After facing several invasive species challenges, Inverewe Garden, are going to be using a specialised form of charcoal making, called biochar, ensuring an environmentally friendly outcome to their eradication mission. A scourge of the invasive species, Rhododendron ponticum, has since spread uncontrollably affecting Inverewe’s shelterbelt. This is having huge ecological disadvantages and posing a threat to the overall existence of the woodland.
The oceanic climate and acidic peaty soil provide the ideal conditions for this plant to grow, and it can spread rapidly. Biochar will be created from collected R. ponticum, with added compost and used to restore the soils nutrients to promote nutrients and future biodiversity
The team at Inverewe became concerned about their R. ponticum problem due to their unique circumstances of wildlife in their woodlands, and the threat that was posed to it and the habitats they cared for. R. ponticum crowds out almost all other plants, forming a dense thicket within which nothing else can grow, and insects and other creatures that live in the woodlands lose their habitat.
Scotland has a unique climate incomparable with the rest of the worlds in which some of its areas retain a huge richness of biodiversity, categorised as rainforests. The west of Scotland’s coastline in particular influences the ecological make-up of woodland and moorland areas significantly. The team there know they have a global responsibility to look after and preserve our rainforests and the species within them.
R. ponticum can be found in 40% of rainforest sites and threatens woodlands preventing the distinctive rainforest flora from surviving. Their worry was with their shelterbelt, which needs to keep renewing itself – as it protects the garden from the Atlantic storms. Another concern is for the plant to spread from the garden to the wider landscape and colonise natural woods and moorland, disrupting their environments.
The removal process can also be very damaging to the soil ecosystem and will be a huge challenge for the team on this project. Consequently, once the woodland has been cleared of R. ponticum, the first job is to restore the balance of soil life. This is critical to achieving successful regeneration as without it, the trees planted and the saplings that self-seed will not have the right conditions to grow and flourish.
Their plan for restoring the soil health of our woodland is to convert the R. ponticum cleared into biochar and return it to the soil. Biochar is a specialised form of charcoal, made under precise burn conditions that mean the pore structure of the original wood-cells remains intact. They will be working at an Exeter Retort, which uses a very low pollution technique to make biochar – burning off environmentally harmful gases, whilst retaining the wood’s carbon. This means that at least 50% of the carbon locked up in the R. ponticum can be returned to the woodland. As biochar is slow to degrade, this carbon can potentially be locked up for thousands of years, which is why this process could be considered a carbon sequestration technique.
Biochar has the potential to help restore the soil life to areas of the woodland that have been cleared. Acidic, highly leached soil, like that at Inverewe, responds better to biochar amendment than other types of soil, because it retains the pore structure of the original wood.
By adding compost to the biochar before returning it to the woodland, it’ll give the fungi and other beneficial organisms a head-start in helping to speed up the process of fungal colonisation. The team have also been experimenting with collecting leaf litter from undisturbed natural woodlands on the estate and culturing the fungi and soil life. This will then be added to the compost and will be used to enrich the biodiversity of the biochar. Over the next few years, they’ll be monitoring the success of the biochar in enriching the soil health of our woodland.
Establishing a species-rich, mixed-age canopy woodland, with high biodiversity, will provide shelter for the rare creatures that live in this part of Scotland – from red squirrels, pine martens and sea eagles down to the rare lichens, ferns, and mosses. It will also shelter Inverewe Garden, providing it with the protection it needs to withstand the climatic pressures of the 21st century.