Impacts of climate change and pollutants in snowmelt on snowbed ecology
Snowbed vegetation in Scotland is dominated by a distinctive bryophyte flora. This type of vegetation is on the edge of its European range in Scotland. Due to its dependence on late snow lie, snowbed vegetation may be threatened by climate change. Snow is a very efficient scavenger of atmospheric pollutants. Due to its melt dynamics these pollutants are released to the underlying vegetation in a highly concentrated 'acid flush'. A survey of changes over this century in the tissue nitrogen content of K. starkei, a snowbed bryophyte, showed this to reflect increases in NOx emissions. A regional survey of tissue nitrogen content of K. starkei across Scotland did not reflect mapped patterns of NO3 deposition. This is because pollutants are concentrated in snowbeds as compared to other systems. Present day tissue nitrogen concentrations in K. starkei are up to 50% higher than those of other upland bryophytes. Sensitivity of K. starkei to acidic pollutants in subnivean conditions and at various stages subsequent to exposure from under the snow has been investigated. Results demonstrate that these pollutants, when received in realistic present day amounts, result in physiological damage to the bryophytes whether they are received by them under the snow, just emerged from the snow, or out of snow cover. Damage was greatest in plants from out of the snow. However, the ability to recover following damage is also much greater in these plants than those which become damaged while still under snow. Damage is both direct, and indirect, affecting the ability of the plants to withstand other stresses. Because of enhanced exposure to pollutants, snowbed vegetation is unlikely to be protected by the current critical loads approach to pollution control. The possible combined effects of pollution and climate change on snowbed bryophyte communities are discussed.