Production, allocation, and stemwood growth efficiency of Pinus taeda L. stands in response to 6 years of intensive management

Loblolly pine (Pinus taeda L.) is a highly plastic species with respect to growth responses to forest management. Loblolly pine is the most planted species across the southern United States, a region with the most expansive and intensively managed forest plantations in the world. Management intensity, using tools such as site preparation and fertilization, is increasing greatly in scope over time. To better define to the productive potential of loblolly pine under intensive management, the influence of 6 years of management with weed control (W), weed control plus irrigation (WI), weed control plus irrigation and fertigation (irrigation with a fertilizer solution) (WIF), or weed control plus irrigation, fertigation, and pest control (WIFP) since plantation establishment on stand productivity in loblolly pine was examined. The site is located near Bainbridge, GA (30°48ʹN latitude and 84°39ʹW longitude) and is of medium quality (site index=18 m, base age 25). Increasing management intensity greatly accelerated stand development and biomass accumulation. At age 6 total production (above plus belowground) was nearly doubled from 50 to 93 Mg ha^-1 in WIFP stands compared to W stands, and standing stem biomass increased from 24 Mg ha^-1 in W stands to 48 Mg ha^-1 in response to WIFP treatment. Stem current annual increment (CAI) peaked at age 5 in the WIF and WIFP stands at 17–18 Mg ha^-1 per year at a basal area between 18 and 21 m^2 ha^-1. Year to year variation in CAI was better explained by previous-year leaf area index (LAI) than current-year LAI. Maximum stemwood production in loblolly pine was achieved through large increases in LAI and small decreases in allocation to woody roots (tap+coarse roots) versus woody shoots (stem+branches) associated with intensive treatments.