Eating acorns

How did people start to eat acorns? Well pretty much in the same way people started to eat all the other plants. A good hunter knows its prey well. He knows its habits including its diet. Animals are the easiest to catch while they are distracted by food. So people observed animals eating plants. The animals would come to the same places every year at the same time and eat the same plants. So people would use this knowledge to ambush the animals on their feeding grounds. But hunting is not easy. Animals don't like to be killed and eaten. And even when they are eating themselves they are constantly on their guard. So hunters often end up with empty hands. After an unsuccessful hunt, and while thinking about what he could eat to stop his stomach rumbling, some bright spark among the hunters probably had a train of thoughts that went like this: 

These animals eat this plant all the time. They must like it a lot. And the animals seem to be OK after eating the plant. I mean they look positively happy. This plant must be good to eat. I am hungry. Ah feck it. I'll give it a try...

Munch Munch Munch....

Hey Grunt what are you chewing? 

This plant that the animals eat all the time. Its good, its different...Try it...

Munch Munch Munch....(everyone is munching)

Hey chief, do you think we can get away with bringing this home for dinner instead of meat? I mean my wife was looking forward to a roast...And she gets really cranky when she is hungry...

Sure, we'll tell them its good for their health and their hair. Come on boys, lets grab a few handfuls of this plant each and lets go home. Its getting late...

The rest is prehistory...

People still hunted and ate the animals, but would also pick and eat the plant that the animal ate. And so salad was invented, which if you are a Serbian, is still best eaten with lots of meat, but can in extreme circumstances be eaten by itself. 



I mean don't get me wrong. People were always omnivores, scavengers, opportunistic hunter gatherers, eating anything that was not fast enough to run away, whether they were plants or animals. They did learn a lot about food from animals though, by observing and copying their behaviour. Well smart people did. The stupid ones tried things that no one ate and died...

Even learning from animals doesn't always work though. Some plants which can be eaten by animals taste horrible. Some can be digested by animals but are indigestible to humans. Some can have harmful affects on human health and some can be outright poisonous to humans. But that's evolution for you...Hit and miss. 

Of course the bright spark in the  above story could have been a woman as well. According to the available anthropological data, hunter gatherer societies did not have strict division of labour. Pretty much everyone did everything more or less. So women were probably part of the hunting and gathering bands and it could have been a woman who first decided to try "that thing that the animals are eating"...

So how did people start eating acorns? Well people hunted rodents, squirrels, deer, wild boar, jay birds, ducks, woodpeckers and all these animals loved eating acorns. They loved acorns so much that acorns made up 25% of their autumn diet. Particularly wild pigs were fond of acorns and herds of these animals could be seen in the oak forests every autumn with their snouts stuck to the ground hovering up the so called acorn blanket. And getting fat and juicy. 

So every autumn hunters would hunt in oak forests trying to catch animals which were feasting on the fallen acorns. Eventually someone somewhere must have tried acorns himself. And if we know that most acorns are bitter and pretty horrible raw, our experimental acorn eater probably went "blah, yuck, horrible, bitter" spitting the half chewed acorn out. But a smart hunter gatherer would soon noticed that squirrels sometimes eat only the upper half of the acorn and throw away the lower part, and he would have wondered why.

Well now we know that this is because the tannin, which makes the acorn bitter, tends to be in the bottom half of the acorn near the cap. But our hunter gatherer would just know that maybe squirrels know something that he doesn't. He would then try the same tactics and would realise that you can eat acorn tops and discard acorn bottoms and avoid most of the yucky bitter stuff. He would also notice that the acorn nut is covered with some sort of dark brown skin, which is very bitter. So our smart hunter gatherer would carefully peel it off the nut before eating it. Now that our hunter gatherer was concentrated on the acorn eating habits of animals, he would also notice that squirrels and other animals prefer certain types of acorns which grew on certain types of oak trees. The animals would always eat them first, and only go on to eat the other types of acorns when their favourite acorns were all eaten. A good hunter gatherer would conclude that there must be something special about these acorns that makes the animals like them so much. So our experimental acorn eater would try these acorns and would find out that they were a lot less bitter or not bitter at all. So he would eat a good few of them and would collect a few to bring to his family. A good hunter gatherer would look at the acorn shape, and he would look at the tree under which he found the acorns, and would remember them, so that next time he would know how to distinguish the sweet acorns from the bitter ones. Then next day the whole family would probably be in the forest collecting and eating acorns. Hunter gatherers never throw away easy food. 

They would still kill and eat animals that eat acorns, like pigs for instance, but they would also collect acorns and eat them too. This is how stuffing was invented which is a great accompaniment to pork... :) 

Eventually a good hunter gatherer would realise that there were two distinct types of oaks and acorns:

The white oaks whose acorns mature in 6 months and taste sweet or slightly bitter; The inside of the acorn shell is hairless. The bark is light in colour, gray to light gray. The leaves mostly lack a bristle on their lobe tips, which are usually rounded.

The red and black oaks whose acorns mature in 18 months and taste bitter to very bitter. The inside of the acorn's shell can be hairless but is in most cases woolly. The bark darker in colour. Its leaves typically have sharp lobe tips, with bristles at the lobe tip.

