Growth and leaf nutrient responses of loblolly and slash pine families to intensive silvicultural management

Intra-specific variation in foliar nutrient response to fertilization treatments and associated growth performance is largely unknown in southern pines. Sixteen open-pollinated families from each of three pine taxa—genetically improved loblolly pine (PTI; Pinus taeda), improved slash pine (PEI; Pinus elliottii var. elliottii), and unimproved slash pine (PEU)—were planted in two locations under a common split–split plot experimental design in north Florida. At each site, two levels of silvicultural treatments (low intensity—no fertilization; high intensity—fertilization and weed control) were implemented. Vector analysis suggested that N, P, and K were nutrients mostly commonly limiting growth, while Mg and Ca were generally not deficient for the three taxa over four different sampling periods during the growing season. The period of highest nutrient demand occurred during the growing season from June to September, with deficiencies easing throughout the remainder of the year. Differential family responses in foliar nutrient levels (especially N and P) were closely associated with current-year foliage biomass production and annual height growth for the three taxa. PTI and PEI families with constant, but minor, foliar N and P deficiencies during the growing season had higher foliage biomass production and height increments than those exhibiting excess, dilution, or severe deficiency. PEU families generally had lower nutrient requirements than PTI and PEI families. Differences in nutrient demand for growth existed between PEU and PEI. Differences between PEI and PEU in foliar nutrient response to intensive management from this study, along with findings in growth performance and crown structure, suggested that PEI had growth strategies more closely aligned with PTA than with PEU. Significant intra-specific differences in growth and nutritional characteristics also indicated that family forestry could be a viable option suited for intensive plantation management because family-specific fertilizer prescriptions may be needed to further improve stand growth.