Studies of Mineral Cycling in a Montane Rain Forest in New Guinea: V. Rates of Cycling in Throughfall and Litter Fall

Abstract

(1) This paper on mineral cycling in lower montane rain forest at an altitude of 2400-2500 m in the Eastern Highlands of New Guinea presents data on rainfall and throughfall, and on the quantities of N, P, K, Ca and Mg reaching the forest floor in rain, throughfall and litter fall. The quantities of these minerals in the litter layer have also been measured. Samples were collected from four sites in contrasting topographical situations. (2) The average throughfall on the four sites was 68 + 3.4% (S.E.) of the rainfall (3960 mm in 1969; 4010 mm in 1970). Stemflow was less than 1% of throughfall. (3) The estimated quantities (kg ha-' yr-1) of minerals in the rainfall were 6.5 N, 0 53 P, 7.3 K, 3.6 Ca and 1.3 Mg, and the mean quantities leached from the canopy on the four sites were 29.6 N, 2-5 P, 71.1 K, 19.0 Ca and 10.9 Mg. The mean returns of minerals in the litter fall were 90.8 N, 5. 1 P, 27.8 K, 94.7 Ca and 19.2 Mg. The return of minerals in throughfall and litter fall was remarkably similar on the four sites but certain minor between-site differences are discussed. (4) The quantities of minerals in the standing crop of litter on the forest floor (mean 6.46 t ha-) were (kg ha-) 91 N, 4.8 P, 11.5 K, 96 Ca and 14.5 Mg. (5) Comparisons are made with mineral cycling studies on other tropical forest sites, and some general conclusions are drawn concerning the differences in nutrient turnover in lowland and montane rain forests. It appears that the amounts of P, K, Ca and Mg returned annually in the throughfall and litter of montane forests overlap with the values found in lowland forest, but the return of nitrogen is lower. This presents particular problems of interpretation in view of the huge amounts of nitrogen present in the soil of the montane forest, and the substantial amounts in the annual throughfall. It is concluded that nitrogen is probably fixed in the phyllosphere and becomes immobilized in the soil and so is unavailable to plants.