A smart hunter gatherer would also notice that some animals which eat acorns, like squirrels and jay birds, collect the acorns in the autumn, store them in holes in the ground and in trees and then eat them during the winter. Someone must have caught a squirrel getting acorns from one of its stashes in the middle of winter. If they tried the acorns from the stash, they would have quickly realised that they were perfectly edible. Now not too many things are edible in the middle of winter, so this must have been a revelation. If I collect acorns in the autumn and store them somewhere, then I will also have something good to eat throughout the winter. Eventually the whole clan would start collecting acorns every autumn. Gathering would take place between September and December. It is a simple job that could be done in three ways: picking the ripe acorns from the ground, causing them to fall by knocking them down from the tree with a long stick and then picking them from the ground, or by climbing the tree and cutting the tips of the branches with ripe acorns using sickles. The second two methods were used to prevent the animals get to the good acorns before people. All three methods were attested in the ethnographic studies. Oaks produce so many acorns that people could in 2 - 3 weeks easily collect enough acorns to last them 2 to 3 years. The question then was how to transport all these acorns from the oak forest to the settlement and how and where to store the acorns. So people invented baskets, like these ones reconstructed from the remains of baskets which were found in the La Draga lake-dwelling site from the Iberian Peninsula which was occupied at least twice between 5300 and 5000 BC by people of Carded Ware Culture. The baskets which contained acorns. 

I believe that people new how to make cordage and how to weave many thousands of years before they made the first basket. The archaeological data confirms that too. Why? Because they didn't need baskets. Baskets are a solution for a particular problem. Baskets are only useful for collecting bitty things in large quantities, transporting them from the collection point to the storage point and then storing them at the storage point. And this situation did not arise until Upper Paleolithic, the time when we find the first permanent settlements of people who collected large quantities of fish, shellfish, snails, acorns and nuts, the bitty things that you can collect, transport and store in baskets. I will dedicate my whole next post to this subject.

But paradoxically, while people put considerable effort and ingenuity into inventing dry storage for acorns above the ground, we find in the archaeological and ethnographic data that acorns were mostly stored in bulk in pits dug into the damp ground. Why did people start storing acorns in this way? Because squirrels and jays, apart from storing acorns in hollow trees and basket like nests, also stored them by burying them in holes in the ground. If people tried acorns from few different squirrel caches, of which some were stored in hollow trees (raised dry baskets) and some in holes in the ground, they would soon realise that the ones which were buried in wet ground, particularly wet clay at the edge of streams, tasted sweater, less bitter. So people soon started digging pits in the ground and burying acorns in them. Acorns which are buried from few weeks to few years, taste sweater because they get leached in contact with the damp ground. The acorns stored like this get dark in colour and are very good for roasting. 

Recent research, based on ethnographic data from America and Sardinia, has proven that clay and particularly red clay, when mixed with unleached acorn meal would, remove up to 80% of tannic acid from acorn meal through chemical and catalytic processes which occur during baking. You can read papers about this type of leaching in these two articles:

"Traditional detoxification of acorn bread with clay" by Timothy Johnsa & Martin Duquettea
"Detoxification and mineral supplementation as functions of geophagy" by Timothy Johnsa & Martin Duquettea

In 2002 an experiment in pit storing of hazelnuts was performed in England. The experiment was intended to prove that storage pits found in the Mesolithic site of Mount Sandel, Northern Ireland were capable of storing hazelnuts for a prolonged period of time. The experiment has demonstrated that hazelnuts will store in pits for 18 weeks, even in conditions that are less than ideal, meaning fully or partially submerged in mud and water, and that the use of a basket lining helps prevent the hazelnuts from spoiling whilst in the water. The experiment demonstrates that the underground storage of hazelnuts is neither a complicated nor a difficult task, but to store hazelnuts successfully in pits does require an understanding of the pit site environment and that responding to this environment in a constructive way ensures success. 

The results of this experiment were published in the article: "Assumptive holes and how to fill them, The contribution presents first results of experiments on pit storage of hazelnuts" by Penny Cunningham

The thing is the original Mesolithic pits from Mount Sandel were probably used not for storing hazelnuts but for storing acorns. 

According to "A Companion to Chinese Archaeology" by Anne P. Underhill, similar type of storage pits lined with baskets and dug in a wet waterlogged ground were found in early neolithic sites in China filled with acorns, and next to dwellings where grind stones were found containing traces of acorns. What is interesting is that the archaeological records from different acorn eating cultures from around the world point to a deliberate choice of waterlogged terrains for these acorn pits, as if people wanted these pits to be flooded and for the acorns to be submerged in water. Why? Because it is the water in the soil that removes the poisonous and bitter tannin from the acorns. And the more water flaws through the pit, the quicker the tannin gets removed. How did people discover this?

Oak forests often grow on flood planes and are often found growing next to ponds or bayous.

Sometimes acorns would fall into the water instead of falling on the dry ground. Our smart hunter gatherer would soon notice that some of the acorns would float on water while most would sink to the bottom. Being smart and inquisitive, both charactheristics of a good hunter gatherer, he would soon realise that the acorns that didn't sink were either infected by fungus, rot or worms and were not good to eat. So our hunter gatherer would start using this as test, to quickly separate good acorns from bad ones. He would simply pour all the acorns that he had collected from the ground into the water and would discard all the ones that didn't sink.This is very important because if you store good and bad acorns together they would soon all be spoiled.

