Willow Tree Fen is a 110 hectare wild fenland site located between Bourne and Spalding in South Lincolnshire.

Purchased by Lincolnshire Wildlife Trust in 2009, the reserve has been transformed from arable land growing beans and cereal to a more traditional fenland landscape of shallow meres, seasonally flooded pastures, hay meadows, reedbeds and ditches.

Willow Tree Fen has been identified as a Flagship Pond site by the Freshwater Habitats Trust due to presence of UK Biodiversity Action Plan (UK BAP) priority species Greater Water-parsnip Sium latifolium and Tubular Water-dropwort Oenanthe fistulosa.

Classified as Nationally Scarce in the UK, and protected under Schedule 8 of the Wildlife and Countryside Act, Greater Water-parsnip, a large robust upright perennial, is found in wet ditches on fens and swamps. It prefers still or slow moving shallow water, is intolerant of disturbance and it does not like being overshadowed by trees.

Tubular Water-dropwort is a rather delicate perennial wildflower which is mainly found in boggy areas such as marshes, pond edges and fens. It doesn’t spread particularly easily to new wetland habitats, tending to prefer permanently wet soil.