[Manual Home] [Chapter Sections]


	Silviculture Manual	S I T E P R E P A R A T I O N Mechanical

5 Site Degradation

The role of site preparation in British Columbia's reforestation program has increased significantly in the past several years. During the period from 1981 to 1990 over 1.2 million hectares of Crown forest land were site prepared. The diversity of forest conditions and management objectives has lead to a wide variety of site preparation methods.

All site preparation disturbs the site to some extent. Soil disturbance can range from beneficial to detrimental depending on the nature of the site and the severity and extent of the disturbance. Site disturbance that leaves the site more suitable for regeneration and that does not impair the site productivity is clearly beneficial. Disturbance from site preparation is considered to be excessive when the long-term site productivity is lowered resulting in diminished stand growth. The application of a site treatment method to achieve early growth and survival should not be at the expense of long-term productivity.

When considering long-term productivity, mechanical site preparation (MSP) is particularly topical. The recent increase in MSP on sites which have traditionally been treated by fire has heightened the concern for site productivity.

5.1 Guidelines

At present, soil conservation guidelines for harvesting are in place on the coast and in the interior. Under the Forest Practices Code, guidelines are covered by the following guidebooks: Soil Conservation, Site Preparation, and Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes. Guidebooks for soil conservation surveys, fire management and rehabilitation are currently under development.

5.2 Rehabilitation

Soil compaction, either naturally occurring or introduced by harvesting, may exceed optimum levels for forest growth. Site preparation has long been seen as a means of reducing compaction. The effectiveness of ripping as a means of alleviating soil compaction depends upon the type of ripper being employed, as well as the type of soil being treated. Winged subsoilers are more effective in reducing compaction than standard rock rippers or brush rakes. Generally, ripping is more effective on coarser-textured, non-cohesive soils. On sites where organic matter has been severely depleted, the benefits of subsoiling are often temporary and nutrient levels remain low. In such cases, subsoiling must be supplemented by some form of organic matter management, such as seeding legumes.

Soil density may also be reduced by other methods of site preparation, which mix organic matter with mineral soil. The Madge rotoclear and Eden relief bedding plow have both provided excellent mixing and compaction reduction, however, operational use is limited by site and cost.

For detailed information on rehabilitation, see Appendix 2, Selected References. Guidelines on rehabilitation are being developed.


[Manual Home] [Chapter Sections]