Patterns and Processes Part II, 21 January 2015
There is a fundamental assumption that underlies a study of landscape metrics: “Processes are linked to, and can be predicted from, some (often unknown) broad-scale spatial pattern.” From the pattern, we can understand the processes. Therefore methods must be developed by which we can qualify and quantify the patterns we see.
Within a given landscape, there are three causes of spatial patterning: local uniqueness, phase differences, and dispersal. Boundaries are created and maintained within the landscape which lead to the identification of patches. These boundaries can be distinguished as “sharp, narrow, persistent” or “blurred, wide, transient,” and they may be difficult to identify. One example of patterning is fragmentation. Fragmentation may occur as the result of many different processes, and it both increases isolation and decreases rare species.
There are certain criteria one must look at when analyzing a landscape. According to Riitters et al. (1995), there are five classes of metrics:
- “Number of classes or cover types”
- “Texture measures (fine or coarse)”
- “Degree to which patches are compact or dissected”
- “Patches are linear or planar”
- “Patch perimeters are complicated or simple in shape”
When examining landscape composition, there are additional metrics:
- “Relative richness: -the proportion of the number of cover types potentially present”
- “Dominance: the deviation from the maximum possible evenness”
- “Diversity: a reflection of richness and how evenly the proportions of cover types are distributed”
- “Connectivity: based on a user-defined threshold, a measure of how connected the patches are”
Finally, there are additional measures of spatial configuration:
- “Probabilities of adjacency–the probability that a grid cell of cover type i is adjacent to cover type j”
- “Contagion–distinguishes between overall landscape patterns that are clumped or rather dissected”
- “Connectivity–how fragmented is a habitat type”
- “Proximity index–the degree to which patches in the landscape are isolated from other patches of the same cover type”
- “Area-weighted average patch size–to account for the frequently observed skewed distribution in patch sizes”
One method of measuring the complexity of a landscape is to look at fractals. It may be easy to identify a patch, but it is more difficult to determine whether that patch is complicated or simple. Fractals identify the fundamental complexity of an object.