Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, thereis a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquaticecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapidresponse times. Using palaeoecological techniques, we can measure properties of time series data todetermine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS.Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, andcharcoal influx), we assess whether a critical transition in diatom community structure was preceded bymeasurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatomcommunity dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yrBP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as atransition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, andFragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, andGomphonema multiforme). We observe a marked increase in compositional variance and rate-of-change priorto this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetationremains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invadeand the vegetation system experiences an increase in both compositional variance and rate-of-change.These trends imply an approaching critical transition in the vegetation and the probable collapse of the localrain forest system.</p
