275 J. Wu, K.B. Jones, H. Li, and O.L. Loucks (eds.), Scaling and Uncertainty Analysis in Ecology: Methods and Applications, 275–295. © 2006 Springer. Printed in the Netherlands. CHAPTER 15 SCALING ISSUES IN MAPPING RIPARIAN ZONES WITH REMOTE SENSING DATA: Quantifying Errors and Sources of Uncertainty THOMAS P. HOLLENHORST, GEORGE E. HOST, AND LUCINDA B. JOHNSON 15.1 INTRODUCTION Riparian zones are the ecotones or transition areas between upland and aquatic ecosystems, located at the margins of rivers, lakes, ponds and wetlands. Their boundaries are defined by changes in soil, moisture, and vegetation (Naiman 2000, Décamps 1996, Gregory et al. 1991). Although these ecosystems may be small relative to the aquatic systems they abut, they perform many important ecosystem services, including shading (thus buffering air and water temperature), retaining nutrients and/or sediments, stabilizing stream banks and littoral zones, and providing organic material (leaves, wood) and critical habitat for a diverse community of plant and animal species (Malanson 1993). Riparian zones are highly variable systems whose structure and composition are shaped by geomorphology, vegetation patterns, disturbance regimes (Décamps 1996), as well as current (Erickson and DeYoung 1993) and perhaps historic land use practices (Foster et al. 2003). Processes that operate over a large range of temporal and spatial scales control these structuring factors. At one end of the time/space continuum are processes such as tectonics, volcanism, glaciation, and climate change. At intermediate spatial and temporal scales are historic land use practices (e.g., burning regimes implemented by native peoples, permanent land cover conversion) and catastrophic flooding. At small scales, localized flooding and land management practices influence the structure and function of riparian zones. Some processes occur over multiple scales and their effects may also vary by scale. The fine-scale variation of vegetative cover resulting from moisture and soil gradients around streams and wetlands has posed a challenge to research scientists and land managers (Muller 1997, Congalton et al. 2002). One of the current