Quercus robur Archives < In Praise of Biodiversity

The Oak, a symbol of old for strength and durability, stirring the imagination throughout the ages, beloved, and of economic importance, will not escape climate change. Its strength and durability will be severely tested, but its diversity may be its rescue

Drawing of Oak leavs and fruit: Walter Hood Fitch - Illustrations of the British Flora (1924) - Permission granted to use under GFDL by Kurt Stueber. Source: www.biolib.de - Permission is granted to copy, distribute and/or modify this image under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. Obtained via: http://luirig.altervista.org/schedenam/fnam.php?taxon=Quercus+robur

The Oak – Stirring the imagination

At times tall, with a lush foliage, at times crooked and gnarled especially on windswept places in for instance coastal areas, the Oak – Quercus robur – is one of Europe’s most well-known and beloved trees. Occurring throughout Europe, present also in localities of North Africa, and up to Central Asia and Asia Minor, the Oak has stirred people’s imagination throughout the ages. It can stand magnificently alone, or grow in forests, and can become 30 meters high. The tree is a symbol of strength and endurance, which is also reflected in its scientific name, robur, which means strenght or force. The Oak is also one of the trees often occurring in folk tales and fairy tales. As such, the Oak has played its role in countries’ and cultures’ fortunes. Many countries and regions have chosen the Oak as a national tree, including Serbia, Cyprus, England, Estonia, France, Germany, Moldova, Romania, Latvia, Lithuania, Poland, the United States, Wales, Galicia and Bulgaria. Oak leaves and branches were frequently used as symbols on coat of arms, coins and the like, but also as wreaths during festivities, and as decoration or ornamentation of houses or cars. The Oak featured also prominently in the German romantic period in paintings and novels. And it has it’s share of medicinal uses. The importance of the Oak for people is reflected in the word “oak”. As the Online Etymology Dictionary writes:

oak (n.)
Old English ac “oak tree,” from Proto-Germanic *aiks (cognates: Old Norse eik, Old Saxon and Old Frisian ek, Middle Dutch eike, Dutch eik, Old High German eih, German Eiche), of uncertain origin with no certain cognates outside Germanic.
The usual Indo-European base for “oak” (*deru-) has become Modern English tree (n.); likewise in Greek and Celtic words for “oak” are from the Indo-European root for “tree,” probably reflecting the importance of the oak to ancient Indo-Europeans. The Old Norse form was eik, but as there were no oaks in Iceland the word came to be used there for “tree” in general. Used in Biblical translations to render Hebrew elah (probably usually “terebinth tree”) and four other words.

The Sacred Oak

Not only nations took to the Oak. Whole cultures regarded the Oak reverently. For the Celts the Oak was a sacred tree; the Druids of the Celts climbed into the trees and cut the mistletoe, and each acorn possessed the soul of a fairy. For Germanic people the Oak was a symbol of the god Donar, a tree representing thunder and lightning, probably because it appears to be more frequently hit by lightning than other trees. Explanations given for that include the Oak’s high amount of starch, which is a good conductor; it’s deep root system; and the fact that the Oak often grows where there are crossing underground water currents. The Greeks associated the Oak with Zeus, and the Romans associated the Oak with Jupiter and dedicated it to the god Pan: the tree brought fertility. But for both Greek and Romans, the Oak was also the sacred tree of the goddess Rhea, resp. Diana. The Dryads were in that Oak cult the nymphs of the Oak. Slavic people revered the god Percula by means of the Oak.

These cultural and religious beliefs have largely disappeared. One important actor in that process was Saint Bonifacius. As the biography by Willibald will have it, Bonifacius cut down the sacred Oak of Donar in Geismar, in present-day Germany, in 723, precisely to prove that the Oak did not have divine powers, or at least that the wrath of distressed gods would not follow. As a result, many germanic people converted to christianity. This event is regarded by many as a key point in the christinanization of north-western Europe. Perhaps it can also be regarded as the starting point of losing respect for the Oak and perhaps the forest in general. Europe (excluding the Russian Federation) is, after all, by now one of the poorest continents in terms of forest. (FAO. 2010.)

