New life for rare habitat

Barn owls are breeding on the site

Barn owls are breeding on the site - Credit: Archant

A defunct and neglected flood defence has been transformed by the Herts and Middlesex Wildlife Trust into a haven for wetland wildlife. The trust’s Jenny Sherwen explains how the work will help rare species

Thorly Wash Nature Reserve

Thorly Wash Nature Reserve - Credit: Archant

Thorley Wash Nature Reserve in the Stort Valley is a rare and important wet grassland in the east of the county between Bishop’s Stortford and Sawbridgeworth. The site was previously owned by the Environment Agency and had a statutory purpose as a flood defence, hence its former name, Thorley Flood Pound. The pound was designed to protect London from flood water, but it did not fulfil its purpose and was decommissioned. The Herts and Middlesex Wildlife Trust acquired the site in December 2010 and began restoration work last September. The work was completed in May and the site reopened.

Disappearing wetlands

After the Second World War, large areas of wet grassland across the UK were drained for agricultural purposes, which mean very few sites remain. Floodplain wetlands have also disappeared as rivers have been adapted for human use. An example is the canalisation of a section of the River Stort to create a navigable waterway, which severed its link to the floodplain. The Stort backwater that surrounds Thorley Wash retains significant biodiversity because there has been no intervention, which means natural flooding can occur. Its importance as a habitat for wildflowers is reflected in its designation as a Site of Special Scientific Interest.

Ragged robin

Ragged robin - Credit: Archant

Wash wildlife

Wet grassland is important not just for wildflowers but can also provide an important breeding habitat for waders such as snipe and redshank. Small mammals also shelter in the grassland and attract hunting barn owls. We were pleased to discover that barn owls bred on the reserve last summer. The network of ditches and seasonal ponds is very important for invertebrates such as dragonflies and damselflies. There are also records for a number of water beetles, which indicate the quality of the habitat. There have been occasional water vole sightings along the Stort in recent years too, and with conservation efforts it is hoped that these populations will spread.

Restoration work

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The reserve was badly in need of attention to protect important botanical species and other grassland wildlife. We removed invasive willow, which if left to its own devices prevents wildflowers emerging because there is too much shade. A strip of mature woodland and some scrubby areas were retained to provide continuity for roosting and breeding birds as well as shelter for invertebrates. Silted up ditches have been re-profiled and trees have been pollarded to ensure their future health. A bridge has been built to allow maintenance vehicles on to the reserve, as well as grazing animals – part of an ongoing management project with livestock. The reserve has been fenced off and grazing will maintain the open grassland habitat, as livestock keeps coarse vegetation like brambles at bay, allowing a variety of rare wildflowers to emerge, which would otherwise be overrun by more dominant plants. All this restoration work may have looked drastic, but it will be very exciting to see the diversity of species that benefit and emerge this year.

New nature trail

Our new nature trail at Thorley is now open and will allow visitors to discover the varied wildlife of the reserve – with some surprises along the way. Access is from the Stort towpath, within easy reach of Thorley, Little Hallingbury, Bishop’s Stortford and Sawbridgeworth. Leaflets are available on site and also from the Three Horse Shoes pub along Spellbrook Lane East.