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.
Patmore Heath is a 7.6 hectare biological Site of Special Scientific Interest in East Hertfordshire, 2 kilometres north-east of Albury, Hertfordshire. The site was notified in 1985 under the Wildlife and Countryside Act 1981. Patmore Heath is home to a large amount of dry grass, as well as marshy-areas. Much turf throughout the SSSI is dominated by Deschampsia, as well as occurrences of Anthoxanthum odoratum.
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.
Herts and Middlesex Wildlife Trust manages over 40 nature reserves covering nearly 810 hectares north of London, in Hertfordshire and the historic county of Middlesex, part of which is divided between the London boroughs of Barnet, Enfield, Harrow and Hillingdon. It has over 21,000 members, and is one of 46 Wildlife Trusts across the UK. It is a Registered Charity, with its Registered Office in St Albans, and had an income in the year to 31 March 2014 of over £1.5 million.
Rye Meads is a 58.5-hectare (145-acre) biological Site of Special Scientific Interest (SSSI) in Rye House, Hoddesdon, Hertfordshire. It is one of series of wetlands and reservoirs situated along the River Lea, to the north-east of London. It is part of the Lea Valley Ramsar site and a Special Protection Area.
Old Park Wood is a 16.7-hectare (41-acre) Site of Special Scientific Interest in Harefield in the London Borough of Hillingdon. The south-east part is an 8-hectare (20-acre) nature reserve owned and managed by the Hertfordshire and Middlesex Wildlife Trust.
Frogmore Meadows is a 4.6-hectare (11-acre) biological Site of Special Scientific Interest in Hertfordshire and Buckinghamshire, north of the village of Chenies. It consists of two meadows in the Chilterns Area of Outstanding Natural Beauty, next to the River Chess, one of which is a Hertfordshire and Middlesex Wildlife Trust nature reserve. The planning authorities are Three Rivers District Council, Dacorum Borough Council and Chiltern District Council.
Sawbridgeworth Marsh is a 6.3-hectare (16-acre) biological Site of Special Scientific Interest (SSSI) near Sawbridgeworth in Hertfordshire, apart from a small area in the north which is in Essex. It is managed by the Essex Wildlife Trust. The planning authorities are East Hertfordshire District Council and Uttlesford 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.
Waterford Heath is a 35.2 hectare Local Nature Reserve in Waterford in Hertfordshire, England. It is owned by Lafarge Tarmac and managed by the Herts and Middlesex Wildlife Trust together with East Hertfordshire District Council and Lafarge.
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.
Thorley Wash or Thorley Flood Pound is a 17.3-hectare biological Site of Special Scientific Interest in Thorley, south of Bishop's Stortford in Hertfordshire. It was formerly a flood pound for the Stort Navigation, which was decommissioned in 2004 and converted to a more natural state. It was purchased by the Herts and Middlesex Wildlife Trust from the Environment Agency in 2011.
Tewinbury is a 7.5-hectare (19-acre) biological Site of Special Scientific Interest near Tewin in Hertfordshire. The local planning authority is East Hertfordshire District Council, and the site is managed by the Herts and Middlesex Wildlife Trust
Fox Covert is a 2.9-hectare (7.2-acre) nature reserve near Royston in North Hertfordshire. It is owned and managed by the Herts and Middlesex Wildlife Trust.
Hill End Pit is a 0.7-hectare (1.7-acre) nature reserve on the site of a former chalk pit, in St Paul's Walden in North Hertfordshire. It was formerly managed by the Herts and Middlesex Wildlife Trust (HMWT). In February 2016 HMWT announced that three sites, Barkway Chalk Pit, Hill End Pit and Pryor's Wood, which HMWT managed on behalf of their owner, North Hertfordshire District Council, were to return to Council management as the Trust was no longer able to meet the cost. It has the largest colony of Azeca goodalli snails in Hertfordshire. Plants include viper's bugloss, cowslip and marjoram, there are butterflies such as common blue and gatekeeper, and many birds including woodpeckers.
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.
The Larches is a 25-hectare (62-acre) nature reserve north of Detling, which is north of Maidstone in Kent. It is managed by Kent Wildlife Trust. It is part of the Wouldham to Detling Escarpment Site of Special Scientific Interest and Nature Conservation Review site, Grade I It is also part of the North Downs Woodlands Special Area of Conservation, and Kent Downs Area of Outstanding Natural Beauty,
