Climate change comes for oak

Like other plants, oak trees are being affected by climate change. But, as Jim Clarke reports, good research is hard to find.

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Winegrowers looking to cope with climate change can respond relatively quickly: vines can be replanted and productive in less than a decade; in the shorter term, irrigation and canopy management might address issues from one harvest to the next. In contrast, imagine how hard it would be to plan if your harvest came 150 years after planting. That’s the challenge the cooperage industry is confronting.

What is known

The long-term nature of an oak tree’s life leaves climate change research to governments and universities rather than in private hands. In France, governmental management of oak forests dates back to 1670, making research the responsibility of today’s Office National des Forêts (ONF). “In the US,” says Christopher Hansen, general manager of Seguin Moreau Napa Cooperage, “most of the land where the trees come from is privately owned, so it’s hard to get any good information about how climate change is affecting them.” The University of Kentucky is doing good research, he says, but work is in its early days.

Three species of oak are typically used for wine barrels: sessile oak (Quercus petraea) and pedunculate oak (Quercus robur) in Europe, and white oak (Quercus alba) in the US.

Each is reacting differently to climate change; if there’s good news to be had, it’s that the most desirable, sessile oak, seems to be coping the best so far.

Researchers have focused on not only the effects of higher temperatures, but also on the impact of higher CO2 levels and drier growing conditions. A 2001 report by A.B. Tate in the Journal of Wine Research reported that CO2 levels were spurring pedunculate and white oak to grow at as much as twice their usual rates, leading to wood that might be weaker and less structurally sound as barrel staves. Pedunculate oak also seems to produce fewer ellagitannins (a type of tannin) under these conditions. These play a major role as antioxidants, absorbing dissolved oxygen; sessile oak’s more pronounced ellagitannins, along with whisky lactones, are the main reasons for sessile oak’s premium status.

Research on white oak in the south-eastern US has focused more on drought effects, which can be devastating; a brief but intense drought in 2011 and 2012 led to the loss of up to 75% of white oaks in some areas. In general, it seems the trees are struggling. “There’s a researcher at the University of Kentucky studying the speed of regrowth of American white oak,” says Hansen. “Some of his data shows that the trees aren’t regenerating or growing at the same speed as they used to.” He notes, however, that this may be the effect of poor forest management practices rather than climate change.

In Europe, “Quercus robur oak grows on lowlands, and sessile oak on slopes and hills, with drier soil,” says researcher Antoine Kremer. As conditions become drier, “the prediction is Quercus robur will be in a more and more difficult situation, rather than petraea.” A 2018 study showed the more desirable Quercus petraea was already expanding into areas where robur was more common in the past, “which would be good for the barrel industry”. 

 

Immediate impacts

Despite the long growth period of a usable oak tree, climate change is affecting the barrel industry in more immediate ways. In Hungary, warmer winters are making harvests difficult. “In our case,” says Peter Molnar, president of Kádár Hungary cooperage, “we can only really go into the forest when the roads are frozen hard because otherwise it just becomes a boggy mess. The expense of repairing the roads becomes more than the trees are worth.” Hansen reports similar problems in the US.

The practical impact of climate change continues even after harvesting. In Burgundy, cooperage François Frères has begun monitoring rainfall itself, rather than relying on government data, to ensure quality seasoning of the wood. “We need enough rainfall to guarantee a quality seasoning, to eliminate the sappiness of the wood,” says managing director Max Gigandet. In the stave yard, Gigandet say they’re stacking more tightly to maximise moisture, and shading the top rows of each pile to lessen sun exposure. Taransaud has done similar research. “We’ve done a good amount of work on how seasoning is affected by drier, warmer summers,” says research and development manager Rémi Teissier du Cros. After several trials, Taransaud found seasoning staves near stands of live trees helped mitigate climate change effects and allowed the mycological process – the breaking down of the wood by fungi – of seasoning to proceed properly. 

Meanwhile, as the wine and whisky industries continue to call for more and more barrels, Hansen is concerned that France’s ONF could respond to demand by allowing younger trees to be cut. So even as research struggles to determine the effects of climate change on cooperages and their raw materials, everyone concerned knows the business is heating up.  

 

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