Vegetation Dynamics in a Grazed Mulga Shrubland Community. II. The Ground Storey

Abstract

Population dynamics of annual forbs and of the grasses Eragrostis xerophila and Monachather paradoxa were studied in relation to a gradient in range condition within a mulga shrubland community in the arid winter rainfall zone of Western Australia.

Frequency of annual forbs appeared to be influenced more by local environmental factors than by grazing. Species which showed definite trends in relation to the range condition gradient were either relatively insensitive to condition changes or occurred at low frequencies and would thus be susceptible to sampling error.

The perennial grass E. xerophila decreased under heavy grazing but also appeared insensitive to relatively small variations in grazing pressure. Regeneration of this species following drought appears to be a protracted process and may be inhibited by ephemeral growth in the immediate post-drought period.

Under severely degraded conditions the semiperennial M. paradoxa displayed a marked reduction in vigour, as reflected in plant size (density/cover ratio), but neither foliar cover nor dry matter production were much affected. The stability of its production under degraded conditions, however, is likely to be reduced relative to sites subjected to more conservative management.