Residual Basal Area

In southern pines, regeneration establishment and development are strongly related to the basal area of the merchantable component of the stand. Data from the CEF and elsewhere suggest that uneven-aged stands can be managed successfully within a range of residual basal area from 10 to 17 m²/ha (45 to 75 square feet per acre) (Baker and others 1996; Farrar 1996; Farrar and others 1984, 1989). At residual basal area levels < 10 m²/ha (45 square feet per acre), the overstory is understocked and growth will not be optimal (although such stands can be rehabilitated to optimal production easily, as discussed earlier). At residual basal areas > 17 m²/ha (75 square feet per acre) at the end of the cutting cycle, regeneration development is adversely affected.

The residual basal area target immediately after harvest must be established in conjunction with the expected length of the cutting cycle, the expected growth of the residual stand, and the upper basal area limit for the species. For example, basal area growth of uneven-aged loblolly-shortleaf pine stands at CEF is 0.5 to 0.7 m²/ha (2 to 3 square feet per acre) annually. If a 5-year cutting cycle is planned, the target residual basal area immediately after the cutting cycle harvest must, therefore, be 14 to 15 m²/ha (60 to 65 square feet per acre), so that stand basal area does not exceed 17 m²/ha (75 square feet per acre) at the end of the cutting cycle. Longer cutting cycles require lower residual basal area levels. 

Thus managing for the proper residual basal area is an important element of uneven-aged silviculture. This is one reason why structural regulation using the basal area, maximum diameter, and q-ratio or the BDq method (Baker and others 1996, Farrar 1996, Marquis 1978) has become popular. The CEF experience and other work suggest that BDq is more than an alphabetical ranking; this order reflects the priority for implementation (Baker and others 1996, Farrar 1996). The importance of maintenance of stand structure is based on obtaining the appropriate basal area; retaining a specified maximum diameter class or a given q is much less important (Guldin and Baker 1998).