1 IntroductionRiverine networks are intricately linked to the landscapes through which they flow (Hynes, 1975*) (see Appendix A) and it is widely accepted that riverine management should occur over whole watersheds (Naiman et al., 1992; Frissell et al., 1986*). Many fundamental theories and models in river ecology have their bases in landscape-scale thinking. While some approaches are naturally borrowed from the field of landscape ecology (see Section 4.2), we assert that much of the research linking landscapes to rivers has arisen relatively independently. For example, the river continuum concept (Vannote et al., 1980*) considers changes in carbon processing and biota with increasing drainage area across entire riverscapes. Sediment routing and nutrient models (see Zweimüller et al., 2008; Tetzlaff et al., 2007) incorporate vegetation type, soil conditions, land use, and lithology over large areas. In this review, we focus on how landscape influences on rivers, and in particular on fish assemblages, have been and can be measured, quantified, and applied to freshwater management problems; we draw on examples from multiple continents.
In Section 2 of this review, we summarize the policy and management drivers for landscape-scale riverine research, remind readers of the ecological drivers, and synthesize the technological advances that have enabled dramatic progress in the field. In Section 3, we describe the development of landscape-scale riverine research through a series of landmark theoretical and review papers. In our Section 4, we consider three important questions with respect to landscape-scale riverine research:
- Has new research effectively incorporated the strengths of new technologies or are we doing the same old thing with more expensive data?
- Have we incorporated key concepts from landscape ecology to improve our understanding of how landscapes affect rivers?
- Have we been able to use landscape analyses to address management and policy needs?
We synthesize existing literature to answer these questions and, in so doing, review progress to date. In Section 5, we use our review to identify opportunities for future efforts.
The roots of landscape-scale riverine research lie not in process-based models or mechanistic research, as in watershed ecology, but in the evaluation of pattern using statistical or correlative models, guided by mechanistic principles. Such analyses necessarily draw heavily on concepts from both river ecology and landscape ecology. Ideas commonly explored in these analyses include correlations between particular land uses and instream conditions, the impact of geographic extent on the strength of these correlations, and the degree to which local relationships between predictor and response variables at a large numbers of sites can be aggregated at larger scales. We define scale as the grain (resolution) and extent of both the predictor variables (generally measures of landscape condition) and the response variables (measures of instream condition and biological response).
We differentiate landscape-scale riverine research from traditional river ecology, riparian ecology, or watershed ecology by (i) the large spatial extent of the analyses, (ii) the use of spatial databases, and (iii) the emphasis on how landforms and land use outside of the active channel or the riparian area affect streams and rivers (Figure 1*). We limit ourselves in this review to research that includes all three of the above features and to projects that consider fish as the biological response of interest. Except for a few examples, we exclude the diverse and important research concerning landscape-scale impacts on other instream biological responses, on physical and chemical habitat, and on terrestrial or marine biota.