Literature Review Exercise
This is a literature survey exercise for the thesis “Integrated tool for landscape ecology analysis: ecoanalyze”. The primary basis of this tool is from the already existing tool called as “Fragstats”. Fragstats has released its latest version which is version 4.0. Fragstats are originally developed before 1982 and has evolved to version 4.0 covering the landscape metrics better in each of the versions. Landscape ecology is about focusing on the spatial patterns of the landscape elements. Landscape ecology is majorly founded on the patterns of the environment that influence the ecological patterns. The pattern of the ecological system can be considered to be a fractal pattern that need to be analyzed as to how it directly influences or corresponds to the habitats. The habitats are in which the organisms live are for example are structured spatially at a number of scales. These patterns interact with the organism perception and behavior to drive higher level of process of population dynamics and behavior. If there is any kind of disruption in the landscape pattern interfere with the maintenance of biodiversity of the habitat and ecological health. Therefore, the idea of quantifying landscapes came to be of much importance in learning the pattern-process relationships (O’Neill et al. 1988, Turner 1990, Turner and Gardner 1991, Baker and Cai 1992, McGarigal and Marks 1995). This kind of pattern-based study has already resulted in a lot of indices for the landscape analysis patterns. These pattern-based development study has been made possible with the advent of GIS technologies. Before we move on to what indices would be included in the Eco analysis tool, we have to understand the importance of landscape and why we need them.
There are many different interpretations of the term “landscape” itself. The landscapes usually include an area of land with mosaic of patches or landscape elements. As per Formal and Gordon (1986) defines landscape as a cluster of interacting ecosystems repeated in a similar pattern throughout the landscape area that is a part of the landscape ecology. The definition of the landscape pattern usually differs with the variants of what is being under study.
An example for the landscape pattern which is relevant to the area of the study can be considered could be a wildlife habitat, we can see the landscape as a mosaic of habitat patches. These habitat patches could be studied with respect to an organism’s perspective and the scaling of the environment (Forman and Godron,1986). These habitat patches can be defined with respect to an organism’s perspective and these landscape sizes would differ as well based on the organism under study. These landscapes occupy some spatial scale. The size of the habitat landscape cannot be defined in a particular fashion. Since the size of the landscapes vary with respect to the organisms, we can’t have any definite definition for the size of the landscape. Right now, Fragstats is used as a software that is compatible with windows and has to be fed with a separate set of output raster to be worked upon with the fragstats. The whole idea is to develop a plug-in with an opensource GIS software such as the QGIS which will use the integrated output file to feed into the landscape analysis. The new plug-in would use the indices that are used with fragstats and will be implemented based on the time available. This will later be used to study a landscape pattern on any of the landscape patterns.
The landscape pattern can be classified in different ways depending on the data that is collected, and the objectives of the types of data collection, there can be four types of spatial data as per (McGarigal and Marks, 1995). The four types of landscape patterns are defined below
1. Spatial point patterns:
These represents a collection of entities where the geographical locations are of primary interest rather than quantitative or qualitative attribute of the entity. Such kind of spatial point data analysis are more clustered than expected by chance to find the spatial scale where it is more or less clustered than expected by chance (greig-smith 1983, Dale 1999)
2. Linear network patterns: As the name suggests, this is a network of landscape elements which intersect to form a network. An example of this kind of network patterns is a map of streams wherein the data consists of nodes or linkages. With respect to the point patterns, the geographic location, nodes and corridors are the primary area of interest. The whole goal of the linear network pattern analysis is that they are used to characterize the physical structure (e.g., corridor density, mesh size, network connectivity and circuitry) of the network and variety of metrics have been developed for the purpose(Forman 1995) (McGarigal and Marks, 1995).
3. Surface patterns:
These are quantitative measurements which vary continuously across the landscape without any explicit boundaries making the data look like representing a three-dimensional surface where the value measured at a geographic surface is represented as a height of the surface. Here we look at sample and figure out how close they are together and how they are arranged closely with other with respect to the measured variable (McGarigal and Marks, 1995).
4. Categorical map patterns: Here in this kind of landscape pattern, the data is represented as a mosaic of discrete patches representing a relatively discrete areas of relatively homogenous environmental conditions at a particular scale. These patch boundaries are shown and distinguished by discontinuities in environmental character from surroundings that are relevant to ecological phenomenon under consideration (Wiens 1976, Kotliar and Wiens
1990). There are certain metrics that are important in the study of the metrics for landscape analysis and the data available. Patch level metrics form the basic building blocks for categorical maps.
Cell level metrics
There can be cell-level metrics which can be defined for individual cells. They can be used to characterize the neighborhood of each of the cell without any regard for patch or class affiliation. An example can be an individual organism dispersing from natural habitat to a neighborhood defined by a dispersal distance (McGarigal and Marks, 1995). This would make the standard output would consist of a vector of cell-based measurements in tabular form. The cell metrics can be used for computing for each of the cell in the landscape and the output for the same would consist of a continuous surface grid or map.
Patch level metrics
After cell level, we can have a patch level metrics that would characterize the context of patches. Patch level metrics are very helpful in giving important information in landscape level investigations. Some of the species are affected by edges and are closely associated with patch interiors. This helps in comparative study of the neighborhood patch that is available which actually helps in understanding the patch and degree of contrast between the patch and the neighborhood (Robbins et al. 1989). The usefulness of this information will depend on the investigation objectives.
