Soil Conservation Guidebook

Table of contents

2 Permanent access structures

To facilitate forest management, part of the forest land base is permanently occupied by roads and other structures that provide access to the forest. Minimizing the amount of productive forest land occupied by these structures is an important objective of forest management.

Permanent access structures include on-block roads, landings, gravel pits, borrow pits, quarries and permanent logging trails that are reasonably required for timber harvesting and other forest management activities. To be considered permanent they must satisfy either of the following two conditions:

Permanent logging trails include any logging trail (including an excavated or bladed trail) that is specifically identified in an approved silviculture prescription as a permanent logging trail. These trails are required for repeated stand entries to carry out periodic harvesting of areas where partial cutting silvicultural systems or commercial thinning operations are prescribed. They will not be reforested or rehabilitated. However, they must be constructed and used in a manner that minimizes soil erosion and sediment delivery to streams. They should be deactivated and left in a stable condition when not in use.

Permanent access structures may be treated (or, in the case of roads and landings, deactivated) to prevent soil erosion or reduce a slope stability hazard. Deactivation of permanent access structures is not the same as rehabilitation of temporary access structures (discussed in a later section of this guidebook). The objectives of deactivation are to leave the structure in a stable and maintenance-free condition.

There is no requirement to grow trees on areas deactivated to a temporary or semi-permanent level. Permanent deactivation requires only that trees be grown on receptive sites for purposes of controlling soil erosion. (Although the objective is not to establish a future commercial crop of trees on these areas, this may be an added benefit in some situations.) Rehabilitation, on the other hand, requires the restoration of soil productivity to facilitate the production of a future commercial crop of trees on the area that was occupied by the temporary access structure.

2.1 Recommended allowable site occupancy by permanent access structures

The proportion of the total area under the prescription (gross cutblock area) to be occupied by permanent access structures should be determined on a site-specific basis. Factors such as soil type, parent material, topography, stand type, silviculture system, harvest methods, equipment standards, management objectives, long-term access requirements, and safety and engineering standards will all affect the area to be occupied by these structures.

The proportion recorded in the prescription should be based on the maximum estimated amount of permanent access structures proposed for the cutblock. In most circumstances, permanent access structures should not occupy more than 7% of the total area under the prescription. Examples of circumstances that may warrant occupancy that exceeds 7% include small cutblocks containing main haul roads, cutblocks with a switchbacking haul road, and other cases where topography and engineering constraints limit the options for road location and development. Where the proportion specified is more than 7% of the area a rationale for the higher level of occupancy should be provided with the prescription.

When the above determinations are made, consideration should be given to measures that will minimize the loss of productive forest land without compromising safety or proper road engineering. Road and landing areas must reflect the minimum specifications necessary for safe harvesting operations.

In areas with existing road networks, the determination of how much additional access may be required should reflect a commitment to minimizing the loss of growing site, and the conversion of productive forest land to no more than 7% of a watershed or forest development planning area.

It should be recognized that safe road design may require the concentration of roads in some areas. Wherever possible, therefore, such concentration should be offset by reducing permanent access construction in other areas so that, over the larger area, soil conservation objectives are still met.

2.2 Estimating the area occupied by permanent access structures

Engineering and design specifications can be used to estimate and rationalize the area that will be occupied by the permanent access structures.

When estimating the area that will be occupied by permanent access structures the width of the structures to be used will depend on what portion of the fill slope will be available for growing a future crop of commercial trees. Widths are measured as horizontal distances taken from the top of the cutslope. The fill slope can be included as part of a permanent access structure (i.e., excluded from the NAR) for either of the following reasons:

  1. the fill slope is a growing medium unfavourable for any of the tree species ecologically acceptable for the site (as described in the next section); or
  2. the fill slope will be kept free of trees to provide adequate visibility for safety purposes, or to facilitate snow removal operations on roads that will be used
    during winter. Where the fill slope will be reforested as part of the NAR, include only the width from the top of the cutslope to the outer edge of the running surface of the road.

For roads located on gentle terrain, the area occupied by the road includes the entire width to the outside edge of the ditches on either side of the road.

Fill slope soil material that is an unfavourable growing medium should not be included in the estimate of the area occupied by permanent access structures, if during deactivation it will be pulled back onto the excavated part of the road.

When determining how much permanent access may be required within a cutblock to facilitate harvesting and forest management activities, consider the amount of access already provided by existing haul roads.

Where a cutblock will be located adjacent to an existing road but will not include the road, and the road provides some or all of the access requirements, the proportion of the cutblock area that may be occupied by permanent access structures should account for this existing access. That is, the limit should account only for the structures that will have to be constructed within the cutblock, not existing access located outside of the cutblock boundary. For example, if a cutblock boundary is located directly adjacent to, but outside of, an existing main haul road, and this provides all of the access necessary to harvest the cutblock, the maximum proportion specified in the prescription should be 0%. Where a new cutblock contains an existing road, the estimate of the proportion of the area occupied by permanent access structures must include the area of the existing road plus any additional permanent access structures proposed for the cutblock. If the existing road is a main haul road, the total area occupied by permanent access structures will likely be much higher than if all the on-block roads had been narrow spur roads only - in some circumstances this may warrant proportions that exceed 7%.

Note that for roadside harvesting operations the portion of roadside work areas located outside of the road prism should not be included in the estimate of the area occupied by permanent access structures. They are part of the NAR (see the section on "Concentrated soil disturbance within the net area to be reforested - Roadside work areas").

When carrying out field inspections to determine compliance with the maximum allowable proportion of permanent access structures, use the assessment and survey procedures contained in the Soil Conservation Survey Guidebook.

2.3 Fill slope soil material

When estimating PAS occupancy for prescription purposes or for compliance assessments, the fill slope growing medium should be evaluated to determine whether or not the fill slope should be included in the road width estimate. If fill slopes are to be part of the NAR, it should be reasonable to expect that seedlings will grow on these areas at a comparable rate to seedlings growing on adjacent undisturbed areas.

Unfavourable growing media

Unfavourable fill slope soils can present physical, chemical, and/or nutrient limitations to seedling growth. The following types of fill slope materials commonly do not support seedling growth comparable to that of seedlings on undisturbed areas, and can reasonably be considered as unfavourable growing media:

Fill slopes of any of these materials should be included in the estimate of the total proportion of the area occupied by permanent access structures, unless local experience confirms that these sidecast materials will support adequate seedling growth.

For further information on classifying favourable or unfavourable soil materials, refer to the Soil Conservation Survey Guidebook or any regional or district guidelines, or consult with one of the Ministry of Forests regional soil specialists.

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