Why Scotland has so many mosses and liverworts
It will come as no surprise to learn that our damp climate is a principal factor in producing our diverse moss and liverwort flora. It is not the absolute amount of rainfall that is crucial, but the absence of long periods of drought and this, coupled with relatively frost-free winters, make our western seaboard a paradise for bryophytes. Added to this oceanic climate is a diverse geology, giving a mixture of rock textures and chemistry, a recently glaciated landscape, with much exposed rock in crags and screes, and turbulent burns in deep ravines to maintain the humidity. This type of climate and landscape is quintessentially Scottish and is shared by very few places elsewhere in the world. The rocky terrain has also meant that tracts of woodland have been left relatively undisturbed, particularly in ravines, and these old woodlands are the heart of our oceanic flora. Our position on the western fringe of Europe also means that much of the best habitat for bryophytes has been only marginally affected by pollution.
The wet, cool climate has also given us vast areas of mire and its associated bryophyte species. Our mountains are high enough to have an alpine flora with some of the better hills being as rich as many places in the Alps, particularly where patches of snow persist well into the summer. We are also far enough north to have some species whose affinities are with the tundra. In the drier east, particularly in the straths of the Spey and the Dee, there are areas with more ‘continental’ species, especially where there are expanses of dry, block scree within the Caledonian pine forest. Some southern species which prefer dry, sun-warmed slopes, can thrive in those places in the east where there are south-facing coasts, as on the Black Isle, in Fife and in Berwickshire. Again in the east, where there is still much arable farming, there is a whole range of ‘weedy bryophytes’ – short-lived species which are most easily seen in stubble fields before they are ploughed again. All these different niches exist in close proximity, giving our small country its extraordinary moss and liverwort diversity.