Wine growers in Australia have long observed that changes in the climate bring their grapes to early maturity -- leading to changes in the balance of flavors and aromas that could bring down the value of wine.

But until recently, those observations had not been matched with the underlying causes of change over the decades. A new study in Nature Climate Change finds that warming and declines in soil moisture, but also vine management practices to lower yields to produce better-quality grapes, brought the fruit to early maturity.

Australia, known for its dark red Shirazes and Cabernet Sauvignons, could see an unsteady course in the value of its wines. If the onset of maturity comes earlier in the season, it means that grapes ripen during a warmer period -- affecting sugar levels, aromas and flavors and changing the unique identity that connoisseurs look for in regional wines.

"Changes in timing of maturity can change the style of wine that is produced," said Leanne Webb, lead author of the study and a research fellow at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia's national science agency. "These changes may be important where regional characteristics are well understood and anticipated by wine consumers."

Webb and her colleagues used vineyard records over an average of 41 years, ending in 2009. In the wine-growing region of southern Australia, grape maturation dates have advanced about eight days per decade, she found, following other examples of changing timelines in natural cycles in the country. Butterflies have shown to emerge at different times from cocoons, a phenomenon scientists attribute to man-made climate change in Australia.

Adaptation options
"In addition to informing the wine industry of adaptation options, we believe our study is also relevant to many other agricultural and non-agricultural sectors where trends in timing of biological phases have been detected," Webb said.

But environmental changes were not the only factor to hasten maturity. Irrigation techniques, pruning and trellising to improve the health and energy-absorbing capacity of the vines since could have inadvertently led to earlier onset.

Wine growers have sought to lower the amount of berries a vine produces to encourage better, sweeter and healthier grapes. Although soil moisture and warming were the more significant factors that led to early ripening, the low yields from wine-grower practices also played a part. Between 1985 and 2009, lower crop yields drove early ripening in four out of 10 sites in the study.

The trend of drier soils could have led to two important effects for maturity. Dry soil encourages the production of the plant hormone abscisic acid in vine roots, which is correlated with earlier maturity of wine grapes. Drier soils are also likely to warm more rapidly in the growing season, affecting the growing temperature.

Strategies to adapt could include managing soil moisture content through increasing irrigation or mulching, choosing better vine-stock roots or managing crop yield, said Webb.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500