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5 Nov 2020

Positive prospects for precarious plants

Written by Shaila Rao, Ecologist
A wooded landscape with mountains in the background, all under a blue sky.
The Caledonian pinewood at Mar Lodge Estate
Flowering plants light up the landscape for everyone to enjoy. The National Trust for Scotland is working hard to conserve some of our rare plant species.

Over 600 plant species have been recorded at Mar Lodge Estate, making it a botanist’s delight. But it’s a also fantastic place to simply enjoy the variety and beauty of the plants that grow lushly in the bottom of the glens to those that crouch among the boulders on the tops of the highest Munros. The flowering spectacle begins in April when woodland flowers such as wood sorrel and wood anemone burst into bloom, before the trees gain their leaves and shade them out. It culminates in August with the amazing show of the heather cloaking the hills in lurid purple.

Mountainous landscape with purple heather.
Heather coming into flower turns the Cairngorm landscape purple in August

Many of the plant species found here are common across the Highlands, but Mar Lodge Estate also supports a good number of plant rarities that won’t be familiar to most people. Some of these plants are rare because they have specific habitat needs and suitable habitats are few and far between. Others are rare due to historical changes in the landscape as a result of past management, such as grazing, burning and deforestation. This has meant that suitable habitats have been lost and the plant populations have become small, isolated and fragmented. In the worst-case scenarios, landscape change and habitat loss may have been so dramatic that the distribution of some species has dwindled to just a handful of sites, where the last remnants precariously hang on.

In 2018, we embarked on two exciting rare plant conservation projects at Mar Lodge Estate for two of these species – twinflower (Linnaea borealis) and alpine blue sow thistle (Cicerbita alpina). Both are common and widespread throughout much of their range in northern and central Europe, but in Scotland they’re at risk of extinction.

Twinflower

Twinflower is a diminutive but iconic plant species of the Caledonian pinewoods. It trails along the forest floor inconspicuously for most of the year and then in June sends up a small flower stem with two stunningly beautiful and incredibly delicate whitish-pink, bell-shaped flowers – hence its name, twinflower. Loss of woodland habitat has been the downfall of this species and its stronghold is now in the remaining Cairngorm pinewoods with just a small number of highly fragmented populations.

Research has discovered that most of the individual populations consist of a single plant or clone that has spread out over countless generations to form each remaining patch, which has serious implications for the species’ future. Firstly, single plant populations have no genetic variability within them and are therefore more susceptible to pathogens or random catastrophic events in the environment. Secondly, the pollinators of twinflower only fly small distances – not far enough to go between the remaining isolated populations. This means that a single plant population can only self-pollinate, rather than cross-pollinate with another individual. Cross-pollination is necessary for viable seed production, to allow twinflower to establish new seedlings and for the population to expand. Self-pollination rarely produces viable seed, so without cross-pollination a single plant population can only grow vegetatively.

A patch of small white flowering plants, with nodding heads.
Profusely flowering twinflower patch in June

At Mar Lodge Estate we have eight known twinflower populations, each of which is a single plant or clone, and all these populations are isolated from one another. The primary aim of our twinflower conservation project, funded in part by the Cairngorms National Park, has been to create new twinflower populations with multiple clones in suitable habitats. These new populations will have genetic variability, so will be able to cross-pollinate and produce viable seed. Over time, this will allow new twinflower plants to establish and for the population to expand healthily and more robustly. Last year we began this process by collecting cuttings from individual Mar Lodge clones and directly transplanting them out at three new sites, thus bringing together different clones into three new populations. This year, working with the neighbouring estates of Invercauld and Balmoral, we collected further twinflower clones and added them to the three new populations we had established in 2019. Now, these three new populations each have a unique combination of clones.

Initial monitoring of the clones we planted in 2019 indicates that the transplants have not only survived but are growing well. In the coming years we’ll add further clones into our three new populations. We also plan to add clones into our original existing populations, so that they become multi-clonal with an opportunity to reproduce successfully for the first time in a long, long time and hopefully expand in the future.

A single twinflower plant, with a pollinator hovering next to it.
Single twinflower stem with a pollinator poised for action

Alpine blue sow thistle

In terms of its habitat and appearance, alpine blue sow thistle is the complete opposite of twinflower. It’s a large showy plant, growing up to 1.5m tall with succulent leaves and a flowering stem topped by a large bright purple-blue flower. In northern and central Europe it likes to live in and on the edge of mountain woodlands, but in Scotland it now only occurs on four inaccessible high-altitude ledges out of the reach of the even the most daring grazing animals. Alpine blue sow thistle is extremely palatable and is sought out by a wide range of herbivores – from slugs and sheep to deer and bears. Its tastiness is reflected in the translations of the Finnish and French names for this plant – ‘bear hay’ and ‘alpine lettuce’. Evidence suggests that it was once more widespread in Scotland, but that centuries of relentless grazing by sheep, cattle and deer have had a profound effect on its distribution. Its last refuge on high-altitude ledges is the only place it can escape hungry mouths.

A thistle plant with broad green leaves and a cluster of blue daisy-like flowers.
Our first successful flowering alpine blue sow thistle

We’re joining with the Royal Botanic Garden Edinburgh (RBGE) in an exciting partnership project to reintroduce alpine blue sow thistle to a number of new sites. The recently reduced grazing pressure on the estate and close proximity to existing alpine blue sow thistle sites made Mar Lodge a prime candidate for reintroduction. After much deliberation over exact site selection, in October 2017 40 plants were introduced to two sites on the estate. These were not high-altitude ledges, but suitable woodland sites well within reach of grazers.

We wanted to test whether these plants could successfully establish in sites similar to where they occur in northern and central Europe. We waited with bated breath when the new growth came up in May 2018, half-expecting the plants to be rapidly consumed by even the relatively low numbers of deer or hares present on the estate. But to our surprise deer and hares have been the least of our problems. Instead, smaller herbivores have been the culprits – in 2018 the plants were voraciously consumed by voles and none of them managed to flower. Further alpine blue sow thistle plants were added to both sites in October 2018 to reinforce the populations. We also added vole cages to a sample of the plants to determine their success with and without vole protection.

Summer 2019 was another story. The vole population had dropped but the conditions were perfect for a bumper black slug year and they made a good job of consuming many leaves. However, the slug impact was not as severe as voles and in 2019 we had our first alpine blue sow thistle flowering spike – who knows when it last flowered on Mar Lodge Estate! Two years after planting, the plants seemed to be gaining some momentum and we wondered what would happen in 2020. This year there was neither a very high vole nor slug population and the plants had their best year yet with five flowering spikes. The plants in the vole cages were most successful – so the cages definitely offer protection both from voles and black slugs.

Two thistle plants in long grass. One has a cluster of small blue flowers; the other has a larger, fluffier purple flower.
Alpine blue sow thistle alongside melancholy thistle

This reintroduction is definitely a learning experience for both RBGE and the Trust, as the aim is to reintroduce alpine blue sow thistle to other sites. If this is to be successful, we need to persevere with the reintroduction at Mar Lodge to determine what is required to establish a vigorous thriving and expanding population of alpine blue sow thistle in the Cairngorms. This year our work will continue, with further additions to the populations at each site. We feel that increased density and numbers of plants may provide the answer to combating the vole and slug predation. We’ll see what summer 2021 brings.

If you’re interested in the plants at Mar Lodge Estate, please pick up or download our Plants of the Pinewood leaflet, which is a helpful ID guide to some of the plants on the estate. Who knows – you could find a new undiscovered twinflower patch for us!

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