Nutrient cycling in a mixed-species plantation of 'Eucalyptus globulus' and 'Acacia mearnsii'

Abstract

A doubling of aboveground biomass production has been observed in mixtures of 'Eucalyptus globulus' Labill. and 'Acacia mearnsii' de Wildeman when compared with monocultures after 11 years of growth. This study examined to what extent increased nitrogen (N) availability and accelerated rates of nutrient cycling may contribute to increased growth in mixtures. Monocultures of 'E. globulus' (E) and 'A. mearnsii' (A) and mixtures of these species were planted in a species replacement series: 100% E, 75% E + 25% A, 50% E + 50% A, 25% E + 75% A, and 100% A. Litterfall mass increased with aboveground biomass production and was highest in 50:50 mixtures and lowest in monocultures. Owing to higher N concentrations of 'A. mearnsii' litter, N contents of annual litterfall were at least twice as high in stands containing A. mearnsii (32-49 kg·ha¹·year–¹) as in 'E. globulus' monocultures (14 kg·ha¹·year¹). Stands with 'A. mearnsii' also cycled higher quantities of phosphorus (P) in annual litterfall than 'E. globulus' monocultures. This study demonstrated that mixing 'A. mearnsii' with 'E. globulus' increased the quantity and rates of N and P cycled through aboveground litterfall when compared with 'E. globulus' monocultures. Thus, mixed-species plantations appear to be a useful silvicultural system to improve nutrition of eucalypts without fertilization.