Witnesses of history

We are all witnesses of history, just as even shortlived creatures like mosquitos are, or even amoebae, be it that one single amoeba does not have much chance to live through a memorable event. Oaks though would be marvellous for that, as they are long-lived. This tree can live up to 500 years, and such a specimen, the Kroezeboom (website in Dutch), lives in the Netherlands (in Overijssel). But both Great Brittain (in Bowthorpe) and France (in Bretagne) have specimens thought be 1,000 years old, Denmark (in Jaegerspris) has one between 1,000 and 1,400 years old, and an Oak in Erle, Germany is estimated to be 1,500 years old. This Oak is probably the oldest Oak in Europe. Such old trees could tell a lot. But an oak shares with amoebae that we can’t hear from an Oak what happened in, say, 1753. Things Oaks, and other trees, can tell us about is for instance the climate, by examining the growth rings, unless such old trees have already hollowed out from the inside out. However, we would have to cut it down to do that, and that would be a shame. Better to rely on trees that have already died off and are, for instance, preserved in peat. Trees are therefore not only of value to us alive, but also when dead.

What about using the Oak for when you’re hungry or sick ?

The Oak is not the best of food sources for us. The acorn contains quite some nourishment that would benefit us, but it is indigestable. On the other hand, ground acorns were used as a coffee substitute, and to make some kind of bread. Otherwise acorns were more suitable for feeding pigs. Even if not really edible, a good crop of acorns was seen as a sign that the harvest would be good.

Medicinally the Oak has much more to offer. I quote from Plants For A Future:

The oak tree has a long history of medicinal use. It is anti-inflammatory, antiseptic, astringent, decongestant, haemostatic and tonic. The bark is the part of the plant that is most commonly used, though other parts such as the galls, seeds and seed cups are also sometimes used. A decoction of the bark is useful in the treatment of chronic diarrhoea, dysentery, intermittent fevers, haemorrhages etc. Externally, it is used to bathe wounds, skin eruptions, sweaty feet, piles etc. It is also used as a vaginal douche for genital inflammations and discharge, and also as a wash for throat and mouth infections. The bark is harvested from branches 5 – 12 years old, and is dried for later use. Any galls produced on the tree are strongly astringent and can be used in the treatment of haemorrhages, chronic diarrhoea, dysentery etc. The plant is used in Bach flower remedies – the keywords for prescribing it are ‘Despondency’, ‘Despair, but never ceasing effort’. A homeopathic remedy is made from the bark. It is used in the treatment of disorders of the spleen and gall bladder. The German Commission E Monographs, a therapeutic guide to herbal medicine, approve Quercus robur Pedunculate Oak for coughs/bronchitis, diarrhoea, inflammation of mouth and pharynx, inflammation of the skin.

(Numbered references to sources removed to improve readibility.)

The Economy of the Oak

Throughout the ages, the Oak has contributed greatly to the economy of countries. Its wood has graced buildings and made great ships possible. Oak wood is strong and is very resistant to insect and fungal attack, as it has a high tannin contents. It is still used for furniture, floors, timber frame buildings, and veneer production. The tannins that make the Oak so suitable for furniture and buidlings, render barrels made from Oak very suitable for storing wines and sprits, as do other compounds from the wood. Oak wood imparts colour, taste and aroma, and does that even more so if charred. The use of Oak for barrels to produce alcoholic drinks continues until today, and oak wood chips are used for smoking a/o fish, meat and cheeses. It’s not only Q. robur that is used in these fashions. Japanese Oak is used in making drums, the bark of the Cork Oak is used to produce wine stoppers, and Northern Red Oak in North America is the most prized of the red oak group for lumber. I didn’t find an economic valuation of the Oak expressed in a monetary value. But the integration of the Oak in the economy can be imagined by the uses listed by the ecocrop database maintained by the FAO:

The Oak’s value

So, the Oak is important to us in spiritual sense, in medical sense, practically in construction, furniture, and for food and beverages, as well as, because of all the previous, in economic sense. What else does it do? The answer to that would be ecological. The relations that the Oak has as a species with lots of other species are numerous indeed. If we stretch the application of the term “ecological” to include the spiritual value it has for us – and surely stretching the term to that is more defensible than the use of the term “ecosystem” to describe related digital gadgets as in ‘the Apple ecosystem’ – then for that aspect alone the Oak is of tremendous value, given the role it has played, and to an extent continues to play, in defining the cultural – if not political – heritage of countries.

