Wood Loading in Headwater Neotropical Forest Streams

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Research in temperate regions has amply demonstrated that wood exerts a critical influence on geomorphic and ecological processes in many streams. However, very little is known of the abundance or function of wood in low-latitude streams, which are likely to have extensive forest cover. Given the known ecological differences between streams in tropical and temperate regions, it is inappropriate to simply extrapolate knowledge of the ecological dynamics of wood from temperate to tropical streams, yet there are essentially no data on wood loading, residence time, or geomorphic function of wood in tropical streams from which to infer the ecological influences of wood in these systems. The first step in understanding the function of wood in tropical streams is to inventory wood loading and residence time for different tropical regions and different stream types. Thus, the primary objectives of the proposed research are to characterize (i) wood loading, (ii) spatial distribution in relation to potential control variables, and (iii) residence time of wood across a neotropical headwater drainage network. Such fundamental research will then provide the basis for studies of the geomorphic and ecological functions of wood in tropical streams.Field research will focus on 1st to 4th order stream channels. The selected field site at La Selva Biological Station and Braulio Carrillo National Park in Costa Rica provides a gradient from high-elevation first-order drainages in mountainous terrain through moderate gradient streams and hillslopes that transition to the Caribbean coastal plain. Ongoing data collection at the site provides information on climate, hydrology, and forest dynamics, and an infrastructure of lodging and trail networks exists for accessing streams. Observations by stream ecologists working at the site indicate the presence of abundant wood and debris dams in at least some portions of the drainage network. The research objectives will be addressed with field work organized around two phases; (1) mapping wood distribution and stream characteristics, and (2) monitoring wood dynamics at a selected subset of mapped sites with repeat visits and interval photography. Research is also designed to test hypotheses regarding the relative importance of different processes of wood introduction to channels and the processes controlling wood retention within different portions of the channel network. The project will extend over three years, and will provide support and training for a PhD candidate, and at least two undergraduate students.Intellectual Merit: The research proposed here represents the first systematic investigation of spatial distribution, wood loading, and residence time of wood in tropical rivers, and as such will provide a critically important foundation for understanding geomorphic and ecological processes in tropical streams, as well as for setting management guidelines in these streams.Broader Impacts: Broader impacts include five components: (1) providing the first documentation of spatial patterns of wood distribution in neotropical headwater drainages and rates and processes of wood retention; (2) creating baseline knowledge of wood in tropical streams that can be used to develop management guidelines for minimizing the impacts of deforestation; (3) training graduate and undergraduate students; (4) establishing interdisciplinary research collaborations with stream ecologists and others working at the tropical research stations where field work will take place; and (5) disseminating the research results through a website, as well as through more traditional disciplinary outlets.