The composition of several arid spinifex grasslands of central Australia in relation to rainfall, soil water relations, and nutrients

Abstract

The study was restricted to communities of Triodia basedowii (hard spinifex) and Plectrachne schinzii (feathertop spinifex), which occur on extensive tracts of featureless sand plains. Measurements of plant cover, size, and weight were made at four sites at the northern, southern, eastern, and western extremities of their distribution as well as centrally. Soil profiles were examined and samples taken for laboratory analyses and nutrition trials in pots.

P. schinzii communities are dominant north of lat. 22°S. and T. basedowii communities south of this latitude. The communities are dominated by the spinifex species, which make up 96 to 98% of the standing crop. The tussocks cover about one-third of the soil surface, the remainder being bare. A sparse layer of small trees, shrubs, and subshrubs is always present.

The soils are uniformly red, deep, and sandy with clay contents exceeding 13 % only in a few northern and eastern soils. Nitrogen and phosphorus contents are very low and did not exceed 0.022% and 0.015 % respectively. Growth of oats and sorghum in pots was markedly affected by lack of phosphorus (nitrogen was not tested). The small range of available water is offset by deep penetration of moisture in the soils.

The uniformity of vegetation and soils was the outstanding feature. Significant differences between areas were found for plant height (due to P. schinzii) and weight per unit area of stand. The latter could not be related to the climatic differences between areas, and may be an historical feature related to fire. The vegetation is a stable edaphic climax subject to and adapted to repeated burning.