Effects of early intensive silviculture on wood properties of loblolly pine

Abstract

Long-term effects of site preparation, early fertilization and weed control on selected wood properties of 22-23 year-old loblolly pine (Pinus taeda L.) were examined. Wood samples were obtained from four regeneration trials established by the North Carolina State Forest Nutrition Cooperative between 1978 and 1981 in southeastern USA. Twelve millimeter breast-height wood samples were extracted from a total of 675 trees (across sites) from five treatments: 1) low site preparation (control), 2) intensive site preparation, 3) intensive site preparation and fertilization, 4) intensive site preparation and weed control, and 5) intensive site preparation, fertilization and weed control. Specific gravity data were collected using an x-ray densitometer. All samples were scanned for ring specific gravity, ring earlywood specific gravity, ring latewood specific gravity and ring latewood proportion.

Across sites and treatments, the transition zone between juvenile and mature wood based on latewood specific gravity was between rings 4 and 15 and the demarcation point between both types of wood varied from rings 12 to 15. Silvicultural treatments did not affect the transition age on two out of the four sites (rings 14 and 15). An increase of 2 years on the transition age was associated to intensive cultural treatments on one site and a decrease of 3-4 years was observed on the remaining site, suggesting a relationship between the patterns of growth with age and the proportion of juvenile wood. The proportion of juvenile wood was not significantly affected by early silviculture on two sites (< 2%) and on one site a 10% decrease on the amount of juvenile wood was observed as a result of intensive cultural treatments. The results suggested that where strong growth responses to fertilization and weed control were observed, the transition age between juvenile and mature wood was unaffected or decreased and when the strong growth responses were related to herbaceous weed control, the transition age increased in intensive silvicultural plots compared to control plots.

Individual tree volume was significantly affected by intensive treatments. Positive responses ranged from 29 to 33%. Despite the increased growth showed by trees under intensive cultural treatments, wood properties were generally not significantly different from those observed on control plots. Intensive site preparation (HSP) and fertilization within intensive site preparation plots (F) resulted in reductions of earlywood specific gravity and total specific gravity, respectively. Weed control (H) showed little effect on most of the properties but on one site was related to an increase on weighted specific gravity. Intensive treatments, on average, resulted in small increases in weighted latewood specific gravity compared to low site preparation and the proportion of latewood was not affected by the treatments at all.