Unusual mid-Holocene abundance of Ulmus in western Ireland: Human impact in the absence of a pathogen?

A Holocene pollen record from Co. Clare, western Ireland, shows unusually high Ulmus pollen frequencies until about 2500 cal. BP, interrupted by four brief episodes of reduced Ulmus pollen between 6000 and 3000 cal. BR Localized anthropogenic disturbance of the vegetation during this interval is inferred from higher magnetic susceptibility of the sediments, indicating soil erosion, and from increased Poaceae and Plantago pollen. The continued abundance of elm at several sites in Ireland, despite human impact, suggests that disease was a less significant factor in the reduction of Irish elm populations than elsewhere in northwestern Europe. It may be that the pathogen, its dispersal agent, or susceptible elm ecotypes were locally absent near the western range margin of elm, reinforcing the argument that the combined effects of human exploitation and a pathogen were necessary to cause the permanent elm decline at 6000 cal. BP in most of northwestern Europe.