Sometimes oak forests get completely submerged for a short period of time during the autumn and spring rains. After the waters recede, the ground would stay covered with wet acorns. If our hunter gatherer ate some of these corns which were submerged in water for a few weeks, he would notice that they tasted much sweater than acorns that he collected from the dry ground and which were not soaked in water. If our hunter gatherer was a smart hunter gatherer, he would soon realise that it is the fact that the acorns were soaked in water for a period of time which made acorns sweater.  So he would soon start soaking acorns in water himself to try to make them sweater. This was done in acorn leaching pits like the ones discovered in archaeological sites in both America (Sauvie Island native American settlements) and Japan (Higashimyo Jomon settlements). 

The data about the american leaching pits was published in the article "Balanophagy in the Pacific Northwest: The Acorn-Leaching Pits at the Sunken Village Wetsite and Comparative Ethnographic Acorn Use" by Bethany Mathews

The data about the Japanese leaching pits was published in the article "Recent Japan-Northwest coast wet site exchange", by Dale Croes

He would see that acorns would release black juice which made water taste bitter and he would soon realise that it is this dark juice that needs to be taken out of the acorns in order to make them sweat. And so water leaching of acorns was invented. Eventually people realised that shelling, crushing and grinding the acorns before leaching them would intensify tannin removal and shorten the leaching time from couple of months to few hours. So you could store your acorns dry into baskets, which is good if you want to carry them around from place to place, and then leach them when you need them.

So to do this type of quick leaching you need to first shell the acorns. Slowly dried acorns are easier to shell because the acorn shrinks and the thin brown bitter covering sticks to the shell so both are easily removed. Breaking the acorn shell and separating the acorn from the shell is the most difficult part of acorn food preparation. Acorns have an elastic shell that resists slow sideways pressure. The best way to break the acorns shell is to put the flat end (the side that used to have the cap) on a firm surface and hit the pointy end with a stone. I believe that it is this process of breaking the acorn shells that often resulted in broken and crushed acorns. I believe that people leaching acorns would have gathered whole and broken acorns and leached them together. And the smart hunter gatherer would soon notice that the crushed pieces leached quicker, and that smaller the bits are the quicker the leaching is. So people started crushing all the acorns before leaching. But they also noticed that just whacking the acorns with a stone scatters the bits everywhere. However if you gently break the shell, take the acorn out, place it on a flat stone, and then press the acorn with another stone and move the pressing stone in a scraping, grinding motion over the acorn, all the bits will stay on the bottom flat stone. And this is how grinders were invented.I will dedicate one of my next post to the grinders.

Now that acorns are shelled and crushed they can be leached by getting them into contact with water. This is done by submerging the acorns into a container containing fresh water in proportion 1 part acorn 3 parts water or more water. The acorns will sink to the bottom and start leaching straight away turning the water dark. Then you wait for a while (up to a day). You then pour out the tanned water and pour in new fresh water and repeat the procedure until the water stops turning dark or until acorns stop tasting biter. Simple. Well actually not so simple if you are a hunter gatherer from Mesolithic. Watertight container were hard to find at that time, because pottery was still not invented...The closest thing to a pot was a pit dug into a waterlogged ground. Exactly what people used for pit leaching. But changing water in a pit is quite a task, so it is much easier to just fill the pit with acorns and water, forged about the whole thing for few months and let the ground water slowly leach the tannins into the ground. Exactly how people used pit leaching. Because of all this I believe that pit leaching is the earliest type of leaching practiced by people.


Once relatively fine woven baskets were invented, it became possible to leach whole acorns or large enough bits of acorns in baskets in couple of days rather than in couple of months.  You needed a deep basket, some strong cordage, a stake and a stream. You fill the basket with a shelled acorns whole or roughly crashed acorns, tie it to the stake which is stuck into the bank and then lower the basket into the stream. You leave it there for couple of days and the flowing stream water will leach the acorns. Like this:

Again the finer the basket, the finer the acorns can be ground and the faster the leaching process will be. From ethnographic data we know that this type of leaching was very common too.

There is another way to leach acorns in a pit without having to take water out. You make a pit in such way that it can slowly drain by itself. You can achieve this by building a mound from a porous material, like sand, and then dig a pit in the mound, by hollowing the center of the mound. You then line the pit with leaves or fine basket or textile and pour the finely ground acorns into the pit. It is important that acorns are ground as finely as possible in order to speed up dissolving of tannin. Then you pour the water over the acorns, fill the pit and wait until the water drains away. As the water slowly drains it dissolves and takes away the tannic acid with it. Then you pour water over the acorns again filling the pit and repeat the whole process. You do that until the acorns are not bitter any more. This artificial pit acorn leaching was recorded by ethnographers in America and it looks like this:

Native American people of the Northern Sierra Mewuk (Miwok) used this leaching technique using flowing fresh water and sand pit as a leaching pit:


Traditionally they would go to the nearest stream and find a sandy area. There they would form out a leaching bed and spread out the acorn flour on top of the clean sand. They would then form a channel bringing the water to the bed and allowing a steady stream to flow over the acorn. Cedar bows were used to allow the incoming water to flow evenly over the flour. Leaching took at least 8-10 hours, depending on how much and how deep the flour was. After 8 hours a taste test was done to determine if the leaching was finished. When the acorn meal was ready, it was picked up off the leaching bed. At that stage the acorn meal resembled wet clay. You would pick the globs of it and gently wash off any sand with water. Because acorn is high in oils not much adheres to it... 

