Pollen analysis
In the most recent section of the Quaternary period, the Holocene or postglacial epoch, the forests began to return, about 11 700 years ago, to the treeless, post-glacial steppes. Pollen analysis has largely clarified how this return migration happened. For Central Europe, there were ten phases as a rule (according to Franz Firbas), which are called pollen zones and given Roman numerals as part of the Blytt–Sernander sequence.