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		Wood in Neotropical Headwater Streams, Costa Rica & Panama
			Numerous studies document the geomorphic and ecological importance of wood in temperate headwater streams. Large wood, typically defined as being at least 1 m long and 10 cm in diameter, increases the roughness of the channel boundaries and promotes storage of fine sediment and organic matter, as well as enhancing localized channel scour that creates pools and overhung banks, which enhances instream habitat diversity. Although the majority of existing literature on instream wood comes from the Pacific Northwest, within the past decade studies from elsewhere in the U.S., as well as Europe, Asia, Australia, and South America have expanded our understanding of regional differences that influence instream wood. Nothing has yet been published, however, on wood in tropical headwater streams.
			In Costa Rica we work at the La Selva Biological Station, a 1600-hectare reserve that includes 730 hectares of old-growth tropical wet forest. We have 30 study sites (each a 50-m length of stream) along small channels (0.1-8.5 km2) tributary to the Puerto Viejo or Sarapiquí Rivers. During our initial field work in March 2007, we surveyed valley and channel characteristics and measured wood load at each study site. Since March 2007, we have returned to La Selva every four months to continue monitoring a subset of 10 study sites. We are using repeat surveys of these sites to characterize mobility and exchange of individual pieces of wood. We have set up stream gages at some of the sites, marked tracer clasts in the streambed for periodic repeat surveys that indicate bed mobility, and anchored fresh pieces of wood in the channel so that we can monitor decay rates. Together, these measurements will allow us to evaluate the relative importance of recruitment, decay, and transport in controlling wood loads at La Selva.
			Our field site in Panama is the Upper Rio Chagres, a 400 km2 catchment that is the main water supply for the Panama Canal. Accessible only by helicopter, the Upper Chagres is a remote, mountainous environment with old growth tropical forest. Unlike the more gentle terrain of La Selva, the steep slopes along the Chagres frequently experience landslides that introduce large volumes of sediment and wood to the main channel. The very large discharges and high rates of wood decay, however, prevent the wood from remaining in the channel for more than 1-2 years. During initial field work in the Upper Chagres during 2002, we noticed the dearth of wood in the stream. Intense rainfall over the uppermost portion of the catchment during July 2007 created numerous landslides, which resulted in large wood jams in the channel. We surveyed three of these jams in February 2008 and will repeat these surveys in February 2009. Although these jams cover up to 2400 m2 and include logs 27 m long and 1.9 m wide, we hypothesize that more than half of the volume of wood in each jam will be gone by February 2009. This is partly based on observations of the dynamic nature of this system; a storm in 1999 of magnitude comparable to the 2007 storm left no remnants of landslides and wood in the channel that were visible during our 2002 field work.
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