There’s something stirring on the peaks of Scotland’s Munros. Recent research by the University of Stirling has reported trees growing at record-breaking heights, such as a rowan standing tall at 1,150m (3,773ft) near the top of Sgurr nan Ceathreamhnan, a Munro in West Affric. This news is hints at the potential restoration of hilltop woodlands lost over thousands of years.

PhD researcher Sarah Watts, from Stirling’s Faculty of Natural Sciences, is at the forefront of this work.

“I have now bagged more than 200 Munros”,

https://www.bbc.com/news/uk-scotland-highlands-islands-65903065

she reveals, her main concern being to record the distribution and altitudes of trees and other mountain plants.

“It was fascinating to find trees growing at the absolute limit of environmental tolerance for these species. Some were 200m above previously known altitudes.”

While this botanical breakthrough is worthy of celebration, it upends much of these researchers’ ideas about what shapes and influences these high-altitude ecosystems.

The prevailing narrative places blame on overgrazing by livestock and deer for the degradation of high-altitude habitats. As Ms. Watts states, these habitats across the Scottish Highlands have largely been lost due to overgrazing. But how accurately does this perspective reflect the full complexity of the situation? While overgrazing certainly impacts regrowth, it doesn’t wholly explain the vast ecological changes witnessed over the millennia.

Five thousand years ago, these mountainsides bore witness to a significant die-off of trees, well before modern grazing practices were implemented. Consequently, it’s clear that overgrazing cannot be the sole or even primary cause of the initial deforestation.

We can infer that their growth is likely influenced by changes in environmental conditions, such as CO2 enrichment.

Research shows that increased CO2 levels can boost tree growth, especially at high altitudes where the air is thinner. The rowan and sitka spruce’s newfound success at these heights is likely a testament to these conditions.

There is no mention of warmer temperatures raising the tree line for these species, which would likely feature prominently if any warming had been detected.

It appears overgrazing is a challenge mainly for regrowth and the natural recovery of these habitats, rather than the initial cause of tree loss. Indeed, addressing overgrazing is critical to protect the nascent revival of these woodlands, but it is just one piece of the ecological puzzle.

The pioneering tree species now making a home at these heights, such as the rowan and the sitka spruce, provide a window into understanding the potential factors that could have prompted the initial die-off. As these species defy previously known limits, thriving in what Ms. Watts describes as:

“the absolute limit of environmental tolerance for these species”

The unprecedented discovery of these high-altitude trees presents an opportunity to explore the resilience and adaptability of these species, and increase our understanding of the historical forces that shaped these landscapes.