Class 3: Understanding Landscape Metrics

Spatial patterns, ecological processes and interactions across ecosystems are key concepts within landscape ecology. Landscapes, for example, are considered to be inherently heterogeneous. Process-based research requires analysis of landscape pattern (also referred to as form) – what underlying processes determine the pattern we see in the landscape? On school of thought suggests that the patterns we see on the map are only one of many potential landscape patterns that may have materialised by such processes.

So what statistical tests can we use to determine whether the observed pattern has been generated by a hypothesised process?

We assume that where things are, especially in relation to other things, will have particular consequences. We can use spatial autocorrelation (see Class 2 notes) to determine the extent to which the variables are distributed in any meaningful pattern, and are associated with each-other. Types of spatial autocorrelation include clustering, dispersed and random.

Pattern Types:

• Patterns generated from a response to environmental conditions (i.e. elevation) are known as first order processes.
• Patterns generated from a response to the distribution and interactions between other variables (i.e. presence of predators) are known as second order processes.

Process Types:

Stationarity

Stationary assumes that the process regime stays the same, and that processes aren’t inherently direction (the processes are isotropic as opposed to anisotropic).

• Stationary processes are processes that do not change (or drift) over space:
• A process that has no variation in intensity over space are known as first-order stationary.
• A process that has no interaction with other variables across space are known as second-order stationary. For these processes, you might use kriging.

There are a number of abiotic (i.e. climate, topography, soils) and biotic (i.e. disturbance, competition, distribution of keystone species) factors operating within a landscape. It is also important to consider human land use impacts on habitats. Landscape patterns are the result of a combination of different processes acting on multiple scales.

Creating and Maintaining Heterogeneity

There are three causes of spatial patterning:

1. Local uniqueness
2. Phase differences caused by disturbances
3. Dispersal

Landscape metrics include the number of cover and class types, texture patterns, compaction of patches, whether patches are planar or linear, and other the patches are complex in shape. However these are difficult to quantify and prove significant.