Using ‘ecological’ in the more conventional way, the Oak plays an outsized role. This tree can be considered the heart of the forest system:

A mature oak tree, standing a hundred feet tall, provides lodging, and often board as well, for more different kinds of animals than any other European tree. Thirty species of birds, forty-five different bugs and over two hundred species of moth have been collected from oaks. Each part of the tree has its own particular lodgers.

This phrase – quoted on several websites – stems from David Attenborough, one of the great, if not the greatest, popularizers of natural history in the old-fashioned sense: going out and looking at and observing in nature. (Attenborough, David. 1995.)

Among those birds are for instance the Eurasian Jay (Garrulus glandarius) who counts the acorn among it’s food sources. Birds such as the Great-spotted Woodpecker (Dendrocopos major), or the Eurasian Nuthatch (Sitta europaea) live from insects that live on and in the Oak’s bark. As for mammals, one would expect a mammal like the the European Red Squirrel (Sciurus vulgaris) to rely on the Oak too. However it does not: it cannot digest acorns, and relies on other fruits instead, notably the hazelnut, the fruit from the hazel tree (Corylus avellana). The Eastern Grey Squirrel (Sciurus carolinensis) from North America, introduced to Great Brittain and Italy, can more easily digest acorns, and this is considered one of the factors that allows this squirrel to outcompete the European Red Squirrel. Mice however, do eat acorns, when they are fallen on the ground. Birds like the Rook (Corvus frugilegus) and Wood Pigeon (Columba palumbus) also eat fallen acorns.

Numerous insect species live on the leaves, the buds and the bark, and in the acorns. Well-known are gall wasps. These wasps secrete chemicals which induce the Oak leaf to grow around the egg or larva and protect these. The best known is the Common Oak Gall Wasp (Cynips quercusfolii) wich produces spherical galls of about 2 cm on the underside of the Oak leaf. Some of these galls can be brightly colored. Other insects, such as the Green Oak Moth (Tortrix viridana) relies on Oak leaves when it is a larva. The larva eats the leaf, then rolls up in an Oak leaf. It transforms into a pupa, which in turn produces the adult moth.

Numerous fungi find a place on the Oak too, and on dead leaves that are fallen on the ground. An exampe is the Edible Beefsteak Fungus (Fistulina hepatica). The leaves on the grounds also feed many invertebrates. The Oak has symbiotic relationships too: associations between the Oak and another species that benefit both. An example is the Orange Oak Bolete (Leccinum quercinum). The fungus gets sugars from the Oak. The Oak is helped by nutrients that the fungus extracts from the soil.

The Encyclopedia of Life records forty-nine different species of gall-wesps, moths, and parasitic or half-parasitic fungi and plants. Aside from this, the Oak provides a place to grow for numerous lichens and mosses, and also higher plants, such as the Mistletoe (Viscum album). The Mistletoe is half-parasitic: it has both green leaves that provides it with energy, and it is rooted in the Oak to extract nutrients that it otherwise would get if it would be rooted in the soil.

And that’s when the Oak is still alive. When it is dead and decaying, many different fungi live from it and help break the wood down so that the tree eventually returns to the soil. It’s not just fungi that benefit from a decaying Oak tree. Such a tree provides roosting sites, for example for owls, and hibernation sites for bats.

To all this we should add the organisms that rely on the Oak indirectly, for instance mice that eat fallen acorns and fall prey to hunting
owls. The Oak then is at the heart of a complex web of relations of food and shelter.