Leaching acorns in this way takes many hours if the acorns were finely ground and requires a lot of work. This is not ideal. People are lazy and laziness is the mother of all invention. So one day someone decided to see what happens if a hot water was poured over the ground acorns. What happened was that acorns submerged in hot water leached a lot faster, taking only two to three hours to lose their bitterness. On the above picture you can see all the equipment needed for this hot water leaching process: 

The fire at the woman's right is used to heat stones. The hot stones are dropped into a watertight bowl (in this case a watertight basket) using wooden grabbers (lying in front of the pit). Boiling basket is coated with a thin layer of acorn gruel. The gruel works like a glue that coats the basket so that no water would leak from it. This is because of the high oil and protein content of acorns which work as adhesives and fillers. Hot stones heat the water up, and the hot water is then poured over the acorn flour using a smaller bowl. The water is poured over a bundle of twigs to lessen the force of the water and distribute the water evenly over the flour. The stones used for water heating has to be carefully chosen so that they don't fracture during the continuous heating and cooling. The best stones for this purpose are basalt stones as the don't shatter under thermal pressure. How did people get the idea to use hot stones for heating water is still a mystery to me. Any ideas?



In addition to using hot water to speed up the process of dissolving the tannin, some smart hunter gatherers also used wood ash to induce chemical reactions which transform tannic acid into harmless chemicals. Early ethnobotanist Huron Smith (1923, pg 66) documented the Menominee method of processing various oak species: "The hulls were flailed off after parching, and the acorn was boiled till almost cooked. The water was then thrown away. Then to fresh water, two cups of wood ash were added. The acorns were put into a net and were pulled out of the water after boiling in this. The third time, they were simmered to clear them of lye water. Then they are ground into meal with mortar and pestle, then sifted in a birch-bark sifter."

There are couple of things that need to know when using water for acorn leaching:

You have to use either only cold water or only hot water for leaching. If you mix cold and hot water or if you put acorns into cold water and then heat the water, the tannin in the acorns will be bound to the acorn meat permanently and you will not be able to remove it. I bet that took a bit of time to figure out. The temperature of water with which you leach the acorns is very important. Heating water over 73 degrees Celsius precooks the starch in the acorn. Cold processing and low temperatures under 65 degrees Celsius  does not cook the starch. Acorn meal that was leached in cold water thickens when cooked, hot-water leached acorn meal does not thicken when cooked.  Also, when you leach the acorns in hot water you also boil off the oil with the tannins, reducing  acorn meal nutrition. So you should choose the leaching water temperature depending on what you want to use acorns for. If you are going to leach and roast whole acorns for snacking then boiling is fine. If you are going to use the acorn for flour it should be cold processed, or you will have to add a binder. But bread was never the intended end product of the acorn meal preparation. In fact, as it is evident from the ethnographic data, the intended end product was an acorn mush, gruel, porridge or an acorn soup. We know from the ethnographic data that even when cereals replaced acorn as the main starch food, mush, gruel, porridge, soup was still the main way people prepared and ate grain.

The ethnobotanist Huron Smith in his work on Menominee method of processing various oak species also says that: after the acorn meal was leached in hot water three times, the fourth time, the meal is cooked in soup stock of deer meat until finished and ready to eat, or made into mush with bear oil seasoning. The old Indians never made pie, but the Menomini now make pie of them.

So aftre leaching, a fresh water and acorn meal were mixed together with some herbs and meat stock and boiled into a thin soup or thicker mush. There were two ways that this type was food was cooked. One way was to boil the mush in a clay or stone pot over a fire. But that had to wait until pottery was invented.

The other way to boil food was by stone boiling in baskets or some other type of watertight but not fire resistant container, such as wooden bowls or containers. This is a very interesting subject and I will dedicate one of my next post to it.

The hot stone cooking was done in this way. Hot rocks the size of tennis balls were heated by fire. Then, they were put into baskets or wooden bowls or containers filled with water and acorn meal. The stones were stirred in the baskets gently and slowly with a wooden paddle or looped stirrer. When the mixture began to boil it was cooked, exactly like when you make a cereal porridge. The stones were then removed from the basket with wooden tongs. 

It is interesting that the hot water leaching cooks the acorn meal at the same time, turning it into a sort of porridge or a thick soup which then only needs one boil to be ready to eat. Exactly like the oat meal of today which is precooked and then dried. 

There is an old story called "Stone Soup". The story involves a stranger coming to a village, building a hearth and placing a pot of water over it. He (or she) puts in stones and invites others to taste the stone soup. The stranger invites others to add an ingredient, and pretty soon, Stone Soup is a collaborative meal full of tasty things. Not to mention a stone or two. Is this a memory of the most ancient way of cooking in water, invented as a byproduct of leaching acorns with hot water?

Meat doesn't need to be boiled. It can be roasted on a spit quite easily. Root vegetables and chestnuts can be roasted on hot coals. Greens and fruit can be eaten raw and so can hazelnuts, almonds and all the other nuts, all except acorns. Acorns are the first type of food which benefited from cooking, boiling in water. Did people invent stone boiling and cooking in water while trying to leach acorns in hot water? 

