RESUMO
Percentage and concentration pollen diagrams from the sediments of two adjacent inter-drumlin hollow lakes near Dungannon, and in two cores from Lough Catherine, suggest that only small reductions in the pollen frequencies of trees such as pine and, at some sites, birch and oak, accompanied reduced Ulmus at the elm decline in these parts of Co. Tyrone. They also confirm that Pteridium aquilinum could sporulate and many herbs were able to flower more freely owing to an opening of the tree canopy. Seventeen radiocarbon dates provide chronologies for the sites and date the elm decline to between 5050 and 5375 B.P., the subsequent start of increased elm pollen percentages to between 5010 and 4850 B.P., and the beginning of a second decline in elm pollen to between 4330 and 4260 B.P. The initial decline in elm pollen values may have been caused by disease and this reduction was superimposed upon a background of small-scale clearances which continued after a general elm regeneration. The question of a general similarity and causation of the second elm decline in Ireland and elsewhere is considered. Chemical, magnetic and pollen preservation data from the Co. Tyrone sites suggest episodes of erosion occurring at the first elm decline and others at the second elm decline.
