The vegetation ecology and native status of Scots pine (Pinus sylvestris L.) in Ireland

Abstract

This thesis examines the vegetation ecology, native status and biodiversity value of Scots pine (Pinus sylvestris L.) in Ireland, using a variety of biogeographical, palaeoecological and ecological approaches at different spatial and temporal scales. P. sylvestris is known to have colonised Ireland relatively early in the postglacial, becoming an important component of certain marginal habitats before undergoing a dramatic decline. The species is widely believed to have been extirpated during the early medieval period. P. sylvestris had been reintroduced to Ireland by the eighteenth century and is currently widespread and naturalising in semi-natural habitats. Ireland’s Native Woodland Scheme provides financial incentives for the planting of native trees of local provenance. Despite its uncertain native status, P. sylvestris has been included in this scheme and is being widely planted in semi-natural habitats. Few studies have addressed the autecology and vegetation ecology of the species in the Irish context. Information on its native status, ecological requirements and biodiversity value is urgently required to inform conservation and forest management strategies. A database of site attributes and Pinus pollen frequencies from 84 palynological sampling sites throughout Ireland was compiled and added to a Geographic Information System. Isopoll maps were prepared at 500 year intervals in order to illustrate the dynamics of Pinus in Ireland throughout the Holocene. Spearman’s rank correlation coefficients for mean Pinus pollen frequencies and site attributes were calculated for each time interval. The arrival, expansion, decline and reintroduction of Pinus were clearly illustrated by the isopoll maps. Pinus pollen frequencies were significantly correlated with altitude and location during various periods of the Holocene. These results generally supported previously described patterns. However, the isopoll maps suggested that high Pinus pollen frequencies persisted in localised areas of western Ireland during the period when Pinus was thought to be extinct in Ireland. The vegetation history of an apparently naturalised pinewood in the Burren over the last 2000 years was examined, with particular reference to the Pinus decline. A relatively stable vegetation history was recorded, despite considerable human activity. The dominant vegetation type was an open pinewood with abundant Corylus. Remarkably, no Pinus decline was recorded. Pinus pollen frequencies consistently exceeded 38% and macrofossil evidence demonstrated the local presence of Pinus at about AD 840. This indicated that a relict population of P. sylvestris has persisted in the Burren to the present day, challenging the established view that P. sylvestris became extinct in Ireland. Botanical surveys were conducted in 20 P. sylvestris woodland plots in Ireland and seven in Scotland. Vegetation, structural and environmental data were analysed using non-parametric and multivariate statistical techniques and synoptic tables were prepared. In the Irish context, P. sylvestris was found to tolerate a wide range of environmental conditions. Soil pH, altitude and slope had important roles in partitioning four reasonably well defined vegetation communities, some of which corresponded to habitats of international conservation importance. Irish pinewoods were found to form an important resource for the conservation of native botanical and habitat diversity. The Irish plots were compared quantitatively with native pinewoods of high biological quality in Scotland and qualitatively with native pinewood types in continental Europe. Each Irish pinewood type was found to correspond, to a greater or lesser extent, to its native counterparts. Irish pinewoods were found to function as native ecosystems. P. sylvestris woodlands are a common feature in the Irish landscape, although they are fragmented and limited in extent compared to their former range. For practical conservation purposes, P. sylvestris should be managed as a native species in woodland habitats in Ireland. P. sylvestris offers forestry potential, native status, broad ecological tolerances and has the potential to support native biodiversity. It therefore has the potential to make a significant, positive contribution to biodiversity conservation and sustainable forest management in Ireland.