Stone boiling was not possible until the invention of watertight containers such as watertight baskets, stone, wood and clay bowls. And there is no evidence that these containers were in existence before the Younger Dryas. There is evidence that people ate acorns even before Younger Dryas but they could have just eaten the sweet acorns either raw or roasted in the fire, in the same way you would roast chestnuts. The burning of the acorn shells and the presence of wood ash would leach the small amount of tannins present in sweet acorns, and would make them sweet and goot do eat. But as I said already, it is only during the Younger Dryas that we see emergence of the first settled communities which were heavily relying on acorns as their staple starch food. These people collected a lot of acorns, stored them and then used them as food all year round. And at the same time we see emergence of basketry, pottery, grinding stones, wooden and stone utensils. Why, if not for processing acorns? One bad thing about storing acorns is that the more tannin the acorns have the longer they stay fresh. Sweet acorns are usually eaten first and bitter acorns are stored for the winter. And to be able to eat bitter acorns, the leaching and cooking technologies had to be invented. All these are "sure signs of the Neolithic". Did processing acorns inspire the transition from Mesolithic to Neolithic?

In the end how did the bread get invented? I believe by accident, as a byproduct of stone cooking of acorn porridge. According to the ethnographic data from America, the stones which were used for boiling acorn porridge were after boiling removed from the basket with wooden tongs. The mush that dried onto the rocks was a special treat that children liked to peel off and eat. These pieces were called "acorn chips." If these acorn chips was so popular it was just a matter of time before these chips stopped being a byproduct and were deliberately made. 

And this is how bread was invented. The only difference between acorn chips and acorn bread is in thickness and size. Once you realize that a lump of thick acorns mush can be baked into acorn bread all that was left to do is to find the best and easiest way to bake the bread without burning it. Here are some possible ways in which you can do it. 

The end result is this, acorn bread, the first bread ever made by people. The food of soldiers and travelers. The food of gods as the old Greeks used to call it.

So there you have it. Everything you ever wanted to know about eating acorns and probably a lot more. This should enable you to do a bit of acorn food making yourself. To get good modern recipes for turning acorns into food you can visit some of these sites:

1. Wild Harvests

2. Acorns: The Inside Story

3. The Best Way to Make Acorn Flour

4. Acorns, Nuts and Other Wild Starches

5. Harvesting the wild: Acorns

6. How to prepare acorn food

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Forest - the shushing place

In Serbian there are many words for forest. The most common word is "šuma". I love this word. It shows how old the Serbian language is and how rooted in nature it is. In Serbian word "šum" means rustling noise, shushing "šššš" "sh" noise, like the noise made by leaves blown and rustled by wind. The same sound is made by animals walking on fallen leaves or moving through the bushes in the undergrowth. 

Here is the sound I am talking about:

1. Light wind rustling sound 
2. Strong wind rustling sound
3. Animals walking on fallen leaves
4. Animals moving through the bushes in the undergrowth

All these sounds are made by leaves, eather on trees or on the ground. The sound is in Serbian called "šum" and the action of making this sound is "šumoriti, šumeti" but also "šuškati" and place where this sound is most heard is called "šuma", the place that makes "šum", the "šu" sound. So word šuma comes from šu + ima = shishing + has = what has a shushing sound, forest or just from šum - a = the shushing place. This is a great example of how words developed from natural sounds.

What is very interesting is that in Armenian "xshum" or "hshum" is the word which means the noise the leaves make when rustled by the wind and the word "ashun" means autumn, the time when dry leaves fall on the ground, the "shushiest" time of the year. 

Central Serbia was until the end of the 19th century covered with ancient oak forest, one of the last ancient oak forests left in Europe. Because of this, the whole area was called "Šumadija" meaning the land of forests.

How did oaks repopulate Europe?

In my post about oaks I talked about the oak tree and how useful this tree was and still is to people. In this post I would like to explain why I believe that people were as useful to the oak trees as the oak trees were useful to people. I believe that the influence that people had on the distribution of oaks in Europe could have been far greater then it is currently accepted. I think that the northward spreading of oaks from their glacial refugiums after the last ice age was actually the result of the northward spreading of humans from the same refugiums. I believe that it was humans who brought the oaks to the north of Europe. Let me explain why I believe that that was the case.

As I said in my last post, fossil pollen evidence in Europe indicates that during the last Glacial Maximum (20 000 years ago), oak species were confined to three main Pleistocene refugiums in southern Europe: Iberia, Italy and the Balkans. Then around 17,000 BC, the global temperature started to increase which resulted in melting of the great Northern Hemisphere ice sheets. This melt down lasted until about 4,000 BC, and the result was a global warming and the increase in sea levels. But this increase in temperature, warming and sea level increase was not uniform. If we look at the global sea levels, we see that during the period of the big melt down, 17,000 BC to about 4,000 BC, they rose by a total of more than 120 meters. This means that if the temperature increase was uniform, the average rate of sea-level rise would have been roughly 1 meter per century. However, when we look at the actual sea level rise figures, we see that the gradual sea level rise at an average rate of 1 meter per century was interrupted by two periods with rates of rise up to 2.5 meters per century, during period 13 000 - 11 000 BC, and period 11 000 -  9 000 BC. The first of these jumps in the amount of ice-sheet melt water entering the world ocean coincides with the beginning of a period of global climate warming called the Bølling-Allerød period. The Bølling-Allerød period was a warm and moist period that occurred during the final stages of the last glacial period. This warm period began around 12,700 BC and ended abruptly around to 10,700 BC. This is the beginning of the cold period called Younger Dryas, also known as "the big freeze". This cold period is thought to have been caused by the collapse of the North American ice sheets. The temperatures in the North Hemisphere were reduced back to near-glacial levels within a decade. Younger Dryas lasted between 10,800 and 9500 BC, when we see the second big jump in temperature and resulting sea level rise rate. 

