Heartwood Forest: A Transformed Landscape

The original landscape

Forest walking map showing the extent of the forest https://heartwood.woodlandtrust.org.uk

Heartwood Forest was created in 2010 by the Woodland Trust. A tract of agricultural land measuring 347 hectares at Sandridge was purchased in 2008. It encompassed old established woodlands including Pismire Spring and Langley Wood. To count as ‘ancient, a wood should have existed for 400 years. Maps dating from 1843, 1822 and 1766 have been inspected for evidence of old woodlands. The 1766 map shows no traces.

However, old names hold clues to former usage. Pismire Spring was named after a wood ant – a Pismire – which sprays urine if disturbed. Spring is the old name given to coppiced woods – usually hazel or hornbeam – which spring back into growth after being cut down.  Well Wood was believed to indicate the site of an old well, but it was not found until a deep round sink hole appeared in recent years. The Trust had it filled in for safety.

What the Woodland Trust achieved in the first 11 years

Paths in the old woods were defined in an attempt to protect bluebells and other plants from trampling feet. 600,000 native trees were planted by volunteers – many of them school children. Most were tiny saplings, with mature specimen trees to give immediate structure to the landscape. They now provide berries, nuts and nesting places. The common lizard has appeared – it probably wandered up from Nomansland Common. British woodland bird populations generally are still decreasing, in spite of new woods being established, but at Heartwood twice as many willow warblers have been recorded as there used to be. 60 Barn Owls were spotted between 2012 and 2021. Greater spotted woodpeckers and skylarks are among the nesting birds

Traditional species-rich hedges have been planted to form a link between woodlands other landscape features. They provide flowers in spring and fruit in autumn as well as cover. Wide wildflower meadows are left uncut in places to produce flowers, seeds and nesting materials.

Thick-legged flower beetle – © Jacques Vanni

The Woodland Trust monitors populations of plants and wildlife at Heartwood Forest: 87 species of bird and 27 of butterflies, 75 species of fungi, 51 lichens, 41 mosses and liverworts, various beetles, and rich annual weed crops. Amongst those ‘weeds’ are Lady’s bedstraw, orchids, (after 6 years of non-interference) and a rare insect – the thick-legged flower beetle which is a bright metallic green and about 10mm in length.

Butterfly populations vary according to weather. In 2019 their numbers increased, then dropped sharply. The species seen at Heartwood include painted lady – a migrant on its relay flight from Africa – which takes 6 generations to get here, and can reach the Arctic Circle. The small blue butterfly isn’t really blue, but is tiny. Large purple emperor butterflies fly around the tops of tall trees and come to land during the first week of July to feed on horse dung and dog excrement.

A new Arboretum covering 11 ha was planned for Heartwood. In 2015-2016, more than 10,000 young saplings of 60 varieties were planted by volunteers, to form Britain’s largest and most comprehensive arboretum of native trees and shrubs. This seems a lot, but not all these little trees will survive in the varied soils on site. So what is a native tree? ‘Native’ includes only species that arrived after the last ice age and before humans had a major influence. When the English Channel opened up – around 7,000 years ago – trees could no longer spread from Europe by normal means (i.e. wind or animal dispersal of seeds.)

What further changes will we see?

Heartwood is a ‘work in progress’. Trees will need to be thinned after15 years. Coppicing the old woods will take place in stages, allowing plants beneath to flourish again. Round Wood was last coppiced in 1990, and a small area has recently been cut down; the results will be monitored. In 20 years or so it will become clear whether the cloned elm trees – supposed to be resistant to Dutch elm disease – are fully disease resistant.

The first wonderful flowering fields at Heartwood will not re-appear. They were the result of disturbing the soil – which is why poppies pop up only the year after soil has been ploughed. But new annual grasslands will become established, with walks and rides for visitors. Skylarks prefer open meadows so their numbers will decline where the forest grows denser. Grass around the trees will gradually die as they grow, but we can hope to see more bats. Wild animals will appear to add to sightings of foxes, squirrels, voles, mice etc. A new field has recently been acquired, via a legacy, to complete the circular walk. Heartwood Forest has only 55 car parking spaces – insufficient at times for the many visitors who would like to come. This will be increased.

This corner of Hertfordshire is gradually being transformed into a rich varied landscape for the protection of wildlife and a place for recreation and appreciation of nature for generations to come.

• Brian Legg has 13 years’ involvement as a volunteer with the Woodland Trust at Heartwood Forest
• This report was first published in volume 146 of the Society’s newsletter in April 2022