Gardens & Designed Landscapes Manager Simon Jones explains why the shelterbelt at Arduaine had to be removed and then replanted.
Evolution is a natural process in the life of a garden – plants mature and die, and must be replaced – but hopefully the overall essence of the garden lives on. Arduaine has long been a green and peaceful place, and we are working hard to keep it that way.
The removal of the former larch shelterbelt in 2021/22, followed by the gradual replanting of a mixed woodland in its place, is very much a climate change response to the increasing amount of pathogens and pesticides that we have to cope with in our gardens. The former shelterbelt was not made of Sitka spruce or Scots pine, as is common in shelterbelts, but from Japanese larch (Larix kaempferi). The presence of the Phytophthora ramorum pathogen (‘sudden oak death’) had an enormous impact on this plantation, since larch is extremely susceptible to it. As the needles fall off the larch trees (which are deciduous conifers), that’s the exact time that sporulation is at its zenith and it just spreads the pathogen throughout the whole garden.
The first outbreak was in 2012; when the disease spread in 2016, we were subsequently issued with a Statutory Plant Health Notice. We had to fell all 914 120-year-old trees.
It was rather daunting to have to fell so many mature trees, so the first thing we did was to understand the actual make-up of the garden, in terms of its plant composition. We have 169 plant families and almost half of those are in the family Ericaceae. Of all the genera represented, from 95 geographical regions of the world, almost half of them are Rhododendron. From a pest and disease point of view, that spells a garden of risk.
We had about 17 acres of woodland that needed to be felled over a 4-year period. However, those larches were entwined with the precious rhododendrons, a collection that we needed to protect. Imagine you had to take down the bricks, mortar and roof of your house without harming any of your possessions inside!
We were also mindful of the ecology of the site and we worked with two different companies to make sure that squirrel dreys had been dismantled and bat roosts were empty – any protected species were considered in the project.
To deliver the felling, we relied on the input and understanding of a diverse range of people and stakeholders, both internal and external to the organisation. Colleagues from across the Trust had a part to play, especially the arborists from Mar Lodge Estate and staff from Crarae Garden. It takes between 4–6 hours to fell each tree, and we were hampered by periods of inclement weather that made it unsafe to work at height, but we got there.
The other element to this mass removal of larches was the huge loss of carbon storage and biomass in the garden. We did some random surveys of specific trees and worked out exactly how much carbon we were going to lose: roughly 500 tonnes of dry carbon, which equated to about 25–30,000 tonnes of wet material. To mitigate some of this loss of carbon, we bought some volcanic rock dust. When rock dust is applied to the ground, it locks carbon back into the soil. The soil levels in Arduaine are incredibly shallow, and nutrients often leach out due to the wet west coast conditions.
We had to burn some of the wood material, to conform to the legislation governed by the Statutory Plant Health Notice, but we had an opportunity to chip the material we didn’t have to burn, which also increased the organic matter on site and helped to increase the soil levels in the landscape.
And we are replanting the woodland! In time, after about 15 years, that will begin to sequester carbon again. We’ve left one tall Scots pine, almost as a reminder that all its friends, the neighbouring larch, have now gone. It’s very much a different landscape.
We shared stories about what we were doing throughout the project, to keep people informed.”
The loss of the larch has created new opportunities for different plants. There’s more light getting into the garden now. A lot of the rhododendron species which are very etiolated and leggy, due to having to reach for the light through a fairly dense canopy, are now the stars of the show. We can also see other plants like tree ferns (Dicksonia antarctica) in the landscape; they’ve become quite prominent.
I was inspired by the new Forth Crossing, which was designed so that cars can drive over in a Force 5 gale doing about 60mph. We mocked up this design and we’re going to introduce some of the structures throughout the most exposed parts of the garden. This will give the garden a little bit of protection from the wind so that new plants have time to grow up to at least 1.5m.
To help protect the plant collection, we have a relationship with Duchy College in Cornwall who carry out micro-propagation for us. We have sent cuttings from a lot of the rhododendrons down to them, and in two or three years we’ll get some nice, clean plant material back. That’s very much conservation in action.
In terms of curation, we were very keen to move away from the monoculture of Japanese larch and move towards one of diversity and resilience. That means we have to bring in lots of different species of trees into the garden while still keeping that sense of place and ambience that people became accustomed to with the larch. From a sustainability point of view, we will also introduce the right species of trees that may mitigate some of the impacts we have from increasing pests and diseases in west coast gardens.