Association between weather conditions, snow-lie and snowbed vegetation
Snowbed vegetation contains both vascular plants and bryophytes. The latest snowbeds cover areas that are of predominantly, if not exclusively, bryophyte flora while the vascular plants are generally confined to the periphery of such late snowbeds. It is hypothesised that the exclusion of vascular flora from the snowbed core is the result of the shortened growing season generated by late-lying snow, which the bryophyte flora is better able to tolerate. The snowbed bryophytes cannot, however, tolerate the competition offered by the vascular flora in the peripheral areas from which they are absent. Data indicate that some of the bryophyte snowbed species are inhabiting optimal conditions in the snowbed core, rather than tolerating sub-optimal conditions. Adaptation and acclimation responses observed in peripheral vascular species indicate that these are inhabiting sub-optimal conditions in the snowbed periphery. The relationship between snow-lie and climate is examined, with to the construction and examination of a second hypothesis that snowbed loyalty in the Scottish Highlands is high, while duration of snow cover is variable. Snow-lie loyalty is the product of prevailing wind conditions, which are persistent and consistent in Scotland leading to consistency in late snowbed location, while the occurrence of mid-winter thaws at all altitudes makes duration of snow cover through accumulated snow depth much more variable. Increased zonal flow in winter has affected snow-lie in the Scottish Highlands, with a slight decrease in snow-lie duration in recent years. It is not clear whether this pattern applies to all altitudes and accumulations at higher levels, especially in the western Highlands, may be increasing as a result of steeper winter-time lapse rates. With late snowbed location varying very little, it is possible that the consequences of global warming may not necessarily mean an extinction of the late snowbed bryophytes in Scotland, which constitute an important part of Britain's montane flora.