Dwarf birch survey in Glen Moriston

As reported in the last edition of Caledonia Wild!, we took Mark Richards on under a 3 month contract in the summer to survey montane scrub and especially dwarf birch in Glen Moriston. Here he reports on the results of his work.

This summer I spent 10 weeks roaming around Glen Moriston, surveying dwarf birch (Betula nana). The survey covered a 21 square kilometre area focussed primarily on Trees For Life's Dundreggan Estate, but also included land on the neighbouring Corrimony Farm and Glenmoriston Lodge estates. The aim was to map the distribution of dwarf birch and also measure individual plants in order to understand more about its ecology and current condition. Monitoring work was also carried out in two mountain woodland exclosures to see how the vegetation is developing after being fenced off from the deer.

Survey results

I am delighted to report that Dundreggan holds some very extensive areas of dwarf birch. These areas occur mostly above 500 metres, on the north-facing slopes and on top of the broad ridge running from Beinn Bhan in the west to Carn na Caorach in the east. Some large areas were also discovered on Corrimony Farm and Glenmoriston Lodge in the northeast of the survey area. We have set up 29 permanent plots around Dundreggan so that we can keep an eye on any changes in the dwarf birch as the new Trees For Life management plan comes into effect.

Dundreggan dwarf birch map: Map of the north of Dundreggan, and the surrounding estates, showing the distribution of dwarf birch that Mark recorded during his survey.

Monitoring results

Monitoring work in the 20 hectare Balnacarn exclosure shows that the dwarf birch (and the surrounding vegetation) have doubled in height since the original baseline survey in 1998. There is also some evidence to suggest that the dwarf birch are spreading because they were found in 73 quadrats this year compared to just 44 quadrats in the original survey.

Monitoring work in the 10 hectare Dundreggan exclosure erected in 2002 shows that the dwarf birch are now almost twice the height of those outside the exclosure, being on average some 13 cm taller. Even more dramatically though, the average number of catkins per plant inside the exclosure is 27 compared with just 2 per plant outside the exclosure – a 13 fold increase!

It was also exciting to find the larvae of the moth Swammerdamia passerella (it has no common name) inside the exclosure. This rare moth feeds on the leaves of dwarf birch and in Scotland is found in only a few locations. I found it in only one other location in the whole of the survey area, so it is unlikely that it is occurring in the exclosure by chance. The presence of half eaten catkins on the plants occupied by the caterpillars suggests that they may feed on these as well as the leaves. Perhaps the higher number of catkins on the dwarf birch inside the exclosure makes them a better habitat for the caterpillars.

Action

The survey results have been fed into the Trees for Life Geographic Information System (computer-based mapping software) and this is being used to identify the best locations for future exclosures. Our aim is to create a network of exclosures that allow the complete spectrum of mountain woodland to develop, ranging from woodland types of the valley floor up to the natural tree line, and beyond to encompass montane scrub. Dundreggan, with its ancient woodland on the lower slopes and abundant dwarf birch on the higher ground, is the perfect place to turn this vision into reality.

Mark Richards

Pages about montane scrub on this site

• Above the Tree Line by Tim Clifford
• Dwarf Birch information resource
• Dwarf birch species profile
• Help us to map the distribution of dwarf birch in Scotland
• Mountain Forest restoration project appeal
• Montane Scrub project update, Caledonia Wild! August 2008
• Dwarf birch survey in Glen Moriston - Summer 2008
• Dwarf birch surveys on Dundreggan
• Montane Scrub Project, Caledonia Wild! November 2008
• We're in the Action for Montane Woodland project
• Montane Scrub Survey in Glen Moriston 2009