Title: Evaluating headwater stream buffers: lessons learned from watershed scale experiments in southwest Washington
Author: Bisson, Peter A.; Claeson, Shannon M.; Wondzell, Steven M.; Foster, Alex D.; Steel, Ashley.
Source: In: Anderson, P.D.; Ronnenberg, K.L., eds. Density management in the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 169–188.
Description: We present preliminary results from an experiment in which alternative forest buff er treatments were applied to clusters of watersheds in southwest Washington using a Before-After-Control-Impact (BACI) design. Th e treatments occurred on small (~2- to 9-ha) headwater catchments, and compared continuous fi xed-width buff ered, discontinuous patch-buff ered, and unbuffered streams to an adjacent unlogged reference catchment. Eight treatment clusters were monitored from 2001 to 2006; four were located in the Black Hills (Capitol State Forest) and four in the Willapa Hills of the Coast Range. Logging took place in 2004 or 2005, depending on the cluster. Th e study streams were too small to support fi shes, but catchments did harbor amphibians, aquatic invertebrates, and riparian mollusks. In addition to biota, we examined water quality, discharge, and organic matter inputs. Th e intent was to monitor the sites two years pre-treatment and three years posttreatment, although unforeseen circumstances caused some exceptions. Overall, results suggested that relatively small but measurable changes in ecological condition occurred in most catchments where logging occurred. Changes were most apparent in streams having no buffers. In catchments with no buff ers, summer water temperature increases were largest, organic matter inputs declined, and drifting invertebrates increased or decreased depending on their trophic guild. Changes in catchments with discontinuous patch buff ers were often complex and generally less detectable, and streams with continuous fi xed-width buff ers tended to exhibit the fewest changes in invertebrate communities and organic matter inputs relative to reference sites. Analyses of ecological response, both physical and biological, were fraught with difficulty. Difficulties in executing the study and analyzing results include operational planning and scheduling, spatial and temporal variability, and unplanned environmental disturbances. Based on our experience, we offer suggestions for future research on riparian management in small watersheds. First, think of watershed-scale studies as interventions that are carried out so as to maximize what we can learn from them, rather than as true experiments. Second, if the study covers several locations, thoroughly characterize diff erences in physical and biological features among the sites before treatments are applied to avoid misinterpreting results. Third, be prepared to accommodate uncontrolled environmental disturbances (e.g., droughts, floods, wildfi res, etc.) that are inevitable in multi-year investigations. Fourth, once the basic experimental layout is established, resist the temptation to switch treatments midway through the study, which will only confound analyses. Finally, when surprises occur, be flexible enough to monitor their eff ects to take advantage of learning opportunities.
Keywords: riparian management, buff ers, headwater streams, small watershed studies, experimental design, BACI.
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Bisson, Peter A.; Claeson, Shannon M.; Wondzell, Steven M.; Foster, Alex D.; Steel, Ashley. 2013. Evaluating headwater stream buffers: lessons learned from watershed scale experiments in southwest Washington. In: Anderson, P.D.; Ronnenberg, K.L., eds. Density management in the 21st century: west side story. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 169–188.
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