Resilience of grapevine yield in response to warming

Aim: To evaluate the effect of elevated temperature on the yield of Shiraz vines in the Barossa Valley of Australia. 

Methods and results: We compiled and analysed 37 pair-wise yield comparisons between heated and control vines spaning seven consecutive vintages from 2009-10. Heating with open-top chambers increased daily average temperature by approx. 2 °C above ambient in realistic vineyard conditions, in comparison to 0.9 to 2.9 °C projected warming for south-eastern Australia (2030-2070). The combination of seasons, varieties, fruit loads, pruning times, and water regimes returned an 8.5-fold variation in the yield of unheated vines. Warming had no statistically significant effect on yield in 32 out of 37 comparisons, reduced yield in 2 and increased yield in 3. 

Conclusion: Projected warming is unlikely to cause widespread reduction of yield in environments with thermal regimes similar to Barossa Valley; extrapolation to cooler or warmer regions is not warranted. 

Significance and impact of the study: The relevance of this finding is three-fold. First, it demonstrates vine resilience against the target of the Paris Agreement setting a long-term goal of holding global warming below 2 °C. Second, further research on adaptation to warming needs to focus on logistic issues such as early harvest, and fruit composition with implications for wine quality, rather than yield. Third, this summary data set is a robust reference to benchmark time-series and modelling analysis of vine yield in response to warming.