Effect of Nutrient Availability and Competition Control on Growth and C, N, and P Dynamics in Loblolly Pine and Slash Pine Plantations in North-Central Florida

The pine plantations of the southern United States play a major role in the economies and carbon cycling of the region. Ensuring their long-term productivity will rely on information re-garding the ecosystem nutrient response to management approaches. Many studies have assessed the effect of silvicultural practices on growth and ecosystem nutrient budget in the current rotation, but little is known about the carry-over effects of treatments used in a rotation on a subsequent rotation’s growth and nutrient dynamics. The purpose of this study was to elucidate how growth and ecosystem carbon, nitrogen, and phosphorus pools respond to species selection loblolly pine and slash pine, fertilization (F), competition control (W) and F+W treatments in one rotation and their carry-over to the subsequent rotation. Two experimental sites, IMPAC and G8, located in north-central Florida were evaluated. I evaluated total tree biomass, soil total carbon, nitrogen and phosphorus, extractable NHv4^+, NOv3^- and POv4^3^-. Allometric equations were used to estimate total biomass and combustion, inductively coupled plasma atomic emission spectroscopy, KCl and Mehlich III extraction methods were used to quantify carbon and nitrogen, phosphorus, extractable nitrogen and phosphorus, respectively. At the end of a 25-year rotation at the G8 site, total tree biomass increased in the order: Control < F < W < FW, with only the FW treatment significantly exceeding the Control. N and P pools and soil NHv4^+, NOv3^- and POv4^3^- were increased by F. Early growth up to age 3 years of the second rotation exceeded the first rotation by ~2-fold. Retreated F and W increased biomass tree growth, while the CF treatments increased growth and CW decreased growth. At the IMPAC site, forest floor phosphorus pools were larger in loblolly pine compared to slash pine. The fertilization of these forests appears to have the potential to increase phosphorus pools and availability across rotations, while competition control alters nitrogen dynamics, poten-tially through an increase in altered organic matter chemistry and nitrogen immobilization poten-tial. Silviculture can increase or decrease growth across rotations, but the effects early in rotation are much smaller than the progress made in genetics and silviculture