Advancement of grapevine maturity in Australia between 1993 and 2006: putative causes, magnitude of trends and viticultural consequences

Background and Aims: Recent warming has accelerated phenological development of many crops. We quantified the rate of change in date of designated maturity (21.8 degrees Brix), date of harvest, and sugar concentration of berries at harvest in Chardonnay, Cabernet Sauvignon and Shiraz between 1993 and 2006. Methods and Results: Data from 18 Australian regions indicated that: (i) the date of designated maturity advanced at rates between -0.5 and -3.1 days/year; (ii) trends in the date of designated maturity were unrelated to trends in yield; (iii) trends of monthly temperature ranged from negligible up to 0.19 degrees C/year; (iv) the rate of change in date of designated maturity was correlated with rate of change of temperature for Chardonnay and Cabernet Sauvignon, but not for Shiraz; (v) harvest was accelerated at a rate between -0.4 and -2.4 days/year; (vi) the rate of change in harvest date for Chardonnay was commensurate with the rate of change in maturity, hence berry sugar concentration at harvest remained stable with time; and (vii) the advancement of harvest for Cabernet Sauvignon and Shiraz only partially offset the advancements in maturity, hence the increase in the concentration of berry sugar at harvest, up to similar to 0.3 degrees Brix/year. Conclusions: Maturity advanced at rates between half and 3 days per year. On a temperature basis, these rates are comparable to long-term rates reported for the northern hemisphere. Significance of the Study: This is the first report of time trends in phenology of grapevine in Australia and provides a benchmark for the industry.