Technical guidelines for genetic conservation and use Cork oak Quercus suber Quercus suber Quercus suber Luis Gil1 and Maria Carolina Varela2 1 Technical University of Madrid, Spain 2 National Agronomy and Fishing Investigation Institute, National EUFORGEN Forest Research Station, Lisbon, Portugal These Technical Guidelines are intended to assist those who cherish the valuable cork oak genepool and its inheritance, through conserving valuable seed sources or use in practical forestry. The focus is on conserving the genetic diversity of the species at the European scale. The recommendations provided in this module should be regarded as a commonly agreed basis to be complemented and further developed in local, national or regional conditions. The Guidelines are based on the available knowledge of the species and on widely accepted methods for the conservation of forest genetic resources. Biology and ecology Cork oak (Quercus suber L.) is an evergreen broad-leaved tree. The species is long lived (200–250 years), commonly growing to a height of 15–20 m but it can reach 25 m under ideal condi- tions. Stem diameter at breast height can reach more than 200 cm. The bark is up to 20 cm thick, porous and furrowed, with deep longitudinal fis- sures. The thick dermal system protects the trees from forest fires. Leaves are alternate, simple and with the mar- gin entire or with 4–7 pairs of acute teeth. They fall during the second year (13–23 months after leaf flush). Cork oak is wind pollinated and has predominantly separate male and female flowers on the same plant. Male inflorescences are long, pedunculate and arise from the axillary buds of the pre- vious year’s branches. Female CorkQuercus oakQuercus suberCork oakQuercus suberCork suber oakQuercus suberCork oakQuercus Quercus suberCork oakQuercus suberCork oakQuercus subersuberCork oakQuercus suberCork Quercus oakQuercus suberCork oakQuercus suberCork oaksuberQuercus suberCork oakQuercus Que suberCork oakQuercus su flowers appear on vigorous new Distribution Importance and use growth. The seed matures either during the year of set or the fol- lowing year. Annual maturation Cork oak requires an annual The primary use of cork oak is is more common in the southern mean temperature of 13–18°C as a source of cork. Cork is ob- cork oak woodlands, whereas and will not tolerate temperatures tained by peeling the bark away biennial maturation is more com- below –10°C. As a result, its nat- from the trunk, leaving a thin lay- mon in northern populations, but ural range includes the coastal er of new cork still covering the individual trees may display both regions of the western Mediter- functional secondary phloem on patterns simultaneously. Within ranean Basin, including Algeria, the trunk. The first harvest (virgin each population, precocious France, Italy, Morocco, Portugal, cork) is made when the tree is individuals show a higher per- Spain and Tunisia, the islands of approximately 25 years old. Sub- centage of annual acorns, while Corsica, Sardinia and Sicily and sequent harvests can be made late-flowering individuals have very limited areas on the islands every 9–12 years. Cork yield is a higher percentage of biennial of Majorca and Minorca. The determined by the circumference acorns. Acorns from southern most extensive forests are on of the tree trunk the harvesting or low-altitude populations are the Atlantic coast of the Iberian frequency and the length of bole usually longer, wider and heavier Peninsula. The easternmost ex- and main branches that can be than those from northern lati- tent of the species is the Adriatic stripped. tudes or higher altitudes. coast of Apulia in Italy. Cork oak was a ne- Cork oak grows mainly on glected species before non-calcareous substrates, pre- the systematic use ferring sandy and of cork as the raw lightly structured material for stop- soils, but is occa- pers to seal bottles sionally found on started. For more than three decarbonated soils. It centuries production of stoppers is found under a wide has been the driving force for range of annual rainfall, sustainable management of cork ranging from 479 mm oak forests. Stopper production in Mamora (Morocco) to uses about 20% of the cork 2400 mm in some north-western while generating more than 80% areas of Portugal and southern of the added value. Spain. The cork left after stoppers Cork oak is commonly grown have been made is used to make in agroforestry systems, known a wide range of products, includ- as montado in Portugal and de- ing insulation panels, floor and hesa in Spain. These are open wall tiles and sound-proofing in woods with low tree density the car industry, as well as for (50–300 trees/ha). In these sys- handicrafts and artistic uses. tems, forage species are com- A number