Effect of Thinning on the Foliage and Forest Floor Properties of Ponderosa Pine Stands

The longest and heaviest needle fascicles were associated with greater thinning intensities of ponderosa pine ( Pinus ponderosa Laws.) stands 8 years after treatment. The foliar nutrient concentrations did not change significantly between the various thinning regimes. In addition the total forest floor in thinned and unthinned ponderosa pine stands ranged from 17.7 to 34.4 metric tons/ha. On a dry weight basis the F2 horizon constituted 74–88% of the total forest floor. However, nutrient concentrations increased from the foliage to the L to the F1 to the F2 which had the greatest concentrations of nutrients but were not affected by thinning intensity. The greater concentrations in the F2 were probably indicative of the more advanced degree of decomposition. Total nutrients in the forest floor were inversely proportional to the degree of thinning. In the stands at the growing stock level of 6.9 and 48.2 m 2 /ha (unthinned) total nitrogen was 213 and 301 kg N/ha, respectively. Other nutrient values were 17 and 27 kg P/ha, 18 and 32 kg S/ha, 56 and 75 kg K/ha, 119 and 154 kg Ca/ha, 75 and 126 kg Mg/ha, 26 and 34 kg Zn/ha, and 88 and 156 kg Mn/ha in the stands with growing stock levels of 6.9 and 48.2 m 2 /ha, respectively.