Heartwood - long term monitoring project

Heartwood is a Woodland Trust project, started in 2009, to convert the farmland at the former Hill End Farm, north of Sandridge, near St Albans into deciduous woodland.
This presents a valuable opportunity to monitor how plants and other wildlife are responding to this development.
Volunteers from Hertfordshire Natural History Society and the Woodland Trust have set up a Monitoring Group, co-chaired by Brian Legg and Agneta Burton to keep track of the changes. On this page you will find information about the project, what is being studied and all the results gathered so far. Scroll down the page to find each topic. More data will be added as it is collected. We are currently monitoring:

  • the new trees as they are planted,
  • veteran trees,
  • lichens,
  • plants,
  • mammals,
  • birds,
  • butterflies,
  • some other invertebrates,
  • fungi,
  • soils.

We have also established some permanent long term monitoring plots. We hope more people will join the monitoring group to both extend the current studies and include more species groups. We would also welcome more people to set up their own studies or study areas, with such a large and diverse site the is plenty of scope for more projects.

Background and history

The Woodland Trust acquired 347 hectares (850 acres) of arable farmland in 2008 and, after obtaining the relevant permissions, tree planting started over the winter of 2009/10. This continued over the following winters with 500,000 saplings planted by March 2016, all by volunteers. A major celebration was held in March 2018 to mark the planting of the 600,000th and last tree at Heartwood.

The complete forest now comprises ancient woodland (18ha), newly planted woodland (250ha), grassland and wildflower meadows (79ha), small areas of natural regeneration, seed sown forest, and wetland.  In addition there is a community orchard with 600 fruit trees and an 11ha arboretum with all the trees and shrubs native to the British Isles.

The full extent of the Heartwood site, which is just north of Sandridge village, is shown on the map in pale green.
The existing ancient woodland (dark green on the map) comprises four blocks known as Langley Wood, Pismire Spring, Well & Pudler?s Wood and Round Wood, all were already designated as County Wildlife Sites. 

The map shows which areas have been planted with trees and when they were planted up to 2014. By that time about 200ha have been planted with native trees sourced in Britain. This involved over 10,000 volunteers from local, community and corporate groups and over 13000 local school children.
In addition a Community Orchard has been established in the south-eastern section of the site (pale blue on the map), see this detailed plan of the varieties of fruit trees planted.

An arboretum showcasing all British native trees was planted in 2015/6 on the east side of the Wheathampstead road. A full colour illustrated guide to the arboretum has been published at ?3.  It describes all the trees and shrubs native to the British Isles with information on their identification, natural distribution and past and present uses. Available from Carpenters Nursery, and Wheathampstead Manor Pharmacy, or by email to brianjlegg@gmail.com.
Visit the Woodland Trust website for more information about Heartwood, tree planting and community events and news.

Environmental Monitoring

Recognising the importance of this development for habitats and wildlife volunteers from the Woodland Trust and Hertfordshire Natural History Society (HNHS) set up a Heartwood Monitoring Group, chaired originally by Ken Smith and Brian Legg. Monitoring of breeding birds and butterflies started in 2009, sapling survival and veteran trees in 2010 and botanical and some invertebrates in 2011 together with the establishment of long-term monitoring plots. Each is discussed in the following sections. We hope that monitoring of bats, badgers, small mammals, fungi and a wider range of invertebrates including moths will start in 2012. An Environmental Impact Assessment was commissioned as part of the planning application in 2009, this contains some baseline information about the site and its wildlife.

Veteran Trees

The existing areas of woodland at Heartwood contain a number of very old - veteran - trees. These have been surveyed, measured and tagged by John Moss and his team of experts. Follow this link for details of the survey method and results.


Birds have been systematically recorded at the site since spring 2009, before any tree planting work had started. Go to the Heartwood Birds page for full information and results and a checklist of birds recorded since 2008.
A standard breeding bird survey, using British Trust for Ornithology methods has been carried out by Ken and Linda Smith each year from 2009, covering all of the land owned by the Woodland Trust.
Follow this  link to see a description of the survey methods and the full results.
The total number of species recorded in the transect surveys has increased over the five years from 35 in 2009 to a total of 63 by 2016 representing an increase in diversity. By 2016, birds that are open ground/farmland specialists were favoured, such as Skylarks. In 2017, the annual breeding bird survey showed a small decline in skylarks (possibly caused as young saplings replace rough grass), with continuing increases in robins, corvids, wrens, meadow pipits, whitethroat and starling.  Highlights included a few willow warblers and a pair of grasshopper warblers ? a photograph of which won the HNHS competition for the bird photograph of 2017. The monthly bird survey  has continued throughout the year and among others shows high numbers of yellow hammer, meadow pipit, linnet, goldfinch, skylark, and starling, with winter numbers swelled by lesser redpoll, redwings and fieldfares.


