Palaeoecological evidence for anthropogenic acidification of a kettle-hole peatland in northern Poland

The Holocene developmental history of a small kettle-hole peatland in northern Poland was studied using radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae with the aim of sorting out the influences of climate change, autogenic succession and human impact. The mire followed the classical succession from lake to a <i>Sphagnum</i>-dominated peatland, but peat accumulation only started about 3000 cal. BP. A rapid shift to wetter conditions, lower pH and higher peat accumulation rate took place about 110—150 years before present, when the vegetation shifted to a <i><i>Sphagnum</i></i>-dominated poor fen with some bog plants. While the first shift to a peat-accumulating system was most likely driven by climate, the second one was probably caused by forest clearance around the mire. This shift towards a <i>Sphagnum</i>-dominated vegetation mirrors both in pattern and timing the changes observed in similar situations in North America and New Zealand. While human activities have overall caused the loss of vast expanses of peatlands worldwide in recent centuries, locally they may have also allowed the development of communities that are now ironically considered to have a high conservation value. However, in the case of the site studied the likely anthropogenic shift to bog vegetation was at the expense of a species-rich poor fen, which today has even higher conservation value than ombrotrophic bogs. Thus this study also illustrates the value of palaeoecology for peatland management and biodiversity conservation.