Study points to earlier ripening of wine grapes
A report says winemakers will have to change the way they manage their vineyards to deal with climate change.
It has found grapes are ripening earlier in many of Australia's wine regions due to rising temperatures and drying soils.
Vine management practices, such as decreasing the crop yield, are also contributing to early ripening, says the report.
Previous research indicated grapes were ripening earlier by about eight days per decade over the past 25 years across southern Australia.
Dr Leanne Webb and her team from the CSIRO have now analysed decades of records from wine-growing regions across that region.
"This has been a study of potential influences on wine-grape maturity trends on a continental scale," she said.
The team studied 10 vineyards growing various varieties in five major wine-growing areas in South Australia, Victoria and Western Australia.
Its results are published in the online edition of Nature Climate Change.
The researchers say their study will help wineries develop strategies to deal with climate change.
"You can see whether there's any buttons or levers you can actually use to make changes if it gets hotter," said study co-author Professor Snow Barlow from the University of Melbourne.
He said most winemakers did not want the fruit to ripen early as this was usually when the weather was hotter.
"Hot vintages are not good for quality wines," he said.
The researchers found early ripening was due to a shift towards a warmer climate, which spurred sugar production, and drier soils which activated stress hormones in the roots that promoted maturation.
Practices such as reducing crop yields - pruning of vines so that more energy goes into producing a smaller number of grapes - also contributes to early ripening.
"It does appear that changes in climate, particularly changes in soil moisture, have been driving the grapes towards maturation and it would appear that some management interventions that have some effect on yield may also have been taking the grapes in that direction," said study co-author Dr Penny Whetton from the CSIRO.
Winners and losers
The researchers used the records of sugar levels kept by the vineyards between 1985 to 2009 to assess how grape maturation times had altered.
They combined this with temperature data from the Bureau of Meteorology, modelling of soil moisture and records of crop yields from the winegrowers.
They found early grape maturation occurred in all the vineyards except Margaret River in Western Australia, which had actually dropped back by about half a day per decade.
"When we first did this work it worried us enormously," said Professor Barlow. "But when we actually looked at the temperature records of Margaret River, it hadn't warmed, so there are regional differences in the degree of warming that has occurred."
Professor Barlow said the biggest losers were on the Mornington Peninsula of Victoria, where some grape varieties had ripened about15 days earlier per decade.
"Traditionally because it's wetter [in the Mornington Peninsula] they hadn't really had to worry about [crop irrigation], but if you look in the last 15 years it hasn't been as wet," said Professor Barlow.
While there is little wine grape growers can do about changing climate, the researchers say the study suggests changes in irrigation practices, soil management and crop yield practices might save them from having to take more radical action such as change styles, varieties or even relocate.
"Soil moisture and the yield are both areas where the grape growers can have some control," said Dr Whetton. "Through this research they can give themselves a bit more control over when the grapes mature."
She said the study also had broader implications for understanding the effects of climate change.
"There isn't a lot of work in the southern hemisphere relating trends in biological systems to changes in climate, so this work is actually quite interesting in more generally demonstrating that connection," she said.
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