Soil Conservation Guidebook

Table of contents

5 Soil disturbance in the net area to be reforested (NAR)

An objective of placing limits on the amount of soil disturbance allowed within the NAR is to ensure that site productivity is maintained and that impacts to other resource values are prevented or mitigated. Harvesting and silviculture activities must be carried out such that the total amount of soil disturbance at any time during operations does not exceed the specified maximum. An exception is when the silviculture prescription specifies the extent to which maximum soil disturbance limits may be temporarily exceeded to construct temporary access structures (see the section "Temporarily exceeding the maximum allowable level of soil disturbance in the net area to be reforested").

Soil disturbance types and related categories are defined in both the Operational Planning Regulation and the Woodlot Licence Forest Management Regulation. Soil disturbance is a general term referring to the following:

Corduroyed trails are constructed using logs and woody debris placed side by side to form a running surface at least 2 m in length capable of supporting machine traffic. These trails must be rehabilitated unless exempted by the district manager.

Compacted areas show evidence of compaction over extensive areas, greater than 100 m2 , and are at least 5 m wide. These areas must be rehabilitated unless exempted by the district manager.

Dispersed disturbance is itself a general term referring to dispersed trails, gouges, and scalps. Dispersed trails include rutted trails (created by ground-based equipment operating on sites when the soil has limited load-bearing strength) and trails showing evidence of compaction caused by repeated machine traffic. Gouges are subdivided into deep gouges, wide gouges, and long gouges. Scalps are divided into wide scalps and very wide scalps. These terms are defined largely by minimum size criteria (e.g., depth into mineral soil, length and width of an area where forest floor or mineral soil has been removed). Some of these categories, such as wide scalps, count as soil disturbance only on more sensitive sites (e.g., wide scalps are tallied only if they occur on sites with "very high" hazard ratings). Definitions of soil disturbance categories are provided in the Operational Planning Regulation. The Soil Conservation Survey Guidebook should be consulted for more detailed descriptions.

5.1 Recommended allowable soil disturbance within the net area to reforested (NAR)

Coastal sites

Soil disturbances of the types and dimensions described in the regulations should not occupy more than 5% of any portion of the NAR for the area under a silviculture prescription.

The actual proportion of the NAR that may be occupied by soil disturbance must be determined for each site and specified in the silviculture prescription. Where it can be demonstrated that similar sites have been harvested and treated with less than 5% of the NAR being occupied by soil disturbance, the lesser amount should be recorded in the silviculture prescription. For example, if an area would normally be harvested with a skyline system and soil disturbance would generally occupy less than 1% of the NAR, this lower amount should be specified in the silviculture prescription.

Interior sites

Before standards units for silviculture prescriptions are delineated, site and soil data must be collected to characterize variability in site sensitivity. The subsequent evaluation of mineral soil sensitivity involves working through hazard assessment keys for soil compaction and puddling, soil displacement, and soil erosion. All three soil disturbance hazards must be considered in the development of a silviculture prescription. However, the most restricting soil disturbance hazard identified within the area to be harvested should be the primary one considered when the proportion of the NAR that may be occupied by soil disturbance is being prescribed. (Refer to the Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook for procedures for determining hazard ratings.) Table 1 provides recommendations on the maximum proportion of the NAR within any standards unit that may be occupied by soil disturbance based on hazard ratings.

The actual proportion of the NAR that may be occupied by soil disturbance must be determined for each standards unit and specified in the silviculture prescription. For areas where cable or aerial harvesting is proposed and soil hazards are not assessed, soil disturbance should not occupy more than 5% of the NAR.

Where soil sensitivity to disturbance varies significantly, the NAR should be stratified into homogenous standards units with separate limits established for each. Where the assessed soil sensitivity to disturbance varies significantly within any portion of the NAR and it is not possible to establish separate homogeneous strata, the most restrictive hazard should be used to determine the sensitivity for that area. This conservative approach will minimize the risk of harvest operations or silvicultural treatments that cause excessive or concentrated soil disturbance in the more sensitive areas.

Table 1. Recommended allowable soil disturbance within the net area to be reforested (NAR) of Interior sites


Leading soil disturbance hazarda Soil sensitivity rating b Allowable soil
disturbance (% NAR)

Soil erosion
VH
5
Soil displacement
VH
5
Soil compaction
VH
5
Soil erosion
H, M, L
10
Soil displacement
H, M, L
10
Soil compaction
H, M, L
10

a For definitions of hazard types and the procedures for determining hazard ratings, refer to the Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook.

b VH = Very High; H = High; M = Moderate; L = Low

5.2 Forest practices that may warrant higher levels of allowable soil disturbance

The district manager may consider approving a greater amount of soil disturbance than the recommended maximum allowable limits if:

Following are six examples of forest practices that may be required to achieve free-growing stocking on some sites. These practices would likely result in soil disturbance occupying more than the recommended maximum proportion of the NAR, and may warrant the approval of silviculture prescriptions that specify higher soil disturbance limits.


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