Good soil and water quality are basic requirements for healthy forests. Soil resource indicators being measured include erosion, compaction and other physical properties and chemical properties such as levels of organic matter.

Soil erosion is not a major factor in Oregon, but landslides sometimes occur, whether or not timber is harvested. Landslides are most common on steeper slopes, during or soon after heavy rainfall. The effect of forest practices on landslides is being studied by many scientists.

Soil compaction eliminates the air spaces in the soil, making it difficult for plants' roots to grow. Water can't penetrate soil as easily, which can increase erosion. Compaction can be caused by logging equipment, grazing, and vehicle travel. Fortunately, these processes affect only small areas of the forest. Modern practices like cable logging help to minimize the role of timber harvest in soil compaction.

Organic matter from decomposing plants improves soil structure, increases water retention, helps organisms that live in the soil, and stores carbon. Forests in western Oregon generally have a higher level of organic matter than forests in eastern Oregon. Many disturbances caused by humans can reduce the amount of organic matter in soil. Timber harvest practices have changed in many ways since the 1970s, to minimize soil disturbance.

Water resource indicators being measured include: stream flow and timing, biological diversity, pH (alkalinity vs. acidity), dissolved oxygen, sedimentation, and temperature.

Changes in stream flow and timing can damage aquatic organisms and their habitat. Because stream flow is naturally quite variable, it is difficult to measure the affect of human activities. There is some evidence that timber harvesting can increase stream flow in small watersheds, especially during the fall. During flood events, this effect is negligible, because the ground becomes saturated whether or not logging has occurred.

Aquatic organisms. Plants and animals living in rivers and lakes require good quality water. If some of them disappear, that could mean that water quality has gotten worse. At this point, scientists don't have enough data to know whether aquatic organisms are becoming less diverse. Studies are focusing on algae, fish and invertebrates like caddisfly larvae.

Other indicators. Generally, water quality in Oregon is good in forest streams. One area of concern is water temperature in lowland areas where development and non-forest use is common. When streamside vegetation is removed, more sunlight can penetrate the water, raising its temperature.

Map courtesy of Oregon Department of Forestry

Oregon's Forest Practice rules require no-cut buffers along fish-bearing streams to increase shade and prevent an increase in water temperature.