Changing Patterns in the Post-Glacial Distribution of Pinus sylvestris in Ireland

Abstract

Pinus sylvestris can grow in a wide variety of habitats and yet even at the zenith of its distribution in the Irish post-glacial it was not a major tree over large areas of north-central Ireland, where Ulmus, Corylus and Quercus dominated. The largest Pinus populations were in upland and western districts, but the pollen records from two mountain areas show that the upland populations disappeared soon after the Ulmus decline. Fire was a factor in the survival of Pinus after the Ulmus decline at a lowland site on coarse-textured acid soil. Four pollen diagrams from the Nephin Beg mountains, Co. Mayo, reveal the history of Pinus at differing altitudes and on contrasting soil types, showing the controlling influence of competi- tive interactions with other trees and peatland. Isolated lowland and bog populations survived into the historic period, and today, after extensive plantation, naturalized populations are building up. Pinus sylvestris is an opportunistic tree that will tolerate many habitats, but only in the absence of its competitors. Analysis of several sites in a small area demonstrates fine-scale pattern in Pinus distributions not detected in surveys covering larger areas. Chang- ing patterns at a local scale provide material for successional hypotheses.