Influence of wind and other environmental variables on wood properties of South African-grown Pinus radiata and Pinus elliottii × caribaea

Abstract Key message The study investigates how wind exposure influences wood density and microfibril angle in two Pinus taxa, revealing greater sensitivity in Pinus elliottii × caribaea and highlighting MFA as a better wind-response indicator. Abstract Wind is one of the most persistent natural forces affecting plants, driving them to adapt their properties for survival. With the projected increase in wind intensity and coverage, commercial forests face growing vulnerability. This study investigated how environmental factors, particularly wind, influence wood density and microfibril angle (MFA) in 14.5-year-old South African-grown Pinus taxa. A 2 × 2 factorial experiment was conducted with two taxa— P. elliottii × caribaea and P. radiata —under high and low wind exposure. Over nine months, solar-powered anemometers recorded wind speed in the plots. Sixteen randomly selected trees were sampled and bark-to-bark wood cores extracted from the north–south and east–west directions at 1.3 m height. Density and MFA were analyzed using SilviScan, and mixed-effects models were developed using weather variables as predictors. Pinus radiata demonstrated better growth in diameter, height, and crown length but showed no significant wind-related effects on wood properties. In contrast, P. elliottii × caribaea was more responsive to wind, with MFA significantly lower in trees from less windy plots. Pinus elliottii × caribaea exhibited distinct annual rings with wide earlywood and narrow latewood, whereas P. radiata had less defined rings with more latewood. Growth rings near the pith were indistinct in both taxa. Cardinal direction significantly influenced MFA, with the highest values in the northern direction. Weather variables notably impacted density and MFA on the northern side across treatments. This study contributes valuable insights into the effects of environmental factors on wood properties. However, growth and development during the juvenile stage remain a complex process, requiring further research to clarify the factors driving property variation in commercial forestry species.