Inputs and Cycling of Mineral Nutrients in a Coastal Subtropical Eucalypt Forest

Abstract

(1) Nutrient budgets have been estimated for eleven elements in a Eucalyptus signatadominated forest 15 m tall, growing on infertile podzolized sands on North Stradbroke Island in subtropical Australia. (2) No single component of the ecosystem rainfall, salt spray, soil or litter mass is sufficient to provide all the net annual nutrient demands of the forest. Although recirculation of mineral nutrients is therefore essential to the maintenance of the forest, turnover of nutrients from the vegetative standing stock is slow relative to deciduous forests on more fertile soils. (3) Rainfall and salt spray provide significant inputs to the forest, especially of chloride, manganese, nitrogen and sodium. Substantial quantities of mineral nutrients from salt spray are subsequently transferred to the forest floor with throughfall (68% of rainfall volume) and stem-flow (677%), but these evergreen trees appear more resistant to leaching losses than deciduous trees observed in temperate regions. (4) The forest dominant exhibits advantageous patterns of nutrient flow relative to its major competitors, by assimilating a smaller amount of nutrients relative to its mass, and by channelling more salt-laden waters to its roots via stem-flow. (5) The decrease in forest stature on older dunes on North Stradbroke Island (500 000 years old or more) may be due in part to gradual loss of nutrients from the ecosystem. Supplies of exchangeable potassium and available phosphorus, for example, are very low relative to uptake demands in the younger pyric-climax forest studied.