Soil conservation

The silviculture prescription must describe how the soil resource will be protected during harvesting and silviculture activities. The Soil Conservation Guidebook provides the direction required in the preparation of the prescription.

General objectives

• To show how harvesting and silviculture activities will be conducted to protect, maintain or enhance the long-term productivity of forest soils.
  
• To show how loss of site productivity occupied by permanent and temporary access structures will be kept to a minimum through good planning and, where feasible, rehabilitation.

Silviculture prescriptions must provide the following soil conservation information:

• sensitivity of the site to soil disturbance
  
• maximum proportion of the area that may be occupied by permanent access structures
  
• maximum proportion of the area that may be occupied by temporary access structures (including excavated or bladed trails)
  
• rehabilitation actions, if any, that will be taken on these planned soil disturbances
  
• general location of and specifications for excavated or bladed trails
  
• maximum proportion of the net area to be reforested that may be occupied by soil disturbance as a result of harvesting, silviculture treatments or hazard abatement activities
  
• maximum permissible reduction or displacement in the forest floor as a result of prescribed burning (if required by the district manager)
  
• maximum forest floor displacement permitted by mechanical site preparation treatments.

Determining the sensitivity of a site to soil disturbance

Site sensitivity to productivity loss is considered in terms of five soil disturbance hazards:
• compaction and puddling hazard
  
• soil displacement hazard
  
• surface soil erosion hazard
  
• mass wasting hazard
  
• forest floor displacement hazard.

A silviculture prescription must record these five soil disturbance hazard ratings and the overall soil sensitivity rating, by SU, in accordance with the soil conservation guidebooks.

Maximum proportion of the area in permanent access structures

The silviculture prescription must set out the maximum proportion, if any, of the total area, under the prescription, that may be occupied by roads, landings, gravel pits and other permanent access structures.

Note: Excavated or bladed skid trails required for repeated stand entries are classed as permanent access structures.

The Soil Conservation Guidebook provides definitions and guidance in deriving this figure.

Maximum proportion of the area in temporary access structures

Temporary access structures include any roads, landings, excavated or bladed trails, or other access structures that are planned for rehabilitation of site productivity after use. These areas are included in the net area to be reforested and must be constructed to facilitate restoration of productivity.

Where temporary access structures are identified in a silviculture prescription, any rehabilitation measures must be described as outlined in the following section on rehabilitation measures and the area must be regenerated to prescribed stocking standards.

Areas where bladed or excavated trails may be constructed

Bladed or excavated trails are those cut to a depth greater than 30 cm into mineral soil and greater than 1.5 m in width.

The silviculture prescription must indicate the general locations where bladed or excavated trails may be constructed, the approximate spacing between trails, the maximum depth and width that trails may be cut into mineral soil and the maximum gradient of trails.

General location may be the whole cutblock, an SU, a specific hillside or a slope description (e.g., less than 60% slope). Details of trail location and specific construction requirements will be provided in the logging plan.

The Soil Conservation Guidebook provides further details on how to describe these trails.

Maximum soil disturbance in the net area to be reforested

The silviculture prescription must set out the maximum proportion, if any, of the net area to be reforested that may be occupied by soil disturbance as a result of harvesting, silviculture treatments or hazard abatement activities. This figure is specified by SU.

This requirement includes two figures.

• maximum allowable soil disturbance by harvesting and mechanical site preparation
  
• maximum allowable forest floor displacement by timber harvesting and mechanical site preparation treatments.

The Soil Conservation Guidebook provides details on how to derive these figures.

Rehabilitation measures

The silviculture prescription must describe any planned rehabilitation measures to be taken on areas of planned soil disturbance. This section does not refer to rehabilitation of areas where allowable soil disturbance levels have been exceeded; those are situations of non-compliance and are handled by remediation orders and other sections of the Forest Practices Code.

The district manager may authorize the holder of a licence to temporarily exceed the maximum soil disturbance limits prescribed. In such cases, the rehabilitation measures required to bring the disturbance back within the prescribed limits must be included in the prescription.

This requirement refers to the rehabilitation and reforestation of temporary access structures.

Rehabilitation measures taken to protect other resource values should be described as “actions to accommodate other resources” under the appropriate part of the previous section. Examples of this type of rehabilitation might include ripping and seeding of landings for range use and clean-up of watercourses for maintaining water quality.

Maximum permissible reduction in the forest floor
as a result of prescribed fire

If required by the district manager, the silviculture prescription must state the maximum amount by which the forest floor may be disturbed or reduced by prescribed burning activities. This figure is given as the absolute reduction (in cm) or the proportional reduction (in per cent) of the F and H soil horizons.

The Fire Management Guidebook provides details on how to derive these figures.

Figure 5. Example of soil conservation section.

Sample calculation

Given information:

Proportion of total area occupied by permanent access

Total area

For the purposes of calculating the proportion of permanent access structures within the area of the SP, use the definition of total area as described in the area summary of the stocking standards section of this guidebook.

Total area = 49.5 ha (all the area inside the marked boundary of the cutblock)

Total area = 49.5 ha

Proportion of permanent access

Proportion of area occupied by permanent access structures =



Note: An additional 0.2 hectare landing and a 0.02 hectare return trail are required, but is prescribed to be rehabilitated, therefore, is considered temporary access and is not included in the permanent access calculation.

Proportion of the net area to be reforested (NAR) occupied by temporary access

The NAR is defined by the Forest Practices Code of British Columbia Act and detailed in the area summary of the stocking standards section of this guidebook. To calculate the proportion of area that will have temporary access constructed in the NAR, it is necessary to determine the amount of temporary access prescribed, if any, within each SU (defined in the soil conservation section of this book).

In this example, all new permanent access structures will be constructed in SU A. In SU B, there is no mappable non-productive area or NCBR. The temporary landing and return trail will be constructed in SU B which is 15 hectares in size.

NAR within SU B = total area of SU B – (permanent structures + mappable non-productive area + immature + (non-commercial brush > 4 ha))

Thus: