Impact of vegetation control and annual fertilization on properties of loblolly pine wood at age 12

Loblolly pine (Pinus taeda L.) stands in the Coastal Plain and Piedmont of Georgia were subjected to four intensive silvicultural regimes to monitor and record relative tree growth. Treatments included: intensive mechanical site preparation, complete vegetation control with multiple applications of herbicides, annual high rates of nitrogen fertilization, and complete vegetation control plus annual high rates of nitrogen fertilization. In response to the intense cultural practices, growth increased 270 percent in the Coastal Plain and 158 percent in the Piedmont compared to the intensive mechanical site preparation treatment. Increment cores were collected from trees at age 12 to determine the effect of treatments on earlywood and latewood specific gravity (SG) and duration of juvenility. Trees were also felled to determine the impact of intensive cultural practices on wood stiffness, strength, and toughness. Annual vegetation control plus annual high rates of nitrogen fertilization increased the diameter of the juvenile wood core 62 percent and thus, the proportion of stem basal area in juvenile wood. Annual ring earlywood SG was not affected by treatments, but annual ring latewood SG was significantly reduced in fertilized and herbicide plus fertilized trees. Vegetation control did not significantly affect SG, strength, stiffness, or toughness but did significantly increase the juvenile core-wood diameter. Annual fertilization alone or in combination with vegetation control reduced weighted stem SG 6 to 10 percent compared to that of the trees receiving only the mechanical site preparation treatment. Annual heavy fertilization alone or in combination with vegetation control significantly reduced toughness, as well as strength and stiffness of juvenile wood. Thus, wood harvested from stands that since planting received annual vegetation control plus annual high rates of nitrogen fertilization would be less desirable for structural lumber production compared to wood from conventionally managed and planted loblolly pine stands.