THE EL NINO SOUTHERN OSCILLATION AND AUSTRALIAN VEGETATION

The El Nino - Southern Oscillation (ENSO) phenomenon has a marked effect on Australia's rainfall. The tendency for major Australian droughts to coincide with ENSO "events" (i.e. anomalously warm sea surface temperatures in the east equatorial Pacific), and for extensive wet periods to accompany "anti-ENSO" events, is well documented. Also well-known is the partial predictability of Australian rainfall anomalies provided by ENSO. Some other ENSO-related characteristics of interannual fluctuations of Australian rainfall are less-widely recognised, viz: - rainfall variability is very large - droughts and wet periods have time scales of about one year - they exhibit very large (continental) spatial scales - they tend to be phase-locked with the annual cycle - they are often followed/preceded by the opposite rainfall anomaly. The character of Australian rainfall fluctuations is thus very different from that of areas where the influence of ENSO is weak, Europe for instance. Rainfall in some other areas, notably southern Africa and India and parts of the Americas, is also strongly affected by ENSO and shares some of the above characteristics. The relevance of these ENSO-related characteristics of Australian rainfall to its vegetation will be discussed. Australian native vegetation is adapted to these characteristics, especially in the semi-arid inland where ENSO's influence is strong. Most introduced plants are not adapted to ENSO and this has sometimes complicated their use here. The combination of ENSO-related rainfall fluctuations and European land-use strategies has resulted in some very rapid, unpredicted and undesirable changes in vegetation in the past two centuries. It has also increased the risk of soil erosion. Recognition of the real character of Australian rainfall fluctuations may help avoid further degradation of soil and vegetation.