Halo thinning: shedding light on ancient woodland and rainforest restoration
A specialist forest management technique known as halo thinning is helping Forestry and Land Scotland (FLS) in its rainforest restoration ambitions.
Celebrating World Rainforest Day (on 22nd June), the restoration of an ancient woodland site at Ardgartan in Argyll and Bute puts into focus how FLS is working to help save Scotland’s temperate rainforests.
A crowded and suffocated but surviving broadleaf stands defiantly in a sea of commercial conifers.
It is a remnant from an ancient woodland that was cut down and re-planted with commercial, non-native conifers – a site known as a Plantations on Ancient Woodland Sites or PAWS. This practice was not uncommon during periods of agricultural and forestry expansion in the 20th century before the ecological importance of native woodland was fully recognised and considered.
The enduring native trees at Ardgartan have become overshadowed by the conifers after four decades. The competition for water, nutrients and light ultimately risks starving the remnant tree, leading to its death.
However, a forest management technique known as halo thinning is giving these veteran and ancient trees the opportunity to breathe again and in time play a key role in restoring the original ecosystem.
FLS Rainforest Projects Coordinator Simon Turner said:
“Halo thinning involves removing non-native conifer trees from directly around a mature, ancient, or ‘veteran’ native tree.
“We use halo thinning where we cannot easily access a stand of trees to do conventional thinning with machinery. The aim is to open up the old native tree so that it survives and becomes more stable and robust prior to the plantation ultimately being clearfelled.
“By clearing this surrounding vegetation, competition for sunlight, water and nutrients is reduced, allowing the older trees, ground flora and epiphytes – specialist plants and micro-organisms that grow on the trees like mosses, liverworts, lichens – to develop into more robust communities.”
At Ardgarten, which sits in Scotland’s rainforest zone, individual broadleaf trees surrounded by non-native conifers were identified using on ground and aerial surveys. These veteran trees were then marked and GPS points taken of their locations. A halo was carefully felled using chainsaws around each tree, avoiding any damage to the remnant native tree in the process. and possible infection through a wound.
Simon added:
“These surviving trees have the potential to become seed trees once the site has been cleared. It is well documented that the best way to repopulate a cleared site is through natural regeneration, using seed from an adjacent seed source that is adapted to the particular environmental conditions.”
Along with techniques such as halo thinning, FLS undertakes larger scale felling where appropriate, ongoing removal of non-native conifer regeneration and invasive species such as rhododendron and deer management as part of its PAWs restoration work in Scotland’s rainforest zone.
FLS is responsible for a third of the area of Scotland’s ‘core’ rainforest with work to restore this precious habitat supported by Scottish Government funding. FLS is also a member of the Alliance for Scotland's Rainforest, a network of more than 40 organisations all working together to restore and protect Scotland’s rainforest.
Notes to editors
- Forestry and Land Scotland (FLS) manages forests and land owned by Scottish Ministers in a way that supports and enables economically sustainable forestry; conserves and enhances the environment; delivers benefits for people and nature; and supports Scottish Ministers in their stewardship of Scotland's national forests and land.
- Media enquiries to media@forestryandland.gov.scot