RESPONSE OF FLOODED GUM (E-GRANDIS) TO INTENSIVE CULTURAL TREATMENTS - BIOMASS AND NUTRIENT CONTENT OF EUCALYPT PLANTATIONS AND NATIVE FORESTS

Effects of intensive cultural treatments on above-ground biomass production and nutrient distribution were examined in flooded gum (Eucalyptus grandis) plantations established in their native habitat near Coffs Harbour, N.S.W., Australia. Flooded gum biomass in the most intensive treatment combination of NPK fertilizers plus weed control and insecticides applied for 6 years was 274 tonnes ha-1 after 9.25 years, more than double the control stand biomass of 133 tonnes ha-1. A further 15 to 20 tonnes ha-1 accumulated as forest floor organic matter, and 6 tonnes ha-1 as understorey shrubs. Acacias developed into small trees in all plots except those treated intensively with weedicides. Maximum nitrogen, phosphorus, and calcium accumulations occurred in the most intensively treated stands (549 kg N ha-1, 50.7 kg P ha-1 and 1118 kg Ca ha-1) and were 2 to 3 times higher than those found in the controls. Fertilizers increased phosphorus concentrations in foliage and branches, and calcium in branches, and decreased nitrogen concentrations in heartwood. The proportions of total biomass and nutrients in various tree components were not altered substantially by the cultural treatments. A thinning treatment was carried out at 9.75 years and E. grandis plus Acacia biomass were determined at 12 years of age. Both responded to the thinning treatment, but there was no further response to the initial fertilizer applications. There was no difference between the biomass of flooded gum in the most intensive treatment and the biomass of flooded gum plus Acacia in all other treatments. Phosphorus contents were also equal regardless of treatment but the nitrogen content of stands with Acacia exceeded the nitrogen content of flooded gum alone. Biomass and nutrient contents of flooded gum and other Eucalyptus plantations were compared with similar data for native eucalypt forests. Native forests have relatively low nutrient contents, whereas plantations exhibit an almost linear increase in nutrient content with increasing biomass. Phosphorus and calcium contents of plantations are higher than those of native forests at equivalent levels of above-ground tree biomass.