Palynological Project - Methodology

The ideal source of material for a palynological study is a vertical core from a bog or from mud that has accumulated at the bottom of a lake over time. Individual samples from regular intervals along the core are removed and treated chemically so that only the pollen remain. Using a microscope, pollen from different plants are identified and counted. The proportions of different pollen types present in each sample are expressed as percentages of the total pollen sum for that sample. These percentages are then plotted on a graph known as a "Pollen Diagram", to produce a series of curves for each species of plant, showing how its abundance changes over time (reading the graph vertically) and how it compares with the other plants growing at the same time (reading the graph horizontally). To make reading the graph easier, it is divided into "zones", each highlighting a particular feature, eg periods when trees are in decline and grasses increase. Based on changes from zone to zone, it is possible to reconstruct how the surrounding landscape changed over time.

In the pollen diagrams illustrated here, significant differences can be observed from zone to zone in, for example, the amount of pollen from trees. In some cases, this seems to be the result of forest-clearance by humans. Sometimes this is to provide grazing for animals, shown by larger quantities of grass and herb pollens, while in other cases the appearance of cereal pollens, from forms of wheat for example, clearly show that humans in the area have started to grow crops. One of the most spectacular features observed in pollen diagrams from all over northwest Europe is the dramatic decline in elm pollen at c.4000 BC, the so-called "Elm Decline". In most cases, this decline coincides with the first pollen evidence for farming, and it was therefore at first interpreted as clearance of woodland by Europe's first farmers. It is now more generally accepted that the Elm Decline was in fact caused by a specific disease, not unlike the "Dutch Elm disease" of the more recent past.