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With the new method, surveyors tally well-spaced trees in a 3.99 m radius plot and record the basal area of layer 1 (dbh >= 12.5 cm) trees around the plot centre. These two measurements are combined to estimate understorey stocking at the sample point.

The new method is suitable for many blocks with dispersed retention.

In assessing regeneration stocking in this small opening, the new method accounts for the edge effect around the perimeter of the opening and the influence of the retained trees in the middle of the opening.

The new method has three main uses. First, it can provide information useful for treatment decision making. Second, it can be used to specify “non-traditional” stocking standards (subject to approval by the Ministry of Forests). Third, it provides insight into the yield implications of a given understorey density.

DFP by well-spaced trees per plot and overstorey basal area

The well-spaced tree count and the basal area around the plot determine the DFP at the plot. DFP (deviation from potential) is a measure of understorey stocking. Three stocking classes are shown – stocked (green), partially stocked (yellow), and open (red) – based on the second approximation DFP table. (Click for high resolution PDF version of table)

The focus of the new method is on the growing space available to seedlings. For this reason, when determining overstorey basal area with the new method, all live overstorey trees are counted – regardless of their economic value, form, species, or health. If standards are required for the retained trees, they must be established separately.

Overstorey trees reduce the growth and future harvest yield of understorey trees by several mechanisms, including a) shading them and b) providing a physical barrier to understorey tree crown expansion. Other mechanisms include competition for soil resources and, in some locations, reducing soil temperature.

Skid trails through areas of heavy retention within the NAR (net area to be reforested) pose problems for existing stocking assessment systems. However, the new method detects the heavy overstorey in the vicinity of plots that fall on the trail and indicates that the trail is “stocked” – in the sense that the trail provides no growth opportunity for seedlings.

Under heavy retention, seedling height growth is reduced. This must be accommodated by either delaying surveys or specifying a minimum height standard that is achievable with the prescribed amount of overwood.

In stands with retention, it is important to establish seedlings with shade tolerance that is appropriate for the amount of overstorey around them.

Understorey trees must meet standards for health, species, height, freedom from brush, etc., in the new method.