Nutrient cycling under 450-year-old Douglas-fir stands

To investigate the movement of elements (N, P, k, Ca, and Mg)from the tree crowns by natural litterfall and leave wash, plotswere established on six 450 year-old growth stands at the H. J.Andrews Experimental Forest. The following are the results of thedata analyses. Elemental concentrations contained in throughfallsamples varied throughout the year and tended to follow a seasonalcycle. Concentrations were lowest during the winter when precipitationwas greatest and highest during the summer months when precipitationwas lowest. Nutrient return in throughfall generally follo,redsame trend as did the concentration curves. The general rio'Alityof the various mineral elements was demonstrated. For example12% of the N, 39% of the P, 74% of the K, 9% of the Ca, and 37% ofthe Mg was returned in the leaf and litter wash. Average litterproduction for all stands during the 2 years was 5.520 metric tons/hectare. Litterfall was maximum during the winter months. Theaverage total kg/hectare return of nutrients in litterfall wasN 26.7, P 4.6, K 75., Ca 49.9, and Mg 3.8. The greatest portion, 63% of the nutrient return, came through needle litterfall.Together, the needle, cone, and twig litterfall accounted for 84%of the total nutrient input through litterfall.