8 Jul 2018

51. Biodiversity among the grapevines of El Hierro

Vines cultivated in El Pinar under the unique conditions of El Hierro. Volcanic soil high above the clouds, to the east
 La Gomera and Tenerife and further still, Africa.  (Photo, O P Harris)

You might be forgiven for drawing a parallel between the biodiversity of the grapevines of El Hierro and that of the island’s wild plants, or even Darwin’s finches in the Gal√°pagos. There is every reason for doing so: on the southern edge of the northern hemisphere’s winegrowing zone, the Trade Winds and the rugged mountainous terrain of the island provide a thousand microclimates and dozens of volcanic soils, and … remoteness over time.

We boast of our distinctive wines produced from varieties of grapes specific to the island – Dr Francesca Fort of the University of Tarragona and her team have identified, using DNA analyses, nineteen varieties specific to the Canaries of which nine correspond to El Hierro alone. Statistically this is a disproportionally high degree of diversity. As far as I know this is not the result of intentional breeding – artificial selection – although a couple of the varieties are considered ‘crosses’.  It seems to be taken for granted that the ‘exclusive’ varieties have evolved through mutation over time on this remote island. This in turn suggests that natural selection has been at work. I cannot accept this attractive idea.

Natural selection requires sexual reproduction, i.e. parents pass characteristics on to their offspring. As the DNA of both parents is recombined, mutations (errors) occur. If the mutation is beneficial, the offspring prosper. If it is harmful, it is not passed on to successive generations. Grapevines are not propagated sexually from seed but by grafting and from cuttings. In a sense every vine in my vineyard is a part of a much older vine that has been growing for many, many years. My second reason is that there has been ridiculously little time in evolutionary terms since the introduction of grapevines – they do not predate colonization at the beginning of the fifteenth century.

From the beginning, settlers brought with them from ‘home’ cuttings of their favourite varieties. Every labourer’s ruined hovel, and there are thousands of them throughout the island, bears witness with a skeletal ghost of a trellis. Many of these imported varieties may have succumbed to the brutal new conditions on the island but some flourished. Some of these, in turn, formed the basis of the island’s wine and brandy industry while others remained testimonial. Winegrowing boomed until the 1850’s when our vineyards were wiped out by powdery mildew. The landowners went and did something else, but the labourers could only remain, scraping out a living. They also looked after their household vines.

In contrast, on the mainland and the rest of wine-producing Europe, the tradition was too ancient and the landowners too wealthy to abandon after phylloxera had gutted their vineyards, too, in the 1850’s. These were replanted with choice European varieties grafted on American stock. Minority varieties were lost.

Phylloxera has never reached El Hierro and the powdery mildew that struck us on the island can be treated with sulfur. In this way, El Hierro became a sort of unique conservatory of pre-phyloxera varieties of grape, perhaps not Merlots or Chardonnays but pretty good all the same. And if one of our varieties, lets call it "X", differs from its supposed parent "Y" somewhere else by a significant degree (in DNA terms), then its more than likely that we have supposed wrongly and had better start looking for "Z".

It seems to me our biodiversity may result from a quirk of history rather than any evolutionary process, that our special varieties are marvelous ‘Rip-Van-Winkles’ that have been asleep for 500 years while their siblings elsewhere fell victim to diseases and agribusiness. Now that we have woken them up, let’s hope we don’t make the same mistakes.