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Rare Aspen Bristle-moss Population Doubles in Scotland Thanks to Volunteers

20 October 2025

 

The known population of Aspen Bristle-moss Orthotrichum pulchellum, a moss once thought extinct in the UK, nearly doubled in Scotland in a single afternoon following a survey near Dinnet, Deeside.

The breakthrough came during a training session organised by Plantlife Scotland. Volunteers were taught how to identify the elusive moss, a tiny epiphyte that grows on the surface of Aspen trees that is notoriously difficult to distinguish from other moss species.

“The Cairngorms is home to some of the UK’s only remaining Aspen woodlands, which provide a crucial habitat for this rare moss,” said Sam Jones, Senior Ecological Advisor for Plantlife Scotland. “Before our survey, about 20 trees were known to support Aspen Bristle-moss — nearly half of the total known UK population. During our session, volunteers increased that number to 49 trees, almost doubling the known population in just one afternoon.”

Aspen Bristle-moss specialises in growing on Aspen Populus tremula trees, meaning its survival is closely linked to the health of these woodlands. The moss had been thought extinct in the UK until its rediscovery in 2003 at three sites, all in or near the Cairngorms National Park.

Aspen Bristle-moss is a part of the unusual and impressively diverse community of moss and lichen species. Mosses, lichens, and other epiphytic species (growing on other plants) form complex microhabitats on the bark of Aspen trees. These trees are amongst the most biodiverse habitats for epiphytes in the UK, with over 300 species recorded growing on Scottish Aspen trees alone.

Simon Ritchie, NatureScot’s Nature Reserve Manager at Muir of Dinnet NNR said: “We’re incredibly fortunate to have this rare bryophyte thriving on Muir of Dinnet NNR, and it was a privilege to take part in such an important survey. We are thrilled that the population has increased and we’re confident that our ongoing conservation of the Aspen woodland will help the Aspen Bristle-moss continue to flourish here.”

With potential for populations of the tiny and hard to spot moss to remain undiscovered, Plantlife is now encouraging further surveys and volunteer involvement. The charity is now revisiting the other know historic sites of this rare species and starting to survey.

“This is just the first step,” said Sam. “By training more people to look for and appreciate these rare species, we hope to build a clearer picture of how Aspen Bristle-moss, and other rare Aspen epiphytes are doing, investigate what we can do to protect them or help them recover, and ensure these unique habitats thrive for future generations.”