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Dynamics of four macro-nutrients were studied in an age series (7, 17, 30, 46 and 56 years) of Himalayan alder (Alnus nepalensis D. Don) plantations in the Kalimpong forest division of the eastern Himalayas. Concentrations of nutrients were in the order N > K > Ca > P in most of the tree components and in understorey vegetation. There was an inverse relationship between nutrient concentrations of perennial parts and diameter at breast height. The relative contributions of standing state of nutrients in different tree components of mature plantations were in the order; bole > branch > below-ground part > twig and leaf > catkin. Sequential arrangement of nutrient storage in tree components was: N > K > Ca > P. Soil total N and available P increased with plantation age. Annual inputs of nutrients (kg ha<sup>-1</sup>) to the forest-floor via litterfall were: 183-235 N, 4·9-7·0 P, 33·5-39·5 K, and 9·2-10·8 Ca. Total annual accretion of N through biological fixation ranged from 29 to 117 kg ha<sup>-1</sup> in different plantations. Turnover rate and turnover time for different nutrients in the age series of plantations fluctuated between 0·10-0·55 year<sup>-1</sup> and 1·8-9·3 years, respectively. Nutrient use efficiencies decreased with plantation age for all nutrients except for calcium. Uptake of nutrients is a more energy consuming process than release.Copyright 1993, 1999 Academic Press |