Mosses and Liverworts in Scotland
Mosses and liverworts are everywhere in Scotland, adding colour and interest to both the most mundane and the most extreme of habitats. In the woodlands, in the mires and on the mountain tops where they are most abundant, the collective texture and pattern of the many species is stunningly beautiful. Mosses and liverworts (collectively called ‘bryophytes’) and the plant communities of which they are major constituents, are more frequent and more diverse in Scotland than in any other part of the UK and in most other parts of Europe. Some of these bryophyte communities, particularly those of the western ‘rain forests’ and the ‘oceanic heaths’, are globally very rare and have species which are limited to a few, often geographically, distant, localities.
In Scotland there are just under 1,000 species of moss and liverwort, some 87% of the UK total. In international terms, Scotland has more than 60% of the European bryophyte flora, including some endemics such as Scottish beard-moss Bryoerythrophyllum caledonicum and Scottish thread-moss Pohlia scotica.
With estimates of the total number of global species ranging from 16,000 to 24,000, it is possible that Scotland may have as much as 5% of the world’s bryophytes. These are astonishing figures, considering the country’s small size and the relative poverty of our flowering plants using the same comparisons.
If you wander into any of the remnants of oak and birch woodland on the west side of Scotland, particularly in Argyll, in the area around Loch Sunart and north to Sleat on the Isle of Skye, you will see that the trees and rocks are covered with a deep carpet of mosses and liverworts, often extending up into the canopy. Closer examination will reveal that it is not all the same plant but a whole range of species, each with its own niche.
In the extensive areas of mire for which Scotland is so important, bryophytes can be even more abundant, certainly in terms of sheer biomass if not in species diversity. The mossy lawns and hummocks in the mires are composed of bog-moss, species of Sphagnum, and the health of these mires is largely dependent on the well-being of the Sphagnum. The dead but only partially decayed remains of these bog-mosses form the principal constituent of peat, an important source of energy in the past.
On the tops of many of our higher hills, particularly in the west, you can walk over great expanses of a soft, grey carpet of Woolly hair-moss Racomitrium lanuginosum with only scattered plants of stiff sedge and mat grass. This monotone changes dramatically in areas where snow lies late into the summer. Here mosses and liverworts are again dominant in the vegetation with the russets and blacks of the liverwort crust over the unstable gravels contrasting with the bright greens and reds of the mosses growing in the melt-water channels. Outcrops of lime-rich rocks also occur high on the hills and are just as important for arctic-alpine bryophytes as they are for lichens and flowering plants.