Ricardo Garcia
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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.