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22 Apr 2021

A heritage response to a contemporary pathogen

Written by Simon Jones, Gardens and Designed Landscapes Manager – South and West
Aerail view of a woodland with dying trees and some green trees
The larch shelterbelt (© I Sinclair)
The team at Arduaine are tackling the complex felling operations of removing almost 900 trees in this beautiful west coast garden.

Arduaine Garden is the 8-hectare creation of James Arthur Campbell and his wife Ethyl, who between 1897 and 1929 embarked on designing and constructing a garden housing both native species and exotic plants from all over the world. The garden is afforded protection by its shelterbelt plantings which function as a windbreak, creating the desired microclimate to grow plants that have no earthly business living so close to the salty Atlantic seaboard.

The unique character of the garden lies in its relationship with one species of tree, the Japanese larch (Larix kaempferi), complemented beautifully by the understorey plantings that together represent 95 geographical regions of the world.

The problem

The garden is facing perhaps its most difficult challenge since its inception. A Statutory Plant Health Notice (SPHN) has been issued, instructing the Trust to remove all 885 Japanese larch trees by 31 March 2022 due to the increasing occurrence of the pathogen Phytophthera ramorum. The deciduous nature of the larch and the almost unique biology of the pathogen mean that the tree perfectly helps sporulation and the subsequent spread of the pathogen. A report and project plans were duly written that set out the detailed logistical plan for the transformation of the shelterbelt.

This may sound simple enough in written text or the spoken word. But the practical reality is far from simple. The bulk of the plant collection was planted at the same time as the larch, meaning the garden has matured in synergy, which makes it extremely difficult to remove the larch without causing significant damage to the understorey.

A garden with large rhododendron bushes and a woodland behind them.
Entrance to the woodland from the lower garden

An analogous way to appreciate this project is to imagine removing the roof, bricks and structure of a house without causing any damage to the possessions inside!

This challenge was initially perceived as a destructive operation. But I would argue that, if delivered properly, the Trust is creating one of the best opportunities a horticulturist could have to curate, design and plant a new diverse, resilient woodland. After all, no gardener has done this in almost 100 years!

The plans

People

For the Trust to deliver this project, we rely on the input and understanding of a diverse range of people and stakeholders, both internal and external to the organisation. And because this is not just a garden project, we cannot forget our colleagues in the regional teams who have all had a part to play in bringing the project to fruition, especially the arborists from Mar Lodge Estate and staff from Crarae Garden.

Three arborists standing in a mixed woodland, wearing blue working gear and wearing helmets.
Arborists from Mar Lodge Estate

Health, safety and environmental considerations

Removal of 885 mature trees is not only a visually devastating operation, but also one that is fraught with risk – risk of causing an injury to a member of staff and risk of causing damage to the local environment. With this in mind, a detailed Aspects and Impacts register was created to detail the various elements that should be managed to minimise risk and mitigate our environmental impact. An example of this is conducting ecological surveys at key stages of the annual felling phases to ensure operations cause minimal disruption to protected fauna like red squirrels and bats.

Communications

This, in many ways, is where projects can quickly come undone. If internal and external stakeholders don’t know or appreciate the details and context of what is being undertaken, how can they support the work? It’s quite simple really – communication is key. A charmingly funny example of the extent of our communication drive happened on a beautiful sunny evening in 2019, when Head Gardener Gregor Anderson and I were due to give a presentation in a local village hall. Despite our best efforts to promote the evening, only one person turned up – suffice to say that this person received the most thorough presentation given to date!

Felling operations

Under the terms of the SPHN, we have to fell the larch and burn all branches and arisings. However, we’re left with many tonnes of ‘waste’ timber and we’d have to pay for its removal and transportation to an approved sawmill for processing. So we purchased a sawmill! Now this timber can be milled to order and used in all Trust properties for cladding, fence posts, timber edging, dahlia stakes, tree stakes, sleepers, etc. This is recycling at its best, creating a resource-efficient solution to a waste problem. Any surplus timber will be chipped back onto the woodland floor to mitigate the carbon loss from tree removal while helping to improve soil content and structure. We’ll also use the timber in the garden itself.

Infrastructure

The garden has a network of narrow paths that were unsuitable for vehicle and machinery access, so the main spine of the garden path needed to be widened to allow access and extraction of the timber to the milling point. These temporary infrastructure changes are not aesthetically pleasing and there are plans to reinstate all the original paths with suitably sourced local aggregate.

A path in a garden is being widened. A man is raking gravel and behind him a small digger is at work.
Widening the path to allow vehicle access

Heritage/conservation

As horticulturists, protecting the plant collection is our primary concern. But there is a degree of acceptance that we can’t protect everything. We decided to tackle this issue in two ways. Firstly, by air layering of rhododendrons (generously taught by rhododendron expert John Hammond), and secondly through the formation of a partnership with Duchy College in Camborne, England, in which the wonderful Ros Smith is going to propagate some of our rhododendron species. Once the protective structure of the larch has been removed, the garden and remaining trees will then be exposed to the coastal elements. To combat this and diffuse the force of the wind, the team will construct artificial windbreaks on the windfirm edge of the garden using the larch, ensuring there will be no metal or plastic fixings.

A wooden windbreak made from felled larch.
A mock windbreak made from larch

In addition, there’s a set of criteria for curating the plants that will make up the new woodland. These have been designed to ensure resilience is delivered in terms of the new plant species:

  • ability to cope with the coastal conditions
  • susceptibility to pests and diseases
  • as a host plant for P. ramorum
  • damp tolerance
  • acid tolerance
  • provision of a red squirrel food source

Once scored, we’ll be left with a group of plants that have both justifiable botanical character and function within this designed landscape. In other words, the plants will have been chosen by process.

Progress

Complex logistical problems aside, I’m confident we can achieve the desired felling result because we have great support from all our colleagues within the Trust as well as external support. To date, we’re around the halfway mark, with 443 trees having been felled. But the team has lost about 28% of the allotted time due to inclement weather.

The future

So, what will the future Arduaine Garden look like? To build genuine horticultural sustainable development principles into the plant collection means that the plants are not chosen through a qualitative approach. This garden must be able to cope with the risks posed by a rapidly changing climate while creating new conservation opportunities. If we understand that Arduaine Garden is like a land-locked island, then surely there’s scope to curate a new woodland canopy plant collection that seeks to collect plants from the temperate island ecosystems of the world. But not exclusively, because the islands are where the impacts of a changing climate will be most sharply felt and we have been given the opportunity to create an ex situ refugia of threatened plants grown in the wet west coast of Scotland.


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