EFFECTS OF TRACTOR LOGGING AND BURNING ON BIOMASS PRODUCTION AND NUTRIENT ACCUMULATION IN <em>ACACIA</em> <em>MANGIUM</em> PLANTATIONS IN SABAH, MALAYSIA

Abstract

Three 3.8-y-old tropical forest plantations of Acacia mangium, established in different ways, were compared in terms of biomass accumulation and the nutrient contents of different above- and below-ground biomass components. On two soil types, stands established on unburned sites where logs had been manually extracted before planting, growth was faster and biomass accumulation almost double compared with stands subjected to the "normal practice" of tractor log extraction and burning before planting. Sites on which secondary forest, after the "Borneo fire" in 1983, had been subjected to burning before planting, showed the lowest rates of growth and biomass production. Most plant nutrients accumulated rapidly in the plantations. About 80 % of the P in the previous rain forest stand had accumulated after 3.8 y in the above-ground biomass of the best-growing A. mangium plantation. Corresponding figures were 68 % for N, 72 % for K, 47 % for Na, 46 % for Zn, 38 % for S, 24 % for Ca and 23% for Mg whereas the proportion of dry matter biomass accumulated was only 19 %. The fast accumulation can be ascribed to the rapid growth of leaves and small branches by young trees and has important implications for the timing of fertiliser treatments in tropical forest plantations.