Therfield Heath holds the status of a Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlife and Countryside Act 1981. The SSSI citation dates back to 1953. More detailed information about the SSSI designation is given by Natural England, here. The main reason for the citation is the chalk grassland habitat and the specific grasses, flowers and insects associated with it.

The chalk grassland habitat has become increasingly rare. The species that inhabit it thrive only in the relatively dry, nutrient-poor conditions that characterise the site. Any additional nutrients – from atmospheric pollution or dog waste, for example – will affect the habitat by allowing larger, more nutrient-hungry species to thrive. Unfortunately, these smother the rarer species.

The area called Therfield Heath SSSI includes 2 SSSI units that are not managed by the Conservators. Unit 5 is Fox Covert, owned and managed by the Herts and Middlesex Wildlife Trust. Unit 6 is Valley Plantation, owned by Edward Darling at Greys Farm.

Local Nature Reserve

The majority of the site is also a Local Nature Reserve declared under Section 21 of the National Parks and Access to the Countryside Act 1949.


Under Section 1 of the Wildlife and Countryside Act 1981, the nests and eggs of wild birds must not be taken, damaged or destroyed and the birds themselves must not be killed or injured . If you allow your dogs to run through areas where the birds are nesting on the ground, you run the risk of your dog disturbing the nesting birds and destroying active nest sites. Some dogs, such as spaniels, are particularly persistent and will search for birds to flush. Please be responsible.


Therfield Heath is home to many invertebrates, some of which are chalk grassland specialists, for example the Chalkhill Blue butterfly. Last year the Herts Invert Project recorded the first Down Shieldbug in Hertfordshire on the site.

If you would like further information on the invertebrates found on site, the most recent survey from the Herts Invert Project can be found here.