Forestry influences on salmonid habitat in the North Thompson River Watershed, British Columbia

Freshwater ecosystems that support juvenile salmonids can be degraded by
human pressures such as forestry. Forestry activities can alter water
temperatures and the delivery and storage of water, nutrients, wood, and
sediment in streams, resulting in changes to the habitat, growth, and
survival of juvenile salmon. Previous research on forestry impacts on
habitat has focused on small, intensively monitored coastal systems. Here
we examined forestry impacts, watershed characteristics, physical habitat,
and stream temperature for 28 midsized tributaries of the North Thompson
River to examine relationships between forestry and juvenile coho stream
habitat in interior watersheds. Forest harvest had a positive correlation
to maximum summer stream temperature. Streams with 35% of the riparian
area harvested since 1970 had maximum summer temperatures 3.7°C higher on
average than those with 5% harvested. Stream gradient explained most of
the variation in physical habitat and had negative correlations to pool
cover, pool depth, and fine sediment cover. Taken together, these results
indicate that watershed characteristics drive physical habitat, but
forestry harvest can be a primary driver of water temperatures.