Abstract:
A replicated before–after-control-impact study was used to test effectiveness of Oregon’s (USA) riparian
protection measures at minimizing increases in summer stream temperature associated with timber harvest.
Sites were located on private and state forest land. Practices on private forests require riparian management
areas around fish-bearing streams; state forest’s prescriptions are similar but wider. Overall we
found no change in maximum temperatures for state forest streams while private sites increased preharvest
to post-harvest on average by 0.7 °C with an observed range of response from -0.9 to 2.5 °C.
The observed increases are less than changes observed with historic management practices. The observed
changes in stream temperature were most strongly correlated with shade levels measured before and
after harvest. Treatment reach length, stream gradient, and changes in the upstream reach stream temperature
were additionally useful in explaining treatment reach temperature change. Our models indicated
that maximum, mean, minimum, and diel fluctuations in summer stream temperature increased
with a reduction in shade, longer treatment reaches, and low gradient. Shade was best predicted by riparian
basal area and tree height. Findings suggest that riparian protection measures that maintain higher
shade such as the state forests were more likely to maintain stream temperatures similar to control
conditions.
