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What is Palaeoecology?

Palaeoecology, as I have already said, is the ecology of the past; most usually the distant past. But palaeoecology can involve investigation into the ecology of some geological period long gone, hundreds of millions of years ago; or it may involve investigating the relatively recent, historic past. Like the remains of a pond from the early 1900’s.

The most direct way to delve into the ecology of the past is by examining sediment, and anything deposited in that sediment, for clues left by living organisms or events. Clues left by the action of the climate on the rocks, by living things living, and dying, and clues left in the sediment themselves as to how they formed, what from, and why.

The sediments most suited to such enquiries are those rich in organic matter, and in Ireland there are plenty of those. Bogs, mires, and lakes.

A lot of palaeoecological studies have been undertaken in areas of uplands, largely because those areas have been assumed to have been interfered with least by human action in the more recent past. Which is reasonable - fewer housing developments, less intensive agriculture, and little industry has traditionally been found in upland areas. They are generally harder to get to, more exposed to the elements, the ground is less fertile and so on. But of course, they are upland areas, and what are uplands now, have been uplands for a long time, certainly for as long as most palaeoecological studies will extend back. And we all know that the climate, flora, and fauna are all different up there. So to get a picture of what life and the environment was like down here, where humans have mostly lived for most of history, in the lowlands, we need to study the palaeoecology of lowland bogs, mires, and lakes.

So, why bogs, mires, and lakes? And what is the difference between a bog and a mire?

Bogs mires and lakes are all wet places, and if sediments remain wet oxygen is largely excluded which makes the sediment anoxic, i.e. deprived of oxygen. This reduces bacterial and microbial activity and so decomposition is reduced to a minimum. There is therefore a better chance of more organic remains being preserved. Additionally, because of this anoxic state, the sediments are high in organic matter, which makes them well suited to radiocarbon dating. So lakes, mires, and bogs contain lots of macro fossils, big enough to see, potentially of both plants and animals, and also microfossils of all sorts.

These environments, as well as being wet, are often acidic, which also reduces microbial action. Siliceous rocks, high in silica, like we have in West Cork,can also give rise to acidic mires. Limestone areas are generally more alkaline, and an added complication with limestone is the effect that the carbonate can have on radiocarbon dating - but we do not have to worry about that here in West Cork.

A bog is generally considered to be both largely populated by sphagnum mosses, and the water comes mostly from the atmosphere, as rain. Mires have a somewhat different flora, not based on sphagnum moss, and the water comes from the ground as well. This means there is more of a mineral component, which affects the nutritional value of the sediment. But of course there are extremes in both cases, and there are all the possibilities in between. A raised bog is a vast community of sphagnum moss that has grown upon itself, above the water table, retaining its own water and taking nutrient and moisture only from the atmosphere, whereas a minerogenic mire is best shown by a river swamp that expands out into a large flat wet area, ground water flowing in all the time and washing in minerals. So really the difference between a bog and a mire is that a bog is low in nutrients, lacking in mineral sediments and largely populated by moss; a mire is high in mineral nutrients, lower in mosses and based on, and interspersed with, influxes of mineral sediment.