Cothill Fen - Saturday, 28th March 2026

Blog by Sally.  Photos by Carol, Julio, Margaret and Sally

Twelve Green Gymmers turned out on a sunny spring morning to meet Stephanie Wilson from Natural England at Cothill School car park, where we were able to load our tools onto the back of Steph's van and make our way along String Lane, an old drover's road, to Cothill Fen, where Steph briefed us on the tasks for our session.  The Fen is owned by Natural England and sits adjacent to Parsonage Moor, which is owned by the Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust (or BBOWT).

Cothill Fen is one of the rare alkaline fens where specialist flora and fauna have evolved over millenia to adapt to the slightly less acidic conditions than are found on normal fens.  The spring water that feeds Cothill (and other alkaline or calcareous fens) percolates through a layer of chalk.  Sometimes, the chalk calcifies on the surface to form tufa, which is a bit similar to the limescale that builds up in our kettles.

The regular volunteers had been busy cutting rush, reed and unwelcome sedges and one of the tasks was to rake up the cut vegetation and move it to the bunds in the pond.  The bunds have two functions - to help keep the fen wet and also to filter the run off from nearby fields, which contain fertilisers.  The alkaline fen species do not thrive in nutrient rich soil.  There was also some more scything to be done.  Jim, David and Barbara helped with this, whilst Dieuwke and Carol raked up after them.

The rest of the group split into two - Julio and Simon made for the fence line at the bottom end of the fen near the wood to clear the fence line of bramble in readiness for replacing some rotten fence posts, whilst Rhi.an, Lesley, Margaret, Izaak and Sally cleared bramble from the fence line along String Lane where emerging pignut and red campion, which are ancient indicator species, would otherwise become smothered.  We also removed some emerging goosegrass (also known as cleavers or sticky bud) for the same reason.  Dr Judy Webb, consultant ecologist, also joined us briefly.  She was busy recording species.

Steph briefs the group

Rhian and Lesley tackling bramble along the fence in String Lane

Izaak eyes up the situation

Izaak and Margaret ponder their next move clearing bramble

Good progress being made.  The heaps of cut bramble were piled onto an existing dead hedge.  

This will be good habitat for invertebrates.

Fallen dead ash tree previously home to jet ants, which Judy had found.  Dead trees are a valuable habitat to a lot of invertebrates, but sadly too many woods are "tidied" with dead wood removed.  

The fen has benefitted from all the conservation restoration efforts over a number of years.

Before restoration, it was almost all impenetrable reed which was out-competing the specialist calcareous fen flora for light.

Turkey tail fungus

Simon takes on the bramble at the perimeter fence

Primroses

A close up of a jet ants' nest, which Judy Webb had found

Break time!

After break, Izaak, Margaret and Rhian joined forces with Julio and Simon to clear more bramble from the perimeter fence in readiness for replacing fence posts.  Initially, Steph thought we might only manage one or two, but in fact 5 rotten posts were replaced, so she was delighted with this.  

Steph and Izaak replacing one of the fence posts

Margaret and Izaak in their fencing attire poised for action

Izaak, Steph and Margaret replacing one of the posts

Two of the rotten posts

The cleared fence line with new posts

Meanwhile, Judy had asked if it would be possible for us to coppice a hazel tree, which was in danger of crowing out a spurge laurel.  Lesley and Sally took up loppers, bowsaws and pruning saws to do this.

The spurge laurel and coppiced hazel stool

A robin looks on

Carol spotted this frog

It was soon time for us to pack up the tools in the back of Steph's van and then we made our way back to the car park, where we said our goodbyes.  It was a good feeling to have left the site having completed the tasks and exceeded Steph's expectations.