Historical and contemporary effects of fire on native woodland vegetation of Killarney, S.W. Ireland

Abstract

Summary: This research investigates the Post-glacial history of fire in the Killarney area, and describes how heathland burning practices have affected the present-day extent and species composition of the native oakwoods. The Post-glacial record of fire occurrence is elucidated through the analysis of pollen and charcoal preserved in small hollow sites within contemporary woodlands. Results from two woods with contrasting disturbance histories over preceding decades are compared. At the less disturbed site, which is radiocarbon-dated, the period of peak fire occurrence was c. 8,500-8,000 years before present. This was a period when the climate was warmer and drier than today, and natural fires occurred in the Kiliarney area. Alder (Alnus glutinosa) was present at this site prior to 9,290 years B.P. This date well precedes all other records for alder in Ireland. Tree age structure analyses in three contemporary oakwoods illustrate the dynamics of oakwood development. The period of most active oak establishment was in the early 19th century for all three woodland areas. Successful oak regeneration was much reduced in the latter part of the 19th century, when it may have been limited by increased incidence of heathland burning, and has been virtually non-existent in the present century. The data are discussed in relation to what is known of past management, from documentary evidence and from palynological data from mor humus deposits. The responses to fire of five tree and shrub species are described. Oak (Quiercus petraea) and Rhododendron ponticum show the strongest recovery; birch (Betula pubescens) and rowan (Sorbus aucuparia) suffered high mortality and showed poor ability to recover; holly (Ilex aquifolium) showed an intermediate response. Comparison of the stand characteristics of burned and unburned woodlands indicates that fire causes a reduction in the species diversity of woodland stands.