Effects of ontogeny and soil nutrient supply on production, allocation, and leaf area efficiency in loblolly and slash pine stands

The effects of ontogeny and soil nutrient supply on aboveground biomass acc umulation, allocation, and stemwood growth efficiency of loblolly (Pinus ta eda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) were invest igated in north-central Florida over 16 years using a 2 + 2 + 2 factorial e xperiment (species, fertilization, weed control). Aboveground biomass growt h responses to the combined fertilizer and weed control treatments (FW) ave raged similar to2- and 2.8-fold for slash and loblolly pine, respectively. In the same treatment, annual needlefall (NF) production for slash pine app roached a "steady state" of 6 Mgha(1) at ages 8-14 years, while loblolly pi ne NF production peaked at 7 Mg.ha(1) at age 10 years, and then declined 17 % following curtailment of the fertilizer treatment. Periodic stemwood biom ass increment (PAI) for the FW treatment for both species culminated at abo ut 15 Mgha(1) year(1) at age 8 years and then declined rapidly (similar to 275%) to <4 Mgha(1) year(1) at 15 years; reductions for the untreated contr ol were considerably slower. The progressive decline in PAI following peak leaf area development was closely associated with a decrease in stemwood pr oduction per unit leaf area (growth efficiency). A unit increase in leaf ar ea index in the 7- to 9-year-old stands produced about 3.0 and 3.1 times mo re stemwood biomass per year than in the 14- to 16-year-old stands for lobl olly and slash pine, respectively.