Data from: Forestry impacts on stream flows and temperatures: A quantitative synthesis of paired catchment studies across the Pacific salmon range

Forestry is pervasive across temperate North America and may influence
aquatic environmental conditions such as flows and temperatures, as well
as important species such as Pacific salmon (Oncorhynchus spp.). While
there have been many large-scale forestry experiments using paired
catchment designs, these studies have yet to be quantitatively
synthesized. Thus, it remains unclear whether forestry impacts are
consistent, context-dependent, or unpredictable. This study aims to
quantitatively synthesize forestry impacts on streamflow and temperature,
through a systematic review and synthesis of paired catchment studies
across the range of Pacific salmon. Specifically, we investigated whether
generalizable relationships exist between forestry intensity (percent
watershed harvested) and impacts to streamflow and temperature. We also
examined whether watershed features (climate, hydrology, lithology) and
harvest method mediated forestry impacts. We extracted information from 35
unique paired-catchments from California to Alaska. Forestry had strong
impacts on peak and low flows and maximum summer water temperatures, but
responses were quite variable. Across all catchments, forestry elevated
peak flows ~20% (n = 31 catchments), reduced low flows ~25% (n = 13
catchments), and increased maximum summer temperatures ~15% (n = 35
catchments) on average. However, these impacts were variable and were not
predictable based on forestry intensity, thus broader stressor-response
relationships were not supported. Forestry impacts on peak flows and
maximum summer temperatures varied spatially. Peak flow impacts increased
with increased northward latitude and temperature impacts decreased with
eastward longitude. However, the magnitude of impacts were unrelated to
other watershed attributes, which included climate (precipitation and
aridity), rain vs. snow hydrology, elevation, and bedrock lithology.
Harvest method and riparian buffer presence also had no detected effects
on forestry impacts across studies and statistical models explained a low
proportion of variation overall. Collectively, our results indicate that
forestry can have substantial impacts on key environmental conditions;
however, the magnitude of impact was variable and could not be clearly
linked to easily-measured watershed characteristics. This implies that
forestry impacts are not broadly predictable. Probabilistic risk models
based on distributions of potential impacts may therefore be more useful
for watershed management in data-poor situations.