The distinctive grains of Fraxinus excelsior have been recorded in deposits of several pre-Holocene interglacial warm stages in the British Isles. Isolated occurrences have been reported from the earlier interglacials but higher frequencies occur only from the Hoxnian interglacial (oxygen isoptope stage 7 or 9) and later. Wood macrofossils of Fraxinus have also been found from the Hoxnian. There are many pollen records from the Ipswichian (oxygen isotope stage 5) some of which are in relatively high percentages. Almost all of these Fraxinus identifications are from the warm, middle mesocratic phases of the interglacial stages, corresponding with the history of Fraxinus in the Holocene. While all Holocene records are for Fraxinus excelsior, some of the earlier records may be referable to other species. Fraxinus pollen has been reported from glacial cold stage contexts but is likely to be derived from reworking of earlier sediments. Isolated occurrences of Fraxinus excelsior pollen in the earlier phases of the Holocene indicate the presence of the tree in localised, small populations in Britain in the Boreal woodland prior to the full development of dense deciduous forest. Notably, one occurs in peat dredged from the North Sea bed on the Dogger Bank, the others are widespread in Britain. Pollen data suggest that before the rise of Alnus pollen around 7,000BP Fraxinus was a native and widespread tree but uncommon except on very favourable calcareous soils, whereas after about that time it increased in population substantially in most areas. As a low pollen producer, however, true Fraxinus population levels may always have been higher than pollen data indicate. After the Alnus rise, Fraxinus pollen frequencies are generally higher and in places considerably so. Most records are still sporadic, but on limestone soils in northern England and chalk areas of the south continuous pollen curves for Fraxinus often become well established several centuries before the Ulmus decline of c.5,000BP. In very favourable locations like southern Cumbria 

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Fraxinus was able to reach up to 25% of tree pollen between 6,000 and 5,000BP, in association with other specialised trees like Taxus baccata and Tilia cordata. As a thermophilous tree Fraxinus excelsior was more suited to spreading during the warm and mild oceanic conditions of the mid-Holocene. The rate of spread seems to have been slow during the pre-Ulmus decline forest phases, with Fraxinus acting as a component of regenerating seral woodland, damp fen-edge locations or in drier fenwood successions. Fraxinus may have replaced Corylus in some situations. Fraxinus was the last of the mesocratic deciduous trees to expand in the Holocene (Birks 1986) and required specialised conditions or the opportunity presented by forest disturbance to become established. The high Fraxinus percentages at sites in pre-Holocene interglacials all coincide with higher non-tree pollen values and probably record conditions after natural disturbance. In the pre-Ulmus decline Holocene Fraxinus frequencies also expand temporarily after episodes of forest disturbance, whether these were created naturally or by the activities of Mesolithic hunter-gatherers. The more open conditions created by Neolithic and later forest clearance and regeneration provided many new opportunities for Fraxinus to colonise new ground and the real expansion of Fraxinus in the later Holocene outside its specialised centres was mainly stimulated by the human opening of the British woodland. Fraxinus percentages are often very high in association with archaeological sites of several periods as human settlement favoured its growth in scrub and hedge communities, and Fraxinus wood is often found in such archaeological contexts.

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