6 Survey methods for soil disturbance
Soil disturbance within the NAR includes such harvesting and site preparation disturbances as unrehabilitated excavated or bladed trails, compacted areas, corduroyed trails, dispersed trails (from repeated machine traffic and wheel or track ruts), and gouges and scalps as defined in the Operational Planning Regulation.
The average levels of soil disturbance in the survey area are determined by transect surveys. Transect surveys must be completed as soon as possible after the disturbance was created to avoid confusion caused by the re-establishment of minor vegetation.
Before doing a transect survey, the surveyor should walk the area to become familiar with the various soil disturbances, to confirm the planned orientation of the transects, and to compare disturbance assessments with co-workers.
Transect surveys are also used for assessing compliance with forest floor displacement limits, where such limits are required.
The objective of stratifying the NAR is to focus a survey on relatively homogeneous areas of soil disturbance that appear to exceed the limits in the prescription or site plan. The intent is not to focus a survey on areas where concentrated disturbance is anticipated (e.g., where trails converge at landings).
Stratification of a standards unit can only be done for either of the following two situations: a) the prescription clearly specifies that the soil disturbance limit applies to a certain size area within the standards unit (e.g., stratification down to one hectare would be appropriate if the prescription specified that the maximum soil disturbance limit of 10% applied to any given hectare of SU "B"),4 or b) a survey is required on a roadside work area (described below), in which case it is necessary to have a separate stratum from the adjacent NAR, to assess compliance with the maximum soil disturbance limit of 25% that is set in regulation.
Where stratification of a standards unit is not permitted, surveying should be carried out only on the whole standards unit if it appears that the average level of soil disturbance over the entire unit exceeds the limit.
For areas where stratification is permitted the following criteria should be followed:
The minimum strata size cannot be less than the area to which the limit applies as specified in the prescription, and should not be less than 1 ha (the minimum recommended area for surveying). Use the same disturbance categories as you would use in surveying the entire standards unit. Ensure that soil disturbance within each stratum is relatively uniform. Do not create strata only to encompass small areas where there is an unavoidable concentration of soil disturbance, such as areas immediately adjacent to landings where numerous trails may be converging, and areas surrounding major trail junctions, or surrounding individual skid trails. Note, however, that these areas can be included as part of a larger stratum.
Roadside work areas are those sites located adjacent to haul roads and used during roadside harvesting operations for decking, loading, processing, and debris disposal. These areas can be subject to concentrated and high levels of soil disturbance. The maximum soil disturbance limit for roadside work areas is 25%, as required in the Timber Harvesting Practices Regulation.5 Prescriptions may identify these areas as separate standards units from adjacent portions of the NAR, which will normally have much lower maximum limits for soil disturbance. If these roadside work areas are not identified as separate standards units, they should be considered as a separate stratum for survey purposes.
Measure soil disturbance in the NAR with transect surveys, classifying survey points at fixed distances along transect lines. Classify survey points according to the soil conditions observed at the point and in the area around the point. Always use the flow chart in Appendix 2 to ensure that soil disturbance is counted appropriately.
At each survey point along a transect line, determine whether soil disturbance exists in accordance with definitions that apply to the prescription for the area. The point observations in these surveys do not involve a fixed plot size.
To classify a survey point, first determine the type of disturbance directly below the point. For example, if the point falls on a small patch of undisturbed forest floor in the middle of a heavily disturbed area, classify the point as undisturbed (field symbol "-").
Most types of disturbance involve size criteria, where the extent of disturbance around the point must also be assessed. For example, a wide gouge (field symbol "W") must be gouged greater than 5 cm into mineral soil (or to bedrock) on at least 80% of a 1.8 x 1.8 m square.
The extent and type of disturbance in the area around the point is a secondary attribute that is also required to classify the point. For example, if the point is gouged deeper than 5 cm, but the area around the point is only scalped less than 5 cm deep, then the point could not be classified as a wide gouge (W). It may be classified as a wide scalp (field symbol "S"), which may or may not count depending on the assessed soil hazards.
Think of the area around the point as a sampling window. The sampling window:
- must include the survey point, but need not be centred around it (Figure 7);
- can be oriented in any direction;
- must be oriented to maximize the amount of disturbed area included within the window (Figure 7);
- must be of the size and shape of the disturbance being assessed; and
- can overlap with the sampling windows of adjacent points (Figure 8).
Figure 7. Sampling window orientation. Orient the sampling window to include the maximum amount of disturbed area. The survey window need not be centred around the survey point.
Figure 8. Sampling windows can overlap.
For soil disturbance to be classified within some gouging and scalping categories, a percentage (usually 80%) of an area must be disturbed to a certain level or depth. The percentage is set lower than 100% to account for the natural variation that occurs with some disturbances (e.g., small patches of forest floor that remain in a scalp).
Window dimensions are specified as a percentage of a square or rectangle. In practice, this means that the dimensions of the disturbance can be smaller if the area is 100% disturbed.
Figure 9 shows typical patterns of disturbance and the equivalent dimensions of smaller squares for two common window sizes (1.8 x 1.8 m for a wide scalp or wide gouge and 3.0 x 3.0 m for a very wide scalp).
Figure 9. Equivalent sampling window sizes. Typical configurations for disturbance occupying 80% of a 1.8 x 1.8 m sampling window are shown in (a), (b), (c), and (d). Examples of disturbance occupying 80% of a 3.0 x 3.0 m sampling window are shown in (e) and (f).