June 11, 2016, by Ricardo Garcia
Harvesting bark from cork oaks in Portugal. Image: APCOR/DKV via Flickr
Increased frequency of climate-related droughts in the oak forest regions of Portugal and Spain threatens valuable foreign revenue from production of corks for the wine industry.
LISBON, 11 June, 2016 − Climate change is threatening cork production in the forests of Spain and Portugal, making it more difficult to produce traditional wine bottle stoppers and putting an ancient and valuable industry at risk.
A recent study by Portuguese researchers shows that cork − the thick bark of an oak tree species found mostly in the Iberian Peninsula − grows at a much slower rate during intense, short-term droughts, which are becoming more frequent in the region as a consequence of global warming.
This makes the traditional nine-year harvesting of bark for bottle stoppers more difficult because the cork may not be thick enough to make a stopper.
Ironically, cork oak forests – called montado in Portugal and dehesa in Spain – are known to be resilient to climate variations, actually acting as a buffer against desertification. But researchers of the Forest Research Centre at the University of Lisbon’s School of Agriculture wanted to find out how exactly the species reacted to periods of low rainfall.
More than one thousand samples of cork oak bark from Coruche, a cork production hotspot around 80 km east of Lisbon, were analysed. The results, published in Climatic Change journal, are twofold.
On the one hand, cork growth is significantly hindered by short-term droughts, of two to 11 months’ duration. Annual growth bark rings were 28-42% thinner in 1995, 1999 and 2005, compared with their expected width. Those were years of severe droughts in Portugal.
On the other hand, the trees react quickly as soon as rainfall resumes normal levels in the following spring, thanks to their complex root system that efficiently soaks water from topsoil and taps it from deep reserves.
“There is an immediate response,” says lead author Vanda Oliveira, who conducted the study alongside co-authors Alexandra Lauw and Helena Pereira.
“If there are more droughts in spring, it is likely that we will see less thickness in cork”
Despite the rapid recovery, the fact is that the effect of droughts is still imprinted on the cork when it is finally peeled off from the tree, once every nine years. Within that timeframe, the bark needs to get thick enough to produce the standard 24 millimetre natural cork stopper. If it grows at a slower pace in one or more years, it is harder for the bark to meet the required dimensions.
But that is precisely what is bound to happen. Scientists predict that the amount of precipitation in Southern Portugal and Spain during spring – which has been diminishing since 1960 – will decrease further by the end of this century.
“If there are more droughts in spring, it is likely that we will see less thickness [in cork],” Oliveira concludes.
A decrease of 30% or more in annual ring width is expected, according to the study. And should this indeed happen, then some sort of adaptation will be necessary in order to keep the cork industry in good health.
Portugal is home of one-third of the world’s cork tree forests, and is responsible for half of the global production. Most of it is exported, generating around €850 million in foreign revenue every year. Cork that is thick enough to produce stoppers is worth around twice as much or more as the slimmer bark, which is used in the manufacture of other products.
The study suggests that extending the regular nine-year cycle between each cork extraction could help overcome the problem. It is a limited solution, though, for most of the cork growth occurs in the first few years immediately after the last extraction.
Irrigation is another alternative, but that has its own drawbacks, such as the prospect of increased water scarcity in the region in the future.
Another possibility would be to reduce the diameter of bottlenecks. João Roquette, CEO of Portuguese winemaking company Esporão, says: “With less cork, there will be less micro-oxygenation. This will affect how the wine evolves. But it could be an advantage in some cases.
On the other hand, Roquette adds, it would be necessary to spend money to adapt the capping machinery and to make thinner but sturdier bottlenecks that do not break easily.
Producers count on forest management as a weapon against climate change. “We can manage the montado so that trees make the best of rainwater when it is there,” says Conceição Silva, head of the technical department at the Coruche Forest Producers Association.
However, Silva argues that cork oak trees react differently in different locations, and that the study carried out at the University of Lisbon is only valid for a specific area.
Portuguese cork multinational Amorim claims that cork oak trees have been around for 45 million years, and the fact that they have survived major climatic changes is telling of their great resilience. – Climate News Network
Ricardo Garcia, an independent journalist based in Portugal and the UK, is an environmental writer/analyst and a journalism trainer.