Class level metrics
After the cell and patch level metrics, there is a class-level metrics. These class-level metrics are integrated over all the patches of a specific type. This would help in finding the greater contribution of large patches to overall index. An example of this would be a habitat fragmentation(Martin 1992). A habitat fragmentation is a landscape level process. Here in class level metrics, it is divided into smaller habitat fragments. This usually involves change in landscape composition structure and functions
Landscape level metrics
The next level of metrics in the hierarchy would be landscape level metrics. These might be aggregated into a weighted average or may reflect on aggregate properties of patch mosaic. This quantification of landscape diversity assumed a role in major focus of landscape ecology. These landscape level metrics might provide with similar or redundant information with different natural algorithms. Landscape level metrics represent the amount and spatial distribution of a single patch which can be considered as a fragmentation index. This makes it important to know what kind of metric we are dealing with even though all of them are related (patch, class and landscape) (O’Neill et al. 1988, Li 1990, Turner 1990, Turner and Gardner 1991).
As per the hierarchy of the landscape patterns, the next item is to figure about the composition of these landscape patterns. These compositions can be quantified, and they are related to variety and types of the metrics. The diversity indices can be used to summarize the species under study in landscape ecology. There are some measures used to find the composition and they are as follows:
Proportional Abundances
Proportional Abundances of each of the classes that can be derived is the proportion of each class relative to entire map (McGarigal and Marks, 1995)
Richness
Richness is the number of different patch types. Indices like the Shannon diversity indices are used to calculate the richness in landscape ecology (McGarigal and Marks, 1995).
Evenness
Evenness index is a relative measurement, and this will help in knowing the presence of different patch types. Evenness is usually expressed as a function of maximum diversity possible for a given richness (McGarigal and Marks, 1995).
Diversity
Diversity can be used to measure the richness and evenness that can be computed which depends on the emphasis placed on these components
Spatial configuration is much more difficult to quantify and refers to the spatial character and
arrangement, position, or orientation of patches within the class or landscape. Some aspects of
configuration, such as patch isolation or patch contagion, are measures of the placement of patch
types relative to other patches, other patch types, or other features of interest. Other aspects of
configuration, such as shape and core area, are measures of the spatial character of the patches
Based on the number of confirmation metrics that can be formulated in either individual patches or a while class or a landscape depending on the kind of emphasis that is needed(Kelley, 1996). Some principal aspects of confirmation and a set of sample metrics are given below
Patch size distribution and density
Patch size represents the fundamental attribute of a spatial character of a patch. Patch density can be defined as a number of patches per unit area.
Patch Shape Complexity
This is more related to the geometry of the patch. It has to either simple and compact, or irregular or convoluted. Shape is difficult to configure as the patch shape complexity are based on relative amount of perimeter per unit area usually, they are indexed in terms of Euclidian shape and it is widely used(Gustafson 1998).
Core Area:
This mostly represent the interior area of patches after using a user defined buffer. The areas are unaffected by the edges of the patch. The core area integrates patch size, shape and edge effect distance for each of the unique landscape measure.
Isolation or Proximity:
Isolation as it suggests is definitely depends on the tendency of the patches to be isolated in space from each other. Proximity is how close they are with respect to the neighborhood patch.
The original proximity index was formulated to consider only patches of the same class within the specified neighborhood. This binary representation of the landscape reflects an island biogeographic perspective on landscape pattern. Alternatively, this metric can be formulated to consider the contributions of all patch types to the isolation of the focal patch, reflecting a landscape mosaic perspective on landscape patterns (Gustafson and Parker, 1992).
Contrast:
Contrast refers to the relative difference among patch types. An example that was given in the fragstats would be to consider a mature forest that would probably have a lower-contrast edge than mature forest adjacent to open field, depending on how the notion of contrast is defined. This can be computed as a contrast-weighted edge density, where each type of edge (i.e., between each pair of patches types) is assigned a contrast weight.
Dispersion.
Dispersion refers to the tendency for patches to be regularly or contagiously distributed (i.e., clumped) with respect to each other. There are many dispersion indices developed for the assessment of spatial point patterns, and many of them have been applied to categorical maps. A common approach is based on nearest-neighbor distances between patches of the same type (Kelley, 1996). This is computed in terms of the relative variability in nearest-neighbor distances among patches; This is usually based on the ratio of the variance to mean nearest neighbor distance.
Contagion & Interspersion.
Contagion refers to the tendency of patch types to be spatially aggregated; that is, to occur in large, aggregated or “contagious” distributions. (O’Neill et.al. 1988; Turner 1989a, 1990). Interspersion/juxtaposition Interspersion/juxtaposition index that increases in value as patches tend to be more evenly Interspersed (O’Neill et.al. 1988; Turner 1989a, 1990). There are other metrics that are generated from the matrix of pairwise adjacencies between all patch types, in which the elements of the matrix are proportional to edges in each pairwise type.
I would need to do more research on including the indices formula in the literature review and also on where I would use the tool in any landscape ecology analysis.