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Genetic conservation of cork oak in need of human intervention

Published: 23/05/2017

Cork has been successfully stoppering bottles for thousands of years thanks to its unique physical properties which allow it to compress to half its size and resist decay, even when submerged in liquid for years. For long-cellared wines, the oxygen stored inside the cork also helps keep the small amount of sulfur dioxide within the wine from disintegrating and becoming smelly.

But stoppers are only one of many products made from the bark of Quercus suber. Already in the ancient Egypt, fisherman used it for keeping their nets stay afloat. It’s used to create flooring, furniture and even footwear.

Cork oak (Quercus suber) is one of the most ancient species in the Mediterranean basin, with fossil remnants dating back to the Tertiary period. Sites in Minorca (only 67 trees) represent a relict zone which has been revealed as the major genetic diversity hotspot for this evergreen broad-leaved tree species.

The industrial use of cork oak has been a positive development in mitigating the decline of cork oak populations that has been observed during the past century and gave rise to a particular type of silvicultural management that maintains forests, ensuring the regeneration and sustainable use of the species over large areas. Portugal is the main cork producing country in the world and has largest area of cork oak. Wine stopper production uses about 20% of the cork, while generating more than 80% added value.

Cork oak forests face challenges mainly related to poor natural regeneration, largely due to cattle grazing. Other problems include ageing stands, damage by pests and drought which have been subject of numerous scientific discussions including those of Quercus suber within the EUFORGEN network (established in 1995). Even though the species is not endangered – its genetic resources are threatened, and thus they need to be properly conserved to safeguard the potential of the cork oak to adapt to changing conditions.

The rationale and genetic conservation strategy have been laid out in a couple of recently published booklets by Gösta Ericksson et al. The authors explain that selection of genetic resource populations for conservation must be based on differentiation of adaptive traits such as survival, growth, fecundity and tolerance to pests and diseases with special attention to marginal populations growing in extreme environmental conditions which may carry particular characteristics particularly valuable for the overall species evolution. This can be achieved by targeting as many site conditions as possible, which according to ‘Pan-European strategy for genetic conservation of forest trees and establishment of a core network of dynamic conservation units’ is estimated to be 41. Unfortunately, 37 of these areas in the total range of distribution of cork oak present gaps. Genetic conservation units should be established there.

It is important to note that genetic conservation is a cyclical process that does not usually interfere with economic use of the conservation populations, so that forest owners are able to continue selling bark for stopper production while at the same time strengthening the efforts to preserve the treasure of various cork oak genes. Strictly, protected nature reserves do not necessarily ensure conservation of genetic resources of cork oak and other forest-tree species. If the area suffers from serious disturbance, then the absence of management may mean withdrawing the only positive human interference still at hand.

The ‘Genetic conservation and management of Quercus suber’ explains how to safeguard cork oak genetic resources within the species’ distribution area in the long-term, while ‘Quercus suber - Recent genetic research’ goes into detail of findings of genetic studies of Quercus suber. Both publications will be presented at the ‘International Cork Oak Congress’ in Sassari on 25 May 2017 where copies will be available.