Within the valleys of the Lye and Boundary brooks a special geological situation (permeable limestone of the Corallian Ridge overlying impermeable Oxford Clay) gives rise to a spring line which has, over thousands of years, formed calcareous (limy) alkaline fen habitats with a range of rare plant and invertebrate species. These were studied by the earliest botanists and entomologists from Oxford University from as long ago as the 1600s, when the site was known as Hogley Bog. A depth of peat and tufa (lime) deposits formed from the calcium-rich spring water and over a metre of this remains, despite historic peat cutting.  Although there are problems of catchment development (reducing spring flow) and brook bank erosion due to flash flooding, 22 plant species from the county Rare Plants Register are still present at the site. This short alkaline fen vegetation type is now the rarest habitat in England due to losses elsewhere. In the Lye Valley the area of quality short fen is still small at around 1.5ha, and loss of a large section occurred due to succession to scrub since grazing ceased about 100 years ago; however two valuable areas of short fen survived and are designated SSSI.

Better management of the two short fen areas has improved habitat condition vastly over the last 6 years.  Grant funding achieved by Natural England and BBOWT (Wild Oxford Project) has enabled a great deal more scrub reduction and more extensive annual cutting and raking of fen vegetation using an army of volunteers, which include the local Friends of Lye Valley group. This cutting and raking simulates grazing activity.  However, the north fen and south fen SSSI sections are still separated by 600m of scrub and secondary woodland on old peat. Isolated plant and invertebrate populations in the two SSSI sections will have a better chance of survival into the future with current plans to remediate ‘stepping stone’ sections of what was old Hogley bog back to a much greater area of high quality fen vegetation; re-joining the best surviving habitat areas.

Pressure to develop nearby is high and catchment protection is needed. Whilst Oxford City Council own part of the project area, most of the rest is in multiple private ownership. Further grant funding and hopefully management agreements with as many of the private owners as possible will also be needed.  

For more information see
http://www.friendsoflyevalley.org.uk/

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