EARTH SURFACE PROCESSES AND LANDFORMS Earth Surf. Process. Landforms 34, 1198–1215 (2009) Copyright © 2009 John Wiley & Sons, Ltd. Published online 2 June 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/esp.1800 John Wiley & Sons, Ltd. Chichester, UK ESP Earth Surface Processes and Landforms EARTH SURFACE PROCESSES AND LANDFORMS Earth Surface Processes and Landforms The Journal of the British Geomorphological Research Group Earth Surf. Process. Landforms 0197-9337 1096-9837 Copyright © 2006 John Wiley & Sons, Ltd. John Wiley & Sons, Ltd. 2006 Earth Science Earth Science 9999 9999 ESP1800 Research Article Research Articles Copyright © 2006 John Wiley & Sons, Ltd. John Wiley & Sons, Ltd. 2006 Wood distribution in neotropical forested headwater streams of La Selva, Costa Rica Wood distribution in headwater streams of La Selva, Costa Rica Daniel Cadol,* Ellen Wohl, Jaime R. Goode and Kristin L. Jaeger Department of Geosciences, Colorado State University, Fort Collins, CO, USA Received 15 July 2008; Revised 9 January 2009; Accepted 19 January 2009 * Correspondence to: Daniel Cadol, Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482 USA. E-mail: cadol@warnercnr.colostate.edu ABSTRACT: Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north-eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1–8·5 km 2 and gradients of 0·2–8%, wood load ranged from 3 to 34·7 m 3 wood/100 m channel and 41–612 m 3 wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two-thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel-bed reaches than in reaches with coarser or finer substrate. Copyright © 2009 John Wiley & Sons, Ltd. KEYWORDS: in-stream wood; tropical streams; fluvial geomorphology; vegetation-channel interaction Introduction Headwater streams are the low-order channels that form a large proportion of a drainage network and strongly influence processes in downstream portions of the network (Freeman et al., 2007). Headwater streams are or were historically forested in many parts of the world, and extensive research along such streams in temperate zones indicates the geomorphic and ecological importance of wood in these streams. Geomorphic effects of wood include increased hydraulic roughness of channel boundaries (Keller and Tally, 1979; Curran and Wohl, 2003; MacFarlane and Wohl, 2003; Daniels and Rhoads, 2004; Wilcox et al., 2006), greater storage of sediment and organic matter on the streambed (Faustini and Jones, 2003), enhanced localized bed and bank scour (Daniels and Rhoads, 2003), and altered local streambed gradient and channel morpho- logy (Keller and Swanson, 1979; Baillie and Davies, 2002; Montgomery et al., 2003; Curran and Wohl, 2003). Ecological effects of wood include increased retention of organic matter and nutrients (Bilby and Likens, 1980; Erman and Lamberti, 1992; Raikow et al., 1995), greater habitat diversity associated with diversity of substrate and hydraulic variables (Bisson et al., 1987; Maser and Sedell, 1994; Kail, 2003), and food and habitat for many species of microbes and invertebrates (Maser and Sedell, 1994; Wright and Flecker, 2004). Until very recently, the great majority of existing studies on the effects of wood in stream channels came from the north-western portion of the US. Within the past decade, investigators have extended this work to streams in other parts of North America (Richmond and Fausch, 1995; Thompson, 1995; Marcus et al., 2002; Magilligan et al., 2008), as well as Europe (Piegay et al., 1999; Gurnell et al., 2000b; Dahlström and Nilsson, 2004; Wyzga and Zawiejska, 2005; Comiti et al., 2006), Australia (Brooks et al., 2003), New Zealand (Baillie and Davies, 2002; Meleason et al., 2005), South America (Andreoli et al., 2007; Comiti et al., 2008; Mao et al., 2008), and Asia (Haga et al., 2002). Together, these studies clearly indicate that wood is of fundamental geomorphic and ecological importance in forested streams around the world, and that systematic removal of both forests and in-stream wood has dramatically decreased the abundance of wood in streams. These studies also indicate that, although the basic functions of wood can be similar in streams across a broad range of environments, important differences also occur between environments. In particular, environmental controls that create variation in the size and abundance of wood introduced to a stream, combined with the rate of wood decay and the magnitude, frequency, and duration of hydraulic forces exerted on the wood, create differences in the residence time and function of wood in streams (Benda et al., 2003; Gurnell, 2003; May and Gresswell, 2003a). Conceptual models of wood dynamics developed for temperate-zone streams provide a starting point, however, from which to examine how wood dynamics differ in other environments. Our intent here is to use data on wood loads from headwater streams in Costa Rica to examine potential differences in wood dynamics between temperate and tropical headwater streams.