WILD IDEAS

Dr Jenni Roche Woodland Ecologist, National Parks and Wildlife Service

Forests challenge us to think in the long-term. The long lives of trees inspire us to look beyond our own lifetimes and into the future, while the history of Ireland’s present tree cover stretches back over 11 millennia to the period after the last Ice Age.

This was a time of rapid ecological change. The first tree species to colonise Ireland was low-growing juniper, followed by birch, hazel and the taller 'canopy' trees. One of the first of these to arrive was Scots pine Pinus sylvestris. The history of Scots pine has long intrigued those with an interest in Ireland’s trees. It became widespread in Ireland and remained so for thousands of years. It was an important component of certain habitats such as raised bogs, river valleys and the uplands. The many pine timbers and stumps preserved beneath our raised and blanket bogs provide evidence of the species’ former abundance. Scots pine entered a massive decline about 4,500 years ago, apparently due to climate change, competition from other species, expansion of the blanket bogs and human activity. The species was widely believed to have become extinct in Ireland around AD 400. Scots pine was reintroduced to Ireland in the mid-seventeenth century and has been widely planted. However, a nagging question remained: did native Scots pine survive in some unknown refuge? It persisted in the Scottish Highlands, where it forms the internationally important Caledonian forest habitat.

The complex history of Scots pine in Ireland has resulted in inconsistencies in the management of the species. For example, the Forest Service included Scots pine in its Native Woodland Scheme, while others regarded it as an invasive alien species. With Professors Fraser Mitchell and Steve Waldren, I embarked on a Ph.D. research project at Trinity College’s Department of Botany, aiming to describe the vegetation of Irish pinewoods, compare them with their Scottish counterparts and clarify the native status of Scots pine in Ireland.

In the Burren in County Clare, in 2006, we surveyed an area known as Rockforest. Scots pine occurs here on limestone pavement, scattered through hazel scrub. Though mature, the pines are small and gnarled in appearance. An examination of the available historical maps and records indicated a long history of woodland cover at Rockforest. We chose to investigate the environmental history of Rockforest further using the techniques of palaeoecology, which is the ecological study of ancient environments.

We extracted a tube of sediment from Rockforest Lough nearby. Lake beds accumulate sediment containing pollen from plants growing in the surrounding area. In this wet, low-oxygen environment, microbial activity is low. Pollen grains are not broken down but are almost perfectly preserved. As sediment builds up over time, an archive of fossil pollen develops. By examining pollen grains under a microscope, it is possible to identify the type of plant they come from. By identifying and counting thousands of pollen grains from different depths, we discovered which plants grew in the area in the past, allowing us to describe vegetation change over time.

Radiocarbon dating showed that the sediment record extends from AD 350 to the present. Usually, Irish pollen records show an absence of pine during this time, with pine pollen increasing following the species’ reintroduction. Unusually, we found continuously high levels of pine pollen throughout, as well as a preserved pine needle dating from AD 840. Further research by Dr Alwynne McGeever (TCD) at nearby Aughrim Swamp in 2016 also showed a continuous pine signal. These studies indicate that native Scots pine has survived at Rockforest, challenging the view that the species became extinct in Ireland.

 Rockforest  Bog Pine, Glenveagh

Our research suggests that Scots pine should be considered native to Ireland, at least at Rockforest. As Ireland’s only known potentially native Scots pine population, it is unique. However, its rarity increases its extinction risk. The site is protected due to its location within a Special Area of Conservation and the state-owned Burren National Park. Seed collection has been carried out (under permit by a registered seed collector) and seedlings are being used to establish off-site populations of Rockforest Scots pine at Ballycroy National Park, Glenveagh National Park and the National Botanic Gardens. However, the scarcity of young Scots pine trees at Rockforest is a concern. Any further seed collection must be compatible with the long-term viability of the population at Rockforest itself. Research by Dr Colin Kelleher (National Botanic Gardens) on the genetics of the population is ongoing and these results are eagerly awaited. Looking to the future and to the long-term future, careful management and monitoring will be needed to ensure the continued survival of these fascinating trees.