Whereas the Oak provides so much for other organisms, the tree relies in turn for its continued existence on other organisms. Most of its fruit, the acorns, are eaten or rot away. It relies on jays or squirrels that bury acorns and then forget some, or die before they can eat them, to successfully sprout new Oaks. Of course, humans can do that too, so, is it necessary to ensure the presence of those animals that do seed dispersal? One study concludes that the replacement costs of one pair of jays for seeding or planting is 4,900 USD or 22,500 USD respectively. (Hougner, Cajsa, et al. 2006.) Not only the Oak is valuabe, the biodiversity it supports and which in turn helps the Oak, is that too.

Will the King of the forest be beaten by Climate Change?

That is a question to which the definite answer is not yet found, and we will probably only find out definitely in the course of time with the ongoing pressures of climate change growing more intense. That said, research has been undertaken to investigate this, but of course, it is very difficult to give definite answers, since that would require laboratory and/or field experiments to be done. While laboratory experiments can be conceived with planting acorns and observing young Oaks under controlled conditions, given the longevity of the tree that is expressed in hundreds of years, it is virtually impossible to say something sensible on basis of direct observations and predict in this way how Oaks will react and what one can best do. In fact, one study concludes reports age-dependent reactions to changes in climate: young trees react differently than older trees. (Rozas, Vicente. 2005.)

This research as so many others of this kind, relies on studying tree-ring growth patterns in relation to various environmental conditions that change over time, specifically climatic conditions. Other studies look at genetics and historical changes (measured in thousands of years). One such study emphasizes the importance of diversity in existing Oak populations in the reaction to climate change. The study “… predicts that substantial evolutionary shifts can be expected in a limited number of generations due to the high level of genetic diversity in oaks, and that gene flow will be an important driver of adaptive evolution.” (Kremer, Antoine. 2010.)
The study continues with the advice to enhance the adaptive potential of local populations by mixing local stocks with seeds or seedlings from other sources during regeneration.

Biodiversity and climate change

In a previous post I referred to the inclusion of genetic diversity in the concept of biodiversity. Studies like the above emphasize how important diversity is to increase the chances of survival for species in the face of climate change. The study referenced above refers to the genetic diversity that exists in Oak populations. The number of subspecies for Q. robur listed in the Catalogue of Life suggests that the Oak is indeed quite diverse. The species is not even agreed upon by everyone.

One article observes that a number of different Oak species are distinguished which by others are assigned to eitehr Q. robur or Q. petraea. It then continues with the observation that the distinction between Q. robur and Q. petraea as species is questionable, since they are interfertile, and these species are by some regarded as ecotypes or subspecies within one composite species of Q. robur. (Gömöry, Dušan, et al. 2001.)

Based on the apparent diversity of the mighty Oak – Quercus robur – perhaps we can be optimistic that its variability that makes it hard to pin down as a species, lets it survive the challenges of climate change.

Sources

In the text above, many sources are not directly indicated to improve readibility. Below follows a list of various sources from which I took information.

Referenced documentation

Attenborough, David. The Private Life of Plants: A Natural History of Plant Behaviour. 1995. London, BBC books.

Hougner, Cajsa, Johan Colding, and Tore Söderqvist.Economic Valuation of a Seed Dispersal Service in the Stockholm National Urban Park, Sweden. Ecological Economics 59, no. 3 (2006): 364-374.

FAO. Global Forest Resources Assessment 2010 : Main Report. 2010. Rome: Food and Agriculture Organization of the United Nations.

Gömöry, Dušan, Igor Yakovlev, Petar Zhelev, Jarmila Jedináková, and Ladislav Paule. Genetic Differentiation of Oak Populations Within the Quercus Robur/Quercus Petraea Complex in Central and Eastern Europe. Heredity 86, no. 5 (2001): 557-563.

Kremer, Antoine. Evolutionary Responses of European Oaks to Climate Change. Ir. For 67 (2010): 53-65.

Rozas, Vicente. Dendrochronology of Pedunculate Oak (Quercus Robur L.) in An Old-growth Pollarded Woodland in Northern Spain: Tree-ring Growth Responses to Climate. Annals of forest Science 62, no. 3 (2005): 209-218.