Effects of intensive fertilization, complete competition control and site quality on aboveground net primary production (ANPP) dynamics of loblolly pine plantations

•ANPP-age relationship in pine plantations under different treatments were modeled.•Site quality and treatments affected the magnitude and timing of maximum ANPP.•Intensive fertilization enhanced ANPP in young stands but reduced ANPP in older stands.•No obvious decline in ANPP was observed in non-fertilized stands.•Sharp decline in ANPP was observed only in the intensively fertilized stands.•Nutrient limitation is not responsible for the observed decline in ANPP.