Introduction - What Is Heterogeneity?

Heterogeneity is variability within a system that accounts for scale. It is the quality of something to be made up of many different parts, elements, kinds, or individuals with these different components occurring at different scales at varying densities. The opposite of heterogeneity is homogeneity, or all parts or components of a place or system being identical or nearly identical. Heterogeneity is synonymous with the variability or complexity of landscapes at both the temporal and spatial scales. In other words, the heterogeneity of a landscape is impacted by the scale at which the heterogeneity is being measured or observed (Fuhlendorf et al. 2017). An example of heterogeneity might be a piece of a rainforest, with many different species of plants and animals and other abiotic components (like streams, patches of shrubs and grass, etc.), while an example of an equally sized homogenous plot of land could be a large lawn with only one species of grass present. However, as will be illustrated below, zooming in or out on these locations will determine whether or not they are viewed as heterogeneous or homogenous.

A visual representation of spatial heterogeneity and scale is given in Figure 1 below. Assume that each level (1, 2, 3, and 4) is a snapshot of the same landscape at a different spatial scale. The bottom level (4) encompasses the largest area and as you work up the levels, the area gets zoomed in and smaller in size. Level 1 (top) is homogenous, the opposite of heterogeneous, because there are no differences in cover as it is measured. At the second level (2) the observer has zoomed out and can now see that there are two distinct components to the landscape (blue and green). The blue and green components seem to occur evenly and without much variation. As the observer moves farther and farther out in view (3 and 4), they observe that there are more than just two components to the landscape and some components occur in greater density than others. There are many different parts (green, blue, orange, yellow) all occurring in varying quantities and in different places (i.e. spatial heterogeneity).  As the observer increases their view, the scale at which they are working increases. The increase in scale also increases the heterogeneity and complexity of the landscape. These same principles can be applied to a landscape viewed through temporal scales of days, months, years, and beyond.

Figure 1. How scale impacts the perceived heterogeneity of the landscape. Conceptual figure provided by Jessica Johnson.