Forming Fens

Holme Fen today is a National Nature Reserve. Along with nearby Woodwalton Fen, these are two tiny remnants of the wild fen habitat that covered a sizeable area of eastern England, before 99% of it was lost due to drainage.

But before there were fens, there was forest. How do we know? Well let’s take a look at how the Fens formed, because the forest got hidden underneath.

As you can see this area has a very flat landscape. It’s also close to sea level and the sea level has been rising for thousands of years.  This meant that water couldn’t drain away very well and rivers flowing into the area were prone to flooding.

As the environment got wetter the forest trees died.

Under boggy conditions, when plants die they can’t decompose properly and instead build up in layers of peat. Peat then acts like a sponge and holds on to the water, so the wetland area gradually expands.

When the forest trees died and toppled over, the big trunks became buried in the peat and have been preserved. Bog oak, as it is called, has been a problem for farmers, who have encountered great lumps of tree trunk while trying to plough their fields. Loads of it has emerged over the years, and when heating was by open fire, bog oak was an important and readily available source of fuel.

So, this landscape was forest, then fen and then farmland. We’ll look at the second change next week.