Not all basal area is created equal: the influence of species and stand development on canopy cover of four common southern pinesThis article is part of a larger document. View the larger document here.
Restoring natural fire regimes and diverse ground cover to planted or old-field origin southern pine stands typically requires a substantial reduction in overstory density. While maintaining full canopy cover (CC) is consistent with maximizing fiber production, this approach does not allow sufficient light to reach the forest floor to accomplish a broader set of objectives. The relationship between stand basal area (BA) and CC has been used to regulate the overwood in shelterwood seed cuttings and is worth exploring for other purposes. Two factors potentially complicating the use of BA as a proxy for CC are: (1) the dynamic relationship between stem diameter and crown size and (2) species-level differences. Data collected as part of a regional inventory (Forest Inventory and Analysis Forest Health Monitoring plots) were used to construct regression models of crown projection area (CPA) for the four most common southern pines (Pinus taeda, PITA; P. elliottii, PIEL; P. echinata, PIEC; P. palustris, PIPA). Species, stem diameter, and live-crown ratio were all identified as important predictor variables (P < 0.05). Relative to a stated objective of achieving 50 percent CC there were some substantial differences in the amount of BA suggested for retention in stands of different average diameter (5- to 18-inch d.b.h, PITA 46 to 70 square feet per acre; PIEL 46 to 64; PIEC 47 to 71; PIPA 50 to 74); the differences among species were somewhat less dramatic. There was a clear tendency for relatively small stems, e.g., <10 inch d.b.h., to have larger crowns per unit stem diameter, implying a given CC could be achieved with less BA. Species shade tolerance also appeared to influence crown-stem allometry, with the more shade-tolerant species tending to provide a given amount of CC with less BA. Both factors, species, and average tree size appear worthy of consideration when attempting to meet residual canopy cover goals.