Stream Temperature Studies

Study Leader: Mike Newton, professor emeritus, Department of Forest Science, OSU College of Forestry

These riparian studies have the general objective of determining whether, and how much, various types of riparian buffer influence stream temperature and productivity, and how much each costs and facilitates future management of the riparian zone.

The studies include two sets of streams. The recent set consists of four small-medium streams on forest industry lands that have not been disturbed for 50+ years, and which were programmed for harvests in 2004-2006. On each of these streams, three designs of clearcuts span the stream. One design follows ODF current rules for buffers. A second design is clearcutting with no residual cover over streams other than shrubs or unmerchantable trees, i.e. maximum sun (relatively few trees). The third design leaves a screen between the arc of sun travel and open water up to 40 feet wide (deep) with just the limited objectives of shading the water while providing maximum opportunity for reforestation with desirable species. The harvest units span the streams for 1000-1200 feet. They are separated by uncut stands of similar size. The study includes 6000-8000 feet of channel length per stream.

Each stream has stand inventory points at intervals of 50 feet, 50 feet upslope on each side of the stream. These help define shade, lean and height of trees, and also an estimate of timber investment with each design. In each stream, thermistors are placed approximately 300–350 feet apart so that each harvest or uncut unit has three or more thermistors recording temperature change in a dynamic setting. Each stream has pre- and post-harvest inventories of stream structure, including pools, surface area, stream volume, velocity and discharge. Cover over the stream is measured with fisheye camera calibrated with net radiometers for determination of energy exchange. This design permits the precise determination of heat gain, and perhaps more importantly, loss, with harvesting and re-entry of water into uncut stands. It also permits an evaluation of the cooling processes that occur with one-sided shade as a function of evaporation and outgoing long-wave radiation. The heat exchange information is developed for two years before harvest and two years afterward. Fish productivity is under investigation, reach by reach.

The older studies involve a set of seven streams that evaluated the interaction of buffer design and vegetation management on future stand development with several species of conifer, stream productivity and stream temperature. These streams provided information indicating that regardless of species planted, nearly full sunlight is needed for successful regeneration. They also provided substantial evidence that opening the canopy increases stream productivity, and that if the residual cover is limited to that which keeps the sun off the water, temperature does not rise above the expected warming trend.

These streams provided the concepts now being evaluated in detail. The old studies also provide excellent demonstrations, now 12 years old, showing that Douglas-fir is likely the most successful species for planting in riparian areas, and that regardless of species, riparian management requires vegetation control for prompt establishment. They also demonstrated that protection from beavers is essential to conifer survival within 50 or more feet of the water. Western redcedar and western hemlock fared poorly in these tests, and no species survived when planted beneath ODF-type buffers dominated by hardwoods.