Something is moving on the peaks of Scotland’s Munros. Recent research from the University of Stirling has found trees growing to record-breaking heights, such as a mountain ash towering 1,150 m (3,773 ft) at the summit of Sgurr nan Ceathreamhnan, a Munro in West Africa. This message is an indication of the possible restoration of montane forests that have been lost over the millennia.
PhD student Sarah Watts from the Faculty of Science at Stirling is spearheading this work.
“I’ve killed over 200 Munros now,”
She reveals that her main concern is to record the distribution and altitude of trees and other mountain plants.
“It was fascinating to find trees that grow at the absolute limit of the environmental sustainability of these species. Some were 200 m above previously known heights.”
While this botanical breakthrough is worthy of celebration, it upends many of these researchers’ ideas about what shapes and influences these high-altitude ecosystems.
The dominant narrative blames overgrazing by cattle and deer for the degradation of high altitude habitats. As Ms Watts notes, these habitats in the Scottish Highlands have largely been lost to overgrazing. But how exactly does this perspective reflect the overall complexity of the situation? While overgrazing certainly affects regrowth, it does not fully explain the vast ecological changes observed over the millennia.
Five thousand years ago, these mountainsides witnessed significant tree dieback, well before modern grazing practices were introduced. Consequently, it is clear that overgrazing cannot be the sole or even primary cause of initial deforestation.
We can conclude that their growth is likely to be affected 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 recent success of mountain ash and Sitka spruce at these elevations is probably evidence of these conditions.
There is no mention that warmer temperatures would raise the treeline for these species, which would likely be evident if warming were detected.
It appears that overgrazing is primarily a challenge to the regrowth and natural restoration of these habitats and is not the original cause of tree loss. Indeed, tackling overgrazing is critical to protecting the incipient revitalization of these forests, but it is only one piece of the ecological puzzle.
The pioneering tree species now native to these elevations, such as mountain ash and Sitka spruce, provide insight into understanding the potential factors that may have triggered the initial dieback. As these species push previously known boundaries, they thrive in what Ms. Watts describes as follows:
“the absolute limit of environmental tolerance for these species”
The unprecedented discovery of these high-altitude trees provides an opportunity to explore the resilience and adaptability of these species and improve our understanding of the historical forces that shaped these landscapes.