During Younger Dryas period, most of Eurasia and North America had been covered by tundra with swaths of taiga.The tundra biome is the coldest of all the biomes. Tundra comes from the Finnish word "tunturi", meaning treeless plain. It is noted for its frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. 

 
Taiga is a high latitude northern hemisphere biome consisting mostly of conifer (fir) and birch forest. Temperature regimes within some of the taiga areas are among the lowest on Earth, since there is a continental aspect to the interior portions of the taiga, making it colder than many locations in the polar desert to the north. Extreme minimums in the taiga are typically lower than those of the tundra. 

So this is what most of the north of Europe was like during the Younger Drias.

Younger Drias was succedded by the Preboreal stage of the Holocene epoch. Preboreal stage lasted from 8,300 to 7,000 BC. It is the first stage of the Holocene epoch. The Preboreal started with an abrubt climate change which resulted in rapid rise of the global temperature and rapid rise of sea waters.

During the Preboreal period, large quantities of tree pollen began to replace the pollen of open-land species, as the most mobile and flexible arboreal (tree) species colonised their way northward, replacing the ice-age tundra plants. Foremost among them were the birches, accompanied by rowan also known as mountain-ash (known as jasen in Serbian) and aspen (known as jasika in Serbian).

This is a rowan tree:

This is an aspen tree:

Especially sensitive to temperature changes and moving northward almost immediately were the dwarf and shrub juniper (known as kleka in Serbian) respectively, which reached a maximum density in the Preboreal, before their niches were shaded out. This is a juniper bush:

Pine soon followed, for which reason the resulting open woodland is often called a birch or a pine-birch forest:

In the yet warmer early Boreal period (7000 - 5500 BC) hazel and pine expanded into the birch woodlands to such a degree that palynologists refer to the resulting ecology as the hazel-pine forest. I am not sure exactly what these forests used to look like because they don't exist any more, but maybe they looked something like this. This is old hazel forest from Britain:

In the late Boreal it was supplanted by the spread of a deciduous forest called the mixed-oak forest. Pine, birch and hazel were reduced in favour of oaks, elm, lime (linden) and alder. The former tundra was now closed by a canopy of dense forest.

Those interested in climatic and vegetative conditions in Europe over the last 150,000 years will find this web page quite interesting.

It is currently accepted that oak started to emerge from refugiums in southern Europe as the ice caps began to retreat at the end of the Younger Drias around 9500 BC. Oaks arrived in North Central Europe by the 8500 BC and to Eastern Britain by 7500 BC. 

But how did the oak forests expand from the southern Europe into Central Europe and Northern Europe? 

How do forests expand? A tree grows out of a seed. This seed falls from the tree branch on the ground and if it falls onto a fertile soil it sprouts into another tree. If the seed falls straight down from the branch the next tree generation will sprout at the distance of the furthest branch reach from the tree trunk, which is maximum 36 meters.

If the seed is light and can be carried by wind, and is falling from a big height during a strong wind, it can be carried away maybe up to the maximum tree height distance from the trunk, which could be up to a 120 meters and maybe even more.

If the tree grows near water and produces fruit or seed which can float on water then the seed can end up anywhere down stream from the tree. If the tree produces fruit which has tiny indigestible seeds, and if the fruit is eaten whole by birds or animals or humans, then the seed can be spread far and wide and deposited during defecation. 

Knowing all this we can understand why biologists believe that forests expand in general at a pace between 250-500 meters per year.

But I believe that the above estimate does not apply to oaks. Oak seed is acorn, and acorns are among some of the heaviest tree seeds in northern hemisphere. So oak seeds can't be carried away very far by the wind so the maximum acorn fall distance from the tree trunk is not more than few meters from the edge of the tree crown. This means that the next generation of oaks sprouting from the fallen acorns will sprout at maximum 40 meters from the parent tree. Oak produces edible seeds, acorns, which are encased in a protective hard shell.

Animals which eat acorns actually eat the seed. To get to the seed they have to break the protective shell and then they chew and eat the seed itself. Once the unprotected chewed seed eds up in a digestive system, it has not chance of sprouting again. There are three creatures that do collect whole acorns, carry then away from the tree and then bury them. These creatures are squirrels, jay birds and people.

Jays are strikingly coloured members of the crow family. 

Like the other members of the crow family, they are shown to be extremely intelligent, and in fact to be as good at problem solving as a seven year old human at a problem solving task. It can be found over a vast region from Western Europe and north-west Africa to the Indian Subcontinent and further to the eastern seaboard of Asia and down into south-east Asia.

Its diet includes a wide range of invertebrates including many pest insects, beech mast and other seeds, fruits such as blackberries and rowan berries, young birds and eggs, bats, and small rodents. Its favourite food is acorns, and jey birds are often found near oaks. Jays collect and bury acorn in large cashes throughout autumn which they then use as food sources during the winter. A single bird can bury up to a several thousand acorns each year, playing a crucial role in the spread of oak woodlands.

