated that TOF associated to human artifacts/urbanized areas constituted the main source of landscape connectivity for the PPM in the open fields under study. Because they do not account for TOF, forest inventories dramatically underestimate landscape connectivity and provide an erroneous picture of the PPM habitat distribution.

Conclusions

We conclude that TOF, especially the ornamental component, must be taken into account when it comes to understanding forest insect landscape dynamics or genetics. The omnipresence of TOF also suggests a potentially huge role in pest dispersal and invasive species expansion.