Relationships beiween Radiation and Canopy Closure Estimates in Streamside Buffers in Western Oregon

Maintenance of buffers for avoiding excessive increases in stream temperature for protecting cold water fisheries is prominent in riparian rules for forested streams in the Pacific Northwest. Four fish-bearing streams with basins of 250-400 ha in western Oregon were studied to determine how arrangement and amount of streamside buffers in clearcut units influenced riparian environments. Buffer designs included no-tree buffers, partial buffers 12 m wide, and iwo-sided buffers 15-30 m wide. Incident solar radiation estimates from fisheye photographs were compared to visual estimates of canopy closure, densiometer estimates of canopy closure, and basal area. Based on individual sample points, regression analyses of radiation estimates resulted in r(2) values of 0.65 for visual estimates of canopy closure; 0.72 for spherical densiometer, directed south; 0.52 for basal area from in-stream sample points placed at 30-m intervals; and 0.63 for basal area from inventory points 15 m from the stream. High variability existed around all of the lines; r(2) values increased 0.10-0.30 when unit means were used. Canopy closure estimators, such as densiometers, can offer less time-consuming and less expensive methods than direct measures of radiation to estimate the amount of radiation that might reach a stream through streamside buffers.