Effects of Riparian Buffer Length on Headwater Stream Temperature

We measured stream temperature and riparian cover at multiple locations in 17 headwater streams in western Washington from October 2006-September 2011 to estimate changes in temperature and cover following timber harvest using three riparian buffer strategies. The four experimental treatments were: a no harvest (reference), 100% of perennial stream buffered with a minimum 50 feet wide buffer (100%), at least 50% of the stream buffered as above (FP), and 0% of the stream length buffered (0%). Riparian cover, measured with a densiometer at 1-m and at the water surface decreased <10% in the 100% treatment, 20-40% in the FP treatment, and >50% in the 0% treatment.  Understory vegetation and woody debris provided a substantial amount of cover in the 0% sites and in the harvested portion of the FP sites. Summer maximum stream temperatures increased in 35 of the 43 monitoring locations on the 11 treatment (harvested) streams, regardless of the buffer treatment.  When measured at the location in the harvest unit furthest downstream, the summer 7-day average maximum daily stream temperature increased by approximately 1°C in the 100% and FP treatments and by 3°C in the 0% treatments. Stream temperature was slightly lower in the second year post-harvest.