Germination and Growth Models of Short-Lived Grass and Forb Populations Based on Long Term Photo-Point Data at Koonamore, South Australia

Long term chart and photo records have been taken regularly at several sites in a cheno- pod shrubland since enclosure of the Koonamore Vegetation Reserve in 1925. Previous studies of seasonality in ephemerals at Koonamore are reviewed. More detailed data on the demography and growth of the ephemeral grasses (Stipa nitida) and forbs (bassias) were obtained from 3-monthly permanent plot charts (1926-31) and annual photopoint records (1926-55). Neither taxon showed strong seasonality, contrary to the results of studies elsewhere. The 5 yr chart data (1926-31) were shown to be an inadequate sample of ephemeral growth patterns due to variability in rainfall. A model was developed which fitted the germination data accurately, indicating that the occurrence of a germination event is closely related to simple environmental variables - namely, temperature and a soil moisture budget based on daily rainfall. The factors controlling the composition of the germination pulse are much less clear.