Even though they are the birds of the forest edge, they are unlikely to venture into the open as they are very poor fliers and can be caught easily by any raptor bird. So jay birds probably contributed to the spread of oaks through the original hazel-pine forests but they were hardly responsible for spreading oaks into the open grasslands. Also how far would a jay bird carry the acorns from the oak tree before burying them? Jay birds are extremely territorial and would defend their territory from all intruders. This type of behaviour means that jays are unlikely to spread the acorns too far from the oak under which they found the acorns. I could not find any precise data about the territory radius of jay birds, but I would say that it is definitely not bigger than one kilometer. So the furthest jay birds would spread the acorns from the oak tree would be up to few kilometers and only through the already existing forest.

Squirrels are agile tree dwelling members of the rodent family.

They are found in many regions of the world, including Europe, Asia and the Americas. There are many subspecies of which the most wide spread is the red squirrel or Eurasian red squirrel which is common throughout Eurasia.
 

Squirrels primarily eat nuts and seeds, but will also eat berries, fungus and insects. Squirrels horde food in small amounts in several locations when it's abundant. Although the red squirrel remembers where it created caches at a better-than-chance level, its spatial memory is not very accurate and durable. It therefore will often have to search for its food caches when it needs them, and many are never found again. These forgotten caches of seeds, if they were buried in the ground, instead become seedlings.

Arboreal predators which pray on squirrels include small mammals such as the pine marten, wild cats, and the stoat, which preys on nestlings as well as foxes which will pray on grown animals in the open as well as birds, including owls and raptors such as the goshawk and buzzards. Squirrels are extremely vulnerable on the ground and in the grassland which is why they never venture too far from trees.

The squirrel foraging home range consist of several acres that overlap the home ranges of other squirrels. Squirrels do not defend these territories. However, there is a dominance hierarchy with others of the same species. In general, older males are dominant over females and younger squirrels. Although they seldom stray farther than few hundred meters from their nest in any one season, they are known to travel up to a few kilometres to get to a good nut tree.So the furthest squirrels would be able to spread the acorns from the oak tree would be a few kilometres and only through the already existing forest.

So neither squirrels nor jay birds were very likely to take acorns out of the forest into the open grassland and bury them there. But people are actually likely to do exactly that as human settlements were usually out in the open near the forest edge.

People would collect the acorns in the forest and then bring them to their settlement and store them in pits dug in the ground. Any acorn dropped anywhere along the way could sprout into a new oak tree. What is more, people could have carried acorns with them during their seasonal hunting or fishing migrations up north in the spring and down south in the autumn or in and out of the steppe while chasing large game. Those acorns could have been brought as the source of starch food, as acorns remain in good condition for a long time and are easy to transport. In my post about acorns in archaeology i presented enough evidence that acorns were a staple starch food of most European Mesolithic and Neolithic communities. So Mesolithic people traveling across Europe with bags of acorns is not a possibility any more but a certainty. Any acorns lost or thrown away would have sprouted along the migration or hunting routes and then spread from there radially.

Oaks are said to have spread originally along the river valleys and then from the river valleys they spread into the surrounding hills. So it is presumed that oaks spread along these river valleys through normal forest creep on the same side of the river and through acorns falling into the water and then being carried away by the current down stream and diagonally across to the other side of the river. In theory this sounds plausible. In practise this is impossible to happen as acorns don't float. Actually the only acorns that do float are fungus infested, worm ridden dead acorns. The way to separate good acorns from bad ones is to dunk them into water and throw away any acorn that floats. So acorns which fall from the oak tree into the water sink straight down to the bottom and would never sprout.

Even if by any chance any of the good acorns did end up floating, they would have been carried down stream, southward not northward, as all rivers flowing just above the glacial refugiums flow southwards. But oaks did spread northwards along the big rivers. They managed to cross from the Balkans into the Panonian basin across giant rivers like Danube and Sava which completely cut the Balkans off from the rest of Europe.

The only place where Balkans is connected to the rest of Europe by land is in Slovenia where we find the Alps. The maximum elevation on which oaks are found is about 1500 meters above the sea level so oaks would have had a great problem finding their way from the Balkans into the Central Europe through the Alps by themselves even with the help of the squirrels and jay birds.

But acorns could have easily been carried up and across the big rivers in dugout canoes by Mesolithic people who lived along the European coast and major rivers and who used rivers as waterways along which they traveled into the center of the European continent. These Mesolithic fishermen could have carried acorns up rivers as the source of starch food. And these acorns could have been dropped by accident or discarded anywhere along the river and on either sides of the river, where they would have sprouted into young new oaks. This would have allowed oaks to quickly spread from the Balkans refugium into the Central Europe and to be already growing in the Main river valley between 8500 and 8000 BC.

This is the Hohenheim chronology of the Oak finds in Germany. You can see that we find oaks in Rhine and Main valleys even before 8000 BC:

If the Main valley oaks came from the Balkan peninsula then they had to cross about 1500 km from the north Balkans to Main valley. During that trip they had to cross high mountains (Alps) and big rivers (Danube, Sava).  If the Main valley oaks came from the Iberian peninsula then they also had to cross about 1500 km from the north Iberia to Main valley. During that trip they had to cross high mountains (Pyrenees‎) and big rivers (Garonne, Rhone, Loire). If the oaks started their expansion from the Balkans or the Iberia immediately after the end of the Younger Dryas, around 9500 BC, that would mean that they had to move at the speed of over 1 km a year to get to the Main river valley on time. These must have been some very speedy, all swimming, all mountain climbing, all singing, all dancing oaks....Not like the oaks we find today...

