Tracing back through time with the tiniest clues

HOLLYHOCKS lean together after the winds, and the bumblebees dodge around each other to feed at the last silky flowers. Now that the pressure's off for taking pollen back to the nest for hungry larvae, most of the workers are out for nectar for themselves, probing deeply into glands at the base of the petals.

Pollen from the central boss of stamens clings to the bees' body hair and some of them seem not to like it. They take time on a leaf to groom it away with their legs not into their pollen baskets but right off their backs and tails. Others have clearly given up caring much what happens to them, lurching around the flowers into a stuporous lethargy.

These are the last weeks of life for worker bumblebees and the last scatterings of pollen from another floriferous summer. Billions of pollen grains, lost to their fertilising purpose, lie on the ground in an invisible, multicoloured dust. Billions more, produced by "anemophilous" wind-loving plants, are still floating around in the sky.

Wind-polinated plants produce phenomenal quantities of featherweight pollen trees such as birch and hazel generate four or five million grains to each cat kin. The grains can travel great distances - beech pollen from Argentina turns up in the peat of Tristan da Cunha, out in mid-Atlantic.

The grains are virtually indestructible if kept wet and shut away from oxygen.

Where layers of pollen have accumulated undisturbed, they form a record of changes in plant life and climate reaching far back into the Ice Age. Pollen trapped in lignite - "brown coal" - on the east shore of Lough Neagh is from birch, pine and spruce which grew there in a warm interglacial period some 60,000 years ago.

Pollen grains from around 11,000 years ago, when the Great Ice Age came to an end, show the herbs creeping back on the tundra (meadowsweet, would you believe!) and the successive waves of shrubs and trees recolonising the land. At around 6,000 years ago, sudden changes in the pollen pattern show the start of Neolithic farming and the beginning of destruction of Ireland's natural forests.

Pollen analysis, now broadened into palaeoecology and palaeoenvironmental studies, dates back more than 60 years in Ireland, to the days when Frank Mitchell, fresh out of Trinity, joined Denmark's Professor Knud Jessen in the first pollen sampling of Irish bogs. Since that time, the dating of pollen samples has become extremely precise, helped by refinements in radiocarbon dating and the tree-ring dating system perfected at Queen's University, Belfast.

Palynology - to use yet another term for pollen studies - has become an essential tool in dreading the Irish landscape". This summer, for example, botanists from University College, Galway, and the University of Kiel worked together from a raft floating on Loch Mor, the fairly large and astonishingly deep lake on Inisheer in the Aran Islands. It has up to 77 feet of water and then a great depth of mud. Using heavy equipment, the team recovered a 46-foot core of sediment.

The deepest layers were laid down towards the end of the last glaciation, between 15,000 and 11,500 years ago, and they will show the very earliest successions of pollen as the cold retreated and plants returned. They have been taken to Kiel University for study by Dr Hartmut Usinger, a pollen analyst bred on the less eventful record of the sediments of Central Europe.

Sediment higher up the core spans the last 11,500 years and it is already under study in the Palaeoenvironmental Research Unit at UCG. It contains not only pollens, but leaves and twigs and fossil animal remains. These will build up a picture of the post-glacial colonisation of the island by plants and wildlife, and the later impact of human settlement.

It should answer many of the questions that have made the Aran Islands so mysterious. Was Inisheer ever wooded, as the Burren was, and did it share the same succession of trees? When did the first farmers arrive, and was it their impact that helped to strip the soil off the island's limestone? How intensive was the farming when the great stone forts of Aran, such as Dun Aonghusa, were in use?

Pollen analysis can be vital to dating archaeological remains and putting them in their human and environmental setting. Another part of this summer's coring programme - led by UCG's Dr Michael O'Connell and Dr Karen Molloy - focused on the archaeology-rich district of south-east Clare, with its deep and sheltered lakes.

One of the main sites, the three-walled fort at Mooghaun, near Dromoland, has recently been excavated as part of the Discovery Programme of research into the Bronze Age. Pollen in the sediments from the edge of Mooghaun Lough, studied by Dr Molloy, shows intense farming activity at about the time the fort was built.

With the new cores of sediment from lakes around Clarecastle, the UCG botanists will continue to build up a detailed regional history of agricultural activity since the arrival of the first farmers, 6,000 years ago.