Systematic monitoring started in Summer 2010 based on a transect in the south west of the site. The transect is walked every week from April to September. So far 29 species have been recorded. In 2017, the butterfly survey showed dramatic increases in small skipper, marbled white, gatekeeper, meadow brown and small heath, and good numbers of large skipper, common blue, speckled wood and ringlet.  A highlight was the first record of a purple emperor.

Follow this link for a description of the survey methods and full results


In 2010, a group of volunteers came together to monitor and manage the existing hedgerows at Heartwood Forest with the objective of increasing their ecological value. At the outset, four hedgerows were identified for continuous review. This was on the basis that they would be retained as hedgerow habitat following the completion of the woodland creation project at Heartwood Forest. Details of the survey methods and results here.


A botanical survey of Heartwood was started in 2011 to record and monitor changes in plant species diversity and composition; particularly with regard to successional changes from arable to woodland habitats both within the natural regeneration area (referred to as ?The Thicket?) and within the sapling plantation plots.  Botanical surveys were also undertaken within Pudler?s and Langley Wood to monitor any potential changes to the ground flora of existing ancient woodland. More details of the survey methods and results are here.


Steve Kelly and members of the Herts and Beds Fungi Group did some exploratory survey work in autumn 2012 and 2013. Details here.
Scarlet Elf Cup, about 1.5cm across in Pudler's Wood in September 2010. These fungi grow on fallen twigs, particularly Hazel.


Monitoring small mammals started in 2012. The group organised one session of trapping and releasing in six locations in early October 2012, under the supervision of Veronica Carnell. Full results of the survey. This has been repeated every year. The small mammal survey in September 2017 revealed large numbers of wood mice and bank voles, smaller numbers of field voles and common shrews, a single yellow-necked mouse and the first water shrew record for the site, interestingly nowhere near water. 
Hares, Rabbits, Muntjac and Fallow Deer are numerous at Heartwood and Foxes have been seen.
Sightings of mammals may be submitted through the HNHS on line recording scheme here

Long Term Monitoring Plots

Three permanently marked sets of plots have been established for long term monitoring of the changes in flora and ground dwelling fauna as Heartwood is developed. The three transects each consist of 20x20 metre plots in an existing area of ancient woodland, at 25 metres from the woodland edge and at 50 metres distance. Initial baseline surveys are taking place in the years 2011-2013 (three to six years after cultivation). Soil cores were taken in March and April 2012 and are being stored dry until money can be found for their composition to be determined. Work is underway on determining soil microbial diversity form these cores. More details and map showing the plots are here.

Insect surveys, consisting of pitfall and yellow-tray trapping, sweep netting, and D-vac sampling were done in 2012 and 2013. Plant surveys have also been started.

It is hoped that local enthusiasts and possibly school and university students will use these plots for their own research as time goes on and that, in the long-term, the techniques used for the baseline surveys will be replicated on a regular basis in order to produce a dataset that rivals the Rothamsted Wilderness experiments for scientific value.

Sapling Survival and Growth

We have set up a network of sampling points throughout the newly planted areas. At each point all saplings within 5m were located, identified to species, scored as alive, dead or missing, their height measured to the nearest 5cm and the evidence of top browsing assessed. The pre and post planting treatments of individual saplings were recorded. These measurements will be repeated in subsequent years.
In the first year a large number of sample points (51) were surveyed and the information used to inform the planting strategy in the second and subsequent years. From these 18 were selected to carry forward.
First year survival was 77% from 2009/10 and 68% from 2010/11 (based on 18 sample plots in each year with an average of 14.3 stems per plot)
In both years the survival rate was highly variable.
For the 2009-2010 plantings the variation was probably caused by poor planting in some areas and losses due to browsing. Survival was particularly poor in the Guinness 'World Record attempt' area.
For the 2010-2011 plantings the low survival was almost certainly caused by dry conditions in spring affecting the later plantings.
Follow this link for more details of the survey methods and the full results

Sampling points have also been established in the areas where natural regeneration is being encouraged, to the south of Pudlers Wood and in an area to the east of the B651.