Productivity of an arid zone shrub (Eremophila gilesii) community in south-western Queensland

Abstract

The above-ground biomass of a monospecific Eremophila gilesii shrub community (69,200 bushes/ha including seedlings) had a mean value of 2106 kg/ha (range 1502-2402 kg/ha) over a year of measurement. Above-ground primary production (biomass increment and litter fall) averaged 0.23 g/m2/day. Rainfall utilization represented 3700 g water/g above-ground dry matter produced. The proportion of the total nitrogen and phosphorus pool incorporated in the organic matter is high when compared with other Australian arid zone shrub vegetation of similar biomass. Litter production varied markedly throughout the period of measurement, and was greatest following falls of rain. Average litter breakdown time was estimated to be 20 months. Litter production and decomposition account for the release of up to 0.33 kg organic phosphorus per hectare each year. About 53% of the phosphorus content in green leaves is extracted before abscission for redistribution within the plant. The intrinsic and extrinsic sources of organic phosphorus provide well over half the phosphorus required for the above-ground production each year. The results are discussed in relation to the possible centre of origin of Eremophila and the adaptation of E. gilesii to its harsh abiotic environment.