As with most other organisms, habitat change is the major threat. Changes associated with global warming may have a severely detrimental effect on our upland bryophyte flora, particularly on the very specialised snow-bed species. Pollution is less of a threat now than it was in the past and we are seeing the re-colonisation of our urban areas by species that are sensitive to dirty air. However, concentrations of pollutants still occur in the snow-pack in the mountains and the effect that this may have on snow-bed species is, as yet, unknown.
Other specific, potentially damaging changes are:
- the construction of hydro-electric schemes,
- roads and drainage for wind farm developments,
- inappropriate afforestation,
- road improvements,
- the loss of wayside and hedgerow trees,
- the infrastructure for skiing and other tourist
developments in wild places.
Knowledge of the importance of our flora is now such that sheer ignorance of the conservation value of our bryophytes is no longer an excuse for damage.
The oceanic-montane heath has a very patchy distribution in our western hills, given that the climate and terrain is suitable over much of the west of Scotland. It seems likely that the practice of muirburn and heavy grazing have taken their toll in the past, particularly on the lower ground. Many of the special species in the heath have limited means of spread after damage and one severe fire could wipe out a local population of this globally important community forever. Muirburn is less common in the west now than it once was but it still goes on and is often uncontrolled.
A number of the best areas of oceanic broadleaf woodland in Scotland (and thus in Europe) are threatened by the seemingly inexorable spread of rhododendron. This was originally planted in the gardens of ‘big houses’ but found the climate in the west to its liking and now totally dominates large areas, often under a canopy of oak trees. It casts a dense shade and its leaf litter is very acidic and decays only slowly so that it eventually smothers the ground flora. In the longer term, this dense covering will also prevent tree regeneration. So, when the current generation of trees dies, there will be no more to replace them.
A number of important woodland areas have schemes to eradicate rhododendron but, at current levels of expenditure and commitment, these schemes are only having a limited impact. We are in danger of losing some of the best moss and liverwort communities in Europe unless we get to grips with this problem.
A large number of mire areas, particularly in southern and eastern Scotland, have been lost to drainage. An even greater loss occurred as a result of afforestation when the tax regime encouraged planting of conifers with scant regard for their impact or whether they would ever produce a crop. This has largely stopped now but it has left considerable areas in the Flow Country and Dumfries and Galloway with damaged mires. In some cases it is feasible to remove the trees and block up the drains but the process of recovery will be a long one. The value of our peatlands is now recognised and large tracts are given some statutory protection. There are still local threats from commercial peat extraction, often for the horticultural industry.
The horticultural trade also provides the demand for another potentially destructive industry – the gathering of live mosses and liverworts for floral displays, wreaths and bouquets. Not a great deal is known about the extent of this industry and at least some firms attempt to operate in a sustainable way by gathering only from conifer plantations that are due for clear-felling. However, the indiscriminate nature of ripping up carpets of moss is unsettling, as even within the most uniform of plantation woodland there are interesting habitats and species.
One unusual but very real threat to bryophytes, and to other lower plants, is the declining number of taxonomists. Without this professional core, it will be more difficult for conservation agencies to get the kind of information they need to provide adequate site protection. The strong amateur tradition in Scottish botany still needs the professional scientist to produce the floras and to carry out the research work that underpins the fieldwork.