The mystery of the British oak

We know that the European oak (Quercus Robur and Quercus Petraea - typical British oaks) survived the ice age in the south of France and the north of Spain, the ice age refuge of Ruisko (DNA revealed that 98% came from that region). Just after the Younger Dryas period climatic conditions in the north of Europe became suitable for oaks to grow there. We suppose that the oak spread itself naturally to the north. But there are problems concerning the arrival of the oak in Britain and Ireland. We know the Ireland was cut off from the British mainland by the rising sea almost immediately after the warming up of the climate. Therefore, we can safely accept that big trees with rather heavy seeds like oak and beech were imported into Ireland by humans. But did the oak reach Britain by itself or was the tree imported? The ice age ended around 8000 BC. The land bridge over the English Channel crumbled around 6500 BC. So the oak had barely some 1500 years to spread itself from the south of France to Britain. As this distance can be calculated as some 1000 km, then this means that the oak spread at an average pace of 750 meters per year. The land bridge probably disintegrated slowly, impassable gaps might have appeared as early as 7000 BC. This means that the continental oaks had even less time to reach Britain.
Biologists accept the fact that forests expand in general at a pace between 250-500 meter per year. Acorns however are amongst the heaviest tree seeds in Europe and on top of that, oaks need suitable soil to grow. An oak will not grow well everywhere. The soil must have been, so to say, prepared by other trees and then oaks 'take over'. We know that jays eat acorns and that they spread them. But no serious study has been done about how far and in which direction the jays disperse acorns. Does the territory of the jays comprise parts of the forest without oaks? Or do they limit their territory to those parts where oaks do grow? Were they responsible for the fast spreading of oaks?

We know that native Americans in the Californian region did not practice agriculture before the white man came, but also that they 'cultivated' oaks, for instance by clearing with controlled fire the shrubs, the undergrowth in the oak forests. Acorns are edible, but it is necessary to wash out the excess tannin with (a lot of) water. It is well possible that agriculture in western Europe was not entirely new to the indigenous population when the real farmers moved in. The native Europeans could have practiced similar habits. They could have carried acorns with them during the Younger Dryas seasonal migrations (and shortly after) to the north. Those acorns must have been considered to be reserve food, in case the hunt was not successful. Acorns remain in good condition for a long time. At the end of the season, they threw away most of the redundant acorns, and then traveled south, for a new acorn harvest awaited them. At the beginning of the Holocene, the climate warmed up considerably and so the wasted acorns had their chance to grow on the spot.

There is a strong possibility that this is how oaks were imported into Britain and Ireland. Not the farmers imported the oak, the migrating hunters-gatherers did. It's even not unthinkable that they deliberately sow acorns. It's after all one of the easiest things to do and the young trees do not require attention. After a few years local acorns could then be harvested. They also must have been very aware of the excellent quality of the oak wood. Planting acorns was probably an excellent exercise with maximum yield for minimum effort.

There is more: a small proportion (2%) of the British oaks originated from the Balkan region, the ice-age refuge of Ivan. The authors of the DNA study propose that the oaks with 'Balkan-DNA' were imported by humans. Those oaks, I propose, were imported by the first farmers. They colonized the south of France (and imported Occitan) and some moved on to the British isles, with 'their' oaks.

 

Reference:
Distribution of chloroplast DNA variation in British oaks the influence of postglacial colonisation and human management.
J. E. Cottrell, et al.