Forty years of change in Scottish grassland vegetation: Increased richness, decreased diversity and increased dominance

Scottish grasslands were found to have changed significantly over this time. Species richness increased, while diversity declined as dominant species increased in cover. Nitrogen-demanding and moisture-requiring species increased, possibly reflecting increases in atmospheric nitrogen deposition and rainfall over this time. In Acid and Nardus grasslands species with low tolerance to very acidic soils increased, possibly reflecting a decrease in sulphur deposition. Overall β-diversity showed no change, indicating that contrary to trends in other habitats, homogenisation has not occurred. In general bryophytes and low-growing forb and grass species declined while taller species increased. This may reflect either the decline in grazing in recent years or the increase in atmospheric nitrogen deposition. Species richness increased but the majority of species declined in cover while a few dominant species increased suggesting that an extinction debt may be establishing. The trade-offs between increased management to reduce the extinction debt and abandonment with increased shrub cover which might be beneficial to other wildlife is discussed.