of high-value, low- monly grown under the trees volume ‘niche’ products are also and grazed by cattle during the made from cork, such as ‘cork summer. paper’, a thin slice of cork ob- tained from cork board. Cork CorkQuercus oakQuercus suberCork oakQuercus suberCork suber oakQuercus suberCork oakQuercus Quercus suberCork oakQuercus suberCork oakQuercus subersuberCork oakQuercus suberCork Quercus oakQuercus suberCork oakQuercus suberCork oaksuberQuercus suberCork oakQuercus Que suberCork oakQuercus su paper is used in printing, book Genetic knowledge haplotypes of this lineage, hence covering, clothing manufacture, its name.. cork ’maroquinerie’ and other Cork oak is highly variable in products. Cork is also used in Neutral markers, such as iso- its adaptation, morphology and making badminton shuttlecocks, zymes, show large genetic varia- phenology. Phenological charac- handles of fishing rods and spe- tion within populations and small teristics such as flower receptiv- cial devices for the space in- differences between them. High- ity, pollen shedding, fruit produc- dustry. est levels of diversity have been tion and seed maturation vary found in southern and Central widely among individuals within Spain. This suggests that the same population. These and the Iberian Peninsula is characteristics relat- a centre of diversity ed to drought tol- and was a glacial re- erance have fugium for the species. high plastic- Marginal areas provide ity. Leaf mor- a significant compo- phology and nent of the total diver- acorn size sity, mainly owing to vary widely. their divergence from Cork quality the mean genetic com- also varies be- position. In addition to tween stands the analysis of nuclear genetic and between variation, several independent trees. and complementary studies us- Cork oak ing chloroplast markers also in- populations differ dicate that cork oak originated in in their adaptation to drought and the western Mediterranean. They low temperatures. Thermophilic also indicate that human activity provenances are more sensitive has not altered the original ge- to frost and stop growing during netic structure of cork oak. Chlo- cold winter months. Provenanc- roplast DNA variants, belong- es from dry sites have better ing to two very distant lineages, water-use efficiency than those have been identified. Lineage from wetter sites. Another fea- ‘suber’ is the most widely distrib- ture related to strategies to face uted and it is composed of four drought and cold is vegetative to eight chlorotypes depending phenology. Apical and basal bud on the technique used. Con- flushing showed significant dif- versely, 19 chlorotypes belong ferences between provenances. to a very different lineage called ‘ilex-coccifera.’ A large majority of Holm oaks (Quercus ilex) and of Kermes oak (Quercus coc- cifera) from Morocco, Iberia, the Balearic Islands, and southern France are also characterized by CorkQuercus oakQuercus suberCork oakQuercus suberCork suber oakQuercus suberCork oakQuercus Quercus suberCork oakQuercus suberCork oakQuercus subersuberCork oakQuercus suberCork Quercus oakQuercus suberCork oakQuercus suberCork oaksuberQuercus suberCork oakQuercus Que suberCork oakQuercus su Threats to Guidelines for genetic genetic diversity conservation and use Cork oak is not endangered, and Genetic resources of cork oak no threats are foreseen at the should be conserved in several in species level as long as cork has situ populations representing the economic value. However, mar- ecogeographic range of the tree. ginal populations, often growing Each population should consist in small and scattered stands of at least 250 trees to ensure at and in restricted habitats, are least 50 reproductive trees. at risk of disappearing. In such The seed used to artificially populations the effective popula- regenerate large populations or tion size (in effect, the number to establish new ones should of reproducing trees) may be be collected from local popula- too small to maintain enough tions or populations growing un- genetic diversity for future gen- der similar edaphoclimatic con- erations. Furthermore, ditions. However, seeds should the trees rarely produce not be collected for this large amounts of seed. purpose in years of low Hybridisation with other seed production. oaks, mainly Holm oak In small and mar- (Quercus ilex L.), may play ginal populations, a major role in the evolution conservation activi- of these populations. ties should aim to Acting together, these factors promote regeneration to increase limit natural regeneration in small the population size. Where seed populations. The threat becomes set is good, the main approach critical when such populations may be to protect the seed are grazed. and seedlings from grazing and Even when