Aldbury Nowers is a 19.7 hectares biological Site of Special Scientific Interest (SSSI) in the Chiltern Hills, north-east of Tring in Hertfordshire. The site was notified in 1990 under the Wildlife and Countryside Act 1981. It is managed by the Hertfordshire and Middlesex Wildlife Trust. The site, formerly known as "Duchie's Piece," comprises two areas of hillside, linked by The Ridgeway. The calcareous meadow element of the site hosts the flowers of chalk grassland and has butterfly habitats with thirty-four different species of butterfly recently recorded, including the Duke of Burgundy, hairstreaks and the Essex skipper. The site also includes a "beech hanger", a type of upland ancient woodland, and is considered one of the best examples of this feature in Hertfordshire.
Ashridge Commons and Woods is a 640.1 hectare biological Site of Special Scientific Interest in Buckinghamshire and Hertfordshire. It is located in Little Gaddesden, and is part of the National Trust Ashridge Estate in the Chilterns Area of Outstanding Natural Beauty.
Plashes Wood is a 71.9-hectare (178-acre) biological Site of Special Scientific Interest south of Standon in Hertfordshire. The local planning authority is East Hertfordshire District Council. The wood is private property.
Wain Wood is an ancient woodland extending to 19.2 hectares near Preston in North Hertfordshire. The site is a Site of Special Scientific Interest which was notified in 1986 under the Wildlife and Countryside Act 1981. The local planning authority is North Hertfordshire District Council. It is a relic of a large forest which extended from Hitchin to Hatfield.
Pegsdon Hills and Hoo Bit is a 79-hectare (200-acre) nature reserve in Pegsdon in Bedfordshire. It is managed by the Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire. The site is on the border between Bedfordshire and Hertfordshire, and it covers Pegsdon Hills and part of the adjacent Deacon Hill in Bedfordshire, and Hoo Bit in Hertfordshire. It is in the Chilterns Area of Outstanding Natural Beauty, and part of the site is designated by Natural England as the Deacon Hill SSSI.
Wormley-Hoddesdonpark Wood South is a 192.5 hectare is a biological site of Special Scientific Interest near Cheshunt in Hertfordshire. It is part of Broxbourne Woods National Nature Reserve, and is listed in A Nature Conservation Review. Wormley Wood is owned and managed by the Woodland Trust. The site is also a Special Area of Conservation.
Wormley-Hoddesdonpark Wood North is a 143.9-hectare (356-acre) woodland area in Hertfordshire which has been designated as a biological site of Special Scientific Interest. The site is listed as Grade 1 in A Nature Conservation Review, and is also designated a Special Area of Conservation. It is in Hoddesdon in the borough of Broxbourne, but part of the site is in East Hertfordshire.
Water End Swallow Holes is a biological site of Special Scientific Interest in Hertfordshire, south-east England. Located in Welham Green and under the planning authority of Welwyn Hatfield District Council, it has an area of 11.3 hectares.
Sherrardspark Wood is a 74.9 hectare biological site of Special Scientific Interest in Welwyn Garden City, Hertfordshire. The site was notified in 1986 under the Wildlife and Countryside Act 1981.
Bricket Wood Common is a 70 hectare open space and biological Site of Special Scientific Interest in Bricket Wood in Hertfordshire. It is managed by St Albans City and District Council together with the Countryside Management Service and Bricket Wood Joint Management Committee.
Northaw Great Wood is a 223.6-hectare (553-acre) biological Site of Special Scientific Interest (SSSI) near Cuffley in Hertfordshire, England. It covers Northaw Great Wood Country Park, which is managed by Welwyn Hatfield Borough Council, Well Wood, Justice Hill and Grimes Bottom. Part of the site is managed by Hertfordshire County Council as a schools' park. The country park is also a local nature reserve.
Benington High Wood is a 20.7-hectare (51-acre) biological Site of Special Scientific Interest in Benington, Hertfordshire. The planning authority is East Hertfordshire District Council.
Knebworth Woods is a 120.8-hectare (299-acre) biological Site of Special Scientific Interest in Knebworth, immediately south of Stevenage in Hertfordshire. The planning authority is North Hertfordshire District Council.
Moor Hall Meadows is a 24.4-hectare (60-acre) biological Site of Special Scientific Interest in Moor Green in Hertfordshire. The local planning authority is East Hertfordshire District Council.
Tring Woodlands is a 23.8-hectare (59-acre) biological Site of Special Scientific Interest in Tring in Hertfordshire. It is part of the Chilterns Area of Outstanding Natural Beauty and the local planning authority is Dacorum District Council. The wood has a rich flora, showing that it is well established. It is a good example of a semi-natural beech wood in Hertfordshire. Plants that are abundant include woodruff, wood anemone and dog's mercury, and there are a variety of woodland birds. There is access to the wood from Hastoe Hill.
Hertford Heath nature reserve is a 28 hectare biological Site of Special Scientific Interest in Hertford Heath in Hertfordshire. It is managed by the Herts and Middlesex Wildlife Trust and the local planning authority is East Hertfordshire District Council.
Millfield Wood is a 9.5-hectare (23-acre) biological Site of Special Scientific Interest north of High Wycombe in Buckinghamshire. It is owned and managed by the Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust, and it is in the Chilterns Areas of Outstanding Natural Beauty.
Broxbourne Woods are a 239.1 hectare National Nature Reserve west of Broxbourne in Hertfordshire. The site is Hertfordshire's only National Nature Reserve, and is also a Special Area of Conservation. It covers Hoddesdonpark Wood, Wormley Wood, Broxbourne Wood and Bencroft Wood. Bencroft and Broxbourne are owned by Hertfordshire County Council, and Hoddesdonpark and Wormley Woods by the Woodland Trust. They are all in Sites of Special Scientific Interest; Wormley Wood and Bencroft Wood form almost all of Wormley-Hoddesdonpark Wood South, and Hoddesdonpark Wood and Broxbourne Wood are part of Wormley-Hoddesdonpark Wood North.
Danemead is a 5.6-hectare nature reserve west of Hoddesdon in Hertfordshire, managed by the Herts and Middlesex Wildlife Trust. It is part of the Wormley-Hoddesdonpark Wood North Site of Special Scientific Interest.
