Height and radial growth trends of Corsican pine in western France

Height and radial growth trends were analysed in Corsican pine (Pinus nigra Arnold ssp. laricio var. Corsicana) plantations in western France. Difference in height growth was tested by comparing the site index of stands established before and after 1950 and the height growth development curves of 13 pairs of young and old stands growing side by side on the same soil type. The site index of the young stands was 20-30% greater than the site index of the old stands. From the period 1921-1991, radial growth increased 45, 31, and 50% in earlywood, latewood (LW) and total ring (TR) area, respectively. The amount of increase depended on cambial age. The LW/TR ratio decreased by 8%. The regional climatic data revealed a significant increase in mean annual temperature of 1.1°C, mean annual minimum temperature (1.5°C), mean summer temperature (2.2°C), and minimum summer temperature (2.3°C) for the period 1950-1997. Because of the negative correlation between summer temperature and ring widths, increased temperature cannot explain the observed increases in growth. Effects of nitrogen inputs, which averaged 6.3 and 11 kg·ha-1·year-1 for bulk and throughfall depositions, respectively; land use history; improvement in silvicultural practices (wider initial spacing, higher thinning); and CO2 fertilization are discussed as possible causes of the observed growth trends.