Multiscale and Cross-Scale Phenomena

Broad Scales Constrain Fine Scales

Many natural phenomena occur at multiple scales and different factors are better at explaining these phenomena at different scales (Turner and Gardner 2015). Cross-scale interactions occur when processes at one scale affect those at higher or lower scales (Allen et al. 2014). Hierarchical confinement is a specific case of cross-scale interactions and refers to when broad scale processes constrain a phenomena occurring at finer scales nested within the broader scale (Walker et al. 2006; Turner and Gardner 2015). In other words, factors that are relevant to broad scale (e.g., climate) constrain the influence of fine scale factors on an observed phenomena (Turner and Gardner 2015). For example, hierarchical confinement occurs when lake temperatures constrain what fish species occur in the lake, despite the presence of suitable vegetation and prey in the lake.

Fine Scale Patterns Become Broad Scale Patterns

Another case of cross-scale interactions is when fine scale phenomena become broad scale phenomena when they occur at the same time (i.e., synchronously) at the extent of a broad scale. This is referred to as “scaling up” or a “revolt” and helps explain why invasions, pest outbreaks, disease epidemics, economic depression, climate change, etc. occur (Holling 2001). Processes like births and deaths that occur asynchronously (or randomly) in time and space at a scale of interest result in relatively stable conditions and do not emerge as trends at broader scales. Thus, trends at small scales do not reflect large-scale trends unless there is synchrony at the extent of the larger scale.

For example, increasing invasive species presence on a single land parcel does not necessarily mean that the species is increasing at the regional scale because the species may be declining on other land parcels (Figure 6). However, when invasive species presence increases across many land parcels at the same time at the extent of the region, regional scale trends of increasing invasive species emerge. A key implication is that fine scale processes occurring over large extents can influence systems at broad scales.