Following last year's survey of montane woodland species on the Dundreggan Estate by Mark Richards, I was pleased to be commissioned to extend the survey this summer across some of the neighbouring estates in Glen Moriston. During August, in mixed bright and damp weather conditions, I covered a total of 16 square kilometres of open hill, between the altitudes of 400 and 660 metres.
The survey methodology was similar to last year with sampling of 25 plots in each kilometre square. A rapid assessment was made of the apparent density of montane species whilst travelling between sample plots. As for last year, the principle species found was dwarf birch (Betula nana). At each plot, measurements of growth and browsing pressure were recorded, along with environmental factors and details of plant communities. Of particular interest is the montane vegetation community Heather-Mountain Bearberry (Calluna vulgaris-Arctostaphylos alpinus) found here on windswept summits at the southern limit of its range.
Dwarf birch was found at 99 sample plots, 28% of those surveyed. In total, 45% of all plots with dwarf birch were found on north facing slopes contrasting to only 10% on south facing slopes. Altitude was found to influence both tree height and catkin production, with mean height reducing as altitude increases. Similarly the mean number of catkins produced by each dwarf birch plant was found to decline as altitude increased.
Aspect was found to have a striking effect on both the height of dwarf birch, and the average number of catkins produced by catkin-bearing trees. Dwarf birch are better adapted to regenerating and growing on north facing slopes given the relatively high distribution and size of trees here. This may be due to a number of factors, for instance cooler conditions may be necessary to germinate seeds and break dormancy whilst dwarf birch appears well adapted to growing on the poorer soils often associated with a northerly aspect in the Highlands. Given that red deer are more likely to browse woody trees and shrubs in winter months it is possible that long lying snow offers protection from browsing deer.
Conversely the mean number of catkins produced by catkin-bearing dwarf birch on south facing slopes was dramatically higher than those produced on slopes of other aspects. The exposure to sunlight of individuals on south facing slopes may account for more catkins being produced there. A third factor which was found to influence catkin production is the height of dwarf birch relative to vegetation. Individuals which had emerged above the surrounding vegetation were found to produce more catkins than those at or below vegetation height. However it was concluded that dwarf birch above vegetation height are also more likely to suffer browsing damage.
Throughout the survey area silver birch (Betula pendula) seedlings were noted at altitudes of up to 530 metres. It was also particularly interesting to find a number of dwarf birch with irregular serrations on the leaf margin, a feature characteristic of silver birch, and it was thought these were possibly hybrids.
Juniper (Juniperus communis ssp communis), creeping willow (Salix repens), rowan (Sorbus aucuparia), Scots pine (Pinus sylvestris) and eared willow (Salix aurita) were found distributed throughout the survey area. It would appear possible to regenerate a diverse range of montane scrub species here and the long term potential to link montane woodland with the semi-natural pinewood in neighbouring glens to the north is certainly an exciting prospect.
However woody trees and shrubs supplement the diet of red deer in winter months, and rowan and willow in particular are relatively palatable and selectively browsed every winter. The reproductive potential of dwarf birch is also likely to be reduced if browsing prevents its emergence above vegetation height. Deer numbers are therefore the limiting factor in establishing montane woodland on open hill ground above Glen Moriston, although much can be achieved by small scale regeneration with deer fenced exclosures.
Overall, it was an enjoyable and fascinating study, and I got used to being alone up on the hills. One particular day, however, I was shocked out of my isolation when, shrouded in low cloud, with visibility down to a few metres and my head down, Alan suddenly appeared with a cheery greeting out of the mist! My photo probably still shows some surprise!
Pages about montane scrub on this site
- Scientists crack genetic code of dwarf birch from Highlands forest restoration site – Press release November 2012
- Trees for Life - Return of the Wee Trees Appeal 2012
- 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