Soil Quality

Soil quality and function are interrelated concepts that represent the range of soil properties and their associated ecological processes. The National Forest Management Act of 1976 and related legislation direct U.S. Department of Agriculture Forest Service managers to maintain the productivity potential of national forest land. The British Columbia Ministry of Forests uses professional assessment to evaluate the impacts of management practices on organic matter (OM) losses (British Columbia Ministry of Forests Forest Practices Code 1997). Even with these mandates and laws, the concept of soil productivity has not been well defined, and the impact of timber removal or fire on the productive potential of soils is not well understood or easily measured (Powers and others 2005). Soil quality has been defined as the capacity of a soil to function within an ecosystem to sustain biological productivity, maintain environmental quality, and promote plant and animal health (Doran and others 1996). In addition, soil health definitions include maintaining the integrity of nutrient cycling and resilience to disturbance or stress (O’Neill and others 2005). Tree or stand growth has often been used as an indicator of soil productivity changes, but growth reductions attributable to management practices may take >20 years to become manifest in many North American ecosystems (Morris and Miller 1994). The forest floor is likely a key element in maintaining healthy ecosystems, but it is also the one most impacted by fire and forest management (Tiedemann and others 2000). Maintaining site organic matter at or near the ecosystem baseline levels may help reduce nutrient losses (McNabb and Cromack 1990), insect (Fellin 1980b) and disease (McDonald and others 2000) outbreaks, and may ultimately reduce many forest health problems. For example, Page-Dumroese and Jurgensen (2006) describe baseline organic matter levels in 13 undisturbed forests around the Northwestern United States. The levels include measurements of downed wood, forest floor and mineral soil organic matter (OM), carbon (C) and nitrogen (N), and they can be used to determine when a site has excess or deficient organic matter stores. Carbon accumulation, as measured by forest floor depth or amounts of downed wood, can be a useful indicator of forest health because forests with OM levels above their historic baseline levels are at risk from increased insect and disease activities or high-intensity fires (Oliver and others 1994).