Archaeology

The pollen story of life in Ireland after the last ice age

14,000 years ago - When the last glaciers retreated from Ireland around 14,000 years ago, the landscape was left bare. After being initially colonised by grass and juniper, woodland began to develop as the climate got warmer around 10,000 years ago.

10,000 years ago - The first woodlands were dominated by hazel and, to a lesser extent, birch. Although hazelnuts, the seeds of hazel, are too large for the wind to disperse, it spread rapidly, covering most of the countryside. Because of this, there is a much higher proportion of pollen from trees, particularly hazel, than any other type of plants in the peat from this time.

This great flourishing of hazel was short-lived as oak and elm, the taller forest trees, were soon to replace it. Oak and elm came into the lowlands at about the same time, around 9,500 years ago. The next 1000 years was the time of the most dense forest cover in Ireland.

9,000 years ago - The first human settlers in Ireland were Mesolithic or Middle Stone Age people who arrived nearly 9,000 years ago. Evidence of their presence has been found mainly by the coast and along major rivers such as the Lower Bann. They were nomadic people living by hunting and gathering, and had little impact on the natural vegetation.

Illustration of a stone-age settlement in Ireland

6,000 years ago - The same is not true of the next wave of settlers, the Neolithic or New Stone Age people, who arrived in Ireland about 6,000 years ago. They brought with them new knowledge and technology from the European mainland, together with cattle, sheep, goats, wheat and barley. To make space for farming, they started the process of forest clearance in Ireland. The peat from this time contains pollen from the plants these farmers brought to Ireland, such as wheat and barley, together with weeds of cultivation such as plantain. There is a sudden fall in the amount of pine and elm pollen at this time, and a corresponding increase in pollen from grasses and plants of disturbed and open ground.

This change in vegetation may have been due to an outbreak of a disease like Dutch Elm Disease, but there is a clear correspondence in the dates of the reduction in elm pollen and the earliest Neolithic settlements. After the initial elm decline and agricultural phase, the forest grew back in many places.

Blanket bog

5,000 years ago - Just before its disappearance, pine was colonising many of the large lowland bogs due to the peatland drying out during a period of relative drought. However, in later years flooding and waterlogging greatly reduced pine cover in Ireland. At this time there were also great changes taking place in the uplands when blanket peat started to expand, often burying older agricultural landscapes. There is no single date that marks the start of blanket peat, and no simple climatic explanation for its expansion.

After the Neolithic came the Bronze Age people about 4,400 years ago, bringing with them distinctive pottery styles, bronze tools and the use of gold for personal adornment. These people had an even greater impact on forest cover and regeneration, with their rising populations and more efficient tools.

3,000 years ago - By 3,000 years ago we can see a landscape similar to our own appearing. Blanket bog had replaced forest in the uplands, and the raised bogs were now largely covered by sphagnum moss instead of pine. Most of the lowland forest was composed of alder, hazel, birch and ash, with relatively little oak and elm. This woodland cover reduced further, possibly due to the colder, wetter climate over the next 1,000 years. This is also when people built the first trackways across bogs in various parts of Ireland.

2,000 years ago - The next 1,000 years, up to 1,000 AD, saw the introduction of the horizontal mill and the mould-board plough to Ireland. This latter invention made farming possible for the first time in the heavier soils. Tree pollen in the peat from this time falls below present day levels, although this may be partly because the present landscape includes tree pollen from field hedges that were not extensive at this time.

Pine plantation

Present day - The pollen record finishes with the return of pine pollen to the peat bogs, due to the commercial planting of pine throughout the 20th century. The peat bogs will record whatever changes we impose on our landscape, provided we protect and cherish these remarkable habitats.