Agri Kultuur June / Junie 2016 | Page 52

Ricardo Garcia https://upload.wikimedia.org/wikipedia/commons/5/57/1-Arraiolos-0050.jpg 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. C limate 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. Production hotspot 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. 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.