Characterising riverine landscapes; history, application and future challenges

Abstract

Advancing our understanding of the structure and functioning of riverine landscapes is a cornerstone of river science (Thorp et al., 2008). This requires empirical data and models of how environmental and ecological patterns relate to biological, chemical and physical processes, and their interactions across spatial and temporal scales that occur at different organisational complexities. Patterns are an indication of the natural spatial and temporal heterogeneity within ecosystems (Levin, 1992). Understanding how riverine landscapes function as ecosystems relies on our ability to capture this heterogeneity across meaningful and interpretable scales (Underwood et al., 2000; Thorp et al., 2008). Imposing order on natural systems, including riverine landscapes, is inherently complex due to their dynamism and high spatiotemporal variability across longitudinal, lateral, vertical and temporal dimensions (Ward, 1989). Classification has a long history in science and has been widely used in different aspects of river science, such as conservation (i.e., Margules and Pressey, 2000; Nel et al., 2009), river management (Rosgen, 1994; Brierley and Fryirs, 2005), and in identifying natural and anthropogenic patterns of biological and physical concerns. Characterisation, by comparison, is a process of describing the distinctive features of a landscape or a river system, whereas classification is a process of ordering objects or environmental variables into groups based on shared characteristics. Classification involves three discrete components: taxonomy, typology and allocation. Taxonomy is an objective procedure consisting of ordering objects into classes based on their measured characteristics, whereas a typology is a subjective, judgemental process of identifying different classes (Newson et al., 1998). Taxonomists have referred to these two processes as natural and special classifications (Sneath and Snokal, 1973). The classification of animals, as undertaken by Linneus, into species is regarded as a natural classification. However, in river science, landscape characterisations or classifications founded on typologies are more common, such as the geographic cycle of Davis (1899), the River Continuum Concept (RCC) by Vannote et al. (1980) and the Montgomery and Buffington (1997) typology developed for mountain drainage basins in the Pacific Northwest, USA.