Dune Heath Regeneration After Conifer Removal
Case Study Type:
Habitat Management Case Study
Sand dune system:
Case Study Subject:
Dune Heath regeneration after conifer removal at The Triangle, Sefton
About The Dune System Engagement Intervention
The Montagu Road Triangle (The Triangle) is a protected Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC) for dune heath. Dune heath is a particularly rare dune habitat, taking about 300 years for lime from seashells in the dune sand to be washed out by rain, so the sand becomes acidic enough for heather to grow. Dune heath often forms along the landward edge of the sand dunes but unfortunately, much of it has been lost to plantations or development, leaving only small, isolated fragments.
The Triangle has an interesting history of human land use. The site was farmed up to the early 20th century – the remains of field boundary banks or ‘cops’ can still be seen today. In 1908, the site formed part of the Freshfield Golf Course which was later requisitioned by the Ministry of Defence during the Second World War, becoming part of Woodvale airfield. The golf course eventually closed and the clubhouse on the Triangle was demolished in the 1950s, leaving the dune heath to develop over time.
What was the change you hoped to make?
Management of the site has been intermittent over the years and the dune heath was at risk of being lost altogether through scrub and tree encroachment without appropriate intervention.
We hoped to start work on restoring this site by reducing thick vegetation and removing invasive shrubs and trees shading out the heather. This would help open up the habitat, letting more light in and allowing the natural growth of heather and other wildflowers from the underlying seed bank.
Our aim was to start the journey of restoring the site to a healthy dune heath; a mosaic of heather, gorse, grassland, bare ground patches, occasional pools and scattered trees, providing a wide variety of habitats to encourage the greatest diversity of plant and animal species.
What was the suggested intervention?
Removal of scrub and trees mostly through mechanical means is the typical intervention to open up the areas of existing heather and to uncover the areas where heather used to be. A literature review of scientific papers on lowland heath restoration was also carried out to help us decide the best approach. We found the following key information:
- No two heaths are the same, what works for one, might not work for another!
- Less intensive techniques that support natural processes typically give better results
- Heather seed needs light to germinate
- Beneath heathlands planted with conifers, heather seeds were typically concentrated in the top 40mm of soil
- Large, viable seed banks of heathland species can survive beneath conifer plantations for up to 40 years
- Removal or disturbance of conifer leaf litter aids seed bank germination
- Heathland restoration following removal of the conifers is unlikely to be significantly constrained by large excesses of soil nutrients or increased pH
The long-term persistence of heathland soils and seed banks under conifer plantations suggested that heathland re-creation should be relatively straightforward if excess litter and brash were removed or disturbed and invasive trees/scrub controlled.
What did you do?
Using historical aerial photographs, we compared the present-day situation with the extent of dune heath that used to occupy the site around the time it was originally designated. Given the funds and time available, we decided to concentrate on restoring the two main areas of heath on the northern and southern parts of the site where heather patches still existed and where the seed bank was still likely to be intact.
The tree and scrub clearance was carried out in three stages (2020, 2021 and 2022) over the winter months each year using external contractors. The works were undertaken using a combination of machinery (e.g. small tracked excavators with tree shears attached) and by hand with chainsaws. Brash was chipped and some trees processed for logs. Both were removed off site by the contractors.
Each year, following the main contractor works, our volunteers kept the areas clear of scrub regeneration. The main issues were birch, poplar and broom seedlings rapidly invading the cleared areas. Small seedlings were hand pulled and larger scrub targeted with tree poppers or cut with hand tools. Cut stumps were spot treated with herbicide.
What modifications, if any, did you make to your initial plan and why?
The original plan included for turf stripping, primarily on the southern part of the site, but based on the literature review, this method risked removing significant amounts of the heather seed bank and damaging existing mycorrhizal networks. It would also have been prohibitively expensive to remove sizable amounts of organic material off-site. Access was also a consideration as large numbers of wagon movements would have been needed along a narrow road in poor condition and a busy bridleway. If we had exposed too much sand, sand blow could have caused an issue with the railway and bridleway immediately adjacent to the site.
Highlight any issues/obstacles & how you overcame them?
The first two phases of scrub clearance were very challenging to achieve with the Covid situation and the restrictions that applied at the time. We also experienced flooding during one winter but fortunately, our contractor was happy to move the start date of the works, giving time for the water levels to drop.
How much did the intervention cost?
Three phases of scrub/tree clearance cost around £40k
What size was the area of the intervention?
What else went well?
We also undertook two simple experiments on heather regrowth based on the literature review: one looking at the effectiveness of manual raking and removing just the pine needle litter layer on an area previously dominated by conifers and the second removing the organic material down to the sand layer in small 1m by 1m patches on an area previously covered by mostly birch saplings.
The manual raking was undertaken by volunteers in the summer after the first phase of scrub clearance in 2020 on the northern part of the site. Heather regrowth by August 2021 in the raked areas was noticeably much higher than the unraked areas. This has continued to be the case each year, confirming that heather seeds need light to germinate, a strong seed bank was still present within the top few centimetres of soil and a simple intervention can make a big impact.
Small sand patches were carried out on the southern part of the site as part of the third phase of scrub clearance in January 2022. Observations over the next year and half on the sand patches showed very little heather regrowth compared to the surrounding areas where the organic layer was left in situ. This showed that we had most likely removed most of the heather seed bank when creating the sand patches.
Although the above experiments were small, the marked difference in heather regrowth between just raking off the pine needle layer compared to the sand patching was clear. Leaving the organic layer may mean more nutrients are present and that for a time, more work may be required to control faster growth of less desirable plant species, but overall, the heather seed bank (and associated mycorrhizal network) is more likely to remain intact and heather growth is stronger. It would be possible to undertake the removal of the pine needle layer on a larger site with appropriate machinery rather than just by hand but as our site was small, this was a fairly easy task with volunteers.
How were the public and others engaged?
Given the removal of scrub and trees on a sensitive site, we had some concerns from the public about what we were doing and why. We made sure to keep the public informed through on-site poster updates and social media posts to explain our chosen method and the reasons why we were doing the work. We also informed key local stakeholders before each stage of works. Overall, the response has been very positive, particularly with the improved access within the site and the reduction in anti-social behaviour.
How were communities/volunteers involved?
COVID restrictions limited the number of events we could hold on site and we were unable to set up a new volunteer group until recently. Our existing Ainsdale NNR volunteers have undertaken scrub management works throughout the project when restrictions allowed and recently, we have set up a new group dedicated to The Triangle to help with future management.
How were local schools or other organisations involved?
Again, COVID restrictions limited our ability to involve local schools in the project. However, towards the end of the project, assisted by a local artist, we engaged with a local primary school through a field visit and art class. The children learnt all about dune heath and the plants and animals that live there as well as what we were doing to look after the site. The children produced impressive artwork of rabbits, heather, emperor moths and heather Colletes bees. These were recreated by a local chainsaw artist who carved the images into wood forming part of two new interpretation boards installed on site.
Is the intervention working?
Please describe how. What has changed?
Yes, heather regrowth (and other heathland plants) has been rapid and more extensive than we had hoped. Scrub and tree seedling regrowth is an ongoing issue and is being kept under control by volunteers to prevent it from reinvading the heath.