Tephra-dated pollen analytical investigations of rapidly-accumulating Irish lowland raised bog have yielded fresh evidence for human impact in the wake of 6th century monastic settlement and Norman influence from the 12th century. The studies have international importance as they establish base-lines for palynological investigations of agriculture in the wake of invasion. The occurrence in the peat profiles of calendrically-dated tephra layers from the eruptions of Icelandic volcanoes in AD 1104, 1362 and 1510 allows late medieval pollen profiles from fifteen sites throughout Ireland to be compared so that human impact and the status of agriculture may be evaluated. The comparative studies show considerable regional variation in the initiation and expansion of agriculture in the lowlands in the first millennium AD.

The course of agriculture at major monastic sites, such as Clonmacnoise, Clonfert and Clonenagh is contrasted with secular activity in the hinterland of urban centres where there is evidence of the Anglo-Norman advance and with sites under Gaelic influence. The new studies disprove the theory that agriculture was brought to the central lowlands with the introduction of monasticism. There is no uniform pattern in the chronology of agricultural advance, neither is there any indication that new farming practices came in with the Normans in the 12 century.