Specific gravity of slash, longleaf, and loblolly pine growth rings formed in mature trees during periods of drought

Studies linking wood properties of the southern pines to climate parameters and/or irrigation treatments have generally used seedlings or mid-rotation age trees, the latter comprised primarily of juvenile wood. To investigate possible drought-induced effects on mature wood physical properties, densitometry data from 50-year-old slash (Pinus elliottii Engelm.), longleaf (Pinus palustris Mill.), and loblolly (taeda L.) pine trees were matched with annual soil moisture values. Each of two growth ring groupings per increment core had a two-year period of ample moisture followed by a two-year period of drought; these were centered at ages of 20 and 38 years. For slash pine, the latewood width was 30% lower (p = 0.011) for the drought period at age 20. Seemingly similar results were obtained for longleaf pine, but the probability (p = 0.051) just exceeded the threshold for significance (alpha = 0.05). No differences were observed for either earlywood or total ring widths. Ring specific gravity (SG) values that were 11% lower for slash pine and 7% lower for longleaf pine can be attributed to drought-related reductions in latewood formation. Unlike other studies with younger trees, both percent latewood and ring SG values for mature loblolly pine were unaffected by drought.