We have the same problem if we look at the chronology of the British oaks. The first oaks were found to have arrived in Britain around 7500 BC. From there it took oaks 2000 years to reach Scotland. Based on genetic evidence, most British oaks came from the Iberian refugium.

The direct shortest distance between north Spain and southern Britain is about 1500 km. Oaks are supposed to have started spreading at some stage after 9500 BC and have arrived to Britain 2000 years later. If we accept what biologists are saying, that oak forests expand in general at maximum pace of 500 meters per year, it would take oaks 3000 years to get to Britain which means that they would not have made it in time to be found in Britain at 7500 BC. 

But the path that oaks had to travel from Iberia to Britain was not straight and there were many high mountains and rivers which oaks needed to cross on their way up north.

This would all extend the distance the oaks needed to cross on their march to Britain to about 2500 km. This means that oaks would need at least 5000 years to expand from Iberia to Britain by expanding at the rate of 500 meters a year.

To make things worse according to latest data the Rhine, combined with the Schelde and Meuse, flowed to the south into the English Channel.

The above map shows the latest insights into how the North Sea was formed. Previously, scientists thought that the Rhine-Meuse-Schelde flowed to the north eventually joining the Ouse. But that idea proved to be wrong. One of the reasons for the southerly course of the Rhine was the forebulge that existed in the north of Holland. The weight of the ice cap upon Scandinavia pushed the earth's crust down and the crust bulged up to the south of it. Once the ice had gone, this bulge gradually flattened. Since 18000 BC, the north of Holland has sunk some 30m. The south of Britain also used to be higher than today. As the water rose quickly we can safely assume that the Channel extended fast to the north, rendering the distance from the south of France longer by each passing day. This would extend the distance that oaks had to cover between the north Iberia and south of Britain even more to maybe 3000 km. This means that oaks would need at least 6000 years to expand from Iberia to Britain by expanding at the rate of 500 meters a year.

But this is all based on a completely wrong premise that oak forest edge can move outwards at the rate between 250 and 500 meters a year, which is actually impossible. Oak forest edge can't move at the rate of even a 250 meter per year. The reason for that is that new oak tree will not produce any acorns until the tree is at least 25 years old. If we take this into account we get the real natural oak forest expansion speed.

If the acorn just falls down and sprouts it can't fall more than the maximum height or diameter of the tree which is not more than 120 meters. At best, if we take into account a possibility of an adventurous jay bird or a squirrel, which would take an acorn as far away as possible from the oak tree to bury it, that would still mean that the acorn would end up no more than few kilometres from the tree trunk. If the acorn then managed to sprout into a new oak, the expansion of the edge of the oak forest would then stop for next 25 years until the new oaks growing at the new edge of the oak forest start producing their own acorns. This means that the oak forests edge would not move 500 meters a year but at most 5000 meters (5 km) every 25 years. This would mean that even if we accept that the distance that oaks needed to cover to get from the north Iberia to the southern England or from the Balkans to the Main valley was only 1500 km, it would have taken oaks 12 500 years to cover that distance by "natural" means.

But if people brought oaks with them, travelling in their dugout canoes along the Atlantic coast, then oaks could have arrived to Britain from their Iberian refugium within a few years. Equally if people brought oaks with them, travelling in their dugout canoes up the river Danube and then down the river Rhine, then oaks could have arrived to Britain from their Balkan refugium within a few years. 

This means that there is a strong possibility that oaks did not spread naturally back into northern Europe from the Mediterranean refugiums . There is a strong possibility that oaks were imported into Britain and Ireland, and into the rest of northern Europe by the migrating hunters-gatherers and fishermen. For these Mesolithic boat people rivers were not barriers.  They actually used rivers as their main migration pathways. This is why we find that the oak expansion pattern is along river valleys and then radially into the hills. 

There is actually a direct proof that acorns were were spread into northern Europe from their Mediterranean refugiums by people. And it can be found in Walsh Marches. Based on genetic evidence, most British oaks came from the Iberian refugium. But not all. The oak population from the border between England and Wales (the Welsh Marches) possessed a haplotype which is common in the Balkan area. This means that it is possible that Britain had been recolonized by oaks from more than one refugium. How did these Balkan oaks arrive to England and Wales? The distance between Balkans and Wales is at least 2500 km. Just imagine how long it would have taken Balkan oaks to arrive to Wales if they were to be spread only by acorn drop, or by squirrels and jay birds...And by the way the closest oaks possessing the same genetic type as Welsh oaks, are scattered individuals along the north coast of France and in a clustered population near Rennes, 300 and 450 km distance from the Welsh Marches. This completely removes the possibility that the Welsh Marches oaks arrived by means of forest creep. They had to be brought to Wales from the Balkans by people.  The only question is when.

It's even not unthinkable that the Mesolithic people has deliberately sown acorns. It's one of the easiest things to do. You stick the acorn into the ground and forget about it. The young trees do not require attention and can take care of themselves. It takes 25 years until new oaks started to produce acorns. But once they do start to produce acorns, they would continue producing them for hundreds of years and would give one of the biggest yields per year of any edible plant. I believe that this must have been known to Mesolithic people and there is more and more evidence that Mesolithic people deliberately planted and cultivated "wild" crops millenniums before "agriculture" was invented. 

I will talk about cultivation versus agriculture in one of my next posts. Until then have fun.