Studies of Mineral Cycling in a Montane Rain Forest in New Guinea: III. The Distribution of Mineral Elements in the Above-Ground Material

Abstract

SUMMARY (1) As a preliminary to studies on mineral cycling in a lower montane rain forest at about 2500 m altitude in New Guinea, estimates have been made of the amounts of six elements (N, P, K, Na, Ca and Mg) in the various fractions of above-ground material. (2) Analyses have been performed on material from nineteen fractions on a single ridge-top plot 20 x 20 m; trees of gbh > 30 cm (trunk wood, trunk bark, branches, twigs, leaves), trees of gbh 4m tall (stems, leaves), saplings and shrubs 1-4 m tall (stems, leaves), plants 1 m tall (stems, leaves), epiphytes (stems, leaves), epiphytic soil, litter and dead trunks and branches. About 2300 analyses have been carried out. (3) The concentrations of N, Ca and Mg generally increased toward the centre of the trunks of large trees, while that of P decreased; K and Na were variable. The concentrations of N, P and Mg in the wood tended to increase with height, but there were no significant trends in the bark. Intraspecific differences were considerable, and interspecific ones large. The mean concentrations of N, P, K and Mg generally increased along the series: trunk wood < branches < trunk bark < twigs < leaves. For Ca they increased along the series trunk wood < branches < leaves < twigs < trunk bark. (4) The concentrations of N, P and K in leaves fell with increasing age, but that of Ca increased and those of Na and Mg were variable. The concentrations of N, P, K and Na were not consistently different in saplings and trees of the same species, but those of Ca and Mg were higher in sapling leaves. (5) The concentrations of all six elements in small trees, saplings, seedlings and climbers varied greatly between species, but the mean values for leaves, or for stems of similar girth, were similar in all these life-forms. The vascular epiphytes differed in their consistently low foliar concentrations of N. (6) The concentrations in the epiphytic bryophytes and lichens were similar to those in epiphytic soil derived largely from them, and the concentration of N was not as low as in the vascular epiphytes. (7) Amounts in the various fractions were first calculated for the 20 x 20 m plot and, after a consideration of the likely errors, for the whole forest, for which the above-ground capital was estimated to be (in kg ha-') 850 N, 49 P, 700 K, 31 Na, 1500 Ca and 210 Mg. The distribution in four major fractions was similar for N and P, and for Ca and Mg. The relative importance of the dead material and epiphytic material with respect to N and P was much greater than suggested by their dry weight contributions. (8) The correlations between the concentrations of particular elements in different parts of the tree, and between different elements in each part of the tree have been considered for eighteen species, and possible explanations are discussed. There was no significant correlation between the leaf concentration and the trunk wood or bark concentration for N, P or K.